ESA Document - Emits - ESA

s
2.7.13.3 Baseline design
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 84 of 422
From the analyses presented above, it is evident that it is not possible to meet all of the
aerobraking constraints with the current vehicle. If the duration is constrained the loads are
unacceptably high. Conversely, if the loads are constrained, the duration is so long that the
additional ∆V that would be required to reduce it to meet the constraint would make the
aerobraking mass savings negligible. Therefore, an aerobraking manoeuvre was not chosen for
the baseline design of this mission case.
2.7.13.4 Manoeuvre budget
A typical manoeuvre budget for an aerobraking phase that reduces the apocentre altitude from
initially 96 000 km to 500 km is 115 m/s, 15 m/s for pericentre control (initial lowering and
subsequent adjustment manoeuvres) and 100 m/s for the perigee raise from the final altitude
2.7.13.5 Options
In addition to the more conventional aerobraking manoeuvre considered, “deep aerobraking” is a
possible option. This would involve deploying an inflatable heat shield (or using an ablative heat
shield), storing the solar arrays, and going deep in the atmosphere to shed the orbital energy in a
limited number, of passes. This option has not been analysed in this study.
2.7.14 Artificial gravity
One of the biggest problems that must be overcome is the harmful effects of weightlessness on
the human body. These effects include loss of bone and muscle mass, loss of red blood cells,
fluid shifting from the lower to the upper body, cardiovascular and neurosensory deconditioning,
and changes in the immune system. The physiological systems start to change immediately upon
launch into microgravity and the time courses of change is different for each of them. For
example, the fluid shift and cardiovascular system start immediately within hours while the
muscle and bone need some time to adjust to microgravity; deconditioning starts after days
(muscle) or weeks (bone). Body fluid and cardiovascular system adapt to new environments in
less than 2 weeks. However, cardiac arrhythmia might be a problem in-flight for some
individuals during elevated workloads. Muscle loss (muscle volume and power) is maximum
within the first 4 weeks, but afterwards the loss rate is reduced (strongly dependent on in-flight
countermeasures). Bone loss, however, continues progressively (1% per month) throughout the
mission in free space. Figure 2-41 summarizes the reactions to microgravity of each of the
physiological systems: