Heat Flow and Physical Properties Package

File:HP3 overview animation.webm

The mission goal was to understand the origin and diversity of terrestrial planets.{{cite conference |url=https://mepag.jpl.nasa.gov/meeting/2012-10/10_2012-1004_MEPAG.pdf |title=InSight – Geophysical Mission to Mars |conference=26th Mars Exploration Program Analysis Group Meeting. 4 October 2012. Monrovia, California. |first=W. Bruce |last=Banerdt |date=2012}} Information from the HP³ heat flow package was expected to reveal whether Mars and Earth formed from the same material, and determine how active the interior of Mars is today.{{r|octoberpres|Home HP3|flow}}{{cite web |url=http://www.nasa.gov/mission_pages/mars/news/insight20120820.html |title=New Insight on Mars Expected From new NASA Mission |publisher=NASA |first=D. C. |last=Agle |date=20 August 2012 |access-date=16 July 2018 |archive-date=29 June 2017 |archive-url=https://web.archive.org/web/20170629161601/https://www.nasa.gov/mission_pages/mars/news/insight20120820.html |url-status=dead }} Additional science goals included determining the thickness of Mars' crust, the composition of its mantle, and thermal characteristics of the interior, such as the temperature gradient and heat flux.{{Cite web|url=https://mars.nasa.gov/insight/mission/science/goals|title=Goals {{!}} Science|last=mars.nasa.gov|website=NASA's InSight Mars Lander|language=en|access-date=2019-09-03}}

Together with the seismometer, the mission will estimate the size of Mars' core and whether the core is liquid or solid.{{cite news |url=http://www.universetoday.com/93843/nasas-proposed-insight-lander-would-peer-to-the-center-of-mars-in-2016/ |title=NASAs Proposed 'InSight' Lander would Peer to the Center of Mars in 2016 |work=Universe Today |first=Ken |last=Kremer |date=2 March 2012 |access-date=27 March 2012}} The vibrations generated by the mole were monitored by SEIS to learn about the local subsurface.{{Cite web|url=https://mars.nasa.gov/insight/timeline/surface-operations|title=Surface Operations {{!}} Timeline|last=mars.nasa.gov|website=NASA's InSight Mars Lander|language=en|access-date=2018-12-24}}

In addition to the mole, HP³ includes an infrared radiometer (HP3-RAD) mounted to the landing platform, also contributed by DLR.{{cite conference |url=http://sites.nationalacademies.org/cs/groups/ssbsite/documents/webpage/ssb_086912.pdf |title=InSight: A Geophysical Mission to a Terrestrial Planet Interior |conference=Committee on Astrobiology and Planetary Science. 6–8 March 2013. Washington, D.C. |first=W. Bruce |last=Banerdt |date=7 March 2013}}{{Cite news |url=https://solarsystem.nasa.gov/missions/insight/in-depth/ |title=InSight: In Depth |work=Solar System Exploration |publisher=NASA |access-date=2 February 2018}}{{cite journal |title=The MASCOT Radiometer MARA for the Hayabusa 2 Mission |journal=Space Science Reviews |first1=M. |last1=Grott |first2=J. |last2=Knollenberg |first3=B. |last3=Borgs |first4=F. |last4=Hänschke |first5=E. |last5=Kessler |first6=J. |last6=Helbert |first7=A. |last7=Maturilli |first8=N. |last8=Müller |display-authors=1 |volume=208 |issue=1–4 |pages=413–431 |date=July 2017 |doi=10.1007/s11214-016-0272-1 |bibcode=2017SSRv..208..413G|s2cid=118245538 }}

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{{stack|File:InSight's HP3 instrument diagram.png}}

The HP³ heat flow probe is made up of the following subsystems:{{cite web |title=HP3 heat flow probe |url=https://www.dlr.de/content/en/articles/missions-projects/insight/heat-flow-probe-hp3.html |website=DLR Portal |access-date=4 June 2020 |language=en}}

• Support Structure (SS) a housing that includes:
• Engineering tether (ET) to communicate between the support structure to the lander
• Science tether (TEM-P) a flex PCB with 14 platinum RTDs for measuring thermal properties of the regolith.
• Tether length monitor (TLM) optical length meter for measuring the deployed length of the science tether
• Infrared radiometer (HP3-RAD) for measuring surface temperature.
• Back end electronics (BEE) electronic control unit
• Mole penetrometer for burrowing beneath the surface
• TEM-A active thermal conductivity sensor
• STATIL tiltmeter for determining orientation and direction of the mole.

File:InSight's HP3 instrument Image-36-full.jpg

HP³ was conceived by Gromov V. V. et al. in 1997,Gromov V.V. et al.: The mobile penetrometer, a "mole" for sub-surface soil investigation. In Proc. of 7th European Space Mechanisms and Tribology Symposium. 1997. and first flown as the PLUTO instrument on the failed 2003 Beagle 2 Mars lander mission. HP³ evolved further and it was proposed in 2001 for a mission to Mercury,[https://www.researchgate.net/publication/223287921_A_heat_flow_and_physical_properties_package_for_the_surface_of_Mercury A heat flow and physical properties package for the surface of Mercury]. Tilman Spohn, Karsten Seiferlin. Planetary and Space Science 49(14-15):1571-1577 December 2001. {{doi|10.1016/S0032-0633(01)00094-0}} in 2009 to the European Space Agency as part of the Humboldt payload on board the ExoMars lander,[http://adsabs.harvard.edu/abs/2009EGUGA..1113520K HP3 on ExoMars]. Krause, C.; Izzo, M.; Re, E.; Mehls, C.; Richter, L.; Coste, P. EGU General Assembly 2009, held 19–24 April 2009 in Vienna, Austria. in 2010 for a mission to the Moon,[https://www.lpi.usra.edu/meetings/lunargeo2010/pdf/3016.pdf Measuring heat flow on the Moon — The Heat Flow and Physical Properties Package HP3.] (PDF) T. Spohn, M. Grott L. Richter, J. Knollenberg, S.E. Smrekar, and the HP3 instrument team. Ground-based Geophysics on the Moon (2010). Lunar and Planetary Institute, conference 2010. and in 2011 it was proposed to NASA's Discovery Program as a payload for InSight Mars lander, known at that time as GEMS (Geophysical Monitoring Station).{{cite conference |url=http://meetingorganizer.copernicus.org/EPSC-DPS2011/EPSC-DPS2011-379-1.pdf |title=Measuring Heat Flow on Mars: The Heat Flow and Physical Properties Package on GEMS |conference=EPSC-DPS Joint Meeting 2011. 2–7 October 2011. Nantes, France. |first1=M. |last1=Grott |first2=T. |last2=Spohn |first3=W. B. |last3=Banerdt |first4=S. |last4=Smrekar |first5=T. L. |last5=Hudson |display-authors=etal |date=October 2011 |bibcode=2011epsc.conf..379G |id=EPSC-DPS2011-379-1}} InSight was launched on 5 May 2018 and landed on 26 November 2018.

The mole is described as a "self-hammering nail" and was designed to burrow below the Martian surface while trailing a tether with embedded heaters and temperature sensors. The goal was to measure the thermal properties of Mars' interior, and thus reveal unique information about the planet's geologic history.[http://esmats.eu/amspapers/pastpapers/pdfs/2016/grygorczuk2.pdf Hammering Mechanism for HP3 Experiment (InSight)]. (PDF) Jerzy Grygorczuk1, Łukasz Wiśniewski1, Bartosz Kędziora1, Maciej Borys, Rafał Przybyła1, Tomasz Kuciński1, Maciej Ossowski, Wojciech Konior, Olaf Krömer, Tilman Spohn, Marta Tokarz and Mateusz Białek. European Space Mechanisms and Tribology Symposium; 2016.

The burrowing mole is a pointed cylinder with a smooth outer surface approximately {{cvt|35|cm}} in length and {{cvt|3.5|cm}} in diameter. It contains a heater to determine thermal conductivity during descent, and it trails a tether equipped with precise heat sensors placed at {{convert|10|cm|abbr=on}} intervals to measure the temperature profile of the subsurface.{{r|octoberpres|Home HP3}}

The mole penetrator unit is designed to be placed near the lander in an area about 3-m long and 2-m wide.{{Cite web|url=https://www.seis-insight.eu/en/public-2/the-insight-mission/instruments-deployment|title=Instruments Deployment - SEIS / Mars InSight|website=www.seis-insight.eu|access-date=2018-12-26}} The total mass of the system is approximately {{cvt|3|kg|abbr=on}} and it consumes a maximum of {{Val|2|ul=watt}}s while the mole is active.{{cite web |title=Heat Probe {{!}} Instruments |url=https://mars.nasa.gov/insight/mission/instruments/hp3 |website=NASA's InSight Mars Lander |date=4 December 2017 |access-date=13 April 2020 |language=en}}

For displacement, the mole uses a motor and a gearbox (provided by Maxon) and a cammed roller that periodically loads a spring connected to a rod that functions as a hammer. After release from the cam, the hammer accelerates downwards to hit the outer casing and cause its penetration through the regolith. Meanwhile, a suppressor mass travels upwards and its kinetic energy is compensated by gravitational potential and compression of a brake spring and wire helix on the opposite side of the mole.

In principle, every {{cvt|50|cm}} the probe puts out a pulse of heat and its sensors measure how the heat pulse changes with time. If the crust material is a thermal conductor, like metal, the pulse will decay quickly. The mole is first allowed to cool down for two days, then it is heated to about {{cvt|10|C|F|abbr=on}} over 24 hours. Temperature sensors within the tether measure how rapidly this happens, which tells scientists the thermal conductivity of the soil.{{cite web |title=NASA's InSight Prepares to Take Mars' Temperature |url=https://www.jpl.nasa.gov/news/news.php?feature=7335 |website=NASA/JPL |access-date=13 April 2020 |date=February 13, 2019}} Together, these measurements yield the rate of heat flowing from the interior.

The HP³ mole was originally expected to take about 40 days to reach {{cvt|5|m|abbr=on}} deep,{{cite web |title=Surface Operations |url=https://mars.nasa.gov/insight/timeline/surface-operations/ |website=NASA's InSight Mars Lander |access-date=13 April 2020 |language=en}} but ultimately achieved only a few centimeters after more than a year of effort. As the mole burrows, it generates vibrations that SEIS can detect, which were hoped to yield information about the Martian subsurface.

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| caption1 = Animation of HP³ being deployed to the surface by InSight's robotic arm (IDA).

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In March 2019, the HP³ began burrowing into the surface sand, but became stalled after several centimeters by what was initially suspected to be a large rock.{{cite web |last1=Dickinson |first1=David |title=Mars Insight's "Mole" Hits a Snag |url=https://www.skyandtelescope.com/astronomy-news/mars-insight-drill-hits-snag/ |website=Sky & Telescope |publisher=AAS Sky Publishing, LLC. |access-date=1 September 2019 |date=11 March 2019}} Further analysis and testing with a replica model on Earth suggested the problem may be due to insufficient friction. In June 2019, more evidence for this was revealed when the support structure was lifted off of the HP³ mole. The Martian regolith appeared to be compressed, leaving a gap around the probe.

A technique was implemented using the lander's robotic arm to press on the soil near the probe to increase soil friction.{{Cite web|url=https://www.skyandtelescope.com/astronomy-news/nasas-strategy-mars-insight-back-drilling/|title=A Strategy to Get the Mars Insight Lander Back in the Drilling Business|last=Dickinson|first=David|date=2019-07-03|website=Sky & Telescope |publisher=AAS Sky Publishing, LLC. |language=en-US|access-date=2019-08-31}}{{Cite web|url=https://www.jpl.nasa.gov/news/news.php?feature=7441|title=NASA's InSight Uncovers the 'Mole'|website=NASA/JPL|access-date=2019-08-31}}{{Cite web|url=https://gizmodo.com/here-s-how-nasa-might-rescue-insight-s-extremely-stuck-1838750453|title=Here's How NASA Might Rescue InSight's Extremely Stuck Heat Probe|last=Dvorsky|first=George|website=Gizmodo|date=3 October 2019 |language=en-US|access-date=2019-10-04}} Ultimately, this method was not able to generate enough downward force, since the HP³ probe was at the limit of the arm's range.{{Cite web|url=https://www.universetoday.com/143782/success-nasa-confirms-the-mole-is-working-again/|title=Success! NASA Confirms the Mole is Working Again.|last=Gough|first=Evan|date=2019-10-18|website=Universe Today|language=en-US|access-date=2019-10-19}}

Instead, the team used the robotic scoop to pin the probe against the edge of its hole. This method appeared successful initially, as the probe continued to dig for two weeks, until it was flush with the surface.{{Cite web|url=https://www.cnet.com/news/nasa-mars-lander-may-be-able-to-save-its-stuck-mole/|title=NASA Mars lander may be able to save its stuck 'mole'|last=Kooser|first=Amanda|website=CNET|language=en|access-date=2019-10-14}}{{Cite web|url=http://www.nasa.gov/feature/jpl/mars-insights-mole-is-moving-again|title=Mars InSight's 'Mole' Is Moving Again|last=Greicius|first=Tony|date=2019-10-17|website=NASA|access-date=2019-10-19}} At this time, the exposed top of the probe was too small for the scoop to press against, so the scoop was re-positioned to press down on the soil near the probe. Unfortunately, this caused the probe to back out again due to unusual soil properties and low atmospheric pressure.{{Cite web|url=https://mars.nasa.gov/news/8529/mars-insights-mole-has-partially-backed-out-of-its-hole?site=insight|title=Mars InSight's Mole Has Partially Backed Out of Its Hole|last=mars.nasa.gov|website=NASA's InSight Mars Lander|language=en|access-date=2019-10-28}} As the probe bounced, loose soil filled the area beneath it and lifted the probe halfway out again.{{cite web |last1=Palca |first1=Joe |title=A 'Mole' Isn't Digging Mars: NASA Engineers Are Trying To Find Out Why |url=https://www.npr.org/2019/11/29/783278261/a-mole-isn-t-digging-mars-nasa-engineers-are-trying-to-find-out-why |website=NPR.org |access-date=29 November 2019 |language=en |date=Nov 29, 2019}} In January 2020, the team used the pinning method again, but once again the probe ejected after the scoop was repositioned.{{Cite web|url=https://spacenews.com/insight-to-try-to-push-mole-into-martian-surface/|title=InSight to try to push mole into Martian surface|date=2020-02-21|website=SpaceNews.com|language=en-US|access-date=2020-02-25}}

In February 2020, the team reevaluated the risks of pushing the back cap of the mole directly using the robotic scoop, and determined the procedure to be acceptable. The procedure progressed slowly due to the requirement to reposition the scoop after each {{val|1.5|u=cm}} of progress. In June 2020, the top of the mole reached the regolith surface.{{cite web |last1=Spohn |first1=Tilman |title=The InSight mission logbook |url=https://www.dlr.de/blogs/en/all-blog-posts/The-InSight-mission-logbook.aspx |website=DLR Blogs |access-date=4 June 2020 |language=en |date=June 3, 2020}} The mole entered the surface at an angle of 30 degrees from vertical, but this angle may decrease if a greater depth is reached.{{Cite web|title=InSight mole making slow progress into Martian surface|url=https://spacenews.com/insight-mole-making-slow-progress-into-martian-surface/|date=2020-05-05|website=SpaceNews.com|language=en-US|access-date=2020-05-07}}

In July 2020, it was revealed that the mole was bouncing in place, underneath the scoop, suggesting insufficient friction to continue digging. A proposed solution was to fill the hole with sand in order to distribute pressure from the robotic scoop, thereby increasing friction. This procedure was performed in early August 2020.{{cite web |last1=Spohn |first1=Tilman |title=Mars InSight mission: The Mole is 'in' and the 'finishing touches' are 'in sight' |url=https://www.dlr.de/blogs/en/desktopdefault.aspx/tabid-5893/9577_read-1144/searchtagid-71788/ |website=DLR Blogs |access-date=7 September 2020 |language=en |date=10 August 2020}}

In late August 2020, a test indicated positive results. The scoop applied a downward force to the sand which covered the mole while hammering strokes were performed. This test resulted in a few millimeters of progress,{{Cite web|title=NASA's Insight Mars lander rescue operation makes progress saving 'stuck' probe {{!}} TESLARATI|url=https://www.teslarati.com/nasa-insight-mars-lander-rescue-mission-update/amp/|access-date=2020-09-17|website=www.teslarati.com|date=4 September 2020 }} and ultimately buried the instrument. In October 2020, the top of the mole was below the surface of Mars, and a decision was made to scrape two more scoops of regolith and tamp it down with the robotic scoop.{{cite web |last1=Gough |first1=Evan |title=InSight's 'Mole' is Now Completely buried! |url=https://www.universetoday.com/148379/insights-mole-is-now-completely-buried/ |website=Universe Today |access-date=19 October 2020 |date=16 October 2020}} Hammering operations were scheduled to continue in January 2021.

Final attempts to get the probe deeper took place on 9 January 2021; after they proved unsuccessful, the decision was made to stop attempting to dig deeper. On January 14, 2021, NASA announced that, as the final attempt to bury the "mole" had failed, the team had given up, with the heat probe portion of the mission declared to be over. The lead scientist for the experiment, Tilman Spohn, said that, "Mars and our heroic mole remain incompatible."{{cite web |last1=Dunn |first1=Marcia |title=RIP: Mars digger bites the dust after 2 years on red planet |url=https://apnews.com/article/technology-planets-mars-07a241714b85f9633ce1c8baf084d16e |website=Associated Press |access-date=14 January 2021 |date=14 January 2021}} The science team determined that the soil properties at the landing location were too different from what the instrument had been designed for. The team attempted many different remedies over several years to get the mole burrowing, but ultimately the attempts did not reach the target depth. The friction between the soil and the probe was not enough for the mole to hammer itself deeper.

The mole did achieve complete burial; the top of the mole is 2 to 3 centimetres below the Martian surface (with the mole itself being about 40 centimetres in length, the depth was thus about 43 centimetres). To be able to produce useful thermal measurements, the minimum required depth was specified as at least 3 metres deep.{{Citation needed|date=January 2021}}

Although unsuccessful, the mole's operations did teach the mission team a lot about the soil at the Insight site, about conducting excavation/drilling on Mars, and about operating the lander's robotic arm. The mole-rescue effort used the arm in ways that were unplanned before the mission. The seismometer (SEIS), radio experiment (RISE) and the weather instruments (TWINS) continued to operate until the end of December 2022.{{Cite web|url=https://www.jpl.nasa.gov/news/nasa-insights-mole-ends-its-journey-on-mars/|title=NASA InSight's 'Mole' Ends Its Journey on Mars|date=14 January 2021|access-date=15 January 2021|publisher=Jet Propulsion Laboratory}}

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{{Gallery

| title = Efforts of HP³ to penetrate the Martian surface

| align = center

| File:PIA23274-Mars-InSightLander-MoleCurrentPosition-20190605.jpg

| Engineering analysis of the mole after the initial problem concluded that the bottom of the mole was about {{convert|12|-|14|in|cm}} deep into Martian ground, with a bit of its top still inside the HP³ support structure.

| File:Insight sol 0209 D000M0209.jpg

| Insight{{'s}} HP³ components after lifting the support structure away from the mole. This image shows a region of compressed regolith around the Mole penetrometer.

| File:Mars InSight Mole Progress October 2019 8529 PIA23379-web 630.gif

| The initial success of the pinning technique is depicted in this time lapse video, which shows the probe burrowing into the regolith.

| File:PIA23213-Mars-InSightLander-MoleBacksOutOfHole-20191026.gif

| HP³ is seen after backing about halfway out of the hole it had burrowed.

| File:D000M0449 Mars InSight Mole push.png

| Insight lander using its scoop to push on the back cap of the HP³ mole.

| File:D000M0540 644463870EDR F0000 0817M.jpg

| HP{{sup|3}} mole at the surface of Mars, with the lander scoop pressing on its back cap.

| File:Insight sol 0599.png

| The mole, after being covered with sand by the robotic scoop

|File:PIA24263-MarsInsightLander-Mole-FinalEfforts-20210109.gif

|Mars InSight Lander - "Mole" - Final Efforts
(9 January 2021)

}}

The HP³ includes an infrared radiometer for measuring surface temperatures, contributed by DLR and based on the MARA radiometer for the Hayabusa2 mission.{{r|Banerdt20130307|in-depth|Grott2017}} HP3-RAD uses thermopile detectors to measure three spectral bands: {{val|8|-|14|u=um}}, {{val|16|-|19|u=um}} and {{val|7.8|-|9.6|u=um}}. HP3-RAD has a mass of {{cvt|120|g}}.

The detector was protected by a removable cover during landing.{{Cite journal|last1=Kopp|first1=Emanuel|last2=Mueller|first2=Nils|last3=Grott|first3=Matthias|last4=Walter|first4=Ingo|last5=Knollenberg|first5=Jörg|last6=Hanschke|first6=Frank|last7=Kessler|first7=Ernst|last8=Meyer|first8=Hans-Georg|editor1-first=Marija|editor1-last=Strojnik|date=2016-09-01|title=HP3-RAD: a compact radiometer design with on-site calibration for in-situ exploration|journal=Infrared Remote Sensing and Instrumentation XXIV|volume=9973|pages=99730T|doi=10.1117/12.2236190|bibcode=2016SPIE.9973E..0TK|s2cid=125699932|url=https://elib.dlr.de/105959/1/SPIE-2016-Paper%209973-28-HP3-RAD-A%20compact%20radiometer%20design.pdf}} The cover also serves as a calibration target for the instrument, supporting on-site calibration of the HP3-RAD.

Infrared radiometers were sent to Mars in 1969 as one of four major instruments on the Mariner 6 and Mariner 7 flyby spacecraft, and the observations helped to trigger a scientific revolution in knowledge about Mars.{{Cite web|url=https://www.acs.org/content/acs/en/education/whatischemistry/landmarks/mars-infrared-spectrometer.html|title=Infrared Spectrometer and the Exploration of Mars|website=American Chemical Society|language=en|access-date=2018-12-26}}{{Cite journal|last=Chdse|first=S. C.|date=1969-03-01|title=Infrared radiometer for the 1969 mariner mission to Mars|journal=Applied Optics|volume=8|issue=3|pages=639|doi=10.1364/AO.8.000639|issn=1559-128X|pmid=20072273|bibcode=1969ApOpt...8..639C }} The Mariner 6 & 7 infrared radiometer results showed that the atmosphere of Mars is composed mostly of carbon dioxide (CO₂), and revealed trace amounts water on the surface of Mars.

• Mini-TES, an infrared instrument on the 2003 Mars Exploration Rovers

{{reflist}}

• [http://esmats.eu/amspapers/pastpapers/pdfs/2016/grygorczuk2.pdf Hammering Mechanism for the HP3 Experiment onboard InSight.] (PDF)

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