GALILEO - Understanding GPS: Principles and Applications - page 582

2,700

1,100

1,200

Figure 10.10 GALILEO satellite dimensions.

• Thermal stability for atomic clocks.

The satellite is based on modular elements in order to separate payload and plat-
form and to allow parallel assembly, integration, and test (AIT) activities. An artistic
picture of the satellite is shown in Figure 10.11.
The data handling and control is based on an integrated control and data unit
that performs the control of the platform and payload. The attitude and orbital con-
trol system (AOCS) strategy is based on the steering of the MEO spacecraft to main-
tain the solar panels oriented towards the Sun (yaw steering). The AOCS will
provide three-axis attitude control during all phases and maneuvers. Several opera-
tional modes are derived from the mission sequence of events.

• The normal mode is the nominal operational mode with full nadir pointing
performance. A yaw steering capability is included to optimize the use of the
solar panels and to support the thermal control of the satellite.

An orbit change mode is provided for orbit acquisition, station-keeping
maneuvers, and end-of-life (EOL) decommissioning. In the current GALILEO
constellation design, very limited need for station-keeping maneuvers is
anticipated.

•

Finally, there are also dedicated Earth and Sun acquisition modes to be used
during launch and early orbit phase (LEOP) as well as in contingency situa-
tions and safe modes for Earth reacquisition and survival mode.

•