ESA Document - Emits - ESA

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Minimum Foot-print dimension 'L' (m)
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Leg Minimum Footprint Dimension (L) as a function of Vertical Height at Thrust Cut-off
(& Vertical Velocity Component- Max. 2 m/s) and Horizontal Velocity [Hv]- Landing Mass 42 tonnes, CoG at 6.0 m
Leg Footprint Dimension (Hv=1.5 m/s, Vv0= 0 m/s) Leg Footprint Dimension (Hv=1.5 m/s, Vv0= max.)
Leg Footprint Dimension (Hv=1 m/s, Vv0= 0 m/s) Leg Footprint Dimension (Hv=1 m/s, Vv0= max.)
Leg Footprint Dimension (Hv=0.5 m/s, Vv0= 0 m/s) Leg Footprint Dimension (Hv= 0.5 m/s, Vv0= max.)
Leg Foot-Print Dimension- Envelope Limit Leg Foot-Print Dimension- Structure Dia Limit
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 358 of 422
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0 0.15 0.3 0.45 0.6 0.75 0.9 1.05 1.2 1.35 1.5 1.65 1.8 1.95
Thrust 'Cut-off' Height (m)
Figure 4-99: Minimum footprint vs. vertical height
The main structure of the SHM is about 4 m in diameter and the maximum allowable envelope
dimension is about 6 m in diameter.
From the graph it can be seen that for a horizontal velocity component up to 1 m/s, a foot print
dimension within about 6 m in diameter can be realised for all vertical velocity cases and
therefore a deployable landing foot is not required. What can also be observed is that a residual
vertical velocity is beneficial to the landing as this component acts against the tendency to topple
and leads to a smaller footprint dimension.
For the higher horizontal velocity of 1.5 m/s, it can be seen that, to realise a footprint dimension
within the enveloping limit, an additional (residual) vertical velocity component is required
(either residual velocity due to the descent of the engine thrust cut-off above about 0.5 m) i.e. a
near zero residual height and vertical velocity at engine thrust cut-off with a horizontal velocity
of 1.5 m/s will lead to the system toppling.
In conclusion, if the a limit to the residual horizontal velocity is set to 1 m/s (requirement on the
control system), a non-deployable or static landing leg system can be realised within the
enveloping dimension of about 6 m in diameter that can remain stable when subject to the
residual vertical velocity and height control dispertions. This shall be assumed to be the baseline.
Additional conclusions from the analysis performed are;
• A Large Mass aids stability as does a residual vertical velocity and height component..
• The landing system leg has to be designed assuming a single leg contact as worst case.
• Leg Loading of the order of 350 000 N (estimate of the load along the angular vector
calculated above).
o This load is mainly influenced by the vertical Force components (Mass, Cut-off
Height, Residual Vertical Velocity).
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