ESA Document - Emits - ESA

s
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 34 of 422
Figure 2-12: Geometry During Mars Phase
Figure 2-13 shows the Earth-Sun-spacecraft geometry for the transfer to Earth. Here, there are no
superior conjunctions.
Figure 2-13: Geometry During Mars-Earth Transfer
2.4.3.2 Earth escape and planetary protection
The TV will be assembled in LEO. To minimise gravity losses, allow a staged solution and
enhance operational safety, the TMI burn is split into three parts. The first two insert into
eccentric orbits, the third and final one into the hyperbolic escape. After each burn, the spent
stages are jettisoned and perform a controlled reentry. Otherwise they would reenter at some
undetermined time and could endanger inhabited regions. The required ∆v for de-orbiting is
budgeted.
The final, escape burn must be biased such that the spent third stage does not hit Mars. After
separation, the TV is retargeted on the course to Mars. This adds to the TV manoeuvre budget.
2.4.3.3 MOI and planetary protection
The assumption is that MOI inserts into a 4-sol orbit (approx 500x96 000 km). The MOI stage is
jettisoned and remains in this orbit, the TV continues to a circular 500 km orbit. It was shown
that the orbit of the MOI stage can be expected to decay within 10 years. A lifetime of over 50
years can be achieved by raising the pericentre altitude to 3000 km. This adds to the MOI stage
budget.
2.4.3.4 The Mars orbit phase
After MOI, the orbit is circularized. The Mars orbit phase is spent in a 500 km circular orbit.
This orbit will remain stable for over 50 years. The operations taking place during this phase are
discussed in separate chapters.