ESA Document - Emits - ESA

s
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 283 of 422
• simplification of the heat transfer with maximal use of thermal decoupling when possible
• use of thermal-regulated bus to recuperate and transfer internal heat (recuperated at the
primary loop level) to heat sinks
• use of switch capability to modulate this transfer and balance the heat inputs from the
outputs, and thus maintain temperatures within a certain bandwidth
This is implemented using appropriate materials and technologies combining passive or active
means.
4.3.4.3.1.1 Thermal bus
• Docked phases
As long as the SHM is docked to the TV, its thermal bus is used (TV secondary loop) providing
a cooling capability when necessary (crew in the cabin). Assuming a dormant mode for most of
the docked phases when unmanned, a steady low cooling capability is required, mainly for
thermostatic control.
Because of the low level of these loads, a direct connection with the Ascent Vehicle primary
loop is foreseen, and the SHM loop capability is used to transfer its heat loads to the TV
secondary loop.
• Descent phases
During de-orbit (from 500 km) and reentry phases (120 km), no external sink is possible or
available because of the aerothermal loads, and a substitute has to be foreseen. The duration of
these two phases being less than 2 hours (no abort possible), no specific system is required but a
pre-conditioning of the vehicle before separation. Relying on the high thermal inertia of the
modules, a natural cooling capability is stored in the structural mass by lowering the
temperatures to a minimum setting (15C).
• Landed phase
A residual heat from the aerothermal phase will penetrate the thermal system and steadily raise
the overall temperatures thanks to the thermal inertia. Until activation of the nominal thermal
management mode of the landed phase (which can possibly take several hours), a system shall
counter balance this temperature rise and provide a cooling capability. Sublimation of water is
retained as the most efficient system for this period.
For nominal and contingency modes, an external bus is designed to provide the required sink. A
biphasic system is retained for its performance with ammonia as the working fluid.
4.3.4.3.1.2 Radiator orientation and location
The choice of the radiator orientation and location is a trade-off between the available
environmental sinks and the configuration constraints.