HP3-PP - Development of the HP3 Permittivity Probe Onboard the ESA ExoMars Mission
The investigation of the surface of other celestial objects, mostly of the planet Mars, currently is the major driver of robotic exploration. For this purpose instruments must be developed, which can autonomously perform field measurements and which fit in the tight resource envelope of a space mission.
The whole instrument is embedded in a mole penetrator, i.e. a mechanical instrument carrier resembling a nail with integrated hammering mechanism, which will deliver the sensors up to a depth of five meters into the Martian soil. This suite of geophysical sensors was initially designed to be a part of the Geophysical Package (GEP) of the ExoMars mission.
After the cancelation of the GEP and the postponement of the ExoMars mission it was decided to continue with the instrument development to a high TRL level as a laboratory model and to propose it to upcoming missions to Mars and the Moon.
The basis of the sensor implementation is derived from classical geoelectric methods. However, driven by the need to accommodate the whole sensor to a down-the-hole instrument, a new front-end electronics has to be developed.
Constrained by the geometric envelope of the HP3 payload compartment, a small sized two channel vector analyser was designed spanning the frequency range of 4 - 20 000 Hz in a step size of 1 Hz. The whole design is already sized for the larger flight qualified electrical components and once fully tested and calibrated should be ready to be used on a flight design campaign on short notice.
The knowledge of the permittivity of a soil can be used not only to characterise the adjacent material in terms of electrical properties, but can also help to detect inhomogenities like layers or inclusions and of course is quite sensitive to even small amounts of water within the soil.
As additional information, it can help to provide “ground truth” for ground penetrating radars in orbit such as the Marsis radar on the MarsExpress mission.
Austrian Academy of Sciences, Space Research Institute (IWF) - Günter Kargl
Austrian Academy of Sciences - Space Research Institute (IWF)
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