ESA Document - Emits - ESA

s
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 23 of 422
These highlevel requirements have the following consequences for the mission case definition:
• Landing on the Martian surface is required. Missions limited to Mars orbit or fly-bys are
not acceptable as design case
• Duration of the stay on the Martian surface shall allow for some excursion (surface EVA)
and sample collection capability (no flag footprint only, as first Apollo mission)
• Mission case shall take into account all the constraints coming from human requirements
(physiology, radiation, habitability, etc.)
From the high-level requirements, a set of more specific technical requirements has been
derived:
2.2.2 Mission-general requirements
• Number of crew: six in total, with three landing on the surface of Mars
• Mars sample collection with EVA required (up to 100 kg) in close proximity of the
landing site
• Launch dates: between 2025 and 2040
• Maximum assembly time in LEO: 6 years (comparable to nominal ISS building time) but
preferably of the order of 2 years to catch up with the opportunity windows to Mars
2.2.3 Safety requirements
The overall safety requirement is a “cultural” choice and depends on the probability of loss of
life the public opinion is ready to accept. A high-level decision between the “pioneer” (high-risk)
approach and the “clerk” (low-risk) approach has to be taken.
For human space flight (ISS, Space Shuttle) the maximum number of acceptable failures leading
to life loss over total number of missions is generally about or equal to 1/200. However, at this
stage this number cannot be verified by analysis, therefore it has been taken only as reference.
For the design only the following requirements have been set:
• All the systems shall be made fail safe and fail operational. Whenever this is not possible
abort scenarios shall be built-in,
• Communication gaps need to be minimised. One week maximum duration is acceptable.
2.2.4 Physiology requirements:
2.2.4.1 Habitability
The habitability requirements can be expressed in terms of “required pressurised volume”,
which, as shown in Figure 2-1, is a function of the mission duration for times less than 100 days.
For longer missions the required volume stays almost constant.