ESA Document - Emits - ESA

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HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 178 of 422
The materials used within the debris and insulation shielding are selected and sized so that both
functions (impact and thermal) can perform optimally under their respective loads. Low
conductivity materials are therefore integrated: the open cell foam (three layers of 10 cm thick,
preferred to closed cells for their better thermal behaviour under vacuum), the Kevlar fabric (5
layers) and the Nextel AF10 ceramic fabric (3 layers) offering also adequate and stable (material
inorganic, therefore no degradation against time to be expected) thermo-optical properties
(measured values: alp=0.24, eps=0.88).
Figure 3-37: Debris shielding/thermal protection (L), Max. Temp. of external layer (Nextel) (R)
Assuming a three-axis-stabilized spacecraft, the temperature evolution of a permanently
illuminated surface (Nextel AF10) is shown in Figure 3-37. Note that beyond a certain range, a
correction appears necessary to come to acceptable temperatures at the hull internal structure
(see following paragraph). The spinning of the spacecraft to homogenize temperatures is not
considered (solar array pointing constraints).
3.3.3.4.6 Thermostatic system
Certain surfaces that cannot be protected by insulating means (docking system for the MAV) are
treated (oxidation anodic, alodine) to minimise heat losses. On the internal face, coils
(circulating fluid from primary loop) thermostatically control the temperature (condensation
avoidance) and the heat exchanges (control of the heat losses). An adequate redistribution of the
rejected heat (thermostatic coils) therefore reduces the use of heater power to the minimum.
When not directly accessible to fluid lines, externally mounted elements will require the use of
strip heaters combined to an adequate insulation.