MERCURY SUN-SYNCHRONOUS POLAR ORBITER WITH A SOLAR SAIL

An innovative mission MESSAGE (MErcury Solar Sailing Advanced Geoscien ce Exploration) is proposed where a solar sail spacecraft of about 240 kg total mass delivers a limited but highly valuable science payload t o a sun-synchronous Mercury orbit in 3 1/2 years. Corresponding operat ion near the terminator offers favorable thermal and remote sensing co nditions for the considered instruments. Since Mercury is still the po orest explored and least known planet of the inner solar system, there is a high level of scientific interest for further exploration. Scien ce objectives and a potential payload package of about 20 kg for the p roposed solar sail mission considering the special orientation and geo metry of a sun-synchronous orbit about Mercury will be discussed. Dete rmination of the elemental composition of the Hermian surface with res pect to major rock forming elements and volatiles could be carried out by a gamma-ray spectrometer. In the current mission architecture the spacecraft will be launched into an Earth escape trajectory with a rel atively low-cost launch option such as TAURUS or ROCKOT with upper sta ges. The sail is used as a transportation means for the interplanetary transfer, for orbit capture upon Mercury arrival, and subsequent adju stment of a sun-synchronous orbit about the planet near the terminator . Due to Mercury's 3:2 spin-orbit coupling the eccentric polar orbit o f 200 km x 6350 km altitude with periapsis above the north pole will a llow complete coverage of the planet's surface within two Mercury year s. Optimized interplanetary trajectories as well as simulations of the orbit about Mercury will be shown. A conceptual design of the spacecr aft including the deployment concept of the square sail of an estimate d size of about 86m x 86m and its support structure will be presented. The lightweight booms are proposed to be manufactured of carbon fibre reinforced plastic profiles that can be stored on a central hub prior to deployment. Possible sail film materials, coatings and folding con cepts will be discussed. In a more advanced scenario two identical sol ar sails could be launched in a stacked configuration by a Med-Lite to realize a dual sun-synchronous Mercury orbiter mission. Copyright (C) 1997 Elsevier Science Ltd.