Large payloads which are designated for operation in space – such as satellites and telescopes for example – have to undergo extensive tests before launch: both vibration testing (environmental and force limited) and cryogenic testing procedures require application-specific force sensors and accelerometers which are up to the test.
Space payload testing
Thermal vacuum chamber testing for mechanical characterizations
Telescope performance depends on stability in the nanometer range, so the stability of the fully instrumented backplanes is critical. They need to be tested in thermal vacuum chambers suitable for testing under cryogenic conditions, and designed to ensure unique thermal stability at temperatures below –250 °C (–420 °F). Testing in the vacuum chamber requires accelerometers and force sensors with ultra-low temperature capabilities.
Backplanes can carry the primary mirror as well as other telescope optics and the entire module of scientific instruments. Testing allows modification of the system so that the backplanes – and ultimately the telescope – can be isolated in the chamber. Some testing environments include a new, layered helium and nitrogen cooling system: this allows the backplanes to reach the low temperatures that simulate operating temperatures in space. They allow for cryogenic optical alignment and testing of multiple primary mirror segments in a process known as "phasing". Testing of this sort calls for accelerometers and force sensors with ultra-low temperature capabilities.
Low-mass and lightweight triaxial accelerometersSpacecraft structures are often made of thin, lightweight materials, so they require low-mass accelerometers sometimes with a mass lower than 1 gram.
Low outgassing cabling solutionHermetically sealed sensors and low-outgassing cabling solutions from Kistler are sometimes authorized for use in thermal vacuum chambers, or they may even be left on the satellite for launch.
Low noise solutions for environmental testing with micro-vibrationsSensor thresholds ranging from very low (100 μg) to the higher g levels. With Kistler's low noise solutions, the same sensor can be used for the entire range.
Space payload environmental vibration testing and force limited vibration testing (FLVT)
Space payloads undergo some of the most exhaustive testing in the world: vibration qualification tests for satellites are just one example. Extensive payload tests are performed during product development in order to optimize the structure, and also in the manufacturing phase to ensure survivability during launch, deployment and long-term operation. To simulate the environmental conditions that a payload must survive during rocket launch, electrodynamic shakers are used for realistic dynamic load testing.
Force limited vibration testing can prevent over-testing that could damage costly satellites. By measuring and limiting the reaction forces between the payload and the slip table, the acceleration is notched at the payload resonances. In actual flight, input acceleration is notched at the payload resonant frequencies, as the mechanical impedance of the structural mount and payload is similar. In shaker testing, space payload interface forces are higher at the payload resonances; this is because the shaker has very high mechanical impedance and is controlled by the enveloped interface acceleration.