Advanced Communications Capabilities for Exploration and Science Systems (ACCESS)
The Advanced Communications Capabilities for Exploration and Science Systems (ACCESS) project operates, maintains, and sustains NASA’s government-owned, contractor-operated ground- and flight-based systems. The project leverages NASA’s 60 plus years of communications and navigation expertise to ensure that missions can send their data back to Earth for scientific discovery.
The ACCESS project is a service provider to the Exploration and Space Communications’ new Near Space Network, which orchestrates mission communications services through both government and commercial assets. For missions utilizing NASA’s government-owned, contractor-operated systems, NSN connects them with ACCESS services.
For increased efficiency, the ACCESS project combined NASA’s historic near space networks: the Space Network, a constellation of Tracking and Data Relay Satellites and associated ground stations, and the Near Earth Network, a global fleet of government and commercial direct-to-Earth ground stations.
TDRS FLEET OPERATIONS
NASA’s Tracking and Data Relay Satellite (TDRS) fleet consists of three generations of spacecraft spanning over 35 years. Each successive generation improved upon the last with additional RF band support and increased automation. There have been 12 TDRS to reach orbit. The first TDRS launched April 4, 1983, and was designed for a mission life of 10 years. The robust satellite lasted 26 years before it was decommissioned in 2009. While they were being built, and prior to launch, TDRS were referred to by letters. After launch, they are referred to by numbers. For example, the first TDRS was called TDRS-A prior to launch, and TDRS-1 once it became operational. The last in the third generation of TDRS, TDRS-M (now called TDRS-13) was launched August 18, 2017, replenishing the fleet for many more years to come.
While a space-based communications network is useful for all sorts of missions, one of the largest early drivers for the network’s development was human space flight. When the network was first being conceived, the Space Shuttle’s development was also on the horizon. A craft that could launch, return to Earth, and launch again later meant crewed missions could become much more frequent. The needs of living people in space to complete their tasks are much greater than the needs of a satellite. One of these needs is increased connectivity with Earth. Once the International Space Station was completed, and humans began to occupy space on a continuous basis, it became necessary to provide two-way communications 24/7 for human health and safety.
What makes the network’s continuous communications possible is TDRS’s geosynchronous orbit. Geosynchronous orbit is a high-altitude orbit of about 22,000 miles. With this orbit, TDRS remains above the same relative point on the ground as the planet rotates. This means TDRS have a wider view of Earth and near-Earth space where most spacecraft operate than the lower-orbit-user spacecraft do. Spacecraft such as the International Space Station or the Hubble Space Telescope send their signals to a TDRS, then the TDRS relays the signal back down a ground station.
The TDRS are grouped in three strategic locations: over the Indian Ocean, the Atlantic Ocean, and the Pacific Ocean. This allows them to relay signals around what is known as “zones of exclusion.”
Now, with NASA’s upcoming Artemis missions, sending the first woman and first person of color to the Moon with an eye towards Mars, connecting our astronauts to Earth is more important than ever. TDRS will be a critical component during Artemis mission launches.