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3.4.3.4 TMI module design
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 240 of 422
The tank design includes an inner and outer vessel(s), stiffening rings, insulation system, a fluid
acquisition system (piping, valves), and a thermal system.
The inner vessel will be constructed from inconel (corrosion resistant) and the outer vessels from
aluminium (lower density). A cylindrical geometry (4.8 m length, 4.7 m diameter) has been
retained for the hydrogen vessel and a nested spherical vessel (4.7 m diameter) for the oxygen
(type Ariane-5 ECP).
The primary objective of the tank thermal design is to minimise the heat transfer to the inner
vessel and optimise its related mass. The heat loads have been considered on the basis of a worst
case assumption).
Sun + IR planet
LH2 LOx LOx
Figure 3-76: Tanks schematic
Sun + IR planet
Boiling of cryogens occurs when temperature exceeds locally the saturation temperature at a
certain pressure. Tanks are initially pressurised at 2 bars before launch, which gives the liquid
properties shown in Table 3-67:
At 2 bars Temperature Latent heat of vaporization Density (liq.)
Saturated hydrogen 22.9 K 4.29E5 J/kg 67.4 kg/m3
Saturated oxygen 97.2 K 2.06E5 J/kg 1120 kg/m3
Table 3-67: Cryogens properties
3.4.3.4.1 Shielding and insulation, passive techniques
In vacuum, Multi Layer Insulation (MLI) is the best=performing insulation compared to other
types including permeable insulations (gas filled powders, evacuated powders) or solid foams
with closed or open cells (Airex, Rohacell).
Insulation Expanded Gas-filled Evacuated Opacified MLI
foams
powder powders powders
Conductivity 0.026 W/m/K 0.019 W/m/K 5.9E-4 W/m/K 3.3E-4 W/m/K 1.4E-5 W/m/K
Table 3-68: Insulation properties
MLI efficiency comes from an effective reduction of conductive and radiative coupling with the
use of multiple layer radiation shields interspaced by an insulant. Without pressure loads, the
equivalent efficiency depends on the number of layers, and the global heat transfer to the vessel
can be simply assessed providing the following hypothesis:
• heat transfer to the fluid per conduction only (steady fluid), no contact resistance