Space-based solar thermal power systems are very appealing as a space power source because they generate power efficiently. However, solar thermal (dynamic) systems currently incorporate rigid concentrators that are relatively heavy and require significant packaging volume and robust deployment schemes. In many ways, these requirements make these systems less appealing than photovoltaic systems. As an alternative to solar thermal power systems with rigid concentrators, solar thermal power systems with thin-film inflation-deployed concentrators have low cost, are lightweight, and are efficiently packaged and deployed. Not only are inflatable concentrators suitable for low Earth orbit and geosynchronous orbit applications, but they can be utilized in deep space missions to concentrate solar energy to high-efficiency solar cells.
SBIR with SRS Technologies, Inc.
A Small Business Innovative Research (SBIR) contract was awarded by NASA Glenn. The contract resulted in the delivery of a 2m x3m inflatable concentrator that was designed and built by SRS Technologies, Inc. The objective of this SBIR was to design, build, demonstrate, and characterize a thin-film, inflatable concentrator that had interfaces for solar thermal power systems. The concentrator delivered to NASA Glenn Research Center (GRC) in late October 1998, was a 2.0- by 3.0-m off-axis parabolic concentrator with a 90° tilt angle and 30° half angle. The ultimate goal of the SBIR was to demonstrate, through testing, that inflatable concentrators for power generation are both a viable and desirable alternative to the rigid concentrator designs that are currently being used. NASA GRC worked closely with the Air Force Research Laboratory at Edwards Air Force Base to finalize contractual agreements and test requirements to support joint testing at NASA GRC in the Tank 6 facility.
The objectives of the test were the following:
- Quantify the thermal performance and optical performance of the test article in a simulated space environment that was provided by GRC’s Tank 6 Solar Simulator
- Use the test data to qualify analytical computer models.
This test was the first in a series of several planned space environmental tests that GRC and the Air Force were planning as part of a technology road map for an inflatable-rigidized concentrator flight experiment that was scheduled for 2001.
Testing at GRC
During the test, thermal performance was measured via thermocouples on the surface of the inflated concentrator and the support torus. Optical performance was characterized via flux intensity measurements at the focal plane via a charge-coupled discharge (CCD) camera. Additional performance data was collected on the catenary strain, torus and canopy pressure, and make-up gas requirements.
Major activities for the Tank 6 test included:
- Setup of the test article and test support equipment
- Integration of the instrumented test article with Tank 6 data collection equipment and the Thiokol inflation controller
- Calibration and verification of data collection, evacuation of the chamber, thermal cycling and data collection
- Repressurization of the chamber, removal and storage of test articles, restoration of Tank 6 to pretest status
- Data reduction