Flight Autonomy Evolution - Autonomous and Autonomic Systems - page 63

spacecraft (for example, for a distributed interferometry mission) to maintain
the collective grouping needed to achieve their overall mission objectives, one
or more (potentially even all) of the constellation will have to possess key
knowledge of all near-neighboring (or possibly all) constellation members in
order to synchronize orbital positions, SI configurations, onboard data pro-
cessing and communication schedules, etc.
The LISA mission is a particularly high technology example of this kind
of constellation mission. LISA, the first space-based attempt to detect grav-
itational radiation, will consist of three spacecraft maintaining a triangular
formation, with each leg of the triangle being 5 million kilometers in length
(Fig. 3.3 ) . The constellation will be located within the earth's orbit about the
Sun, about 20 ◦ “behind” the earth. Each spacecraft in the constellation will
mount two lasers. Each laser will be directed toward a cube (called a proof
mass) floating “drag free” within a containment cell housed within one of the
other spacecraft. So each spacecraft mounts two lasers and two cubes, and
each triangle leg is formed by two laser beams. The first beam is directed
Fig. 3.3. Laser beam exchanges between the three laser interferometer space
antenna (LISA) spacecraft