ESA Document - Emits - ESA

s
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 78 of 422
be allowed. In this case northern latitudes are preferred as the dust storms coincide with
the winter.
2.7.12 Abort Options
In the event of a failure or emergency that precludes completion as planned, the mission will
have to be aborted. Two categories of failures have been considered:
• Failures in equipment/subsystems
• Failures in manoeuvres/operations
The first category is dealt with at subsystem design level by making the design fail safe. For the
second category, mission-abort scenarios have been considered.
In the event of a mission abort, the original mission objectives shift to a safe return of the crew,
as soon as possible and within the constraints dictated by the system design. Any defined abort
scenario must be consistent with all budgets imposed for the various subsystems, e.g., propellant,
thermal, structural, power or ECLSS consumables.
Firstly, the abort options for each phase of the mission require study. Then the cost (in terms of
the budget of each relevant subsystem) must be quantified for each identified option. The
outcome is to know what can conceivably be done to save the crew at each point of the mission.
The options for a mission abort strongly depend on the selected scenario. Here, the study is
limited to the baseline scenario as studied for the 2033 launch opportunity.
First, the options per mission phase were analysed. Then, the abort cost for each option was
quantified and listed.
2.7.12.1 Phase-by-phase analysis
The mission phases were studied chronologically, starting from Earth escape and ending with the
return trajectory from Mars to Earth.
2.7.12.1.1 Abort during Earth escape
The Earth escape sequence is split into three manoeuvres, each of which further raises the
apogee until a hyperbolic orbit with the required orbital parameters is achieved. Any of these
burns can be prematurely terminated. For over 90% of the total manoeuvre duration, abort leaves
the spacecraft still in a wide elliptical orbit around the Earth. The crew will have to wait until the
next perigee to be able to then board the entry capsule and return to Earth’s surface.
2.7.12.1.2 Fast abort during Mars transfer
The fast option requires a large DSM to insert the spacecraft into a trajectory that intersects the
Earth’s orbit. The nominal mission parameters are shown for comparison with the abort transfer
characteristics in Table 2-27:
• Earth escape date: 8 April 2033
• Nominal Mars arrival date: 24 October 2033
• Nominal Earth arrival date: October - November 2035
• Nominal mission duration (maximum): 962 days
• Nominal Earth arrival velocity (maximum): 3.052 km/s