ESA Document - Emits - ESA

s
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 336 of 422
The deorbit manoeuvre is at least 96 m/s and increases more than fivefold for a steep entry. This
is an important factor to be taken into account in the final selection of the entry strategy. The
following table lists the minimum and maximum values for all regarded trajectories occurring in
the regarded entry corridor. On the basis of the provided information and taking into account the
results of the aerothermodynamics analysis, this corridor must be narrowed down considerably
and a baseline entry trajectory must be selected to obtain an optimal compromise between
structural and thermal loads, duration, controllability, accuracy and deorbit manoeuvre propellant
requirements.
Based on the current analysis, a target entry angle of -4º appears to constitute an acceptable
compromise but this should be verified.
4.4.1.4 Options
Minimum Maximum
De-orbit burn size [m/s] 96 521
Entry FPA [º] -2 -15
Entry velocity [km/s] 2.990 3.358
Final altitude [km] 13 15
Flight time [s] 227 2450
Max g-load 0.73 4.4
Max dynamic Pressure [Pa] 570 3450
Table 4-37: Summary of Min/Max Characteristics for Regarded Entry Corridor
Different inflatable aeroshell sizes were considered for comparison with the 490.87 m 2 baseline.
A considerably smaller aeroshell reference area size of 300 m 2 is marginally acceptable. It barely
meets the 10 km constraint for attaining parachute deployment velocity. This should be regarded
as the lowest possible value when using inflatable aeroshell technology for the given entry mass
range.
In the course of the CDF study the use of a rigid lifting body with a moderate lift/drag ratio of
0.83 was also considered instead of the inflatable aeroshell with an L/D of about 0.3. The results
are not presented here but further analysis in that direction can be undertaken at a later stage.
4.4.2 Aerothermodynamics
4.4.2.1 Requirements and design drivers
The MEV design was driven by four requirements; the total mass (40 tonnes to 50m tonnes), the
terminal velocity at 2000m of altitude (100m/s) due to the retro-rockets thrust and the design of
the landing vehicle (vertical cylinder with the MAV at the top and retro-rockets at the bottom)
and the g-load during the entry and descent phase.
Trajectories atmospheric entries are functions of parameters as entry conditions (velocity and
flight path angle) and the ballistic coefficients of the vehicle (ratio of the reference surface over
mass and drag coefficient).