Pre-Phase A Report - Lisa - Nasa

172 Chapter 9 Science and Mission Operations
9.3.3 Orbit acquisition
Spacecraft computer performs attitude control and orbit manoeuvres with direct access to
star tracker data. During this orbit acquisition phase some subsystem tests are envisaged.
Release of drag-sensor vacuum enclosure seal will be done (pyrotechnic device operation).
Feep seals are released. These activities are initiated by the spacecraft computer.
Functional tests of all electrical/mechanical subsystems, including pointing device, lasers,
discharge system, drag-free sensor electronics, drag-free clamping device, USO,interferometer
electronics, star trackers, feep electronics, CPU and PCU. Performance tests of subset
of electrical/mechanical subsystems, including pointing device, lasers, discharge system,
drag-free sensor electronics, drag-free clamping device, USO, interferometer electronics,
star trackers, CPU and PCU.
Payload orbit/attitude constraints - keep sun outside field-of-view of telescopes.
9.3.4 Attitude acquisition
This phase includes calibration activities controlled by spacecraft but where payload computer
requires access to star tracker data and ACS calibration information. There will be
a progressive transfer of attitude control from spacecraft computer to payload computer.
Full payload functionality is required. Sequential commissioning of drag-free operation
under autonomous payload computer control. Data transfer from payload computer to
spacecraft computer. Telemetry and ground command is via spacecraft computer with
commands passed to payload computer for implementation. Spacecraft computer monitors
orbit and attitude, including sun sensor data.
9.3.5 Science mode
Attitude control solely by payload computer. Full payload functionality and performance
required under autonomous payload computer control. Payload computer is collecting
science and housekeeping (h/k) data. Data are transferred from payload computer to
spacecraft computer. Telemetry and ground command is via spacecraft computer with
commands passed to payload computer for implementation. Spacecraft computer monitors
orbit and attitude.
9.3.6 Safe mode
This mode may be invoked by the spacecraft in the event of attitude disturbance beyond
the range of controllability of the drag-free system putting the mission in jeopardy. In this
event the spacecraft computer may invoke safety and power saving routines. Depending
on the severity of the situation the power saving priorities are given in the list below:
3-3-1999 9:33 Corrected version 2.08