ESA Document - Emits - ESA

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4.4.6 Mechanisms
HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 356 of 422
4.4.6.1 Requirements and design drivers
The HMM science requirements do not state any specific requirements applicable to the DM
mechanisms. As a result of the DM’s configuration, the following necessary mechanisms and
their requirements can be derived:
• Vehicle Stage Separation System
o Release & Separation of De-orbit Propulsion Module.
• Separation System
o Heat Shield Jettison System.
• Deployable Landing Leg System
4.4.6.2 Assumptions and trade-offs
The requirement for a deployable landing leg system is dependent upon the dynamics of the
Landing Vehicle. The Footprint dimension is sized to prevent the vehicle from toppling when
contact with the ground happens and there is a residual horizontal velocity component acting on
the system.
Essentially, this can de (simplistically) analysed by looking at the situation when the horizontal
and vertical force moment components are in equilibrium i.e. the point of initiating the topple
moment when the horizontal moment component is greater than the vertical moment component.
Figure 4-98 shows the principle force or moment balance system:
Figure 4-98: Momentum balance system
Hv = Height at which the engine thrust is cut-off.
• Max. Height for ‘Thrust’ cut-off = 2 m max.
Vv = The residual Vertical Velocity at the moment of engine thrust cut-off
• Final Vertical Velocity= 0→2 m/s, g=3.8 m/s2)