Gimbaled array of four 1-m diameter inflatable membrane antennas developed by Glenn and SRS; installed at Georgia Tech.

To improve the quality and reliability of space communication, NASA’s Glenn Research Center is developing lightweight, deployable antenna technology. The Antenna, Microwave and Optical Systems (RCA) Branch at Glenn is leading two projects in this area: Inflatable Membrane and Hybrid Inflatable antennas.

Glenn’s RCA Branch is currently developing an agency-wide large deployable antenna roadmap, which will focus the efforts of all NASA centers in this area. They are collaborating with Langley Research Center, the Jet Propulsion Laboratory and the following organizations on the deployable antenna projects: SRS Technologies, John Hopkins University, ILC Dover, Cornerstone Research Group, Infoscitex and Mevicon.

SRS 2.5 meter Inflatable Radome Antenna System Undergoing evaluation in Glenn's near-field antenna range.

Three years ago, Glenn began pursuing the development of large, lightweight deployable antennas. The ultimate objectives of the project are to develop a deployable antenna technology that has the following characteristics:

1. Surface accuracy consistent with Ka-band operation, possibly implying active surface control (surface can be adjusted to compensate for factors like thermal distortion)
2. On-orbit rigidization (antenna becomes stiff)
3. Aerial densities (antenna mass divided by surface area) below 2 kg/m2, preferably below 1.0 kg/m2
4. Minimal risk deployment mechanism, possibly with back-up
5. Minimal spacecraft power requirements for deployment
6. Articulated feed (provides adjustable phase and possibly amplitude) for fine beam pointing
7. Deployed-to-packaged volume ratios exceeding 10:1

4 X 6 meter SRS inflatable membrane reflector, with rigidized torus, positioned for testing in Glenn's near-field antenna range.

Of the two types of inflatable antennas, the inflatable membrane is the furthest in the development cycle since a 4 x 6 meter prototype has already been built. This antenna is made of thin polymer films that form a reflector surface and a canopy. The goal is to have the antenna membrane rigidize and maintain its shape once it has been deployed in space.

Inflatable membrane antennas offer several key advantages over other types. One possible advantage is that the primary reflector surface is a smooth, true parabolic surface, which is unlike mesh-type reflector systems that are composed of small, flat triangular sections to make them appear parabolic. The antenna’s low aerial density makes it very lightweight. Finally, the packaging efficiency (ratio of deployed to package volume) is high since the expandable antenna can be compacted to fit inside a small package.

Hybrid inflatable antenna concept using a novel shape-memory polymer composite reflector system for deployment.

The second type of antenna is known as the hybrid inflatable antenna. This antenna has a shape memory polymer composite surface and no inflation is necessary. When the antenna is deployed, solar energy or embedded wire heats the material changing it from a plastic to an elastic state. Once the material cools, the material returns to a plastic state and is ready for use as a sturdy antenna.

Hybrid inflatable antenna concept using a novel shape-memory polymer composite reflector system for deployment.

Similar to the inflatable membrane antenna, the hybrid inflatable is a true paraboloid. However, it does not require inflation or post-deployment rigidization because of its shape memory polymer material. The concept also involves a fixed, rigid, back-up reflector in the event of an unlikely deployment issue.

Inflatable antenna technology is vital to extended missions that require high data rates for space communication. In the near future, this technology may be used to achieve communication rates approaching 1 GBPS from a Mars relay satellite to Earth. This will enhance NASA’s continued efforts to realize the Vision for Space Exploration by exploring the moon, Mars and beyond.