Computer Science
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002iaf..confe.671k&link_type=abstract
IAF abstracts, 34th COSPAR Scientific Assembly, The Second World Space Congress, held 10-19 October, 2002 in Houston, TX, USA.,
Computer Science
Scientific paper
DARWIN is an optical space interferometer and a cornerstone mission in the Horizon 2000+ programme of ESA, with a foreseen launch in 2014. It has the ambitious mission objectives of: a) detection and analysis of planets orbiting nearby stars, searching for earth-like conditions and life and b) high resolution imaging by aperture synthesis. The continuing exploration of celestial objects and the associated strive for a better understanding of the universe push the development of new telescopes to increasing angular resolutions. Using several small collecting telescopes and a beam combiner allows us to build an instrument with an angular resolution normally associated with monolithic telescopes of much larger diameters. The relative positions of the telescopes are selected such that when the optical signals, collected by the individual telescopes, are coherently combined, the small angular distance between the planet and the star can be resolved. The mission is implemented on several telescope spacecraft and one beam-combining spacecraft, possibility augmented by a spacecraft dedicated to ground communication and metrology. The beam combiner and the telescope spacecraft fly in one plane with the telescope spacecraft at equal distance from the beam combiner. The resolution of the interferometer is adjusted by changing the inter satellite distance. Analysis of the planetary light requires that the stellar light is suppressed to a high degree. This is done by a technique called nulling interferometry, in essence this means that achromatic phase shifts are applied to the beams before recombination such that the on-axis light, i.e. stellar light, is cancelled by destructive interference, while the much weaker planetary light interferes constructively. The required stellar light rejection ratio (105 - 106), imposes severe optical requirements: a) the optical path differences from the object via the individual telescopes to the beam combiner must not deviate by more than a few 10 nanometers, b) the telescopes should have an attitude control better than 12 mas and c) the interfering beams should have amplitudes matched to better than 1%. The spectral range between 5 and 18 μm has been selected since the ratio between planetary and stellar light is improved by roughly 3 orders of magnitude compared to the visible spectrum and since absorption bands of important tracers of life (H2O, O3 and CO2) are present in this range. Operating in the infrared band requires that all optical components be cooled to roughly 40 K, which can be achieved by passive cooling. Only the detector requires active cooling. The technology required for precision formation flying and formation deployment, i.e. inter-satellite radio frequency ranging, inter-spacecraft high precision range (rate) laser metrology, micro-Newton FEEP thrusters and the associated control software, require an in-flight demonstration. it is planned to perform this demonstration on ESA's SMART-2 mission to be launched in 2006.
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