ESA Document - Emits - ESA

s
3.3.3.2 Assumptions
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 168 of 422
• Incidental thermal fluxes are the result of the vehicle attitude against the relative location of
the different heat sources (the Sun or a planet). A conservative approach is to consider
envelopes through worst-case scenarios:
• maximization of the absorbed radiative energy (normal incidence) for hot cases,
minimisation of the absorbed radiative energy (maximization of the Sun angle) for the
cold case
• Environmental heat loads values are shown in Table 3-21:
Solar flux [W/m 2 ] Planet albedo Planet IR [W/m 2 ]
Hot case (Earth LEO, WS, 1 AU) 1423 0.33 241
Hot case (Venus swing-by, 0.7 AU) 1 2904 negligible negligible
Hot case (Mars orbit, perihelion, 1.38 AU) 2 717 0.29 (subsolar) 470 (subsolar) to 30
Cold case (Mars orbit, aphelion, 1.66 AU) 3 493 0.29 (subsolar) 315 (subsolar) to 30
Table 3-21: Thermal cases definition
Note that the Venus swing-by is an option. That with respect to Mars arrival and departure dates,
the vehicle passes aphelion and perihelion. That for the hot case with Mars, and cold cases
around Mars depend in a certain extent on the orbit of the spacecraft (and thermal characteristics
of the underneath regions). The worst cold case is sought with long eclipse duration: 500 km
circular orbit and a coplanar Sun (beta 0) give a 13.6 mn eclipse out of a 40.2 mn orbit.
• Thermal design shall manage all internal heat loads resulting from the human activities and
various dissipating equipments:
• Total mean heat load of 12.3kW during LEO
• Heat load turndown ratio of 1.2
• Metabolic dissipation is estimated to be 110W (steady activity) or 295W (active state) per
crew.
3.3.3.3 Baseline thermal design
The design block proposed is based on the exploitation of existing heritage: space stations on one
hand (ISS, Skylab), and visiting/orbiting vehicles on the other hand (STS, Apollo, Soyuz).
Undergoing or foreseen technological developments, and in general non-qualified hardware, are
excluded.
The thermal control philosophy adopted for such vehicle is standard and relies on the following
approach:
• simplification of the heat transfer with maximal use of thermal decoupling when possible
• use of thermal regulated bus to recuperate and transfer internal heat 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.