Editing Atmospheric entry (section)

====Super light-weight ablator====
''SLA'' in ''SLA-561V'' stands for ''super light-weight ablator''. SLA-561V is a proprietary ablative made by [[Lockheed Martin]] that has been used as the primary TPS material on all of the 70° sphere-cone entry vehicles sent by NASA to Mars other than the [[Mars Science Laboratory]] (MSL). SLA-561V begins significant ablation at a heat flux of approximately 110&nbsp;W/cm<sup>2</sup>, but will fail for heat fluxes greater than 300&nbsp;W/cm<sup>2</sup>. The MSL aeroshell TPS is currently designed to withstand a peak heat flux of 234&nbsp;W/cm<sup>2</sup>. The peak heat flux experienced by the ''[[Viking 1]]'' aeroshell which landed on Mars was 21&nbsp;W/cm<sup>2</sup>. For ''Viking 1'', the TPS acted as a charred thermal insulator and never experienced significant ablation. ''Viking 1'' was the first Mars lander and based upon a very conservative design. The Viking aeroshell had a base diameter of 3.54&nbsp;meters (the largest used on Mars until Mars Science Laboratory). SLA-561V is applied by packing the ablative material into a honeycomb core that is pre-bonded to the aeroshell's structure thus enabling construction of a large heat shield.<ref>{{cite tech report
| first=Huy
| last=Tran
| author2=Michael Tauber
| author3=William Henline
| author4=Duoc Tran
| author5=Alan Cartledge
| author6=Frank Hui
| author7=Norm Zimmerman
| title=Ames Research Center Shear Tests of SLA-561V Heat Shield Material for Mars-Pathfinder
| number=NASA Technical Memorandum 110402
| institution=NASA Ames Research Center
| year=1996
| url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19960049758_1996080506.pdf
| access-date=July 7, 2017
| archive-date=September 25, 2020
| archive-url=https://web.archive.org/web/20200925143246/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19960049758_1996080506.pdf
| url-status=live
}}</ref>