Minimize Space Segment

The satellite configuration is dictated by mission Requirements (minimization of air drag forces and torques) and engineering constraints (the available volume under the launch vehicle fairing, with no deployable parts; passive aerodynamic stability).

The satellite body has the shape of an octagonal prism, About 5.3 m long and with a transversal cross section of 1.1 m2. Seven main platforms , called floors, horizontal in the launch configuration, divide the volume inside the spacecraft body into compartments.

Artist's impression of GOCE in orbit

It is fundamental that the position of the Gradiometer is such that its center is as much as possible close to the Spacecraft CoM, to minimize the angular accelerations produced on the sensors by the lateral drag forces. This explains the mounting of the EGG in the central part of the SC body.

The in-orbit attitude of the Spacecraft is such that the body has a Sun facing hot side and a shadowed cold side that is almost invariable during the mission. That characteristic is exploited to mount on the shadowed side a radiator used to keep a stable thermal environment to the Gradiometer. The SST receiver electronic and the transponder are distributed on the sixth floor and the second floor respectively.

The star trackers are mounted as close as possible to the Gradiometer to reduce misalignment during mission operation. The micro-propulsion was originally justified by the need to guarantee the linear acceleration control along the Y and Z Axes of the S/C and for the pointing control. Their presence was also concurring to the angular acceleration control about the Gradiometer sensor axis and to the Gradiometer Calibration.

The development of the micro-propulsion thrusters has been pursued via a pre-verification program, suite for determining the best candidate between cold gas and FEEP technology. In July 2003, the use of micro-propulsion was abandoned because the development maturity was no longer in line with the need of the GOCE program. The control strategy of the spacecraft has been then revisited and redefined, by maximizing the use of already present capability and minimizing the impacts of cost and schedule. A simpler calibration system “Gradiometer Calibration Device” (GCD) has been added to the GOCE on board functions for allowing the performance of the in flight calibration of the Gradiometer.
The angular acceleration control and the Spacecraft pointing was charged to the magnetic torquers, and the cross-track linear acceleration control was abandoned. Their effect on the overall science performance was smoothed introducing the capability to fly in the wind instead of maintaining a rigid three axis stable attitude.

The xenon tank is placed at the satellite's lower end close to the ion thrusters for short xenon lines. The solar array consists of six panels, 2 wings self-supporting and 4 body panels mounted directly to the S/C body, with necessary thermal isolation installed.
Other Instruments and equipment are mounted by brackets on the edge of solar array wings in the following configuration: