demonstrator considerably, defeating the objective of performing an inexpensive and rapid experiment. The possibility that such a delay will occur will need to be the subject of careful risk analysis but. at first, glance, it does not seem positive. Another important problem, and one that is very well appreciated in the European space community, is that all Shuttle payloads must be built to strict quality control and system safety constraints. This would involve use of only approved components, full component traceability, thorough testing, detailed analysis including fracture mechanics, undertaking lengthy safety reviews and documentation compilation. While none of these are impossible, they all conflict with the driving objective to minimise costs. 3.2.2 Spacelab E-l Spacelab was built essentially as the European contribution to the US Space Shuttle program, and consists primarily of a pressurised module that is placed in the Shuttle payload bay and provides a shirt-sleeve environment for research. In addition, most Spacelab flights also include the use of an unpressurised pallet structure behind the pressurised module. On the three Spacelab flights that have included a major European contribution (Spacelab 1, 1983; the German Spacelab DI. 1985; and the IML mission, 1992) such pallet structures have been used for experiments that require exposure to space and the Earth. (Figure 3.2-3) The Spacelab E-l mission in 1995 is also planned to include an unpressurised structure, designated the Unique Support Structure (USS).[11] The USS is shown in Figure 3.2-4 and is essentially a derivative of the SPAS and the Eureca structures. Its mechanical interfaces are similar to Eureca, with experiments mounted on 0.7 m x 0.7 m Equipment Support Panels (ESPs). A
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