Reconstructed Performance of the Supersonic Parachute of the Mars InSight Lander

Abstract

On 26 November 2018, the Mars InSight lander successfully touched down at Elysium Planitia and began its 26 month prime mission. The entry, descent, and landing sequence of InSight included an 11.8 m supersonically deployed disk–gap–band parachute. This paper describes the reconstructed performance of the supersonic parachute of InSight on Mars. Measurements from the onboard inertial measurement unit along with prelaunch measurements of the parachute system and spacecraft, assumptions about the aerodynamics of the vehicle, and models for the Martian atmosphere have been used to reconstruct the trajectory of the spacecraft and the performance of the parachute system. The reconstruction results were compared against preflight 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 preflight 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 peak inflation load was 45 kN, well below the 67 kN design limit load of the parachute. Following deployment of the parachute, the rotational rates of the vehicle and the dynamics of the system were in excellent agreement with preflight expectations.