Correcting Thermal Deformations in an Active Composite Reflector
- Created: Thursday, 01 December 2011
Composite actuators can be embedded into an easy-to-manufacture flat surface.
Large, high-precision composite reflectors for future space missions are costly to manufacture, and heavy. An active composite reflector capable of adjusting shape in situ to maintain required tolerances can be lighter and cheaper to manufacture.
An active composite reflector testbed
was developed that uses an array of piezoelectric
composite actuators embedded
in the back face sheet of a 0.8-m reflector
panel. Each individually addressable
actuator can be commanded from –500
to +1,500 V, and the flatness of the panel
can be controlled to tolerances of 100
nm. Measuring the surface flatness at
this resolution required the use of a
speckle holography interferometer system
in the Precision Environmental Test
Enclosure (PETE) at JPL.
The existing testbed combines the PETE for test environment stability, the speckle holography system for measuring out-of-plane deformations, the active panel including an array of individually addressable actuators, a FLIR thermal camera to measure thermal profiles across the reflector, and a heat source. Use of an array of flat piezoelectric actuators to correct thermal deformations is a promising new application for these actuators, as is the use of this actuator technology for surface flatness and wavefront control. An isogrid of these actuators is moving one step closer to a fully active face sheet, with the significant advantage of ease in manufacturing. No extensive rib structure or other actuation backing structure is required, as these actuators can be applied directly to an easy-to-manufacture flat surface.
Any mission with a surface flatness requirement for a panel or reflector structure could adopt this actuator array concept to create lighter structures and enable improved performance on orbit. The thermal environment on orbit tends to include variations in temperature during shadowing or changes in angle. Because of this, a purely passive system is not an effective way to maintain flatness at the scale of microns over several meters.
This technology is specifically referring to correcting thermal deformations of a large, flat structure to a specified tolerance. However, the underlying concept (an array of actuators on the back face of a panel for correcting the flatness of the front face) could be extended to many applications, including energy harvesting, changing the wavefront of an optical system, and correcting the flatness of an array of segmented deployable panels.
This work was done by Samuel C. Bradford and Gregory S. Agnes of Caltech, and William K. Wilkie of Langley Research Center for NASA’s Jet Propulsion Laboratory.
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