11.5 Design of Landing Gear Mechanism
381
where: S is vertical displacement of primary strut; S 0 is reserved safety distance from
the lowest point of the lunar lander structure to landing surface; T is height of the
footpad; H is depression depth of the lunar lander after landing relative to landing
surface.
Generally, the distance from center of mass of the lunar lander to the lowest point
of main structure L 0 is known. So, after L hmin is determined, height of center of mass
of the lunar lander H 0 could be derived from:
H 0 = L hmin + L 0
(11.6)
The value of L v is determined through simulation of landing stability. At preliminary design, a preliminary value of L v is estimated with principle of energy transformation. In order to assure that the lunar lander would not turn over in landing
process, the following formulation should be met.
W D ≤ W H = m max g
h
(11.7)
where: W D is kinetic energy of the lunar lander when the lunar lander starts to
turn over; W H is increasing of potential energy of the lunar lander relative to that
at touchdown when center of mass of the lunar lander moves into vertical plane
including the connecting line of spherical joints of two adjacent footpads; m max is
possible maximum landing mass at touchdown; g’ is gravity acceleration on landing
surface; h is increasing height of center of mass of the lunar lander in turn over
process.
Deduced from Eq. (11.7), the lunar lander would not turn over if kinetic energy
at touchdown was less than increasing of potential energy in landing process.
Assuming the primary strut is not compressed and the footpad does not subsidence,
the value of h is estimated as follows:
h =
H
2
0 + L
2
V − H 0
In actual landing process, the struts would absorb some part of energy and height
of center of mass will decrease due to compression of the primary strut. Therefore,
above estimation was conservative.
3) Analysis and determination of cushion capability
Total energy to be absorbed by the landing gear mechanism consisted of two parts:
one was kinetic energy of the lunar lander at touchdown and the other was potential
energy reduction of the lunar lander due to strut cushion and footpad subsidence.
(1) Hypothesis of cushion energy. At preliminary design, it was assumed that
potential energy reduction due to footpad subsidence was equal to deformation
energy absorbed by landing surface. Such hypothesis was physically similar
with situation of landing on a rigid surface.
The energy absorbed by the primary strut in landing process is:
381
where: S is vertical displacement of primary strut; S 0 is reserved safety distance from
the lowest point of the lunar lander structure to landing surface; T is height of the
footpad; H is depression depth of the lunar lander after landing relative to landing
surface.
Generally, the distance from center of mass of the lunar lander to the lowest point
of main structure L 0 is known. So, after L hmin is determined, height of center of mass
of the lunar lander H 0 could be derived from:
H 0 = L hmin + L 0
(11.6)
The value of L v is determined through simulation of landing stability. At preliminary design, a preliminary value of L v is estimated with principle of energy transformation. In order to assure that the lunar lander would not turn over in landing
process, the following formulation should be met.
W D ≤ W H = m max g
h
(11.7)
where: W D is kinetic energy of the lunar lander when the lunar lander starts to
turn over; W H is increasing of potential energy of the lunar lander relative to that
at touchdown when center of mass of the lunar lander moves into vertical plane
including the connecting line of spherical joints of two adjacent footpads; m max is
possible maximum landing mass at touchdown; g’ is gravity acceleration on landing
surface; h is increasing height of center of mass of the lunar lander in turn over
process.
Deduced from Eq. (11.7), the lunar lander would not turn over if kinetic energy
at touchdown was less than increasing of potential energy in landing process.
Assuming the primary strut is not compressed and the footpad does not subsidence,
the value of h is estimated as follows:
h =
H
2
0 + L
2
V − H 0
In actual landing process, the struts would absorb some part of energy and height
of center of mass will decrease due to compression of the primary strut. Therefore,
above estimation was conservative.
3) Analysis and determination of cushion capability
Total energy to be absorbed by the landing gear mechanism consisted of two parts:
one was kinetic energy of the lunar lander at touchdown and the other was potential
energy reduction of the lunar lander due to strut cushion and footpad subsidence.
(1) Hypothesis of cushion energy. At preliminary design, it was assumed that
potential energy reduction due to footpad subsidence was equal to deformation
energy absorbed by landing surface. Such hypothesis was physically similar
with situation of landing on a rigid surface.
The energy absorbed by the primary strut in landing process is: