Title: Large Aperture, Solid Surface Deployable Reflector
Primary Author: Taylor, Robert
Organization: CTD, Composite Technology Development
Co-Author(s): Robert Taylor, Dana Turse, Phil Keller, Larry Adams
The goal of the this NASA Advanced Component Technology (ACT) program is to develop an off-set fed, TEMBOÆ continuous composite surface deployable reflector for earth science applications. This type of reflector will offer a parabolic surface accurate enough for RF science measurements up to Ka band, including a clean aperture with no edge effects. The reflector will package for launch in 1/3 the deployed width and can be sized for deployed apertures from 2.5m to 6m. A 4m development reflector is being built and tested to demonstrate these capabilities.
The solid surface deployable reflector technology could be applied to any RF measurements that require an antenna reflector to concentrate the signal. This includes radiometer and radar applications for measurements of sea surface roughness, sea salinity, cloud profiling, atmospheric limb sounding, and snowpack characteristics. The 1/3 width packaging capability of the reflector allows a larger aperture for higher resolution or higher gain/noise ratios in the same available launch volume. The reflector could be mounted to the RF instrument at the centerline keel or from an edge rib depending upon mission requirements. Also, to reduce the stowed length, the reflector could fold in half after reducing the width with a corresponding increase in complexity.
Recent earth science missions including AQUARIUS and ACE have performed trade studies to consider ways to increase the available aperture to meet science goals. However, the cost, complexity and risk of existing deployable reflectors for these missions resulted in the selection of a smaller rigid reflector for the final flight configurations.
The operating frequencies chosen for different earth science measurements are dictated by the physics of each type of observation. The resolution obtained for the measurement is proportional to the aperture and inversely proportional to the frequency. Therefore, for similar resolution in the data taken, the aperture of the instrument should decrease as the frequency increases for different missions. However, existing and planned earth science RF missions instead have been a step function, with two large aperture missions planned, and the remaining missions falling at almost the same aperture, regardless of frequency. The reasonable explanation is that missions have selected the aperture based on the available types of reflectors. The very large apertures are deployable mesh reflectors for SMAP and DESDynI and the remainder are rigid reflectors. Rigid reflectors can only be sized in most cases to 1m because these RF missions are either dedicated small satellite missions or smaller payloads on large earth science platforms. For AQUARIUS and WindSat, the small launch vehicle envelope was maximized to provide an aperture of roughly 2.5m.
This ACT program is intended to provide an alternative reflector for RF measurements, providing larger apertures from L through Ka bands. The large aperture, solid surface deployable reflector also meets the needs of science missions by providing a clean, continuous aperture for consistent data across the field of view. Significant progress has been made towards these goals, with a reflector surface and backing structure fabricated and tooling built to package and deploy the reflector.