USING THE ANCHORING DEVICE OF A COMET LANDER TO DETERMINE SURFACE MECHANICAL-PROPERTIES

Owning to the low surface gravity of the Rosetta target comet 46P/Wirt anen, a means of anchoring the Rosetta Lander to the cometary surface will be necessary. This task can be accomplished by firing an anchor i nto the cometary soil immediately after touchdown to prevent a rebound of the spacecraft from the surface or subsequent ejection by other fo rces, and to allow for mechanical activities (drilling, etc.) at the l anding site. The rational for anchoring is examined, based on estimate s of the main forces likely to act on the spacecraft after landing. We report on the development of an anchoring device using a pyrotechnic gas generator as a power source and an instrumented anchor. In additio n to the anchoring function, which is the primary purpose of this syst em, the integration of acceleration and temperature sensors into the t ip offers the possibility to determine some important material propert ies of the cometary surface layer. The accelerometer is designed to me asure the deceleration history of the projectile and is thus expected to give information on how the material properties (in particular stre ngth) change within the penetrated layer(s), while the temperature sen sor will measure temperature variations at the depth at which the anch or finally comes to rest. As the mechanical properties of the material are not known, it is difficult to predict the final depth of the anch or with any great certainty, but it may well be greater than that reac hed by any other of the lander's instruments. The instrumented anchor will be part of the MUPUS experiment, selected to form part of the Ros etta Lander payload. We report on results of laboratory simulations of anchor penetration performed at the Institut fur Weltraumforschung, G raz, and compare these with models of projectile penetration. The valu e of the results expected from the penetrometry experiment in the cont ext of an improved understanding of cometary processes is discussed. ( C) 1998 Elsevier Science Ltd. All rights reserved.