The SpaceCraft

The following text can be found in the "Mission Paper" document. You can download the full document from http://www.lunarsat.de/edu/missionpaper.doc.

LunarSat -hardly the size of a refrigerator- uses a bipropellant approach with Hydrozine and Nitrogen-Tetroxide as oxidyzer for the main thrusters, providing a specific impulse of 289 s. The orbital insertion and attitude control maneuvers during the LunarSat mission require a total velocity increment amounting to 1300 m/s. These maneuvers are performed using a dual-mode propulsion system, bipropellant main engines and monopropellant attitude thrusters use the same fuel (hydrazine). A single main engine with a total thrust of 44 Newton and two 1 N attitude engines will blast the probe towards the Moon. This rather classical approach allows the use of off-the-shelf products and therefore leads to a major cost reduction.

Two body-mounted Gallium-Arsenide solar arrays together with a Lithium-Ion battery -the first flown as a critical element on a space mission- provide a total power of 100 Watt on average. This choice is mission critical, as LunarSat will encounter major solar eclipse once in its lifetime.

The LunarSat communication subsystem is based on a coherent transponder concept. It employs a pair of omni-directional antennas for command uplink and a special configuration of transmit patch antennas for telemetry downlink. For high data rate transmission an array of four S-band patches is used. For low data rates and in contingency modes, an omnidirectional transmit antenna mode is available, allowing a constant communication link as long as LunarSat is in the line of sight. The selected design offers relatively high data rates and ESA / CCSDS compatibility at low cost, low development risk and low mass, the implementation in a fast-track program is feasible.