Pre-Phase A Report - Lisa - Nasa

Chapter 7
Spacecraft Design
7.1 System configuration
7.1.1 Spacecraft
The spacecraft configuration is shown in Figure 7.1 . It consists of a cylinder with a
height of 480 mm and a diameter of 1800 mm. It supports a Y-shaped tubular structure,
the payload thermal shield, which serves to reduce the effects of changes in the solar
luminosity on the optical assemblies contained in the two arms of the Y. A top lid across
the cylinder (not shown in Figure 7.1) prevents sunlight from striking the payload thermal
shield. The spacecraft equipment is mounted on the inside wall of the structural cylinder.
Extending out from the structural cylinder is a sun shield that keeps sunlight off the
cylinder wall. The main solar panels are mounted on this sun shield.
The spacecraft structural cylinder and the payload thermal shield are made of a graphiteepoxy
composite chosen for its low coefficient of thermal expansion. The payload thermal
shield is gold-coated and suspended by stressed fiberglass bands from the spacecraft cylinder
to thermally isolate it from the spacecraft. The optical assemblies are in turn thermally
isolated from the payload thermal shield. On the outside of the spacecraft cylinder the
FEEP (Field Emission Electric Propulsion) thruster blocks are mounted in six clusters of
four thrusters each.
Outside of the payload thermal shield, pointing parallel to the arms, star trackers are
mounted on the lower side of the solar panel rim. For redundancy, a total of 4 star
trackers are used. In addition Fine Sun Sensors and Sun Acquisition Sensors are mounted
on the spacecraft.
Two steerable 30 cm diameter high-gain X-band antennas are mounted via suitable interface
structures on the outside of the spacecraft, far enough inside the central cylinder
diameter to avoid interference problems during separation. The antennas, used during the
operational phase, provide the necessary 2π coverage in azimuth. Low- and medium-gain
antennas are mounted on short booms at the lower side of the structural cylinder.
In the operational heliocentric orbit the spacecraft nominal orientation is such that the
YZ-plane coincides with the plane of the interferometer. Thus the spacecraft X-axes
make an angle of 30◦ with the Sun direction. The angle between the X-axis and the Earth
Corrected version 2.08 143 3-3-1999 9:33