3/7/2023 0 Comments Nasa space shuttle equipmentThe maximum temperature ranges and the margins used in spacecraft design and testing are shown in Fig. Assembly level tests are performed at the limits of the Protoflight temperature range and the spacecraft is typically exposed to several temperature cycles between extremes or to long dwell times at the extremes. The spacecraft is expected to function in a predictable manner inside these extended ranges and is also expected to return to performance within specification once temperatures return to the Allowable Flight temperature range. This second range is referred to as Qualification or Protoflight range. Ultimately, the design is tested over temperature ranges that include a predetermined amount of margin on both sides of this Allowable range. Commonly, the temperature range over which the spacecraft is expected to function during nominal operation is referred to as the Allowable Flight temperature range. Temperature requirements are specified in terms of ranges. Thermal design requirements are most typically expressed as temperature requirements, but it is not unusual that temperature requirements are also accompanied by requirements addressing temporal temperature stability, spatial gradients, heat flow, and minimum duration for the survival of arbitrary extreme conditions. Final performance of the spacecraft is compared to these requirements and validated by either test or analysis. These thermal design requirements are considered specified performance parameters for a given set of conditions. The propulsion system thermal control must be qualified as an integrated subsystem. Thermal modeling used for thermal control subsystem design must be validated through testing because of the many interacting variables. Over temperature propellant is unacceptable as well, so there also must be fault tolerance protection from failed-on heaters. Because freezing and the subsequent rupture and loss of containment is unacceptable, the thermal control system should be redundant and fault tolerant. Freezing can form freeze blocks, and on thawing, the rising temperatures between freeze blocks can result in hydrostatic pressures that can exceed rupture pressures.Įxperience has shown that it is preferable to have thermal control to prevent propellant freezing. Even though propellants can decrease in volume on freezing, frozen propellants still have the potential to rupture the system. If propellants freeze, they are not available for utilization, possibly rendering a must-work system inoperable until thawed. The thermal operating limits for propellants are probably the narrowest of thermal limits for the spacecraft, and special propulsion system thermal control is required to keep them within the specified range. Most spacecraft equipment have qualified operating temperature limits that are narrower than the extremely low or high temperatures that can be experienced in space. Manha, in Safety Design for Space Systems, 2009 20.2.3 Thermal Control
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