(Duration of 6 days)
A MEMS-based (Micro-Electro-Mechanical System) micropropulsion system has been manufactured and integrated on the Prisma by NanoSpace.
This miniaturised propulsion system is in principle similar to a conventional cold gas system – though with the functional difference that the thrust can be modulated proportionally in the sub milli-Newton range instead of through on/off modulation.
The cold gas micropropulsion system includes a number of novel MEMS devices; the thruster chips, the Isolation valve with filter, the pressure relief valve, and one of the pressure sensors are based on innovative MEMS technology.
The MEMS thruster chip includes proportional valves to regulate the mass flow (and thus thrust), and chamber/nozzles with internal gas heaters with the purpose to improve the specific impulse. Four complete and individually controllable thrusters are integrated into the single chip show in the figure.
The purpose of the flight experiment is to demonstrate functionality and performance of the MEMS-based microthrusters and all the other MEMS novel components in the system. For many of these components Prisma is the maiden spaceflight.
Telemetry data from the spacecraft, such as electrical signals, power, pressures and thermal properties, verifies the functionality of the stand-alone MEMS-products in the system. Regarding the thrusters, different methods to evaluate performance will be used:
Using this data, the actual force generated by the micropropulsion system can be derived. The experiments will verify thrust from 1 milli-Newton and lower.
One experiment is to demonstrate the effective impulse of the thrusters by applying thrust commands while the spacecraft attitude is maintained by the reaction wheels. In this way, the thruster impulse will constitute an external disturbance which is compensated for by the attitude control. As a result, there will be a change on the reaction wheel speed. Distributing commands over e.g. a full orbit revolution will result in significant change in reaction wheel speed even for very low thrust levels (down to tens of micro-Newton). Simulations of reaction wheel response have been done and show that the angular momentum from the reaction wheel response can be clearly detected for such thrust levels.
Another series of experiments is to apply delta V to the spacecraft. The strategy here is to apply thrust during one orbit. The results of the relative position change and velocity change of the main spacecraft will then be evaluated. Simulations have shown that the response from the thruster commanding is clearly detected, as seen in the figure below. Also after on-ground post processing of the GPS data a precise orbit determination with a high accuracy down to cm levels can be achieved.
