Extended Aperture Systems
RTR No. 233-01-03-22
Quarterly progress Report 5/10/94
Inflatable Antenna Radiometer System: The systems study is continuing, with monthly meetings to summarize progress. The study is a Phase A type effort intended to determine the feasibility and engineering issues involved in a LEO large aperture radiometer satellite system based on inflatable technology. The study includes the following disciplines: antennas, structures, radiometry, controls, thermal, mission operations, packaging, and systems. The study is planned to be completed in about 1 month, with about 3 months to write up results and conclusions. Recent results of radiometer sensor error analyses caused a change in the system concept to a near-Nadir sensor for soil moisture (L-band) and surface temperature (C-band). The findings will be used for a submittal for a Phase B IN-STEP experiment for an in-space validation of the technology.
Laboratory Radiometer System: This 4.3 GHz precision radiometer system capable of operating in the total power, Dicke, and noise injection mode is designed to provide enabling technology improvements in radiometer sensitivity, component stability, and calibration techniques. The build phase is now completed and testing is underway. Problems have been resolved in powerline interference with the Dicke clock and gain variation when operating in the balanced Dicke mode. Allan variance techniques have been adapted for analyses of the noise errors of the radiometer.
S-band Measurements of Inflatable Reflector Materials: The S-band radiometer has been returned to operational form from being on loan to the University of Massachusetts. A control board lost in shipment needed to be rebuilt in this process. The system is now being fitted with a new data handling system and will soon be in calibration runs, preparing for June-July emissivity measurements of selected samples of inflatable materials to which reflecting metals have been deposited.
Other: In a phase-out effort from previous programs, tests are underway at the MMA near-field facility to determine the suitability of variable-geometry subreflectors at beam scanning for real-aperture geostationary antenna.
Meetings:
(1) Bruce Kendall presented this program and plans for F.Y. 95 to the Sensor Working Group meeting on May 5, at NASA LaRC.
(2) Several multidiscipline meetings have been conducted at LaRC (in addition to the system study noted above) to identify the key material and structures technology issues that are required to enable radiometer missions of extended duration. These meetings have involved several NASA Centers including JPL, and several universities as active participants. The key technology development issues will be highlighted in the F.Y. 95 Budget Submittal.
Issues: None