4 Final Report - Emits - ESA

4 Final
4.5 Satellite
Report
4.5.1 Configuration
The basic features of the suggested baseline configuration as derived by the trade-offs documented in
[RD 7] are as follows:
• dual wing steerable solar array,
• payload on top panel (launch) / Nadir panel (operation),
• no yaw flip manoeuvre.
The selected spacecraft configuration based on above inputs has been influenced by the choice of the
favourable design of the chemical propulsion system as well as by the heritage available from similar
projects. The resulting external configuration of the spacecraft in stowed condition is shown in Figure
4.5-1.
The payload is connected to the platform via 3 bi-pods providing iso-static mounting conditions. The
configuration of these bi-pods has still to be iterated and the provision of suitable hard-points in the
platform, accordingly.
The solar array wings are stowed on the side panels which correspond to the North and South panel
during operational mode.
The PDT antenna system comprises a deployable boom and is also folded to a side panel. The
deployable boom is needed in order to provide visibility between antenna and ground station which is
challenged by the big payload and, moreover, by the manoeuvres which point the complete spacecraft
to the scene of interest.
A similar problem concerns the S-Bd antenna which is roughly Nadir oriented (the complementary
Zenith oriented antenna is hidden behind the spacecraft). Since this S-Bd antenna needs a
hemispherical field of view, a mounting on the payload close to the entrance of the big baffle has been
selected.
This accommodation of platform equipment on the payload does not seem to be necessary for the
infrared Earth sensors (IRES). Their field of view requirement is about 20 degree half cone angle and
may be provided by putting these sensors on a pedestal.
The situation is even a little more comfortable for the star trackers. They shall be aligned as close as
possible with the payload line of sight direction in order to achieve the maximum attitude knowledge
accuracy. However, they must also consider a certain Earth exclusion angle which yields an off-Nadir
viewing direction. This together with the even narrower field of view (~15 degree half cone angle)
allows to accommodate the star trackers directly on the top panel. This position may be revised in a
later phase since the neighbouring payload radiator may evolve and the contribution of thermo-elastic
deformations to the pointing knowledge budget may be optimised by mounting the star trackers
directly on the payload.
Page 4-48 Doc. No: GOC-ASG-RP-002
Issue: 2
Astrium GmbH Date: 13.05.2009