ESA Document - Emits - ESA

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Insulation structure (external)
Foam + betacloth
Window shutter (int.)
thermal insulation during night
Insulation legs (ext.):
aluminium foil where no mechanism
Insulation oxygen tanks (int.)
+ cryocooling
Insulation of the hatches
4.3.4.3.6 Fuel cells
Figure 4-40: Thermal system configuration
Heating system (internal)
Primary loop + coil system (int.)
Secondary loop system (int.)
pump, heat exchanger
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 289 of 422
Body mounted radiator (ext.)
lateral cylinder of 10 m 2 (2 m high),
white painted
Insulation of the bottom + protection
versus plumes
Because of its high energy density, hydrogen is normally retained as the fuel and oxygen as its
reactant. Related technologies regarding the electrolytes have been addressed in the power
section. Whichever choice, thermal management of the fuel cells is essential:
• to guarantee the operating temperature of the chemical reaction
• to preheat the cryogenics reactants before entering the stacks
• to cool down each stack, because of the highly exothermic chemical reaction (141.9
MJ/kg)
The cooling capability of the stacks is provided by a coil system connected to the coldest sink
through a dedicated secondary loop heat exchanger. The fluid used for this loop is a fluorinated
hydrocarbon coolant. A temperature actuated flow control valve maintains and regulates the
coolant exit temperature.
As preliminary inputs for heating power, the PEM cells used in the STS (7 kW per unit) are
assumed with 2.4 kW for start up and 1.1 kW in nominal mode.
Note that, the water by-product used for life support can be used also as a coolant in the thermal
management system. An integrated system (thermal / power / life support) possibly based on
regenerative cells seems promising for mass saving (transfer vehicle for instance).
4.3.4.3.7 Cryogenic storage for fuel cells tanks
Fuel cells are used for the MEV require the storage of liquid hydrogen and oxygen, and an
appropriate thermal design to maintain the related boil-off (BO) to an acceptable level. The
objective is to have after 24 months, 119 kg of hydrogen and 955 kg of oxygen (input from
power subsystem).
The tanks are identical in shape and their geometry is a sphere. They are located in an
unpressurised section of the MEV to minimise parasitic heat transfer from surrounding elements
(gas conduction). Passive insulation is used to isolate the tanks from their radiative environment.
The MLI is a stack of n layers of Double Aluminized Mylar (DAM) with an external goldenized
layer.