ESA Document - Emits - ESA
ESA Document - Emits - ESA ESA Document - Emits - ESA
s 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.
s Figure 3-38: Power required to maintain temperature (L), Coil system + heat pipes schematic (R) ATC#1 HMM Assessment Study Report: CDF-20(A) February 2004 page 179 of 422 The insulating/debris shielding system as presented provides an equivalent thermal conductivity of 0.07 W/m 2 /K. Therefore, maintaining in the worst cold case an internal wall above dew point (14C for 75% humidity) would require a power density of 11.5W/m 2 . Two systems are proposed: • a network of heaters homogeneously distributed on the internal shell corresponding to a installed power of 5580W (assuming the vehicle as a cylinder 6 x 14 m). Two equivalent circuits (main and redundant) are foreseen, piloted each by a control unit. For safety, each circuit will be equipped with over temperature thermostats to protect against a failed-on heater switch. • a network of coils / heat pipes mounted on the internal shell to transfer / homogenize the rejected heat from main loop. With a mean rejected dissipation of 12 kW, there should be no need to draw power from the system for the heaters. However, to save mass, the network of coil / heat pipes will only be specifically located to sensible zones, sustained when and where necessary by the heaters system. Figure 3-39: Overall view of radiators (size: 2 x 57m 2 ) ATC#2
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s<br />
Figure 3-38: Power required to maintain temperature (L), Coil system + heat pipes schematic (R)<br />
ATC#1<br />
HMM<br />
Assessment Study<br />
Report: CDF-20(A)<br />
February 2004<br />
page 179 of 422<br />
The insulating/debris shielding system as presented provides an equivalent thermal conductivity<br />
of 0.07 W/m 2 /K. Therefore, maintaining in the worst cold case an internal wall above dew point<br />
(14C for 75% humidity) would require a power density of 11.5W/m 2 .<br />
Two systems are proposed:<br />
• a network of heaters homogeneously distributed on the internal shell corresponding to a<br />
installed power of 5580W (assuming the vehicle as a cylinder 6 x 14 m). Two equivalent<br />
circuits (main and redundant) are foreseen, piloted each by a control unit. For safety, each<br />
circuit will be equipped with over temperature thermostats to protect against a failed-on<br />
heater switch.<br />
• a network of coils / heat pipes mounted on the internal shell to transfer / homogenize the<br />
rejected heat from main loop.<br />
With a mean rejected dissipation of 12 kW, there should be no need to draw power from the<br />
system for the heaters. However, to save mass, the network of coil / heat pipes will only be<br />
specifically located to sensible zones, sustained when and where necessary by the heaters<br />
system.<br />
Figure 3-39: Overall view of radiators (size: 2 x 57m 2 )<br />
ATC#2
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