ESA Document - Emits - ESA

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4.4.1.2 Assumptions and trade-offs
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 332 of 422
Figure 4-67: Assumed Atmospheric Density and Temperature Model
The following assumptions are made:
• Total mass of MEV at entry, including aeroshell: 46 500 kg
• Initial circular orbital altitude: 500 km
• Aerodynamic reference area 490.87 m 2
• Lift coefficient: 0.348
• Drag coefficient: 1.142
• Lift over drag: 0.305
• Aerodynamic parameters are assumed as independent of Mach number
• Angle of attack with respect to incident flow: fixed
• Control parameter: bank angle around direction of incident flow
• Atmospheric density model: Simplified approximation of a low density profile of
MarsGRAM 2001, as shown above, not regarding positional, diurnal, seasonal and solaractivity-related
variations
• Atmospheric temperature: Approximation of a temperature profile from MarsGRAM
2001
• Parachute deployment conditions: velocity < Mach 2 at altitude > 10 km
4.4.1.3 Baseline design
A wide corridor of possible entry angles was studied for the given configuration as described in
the previous section. This corridor ranges from -2º to -15º with respect to the local horizon in a
rotating Mars-fixed frame.
For all steep entry angles, starting with -3º, the bank angle is assumed to remain fixed at a value
of 30º. This will leave ample control margins to cope with uncertainties in the atmospheric or
aerodynamic properties.
For a very shallow entry, this control strategy is not appropriate. For the -2º case, a much larger
initial bank angle is required to prevent a skip-out, for this, 110º is chosen. When the danger of
skip-out is over, the body rolls to a bank angle of 0. Even shallower entry angles would require
an initial bank angle of up to 180º. The upper limit to the entry corridor is at around -1.9º, where
even with a full-downward lift, skip-out cannot be prevented.