4 Final Report - Emits - ESA

4 Final
Report
The lateral in-plane equipment panel loads will be transferred to the central cylinder via the floors in
shear. The lateral out-of-plane equipment panel loads will be transferred to the central cylinder via the
shear webs and floors in tension/compression.
The tanks are grouped closely around the central structure. Thus the tank load path is very short and
mass-effective, the tanks will laterally be supported by the tank floors and axially by struts from the
lower tank boss to the LVA ring side.
CFRP Outgassing
Water and carbohydrate evaporation in the vicinity of the instruments needs to be limited to avoid e.g.
ice on cold optical surfaces. Any critical CFRP surface shall be sealed by an aluminium barrier foil of
typically 20 microns. In the past, this was done successfully e.g. on all inner surfaces of the 6.8 m long
XMM telescope tube structure.
Distortion Assessment
Pointing stability depends on thermal and moisture release distortions and therefore on configuration,
material selection, method of construction, changes in average temperature and temperature
gradients.
A similar stringent requirement also exists for MTG. It is therefore assumed that, through the high
degree of similarity between the two satellites, that the Geo-Oculus environment would yield
distortions of similar magnitude. Therefore, it is confidently believed that distortions should not be an
issue for Geo-Oculus.
Launch Vehicle Vibrations
The Frequency requirements for the S/C hard mounted at the I/F to the launch adapter are taken from
Soyuz since it is the worse case compared to Ariane 5:
• 15 Hz in lateral + 15% margin
• 35 Hz in longitudinal + 15% margin
Considering stiffness the main driver for the fist axial frequency is tank mass and the stiffness of the
underlying support. To optimise stiffness performance the heavy and light tanks are diagonally
opposite as to maintain a central centre of gravity position, also the supporting struts are categorised
into heavy or light struts each providing the best support stiffness for the respective tank mass.
The first lateral mode is largely driven by the X axis centre of gravity position, this is heavily influenced
by the mass of any +X top floor mounted equipments and instruments.
To estimate the first lateral frequencies of the Geo-Oculus spacecraft, the performance of the reported
performance of MTG spacecraft has been examined and scaled as appropriate. Scaling has taken
account of the comparative propellant mass and instrument mass associated with the Geo-Oculus
spacecraft.
The MTG spacecraft is viewed as a suitable foundation given the spacecraft architecture is similar to
Geo-Oculus and likewise is largely based on E3000 heritage, the most significant differences is an
extra 150kg approx located on the spacecraft +X floor and an extra propellant mass of 178Kg.
The first lateral and longitudinal frequencies are as follows,
Doc. No: GOC-ASG-RP-002 Page 4-75
Issue: 2
Date: 13.05.2009 Astrium GmbH