ESA Document - Emits - ESA

s
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 244 of 422
Basic components of a TB cycle are the compressor (acts on the working gas), the counterflow
heat exchanger (recuperative HX) and the turbine (expansion of the gas and extraction of energy
from the tank). This latest, miniaturized and operating at speeds of the order of 100 000 rpm is a
critical and challenging component to optimise. Note that the high-frequency electronics raise
reliability issues if used longer than 3 years.
3.4.3.4.5 Resources sharing
The tanks are mounted on a truss structure, which allows certain resources to be shared:
• a common sunshade system, deployable, mounted temporarily on the truss until the
launch would be cost effective
• a common cooling system (He) does not seem very effective, increasing the number of
connections (piping) and would suppose also extravehicular activities to mate the transfer
lines
• a common power system would provide required energy for refrigeration
3.4.3.4.6 Synthesis
Type 1.
Identified system Advantage Disadvantage
Passive insulation, no sun
shade
Type 2.
Thermal system at tank level
(sunshade, refrigeration)
Individual tanks, orbiting
until final assembly (possible
fly in formation to simplify
final integration)
Type 3.
Integrated thermal design on
truss
Type 4.
Thermal system at tank level:
passive insulation,
refrigeration
No on-board capability
Recuperation by a dedicated
system in charge of
progressive assembly
Simplicity, no power or mechanisms
required
The assembly is delayed until all the
elements are in orbit (reduction of assembly
cost, EVA)
Sharing of resources, low mass impact per
tank. Possible commonalities (power,
cooling or shade system).
Possible use of the transfer vehicle if
already present for these functions
Optimisation of the functions, little
redundancy: operational capability on the
dedicated system only
Table 3-71: Synthesis
Not effective with high mass dedicated to
insulation
Residual BO (and pressure rise) shall be
tolerated per design
Recuperation of the tank is problematic
=> low performance if no reflective or shade
system is used, loss of propellant (BO), high
structural index, high mass penalty.
Cost of a spacecraft per tank launched
Spacecraft mass reduce propellant mass
=> high mass and cost penalty
Requires an immediate assembly (automatic or
EVA). EVA appears improbable if not in the
proximity of ISS
If a sunshade is deployed, has to be removed
before launch
=> sequential assembly seems problematic
The dedicated system needs significant
resources to be operational during the
complete assembly