ESA Document - Emits - ESA

s
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 287 of 422
Figure 4-37: CLRC Beagle2 study (L), Aerogel thermal conductivity versus pressure (R)
The low density of Aerogel combined with its good thermal insulation makes it an ideal
candidate but would need an encapsulation (honeycomb cells for example). If a monolithic
structure (aluminium) is retained, insulation materials can be added in a multi-layer design
combining radiative (goldenized layer) to conductive insulation (foams). The double requirement
to perform in vacuum and in pressurised environment can be answered by installing different
type of foams (closed cell inside, open cell outside).
goldised foil
betacloth
int. foam
structure
ext. foam
Figure 4-38: Insulation layout
The choice of external layer results as a compromise between the different constraints brought
by the Martian and vacuum environment. The principle of a cold radiative skin completed by
heat input when necessary is preferred for its simplicity, providing the existing resources of
energy (released heat from units and metabolic). Betacloth is retained as the external layer of the
SHM to avoid undesirable heating from the Sun during the transfer phase. Its high emittance
(high energy exchanged during nights) is somewhat counterbalanced by the high thermal inertia
of the vehicle. Its strength is also seen as an advantage.
4.3.4.3.4 The thermostatic system
Certain surfaces that cannot be protected by insulating means (interface between MAV and
ascent vehicle) are treated (oxidation anodic, alodine) to minimise heat transfer. 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.