Mercury sun-synchronous polar orbiter with a solar sail

Abstract

An innovative mission MESSAGE (MErcury Solar Sailing Advanced Geoscience Exploration) is proposed where a solar sail spacecraft of about 240kg total mass delivers a limited but highly valuable science payload to a sun-synchronous Mercury orbit in 312 years. Corresponding operation near the terminator offers favorable thermal and remote sensing conditions for the considered instruments. Since Mercury is still the poorest explored and least known planet of the inner solar system, there is a high level of scientific interest for further exploration. Science objectives and a potential payload package of about 20 kg for the proposed solar sail mission considering the special orientation and geometry of a sun-synchronous orbit about Mercury will be discussed. Determination of the elemental composition of the Hermian surface with respect 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 relatively low-cost launch option such as TAURUS or ROCKOT with upper stages. The sail is used as a transportation means for the interplanetary transfer, for orbit capture upon Mercury arrival, and subsequent adjustment of a sun-synchronous orbit about the planet near the terminator. Due to Mercury's 3:2 spin-orbit coupling the eccentric polar orbit of 200 km × 6350 km altitude with periapsis above the north pole will allow complete coverage of the planet's surface within two Mercury years. Optimized interplanetary trajectories as well as simulations of the orbit about Mercury will be shown. A conceptual design of the spacecraft including the deployment concept of the square sail of an estimated size of about 86m × 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 concepts will be discussed. In a more advanced scenario two identical solar sails could be launched in a stacked configuration by a Med-Lite to realize a dual sun-synchronous Mercury orbiter mission.