Sky crane (landing system)

{{Further|List of landing ellipses on extraterrestrial bodies}}

The first NASA rover, Sojourner (on the Mars Pathfinder lander), and twin rovers Spirit and Opportunity, used a combination of parachutes, retrorockets, and airbags for landing. Curiosity, launched in 2011, weighs nearly 900 kg, and was too heavy to be landed this way, as the airbags needed for it would be too heavy to be launched on a rocket.{{cite web |last1=Teitel |first1=Amy Shira |title=Sky Crane - how to land Curiosity on the surface of Mars |url=https://blogs.scientificamerican.com/guest-blog/sky-crane-how-to-land-curiosity-on-the-surface-of-mars/ |website=Scientific American Blog Network |access-date=26 August 2023 |language=en}} Instead, a landing system that combined a protective aeroshell, supersonic parachutes, and sky crane was developed by the Jet Propulsion Laboratory (JPL) under Adam Steltzner.{{cite journal |title=366 days: Nature's 10 |journal=Nature |date=1 December 2012 |volume=492 |issue=7429 |pages=335–343 |doi=10.1038/492335a |pmid=23257862 |url=https://www.nature.com/articles/492335a |language=en |issn=1476-4687 |last1=Heuer |first1=R. D. |last2=Rosenzweig |first2=C. |last3=Steltzner |first3=A. |last4=Blanpain |first4=C. |last5=Iorns |first5=E. |last6=Wang |first6=J. |last7=Handelsman |first7=J. |last8=Gowers |first8=T. |last9=De Bernardinis |first9=B. |last10=Fouchier |first10=R. |bibcode=2012Natur.492..335. |s2cid=4418086 |doi-access=free }}{{cite web |last1=Palca |first1=Joe |title=Crazy Smart: When A Rocker Designs A Mars Lander |url=https://www.npr.org/2012/08/03/157597270/crazy-smart-when-a-rocker-designs-a-mars-lander |publisher=NPR |access-date=28 August 2023}}{{cite web |title=The Sky Crane Solution {{!}} APPEL Knowledge Services |url=https://appel.nasa.gov/2012/07/31/the-sky-crane-solution/ |website=appel.nasa.gov |access-date=26 August 2023}} Sky crane is "an eight-rocket jetpack attached to the rover".{{cite web |title=Strange but True: Curiosity's Sky Crane {{!}} Science Mission Directorate |url=https://science.nasa.gov/science-news/science-at-nasa/2012/30jul_skycrane |website=science.nasa.gov |access-date=26 August 2023}} {{PD-notice}} This system is also much more precise: while the Mars Exploration Rovers could have landed anywhere within their respective 93-mile by 12-mile (150 by 20 kilometer) landing ellipses, Mars Science Laboratory landed within a 12-mile (20-kilometer) ellipse.{{cite web |title=Image Gallery: Perseverance Rover - NASA |url=https://mars.nasa.gov/mars2020/multimedia/images/index.cfm?imageid=3650 |website=mars.nasa.gov |access-date=26 August 2023 |language=en}} {{PD-notice}} Mars 2020 has even more precise system, and landing ellipse of 7.7 by 6.6 km.{{cite web |title=Perseverance Rover Landing Ellipse in Jezero Crater |url=https://mars.nasa.gov/resources/25491/perseverance-rover-landing-ellipse-in-jezero-crater/ |website=NASA Mars Exploration |access-date=22 January 2024 |language=en}}

The Curiosity team invented the sky crane system by studying old Viking landing system—its engines are "an upgraded 'reinvention' of Viking’s throttleable engines"—and landing experience from previous rovers. The sky crane works much like a helicopter, and the team even consulted with Sikorsky Skycrane helicopter engineers and pilots.{{cite web |last1=Betz |first1=Eric |title=The Skycrane: How NASA's Perseverance rover will land on Mars |url=https://www.astronomy.com/space-exploration/the-skycrane-how-nasas-perseverance-rover-will-land-on-mars/ |website=Astronomy Magazine |access-date=26 August 2023 |date=18 February 2021}}

File:Pathfinder_Air_Bags_-_GPN-2000-000484.jpg|Airbags used for the Sojourner, Spirit and Opportunity rovers.

File:PIA15279 3rovers-stand D2011 1215 D521.jpg|Comparison of the Sojourner, Mars Exploration Rovers, and the Curiosity

File:PIA24377-MarsProbes-LandingEllipses-20210127.jpg|Comparison of landing ellipses for Perseverance, Curiosity, InSight lander, Phoenix lander, and Mars Pathfinder.

Curiosity was the first rover landed using the sky crane maneuver. Following the parachute braking, at about {{convert|1.8|km|mi|abbr=on}} altitude, still travelling at about {{convert|100|m/s|mph kph|abbr=on}}, the rover and descent stage dropped out of the aeroshell.{{cite web |title=Final Minutes of Curiosity's Arrival at Mars |url=https://www.nasa.gov/mission_pages/msl/multimedia/gallery/pia13282.html |website=NASA |access-date=27 August 2023 |date=16 July 2018}} The descent stage is a platform above the rover with eight variable thrust monopropellant hydrazine rocket thrusters on arms extending around this platform to slow the descent. Each rocket thruster, called a Mars Lander Engine (MLE),{{Cite report |last=Way |first=David W. |title=Mars Science Laboratory: Entry, Descent, and Landing System Performance – System and Technology Challenges for Landing on the Earth, Moon, and Mars |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090007730_2009006430.pdf |display-authors=etal |access-date=2023-09-10 |archive-date=2014-02-25 |archive-url=https://web.archive.org/web/20140225022544/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090007730_2009006430.pdf |url-status=bot: unknown }} produces {{convert|400|to|3100|N|lbf|abbr=on}} of thrust. A radar altimeter measured altitude and velocity, feeding data to the rover's flight computer. Meanwhile, the rover transformed from its stowed flight configuration to a landing configuration while being lowered beneath the descent stage by the sky crane system.

This system consists of a bridle lowering the rover on three nylon tethers and an electrical cable carrying information and power between the descent stage and rover. As the support and data cables unreeled, the rover's six motorized wheels snapped into position. At roughly {{convert|7.5|m|abbr=on}} below the descent stage the sky crane system slowed to a halt and the rover touched down. After the rover touched down, it waited two seconds to confirm that it was on solid ground by detecting the weight on the wheels and fired several pyrotechnic fasteners activating cable cutters on the bridle and umbilical cords to free itself from the descent stage. The descent stage then flew away to a crash landing {{convert|650|m|foot|abbr=on}} away.{{cite web |url=http://www.nasa.gov/mission_pages/msl/news/msl20120807.html |title=Orbiter Images NASA's Martian Landscape Additions |access-date=August 9, 2012 |date=August 8, 2012 |work=NASA}} {{PD-notice}}

File:675608main_edl20120809-full.jpg|Curiosity EDL profile

File:MSL-spacecraft-exploded-view.png|MSL spacecraft exploded view. Sky crane is in the middle(3).

File:MSL_DescentStage.jpg|Curiosity sky crane at the JPL

Curiosity's Seven Minutes of Terror.ogv|Curiosity's Seven Minutes of Terror

File:593472main pia14838 full Curiosity and Descent Stage, Artist's Concept.jpg|The powered descent stage

File:593484main pia14839 full Curiosity's Sky Crane Maneuver, Artist's Concept.jpg|Artist's conception of Curiosity being lowered from the rocket-powered descent stage.

File:593496main_pia14840_full_Curiosity_Touching_Down,_Artist's_Concept.jpg|Final stage of the landing before sky crane's separation

The sky crane system was updated for the Perseverance rover weighing 1,025 kg, which is heavier than its predecessor.{{cite web |last1=Buongiorno |first1=Caitlyn |title=Mars Madness: How Perseverance will stick the landing during its 7 minutes of terror |url=https://www.astronomy.com/science/mars-madness-how-perseverance-will-stick-the-landing-during-its-7-minutes-of-terror/ |website=Astronomy Magazine |access-date=27 August 2023 |date=17 February 2021}} During the atmospheric entry, the spacecraft jettisoned the lower heat shield and deployed a parachute from the backshell to slow the descent to a controlled speed. It happens about 240 seconds after entry, at an altitude of about 7 miles (11 kilometers) and a velocity of about 940 mph (1,512 kph). The EDL got new Terrain-Relative Navigation technology, that uses a special camera to quickly identify features on the surface. It is then compared to an onboard map to determine exactly where the rover is heading. Mission team members have mapped in advance the safest areas of the landing zone. If Perseverance can tell that it's headed for more hazardous terrain, it picks the safest spot it can reach and gets ready for the next step. With the craft moving under {{cvt|320|kph|mph m/s}} and about {{cvt|1.9|km}} from the surface, the rover and sky crane assembly detached from the backshell, and rockets on the sky crane controlled the remaining descent to the planet. As the descent stage levels out and slows to its final descent speed of about 1.7 miles per hour (2.7 kilometers per hour), it initiates the sky crane maneuver. With about 12 seconds before touchdown, at about 66 feet (20 meters) above the surface, the descent stage lowers the rover on a set of cables about 21 feet (6.4 meters) long until it confirmed touchdown, detached the cables, and flew a distance away to avoid damaging the rover. Meanwhile, the rover unstows its mobility system, locking its legs and wheels into landing position.{{cite web |title=Entry, Descent and Landing (EDL) - NASA |url=https://mars.nasa.gov/mars2020/timeline/landing/entry-descent-landing/ |website=mars.nasa.gov |access-date=26 August 2023 |language=en}} {{PD-notice}}{{cite web |title='7 minutes of terror': Perseverance rover's nail-biting landing phase |url=https://phys.org/news/2021-02-minutes-terror-perserverance-rover-nail-biting.html |website=phys.org |access-date=26 August 2023 |language=en}}

Perseverance successfully landed on the surface of Mars on 18 February 2021 at 20:55 UTC.{{cite news |last=Strickland|first=Ashley|date=19 February 2021|title=Incredible new images shared by Perseverance rover after Mars landing|publisher=CNN|url=https://www.cnn.com/2021/02/19/world/mars-rover-new-images-scn-trnd/index.html|access-date=20 February 2021}} Ingenuity reported back to NASA via the communications systems on Perseverance the following day, confirming its status.{{cite web|url=https://www.cnn.com/2021/02/20/world/mars-ingenuity-helicopter-update-scn-trnd/index.html|title=Ingenuity helicopter phones home from Mars|first=Ashley|last=Strickland|date=20 February 2021|access-date=22 February 2021|publisher=CNN}} NASA also confirmed that the on-board microphone on Perseverance had survived EDL, along with other high-end visual recording devices, and released the first audio recorded on the surface of Mars shortly after landing,{{cite web |url=https://www.cnn.com/2021/02/22/world/mars-rover-new-video-images-scn-trnd/index.html|title=NASA shares first video and audio, new images from Mars Perseverance rover|first=Ashley|last=Strickland|date=23 February 2021|access-date=23 February 2021|publisher=CNN}} capturing the sound of a Martian wind.{{cite web|last=Crane|first=Leah|title=Perseverance rover has sent back stunning video and audio from Mars|url=https://www.newscientist.com/article/2268810-perseverance-rover-has-sent-back-stunning-video-and-audio-from-mars/|date=2021-02-22|access-date=2021-02-24|website=New Scientist}}

File:Perseverance Rover's Entry, Descent and Landing Profile.png|Perseverance EDL Profile

File:PIA24128-Mars-Mars2020-PerseveranceRover-20201015.jpg|Mars 2020 expanded illustration. Sky crane is in the middle.

File:Perseverance_SkyCrane.jpg|Perseverance sky crane

File:PIA23466-Mars2020Rover-SeparationTest-20190928.jpg|Sky crane separation test

Perseverance Rover's Descent and Touchdown on Mars Onboard Camera Views .webm|Perseverance descent and touchdown on Mars (onboard camera views)

File:Mars_Perseverance_EUF_0001_0667022672_630ECV_N0010052EDLC00001_0010LUJ01.png|The sky crane photographed from the rover during descent

File:NASA-MarsPerseveranceRover-LandingDrop-20210218.png|The rover photographed from the sky crane during descent

{{reflist}}

• [https://www.newyorker.com/magazine/2013/04/22/the-martian-chroniclers "The Martian Chroniclers"] at The New Yorker

{{Mars rovers}}

Category:Aerospace engineering

Category:Flight phases

Category:Mars Science Laboratory

Category:Mars 2020