Effects of the Phoenix Lander descent thruster plume on the Martian surface

• Published in: Journal of Geophysical Research - Planets Vol. 113; no. E3; pp. E00A11 - n/a
• Main Authors: Plemmons, D. H., Mehta, M., Clark, B. C., Kounaves, S. P., Peach Jr, L. L., Renno, N. O., Tamppari, L., Young, S. M. M.
• Format: Journal Article
• Language: English
• Published: American Geophysical Union 01-03-2008; Blackwell Publishing Ltd
• Subjects: Composition; Instruments and techniques; Mars; Planetary Sciences; Solar System Objects; Solid Surface Planets; Mars; composition; instruments and techniques
• ISSN: 0148-0227; 2156-2202
• DOI: 10.1029/2007JE003059

The exhaust plume of Phoenix's hydrazine monopropellant pulsed descent thrusters will impact the surface of Mars during its descent and landing phase in the northern polar region. Experimental and computational studies have been performed to characterize the chemical compounds in the thruster exhausts. No undecomposed hydrazine is observed above the instrument detection limit of 0.2%. Forty‐five percent ammonia is measured in the exhaust at steady state. Water vapor is observed at a level of 0.25%, consistent with fuel purity analysis results. Moreover, the dynamic interactions of the thruster plumes with the ground have been studied. Large pressure overshoots are produced at the ground during the ramp‐up and ramp‐down phases of the duty cycle of Phoenix's pulsed engines. These pressure overshoots are superimposed on the 10 Hz quasi‐steady ground pressure perturbations with amplitude of about 5 kPa (at touchdown altitude) and have a maximum amplitude of about 20–40 kPa. A theoretical explanation for the physics that causes these pressure perturbations is briefly described in this article. The potential for soil erosion and uplifting at the landing site is also discussed. The objectives of the research described in this article are to provide empirical and theoretical data for the Phoenix Science Team to mitigate any potential problem. The data will also be used to ensure proper interpretation of the results from on‐board scientific instrumentation when Martian soil samples are analyzed.