Initial Habitat Orientation
Mission calls for a vertical landing of the stack, consisting of the
integrated ascent/descent stage and the habitation module, with the two
lined up vertically. The habitation module is then lowered, as can be
seen in the agenda for Day 1.
The obvious thought when trying to trim unnecessary structural mass from
the stack is to forego the added strcture and lowering mechanisms and land
the habitation module in a horizontal fashion, eliminating the need to move
it from an original vertical state.
There are numerous avantages to this arrangement:
- The weight and expense of lowering mechanisms and the controlling gears
or circuitry can be removed
- It eliminates the risks involved in lowering the 12,000 lb,
- Redundant sets of trusses can be removed
- Stereo-optical cameras recording footage and governing the landing
would be more effective if farther separated
- Thrusters are more powerful if farther separated, and exhaust will
affect less surface area of the hull
- It remains possible for the crew to move about in the cabin during the
many lengthy descent
- The descent will push the crew towards the floor instead of the rear
wall of the habitat
- There may be a lower development cost if a motor is used to lower the
However, on close inspection one realizes that the advantages are more
then countered by additional mass required in structure and other
- External structure would be needed to stabilize the hab module, mount
the engines, and distribute the stress of burns (more than is removed
from the lowering apparatus)
- There would be less stability
- Thrusters have less torque, use more fuel and operate more slowly at
a time when 10ths of seconds count
- The jacks to level the module after landing would have to be stronger
and need more gearing
to lift the full weight of the module vs the lower weight of the bracing
- More assembly in space would be required to attach the rocket to the
center of the module, with its associated costs, and potential for failure
- The stack would be more volumnous at launch with the uncollapsible extra
trusses and framework
The vertical alternative obviously wins. A useful alternative might be
to build lowering gear that can be salvaged from the first module and used
for subsequent modules, and/or put to other uses.
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