ESA Document - Emits - ESA

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HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 81 of 422
• Mars escape: 3 December 2033
• Hyperbolic escape velocity: 5.94 km/s
• TVI from 500 km orbit: 4.25 km/s, from HEO at least 3 km/s
• Mars-Venus-transfer: 179 days
• Venus swing-by minimum altitude: 6600 km
• Venus-Earth transfer: 188 days
• Earth arrival date: 5 December 2034 (around one year earlier than nominal)
• Total transfer duration: 367 days
• Earth arrival hyperbolic velocity: 4.74 km/s
• No deterministic midcourse manoeuvres
The total transfer duration is only one year, so arrival would occur one year earlier than for the
nominal mission. The hyperbolic Earth arrival velocity is larger than in the nominal case but
smaller than for the slow abort during Mars transfer (see above).
The problem is the high escape velocity required from Mars. Insertion into the Venus transfer
from the 500 km final orbit around Mars would cost 4.25 km/s, from the initial HEO at least 3
km/s. This value applies only if the HEO is oriented exactly as required for the escape, which is
not the case. The escape manoeuvre from HEO would therefore incur a further large penalty.
In the case of LMO, to provide the system with the required ∆V for the TVI, more propulsion
modules should be added to the TEI, increasing the total mass to LEO by 1000 tonnes. In the
case of HEO, the required ∆V can be provided by the second stage of the MOI plus the TEI
without any mass penalty.
The only other option appears to be to cancel the Mars landing and wait in orbit around Mars for
the nominal return window in May 2035.
2.7.12.1.6 Abort after TEI
No option was found for abort after TEI.
2.7.12.2 Options
In addition to the regarded cases, there is a huge variety of other scenarios for which abort and
recovery strategies need to be analysed. These relate primarily to the cases where critical
manoeuvres are not fully executed due to a failure. Some examples are:
• Incomplete execution of the TMI burn. A distinction must be made between two cases:
- Failure while still in Earth orbit: This implies that the burn completed so far was
not yet sufficient to inject into hyperbolic escape. A decision on whether to
proceed with the burn at the next perigee pass, whether to abort and return the
crew to Earth or to proceed in any other way must be made based on the gravity
of the failure, the chances for recovery and the orbit achieved so far.
- Failure after achieving escape: This implies that a hyperbolic orbit was achieved.
Depending on the time of failure, the resulting heliocentric orbit will range from
very close to the Earth orbit to very close to the nominal Mars transfer. Again, the
abort/recovery options depend on the spacecraft and orbital conditions achieved.
• Incomplete execution of MOI: Again a case distinction is necessary:
- Failure after reaching a bound orbit: The burn removed enough orbital energy to
insert into a possibly quite wide elliptical orbit around Mars. The reaction must
again depend on the case and could consist of immediate stabilization of the orbit