Test & measurement
Space testing S
Kistler’s space testing expertise and its experience of working with aerospace centres around the world allows it to offer a proven choice of sensors that are designed for space payload or rocket testing
S
pace flight is an exceptionally demanding industry for new product development and quality control. Equipment often has
to be lightweight, robust and durable because it is subject to challenging environments characterised by broad and extreme temperature ranges, pressure fluctuations, shock and vibration levels.
Kistler works in partnership with renowned
aerospace centres all around the world. The company’s space testing expertise allows it to offer a proven choice of force, torque, pressure and acceleration sensors based on piezoelectric (PE), integrated electronic piezoelectric (IEPE), strain gauge or piezoresistive technologies and that are designed for space payload or rocket testing.
Best-of-market features of Kistler’s
measurement equipment include: widest triaxial force capability, highest sensitivity for micro-vibration measurements, maximum stability even at very high temperatures, and most sensitive cryogenic capability.
Kistler
www.kistler.com
Space payload environmental vibration teSting and force limited vibration teSting (flvt)
atellites undergo a stressful journey from the launch pad until they reach their final orbit. A failure in any one of their
components may result in malfunctioning of the satellite, which is expensive and will delay the programme for years. And no “repair service” is available in case the satellite is damaged. This makes it vital for all space systems – such
as satellites – to undergo an intensive programme of pre-launch tests. These include the Force Limited Vibration
Test, or FLVT. This test, conducted at ground level, involves subjecting the satellite to all vibrations that are likely to occur during its flight from earth to orbit. If a problem arises, corrective actions can be taken. Vibrations are generated during these flight
phases: at launch phase, due to acceleration and operating engines; during transonic flight, when the sound barrier is broken; and near orbit, when the protection cover is removed from the launch vehicle. Each of these phases creates specific spectra of different vibrations. The FLVT aims to be a realistic test that
simulates real conditions. Typically, vibration tests are carried out on shakers. However, there is one problem: the shaker
and the launch vehicle each display different dynamical behaviours – the mechanical impedance of the shaker is very high at its resonance. This may lead to overtesting at the shaker's resonance frequency. The dynamic forces acting on the test object can be far too high, so the force must be limited. This is achieved by positioning force sensors between
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the test object and the shaker. The force sensors will limit the maximum
vibration at the shaker’s resonance, which is the main objective of an FLVT. Force sensors for FLVT must be rigid, and
they require a wide measuring range. Therefore, the NASA HDBK 7004C states: “The high degree of linearity, dynamic range, rigidity, and stability of quartz make it an excellent transducer material for both accelerometers and force gauges.” Kistler has designed a comprehensive product
portfolio for these environmental testing applications. It includes low-mass and lightweight triaxial accelerometers, three-component force sensors, preloaded force links for easy mounting, cabling equipment and related signal conditioners. The company’s lightweight solutions feature superior characteristics such as low outgassing, low noise and low crosstalk.
Important technologies for the application Low outgassing: Exposure to the high vacuum level of a space environment induces material outgassing, thereby releasing entrapped gas. This can condense on surfaces, such as camera lenses, thereby rendering them inoperative for the intended application. Force sensors may also be used in vacuum chambers. Kistler offers hermetically sealed sensors and low outgassing cables suitable for those cases. Optimal mounting: If not limited by space and frequency response requirements, it is recommended to apply sensors from the
preloaded force link family. Those are already calibrated and can directly interface the force ring. If space is limited and the stiffness of the system needs to be optimised for a wider frequency response, the application of load cell sensors is the preferred choice. Preloading is accomplished within the customer force ring and demands for an on-site calibration. Low crosstalk: The resulting forces and moments are calculated through the three signals provided by each sensor around the force ring. The lower the crosstalk, the higher the force measurement and moment calculation accuracy. Easy summing: Charge output sensors do not only allow an easy preloading. It is also possible to pre-sum signal packages by connecting the respective cables prior to the conditioning stage. The modern charge amplifiers allow a convenient and flexible summation, too. This allows the user to optimise the number of required DAQ channels without using inconvenient voltage summing methods.
August 2019 Instrumentation Monthly
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