Scientific and Technical Aerospace Reports Volume 39 April 6, 2001

climatic variations. This can only be achieved through a precise knowledge of the structure thermosphere and of its temporal variations.
Last but not least, insertion in Mars orbit of future scientific or telecommunication satellites will certainly rely on aerocapture
and aerobraking which, compared to the classical chemical technique, allow for a very large mass saving. Reliable and safe
orbit insertion and orbital operations require that accurate models of the structure of the atmosphere and its predicted variations
be available. The response of the Martian environment above about 100 km to the various processes mentioned above are at present
very poorly constrained by available measurements. Upcoming missions to Mars such as Planet-B and Mars Express will not provide
in situ measurements down to the lower thermosphere of Mars, in the altitude range between 100 and 150 km where considerable
variability has been observed recently by the Mars Global Surveyor (MGS) Accelerometer during aerobraking campaigns.
The Mars Thermospheric General Circulation Model (MTGCM) is a 3-D modeling tool that is presently being used to simulate
the Mars upper atmosphere structure and dynamics in the altitude range from about 70 to 300 km. The simulation runs for various
solar fluxes, seasons, and dust heating conditions were only crudely constrained by Mariner, Viking, Pathfinder, and MGS
observations since the available in-situ data span only a fraction of the solar cycle and Mars seasons. A long-term program to monitor
the structure of the Martian thermosphere from about 100 km up to about 250 km is thus proposed which can take benefit of
multiple opportunities to provide the necessary coverage of the various conditions which affect the global environment of Mars.
The ultimate goal is to build a data base for the climatology of the lower thermosphere of Mars which can be used to constrain
the models.
Author
Atmospheric Models; Mars Atmosphere; Thermosphere; Accelerometers; Instrument Packages
20010023050 Centre des Etudes Terrestraire et Planetaire, Saint Maur des Fosses, France
ARES, an Electric Field Experiment for NETLANDER
Berthelier, J. J., Centre des Etudes Terrestraire et Planetaire, France; Grard, R., European Space Agency. European Space
Research and Technology Center, ESTEC, Netherlands; Laasko, H., FMI, Finland; Parrot, M., Centre National de la Recherche
Scientifique, France; Concepts and Approaches for Mars Exploration; July 2000, Part 1, pp. 21-22; In English; See also
20010023036; No Copyright; Avail: CASI; A01, Hardcopy; A03, Microfiche
The conditions which prevail in the atmospheres of most planets in the Solar System, in particular the telluric ones, are likely
to give rise to their electrification. The resulting processes, which are of major importance for meteorology and climatology on
Earth, may also be significant for atmospheric and surface processes on the other planets and specifically on Mars. With an average
pressure between 5 and 10 mb, the atmosphere near the surface of Mars is comparable to the Earth’s stratosphere at an altitude
of 35 to 40 kilometers. The main difference lies in the composition, since the major constituent on Mars is the carbon dioxide CO2.
Ionization is mainly due to cosmic rays and during daytime, photoionization by solar EUV and soft X-rays. In absence of actual
data, most authors have assumed that the electric conductivity of the atmosphere at ground level is approx. 10(exp -11) S/m, comparable
to the values measured in the terrestrial stratosphere at an equivalent pressure, increasing with altitude at a rate defined
by the atmospheric scale-height. Owing to its large conductivity, the lower ionosphere of Mars can be considered equipotential.
On the surface of the planet the situation is different from the case of the Earth: due to the lack of liquid water, at least down to
a depth possibly larger than about 1 km, the ground electric conductivity is certainly rather small, with values in the range 10(exp
-10) to 10(exp -12) S/m quoted by most authors. If the free electron density varies, as indicated by models from less than 1 electron/cu
cm at night to 10(exp 2) electrons/cu cm during daytime, the situation may be complex depending on the ground conductivity
with the Martian soil appearing with respect to the atmosphere as a conductor during night and as an insulator during daytime.
Derived from text
Mars Atmosphere; Electrical Resistivity; Electric Fields; Atmospheric Electricity; Instrument Packages; Electric Field Strength
20010023051 Von Hoerner und Sulger Electronic G.m.b.H., Schwetzingen, Germany
European Tracked Micro-Rovers for Planetary Surface Exploration
Bertrand, R., Von Hoerner und Sulger Electronic G.m.b.H., Germany; Klingelhofer, G., Mainz Univ., Germany; Rieder, R., Max-
Planck-Inst. fuer Chemie, Germany; vanWinnendael, M., European Space Agency. European Space Research and Technology
Center, ESTEC, Netherlands; Zelikman, M., Space Systems Finland, Finland; Concepts and Approaches for Mars Exploration;
July 2000, Part 1, pp. 23-24; In English; See also 20010023036; No Copyright; Avail: CASI; A01, Hardcopy; A03, Microfiche
During the Mars Pathfinder mission, the 10-kg-rover Sojourner proved to be the enabling technology for efficient exploration
of the landing site. At the same time as larger rovers are planned, certain missions also call for low-mass-rovers. They are needed
not only to collect samples for return to Earth, but to deploy scientific instruments at relevant samples for in-situ measurements.
For both mission types, the rover system must be as small and light as possible, accommodating a maximum of payloads or samples
at the same time. In Europe, nano-rover technology has been developed for many years. One of the most advanced concepts is
the tracked microrover Nanokhod, developed most recently in the frame of ESA’s Technology Research Programme. With a total
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