Abstract
Space instruments are designed to be highly optimised, mass efficient hardware required to operate in extreme environments. Building and testing is extremely costly, and damage that appears to have no impact on performance at normal ambient conditions can have disastrous implications when in operation. The Mid-Infrared Instrument is one of four instruments to be used on the James Webb Space Telescope which is due for launch in 2018. This telescope will be successor to the Hubble Space Telescope and is the largest space-based astronomy project ever to be conceived. Critical to operation of the Mid-Infrared Instrument is its primary structure, which provides both a stable platform and thermal isolation for the scientific instruments. The primary structure contains strain-absorbing flexures and this article summarises how these have been instrumented with a novel strain gauge system designed to protect the structure from damage. Compatible with space flight requirements, the gauges have been used in both ambient and cryogenic environments and were successfully used to support various tasks including integration to the spacecraft. The article also discusses limitations to using the strain gauge instrumentation and other implications that should be considered if such a system is to be used for similar applications in future.
Highlights
The James Webb Space Telescope (JWST1) is an observatory-class spacecraft intended to serve the worldwide astronomy community following the example of the Hubble Space Telescope, whose scientific output has revolutionised space-based optical astronomy since it was launched in 1990
JWST is currently scheduled for launch in 2018, and its four science instruments have been delivered to NASA for integration onto the spacecraft
We present the key measurements and a comparison with finite element (FE) model predictions, demonstrating the importance of the device in mitigating risk of structural distortion and misalignment of the instrument
Summary
The James Webb Space Telescope (JWST1) is an observatory-class spacecraft intended to serve the worldwide astronomy community following the example of the Hubble Space Telescope, whose scientific output has revolutionised space-based optical astronomy since it was launched in 1990. In order to provide continuous measurement of the response of the primary structure hexapod to integration, g release and thermoelastic loads, we have installed a strain gauge array on the flexures. To minimise loads on the MIRI cryocooler, the MIRI primary structure must provide thermal isolation This is achieved by a carbon fibre hexapod,[4] supplied by Technical University of Denmark, with invar end fittings and brackets that connect to an aluminium optical bench, called the deck (Figure 1(b)), supplied by the University of Leicester. At the base of the hexapod, the brackets provide interface to the spacecraft and at the top they connect to the deck This requires two different bracket designs to be adopted (Figure 1(c) and (d)). An important lesson learnt was that if FBGs are to be used, their implementation needs to be considered in the hardware design from the outset as they are extremely difficult to retrofit to existing hardware
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