Editing Mars Science Laboratory (section)

=== EDL event–August 6, 2012 ===
[[File:20090428MSLEntry1.jpg|thumb|Martian atmosphere entry events from cruise stage separation to parachute deployment]]
Despite its late hour, particularly on the east coast of the United States where it was 1:31&nbsp;a.m.,<ref name="Space-20120806" /> the landing generated significant public interest. 3.2 million watched the landing live with most watching online instead of on television via [[NASA TV]] or cable news networks covering the event live.<ref>{{cite news |last=Kerr |first=Dara |title=Viewers opted for the Web over TV to watch Curiosity's landing |url=http://news.cnet.com/8301-1023_3-57489660-93/viewers-opted-for-the-web-over-tv-to-watch-curiositys-landing/ |access-date=August 9, 2012 |newspaper=CNET |date=August 9, 2012}}</ref> The final landing place for the rover was less than {{convert|2.4|km|abbr=on}}  from its target after a {{convert|563270400|km|abbr=on}} journey.<ref name="cnn.com"/> In addition to streaming and traditional video viewing, JPL made [[Eyes on the Solar System]], a three-dimensional real time simulation of entry, descent and landing based on real data. ''Curiosity''{{'s}} touchdown time as represented in the software, based on JPL predictions, was less than 1 second different from reality.<ref>{{cite news |last=Ellison |first=Doug |title=MSL Sol 4 briefing |url=https://www.youtube.com/watch?v=y_FH6PByZeY  |archive-url=https://ghostarchive.org/varchive/youtube/20211212/y_FH6PByZeY| archive-date=2021-12-12 |url-status=live|newspaper=YouTube}}{{cbignore}}</ref>

The EDL phase of the MSL spaceflight mission to Mars took only seven minutes and unfolded automatically, as programmed by JPL engineers in advance, in a precise order, with the entry, descent and landing sequence occurring in four distinct event phases:<ref name="Mission Timeline: Entry, Descent, and Landing"/><ref name="Mars Science Laboratory Entry, Descent, and Landing Triggers"/>

==== Guided entry ====
[[File:593419main pia14834-full full Mars Science Laboratory Guided Entry at Mars.jpg|thumb|left|The guided entry is the phase that allowed the spacecraft to steer with accuracy to its planned landing site.]]
Precision guided entry made use of onboard computing ability to steer itself toward the pre-determined landing site, improving landing accuracy from a range of hundreds of kilometers to {{convert|20|km|mi|sp=us}}. This capability helped remove some of the uncertainties of landing hazards that might be present in larger landing ellipses.<ref>{{cite web |url=http://mars.jpl.nasa.gov/msl/mission/technology/insituexploration/edl/guidedentry/ |title=MSL – Guided Entry |access-date=August 8, 2012 |year=2011 |work=[[JPL]] |publisher=NASA}}</ref> Steering was achieved by the combined use of thrusters and ejectable balance masses.<ref name='Guided entry'>{{cite journal |title=The RCS Attitude Controller for the Exo-Atmospheric And Guided Entry Phases of the Mars Science Laboratory |journal=Planetary Probe |first1=Paul B. |last1=Brugarolas |first2=A. Miguel |last2=San Martin |first3=Edward C. |last3=Wong |url=http://www.planetaryprobe.eu/IPPW7/proceedings/IPPW7%20Proceedings/Papers/Session5/p453.pdf |access-date=August 8, 2012}}</ref> The ejectable balance masses shift the capsule center of mass enabling generation of a [[Lift (force)|lift vector]] during the atmospheric phase. A navigation computer integrated the measurements to estimate the position and [[Attitude control (spacecraft)|attitude]] of the capsule that generated automated torque commands. This was the first planetary mission to use precision landing techniques.

The rover was folded up within an [[aeroshell]] that protected it during the travel through space and during the [[atmospheric entry]] at Mars. Ten minutes before atmospheric entry the aeroshell separated from the cruise stage that provided power, communications and propulsion during the long flight to Mars. One minute after separation from the cruise stage thrusters on the aeroshell fired to cancel out the spacecraft's 2-rpm rotation and achieved an orientation with the heat shield facing Mars in preparation for [[Atmospheric entry]].<ref name="spaceflightnow.com_1"/> The heat shield is made of [[phenolic impregnated carbon ablator]] (PICA). The {{convert|4.5|m|abbr=on}} diameter heat shield, which is the largest heat shield ever flown in space,<ref name="nasa8"/> reduced the velocity of the spacecraft by [[Ablative heat shield|ablation against the Martian atmosphere]], from the atmospheric interface velocity of approximately {{convert|5.8|km/s|abbr=on}} down to approximately {{convert|470|m/s|abbr=on}}, where parachute deployment was possible about four minutes later. One minute and 15 seconds after entry the heat shield experienced peak temperatures of up to {{convert|2090|C|F|abbr=on}} as atmospheric pressure converted kinetic energy into heat. Ten seconds after peak heating, that deceleration peaked out at 15 [[g-force|g]].<ref name="spaceflightnow.com_1"/>

Much of the reduction of the landing precision error was accomplished by an entry guidance algorithm, derived from the algorithm used for guidance of the [[Apollo Command Module]]s returning to Earth in the [[Apollo program]].<ref name="spaceflightnow.com_1"/> This guidance uses the lifting force experienced by the aeroshell to "fly out" any detected error in range and thereby arrive at the targeted landing site. In order for the aeroshell to have lift, its center of mass is offset from the axial centerline that results in an off-center trim angle in atmospheric flight. This was accomplished by ejecting ballast masses consisting of two {{convert|75|kg|lbs|abbr=on}} [[tungsten]] weights minutes before atmospheric entry.<ref name="spaceflightnow.com_1"/> The lift vector was controlled by four sets of two [[reaction control system]] (RCS) thrusters that produced approximately {{convert|500|N|lbf|abbr=on}} of thrust per pair. This ability to change the pointing of the direction of lift allowed the spacecraft to react to the ambient environment, and steer toward the landing zone. Prior to parachute deployment the entry vehicle ejected more ballast mass consisting of six {{convert|25|kg|lbs|abbr=on}} tungsten weights such that the [[center of gravity]] offset was removed.<ref name="spaceflightnow.com_1"/>

==== Parachute descent ====
[[File:MSL parachute.jpg|thumb|left|MSL's parachute is {{convert|16|m|ft|abbr=on}} in diameter.]]
[[File:MRO sees Curiosity landing.jpg|thumb|NASA's ''Curiosity'' rover and its parachute were spotted by NASA's [[Mars Reconnaissance Orbiter]] as the probe descended to the surface. August 6, 2012.]]
When the entry phase was complete and the capsule slowed to about {{convert|470|m/s|abbr=on}} at about {{convert|10|km|mi|abbr=on}} altitude, the supersonic [[parachute]] deployed,<ref name="EntryDescentLanding"/> as was done by previous landers such as [[Viking program|Viking]], Mars Pathfinder and the Mars Exploration Rovers. The parachute has 80 suspension lines, is over {{convert|50|m|ft|abbr=on}} long, and is about {{convert|16|m|ft|abbr=on}} in diameter.<ref name="ParaTest"/> Capable of being deployed at Mach 2.2, the parachute can generate up to {{convert|289|kN|lbf|abbr=on}} of [[drag (physics)|drag force]] in the Martian atmosphere.<ref name="ParaTest"/> After the parachute was deployed, the heat shield separated and fell away. A camera beneath the rover acquired about 5 frames per second (with resolution of 1600×1200 pixels) below {{convert|3.7|km|mi|abbr=on}} during a period of about 2 minutes until the rover sensors confirmed successful landing.<ref name="Mars Descent Imager (MARDI)"/> The ''Mars Reconnaissance Orbiter'' team were able to acquire an image of the MSL descending under the parachute.<ref name="planetary"/>

==== Powered descent ====
[[File:593472main pia14838 full Curiosity and Descent Stage, Artist's Concept.jpg|thumb|The powered descent stage]]
Following the parachute braking, at about {{convert|1.8|km|mi|abbr=on}} altitude, still travelling at about {{convert|100|m/s|mph|abbr=on}}, the rover and descent stage dropped out of the aeroshell.<ref name="EntryDescentLanding"/> The descent stage is a platform above the rover with eight variable thrust [[monopropellant rocket|monopropellant]] [[hydrazine]] rocket thrusters on arms extending around this platform to slow the descent. Each rocket thruster, called a Mars Lander Engine (MLE),<ref name="report"/> produces {{convert|400|to|3100|N|lbf|abbr=on}} of thrust and were derived from those used on the Viking landers.<ref name="aerojetMSLengines"/> 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.

==== {{anchor|Sky crane landing}} Sky crane ====
{{Main|Sky crane (landing system)}}
<!-- This Anchor tag serves to provide a permanent target for incoming section links. Please do not move it out of the section heading, even though it disrupts edit summary generation (you can manually fix the edit summary before saving your changes). Please do not modify it, even if you modify the section title. See [[Template:Anchor]] for details. (This text: [[Template:Anchor comment]]) -->

[[File:675608main_edl20120809-full.jpg|thumb|Entry events from parachute deployment through powered descent ending at sky crane flyaway]]
[[File:593484main pia14839 full Curiosity's Sky Crane Maneuver, Artist's Concept.jpg|thumb|Artist's conceptIon of ''Curiosity'' being lowered from the rocket-powered descent stage]]

For several reasons, a different landing system was chosen for MSL compared to previous Mars landers and rovers. ''Curiosity'' was considered too heavy to use the airbag landing system as used on the [[Mars Pathfinder]] and [[Mars Exploration Rover]]s. A legged lander approach would have caused several design problems.<ref name="spaceflightnow.com_1"/> It would have needed to have engines high enough above the ground when landing not to form a dust cloud that could damage the rover's instruments. This would have required long landing legs that would need to have significant width to keep the center of gravity low. A legged lander would have also required ramps so the rover could drive down to the surface, which would have incurred extra risk to the mission on the chance rocks or tilt would prevent ''Curiosity'' from being able to drive off the lander successfully. Faced with these challenges, the MSL engineers came up with a novel alternative solution: the sky crane.<ref name="spaceflightnow.com_1"/> The sky crane system lowered the rover with a {{convert|7.6|m|foot|abbr=on}}<ref name="spaceflightnow.com_1"/> tether to a soft landing—wheels down—on the surface of Mars.<ref name="EntryDescentLanding"/><ref name="scientificamerican"/><ref name="Mars rover lands on Xbox Live"/> 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 fastener|pyros]] (small explosive devices) 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.<ref>{{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}}</ref> The sky crane concept had never been used in missions before.<ref name="youtube"/>