Entry, Descent, and Landing Performance of the Mars Phoenix Lander

On 25 May 2008, the Mars Phoenix Lander successfully landed on the northern arctic plains of Mars. An overview of reconstruction analyses performed on each entry, descent, and landing phase to assess the performance of Phoenix as it descended is presented and a comparison to preentry predictions is provided. The landing occurred 21 km further downrange than the predicted landing location. Analysis of the flight data revealed that the primary cause of Phoenix's downrange landing was a higher trim total angle of attack during the hypersonic phase of the entry, which resulted in Phoenix flying a slightly lifting trajectory. The likely cause of this higher trim attitude was a combination of a larger radial center-of-gravity offset than the preflight measurement and a lower hypersonic aerodynamic static stability than predicted. Parachute deployment was 6.4 s later than predicted. The parachute deployment and inflation process occurred as expected with no anomalies identified. The subsequent parachute descent and powered terminal landing also behaved as expected. A reconstruction of the landing day atmospheric density profile was found to be less dense than the best a priori prediction, ranging from a few percent to 8% lower in the altitude region where nearly all of the deceleration occurs. A comparison of the flight reconstructed trajectory parameters showed that the actual Phoenix entry, descent, and landing was close to preentry predictions.