Editing Mars Pathfinder (section)

==Entry, descent and landing==
[[File:Landing sequence.gif|thumb|Landing sequence]]
[[File:Mars Pathfinder.jpg|thumb|''Mars Pathfinder'' during final assembly showing the aeroshell, cruise ring and solid rocket motor]]

''Mars Pathfinder'' entered the Martian atmosphere and landed using an innovative system involving an entry capsule, a supersonic [[parachute]], followed by solid rockets and large airbags to cushion the impact.

''Mars Pathfinder'' directly entered Mars atmosphere in a retrograde direction from a hyperbolic trajectory at {{cvt|6.1|km/s|mph}} using an atmospheric entry aeroshell (capsule) that was derived from the original Viking Mars lander design. The aeroshell consisted of a back shell and a specially designed ablative heatshield to slow to {{cvt|370|m/s|mph}} where a supersonic disk-gap-band parachute was inflated to slow its descent through the thin Martian atmosphere to {{cvt|68|m/s|mph}}. The lander's on-board computer used redundant on-board accelerometers to determine the timing of the parachute inflation. Twenty seconds later the heatshield was pyrotechnically released. Another twenty seconds later the lander was separated and lowered from the backshell on a {{cvt|20|m|ft}} bridle. When the lander reached {{cvt|1.6|km|ft}} above the surface, a radar was used by the on-board computer to determine altitude and descent velocity. This information was used by the computer to determine the precise timing of the landing events that followed.<ref>{{Cite web|title=Mars Pathfinder - Entry Descent and Landing|url=https://mars.nasa.gov/MPF/mpf/edl/edl1.html|access-date=2021-02-16|website=mars.nasa.gov}}</ref>

[[File:Pathfinder Air Bags - GPN-2000-000484.jpg|thumb|right|200px|The ''Pathfinder'' air bags are tested in June 1995]]
Once the lander was {{cvt|355|m|ft}} above the ground, airbags were inflated in less than a second using three gas generators.<ref>{{Cite web|title=Mars Pathfinder Lander Description|url=https://pdsimage2.wr.usgs.gov/Missions/Mars_Pathfinder/mpim_0001/document/insthost.htm|access-date=31 March 2021|website=pdsimage.wr|publisher=[[USGS]]|archive-date=March 11, 2021|archive-url=https://web.archive.org/web/20210311004210/https://pdsimage2.wr.usgs.gov/Missions/Mars_Pathfinder/mpim_0001/document/insthost.htm|url-status=dead}}</ref> The airbags were made of four inter-connected multi-layer [[vectran]] bags that surrounded the tetrahedron lander. They were designed and tested to accommodate grazing angle impacts as high as {{cvt|28|m/s|mph}}. However, as the airbags were designed for no more than about {{cvt|15|m/s|mph}} vertical impacts, three solid retrorockets were mounted above the lander in the backshell.<ref>{{Cite web|title=Rocket Assisted Descent – The RAD Rocket Motors|url=https://mars.nasa.gov/MPF/mpf/rad.html|access-date=2021-02-16|website=mars.nasa.gov}}</ref> These were fired at {{cvt|98|m|ft}} above the ground. The lander's on-board computer estimated the best time to fire the rockets and cut the bridle so that the lander velocity would be reduced to about zero between {{cvt|15|and|25|m|ft}} above the ground. After 2.3&nbsp;seconds, while the rockets were still firing, the lander cut the bridle loose about {{cvt|21.5|m|ft}} above the ground and fell to the ground. The rockets flew up and away with the backshell and parachute (they have since been sighted by orbital images). The lander impacted at {{cvt|14|m/s|mph}} and limited the impact to only 18 G of deceleration. The first bounce was {{cvt|15.7|m|ft}} high and the lander continued bouncing for at least 15 additional bounces (accelerometer data recording did not continue through all of the bounces).<ref>{{Cite journal|last1=Spencer|first1=David A.|last2=Blanchard|first2=Robert C.|last3=Braun|first3=Robert D.|last4=Kallemeyn|first4=Pieter H.|last5=Thurman|first5=Sam W.|date=March 1998|title=Mars Pathfinder Entry, Descent, and Landing Reconstruction|url=http://dx.doi.org/10.2514/2.3478|journal=Journal of Spacecraft and Rockets|volume=36|issue=3|pages=357–366|doi=10.2514/2.3478|issn=0022-4650}}</ref>

The entire entry, descent and landing process was completed in four minutes.

Once the lander stopped rolling, the airbags deflated and retracted toward the lander using four winches mounted on the lander "petals". Designed to right itself from any initial orientation, the lander happened to roll right side up onto its base petal. Eighty-seven minutes after landing, the petals were deployed with ''Sojourner'' rover and the solar panels attached on the inside.<ref name=nssdca/>

The lander arrived at night at 2:56:55 Mars local solar time (16:56:55 UTC) on July 4, 1997. The lander had to wait until sunrise to send its first digital signals and images to Earth. The landing site was located at 19.30° north latitude and 33.52° west longitude in Ares Vallis, only {{cvt|19|km|mi}} southwest of the center of the {{cvt|200|km|mi}} wide landing site ellipse. During [[Timekeeping on Mars#Sols|Sol]] 1, the first Martian solar day the lander spent on the planet, the lander took pictures and made some meteorological measurements. Once the data was received, the engineers realized that one of the airbags had not fully deflated and could be a problem for the forthcoming traverse of ''Sojourner''{{'}}s descent ramp. To solve the problem, they sent commands to the lander to raise one of its petals and perform additional retraction to flatten the airbag. The procedure was a success and on Sol 2, ''Sojourner'' was released, stood up and backed down one of two ramps.<ref name=nssdca>{{Cite web|title=NASA – NSSDCA – Spacecraft – Details|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1996-068A|access-date=2021-02-16|website=nssdc.gsfc.nasa.gov}}</ref>