The structural subsystem of a spacecraft is analogous to the skeleton of the human body in function and form. Both serve to carry loads for motion through inertial space and to maintain the shape of a covering membrane that protects internal components against adverse environmental factors. Specifically, the spacecraft structure will serve to: (1) carry loads applied during launch, lunar delivery, and landing; (2) support the spacecraft thermal material, the skin of the craft; and (3) provide the internal components with infrastructure attachment points and micrometeorite impact protection for the duration of the mission, in space and on the lunar surface.
Micrometeorite protection should also be provided by the skin panels but further study needs to be conducted to resolve what level of kinetic energy protection from incoming particles should be provided. Outgassing from the spacecraft materials could also be a problem during this portion of the mission. Material selection should consider outgassing as a criterion.
The spacecraft bus structure should be able to withstand the NGC actuation and propulsion forces needed for maneuvering and orbit changes. Careful planning with these groups should be made for thruster placement, thruster strength, and momentum wheel placement. The spacecraft should be designed so that any antennae, solar panels, or other externally deployed equipment will not be physically hindered in there operation by the spacecraft structure.
As mentioned previously, the actual landing regime is yet to be determined. The structures group should work in close coordination with the oxygen production and propulsion teams to ascertain the jeopardy posed to the oxygen production mission by lunar soil sample contamination by landing exhausts. The possibility of the use of a lunar rover for sample collection may make a soft touch landing possible even if the immediate landing site is contaminated. The likelihood of a controlled freefall landing has been discussed and would include a ten meter drop to the lunar surface. The landing gear and possibly a crushable material system, similar to that used in military equipment airdrops, must limit the acceleration of the general bus structure to the g-force tolerances imposed by the WEAKEST internal hardware member. The prime consideration of the landing accelerations is the SURVIVAL OF THE OXYGEN PRODUCTION PLANT AND THE SOIL COLLECTION SYSTEM. Currently 10 g's has been set as an arbitrary maximum for the landing accelerations of the bus structure and its internal payload. Also, the final maximum displacement of the spacecraft from the lunar surface horizontal must be considered of reasons of spacecraft stability and operation of possible gravity intensive devices such as shakers on the oxygen production plant.
|Input Group||Interface/Information||Output Group|
|Initial Spacecraft Mass Estimate||Propulsion|
|Propulsion||Launch Vehicle Payload Size Constraints|
|Propulsion||Refined Spacecraft Mass Estimate|
|All Systems||Component Mass/Volume/Mounting Constraints|
|All Systems||Component Acceleration Limits|
|All Systems||Dynamic Loading Constraints|
|All Systems||Micrometeorite Protection Requirements|
|All Systems||Radiation Protection|
|All Systems||Thermal Protection||Thermal|
|Sensors/O2||Sample Collection System|
|Sensors||Micro Satellite Integration|
|Propulsion||Main Propulsion Vibrations|
|NGC||Maneuvering Loads (DeltaV's, Torques)|
|NGC/Propulsion||RCS/MPS Propellant Consumption|
|Propulsion||RCS Thruster Placement|
|Propulsion||RCS/MPS Propellant Tank Volume/Pressure|
|Propulsion||RCS/MPS Pressurization Tank Volume/Pressure|
|NGC/Com.||Antenna Pointing Requirements|
|Power||Electrical Bus Grounding|
|Power||Battery/Solar Panel Attachment|
|Landing Phase Accelerations (max)||NGC|
|Landing Hazard Identification||NGC|
|Landing Design Requirements||NGC|
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CSR/TSGC Team Web