By Dr. Gary L. Deel, Ph.D., J.D.
Faculty Director, School of Business, American Military University
The Space-Based Infrared System (SBIRS) is a constellation of satellites — currently four with two more tentatively scheduled for future deployment — used primarily by the United States military for early missile warning and defense.
The primary mission of the SBIRS constellation is to assist the U.S. Air Force with early missile warning and defense in the event of a long-range attack. The details of most of the individual satellite orbits are classified for national security reasons, but the constellation includes a mix of geostationary satellites (GEO) and sensor payloads on highly elliptical Earth orbit satellites (HEO).
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Details available on SBIRS-GEO satellite communications systems are limited, but the platforms utilize secure communications networks, GPS, and an anti-spoof module (SAASM) to ensure GPS relay accuracy. The satellite constellation is operated by the 460th Space Wing located at Buckley Air Force Base in Colorado.
The Lockheed A2100 platform, which was used for these satellites, generally uses a 3kW solar array to generate power for the spacecraft and a 100 amp-hour battery to store excess power the systems do not need at any given time. Based on the launch vehicle, each SBIRS-GEO satellite weighs between 9,259 pounds (4,200 kg) and 10,803 pounds (4,900 kg.)
To protect the sensitive infrared instruments onboard each SBIRS-GEO spacecraft, the A2100 platform deploys a light shade that blocks exposure to direct sunlight. The Short Schmidt telescopes also feature passive thermal cooling mechanisms to prevent overheating.
The A2100 platform uses star trackers, earth/sun sensors, and inertial measurement systems to determine attitude with an accuracy better than 0.05 degrees.
The A2100 platform uses small thrusters and reaction wheels to adjust its attitude in orbit. These control systems stabilize the spacecraft along three axes.
Data handling on the SBIRS-GEO satellites is another highly secretive area. However, other satellites that have employed the Lockheed A2100 bus, such as the GOES-R class spacecraft, have used a RAD-750 flight computer manufactured by BAE Systems, and PID 238 communications protocols.
Propulsion on the A2100 platform is usually provided by a LEROS-1c main engine (made by Moog ISP). The engine uses mixed oxides of nitrogen and hydrazine as propellants; the bus can hold about 5,511 pounds (2.5 metric tons) of propellant, and the engine is capable of delivering between 386 N and 470 N of thrust.
The SBIRS is just one of many tools that the U.S. government uses to keep its citizens safe. Early missile warning systems are an indispensable part of our national defense strategy, and future missions to maintain and bolster these efforts deserve public support.
About the Author
Dr. Gary Deel is a Faculty Director with the School of Business at American Military University. He holds a J.D. in Law and a Ph.D. in Hospitality/Business Management. Gary teaches human resources and employment law classes for American Military University, the University of Central Florida, Colorado State University and others.