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

Abstract

[1] 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.

OSIRIS-REx Contamination Control Strategy and Implementation

“…While the science team for NASA's Phoenix mission to Mars was interested in understanding thruster plume products (Plemmons et al 2008), OSIRIS-REx is the first mission to impose a maximum hydrazine flux as a scientific requirement, and as such there was no existing precedent (model-based, testing-based, or otherwise) to aid in defining the appropriate limit. In the absence of historical knowledge, the team used analogy to the amino acid limit of 180 ng/cm 2 on the TAGSAM head.…”

The discovery of liquid water on Mars and its implications for astrobiology

“…Tests with the Phoenix thruster engine did not show any evidence of hydrazine in the plume above a detection level of 0.2%. 28 Moreover, since hydrazine freezes at about 275 K, any traces of hydrazine would freeze at the landing site temperatures. Thus, except for possible trace amounts of fuel impurities, ammonia is the only contaminant from the Phoenix thruster plume.…”

“…27 The compression of the thruster plume on the ice produced pressure and temperature perturbations of about 10-35 kPa and 1000 K and caused a ~ 1 mm thick layer of ice to melt and salty mud to be splashed under the lander. 27,28 In order to minimize contamination, Phoenix used high purity hydrazine to power its engines. The byproducts of the combustion of hydrazine are water vapor, nitrogen, hydrogen and ammonia.…”

Introduction to special section on the Phoenix Mission: Landing Site Characterization Experiments, Mission Overviews, and Expected Science

“…The RA will be deployed and tested throughout its range of motion. The effects of the thruster plumes on the digging area will be assessed [ Plemmons et al , 2008]. The final step for characterization is to deliver a surface sample to the TEGA instrument.…”