ESA Document - Emits - ESA

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2.2.4.2 Accelerations
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 25 of 422
The requirements for maximum g-loads vary depending on the body axes considered (see Figure
2-3 for body axes). Crew seats are oriented so that the g-loads during the critical phases (i.e.
launch and landing. etc) are along the +Gx direction, direction in which higher loads can be
sustained. The maximum allowable loads along that axis are shown in Figure 2-4.
Acceleration, g
7.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
Figure 2-3: Body axes directions
Maximum g-loads allowable in the +Gx axis
Mission Phases
Earth Departure
Mars Arrival
Mars Departure
Earth Arrival
Figure 2-4: Maximum allowable g-loads in the +Gx direction
Maximum allowable g-loads at Mars arrival, Mars departure and Earth return are lower to
account for crew deconditioning after experiencing microgravity for several months. Due to the
lack of data for very long durations during microgravity, after a certain threshold time the
maximum g-loads have been assumed as constant (optimistic approach).
The requirements for sustained g-loads are not only a function of the direction but also depend
on the time of exposure. As shown in Figure 2-5, long-duration g-load limits depend linearly on
the time of exposure. The +Gx axis direction has the highest allowable loads and –Gz the one
with the lowest. Figure 2-5 data do not consider microgravity exposure.