ESA Document - Emits - ESA

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HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 293 of 422
thickness (6.2 mm aluminium shell to match a internal pressure of 1 MPa) allows a good
spreading of energy from the poles to the equatorial belt. Optimised mechanical support systems
for the cryogen tanks should also be considered (PODS for example). The tanks are in an
unpressurised section, so that –23C can be reached as a radiative environment.
In these conditions, the moderate heat lift required (0.5 to 1W between 20 to 30K) to counter BO
does not require significant development but modifications of existing hardware (Stirling
coolers). If the environment has to be modified (external tanks submitted to environmental
loads), or because of a more integrated system (with ECLS) resulting in larger tanks, the use of
higher heat lift capability may become necessary and the choice of the cooling system oriented to
recuperative systems (reverse Brayton, Joule Thomson cycles).
As previously seen and within the study’s hypothesis, the oxygen tanks do not necessarily
require a cooling capability. A tolerance to boil-off is accepted per design with an increased
initial mass of oxygen liquid.
Oxygen Per tank
Budget total
case sink [K] nbr of tank diameter MLI layers liquid pressure nbre of heat lift mass liquid thickness structural thermal input power thermal input power total mass
[m]
temp. [K] (MPa) cryo units [W] [kg] tank [mm] mass [kg] mass [kg] [W] mass [kg] [W] liquid [kg]
1 250 1 1.36 40 97.2 0.2 0 0 1454.6 1.3 19.8 4.8 0.0 4.8 0.0 1454.6
2 250 2 1.12 40 97.2 0.2 0 0 812.4 1.0 11.0 3.2 0.0 6.5 0.0 1624.9
3 250 3 1 40 97.2 0.2 0 0 578.3 0.9 7.9 2.6 0.0 7.7 0.0 1734.9
4 250 4 0.92 40 97.2 0.2 0 0 450.3 0.9 6.1 2.2 0.0 8.7 0.0 1801.2
5 250 1 1.46 40 119.6 1 0 0 1589.6 6.8 122.4 5.5 0.0 5.5 0.0 1589.6
6 250 2 1.22 40 119.6 1 0 0 927.5 5.7 71.4 3.8 0.0 7.7 0.0 1855.0
Table 4-13: Options
Case 1, a tank of a diameter 1.36 m appears as the best solution of a no coolers trade-off and
could be integrated with the 2 hydrogen tanks. However, an appreciable mass saving could be
obtained with a cooling capability and is the option to prefer for an optimised system.
4.3.4.4 Budget
4.3.4.4.1 Synthesis per subsystem (main features)
Fluid loops
Primary loop Pump assembly: 67 kg, 463W nominal (950kg/hr) (x 2)
Condenser heat exchangers: 20.6 kg (x 2),cold plates: 3.4 kg (x 10), valves (on/off, manual):
4 kg (x 20)
120 kg of tubing (dry including insulation, brackets) + 20 kg of water
Secondary loop Pump assembly: 56.7 kg, 311W nominal (x 2)
Heat exchangers: 15.9 kg (x 4), cold plates: 3.4kg (x 5), valves (on/off, manual): 4 kg (x 5)
36 kg of tubing (dry including insulation, brackets) + 31 kg of ammonia
Body-mounted
radiator
Passive thermal control
Cylindrical/conical radiator of 22 m 2 , 0 kg (transferred to structure budget)
Insulation 193 kg for the main body of the transfer vehicle (to check the status of PMOD).
50 kg are provisioned for specific external and internal elements insulation.
Heating system 728W installed power
Two control units (1 on), each 6 kg, 29W when shell heaters are 100% duty cycle