Pre-Phase A Report - Lisa - Nasa

170 Chapter 9 Science and Mission Operations
will be primarily a group of experts who, once the spacecraft and experiment have been
successfully commissioned, will only take control on comparatively rare occasions.
9.1.2 Scientific commissioning
After the initial switch-on and simple verification of operation of all the scientific subsystems,
the commissioning takes place which includes the following:
• Pointing acquisition using startrackers and laser beams.
• Beam profile characterisation and choice of operating pointing.
• Measurement of orbit parameters using ground stations to track spacecraft, supplemented
by observed laser Doppler shifts, and orbit adjustment using FEEPs.
• Establishment of drag-free control loop using the signals from the accelerometer,
the startrackers and the laser interferometer.
• Closing of the phased lock loops on the laser transceivers.
In all these cases there will be tests performed to characterise the operation of subsystems
followed by analysis of the data by the experiment team and adjustment of operating
parameters. The scientific commissioning will provide the information about the operating
conditions which will be used for scientific data acquisition.
9.1.3 Scientific data acquisition
During scientific data acquisition the goal will be to operate the observatory with very
few interruptions for long periods, typically half or one year which will provide near
continuos data sets which will be analysed to separate the GW signals from many different
astrophysical sources. The steady data acquisition will be interrupted for periods of
adjustment such as making changes to the relative space craft velocity. It may also be
interrupted by events such as solar flares which may cause result in disturbances to the
drag-free sensor proof mass.
Scientific operations are will consist of long periods of routine operations during which
searches for transient events will be carried out. This will be followed by computationally
intensive data analysis looking for long duration signals. Since the data can be readily
stored on board and transmitted to Earth during one 8 hour shift when the constellation
is in view of the principal ground station it is anticipated that scientific operations can be
organised remotely by networking teams in different laboratories. So the infrastructure
for operations will be comparatively modest compared with many space observatories
and the operations cost is likely to be modest compared to major ground based optical
observatories. Thus there should be no financial barriers to exploiting any excess life that
the observatory has over and above the design life used for the engineering specifications.
It is thus important that if possible the mission consumables are sized to permit extended
operations over 10 to 20 years.
3-3-1999 9:33 Corrected version 2.08