Spacecraft Technology Structure A satellite structure must fulfill various requirements. First of all, it must resist the loads induced by the launch environment (acceleration, acoustics thermal), met all the functional performances required on orbit such as dimensional stability for example, but it must also interface with some other subsystems such as : thermal control, optical components, electronic equipment, mechanisms, etc. The structure will be the skeleton used during the assembly process of these subsystems into the satellite and then it must provide very clean interfaces to each individual element in order to simplify the sequence of integration.

Spacecraft Technology Structure 3. Finally , the concept must be compatible with the standard manufacturing process and use standard components(sheet-iron, tube,...) every time it is possible.

Spacecraft structures are mainly divided in two categories : The Primary structure or main structure, whose purpose is to transmit loads to the base of the satellite through specifically design components (central tube, honeycomb platform, bar truss, etc.). This structure provides the attachment points for the payload and the associated equipments. Failure of the primary structure leads to a complete collapse of the satellite.

The Secondary structures, such as baffle, thermal blanket support themselves and are attached to the primary structure which guaranties the overall structural integrity. A secondary structure failure is not a problem for the structural integrity, but it could have some important impacts on the mission if it alters the thermal control, the electrical continuity, the mechanisms or if it crosses an optical path.

For the new generation of large satellites, we must consider a third type of structure: Flexible appendages such as antenna reflectors and solar arrays. These structures have generally low resonant frequencies which interact directly on the dynamic behavior of the satellite and require a special care for design. Finally, some spacecraft structures are more complex than the ones described above, and cannot be described with general rules due to their uniqueness and particular requirements . Among these are the manned spacecraft structures (orbiter and space station) and the future lunar outposts.

Primary power: The continuity of the primary power supply is another important consideration in the design of transmit-receive earth stations. Apart from the smallest stations, power backup in the form of multiple feeds from the commercial power source and/or batteries and generators is provided. If the commercial power fails, batteries immediately take over with no interruption. At the same time, the standby generators start up, and once they are up to speed they automatically take over from the batteries.

Primary power The primary electrical power for operating the electronic equipment is obtained from solar cells. Individual cells can generate only small amounts of power, and therefore, arrays of cells in series-parallel connection are required.

Primary power The solar cell panels for the HS 376 satellite manufactured by Hughes Space and Communications Company. In geostationary orbit the telescoped panel is fully extended so that both are exposed to sun- light. At the beginning of life, the panels produce 940 W dc power, which may drop to 760 W at the end of 10 years. During eclipse, power is provided by two nickel-cadmium (Ni-Cd) longlife batteries, which will deliver 830 W. At the end of life, battery recharge time is less than 16 h.

Satellite eclipse time as a function of the current day of the year.

Primary power Capacity of cylindrical and solar-sail satellites, the cross-over point is estimated to be about 2kW, where the solar-sail type is more economical than the cylindrical type (Hyndman, 1991).