ESA Document - Emits - ESA

s
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 174 of 422
could challenge this robustness with the same level of safety. Significant efforts
would have to be spent in this case (evaporators).
• Design of the secondary loop depends on the heat rejection requirements.
3.3.3.4.4 Heat rejection system
Radiator type Advantages Disadvantages
Body mounted radiator
Hybrid body mounted rad.
Deployable radiator
Highly integrated, good protection of sensible
thermal connection against perforation
All critical elements are potentially accessible
without EVA
Contribute to radiation protection
Virtually independent to attitude control (and
its failure) if adequately sized
Increase the radiative surface when limited by
configuration
Heat rejection capability can be modulated
with adequate opening/closing of the covers
High performance (each side can be a
radiative surfaces)
Optimised heat rejection with possible
pointing capability
Pointing capability prevents coating
degradation by minimising solar radiation
impingement
low performance
heat rejection capability is limited by available
surface and environment
system complex, shall be compatible with the
radiation protection or be located in a non
habitable zone
The deployable covers radiative capability are
sensitive to attitude control performance
Total or partial loss of the heat rejection if
covers mechanisms failed to open
Total or partial loss of the heat rejection if
perforated (debris, meteorides), or if failed
during deployment
To recover from a failure requires an EVA
Refolding the radiator is risky
Table 3-26: Heat rejection systems
The supporting structures of a radiative surface can be either the body of the spacecraft itself or a
dedicated deployable frame. Both systems present a number of advantages and drawbacks. A
deployable system has a higher performance but is more susceptible to certain failures
(deployment, perforation). With an extensive commissioning in LEO, the risk of deployment can
be easily overcome as long as ulterior re-folding is not considered. Regarding perforation, the
highest risk comes from LEO debris (size > 1 cm) and an intervention can be assumed without
excessive constraints. Meteorites remain nevertheless a permanent threat during cruise but the
risk to the radiator can be limited with a bumper (protection of the fluid line by a certain
aluminium thickness). The partial or complete loss of a radiator is possible, but an appropriate
redundancy can be foreseen.
The feasibility of mounting a radiator on the structural spacecraft body depends on the resources
allocated by the system. Less efficient than a deployable radiator because of parasitic heat loads
(from environment and from the spacecraft), mass and power penalties can become significant if
a certain radiator efficiency is targeted. This is especially true for a large body (14 m x 6 m
cylinder) and if implemented around a habitable zone (higher insulation mass to isolate the