Space Network Ground Terminal in Guam. Credit: NASA
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NASA's Ground Stations: Solid Footing on the Ground for a Better View of the Sky

By Matthew D. Peters

June 18, 2018

This blog post was written prior to a reorganization of ESC’s projects and networks in support of the agency’s commercialization effort. Though accurate at the time of publication, it is no longer being updated and may contain broken links or outdated information. For more information about the reorganization, click here.

Since the beginning of humankind’s exploration of our solar system, we have needed a way to communicate with and track our spacecraft. Today, the Space Network (SN) provides this important service. The SN is a system of ground-based antennas and satellites in orbit around Earth. Without the SN, missions such as the Hubble Space Telescope or the International Space Station could not communicate their unique scientific discoveries with us. Space communications and tracking technology has experienced many changes before reaching the system we have today.

The first tracking system in the United States was a series of ground stations known as Minitrack. Minitrack was so called because it used smaller, lighter transmitters than other radio-frequency systems at the time. It became operational in 1957, nearly a year before the establishment of NASA. At that time, in order to communicate with Earth, orbiting spacecraft needed to have an unobstructed view of a station on the ground with antennas capable of receiving the satellite’s signal. Minitrack consisted of 10 stations situated around the world to maximize contact with orbiting spacecraft such as Explorer 1, the first satellite the United States put into orbit.

As time progressed, the U.S.’s space communications needs changed. To accommodate higher frequency radio signals and incorporate new communication techniques, NASA upgraded the Minitrack stations and built new stations with parabolic antennas. This established the Spacecraft Tracking and Data Acquisition Network (STADAN) in 1960. The added stations also increased the duration in which a spacecraft could stay in contact with the ground. In addition to supporting NASA spacecraft, STADAN supported commercial satellites such as Intelsat I, the first privately owned satellite placed in geosynchronous orbit.

Geosynchronous orbit is an important concept in space communications. In this high-altitude orbit, a satellite always stays above the same relative point on the ground as the planet rotates, so that it can remain in constant contact with a ground station. Instead of needing to move to track these satellites, ground antennas can remain fixed which makes them easier to operate and maintain.

By the early 1960s, human spaceflight became a priority for the United States in the hopes of putting an American on the moon. This created a need for real-time voice communication. For this purpose, a separate network of ground stations known as the Manned Space Flight Network (MSFN) was developed. STADAN remained operational for uncrewed missions.

By the 1970s, NASA had achieved its goal of a crewed lunar landing, and the frequency of crewed missions slowed considerably. There was no longer a need for two separate networks. NASA combined STADAN and MSFN, decreasing the number of ground stations into the more efficient Spaceflight Tracking and Data Network (STDN).

The STDN provided the highest capacity, most accurate, and reliable space communications of its day, but no matter how good a ground-based network is, it will always be constrained by the curvature of Earth. Without line of sight to a ground antenna, communication was not possible. This meant spacecraft only had about twelve minutes of coverage per 90-minute orbit.

In order to increase communications coverage of Earth, a network of geosynchronous satellites known as Tracking and Data Relay Satellites (TDRS) were built. These satellites, along with the White Sands Ground Terminal (WSGT) in White Sands, New Mexico, comprised the SN, which became operational in the 1980s. Rather than needing line of sight to a ground station, spacecraft in low-Earth orbit only need to see one of the TDRS. The satellites are placed at 120 degree angles around the globe so that at least one of them is visible to orbiting spacecraft at all times. The TDRS routes the spacecraft’s signals down to WSGT, vastly increasing the communications coverage of Earth. This new configuration eliminated the need for a large portion of the existing ground stations. Many of the ground stations became part of the Near Earth Network, which provides communications support to science missions that do not require around-the-clock coverage.

Even with this increased coverage, there was a “blind spot” in the network over the Indian Ocean known as the zone of exclusion. When a spacecraft orbited over this area, it had no contact with Earth. The Guam Remote Ground Terminal was built in 1998 in order to close this gap, making nearly 100 percent coverage possible.

Over the decades, the SN has expanded to support more missions and provide higher data rates. There are now 10 TDRS in operational use. Automation within the ground stations has increased to make them more efficient. The SN provides up to 600 hours of customer service every day for a wide range of missions.

NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages and operates the Space Network. NASA’s Space Communications and Navigation program (SCaN), part of the Human Exploration and Operations Mission Directorate at the agency’s Headquarters in Washington, provides strategic and programmatic oversight for the network.