ESA Document - Emits - ESA

s
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 169 of 422
This is implemented with the use of appropriate materials and technologies combining passive or
active means.
3.3.3.4 Habitation module thermal control
3.3.3.4.1 Overall architecture and safety
Thermal architecture shall be designed to guaranty a sufficient performance for the complete
lifetime of the vehicle. By understanding the functions needed for this performance, this report
can outline the limiting factors of this subsystem and design the adequate reliability. The thermal
functions required are an acquisition system, a heat transport system, a heat rejection system, an
insulating system and a control and command system, as shown in Table 3-22:
Functions Basic features Risks and required reliability
Acquisition system Extraction of heat from the environment (air)
or from dissipating equipment
Heat transport system Transfer the heat via a medium (liquid in
general). A pressure differential is needed
between input and output.
Normally associated with a primary loop.
Heat rejection system The medium is cooled down thanks to a cold
sink (deep-space) and its energy decreased
before reentering the loop.
Normally associated to a secondary loop
Insulating system and
thermal protection
Control and command
system, thermostatic
system
Overall heat balance is sized to optimise
thermal budget (power in general). Adiabatic
walls are targeted per simplification
A modulation of the heat transfer (depending
on the heat loads) is required to optimise the
system. A feedback/monitoring of temperature
(medium, air) pilots this modulation.
Sensible to wear out problems
Internal individual units (accessible). Shall be
isolable => redundancy + spare
Similar to above
High sensitivity to impact, ageing
External/internal: access could be difficult =>
oversizing or redundancy
Low to moderate sensitivity to impact, ageing
External: access and replacement difficult =>
oversizing possible
Related to CPU/CU, telemetry problems.
Redundancy + spare. All controlled units shall
be operable manually
Table 3-22: Thermal systems functions
In a first approach, this report can identify different type of failures associated to the thermal
control elements:
• Beginning of life or infancy-related problems occurring in the first months. The failure rate is
the highest of the TCS lifetime (depends on the quality of testing). The spacecraft is still in
LEO orbit (extensive commissioning probable) and replacement can be easily performed.
• Random failure such as meteorite impact on a radiator. Critical or catastrophic depending on
the redundancy level. Replacement of external elements during flight is bound to feasibility
of an EVA.
• Degradation and wear out problems can be solved by spare units when located internally.
External thermal control elements shall also perform well in a degraded mode (EOL analysis,
ageing testing)