Reconstructed Performance of the Mars InSight Lander's Supersonic Parachute & Comparison with the Phoenix Lander

Abstract

On November 26th, 2018 the Mars InSight lander successfully touched down at Elysium Planitia. InSight's Entry, Descent, and Landing sequence included an 11.8-m superson-ically deployed Disk-Gap-Band parachute that was a largely build-to-print version of the parachute used to successfully land the Phoenix lander a decade earlier. This paper describes the reconstructed performance of InSight's supersonic parachute at Mars, highlighting the differences and similarities with the performance of Phoenix's parachute. Measurements from the onboard inertial measurement unit along with pre-launch measurements of the parachute system and spacecraft, assumptions about the vehicle's aerodynamics, and models for the Martian atmosphere were used to reconstruct the spacecraft's trajectory and the parachute system's performance. The reconstruction results were compared against pre-flight predictions. Reconstruction of the InSight trajectory leading up to parachute deployment showed that the vehicle trimmed in a lift-down orientation during entry and thus experienced greater deceleration than expected by most pre-flight simulations. This led to parachute deployment conditions that diverged from the nominal preflight predictions. The parachute was mortar-deployed at a Mach number of approximately 1.5, below the nominal preflight expectation of 1.66. The approximate dynamic pressure at mortar fire was between 518 Pa and 546 Pa, which agreed well with pre-flight expectations. The mortar system performed nominally, and the system's deployment (0.755 s) and inflation (1.1 s) times were in line with pre-flight modeling. The peak inflation load was 45 kN, well below the parachute's 67 kN design limit load. Following deployment of the parachute, the vehicle's rotational rates and the dynamics of the system were in excellent agreement with pre-flight expectations. The performance of the InSight parachute system was also found to agree well with that of the Phoenix parachute system, as expected given the similarities between the two systems.