70 meter antenna used for deep space communications in Goldstone, CA (Credit: NASA).

Reliable, efficient space communication networks are essential for NASA’s future exploration missions. NASA currently uses two communication systems to accomplish this: 1) the Near-Earth Space Network and 2) the Deep Space Network (DSN). The Near-Earth network facilitates communication between Earth’s ground stations and Low-Earth orbiting spacecraft. The DSN enables ground stations to communicate directly with deep space probes that travel past the moon.

The current architecture of the Deep Space Network consists of a set of individually functioning, large aperture (34 meter) antennas located in Australia, Spain, and California (U.S.) that are used to communicate with deep space probes. The proposed next generation DSN architecture consists of an array of hundreds of smaller aperture (12 meter) antennas, which can be coherently combined to provide equal or better performance than the present-day, single large aperture antenna system, but with more flexibility and at a much lower cost.

NASA Glenn Research Center’s Antenna, Microwave, and Optical Systems Branch (RCA) is evaluating potential sites for placement of the next generation DSN antennas. Glenn has been conducting Ka-band (the DSN frequency of operation) propagation and atmospheric studies for the last 10 years. These studies are essential for site characterization for the next generation DSN architecture and place Glenn in a pivotal role in deciding where the next DSN sites should be located.

Artist’s conception of the new Deep Space Network, consisting of an array of hundreds of small aperture antennas (Credit: NASA).

Since late 2005, Glenn’s RCA Branch has been working with the Jet Propulsion Laboratory (JPL) to characterize the site quality of candidate locations all around the world for the next generation DSN. The evaluations are performed using site test interferometers and mainly depend on how the weather affects antenna performance in an array environment at the Ka-band frequency (26 GHz – 40 GHz). These instruments directly measure the variations in the arrival time of a communications signal traveling between two locations separated by some distance. These variations are caused by water vapor in the atmosphere. Thus, a good site for the new DSN array is characterized by a small amount of rainfall and low water vapor content in the troposphere (lower layer of the atmosphere). These environmental effects will impact the quality and availability of the communications signal.

As of November 1, 2007, Glenn’s two-element site test interferometer has been deployed at Goldstone, CA (the current DSN location in the U.S.) for approximately six months. Six additional months of data collection are required to obtain statistically relevant information. Presently, a second set of interferometers is being designed at Glenn for deployment in New Mexico to provide a basis for the comparison of sites.

Photographs of the two-element site test interferometer presently deployed at Goldstone, CA., (BOTH -- Credit: J. Nessel).