Hubble Space Telescope#Key projects

File:Astronaut Owen Garriott Performs EVA During Skylab 3 - GPN-2002-000065.jpg working next to Skylab's crewed solar space observatory, 1973]]

In 1923, Hermann Oberth—considered a father of modern rocketry, along with Robert H. Goddard and Konstantin Tsiolkovsky—published {{lang|de|Die Rakete zu den Planetenräumen}} ("The Rocket into Planetary Space"), which mentioned how a telescope could be propelled into Earth orbit by a rocket.{{cite book |last=Oberth |first=Hermann |title=Die Rakete zu den Planetenräumen |date=1923 |publisher=R. Oldenbourg-Verlay |page=85 |language=de}}

File:1946- Lyman Spitzer (4526166350).jpg played a major role in the birth of the Hubble Space Telescope project.|alt=Lyman Spitzer played a major role in the birth of the Hubble Space Telescope project.]]

The history of the Hubble Space Telescope can be traced to 1946, to astronomer Lyman Spitzer's paper "Astronomical advantages of an extraterrestrial observatory".Spitzer, Lyman Jr., "Report to Project Rand: Astronomical Advantages of an Extra-Terrestrial Observatory", reprinted in [https://history.nasa.gov/SP-4407/vol5/ExploreUnknown.pdf NASA SP-2001-4407: Exploring the Unknown] {{Webarchive|url=https://web.archive.org/web/20170120024958/https://history.nasa.gov/SP-4407/vol5/ExploreUnknown.pdf |date=January 20, 2017 }}, Chapter 3, Document III-1, p. 546. In it, he discussed the two main advantages that a space-based observatory would have over ground-based telescopes. First, the angular resolution (the smallest separation at which objects can be clearly distinguished) would be limited only by diffraction, rather than by the turbulence in the atmosphere, which causes stars to twinkle, known to astronomers as seeing. At that time ground-based telescopes were limited to resolutions of 0.5–1.0 arcseconds, compared to a theoretical diffraction-limited resolution of about 0.05 arcsec for an optical telescope with a mirror {{cvt|2.5|m}} in diameter. Second, a space-based telescope could observe infrared and ultraviolet light, which are strongly absorbed by the atmosphere of Earth.

Spitzer devoted much of his career to pushing for the development of a space telescope.{{Cite web|title=Celebrating Lyman Spitzer, the father of PPPL and the Hubble Space Telescope|url=https://research.princeton.edu/news/celebrating-lyman-spitzer-father-pppl-and-hubble-space-telescope|access-date=December 4, 2021|website=Office of the Dean for Research|archive-date=December 7, 2021|archive-url=https://web.archive.org/web/20211207155008/https://research.princeton.edu/news/celebrating-lyman-spitzer-father-pppl-and-hubble-space-telescope|url-status=live}} In 1962, a report by the U.S. National Academy of Sciences recommended development of a space telescope as part of the space program, and in 1965, Spitzer was appointed as head of a committee given the task of defining scientific objectives for a large space telescope.{{cite web |url=http://www.spitzer.caltech.edu/about/spitzer.shtml|title=About Lyman Spitzer, Jr|publisher=Caltech|access-date=April 26, 2008|archive-url=https://web.archive.org/web/20080327091202/http://www.spitzer.caltech.edu/about/spitzer.shtml|archive-date=March 27, 2008}}

File:Nancy Grace Roman with Space Telescope Model in 1966 (27154772837).jpg with a model of the Large Space Telescope that was eventually developed as the Hubble Space Telescope. While listed as a 1966 photo, this design was not the standard until the mid-1970s.]]

Also crucial was the work of Nancy Grace Roman, the "Mother of Hubble".{{Cite web|last=Smith|first=Yvette|date=May 15, 2020|title=Nancy Grace Roman: The Mother of Hubble|url=http://www.nasa.gov/image-feature/nancy-grace-roman-the-mother-of-hubble-2|access-date=December 4, 2021|website=NASA|archive-date=December 7, 2021|archive-url=https://web.archive.org/web/20211207160733/https://www.nasa.gov/image-feature/nancy-grace-roman-the-mother-of-hubble-2/|url-status=live}} Well before it became an official NASA project, she gave public lectures touting the scientific value of the telescope. After it was approved, she became the program scientist, setting up the steering committee in charge of making astronomer needs feasible to implement{{Cite web|title=Explorer 1 {{!}} Stories {{!}} Nancy Grace Roman|url=https://explorer1.jpl.nasa.gov/stories/nancy-grace-roman/|access-date=December 4, 2021|website=explorer1.jpl.nasa.gov|archive-date=May 31, 2022|archive-url=https://web.archive.org/web/20220531015937/https://explorer1.jpl.nasa.gov/stories/nancy-grace-roman/|url-status=live}} and writing testimony to Congress throughout the 1970s to advocate continued funding of the telescope.{{Cite journal |author= Roman, Nancy Grace |title= Nancy Grace Roman and the Dawn of Space Astronomy |journal= Annual Review of Astronomy and Astrophysics |volume= 57 |pages= 1–34 |year= 2019 |doi= 10.1146/annurev-astro-091918-104446 |bibcode= 2019ARA&A..57....1R |doi-access= free}} Her work as project scientist helped set the standards for NASA's operation of large scientific projects.{{cite book |last= Williams |first= Robert |date= October 1, 2018 |title= Hubble Deep Field and the Distant Universe |url= https://iopscience.iop.org/book/978-0-7503-1756-6 |location= Bristol, UK |publisher= IOP Publishing |pages= 2–9 |isbn= 978-0-7503-1756-6 |archive-date= June 5, 2020 |archive-url= https://web.archive.org/web/20200605012705/https://iopscience.iop.org/book/978-0-7503-1756-6 |url-status= live}}

Space-based astronomy had begun on a very small scale following World War II, as scientists made use of developments that had taken place in rocket technology. The first ultraviolet spectrum of the Sun was obtained in 1946,{{cite journal|title=Solar Ultraviolet Spectrum to 88 Kilometers|last1=Baum |first1=W. A.|display-authors=4|last2=Johnson |first2=F. S.|last3=Oberly |first3=J. J. |last4=Rockwood |first4=C. C.|last5=Strain |first5=C. V.|last6=Tousey |first6=R.|journal=Physical Review|volume=70|pages=781–782|date=November 1946|doi=10.1103/PhysRev.70.781|issue=9–10 |bibcode=1946PhRv...70..781B}} and NASA launched the Orbiting Solar Observatory (OSO) to obtain UV, X-ray, and gamma-ray spectra in 1962.{{cite web|url=https://heasarc.gsfc.nasa.gov/docs/heasarc/missions/oso1.html|title=The First Orbiting Solar Observatory|date=June 26, 2003|work=heasarc.gsfc.nasa.gov|publisher=NASA Goddard Space Flight Center|access-date=September 25, 2011|archive-date=May 3, 2019|archive-url=https://web.archive.org/web/20190503001707/https://heasarc.gsfc.nasa.gov/docs/heasarc/missions/oso1.html|url-status=live}} {{PD-notice}} An orbiting solar telescope was launched in 1962 by the United Kingdom as part of the Ariel programme, and in 1966 NASA launched the first Orbiting Astronomical Observatory (OAO) mission. OAO-1's battery failed after three days, terminating the mission. It was followed by Orbiting Astronomical Observatory 2 (OAO-2), which carried out ultraviolet observations of stars and galaxies from its launch in 1968 until 1972, well beyond its original planned lifetime of one year.{{cite web |url=http://nasascience.nasa.gov/missions/oao|title=OAO|publisher=NASA|access-date=April 26, 2008|url-status=dead|archive-url=https://web.archive.org/web/20080916121848/http://nasascience.nasa.gov/missions/oao |archive-date=September 16, 2008}} {{PD-notice}}

The OSO and OAO missions demonstrated the important role space-based observations could play in astronomy. In 1968, NASA developed firm plans for a space-based reflecting telescope with a mirror {{cvt|3|m}} in diameter, known provisionally as the Large Orbiting Telescope or Large Space Telescope (LST), with a launch slated for 1979. These plans emphasized the need for crewed maintenance missions to the telescope to ensure such a costly program had a lengthy working life, and the concurrent development of plans for the reusable Space Shuttle indicated that the technology to allow this was soon to become available.{{sfn|Spitzer|1979|p=32}}

The continuing success of the OAO program encouraged increasingly strong consensus within the astronomical community that the LST should be a major goal. In 1970, NASA established two committees, one to plan the engineering side of the space telescope project, and the other to determine the scientific goals of the mission. Once these had been established, the next hurdle for NASA was to obtain funding for the instrument, which would be far more costly than any Earth-based telescope. The U.S. Congress questioned many aspects of the proposed budget for the telescope and forced cuts in the budget for the planning stages, which at the time consisted of very detailed studies of potential instruments and hardware for the telescope. In 1974, public spending cuts led to Congress deleting all funding for the telescope project.{{sfn|Spitzer|1979|pp=33–34}}

In 1977, then NASA Administrator James C. Fletcher proposed a token $5 million for Hubble in NASA's budget. Then NASA Associate Administrator for Space Science, Noel Hinners, instead cut all funding for Hubble, gambling that this would galvanize the scientific community into fighting for full funding. As Hinners recalls:{{cite web

|url=https://historycollection.jsc.nasa.gov/JSCHistoryPortal/history/oral_histories/NASA_HQ/Administrators/HinnersNW/HinnersNW_8-19-10.htm

|title=NASA Headquarters Oral History Project – Noel W. Hinners

|date=August 19, 2010

|website=Johnson Space Center History Portal

|publisher=NASA

|access-date=July 14, 2022

|archive-date=July 15, 2022

|archive-url=https://web.archive.org/web/20220715150041/https://historycollection.jsc.nasa.gov/JSCHistoryPortal/history/oral_histories/NASA_HQ/Administrators/HinnersNW/HinnersNW_8-19-10.htm

|url-status=live

}}

{{blockquote

|text=It was clear that year that we weren't going to be able to get a full-up start. There was some opposition on [Capitol] Hill to getting a new start on [Hubble]. It was driven, in large part as I recall, by the budget situation. Jim Fletcher proposed that we put in $5 million as a placeholder. I didn't like that idea. It was, in today's vernacular, a "sop" to the astronomy community. "There's something in there, so all is well".

I figured in my own little head that to get that community energized we'd be better off zeroing it out. Then they would say, "Whoa, we're in deep trouble", and it would marshal the troops. So I advocated that we not put anything in. I don't remember any of the detailed discussions or whether there were any, but Jim went along with that so we zeroed it out. It had, from my perspective, the desired impact of stimulating the astronomy community to renew their efforts on the lobbying front. While I like to think in hindsight it was a brilliant political move, I'm not sure I thought it through all that well. It was something that was spur of the moment.

[...] $5 million would let them think that all is well anyway, but it's not. So let's give them a message. My own thinking, get them stimulated to get into action. Zeroing it out would certainly give that message. I think it was as simple as that. Didn't talk to anybody else about doing it first, just, "Let's go do that". Voila, it worked. Don't know whether I'd do that again.

}}

The political ploy worked. In response to Hubble being zeroed out of NASA's budget, a nationwide lobbying effort was coordinated among astronomers. Many astronomers met congressmen and senators in person, and large-scale letter-writing campaigns were organized. The National Academy of Sciences published a report emphasizing the need for a space telescope, and eventually, the Senate agreed to half the budget that had originally been approved by Congress.{{sfn|Spitzer|1979|p=34}}

The funding issues led to a reduction in the scale of the project, with the proposed mirror diameter reduced from 3 m to 2.4 m, both to cut costs{{cite book|last=Andersen |first=Geoff|title=The telescope: its history, technology, and future|date=2007|publisher=Princeton University Press|isbn=978-0-691-12979-2|page=[https://archive.org/details/telescopeitshist00ande/page/116 116] |url=https://archive.org/details/telescopeitshist00ande/page/116}} and to allow a more compact and effective configuration for the telescope hardware. A proposed precursor {{cvt|1.5|m}} space telescope to test the systems to be used on the main satellite was dropped, and budgetary concerns also prompted collaboration with the European Space Agency (ESA). ESA agreed to provide funding and supply one of the first generation instruments for the telescope, as well as the solar cells that would power it, and staff to work on the telescope in the United States, in return for European astronomers being guaranteed at least 15% of the observing time on the telescope."Memorandum of Understanding Between The European Space Agency and The United States National Aeronautics and Space Administration", reprinted in [https://history.nasa.gov/SP-4407/vol5/ExploreUnknown.pdf NASA SP-2001-4407: Exploring the Unknown] {{Webarchive|url=https://web.archive.org/web/20170120024958/https://history.nasa.gov/SP-4407/vol5/ExploreUnknown.pdf|date=January 20, 2017}} Chapter 3, Document III-29, p. 671. Congress eventually approved funding of US$36 million for 1978, and the design of the LST began in earnest, aiming for a launch date of 1983.{{sfn|Spitzer|1979|p=34}} In 1983, the telescope was named after Edwin Hubble,{{cite web|url=https://history.nasa.gov/hubble/chron.html|last=Okolski|first=Gabriel|title=A Chronology of the Hubble Space Telescope|publisher=NASA|access-date=April 26, 2008|archive-date=June 27, 2008|archive-url=https://web.archive.org/web/20080627010420/http://history.nasa.gov/hubble/chron.html|url-status=live}} {{PD-notice}} who confirmed one of the greatest scientific discoveries of the 20th century, made by Georges Lemaître, that the universe is expanding.{{cite web|url=http://hubble.nasa.gov/overview/conception-part1.php|title=The Path to Hubble Space Telescope|publisher=NASA|access-date=April 26, 2008|url-status=dead|archive-url=https://web.archive.org/web/20080524211736/http://hubble.nasa.gov/overview/conception-part1.php|archive-date=May 24, 2008}} {{PD-notice}}

File:Hubble mirror polishing.jpg

Once the Space Telescope project had been given the go-ahead, work on the program was divided among many institutions. Marshall Space Flight Center (MSFC) was given responsibility for the design, development, and construction of the telescope, while Goddard Space Flight Center was given overall control of the scientific instruments and ground-control center for the mission.{{sfn|Dunar|Waring|1999|pp=487–488}} MSFC commissioned the optics company Perkin-Elmer to design and build the optical telescope assembly (OTA) and Fine Guidance Sensors for the space telescope. Lockheed was commissioned to construct and integrate the spacecraft in which the telescope would be housed.{{sfn|Dunar|Waring|1999|p=489}}

Optically, the HST is a Cassegrain reflector of Ritchey–Chrétien design, as are most large professional telescopes. This design, with two hyperbolic mirrors, is known for good imaging performance over a wide field of view, with the disadvantage that the mirrors have shapes that are hard to fabricate and test. The mirror and optical systems of the telescope determine the final performance, and they were designed to exacting specifications. Optical telescopes typically have mirrors polished to an accuracy of about a tenth of the wavelength of visible light, but the Space Telescope was to be used for observations from the visible through the ultraviolet (shorter wavelengths) and was specified to be diffraction limited to take full advantage of the space environment. Therefore, its mirror needed to be polished to an accuracy of 10 nanometers, or about 1/65 of the wavelength of red light.{{cite journal |last=Waldrop |first=M. M. |date=August 17, 1990 |title=Hubble: The Case of the Single-Point Failure |journal=Science Magazine |volume=249 |issue=4970 |pages=735–736 |bibcode=1990Sci...249..735W |doi=10.1126/science.249.4970.735 |pmid=17756776}} On the long wavelength end, the OTA was not designed with optimum infrared performance in mind—for example, the mirrors are kept at stable (and warm, about 15 °C) temperatures by heaters. This limits Hubble's performance as an infrared telescope.

File:A20010288000 NASM2017-10014 (cropped).jpg

Perkin-Elmer (PE) intended to use custom-built and extremely sophisticated computer-controlled polishing machines to grind the mirror to the required shape.{{sfn|Dunar|Waring|1999|p=489}} However, in case their cutting-edge technology ran into difficulties, NASA demanded that PE sub-contract to Kodak to construct a back-up mirror using traditional mirror-polishing techniques.{{sfn|Allen|Angel|Mangus|Rodney|1990|pp=3–4}} (The team of Kodak and Itek also bid on the original mirror polishing work. Their bid called for the two companies to double-check each other's work, which would have almost certainly caught the polishing error that later caused problems.){{cite news|url=https://query.nytimes.com/gst/fullpage.html?res=9C0CEEDF1731F93BA15754C0A966958260|title=Losing Bid Offered Two Tests on Hubble|agency=Associated Press|date=July 28, 1990|newspaper=The New York Times|access-date=April 26, 2008|archive-date=February 4, 2009|archive-url=https://web.archive.org/web/20090204215644/http://query.nytimes.com/gst/fullpage.html?res=9C0CEEDF1731F93BA15754C0A966958260|url-status=live}} The Kodak mirror is now on permanent display at the National Air and Space Museum.{{cite press release|title=Hubble Space Telescope Stand-in Gets Starring Role|date=September 21, 2001|url=http://www.gsfc.nasa.gov/news-release/releases/2001/h01-185.htm|author=Goddard Space Flight Center|publisher=NASA|access-date=April 26, 2008|url-status=dead|archive-url=https://web.archive.org/web/20080226075115/http://www.gsfc.nasa.gov/news-release/releases/2001/h01-185.htm|archive-date=February 26, 2008}} {{PD-notice}}{{cite web|title=Backup Mirror, Hubble Space Telescope|url=http://www.nasm.si.edu/collections/artifact.cfm?id=A20010288000|publisher=National Air and Space Museum|access-date=November 4, 2012|archive-url=https://web.archive.org/web/20121102124612/http://airandspace.si.edu/collections/artifact.cfm?id=A20010288000 |archive-date=November 2, 2012}} An Itek mirror built as part of the effort is now used in the 2.4 m telescope at the Magdalena Ridge Observatory.{{cite tech report|author=Magdalena Ridge Observatory|title=2.4m Observatory Technical Note|date=January 1, 2008|url=http://www.mro.nmt.edu/data/2.4m/doc-public/OTN-Overview.pdf|access-date=January 21, 2013|page=2|version=1.6|archive-date=March 4, 2016|archive-url=https://web.archive.org/web/20160304103937/http://www.mro.nmt.edu/data/2.4m/doc-public/OTN-Overview.pdf|url-status=live}}

Construction of the Perkin-Elmer mirror began in 1979, starting with a blank manufactured by Corning from their ultra-low expansion glass. To keep the mirror's weight to a minimum it consisted of top and bottom plates, each {{cvt|25|mm}} thick, sandwiching a honeycomb lattice. Perkin-Elmer simulated microgravity by supporting the mirror from the back with 130 rods that exerted varying amounts of force.{{cite conference|title=Design and fabrication of the NASA 2.4-meter space telescope|first1=Daniel J.|last1=McCarthy|first2=Terence A.|last2=Facey|editor-first1=Paul R. |editor-last1=Yoder, Jr. |work=Proc. SPIE 0330, Optical Systems Engineering II|series=Optical Systems Engineering II |pages=139–143|date=1982|volume=0330 |publisher=International Society for Optics and Photonics|doi=10.1117/12.934268}} This ensured the mirror's final shape would be correct and to specification when deployed. Mirror polishing continued until May 1981. NASA reports at the time questioned Perkin-Elmer's managerial structure, and the polishing began to slip behind schedule and over budget. To save money, NASA halted work on the back-up mirror and moved the launch date of the telescope to October 1984.{{sfn|Dunar|Waring|1999|p=496}} The mirror was completed by the end of 1981; it was washed using {{cvt|9100|L}} of hot, deionized water and then received a reflective coating of 65 nm-thick aluminum and a protective coating of 25 nm-thick magnesium fluoride.{{cite journal|title=The Performance of HST as an Infrared Telescope|first1=M.|last1=Robberto|first2=A.|last2=Sivaramakrishnan|first3=J. J.|last3=Bacinski|first4=Daniele|last4=Calzetti|first5=J. E.|last5=Krist|first6=J. W.|last6=MacKenty|first7=J.|last7=Piquero|first8=M.|last8=Stiavelli|journal=Proc. SPIE|volume=4013|pages=386–393|date=2000|doi=10.1117/12.394037|series=UV, Optical, and IR Space Telescopes and Instruments|editor1-last=Breckinridge|editor1-first=James B.|editor2-last=Jakobsen|editor2-first=Peter|bibcode=2000SPIE.4013..386R|citeseerx=10.1.1.358.1298 |s2cid=14992130}} {{PD-notice}}{{cite book|title=The Space Telescope|publisher=Michael Friedman|location=New York|first=David|last=Ghitelman|page=[https://archive.org/details/spacetelescope00ghit/page/32 32]|date=1987 |isbn=978-0-8317-7971-9|url=https://archive.org/details/spacetelescope00ghit/page/32}}

File:Early stages of Hubble construction.jpg

Doubts continued to be expressed about Perkin-Elmer's competence on a project of this importance, as their budget and timescale for producing the rest of the OTA continued to inflate. In response to a schedule described as "unsettled and changing daily", NASA postponed the launch date of the telescope until April 1985. Perkin-Elmer's schedules continued to slip at a rate of about one month per quarter, and at times delays reached one day for each day of work. NASA was forced to postpone the launch date until March and then September 1986. By this time, the total project budget had risen to US$1.175 billion.{{sfn|Dunar|Waring|1999|p=504}}

The spacecraft in which the telescope and instruments were to be housed was another major engineering challenge. It would have to withstand frequent passages from direct sunlight into the darkness of Earth's shadow, which would cause major changes in temperature, while being stable enough to allow extremely accurate pointing of the telescope. A shroud of multi-layer insulation keeps the temperature within the telescope stable and surrounds a light aluminum shell in which the telescope and instruments sit. Within the shell, a graphite-epoxy frame keeps the working parts of the telescope firmly aligned.{{cite web|url=http://www.gsfc.nasa.gov/gsfc/service/gallery/fact_sheets/spacesci/hst3-01/hubble_space_telescope_systems.htm|title=Hubble Space Telescope Systems|publisher=Goddard Space Flight Center|access-date=April 26, 2008|url-status=dead|archive-url=https://web.archive.org/web/20030317035553/http://www.gsfc.nasa.gov/gsfc/service/gallery/fact_sheets/spacesci/hst3-01/hubble_space_telescope_systems.htm|archive-date=March 17, 2003}} {{PD-notice}} Because graphite composites are hygroscopic, there was a risk that water vapor absorbed by the truss while in Lockheed's clean room would later be expressed in the vacuum of space; resulting in the telescope's instruments being covered by ice. To reduce that risk, a nitrogen gas purge was performed before launching the telescope into space.Ghitelman, David (1987) The Space Telescope, New York: Michael Friedman Publishing, p. 50.

As well as electrical power systems, the Pointing Control System controls HST orientation using five types of sensors (magnetic sensors, optical sensors, and six gyroscopes) and two types of actuators (reaction wheels and magnetic torquers).

While construction of the spacecraft in which the telescope and instruments would be housed proceeded somewhat more smoothly than the construction of the OTA, Lockheed experienced some budget and schedule slippage, and by the summer 1985, construction of the spacecraft was 30% over budget and three months behind schedule. An MSFC report said Lockheed tended to rely on NASA directions rather than take their own initiative in the construction.{{sfn|Dunar|Waring|1999|p=508}}

File:DF-224.jpg

The two initial, primary computers on the HST were the 1.25 MHz DF-224 system, built by Rockwell Autonetics, which contained three redundant CPUs, and two redundant NSSC-1 (NASA Standard Spacecraft Computer, Model 1) systems, developed by Westinghouse and GSFC using diode–transistor logic (DTL). A co-processor for the DF-224 was added during Servicing Mission 1 in 1993, which consisted of two redundant strings of an Intel-based 80386 processor with an 80387 math co-processor.{{cite web|url=http://asd.gsfc.nasa.gov/archive/hubble/a_pdf/news/facts/CoProcessor.pdf|title=Co-Processor|series=NASA Facts|publisher=NASA|date=June 1993|id=NF-193|access-date=May 16, 2016|archive-date=July 23, 2012|archive-url=https://web.archive.org/web/20120723055334/http://asd.gsfc.nasa.gov/archive/hubble/a_pdf/news/facts/CoProcessor.pdf|url-status=live}} {{PD-notice}} The DF-224 and its 386 co-processor were replaced by a 25 MHz Intel-based 80486 processor system during Servicing Mission 3A in 1999.{{cite web|url=http://asd.gsfc.nasa.gov/archive/hubble/a_pdf/news/facts/FS09.pdf|title=Hubble Space Telescope Servicing Mission 3A: New Advanced Computer|series=NASA Facts|publisher=NASA|date=1999|id=FS-1999-06-009-GSFC|access-date=May 16, 2016|archive-date=May 9, 2016|archive-url=https://web.archive.org/web/20160509132748/http://asd.gsfc.nasa.gov/archive/hubble/a_pdf/news/facts/FS09.pdf|url-status=live}} The new computer is 20 times faster, with six times more memory, than the DF-224 it replaced. It increases throughput by moving some computing tasks from the ground to the spacecraft and saves money by allowing the use of modern programming languages.{{cite tech report|url=https://asd.gsfc.nasa.gov/archive/hubble/a_pdf/news/SM3A-MediaGuide.pdf|title=Hubble Space Telescope Servicing Mission 3A Media Reference Guide|publisher=NASA|author=Lockheed Martin Missiles and Space|access-date=April 7, 2022|pages=5–9 and Section 7.1.1|archive-date=November 25, 2011|archive-url=https://web.archive.org/web/20111125161422/http://hubble.nasa.gov/a_pdf/news/SM3A-MediaGuide.pdf|url-status=live}} {{PD-notice}}

Additionally, some of the science instruments and components had their own embedded microprocessor-based control systems. The MATs (Multiple Access Transponder) components, MAT-1 and MAT-2, use Hughes Aircraft CDP1802CD microprocessors.{{cite journal|url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160005759.pdf|title=How Long Can the Hubble Space Telescope Operate Reliably? A Total Dose Perspective|journal=IEEE Transactions on Nuclear Science|first1=M. A.|last1=Xapsos|first2=C.|last2=Stauffer|first3=T.|last3=Jordan|first4=C.|last4=Poivey|first5=D. N.|last5=Haskins|first6=G.|last6=Lum|first7=A. M.|last7=Pergosky|first8=D. C.|last8=Smith|first9=K. A.|last9=LaBel|volume=61|issue=6|pages=3356–3362|date=December 2014|bibcode=2014ITNS...61.3356X|doi=10.1109/TNS.2014.2360827|hdl=2060/20160005759|s2cid=1792941|hdl-access=free|access-date=July 7, 2017|archive-date=February 27, 2017|archive-url=https://web.archive.org/web/20170227173247/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160005759.pdf|url-status=live}} {{PD-notice}} The Wide Field and Planetary Camera (WFPC) also used an RCA 1802 microprocessor (or possibly the older 1801 version).{{cite magazine|url=http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/35164/1/93-0731.pdf|title=Hubble Space Telescope's Wide Field/Planetary Camera|magazine=Shutterbug|first=A.|last=Afshari|date=January 1993|url-status=dead|archive-url=https://web.archive.org/web/20161006205644/http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/35164/1/93-0731.pdf|archive-date=October 6, 2016}} {{PD-notice}} The WFPC-1 was replaced by the WFPC-2 during Servicing Mission 1 in 1993, which was then replaced by the Wide Field Camera 3 (WFC3) during Servicing Mission 4 in 2009. The upgrade extended Hubble's capability of seeing deeper into the universe and providing images in three broad regions of the spectrum.{{Cite web|title=The 'Camera That Saved Hubble'|url=https://www.jpl.nasa.gov/news/the-camera-that-saved-hubble|access-date=November 27, 2021|website=NASA Jet Propulsion Laboratory (JPL)|archive-date=November 27, 2021|archive-url=https://web.archive.org/web/20211127133956/https://www.jpl.nasa.gov/news/the-camera-that-saved-hubble|url-status=live}}{{Cite web|last=Garner|first=Rob|date=August 22, 2016|title=Hubble Space Telescope – Wide Field Camera 3|url=http://www.nasa.gov/content/hubble-space-telescope-wide-field-camera-3|access-date=November 27, 2021|website=NASA|archive-date=November 13, 2021|archive-url=https://web.archive.org/web/20211113213252/https://www.nasa.gov/content/hubble-space-telescope-wide-field-camera-3/|url-status=live}}

{{Main|Wide Field and Planetary Camera|Goddard High Resolution Spectrograph|High Speed Photometer|Faint Object Camera|Faint Object Spectrograph}}

File:HubbleExploded edit 1.svg of the Hubble Space Telescope]]

When launched, the HST carried five scientific instruments: the Wide Field and Planetary Camera (WF/PC), Goddard High Resolution Spectrograph (GHRS), High Speed Photometer (HSP), Faint Object Camera (FOC) and the Faint Object Spectrograph (FOS). WF/PC used a radial instrument bay, and the other four instruments were each installed in an axial instrument bay.

WF/PC was a high-resolution imaging device primarily intended for optical observations. It was built by NASA's Jet Propulsion Laboratory, and incorporated a set of 48 filters isolating spectral lines of particular astrophysical interest. The instrument contained eight charge-coupled device (CCD) chips divided between two cameras, each using four CCDs. Each CCD has a resolution of 0.64 megapixels.{{cite web|url=https://esahubble.org/about/general/instruments/wfpc2/|title=Hubble's Instruments: WFPC2 Wide Field Planetary Camera 2|website=esahubble.org|publisher=European Space Agency|access-date=April 7, 2022|archive-date=April 7, 2022|archive-url=https://web.archive.org/web/20220407073748/https://esahubble.org/about/general/instruments/wfpc2/|url-status=live}} The wide field camera (WFC) covered a large angular field at the expense of resolution, while the planetary camera (PC) took images at a longer effective focal length than the WF chips, giving it a greater magnification.{{cite tech report|title=The Space Telescope Observatory|number=CP-2244|publisher=NASA|editor-first=Donald N. B.|editor-last=Hall|url=https://ntrs.nasa.gov/citations/19820025420|date=1982|access-date=April 7, 2022|archive-date=April 7, 2022|archive-url=https://web.archive.org/web/20220407073748/https://ntrs.nasa.gov/citations/19820025420|url-status=live}}

The Goddard High Resolution Spectrograph (GHRS) was a spectrograph designed to operate in the ultraviolet. It was built by the Goddard Space Flight Center and could achieve a spectral resolution of 90,000.{{cite journal |author=Brandt |first1=J. C. |last2=Heap |first2=S. R. |last3=Beaver |first3=E. A. |last4=Boggess |first4=A. |last5=Carpenter |first5=K. G. |last6=Ebbets |first6=D. C. |last7=Hutchings |first7=J. B. |last8=Jura |first8=M. |last9=Leckrone |first9=D. S. |date=1994 |title=The Goddard High Resolution Spectrograph: Instrument, goals, and science results |journal=Publications of the Astronomical Society of the Pacific |volume=106 |pages=890–908 |bibcode=1994PASP..106..890B |doi=10.1086/133457 |doi-access=|s2cid=120181145 }} Also optimized for ultraviolet observations were the FOC and FOS, which were capable of the highest spatial resolution of any instruments on Hubble. Rather than CCDs, these three instruments used photon-counting digicons as their detectors. The FOC was constructed by ESA, while the University of California, San Diego, and Martin Marietta Corporation built the FOS.

The final instrument was the HSP, designed and built at the University of Wisconsin–Madison. It was optimized for visible and ultraviolet light observations of variable stars and other astronomical objects varying in brightness. It could take up to 100,000 measurements per second with a photometric accuracy of about 2% or better.Bless, R. C.; Walter, L. E.; White R. L. (1992) High Speed Photometer Instrument Handbook v 3.0 STSci.

HST's guidance system can also be used as a scientific instrument. Its three Fine Guidance Sensors (FGS) are primarily used to keep the telescope accurately pointed during an observation, but can also be used to carry out extremely accurate astrometry; measurements accurate to within 0.0003 arcseconds have been achieved.{{cite conference |author=Benedict |first1=G. Fritz |last2=McArthur |first2=Barbara E. |date=2005 |editor-last=Kurtz |editor-first=D. W. |title=High-precision stellar parallaxes from Hubble Space Telescope fine guidance sensors |url=https://pdfs.semanticscholar.org/ce07/0e358a8f3ed7a8bb7b470fc2986c8833d3f0.pdf |conference=IAU Colloquium #196 |publisher=Cambridge University Press |pages=333–346 |bibcode=2005tvnv.conf..333B |doi=10.1017/S1743921305001511 |archive-url=https://web.archive.org/web/20200227131024/https://pdfs.semanticscholar.org/ce07/0e358a8f3ed7a8bb7b470fc2986c8833d3f0.pdf |archive-date=February 27, 2020 |work=Transits of Venus: New Views of the Solar System and Galaxy |s2cid=123078909 |url-status=dead}}

{{Main|Space Telescope Science Institute}}

File:Hubble Control Centre.jpg

The Space Telescope Science Institute (STScI) is responsible for the scientific operation of the telescope and the delivery of data products to astronomers. STScI is operated by the Association of Universities for Research in Astronomy (AURA) and is physically located in Baltimore, Maryland on the Homewood campus of Johns Hopkins University, one of the 39 U.S. universities and seven international affiliates that make up the AURA consortium. STScI was established in 1981{{cite book |url=https://books.google.com/books?id=jEurac1jvsAC&pg=PA244 |title=AURA and Its US National Observatories |publisher=Cambridge University Press |first=Frank K. |last=Edmondson |page=244 |date=1997 |isbn=978-0-521-55345-2 |access-date=January 7, 2022 |archive-date=July 15, 2022 |archive-url=https://web.archive.org/web/20220715150041/https://books.google.com/books?id=jEurac1jvsAC&pg=PA244 |url-status=live }}{{cite web |url=http://www.aura-astronomy.org/about.asp |title=About AURA |publisher=AURA |access-date=November 6, 2012 |archive-date=September 29, 2018 |archive-url=https://web.archive.org/web/20180929155829/http://www.aura-astronomy.org/about.asp |url-status=live }} after something of a power struggle between NASA and the scientific community at large. NASA had wanted to keep this function in-house, but scientists wanted it to be based in an academic establishment.{{sfn|Dunar|Waring|1999|pp=486–487}}Roman, Nancy Grace. "Exploring the Universe: Space-Based Astronomy and Astrophysics", in [https://history.nasa.gov/SP-4407/vol5/ExploreUnknown.pdf NASA SP-2001-4407: Exploring the Unknown] {{Webarchive|url=https://web.archive.org/web/20170120024958/https://history.nasa.gov/SP-4407/vol5/ExploreUnknown.pdf |date=January 20, 2017 }} (PDF). NASA. Chapter 3, p. 536. The Space Telescope European Coordinating Facility (ST-ECF), established at Garching bei München near Munich in 1984, provided similar support for European astronomers until 2011, when these activities were moved to the European Space Astronomy Centre.{{Cite web |title=Closure of ST-ECF |url=http://www.stecf.org/ECFclosure.php |access-date=April 7, 2022 |website=www.stecf.org}}

One complex task that falls to STScI is scheduling observations for the telescope.{{cite web |url=https://www.stsci.edu/hst/observing/scheduling |title=Scheduling |publisher=Space Telescope Science Institute |website=stsci.edu |access-date=April 7, 2022 |archive-date=July 15, 2022 |archive-url=https://web.archive.org/web/20220715144805/https://www.stsci.edu/hst/observing/scheduling |url-status=live }} Hubble is in a low-Earth orbit to enable servicing missions, which results in most astronomical targets being occulted by the Earth for slightly less than half of each orbit. Observations cannot take place when the telescope passes through the South Atlantic Anomaly due to elevated radiation levels, and there are also sizable exclusion zones around the Sun (precluding observations of Mercury), Moon and Earth. The solar avoidance angle is about 50°, to keep sunlight from illuminating any part of the OTA. Earth and Moon avoidance keeps bright light out of the FGSs, and keeps scattered light from entering the instruments. If the FGSs are turned off, the Moon and Earth can be observed. Earth observations were used very early in the program to generate flat-fields for the WFPC1 instrument. There is a so-called continuous viewing zone (CVZ), within roughly 24° of Hubble's orbital poles, in which targets are not occulted for long periods.{{Cite web |date=January 15, 1996 |title=Hubble's Deepest View of the Universe Unveils Bewildering Galaxies across Billions of Years |url=http://hubblesite.org/contents/news-releases/1996/news-1996-01 |access-date=April 7, 2022 |website=HubbleSite.org |publisher=Space Telescope Science Institute |language=en |archive-date=July 15, 2022 |archive-url=https://web.archive.org/web/20220715150044/https://hubblesite.org/contents/news-releases/1996/news-1996-01.html |url-status=live }}{{Cite journal |last1=Adler |first1=David S. |last2=Kinzel |first2=Wayne |last3=Jordan |first3=Ian |date=August 6, 2014 |editor-last=Peck |editor-first=Alison B. |editor2-last=Benn |editor2-first=Chris R. |editor3-last=Seaman |editor3-first=Robert L. |title=Planning and scheduling at STScI: from Hubble to the James Webb Space Telescope |url=http://proceedings.spiedigitallibrary.org/proceeding.aspx?doi=10.1117/12.2054932 |journal=Proc. SPIE 9149, Observatory Operations: Strategies, Processes, and Systems V |series=Observatory Operations: Strategies, Processes, and Systems V |volume=9149 |location=Montréal, Quebec, Canada |pages=91490D |doi=10.1117/12.2054932 |bibcode=2014SPIE.9149E..0DA |s2cid=122694163 |access-date=July 15, 2022 |archive-date=July 15, 2022 |archive-url=https://web.archive.org/web/20220715150044/https://www.spiedigitallibrary.org/conference-proceedings-of-spie/9149/1/Planning-and-scheduling-at-STScI--from-Hubble-to-the/10.1117/12.2054932.short?SSO=1 |url-status=live }}{{Cite web |title=HST Cycle 26 Primer Orbital Constraints – HST User Documentation |url=https://hst-docs.stsci.edu/hsp/past-hst-proposal-opportunities/the-hubble-space-telescope-primer-for-cycle-26/hst-cycle-26-primer-orbital-constraints |access-date=July 16, 2022 |website=hst-docs.stsci.edu |archive-date=July 16, 2022 |archive-url=https://web.archive.org/web/20220716221122/https://hst-docs.stsci.edu/hsp/past-hst-proposal-opportunities/the-hubble-space-telescope-primer-for-cycle-26/hst-cycle-26-primer-orbital-constraints |url-status=live }}

{{multiple image

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| image1 = Diagram of Hubble's orbit.jpg

| caption1 = Hubble's low orbit means many targets are visible for slightly more than half of an orbit's elapsed time, since they are blocked from view by the Earth for almost one-half of each orbit.

| image2 = Animation of Hubble Space Telescope trajectory.gif

| caption2 = Animation of Hubble's orbit from October 31, 2018, to December 25, 2018; Earth is not shown.

}}

Due to the precession of the orbit, the location of the CVZ moves slowly over a period of eight weeks. Because the limb of the Earth is always within about 30° of regions within the CVZ, the brightness of scattered earthshine may be elevated for long periods during CVZ observations. Hubble orbits in low Earth orbit at an altitude of approximately {{convert|540|km|sp=us}} and an inclination of 28.5°. The position along its orbit changes over time in a way that is not accurately predictable. The density of the upper atmosphere varies according to many factors, and this means Hubble's predicted position for six weeks' time could be in error by up to {{convert|4000|km|abbr=on}}. Observation schedules are typically finalized only a few days in advance, as a longer lead time would mean there was a chance the target would be unobservable by the time it was due to be observed.{{sfn|Strolger|Rose|2017|p=46}} Engineering support for HST is provided by NASA and contractor personnel at the Goddard Space Flight Center in Greenbelt, Maryland, {{convert|48|km|abbr=on}} south of the STScI. Hubble's operation is monitored 24 hours per day by four teams of flight controllers who make up Hubble's Flight Operations Team.

File:STS-31 Hubble launch roll and pitch.jpg lifting off, carrying Hubble into orbit]]

File:1990 s31 IMAX view of HST release.jpg

By January 1986, the planned launch date for Hubble that October looked feasible, but the Challenger disaster brought the U.S. space program to a halt, grounded the Shuttle fleet, and forced the launch to be postponed for several years. During this delay the telescope was kept in a clean room, powered up and purged with nitrogen, until a launch could be rescheduled. This costly situation (about {{US$|6 million}} per month) pushed the overall costs of the project higher. However, this delay allowed time for engineers to perform extensive tests, swap out a possibly failure-prone battery, and make other improvements.{{sfn|Tatarewicz|1998|p=371}} Furthermore, the ground software needed to control Hubble was not ready in 1986, and was barely ready by the 1990 launch.{{cite news |title=Telescope Is Set to Peer at Space and Time |first=John |last=Wilford |url=https://query.nytimes.com/gst/fullpage.html?res=9C0CE3D6153AF93AA35757C0A966958260&sec=&spon=&pagewanted=all |work=The New York Times |date=April 9, 1990 |access-date=January 19, 2009 |archive-date=November 11, 2012 |archive-url=https://web.archive.org/web/20121111141710/http://www.nytimes.com/1990/04/09/us/telescope-is-set-to-peer-at-space-and-time.html |url-status=live }} Following the resumption of shuttle flights, {{OV|Discovery}} successfully launched the Hubble on April 24, 1990, as part of the STS-31 mission.{{cite web |url=http://science.ksc.nasa.gov/shuttle/missions/sts-31/mission-sts-31.html |title=STS-31 |publisher=NASA |access-date=April 26, 2008 |archive-date=August 15, 2011 |archive-url=https://web.archive.org/web/20110815191242/http://science.ksc.nasa.gov/shuttle/missions/sts-31/mission-sts-31.html |url-status=live }}

At launch, NASA had spent approximately {{US$|4.7 billion}} in inflation-adjusted 2010 dollars on the project.{{cite web |url=http://www.nasa.gov/pdf/499224main_JWST-ICRP_Report-FINAL.pdf |title=James Webb Space Telescope (JWST) Independent Comprehensive Review Panel (ICRP) Final Report |page=32 |publisher=NASA |access-date=April 7, 2022 |archive-date=November 17, 2021 |archive-url=https://web.archive.org/web/20211117185346/https://www.nasa.gov/pdf/499224main_JWST-ICRP_Report-FINAL.pdf |url-status=live }} Hubble's cumulative costs are estimated to be about {{US$|11.3 billion}} in 2015 dollars, which include all subsequent servicing costs, but not ongoing operations, making it the most expensive science mission in NASA history.{{cite book |title=Powering Science: NASA's Large Strategic Science Missions |url=https://nap.nationalacademies.org/catalog/24857/powering-science-nasas-large-strategic-science-missions |publisher=The National Academies of Sciences, Engineering, and Medicine |page=11, footnote 4 |doi=10.17226/24857 |date=2017 |isbn=978-0-309-46383-6 |access-date=April 7, 2022 |archive-date=April 21, 2022 |archive-url=https://web.archive.org/web/20220421203447/https://nap.nationalacademies.org/catalog/24857/powering-science-nasas-large-strategic-science-missions |url-status=live }}

Hubble accommodates five science instruments at a given time, plus the Fine Guidance Sensors, which are mainly used for aiming the telescope but are occasionally used for scientific astrometry measurements. Early instruments were replaced with more advanced ones during the Shuttle servicing missions. COSTAR was a corrective optics device rather than a science instrument, but occupied one of the four axial instrument bays.

Since the final servicing mission in 2009, the four active instruments have been ACS, COS, STIS and WFC3. NICMOS is kept in hibernation, but may be revived if WFC3 were to fail in the future.

• Advanced Camera for Surveys (ACS; 2002–present)
• Cosmic Origins Spectrograph (COS; 2009–present)
• Corrective Optics Space Telescope Axial Replacement (COSTAR; 1993–2009)
• Faint Object Camera (FOC; 1990–2002)
• Faint Object Spectrograph (FOS; 1990–1997)
• Fine Guidance Sensor (FGS; 1990–present)
• Goddard High Resolution Spectrograph (GHRS/HRS; 1990–1997)
• High Speed Photometer (HSP; 1990–1993)
• Near Infrared Camera and Multi-Object Spectrometer (NICMOS; 1997–present, hibernating since 2008)
• Space Telescope Imaging Spectrograph (STIS; 1997–present (non-operative 2004–2009))
• Wide Field and Planetary Camera (WFPC; 1990–1993)
• Wide Field and Planetary Camera 2 (WFPC2; 1993–2009)
• Wide Field Camera 3 (WFC3; 2009–present)

Of the former instruments, three (COSTAR, FOS and WFPC2) are displayed in the Smithsonian National Air and Space Museum.{{Cite news |last=Greenfieldboyce |first=Nell |date=November 18, 2009 |title=Camera That Saved Hubble Now On Display |language=en |work=NPR |url=https://www.npr.org/templates/story/story.php?storyId=120539846 |access-date=April 7, 2022 |archive-date=December 30, 2021 |archive-url=https://web.archive.org/web/20211230042239/https://www.npr.org/templates/story/story.php?storyId=120539846 |url-status=live }}{{Cite web |date=September 11, 2001 |title=Greater accuracy deepens understanding – Hubble's Faint Object Spectrograph re-calibrated |url=https://esahubble.org/news/heic0112/ |url-status=live |archive-url=https://web.archive.org/web/20220715150042/https://esahubble.org/news/heic0112/ |archive-date=July 15, 2022 |access-date=April 7, 2022 |website=ESA/Hubble |language=en-us}} The FOC is in the Dornier museum, Germany.{{Cite web |title=Hubble's Instruments: FOC – Faint Object Camera |url=https://esahubble.org/about/general/instruments/foc/ |url-status=live |archive-url=https://web.archive.org/web/20220504113333/https://esahubble.org/about/general/instruments/foc/ |archive-date=May 4, 2022 |access-date=April 7, 2022 |website=ESA/Hubble |language=en-us}} The HSP is in the Space Place at the University of Wisconsin–Madison.{{Cite web |last=Devitt |first=Terry |date=April 21, 2015 |title=Wisconsin contributions helped Hubble Space Telescope soar |url=https://news.wisc.edu/wisconsin-contributions-helped-hubble-space-telescope-soar/ |access-date=April 7, 2022 |website=University of Wisconsin-Madison News |language=en-US |archive-date=December 24, 2021 |archive-url=https://web.archive.org/web/20211224082240/https://news.wisc.edu/wisconsin-contributions-helped-hubble-space-telescope-soar/ |url-status=live }} The first WFPC was dismantled, and some components were then re-used in WFC3.{{Cite web |last=Plait |first=Phil |author-link=Phil Plait |date=1999 |title=Hubble's Next Next Generation |url=http://www.badastronomy.com/bitesize/wfc3.html |access-date=April 7, 2022 |website=Bitesize astronomy |archive-date=May 31, 2022 |archive-url=https://web.archive.org/web/20220531010526/http://www.badastronomy.com/bitesize/wfc3.html |url-status=live }}{{Cite web |date=2001 |title=Hubble Space Telescope Wide Field Camera 3: Capabilities and Scientific Programs |url=https://www.stsci.edu/~WFC3/resources/WFC3-WhitePaper-2001.pdf |access-date=April 6, 2022 |website=Space Telescope Science Institute |archive-date=July 15, 2022 |archive-url=https://web.archive.org/web/20220715150040/https://www.stsci.edu/~WFC3/resources/WFC3-WhitePaper-2001.pdf |url-status=live }}

File:Hubble PSF with flawed optics.jpg

Within weeks of the launch of the telescope, the returned images indicated a serious problem with the optical system. Although the first images appeared to be sharper than those of ground-based telescopes, Hubble failed to achieve a final sharp focus and the best image quality obtained was drastically lower than expected. Images of point sources spread out over a radius of more than one arcsecond, instead of having a point spread function (PSF) concentrated within a circle 0.1 arcseconds (485 nrad) in diameter, as had been specified in the design criteria.{{cite journal |title=The imaging performance of the Hubble Space Telescope |journal=Astrophysical Journal Letters |first1=Christopher J. |last1=Burrows |first2=Jon A. |display-authors=4 |last2=Holtzman |first3=S. M. |last3=Faber |first4=Pierre Y. |last4=Bely |first5=Hashima |last5=Hasan |first6=C. R. |last6=Lynds |first7=Daniel |last7=Schroeder |volume=369 |pages=L21–L25 |date=March 10, 1991 |doi=10.1086/185950 |bibcode=1991ApJ...369L..21B}}{{cite web |url=https://www.stsci.edu/files/live/sites/www/files/home/hst/documentation/_documents/wfpc2/wfpc2_ihb_cycle17.pdf |title=WFPC2 Instrument Handbook |at=Chapter 5.1 |publisher=STScI |date=2008 |last1=McMaster |first1=Matt |last2=Biretta |first2=John |location=Baltimore |version=10.0 |access-date=April 7, 2022 |archive-date=July 15, 2022 |archive-url=https://web.archive.org/web/20220715150041/https://www.stsci.edu/files/live/sites/www/files/home/hst/documentation/_documents/wfpc2/wfpc2_ihb_cycle17.pdf |url-status=live }}

Analysis of the flawed images revealed that the primary mirror had been polished to the wrong shape. Although it was believed to be one of the most precisely figured optical mirrors ever made, smooth to about 10 nanometers, the outer perimeter was too flat by about 2200 nanometers (about {{frac|450}} mm or {{frac|11000}} inch).{{cite web |url=http://asd.gsfc.nasa.gov/archive/hubble/missions/sm1.html |title=Servicing Mission 1 |publisher=NASA |access-date=March 28, 2016 |archive-url=https://web.archive.org/web/20080420202154/http://hubble.nasa.gov/missions/sm1.php |archive-date=April 20, 2008}} This difference was catastrophic, introducing severe spherical aberration, a flaw in which light reflecting off the edge of a mirror focuses on a different point from the light reflecting off its center.{{sfn|Tatarewicz|1998|p=375}}

The effect of the mirror flaw on scientific observations depended on the particular observation—the core of the aberrated PSF was sharp enough to permit high-resolution observations of bright objects, and spectroscopy of point sources was affected only through a sensitivity loss. However, the loss of light to the large, out-of-focus halo severely reduced the usefulness of the telescope for faint objects or high-contrast imaging. This meant nearly all the cosmological programs were essentially impossible, since they required observation of exceptionally faint objects.{{sfn|Tatarewicz|1998|p=375}} This led politicians to question NASA's competence, scientists to rue the cost which could have gone to more productive endeavors, and comedians to make jokes about NASA and the telescope. In the 1991 comedy The Naked Gun 2½: The Smell of Fear, in a scene where historical disasters are displayed, Hubble is pictured with RMS Titanic and LZ 129 Hindenburg.{{cite web |author=Powell |first=Corey S. |date=April 24, 2015 |title=The Many Resurrections of the Hubble Space Telescope |url=https://www.discovermagazine.com/the-sciences/the-many-resurrections-of-the-hubble-space-telescope |url-status=live |archive-url=https://web.archive.org/web/20220715150043/https://www.discovermagazine.com/the-sciences/the-many-resurrections-of-the-hubble-space-telescope |archive-date=July 15, 2022 |access-date=December 16, 2020 |work=Discover Magazine}}{{sfn|Tatarewicz|1998|p=373}} Nonetheless, during the first three years of the Hubble mission, before the optical corrections, the telescope carried out a large number of productive observations of less demanding targets.{{cite journal |author=Goodwin, Irwin |date=1994 |title=Hubble repair improves vision and helps restore NASA's image |journal=Physics Today |volume=47 |issue=3 |page=42 |author2=Cioffi, Denis F. |doi=10.1063/1.2808434 |bibcode=1994PhT....47c..42G}} The error was well characterized and stable, enabling astronomers to partially compensate for the defective mirror by using sophisticated image processing techniques such as deconvolution.{{sfn|Dunar|Waring|1999|pp=514–515}}

File:PIA22913-HubbleSpaceTelescope-ComparisonOfCameraImages-20181204.jpg as seen with WFPC1 in 1993 before corrective optics (left), with WFPC2 in 1994 after correction (center), and with WFC3 in 2018 (right).]]

A commission headed by Lew Allen, director of the Jet Propulsion Laboratory, was established to determine how the error could have arisen. The Allen Commission found that a reflective null corrector, a testing device used to achieve a properly shaped non-spherical mirror, had been incorrectly assembled—one lens was out of position by {{convert|1.3|mm|in|abbr=on}}.{{sfn|Allen|Angel|Mangus|Rodney|1990|p=7-1|ps=: The spacing of the field lens in the corrector was to have been done by laser measurements off the end of an invar bar. Instead of illuminating the end of the bar, however, the laser in fact was reflected from a worn spot on a black-anodized metal cap placed over the end of the bar to isolate its center (visible through a hole in the cap). The technician who performed the test noted an unexpected gap between the field lens and its supporting structure in the corrector and filled it in with an ordinary metal washer.}} During the initial grinding and polishing of the mirror, Perkin-Elmer analyzed its surface with two conventional refractive null correctors. However, for the final manufacturing step (figuring), they switched to the custom-built reflective null corrector, designed explicitly to meet very strict tolerances. The incorrect assembly of this device resulted in the mirror being ground very precisely but to the wrong shape. During fabrication, a few tests using conventional null correctors correctly reported spherical aberration. But these results were dismissed, thus missing the opportunity to catch the error, because the reflective null corrector was considered more accurate.{{sfn|Dunar|Waring|1999|p=512|ps=: "the firm's optical operations personnel dismissed the evidence as itself flawed. They believed the other two null correctors were less accurate than the reflective null corrector and so could not verify its reliability. Since they assumed the perfection of the mirror and reflective null corrector, they rejected falsifying information from independent tests, believed no problems existed, and reported only good news."}}

The commission blamed the failings primarily on Perkin-Elmer. Relations between NASA and the optics company had been severely strained during the telescope construction, due to frequent schedule slippage and cost overruns. NASA found that Perkin-Elmer did not review or supervise the mirror construction adequately, did not assign its best optical scientists to the project (as it had for the prototype), and in particular did not involve the optical designers in the construction and verification of the mirror. While the commission heavily criticized Perkin-Elmer for these managerial failings, NASA was also criticized for not picking up on the quality control shortcomings, such as relying totally on test results from a single instrument.{{sfn|Allen|Angel|Mangus|Rodney|1990|p=10-1}}

File:Feustel moving COSTAR.jpg during SM4 in 2009]]

Many feared that Hubble would be abandoned.{{sfn|Tatarewicz|1998|p=374}} The design of the telescope had always incorporated servicing missions, and astronomers immediately began to seek potential solutions to the problem that could be applied at the first servicing mission, scheduled for 1993. While Kodak had ground a back-up mirror for Hubble, it would have been impossible to replace the mirror in orbit, and too expensive and time-consuming to bring the telescope back to Earth for a refit. Instead, the fact that the mirror had been ground so precisely to the wrong shape led to the design of new optical components with exactly the same error but in the opposite sense, to be added to the telescope at the servicing mission, effectively acting as "spectacles" to correct the spherical aberration.{{Cite book |last=Chaisson |first=Eric |url=http://archive.org/details/hubblewarsastrop00chai |title=The Hubble wars: astrophysics meets astropolitics in the two-billion-dollar struggle over the Hubble Space Telescope |date=1994 |publisher=New York : HarperCollins Publishers |others=Internet Archive |isbn=978-0-06-017114-8 |page=184 |language=en-us}}{{cite journal |journal=Popular Science |url=https://books.google.com/books?id=lQEAAAAAMBAJ&pg=PA72 |date=October 1990 |title=The Trouble with Hubble |first=Arthur |last=Fisher |page=100 |access-date=November 8, 2012 |archive-date=January 8, 2022 |archive-url=https://web.archive.org/web/20220108230555/https://books.google.com/books?id=lQEAAAAAMBAJ&pg=PA72 |url-status=live }}

The first step was a precise characterization of the error in the main mirror. Working backwards from images of point sources, astronomers determined that the conic constant of the mirror as built was {{val|−1.01390|0.0002|fmt=none}}, instead of the intended {{val|−1.00230|fmt=none}}.{{cite tech report |title=Image inversion analysis of the HST OTA (Hubble Space Telescope Optical Telescope Assembly), phase A |publisher=TRW, Inc. Space and Technology Group |first=M. M. |last=Litvac |date=1991 |bibcode=1991trw..rept.....L}}{{cite journal |title=Optical Prescription of the HST |journal=Calibrating Hubble Space Telescope. Post Servicing Mission |pages=132 |url=http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/31621/1/95-1205_A1b.pdf |hdl=2014/31621 |date=July 1995 |publisher=NASA JPL |last1=Redding |first1=David C. |last2=Sirlin |first2=S. |last3=Boden |first3=A. |last4=Mo |first4=J. |last5=Hanisch |first5=B. |last6=Furey |first6=L. |url-status=dead|archive-url=https://web.archive.org/web/20150501140016/http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/31621/1/95-1205_A1b.pdf |archive-date=May 1, 2015|bibcode=1995chst.conf..132R}} The same number was also derived by analyzing the null corrector used by Perkin-Elmer to figure the mirror, as well as by analyzing interferograms obtained during ground testing of the mirror.{{sfn|Allen|Angel|Mangus|Rodney|1990|pp=E-1}}

Because of the way the HST's instruments were designed, two different sets of correctors were required. The design of the Wide Field and Planetary Camera 2, already planned to replace the existing WF/PC, included relay mirrors to direct light onto the four separate charge-coupled device (CCD) chips making up its two cameras. An inverse error built into their surfaces could completely cancel the aberration of the primary. However, the other instruments lacked any intermediate surfaces that could be configured in this way, and so required an external correction device.{{sfn|Tatarewicz|1998|p=376}}

The Corrective Optics Space Telescope Axial Replacement (COSTAR) system was designed to correct the spherical aberration for light focused at the FOC, FOS, and GHRS. It consists of two mirrors in the light path with one ground to correct the aberration.{{cite journal |author=Jedrzejewski |first1=R. I. |last2=Hartig |first2=G. |last3=Jakobsen |first3=P. |last4=Ford |first4=H. C. |date=1994 |title=In-orbit performance of the COSTAR-corrected Faint Object Camera |journal=Astrophysical Journal Letters |volume=435 |pages=L7–L10 |bibcode=1994ApJ...435L...7J |doi=10.1086/187581}} To fit the COSTAR system onto the telescope, one of the other instruments had to be removed, and astronomers selected the High Speed Photometer to be sacrificed.{{sfn|Tatarewicz|1998|p=376}} By 2002, all the original instruments requiring COSTAR had been replaced by instruments with their own corrective optics. COSTAR was then removed and returned to Earth in 2009 where it is exhibited at the National Air and Space Museum in Washington, D.C.{{Cite news|title=Camera That Saved Hubble Now On Display|work=NPR|url=https://www.npr.org/templates/story/story.php?storyId=120539846|access-date=December 30, 2021|archive-date=December 30, 2021|archive-url=https://web.archive.org/web/20211230042239/https://www.npr.org/templates/story/story.php?storyId=120539846|url-status=live}} The area previously used by COSTAR is now occupied by the Cosmic Origins Spectrograph.{{cite web |title=Hubble Essentials |url=http://hubblesite.org/the_telescope/hubble_essentials/ |url-status=dead |archive-url=https://web.archive.org/web/20121028200607/http://hubblesite.org/the_telescope/hubble_essentials/ |archive-date=October 28, 2012 |access-date=November 8, 2012 |website=HubbleSite.org |publisher=Space Telescope Science Institute}}

Hubble was designed to accommodate regular servicing and equipment upgrades while in orbit. Instruments and limited life items were designed as orbital replacement units.{{Cite web |date=2013-02-19 |title=Hubble Space Telescope (HST) Archive System |url=http://setas-www.larc.nasa.gov/HUBBLE/HARDWARE/hubble_ORU.html |access-date=2024-01-31 |archive-url=https://web.archive.org/web/20130219022932/http://setas-www.larc.nasa.gov/HUBBLE/HARDWARE/hubble_ORU.html |archive-date=February 19, 2013 }} Five servicing missions (SM 1, 2, 3A, 3B, and 4) were flown by NASA Space Shuttles, the first in December 1993 and the last in May 2009.{{cite web |url=https://www.nationalgeographic.com/hubble-timeline/ |title=The Secret to Hubble's Success |work=National Geographic |first1=Jason |last1=Treat |first2=Anna |last2=Scalamogna |first3=Eve |last3=Conant |date=2015 |access-date=April 25, 2015 |archive-date=April 28, 2015 |archive-url=https://web.archive.org/web/20150428040059/http://www.nationalgeographic.com/hubble-timeline/ |url-status=live }} Servicing missions were delicate operations that began with maneuvering to intercept the telescope in orbit and carefully retrieving it with the shuttle's mechanical arm. The necessary work was then carried out in multiple tethered spacewalks over a period of four to five days. After a visual inspection of the telescope, astronauts conducted repairs, replaced failed or degraded components, upgraded equipment, and installed new instruments. Once work was completed, the telescope was redeployed, typically after boosting to a higher orbit to address the orbital decay caused by atmospheric drag.{{cite web |url=https://www.nytimes.com/video/science/100000003647066/hubble-reflects-the-cosmos.html |title=Hubble Reflects the Cosmos |work=The New York Times |first1=Jason |last1=Overbye |first2=Jonathan |last2=Corum |first3=Jason |last3=Drakeford |date=April 24, 2015 |access-date=April 25, 2015 |archive-date=February 2, 2019 |archive-url=https://web.archive.org/web/20190202112051/https://www.nytimes.com/video/science/100000003647066/hubble-reflects-the-cosmos.html |url-status=live }}

{{Main|STS-61}}

File:Upgrading Hubble during SM1.jpg

The first Hubble servicing mission was scheduled for 1993 before the mirror problem was discovered. It assumed greater importance, as the astronauts would need to do extensive work to install corrective optics; failure would have resulted in either abandoning Hubble or accepting its permanent disability. Other components failed before the mission, causing the repair cost to rise to $500 million (not including the cost of the shuttle flight). A successful repair would help demonstrate the viability of building Space Station Alpha.{{sfn|Tatarewicz|1998|pp=374,378,381,388}}

STS-49 in 1992 demonstrated the difficulty of space work. While its rescue of Intelsat 603 received praise, the astronauts had taken possibly reckless risks in doing so. Neither the rescue nor the unrelated assembly of prototype space station components occurred as the astronauts had trained, causing NASA to reassess planning and training, including for the Hubble repair. The agency assigned to the mission Story Musgrave—who had worked on satellite repair procedures since 1976—and six other experienced astronauts, including two from STS-49. The first mission director since Project Apollo{{clarify|date=August 2023}} would coordinate a crew with 16 previous shuttle flights. The astronauts were trained to use about a hundred specialized tools.{{sfn|Tatarewicz|1998|pp=380-381,384–387}}

Heat had been the problem on prior spacewalks, which occurred in sunlight. Hubble needed to be repaired out of sunlight. Musgrave discovered during vacuum training, seven months before the mission, that spacesuit gloves did not sufficiently protect against the cold of space. After STS-57 confirmed the issue in orbit, NASA quickly changed equipment, procedures, and flight plan. Seven total mission simulations occurred before launch, the most thorough preparation in shuttle history. No complete Hubble mockup existed, so the astronauts studied many separate models (including one at the Smithsonian) and mentally combined their varying and contradictory details.{{sfn|Tatarewicz|1998|pp=384–387}}

Service Mission 1 flew aboard Endeavour in December 1993, and involved installation of several instruments and other equipment over ten days. Most importantly, the High Speed Photometer was replaced with the COSTAR corrective optics package, and WF/PC was replaced with the Wide Field and Planetary Camera 2 (WFPC2) with an internal optical correction system. The solar arrays and their drive electronics were also replaced, as well as four gyroscopes in the telescope pointing system, two electrical control units and other electrical components, and two magnetometers. The onboard computers were upgraded with added coprocessors, and Hubble's orbit was boosted.

On January 13, 1994, NASA declared the mission a complete success and showed the first sharper images.{{cite journal |title=The on-orbit performance of WFPC2 |journal=Astrophysical Journal Letters |first1=J. T. |last1=Trauger |first2=G. E. |last2=Ballester |first3=C. J. |last3=Burrows |first4=S. |last4=Casertano |first5=J. T. |last5=Clarke |first6=D. |last6=Crisp |first7=R. W. |last7=Evans |first8=J. S. |last8=Gallagher III |first9=R. E. |last9=Griffiths |display-authors=4 |volume=435 |pages=L3–L6 |date=1994 |bibcode=1994ApJ...435L...3T |doi=10.1086/187580 |url=https://authors.library.caltech.edu/53641/ |access-date=January 7, 2022 |archive-date=January 7, 2022 |archive-url=https://web.archive.org/web/20220107163225/https://authors.library.caltech.edu/53641/ |url-status=live }} The mission was one of the most complex performed to that date, involving five long extra-vehicular activity periods. Its success was a boon for NASA, as well as for the astronomers who now had a more capable space telescope.{{Cite web |last=DeVorkin |first=David |date=April 24, 2020 |title=Telling Hubble's Story for 30 Years |url=https://airandspace.si.edu/stories/editorial/telling-hubbles-story-30-years |access-date=April 7, 2022 |website=National Air and Space Museum |publisher=Smithsonian Institution |language=en |archive-date=December 31, 2021 |archive-url=https://web.archive.org/web/20211231011831/https://airandspace.si.edu/stories/editorial/telling-hubbles-story-30-years |url-status=live }}

{{Main|STS-82}}

File:Hubble Space Telescope (27946391011).jpg

Servicing Mission 2, flown by Discovery in February 1997, replaced the GHRS and the FOS with the Space Telescope Imaging Spectrograph (STIS) and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), replaced an Engineering and Science Tape Recorder with a new Solid State Recorder, and repaired thermal insulation.{{cite web |url=http://hubble.nasa.gov/missions/sm2.php |title=Servicing Mission 2 |publisher=NASA |access-date=April 26, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20080419153631/http://hubble.nasa.gov/missions/sm2.php |archive-date=April 19, 2008}} NICMOS contained a heat sink of solid nitrogen to reduce the thermal noise from the instrument, but shortly after it was installed, an unexpected thermal expansion resulted in part of the heat sink coming into contact with an optical baffle. This led to an increased warming rate for the instrument and reduced its original expected lifetime of 4.5 years to about two years.{{cite web |url=http://www.stsci.edu/hst/nicmos/performance/temperature |title=NICMOS Thermal History |publisher=STScI |access-date=April 26, 2008 |archive-date=May 24, 2012 |archive-url=https://archive.today/20120524183957/http://www.stsci.edu/hst/nicmos/performance/temperature |url-status=live }}

{{Main|STS-103}}

Servicing Mission 3A, flown by Discovery, took place in December 1999, and was a split-off from Servicing Mission{{nbsp}}3 after three of the six onboard gyroscopes had failed. The fourth failed a few weeks before the mission, rendering the telescope incapable of performing scientific observations. The mission replaced all six gyroscopes, replaced a Fine Guidance Sensor and the computer, installed a Voltage/temperature Improvement Kit (VIK) to prevent battery overcharging, and replaced thermal insulation blankets.{{cite web |url=http://sm3a.gsfc.nasa.gov/overview.html |title=Servicing Mission 3A Overview |publisher=NASA |access-date=April 26, 2008 |archive-date=May 9, 2008 |archive-url=https://web.archive.org/web/20080509190700/http://sm3a.gsfc.nasa.gov/overview.html |url-status=live }}

{{Main|STS-109}}

Servicing Mission 3B flown by Columbia in March 2002 saw the installation of a new instrument, with the FOC (which, except for the Fine Guidance Sensors when used for astrometry, was the last of the original instruments) being replaced by the Advanced Camera for Surveys (ACS). This meant COSTAR was no longer required, since all new instruments had built-in correction for the main mirror aberration.{{cite web |at=Corrective Optics Space Telescope Axial Replacement |title=HST |url=http://www.stsci.edu/hst/HST_overview/index_html#costar |publisher=STScI |access-date=November 4, 2012 |archive-date=July 15, 2022 |archive-url=https://web.archive.org/web/20220715150044/https://www.stsci.edu/hst#costar |url-status=live }} The mission also revived NICMOS by installing a closed-cycle cooler and replaced the solar arrays for the second time, providing 30 percent more power.{{cite web |url=http://hubble.nasa.gov/missions/sm3b.php |title=Servicing Mission 3 |publisher=NASA |access-date=April 26, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20080407164008/http://hubble.nasa.gov/missions/sm3b.php |archive-date=April 7, 2008}}

{{clear}}

{{Main|STS-125}}

{{multiple image

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| image1 = STS-125 May 17 EVA.jpg

| caption1 = Hubble during Servicing Mission 4

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| caption2 = Hubble after release

}}

Plans called for Hubble to be serviced in February 2005, but the Columbia disaster in 2003, in which the orbiter disintegrated on re-entry into the atmosphere, had wide-ranging effects to the Hubble program and other NASA missions. NASA Administrator Sean O'Keefe decided all future shuttle missions had to be able to reach the safe haven of the International Space Station should in-flight problems develop. As no shuttles were capable of reaching both HST and the space station during the same mission, future crewed service missions were canceled.{{cite web |url=http://www.stsci.edu/resources/sm4meeting.html |archive-url=https://web.archive.org/web/20080511180517/http://www.stsci.edu/resources/sm4meeting.html |url-status=dead |archive-date=May 11, 2008 |title=Servicing Mission 4 Cancelled |publisher=STScI |date=January 16, 2004 |access-date=April 28, 2008 }} This decision was criticized by numerous astronomers who felt Hubble was valuable enough to merit the human risk.{{cite book |url=http://www.nap.edu/catalog.php?record_id=11169 |title=Assessment of Options for Extending the Life of the Hubble Space Telescope: Final Report |publisher=The National Academies |date=2005 |doi=10.17226/11169 |isbn=978-0-309-09530-3 |access-date=December 9, 2012 |archive-date=July 15, 2022 |archive-url=https://web.archive.org/web/20220715150046/https://nap.nationalacademies.org/catalog/11169/assessment-of-options-for-extending-the-life-of-the-hubble-space-telescope |url-status=live }} Chapter 7, "Given the intrinsic value of a serviced Hubble, and the high likelihood of success for a shuttle servicing mission, the committee judges that such a mission is worth the risk." HST's planned successor, the James Webb Space Telescope (JWST), by 2004 was not expected to launch until at least 2011. JWST was eventually launched in December 2021.{{cite press release |url=https://www.arianespace.com/press-release/ariane-5-successful-launch-webb-space-telescope/ |title=Ariane 5 goes down in history with successful launch of Webb |work=Arianespace |date=December 25, 2021 |access-date=December 25, 2021 |archive-url=https://web.archive.org/web/20220310095539/https://www.arianespace.com/press-release/ariane-5-successful-launch-webb-space-telescope/ |archive-date=March 10, 2022 |url-status=live }} A gap in space-observing capabilities between a decommissioning of Hubble and the commissioning of a successor was of major concern to many astronomers, given the significant scientific impact of HST.{{cite web |url=https://www.nsf.gov/mps/ast/aaac/reports/annual/aaac_2004_report.pdf |title=2004 Annual Report |publisher=Astronomy and Astrophysics Advisory Committee |at=Section 3.1{{snd}}The Scientific Impact of the HST SM4 Cancellation |date=March 15, 2004 |access-date=November 5, 2012 |archive-date=March 27, 2019 |archive-url=https://web.archive.org/web/20190327090117/https://www.nsf.gov/mps/ast/aaac/reports/annual/aaac_2004_report.pdf |url-status=live }} The consideration that JWST will not be located in low Earth orbit, and therefore cannot be easily upgraded or repaired in the event of an early failure, only made concerns more acute. On the other hand, NASA officials were concerned that continuing to service Hubble would consume funds from other programs and delay the JWST.{{Cite journal |last=Guinnessy |first=Paul |date=September 2003 |title=Astronomers Lobby for New Lease on Hubble's Life |url=http://physicstoday.scitation.org/doi/10.1063/1.1620825 |journal=Physics Today |language=en |volume=56 |issue=9 |pages=29–31 |doi=10.1063/1.1620825 |bibcode=2003PhT....56i..29G |access-date=April 6, 2022 |archive-date=July 15, 2022 |archive-url=https://web.archive.org/web/20220715150045/https://physicstoday.scitation.org/doi/10.1063/1.1620825 |url-status=live }}

In January 2004, O'Keefe said he would review his decision to cancel the final servicing mission to HST, due to public outcry and requests from Congress for NASA to look for a way to save it. The National Academy of Sciences convened an official panel, which recommended in July 2004 that the HST should be preserved despite the apparent risks. Their report urged "NASA should take no actions that would preclude a space shuttle servicing mission to the Hubble Space Telescope".{{cite news |author=Leary |first=Warren E. |date=July 14, 2004 |title=Panel Urges NASA to Save Hubble Space Telescope |url=https://www.nytimes.com/2004/07/14/us/panel-urges-nasa-to-save-hubble-space-telescope.html |url-status=live |archive-url=https://web.archive.org/web/20180216104758/http://www.nytimes.com/2004/07/14/us/panel-urges-nasa-to-save-hubble-space-telescope.html |archive-date=February 16, 2018 |access-date=November 8, 2012 |work=The New York Times }} In August 2004, O'Keefe asked Goddard Space Flight Center to prepare a detailed proposal for a robotic service mission. These plans were later canceled, the robotic mission being described as "not feasible".{{cite news |last=Gugliotta |first=Guy |date=April 12, 2005 |title=Nominee Backs a Review of NASA's Hubble Decision |url=https://www.washingtonpost.com/wp-dyn/content/article/2005/04/12/AR2005041201646.html |url-status=live |archive-url=https://web.archive.org/web/20170706134527/http://www.washingtonpost.com/wp-dyn/content/article/2005/04/12/AR2005041201646.html |archive-date=July 6, 2017 |access-date=January 10, 2007 |newspaper=The Washington Post }} In late 2004, several Congressional members, led by Senator Barbara Mikulski, held public hearings and carried on a fight with much public support (including thousands of letters from school children across the U.S.) to get the Bush Administration and NASA to reconsider the decision to drop plans for a Hubble rescue mission.{{cite press release |url=http://mikulski.senate.gov/record.cfm?id=231696 |title=Mikulski Vows To Fight For Hubble |date=February 7, 2005 |publisher=Barbara Mikulski |access-date=April 26, 2008 |archive-url=https://web.archive.org/web/20080430100658/http://mikulski.senate.gov/record.cfm?id=231696 |archive-date=April 30, 2008}}

File:218582main Batt FS img1 lg.jpg

The nomination in April 2005 of a new NASA Administrator, Michael D. Griffin, changed the situation, as Griffin stated he would consider a crewed servicing mission.{{cite news |url=http://www.nbcnews.com/id/15489217 |title=NASA gives green light to Hubble rescue |first=Alan |last=Boyle |publisher=NBC News |date=October 31, 2006 |access-date=January 10, 2007 |archive-date=November 4, 2013 |archive-url=https://web.archive.org/web/20131104010540/http://www.nbcnews.com/id/15489217/ |url-status=dead }} Soon after his appointment Griffin authorized Goddard to proceed with preparations for a crewed Hubble maintenance flight, saying he would make the final decision after the next two shuttle missions. In October 2006 Griffin gave the final go-ahead, and the 11-day mission by Atlantis was scheduled for October 2008. Hubble's main data-handling unit failed in September 2008,{{cite web |url=http://www.sciencenews.org/view/generic/id/37004/description/Hubble_suddenly_quiet |title=Hubble suddenly quiet |last=Cowen |first=Ron |publisher=ScienceNews |date=September 29, 2008 |access-date=November 8, 2012}} halting all reporting of scientific data until its back-up was brought online on October 25, 2008.{{cite web |url=https://www.newscientist.com/article/dn15056-hubble-reopens-an-eye.html |title=Hubble re-opens an eye |last=Courtland |first=Rachel |work=New Scientist |date=October 28, 2008 |access-date=October 29, 2008 |archive-url=https://web.archive.org/web/20081029124801/http://space.newscientist.com/article/dn15056-hubble-reopens-an-eye.html |archive-date=October 29, 2008}} Since a failure of the backup unit would leave the HST helpless, the service mission was postponed to incorporate a replacement for the primary unit.

Servicing Mission 4 (SM4), flown by Atlantis in May 2009, was the last scheduled shuttle mission for HST.{{cite web |url=http://www.nasa.gov/home/hqnews/2008/dec/HQ_08-320_Hubble_May2009.html |title=NASA Sets Target Shuttle Launch Date for Hubble Servicing Mission |publisher=NASA |date=December 4, 2008 |access-date=December 5, 2008 |archive-date=December 6, 2008 |archive-url=https://web.archive.org/web/20081206005041/http://www.nasa.gov/home/hqnews/2008/dec/HQ_08-320_Hubble_May2009.html |url-status=live }} SM4 installed the replacement data-handling unit, repaired the ACS and STIS systems, installed improved nickel hydrogen batteries, and replaced other components including all six gyroscopes. SM4 also installed two new observation instruments—Wide Field Camera 3 (WFC3) and the Cosmic Origins Spectrograph (COS){{cite web |url=http://www.nasa.gov/mission_pages/hubble/science/ero_images.html |title=Hubble Opens New Eyes on the Universe |publisher=NASA |date=September 9, 2009 |access-date=May 28, 2012 |archive-date=May 27, 2012 |archive-url=https://web.archive.org/web/20120527231309/http://www.nasa.gov/mission_pages/hubble/science/ero_images.html |url-status=live }}—and the Soft Capture and Rendezvous System, which will enable the future rendezvous, capture, and safe disposal of Hubble by either a crewed or robotic mission.{{cite web |url=http://www.nasa.gov/mission_pages/hubble/servicing/SM4/main/SCRS_FS_HTML.html |title=The Soft Capture and Rendezvous System |publisher=NASA |access-date=May 20, 2009 |archive-date=September 11, 2008 |archive-url=https://web.archive.org/web/20080911224222/http://www.nasa.gov/mission_pages/hubble/servicing/SM4/main/SCRS_FS_HTML.html |url-status=live }} Except for the ACS's High Resolution Channel, which could not be repaired and was disabled,{{cite news |url=https://www.nytimes.com/2009/09/10/science/space/10hubble.html |title=After Hubble Repair, New Images From Space |work=The New York Times |first=Dennis |last=Overbye |date=September 9, 2009 |access-date=August 1, 2015 |archive-date=November 21, 2015 |archive-url=https://web.archive.org/web/20151121090246/http://www.nytimes.com/2009/09/10/science/space/10hubble.html |url-status=live }}{{cite news |url=https://www.nytimes.com/2009/05/18/science/space/18hubble.html |title=After a Yank, 'Surgery' on Hubble Optics |work=The New York Times |first=Dennis |last=Overbye |date=May 17, 2009 |access-date=August 1, 2015 |archive-date=October 4, 2013 |archive-url=https://web.archive.org/web/20131004060543/http://www.nytimes.com/2009/05/18/science/space/18hubble.html |url-status=live }}{{cite web |url=https://www.spacetelescope.org/about/history/acs_repair/ |title=Repair of the Advanced Camera for Surveys |work=SpaceTelescope.org |access-date=August 1, 2015}} the work accomplished during SM4 rendered the telescope fully functional.

File:Pillars of creation 2014 HST WFC3-UVIS full-res denoised.jpg, shows stars forming in the Eagle Nebula.]]

Since the start of the program, a number of research projects have been carried out, some of them almost solely with Hubble, others coordinated facilities such as Chandra X-ray Observatory and ESO's Very Large Telescope. Although the Hubble observatory is nearing the end of its life, there are still major projects scheduled for it. One example is the current (2022) ULLYSES project (Ultraviolet Legacy Library of Young Stars as Essential Standards) which will last for three years to observe a set of high- and low-mass young stars and will shed light on star formation and composition. Another is the OPAL project (Outer Planet Atmospheres Legacy), which is focussed on understanding the evolution and dynamics of the atmosphere of the outer planets (such as Jupiter and Uranus) by making baseline observations over an extended period.{{cite web |title=Outer Planet Atmospheres Legacy (OPAL) |url=https://archive.stsci.edu/prepds/opal/ |access-date=30 March 2023 |archive-date=March 30, 2023 |archive-url=https://web.archive.org/web/20230330010627/https://archive.stsci.edu/prepds/opal/ |url-status=live }}

In an August 2013 press release, CANDELS was referred to as "the largest project in the history of Hubble". The survey "aims to explore galactic evolution in the early Universe, and the first seeds of cosmic structure at less than one billion years after the Big Bang."{{cite web |url=http://www.spacetelescope.org/news/heic1315/#3 |title=Hubble explores the origins of modern galaxies |work=SpaceTelescope.org |id=heic1315 |date=August 15, 2013 |access-date=October 4, 2013 |archive-date=November 24, 2020 |archive-url=https://web.archive.org/web/20201124011402/https://www.spacetelescope.org/news/heic1315/#3 |url-status=live }} The CANDELS project site describes the survey's goals as the following:{{cite web |url=http://candels.ucolick.org/survey/Survey_Desc.html |title=Survey Description |work=CANDELS |via=UCOLick.org |access-date=October 4, 2013 |url-status=dead |archive-url=https://web.archive.org/web/20131020092530/http://candels.ucolick.org/survey/Survey_Desc.html |archive-date=October 20, 2013}}

The Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey is designed to document the first third of galactic evolution from z = 8 to 1.5 via deep imaging of more than 250,000 galaxies with WFC3/IR and ACS. It will also find the first Type Ia SNe beyond z > 1.5 and establish their accuracy as standard candles for cosmology. Five premier multi-wavelength sky regions are selected; each has multi-wavelength data from Spitzer and other facilities, and has extensive spectroscopy of the brighter galaxies. The use of five widely separated fields mitigates cosmic variance and yields statistically robust and complete samples of galaxies down to 10⁹ solar masses out to z ~ 8.

File:Color image of galaxy cluster MCS J0416.1–2403.jpg.]]

The program, officially named "Hubble Deep Fields Initiative 2012", is aimed to advance the knowledge of early galaxy formation by studying high-redshift galaxies in blank fields with the help of gravitational lensing to see the "faintest galaxies in the distant universe".{{cite web |url=http://www.stsci.edu/hst/campaigns/frontier-fields/documents/HDFI_SWGReport2012.pdf |title=Hubble Deep Fields Initiative 2012 Science Working Group Report |work=STScI.edu |date=2012 |access-date=June 29, 2015 |archive-date=July 15, 2022 |archive-url=https://web.archive.org/web/20220715150044/https://www.stsci.edu/hst |url-status=live }} The Frontier Fields web page describes the goals of the program being:

• to reveal hitherto inaccessible populations of z = 5–10 galaxies that are ten to fifty times fainter intrinsically than any presently known
• to solidify our understanding of the stellar masses and star formation histories of sub-L* galaxies at the earliest times
• to provide the first statistically meaningful morphological characterization of star forming galaxies at z > 5
• to find z > 8 galaxies stretched out enough by cluster lensing to discern internal structure and/or magnified enough by cluster lensing for spectroscopic follow-up.{{cite web |url=http://www.stsci.edu/hst/campaigns/frontier-fields |title=Hubble Space Telescope: Frontier Fields |work=STScI.edu |access-date=October 4, 2013 |archive-date=July 15, 2022 |archive-url=https://web.archive.org/web/20220715150048/https://www.stsci.edu/hst |url-status=live }}

The Cosmic Evolution Survey (COSMOS){{Cite web|url=http://cosmos.astro.caltech.edu/|title=Home Page|website=COSMOS|access-date=August 31, 2019|archive-date=January 5, 2016|archive-url=https://web.archive.org/web/20160105073739/http://cosmos.astro.caltech.edu/|url-status=live}} is an astronomical survey designed to probe the formation and evolution of galaxies as a function of both cosmic time (redshift) and the local galaxy environment. The survey covers a two square degree equatorial field with spectroscopy and X-ray to radio imaging by most of the major space-based telescopes and a number of large ground based telescopes,{{Cite web|url=https://cosmos.astro.caltech.edu/page/astronomers|title=For Astronomers|website=COSMOS|access-date=November 2, 2020|archive-date=October 25, 2020|archive-url=https://web.archive.org/web/20201025190033/http://cosmos.astro.caltech.edu/page/astronomers|url-status=live}} making it a key focus region of extragalactic astrophysics. COSMOS was launched in 2006 as the largest project pursued by the Hubble Space Telescope at the time, and still is the largest continuous area of sky covered for the purposes of mapping deep space in blank fields, 2.5 times the area of the moon on the sky and 17 times larger than the largest of the CANDELS regions. The COSMOS scientific collaboration that was forged from the initial COSMOS survey is the largest and longest-running extragalactic collaboration, known for its collegiality and openness. The study of galaxies in their environment can be done only with large areas of the sky, larger than a half square degree.{{Cite web|url=http://hubblesite.org/contents/news-releases/2007/news-2007-01|title=Hubble Maps the Cosmic Web of "Clumpy" Dark Matter in 3-D|website=HubbleSite.org|publisher=Space Telescope Science Institute|access-date=November 2, 2020|archive-date=July 15, 2022|archive-url=https://web.archive.org/web/20220715150152/https://hubblesite.org/contents/news-releases/2007/news-2007-01.html|url-status=live}} More than two million galaxies are detected, spanning 90% of the age of the Universe. The COSMOS collaboration is led by Caitlin Casey, Jeyhan Kartaltepe, and Vernesa Smolcic and involves more than 200 scientists in a dozen countries.

The Cluster Lensing and Supernova survey with Hubble (CLASH) was a Treasury Program from 2010 to 2013 conducted by the Hubble Space Telescope to observe 25 massive galaxy clusters by using gravitational lensing. CLASH aimed to examine the distribution of dark matter and dark energy in massive galaxy clusters with the new instruments installed in 2009. Imagery showing the effects of gravitational lensing is one means of detecting dark matter and dark energy, and CLASH focused on trying to gain a better understanding of both mysterious topics.https://www.stsci.edu/~postman/CLASH/ . Retrieved 27 March 2025.

File:Largest Mosaic of Andromeda by Hubble jan 16 2025-extra details.jpg

The Panchromatic Hubble Andromeda Treasury and Panchromatic Hubble Andromeda Southern Treasury (PHAT and PHAST) were observations done by Hubble from July 2010 to October 2013 to map the northern half of the Andromeda Galaxy and from December 2021 to January 2024 to map the southern half. Andromeda is the nearest large galaxy to the Milky Way Galaxy and Hubble created the highest resolution and most detailed photomosaic ever of Andromeda. 200 million stars can be seen in this combined image of both Treasury Programs out of a total of 1 trillion stars in Andromeda. Each star looks like a grain of sand. The northern half, PHAT, was mapped in near-ultraviolet, visible, and near-infrared wavelengths in 828 orbits and was released in January 2015. The southern half, PHAST, was mapped in near-ultraviolet and visible wavelengths in 195 orbits and was released in January 2025. Observing Andromeda in this detail is the best alternative to observing the Milky Way Galaxy because Earth is within the Milky Way and cannot observe most of the Milky Way due to the galaxy itself blocking observations of 20% of the sky and most of the galaxy. To achieve this mosaic 1,023 Hubble orbits were needed. The mosaic image is made up of at least 2.5 billion pixels.{{cite web |url=https://www.stsci.edu/contents/media/images/2015/02/3476-Image |title=Hubble M31 PHAT Mosaic |publisher=Space Telescope Science Institute |access-date=27 March 2025}}{{cite journal |title=PHAST. The Panchromatic Hubble Andromeda Southern Treasury. I. Ultraviolet and Optical Photometry of over 90 Million Stars in M31 |vauthors=Chen Z, Williams B, Lang D, Dolphin A, Durbin M, Dalcanton JJ, Smercina A, Girardi L, Murray CE, Bell EF, Boyer ML, D'Souza R, Gilbert K, Gordon K, Guhathakurta P, Hammer F, Johnson LC, Lauer TR, Lazzarini M, Murphy JW, Patel E, Quirk A, Díaz Rodríguez M, Roman-Duval JC, Sanderson RE, Seth A, Wainer TM, Weisz DR |journal=The Astrophysical Journal |volume=979 |number=1 |date=2025 |page=35 |doi=10.3847/1538-4357/ad7e2b |doi-access=free|bibcode=2025ApJ...979...35C }}{{cite web |url=https://www.stsci.edu/contents/news-releases/2025/news-2025-005 |title=NASA's Hubble Traces Hidden History of Andromeda Galaxy |publisher=Space Telescope Science Institute |date=16 January 2025 |access-date=27 March 2025}}{{cite journal |url=https://ui.adsabs.harvard.edu/abs/2012ApJS..200...18D/abstract |title=The Panchromatic Hubble Andromeda Treasury |vauthors= Dalcanton, JJ, Williams, BF, Lang, D, Lauer, TR, Kalirai, JS, Seth, AC, Dolphin, A, Rosenfield, P, Weisz, DR, Bell, EF, Bianchi, LC, Boyer, ML, Caldwell, N, Dong, H, Dorman, CE, Gilbert, KM, Girardi, L, Gogarten, SM, Gordon, KD, Guhathakurta, P, Hodge, PW, Holtzman, JA, Johnson, LC, Larsen, SS, Lewis, A, Melbourne, JL, Olsen, KAG, Rix, HW, Rosema, K, Saha, A, Sarajedini, A, Skillman, ED, Stanek, KZ |journal=The Astrophysical Journal Supplement |date=2012 |volume=200 |issue=2 |page=18 |doi=10.1088/0067-0049/200/2/18 |arxiv=1204.0010|bibcode=2012ApJS..200...18D }}

File:EmissionNebula NGC6357.jpg with nebula]]

Anyone can apply for time on the telescope; there are no restrictions on nationality or academic affiliation, but funding for analysis is available only to U.S. institutions.{{sfn|Strolger|Rose|2017|p=11}} Competition for time on the telescope is intense, with about one-fifth of the proposals submitted in each cycle earning time on the schedule.{{cite web |url=http://www.stsci.edu/hst/HST_overview |title=HST Overview |publisher=NASA |date=June 21, 2010 |access-date=November 4, 2012 |at=Mission Operations and Observations |archive-date=July 15, 2022 |archive-url=https://web.archive.org/web/20220715150146/https://www.stsci.edu/hst |url-status=live }}

Calls for proposals are issued roughly annually, with time allocated for a cycle lasting about one year. Proposals are divided into several categories; "general observer" proposals are the most common, covering routine observations. "Snapshot observations" are those in which targets require only 45 minutes or less of telescope time, including overheads such as acquiring the target. Snapshot observations are used to fill in gaps in the telescope schedule that cannot be filled by regular general observer programs.{{sfn|Strolger|Rose|2017|p=21}}

Astronomers may make "Target of Opportunity" proposals, in which observations are scheduled if a transient event covered by the proposal occurs during the scheduling cycle. In addition, up to 10% of the telescope time is designated "director's discretionary" (DD) time. Astronomers can apply to use DD time at any time of year, and it is typically awarded for study of unexpected transient phenomena such as supernovae.{{sfn|Strolger|Rose|2017|p=37}}

Other uses of DD time have included the observations that led to views of the Hubble Deep Field and Hubble Ultra Deep Field, and in the first four cycles of telescope time, observations that were carried out by amateur astronomers.

In 2012, the ESA held a contest for public image processing of Hubble data to encourage the discovery of "hidden treasures" in the raw Hubble data.{{Cite web |title=Hubble's Hidden Treasures 2012 |url=https://esahubble.org/projects/hiddentreasures/ |access-date=April 7, 2022 |website=ESA/Hubble |language=en |archive-date=May 2, 2022 |archive-url=https://web.archive.org/web/20220502005140/https://esahubble.org/projects/hiddentreasures/ |url-status=live }}{{Cite web |last=Goddard |first=Louis |date=August 27, 2012 |title=Hubble image processing competition creates stunning new views from old data |url=https://www.theverge.com/2012/8/27/3271105/hubble-image-processing-competition-winners |url-status=live |archive-url=https://web.archive.org/web/20220407173339/https://www.theverge.com/2012/8/27/3271105/hubble-image-processing-competition-winners |archive-date=April 7, 2022 |access-date=April 7, 2022 |website=The Verge |language=en}}

File:Hubble Space Telescope in Orion.jpg

The first director of STScI, Riccardo Giacconi, announced in 1986 that he intended to devote some of his director discretionary time to allowing amateur astronomers to use the telescope. The total time to be allocated was only a few hours per cycle but excited great interest among amateur astronomers.

Proposals for amateur time were stringently reviewed by a committee of amateur astronomers, and time was awarded only to proposals that were deemed to have genuine scientific merit, did not duplicate proposals made by professionals, and required the unique capabilities of the space telescope. Thirteen amateur astronomers were awarded time on the telescope, with observations being carried out between 1990 and 1997.{{cite journal |url=https://www.thefreelibrary.com/The+demise+of+the+HST+amateur+program.-a019661324 |title=The Demise of the HST Amateur Program |journal=Sky & Telescope |first=Stephen James |last=O'Meara |editor-first=Edwin L. |editor-last=Aguirre |volume=96 |issue=6 |page=97 |date=June 1997 |bibcode=1997S&T....93f..97O |access-date=February 9, 2019 |archive-date=February 9, 2019 |archive-url=https://web.archive.org/web/20190209124219/https://www.thefreelibrary.com/The+demise+of+the+HST+amateur+program.-a019661324 |url-status=live }} One such study was "Transition Comets—UV Search for OH". The first proposal, "A Hubble Space Telescope Study of Posteclipse Brightening and Albedo Changes on Io", was published in Icarus,{{cite journal |title=A Hubble Space Telescope Study of Posteclipse Brightening and Albedo Changes on Io |journal=Icarus |first1=James J. |last1=Secosky |first2=Michael |last2=Potter |volume=111 |issue=1 |pages=73–78 |date=September 1994 |doi=10.1006/icar.1994.1134 |bibcode=1994Icar..111...73S}} a journal devoted to solar system studies. A second study from another group of amateurs was also published in Icarus.{{cite journal |url=http://scripts.mit.edu/~paleomag/articles/Storrs_1999_Icarus.pdf |title=Imaging Observations of Asteroids with Hubble Space Telescope |journal=Icarus |first1=Alex |last1=Storrs |first2=Ben |last2=Weiss |first3=Ben |last3=Zellner |first4=Win |last4=Burleson |first5=Rukmini |last5=Sichitiu |first6=Eddie |last6=Wells |first7=Charles |last7=Kowal |first8=David |last8=Tholen |display-authors=4 |volume=137 |issue=2 |pages=260–268 |date=February 1999 |doi=10.1006/icar.1999.6047 |bibcode=1999Icar..137..260S |url-status=dead |archive-url=https://web.archive.org/web/20120225134811/http://scripts.mit.edu/~paleomag/articles/Storrs_1999_Icarus.pdf |archive-date=February 25, 2012}} After that time, however, budget reductions at STScI made the support of work by amateur astronomers untenable, and no additional amateur programs have been carried out.{{cite news |last=Walthert |first=Matthew |date=April 24, 2015 |title=Open Mic Night at the Hubble Telescope |work=Motherboard |url=https://www.vice.com/en/article/open-mic-night-at-the-hubble-telescope/ |access-date=April 6, 2022 |archive-date=April 7, 2022 |archive-url=https://web.archive.org/web/20220407034408/https://www.vice.com/en/article/vvbnj3/open-mic-night-at-the-hubble-telescope |url-status=live }}

Regular Hubble proposals still include findings or discovered objects by amateurs and citizen scientists. These observations are often in a collaboration with professional astronomers. One of the earliest such observations is the Great White Spot of 1990{{Cite web|title=NASA's Hubble Space Telescope Views Major Storm On Saturn|url=http://hubblesite.org/contents/news-releases/1991/news-1991-04|access-date=October 22, 2020|website=HubbleSite.org|publisher=Space Telescope Science Institute|archive-date=July 15, 2022|archive-url=https://web.archive.org/web/20220715150146/https://hubblesite.org/contents/news-releases/1991/news-1991-04.html|url-status=live}} on planet Saturn, discovered by amateur astronomer S. Wilber{{Cite journal|last1=Wilber|first1=S.|last2=Tatum|first2=R.|last3=Kidger|first3=M.|last4=Gonzalez|first4=V.|last5=Hernandez|first5=F.|date=October 1, 1990|title=Saturn|url=http://adsabs.harvard.edu/abs/1990IAUC.5109....1W|journal=International Astronomical Union Circular|issue=5109|pages=1|bibcode=1990IAUC.5109....1W|access-date=October 22, 2020|archive-date=July 15, 2022|archive-url=https://web.archive.org/web/20220715150148/https://ui.adsabs.harvard.edu/abs/1990IAUC.5109....1W/abstract|url-status=live}} and observed by HST under a proposal by J. Westphal (Caltech).{{Cite web|title=HST Proposal Search|url=https://archive.stsci.edu/proposal_search.php?id=3109&mission=hst|access-date=October 22, 2020|website=archive.stsci.edu|archive-date=July 15, 2022|archive-url=https://web.archive.org/web/20220715150221/https://archive.stsci.edu/proposal_search.php?id=3109&mission=hst|url-status=live}}{{Cite web|title=HST Proposal Search|url=https://archive.stsci.edu/proposal_search.php?id=3090&mission=hst|access-date=October 22, 2020|website=archive.stsci.edu|archive-date=July 15, 2022|archive-url=https://web.archive.org/web/20220715150146/https://archive.stsci.edu/proposal_search.php?id=3090&mission=hst|url-status=live}} Later professional-amateur observations by Hubble include discoveries by the Galaxy Zoo project, such as Voorwerpjes and Green Pea galaxies.{{Cite journal|last1=Keel|first1=William C.|last2=Maksym|first2=W. Peter|last3=Bennert|first3=Vardha N.|last4=Lintott|first4=Chris J.|last5=Chojnowski|first5=S. Drew|last6=Moiseev|first6=Alexei|last7=Smirnova|first7=Aleksandrina|last8=Schawinski|first8=Kevin|last9=Urry|first9=C. Megan|last10=Evans|first10=Daniel A.|last11=Pancoast|first11=Anna|date=May 1, 2015|title=HST Imaging of Fading AGN Candidates. I. Host-galaxy Properties and Origin of the Extended Gas|journal=The Astronomical Journal|volume=149|issue=5|pages=155|doi=10.1088/0004-6256/149/5/155|arxiv=1408.5159|bibcode=2015AJ....149..155K|doi-access=free}}{{Cite journal|last1=Henry|first1=Alaina|last2=Scarlata|first2=Claudia|last3=Martin|first3=Crystal L.|last4=Erb|first4=Dawn|date=August 1, 2015|title=Lyalpha Emission from Green Peas: The Role of Circumgalactic Gas Density, Covering, and Kinematics|url=http://adsabs.harvard.edu/abs/2015ApJ...809...19H|journal=The Astrophysical Journal|volume=809|issue=1|pages=19|doi=10.1088/0004-637X/809/1/19|arxiv=1505.05149|bibcode=2015ApJ...809...19H|s2cid=119210958|access-date=October 22, 2020|archive-date=July 15, 2022|archive-url=https://web.archive.org/web/20220715150147/https://ui.adsabs.harvard.edu/abs/2015ApJ...809...19H/abstract|url-status=live}} The "Gems of the Galaxies" program is based on a list of objects by Galaxy Zoo volunteers that was shortened with the help of an online vote.{{Cite web|title=HST Proposal Search|url=https://archive.stsci.edu/proposal_search.php?id=15445&mission=hst|access-date=October 22, 2020|website=archive.stsci.edu|archive-date=July 15, 2022|archive-url=https://web.archive.org/web/20220715150146/https://archive.stsci.edu/proposal_search.php?id=15445&mission=hst|url-status=live}} Additionally there are observations of minor planets discovered by amateur astronomers, such as 2I/Borisov and changes in the atmosphere of the gas giants Jupiter and Saturn or the ice giants Uranus and Neptune.{{Cite web|title=Hubble Images Suggest Rogue Asteroid Smacked Jupiter|url=http://hubblesite.org/contents/news-releases/2010/news-2010-16|access-date=October 22, 2020|website=HubbleSite.org|publisher=Space Telescope Science Institute|archive-date=July 15, 2022|archive-url=https://web.archive.org/web/20220715150147/https://hubblesite.org/contents/news-releases/2010/news-2010-16.html|url-status=live}}{{Cite web|title=Hubble Confirms New Dark Spot on Neptune|url=http://hubblesite.org/contents/news-releases/2016/news-2016-22|access-date=October 22, 2020|website=HubbleSite.org|publisher=Space Telescope Science Institute|archive-date=July 15, 2022|archive-url=https://web.archive.org/web/20220715150148/https://hubblesite.org/contents/news-releases/2016/news-2016-22.html|url-status=live}} In the pro-am collaboration backyard worlds the HST was used to observe a planetary mass object, called WISE J0830+2837. The non-detection by the HST helped to classify this peculiar object.{{Cite journal|last1=Bardalez Gagliuffi|first1=Daniella C.|last2=Faherty|first2=Jacqueline K.|author2-link=Jackie Faherty|last3=Schneider|first3=Adam C.|last4=Meisner|first4=Aaron|last5=Caselden|first5=Dan|last6=Colin|first6=Guillaume|last7=Goodman|first7=Sam|last8=Kirkpatrick|first8=J. Davy|last9=Kuchner|first9=Marc|last10=Gagné|first10=Jonathan|last11=Logsdon|first11=Sarah E.|date=June 1, 2020|title=WISEA J083011.95+283716.0: A Missing Link Planetary-mass Object|journal=The Astrophysical Journal|volume=895|issue=2|pages=145|doi=10.3847/1538-4357/ab8d25|arxiv=2004.12829|bibcode=2020ApJ...895..145B|s2cid=216553879|doi-access=free }}

File:NASA-HubbleLegacyFieldZoomOut-20190502.webm (50-second video)