Abstract
The Department of Automation at DTU has developed the Advanced
Stellar Compass (ASC), a fully autonomous star tracker, for use as
high precision attitude reference onboard spacecrafts. The ASC is
composed of a CCD-based camera and a powerful microprocessor
containing star catalogue, image-analysis software and a search
engine. The unit autonomously performs all tasks necessary to
calculate the inertial attitude from a star image. To allow for
flexible attitude manoeuvres, the ASC can, simultaneously, drive
from one to four cameras, efficiently removing dropouts from,
e.g., sun blinding of one camera. The key features of the ASC are
fast and extremely robust arcsecond accuracy in a miniature
design. Due to the attractive ratios of performance to mass, power
and cost, the ASC has been selected as the baseline attitude
sensor for a suite of missions by the major space agencies of the
world. Generally, it is difficult to test and verify the true
robustness and accuracy of a star tracker on ground. This is
caused by the fact that only real-sky tests offer high fidelity
stimulation of the sensor, while the atmosphere instabilities
result in a dominant noise source intrinsically limiting the
achievable accuracy. This paper compares in-orbit performance with
ground test starting with a brief summary of the ASC
configurations on the missions referenced, i.e. Teamsat, ASTRID2
and Oersted. Then the in-orbit operation and performance of the
ASC with special emphasis on robustness and closed loop operation
aspects is discussed based on specific attitude manoeuvres. This
is followed by a comparison between ground-test and in orbit
operation in situations where the instrument for some reason has
to operate close to bright objects. For reference, simulations and
in-orbit performance of stray light baffles are given. Finally,
the accuracy over the lifetime is discussed. The importance of the
last topic is augmented by factors such as radiation, aging by
direct sun exposure and non-stellar objects.
Original language | English |
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Title of host publication | ESA 4th Symposion on Spacecraft Guidance Navigation and Control |
Publisher | ESTEC, European Space Agency |
Publication date | 1999 |
Publication status | Published - 1999 |
Event | 4th ESA International Conference on Spacecraft Guidance, Navigation and Control - Noordwijk, Netherlands Duration: 18 Oct 1999 → 21 Oct 1999 |
Conference
Conference | 4th ESA International Conference on Spacecraft Guidance, Navigation and Control |
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Country/Territory | Netherlands |
City | Noordwijk |
Period | 18/10/1999 → 21/10/1999 |