Mars EXPRESS observation of the PHOENIX entry: simulations, planning, results and lessons learned

摘要

NASA’s PHOENIX spacecraft has successfully landed on Mars on 25 May 2008. ESA supported the event by recording signals from PHOENIX by the Mars EXPRESS spacecraft using its lander communication subsystem. Following numerical simulations of the probe entry plume emission, two Mars EXPRESS instruments, namely the High Resolution and Stereo Camera (HRSC) and the Ultraviolet and Infrared Spectrometer (SPICAM), were switched on in to observe the emission associated with the atmospheric entry. No positive detection was reported unfortunately. This article reports on the simulations, the planning, and the results. The non-detection by the UV spectrometer was due to a wrong instrument setting. Result for the camera is tentatively explained by the level of emission in the visible range. Lessons learned are given in the conclusions: the entry probe trajectory should be communicated as soon as possible to all interested parties, within the boundary conditions of confidentiality obviously. It is important to plan some redundancy to prevent incorrect instrument operations. A multi-instrument multi-spacecraft campaign should be encouraged by all means. Since detection of such faint signal is challenging, the integration time must be properly matched to the event duration. Payload operational (exclusion) rules should be discussed in an open way, to check whether the prudence of such measures is procedural or physical. The numerical simulations discussed in this paper have been focused on IR radiation in the lower density flow wake, using a DSMC/line-by-line method. These could be complemented with other numerical approaches more focused in the VUV–visible region in the high-pressure bow-shock region, using continuum Navier–Stokes fluid methods, which would yield information on the contribution to the emission spectrum from minor flow species such as CN, C_2 and C.