Pre-Phase A Report - Lisa - Nasa

144 Chapter 7 Spacecraft Design
Radiator
Plate
Solar
Arrays
Y-shaped
Payload
Figure 7.1 One of the three identical LISA spacecraft. The main structure is
aringwithadiameterof1.8 m, and a height of 0.48 m, made from graphiteepoxy
for low thermal expansion. A lid on top of the spacecraft is removed to
allow view at the Y-shaped thermal shield (indicated here as semitransparent)
encasing the two payload arms.
direction varies between about 78 ◦ and 84 ◦ . The major part of this variation is due to
the eccentricity of the Earth orbit. As the interferometer rotates in the apparent orbital
plane, making one revolution per year, while the apparent plane moves along the Earth
orbit around the Sun, the spacecraft rotate about their X-axes at a rate of about 1 ◦ /day,
while the X-axes precess at about the same rate.
Figure 7.2 shows the interior of the spacecraft and the lay-out for the payload. The two
optical assemblies each contain a 30 cm diameter telescope and an optical bench centered
about a platinum-gold alloy proof mass. Telescope and optical bench are mounted from
the payload cylinder, a graphite-epoxy cylinder which is gold-coated to thermally isolate it
from the payload thermal shield. the optical bench is supported from its payload cylinder
by ceramic rods with small thermal conductivity. The payload cylinders are attached at
the front to two actuators (not shown) and at the rear to a flexure mount.
7.1.2 Propulsion module
At launch, each spacecraft is attached to a propulsion module. The propulsion module
provides the capability to maneuver the spacecraft/propulsion module composites into the
final orbits, using solar electric propulsion (SEP). The deployed configuration is shown in
Figure 7.3 .
After reaching the final orbits, about 13 months after launch, the propulsion modules are
separated from the spacecraft to avoid having excess mass and solar panels near the proof
masses within the spacecraft.
3-3-1999 9:33 Corrected version 2.08