Key Technology used in the Lunar Mission BW1
	Propulsion System
	Power Supply System
	Attitude Determination and Control System
	Command and Data Handling
	Communication System

 

Propulsion System

The propulsion system provides the thrust during all flight phases and for desaturation of the reaction wheels. A cluster combined of a thermal arcjet and four or more pulsed plasma thrusters (PPT) is the configuration currently under consideration. Both systems will be tested and validated during the PERSEUS mission, the second small satellite of the programme. An ammonia-fueld thermal arcjet should generate ~100 mN thrust requiring around 1 kW power. A previous version was developed and built for the amateur radio satellite Amsat Oscar 40/P3-D (launched in 2000). Four or more pulsed plasma thrusters with PTFE (Polytetraflourethylene a.k.a. Teflon®) as propellant yielding ~6 mN thrust and consuming at least 250 W are used for cruise and attitude operations in cislunar and lunar space. Careful optimization of the thrust profile is mandatory because of perturbating accelerations which are in the same order of magnitude as the provided thrust. In preparation for the lunar mission complex orbit and attitude manoeuvres as well as autonomous guidance, navigation and control operations are planned during the PERSEUS and the DESIRE/CERMIT missions.

 

Power Supply System

A first configuration of the power supply system was identified to meet the requirements of the propulsion system based on the mission scenario and taking aging and degradation effects and redundancy considerations into account. The power supply system has to be capable to provide ~1 kW for approx. one hour. In this configuration the electrical power will be generated by six solar panels with an overall size of ~6 m2 – two body mounted, two on each side. The solar panels will be folded during launch and deployed and locked in a fixed position after check-out and testing. Orientation towards the sun to charge the batteries has to be done by changing the satellite’s attitude. Modern Gallium-Arsenide triple junction solar cells with an efficiency of more than 26% are required as well as Li-Ion batteries with a minimum capacity of 100 Ah used for power storage to fulfil the conditions of mass, volume and performance. The planned spacecraft bus voltage is 28 V (unregulated).

 

Attitude Determination and Control System
The satellite will be a 3-axis stabilized spacecraft. The Attitude Control System (ACS) of the FLYING LAPTOP which is currently being designed will be adapted to meet the requirements for the lunar observation instruments and for target pointing observation to provide manoeuvring capabilities.

 

Command and Data Handling

The on-board computer architecture designed for the FLYING LAPTOP will be used for the LUNAR MISSION BW1 and adjusted in accordance to the mission objectives. The system is currently under development at the Fraunhofer Institute in Berlin, Germany. For the FLYING LAPTOP it will consist of four field programmable gate array (FPGA) computers – two hot and two cold redundant – including at least two 1 Gbit mass memory modules and 200 MBit telemetry storage.

 

Communication System
The usage of KA-band (30/20 GHz) frequencies will allow broadband communication with the satellite’s primary antenna with a diameter of 1 m and small ground station dishes. As a supplement a S-band system is installed and also usable for telemetry and telecommand. Both systems will be tested during the FLYING LAPTOP mission.