Abstract
The metrology of membrane structures, especially inflatable, curved, optical surfaces, remains challenging. Internal pressure, mechanical membrane properties, and circumferential boundary conditions imbue highly dynamic slopes to the final optic surface. Here, we present our method and experimental results for measuring a 1 m inflatable reflector’s shape response to dynamic perturbations in a thermal vacuum chamber. Our method uses phase-measuring deflectometry to track shape change in response to pressure change, thermal gradient, and controlled puncture. We use an initial measurement as a virtual null reference, allowing us to compare 500 mm of measurable aperture of the concave f/2, 1-meter diameter inflatable optic. We built a custom deflectometer that attaches to the TVAC window to make full use of its clear aperture, with kinematic references behind the test article for calibration. Our method produces 500 × 500 pixel resolution 3D surface maps with a repeatability of 150 nm RMS within a cryogenic vacuum environment (T = 140 K, P = 0.11 Pa).
Highlights
Gossamer space structures are not a recent invention
Thermal Vacuum Chamber (TVAC) testing is a regular milestone in space hardware verification; emulating the conditions of device operation in space is important to predict the behavior of hardware already tested on land
TVAC testing results are reported for a 1 m inflatable membrane reflector in response to perturbations in low-temperature, near-vacuum conditions
Summary
Gossamer space structures are not a recent invention. From the Inflatable Aperture Experiment in 1996 to the sunshield assembly of the James Webb Space Telescope, membrane spacecraft assemblies continue to be actively deployed [1]. OASIS is a proposed ~14 to 20-meter class space observatory that will perform high spectral resolution observations at terahertz frequencies [2]. The advantage for such structures is that they can achieve 7X the collecting area as space observatories with traditionally polished apertures for less than one third of the mass [3]. A spaceborne observatory with a 14 meter diameter size produces a signal-to-noise ratio unobtainable at ground level for far-infrared spectra, enabling the quantitative science of detecting water in distant protoplanetary disks and solar system objects. OOuurr rreeqquuiirreemmeenntt ffoorr aa ggeenneerraall mmeettrroollooggyy tteecchhnniiqquuee rreeqquuiirreedd ccaappttuurriinngg ssuurrffaaccee sshapes tthhat aarree rreellaattiivveellyy uunnkknnoowwnn dduuee ttoo llaatteenntt wwrriinnkklleess aanndd ppoossssiibbllee tthheerrmmooffoorrmmiinng vvaarriiaation. TThhee ccoonnvveexx MMyyllaarr ssuurrffaaccee iiss kknnoowwnn aass tthhee ccaannooppyy. IInn tthhee fifinnaall ffuullll--ssiizzeedd aasssseemmbbllyy,, tthhee ccaannooppyy wwiillll bbee bbtilloaancckkwppaoovllyeyilimemnigiddtehe,,sww(h~h8ici0ch–h6isi6so0opμpamqaqu).ueeininthtehevivsiisbilbelbeubtuttratrnasnpsapreanretnwt iwthitshomsoemloeslsoisns tihnethtaergtaertgoepteorpateiroanwavelengths (~80–660 μm)
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