The ESA-mission DARWIN will be a formation-flying interferometer, consisting of a total of eight spacecraft whereof six will carry telescopes. Launch is planned for 2015. The primary aim is to detect earth-like planets around nearby stars, and to determine whether there are any signs of life.
The interferometry requires precise and stable positioning of the spacecraft in the constellation, which puts high demands on the attitude and position control system. The purpose of this report is to evaluate both current and emerging micropropulsion technologies, resulting in a recommendation and further investigation of the systems best suited for the DARWIN micropropulsion system. Field-Emission Electric Propulsion (FEEP), colloid thrusters, Cold Gas Microthrusters and pulsed-plasma thrusters (PPT) are among the technologies included in the study. Separate trade-offs are made for precision-pointing and coarse manoeuvres, taking into account properties such as thrust resolution and range, power consumption, mass and volume. In addition, key mission drivers of DARWIN are closely assessed. Contamination of the telescopes and other highly sensitive optical hardware is one of the main issues, together with the extreme demands on resolution and variable thrust in the micronewton range. The cryogenic payload needs to be kept at temperatures down to 40 K, which adds thermal restrictions on the propulsion system. Furthermore, since the mission lifetime is set to 5 years with a possible extension to 10 years, reliability and lifetime are other major factors.
It is found that the emerging concept of micromachined Cold Gas Thrusters appears to be the most promising choice. Cold Gas Microthrusters with internal heating have a number of advantages that make them more favourable than other systems, for example clean propellant, low power consumption and a wide thrust range. The low specific impulse is the main drawback. With internal heating however it exceeds 100 s, which seems acceptable for DARWIN.
Author: Kilter, Mikael
Source: Luleå University of Technology
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