Space Situational Awareness

AFSPC explores Allen Telescope Array for Space Surveillance

View official AFSPC press release here

An important and high visibility mission of the United States Air Force Space Command (AFSPC) is Space Surveillance. Knowing exactly where orbiting objects are located in space at any given instant is key to ensuring safe space operations. The significance of the mission has become even more acute with the recent collision of an Iridium Satellite and an inoperable Russian Cosmos Satellite, which destroyed both satellites and created two large fields of space debris. This debris will be a risk to other satellites for years to come as the debris fields expand and their orbits degrade toward Earth.

AFSPC is one of a few organizations responsible for obtaining and maintaining the awareness needed for successful and safe space operations. The command develops, maintains and shares a comprehensive and accurate catalog of orbiting space objects, while constantly seeking methods to improve their Space Surveillance Network (SSN), a global network of radar and optical sensors that detect and track orbiting space objects. AF Space Command is exploring opportunities in academia and the commercial sector that could provide suitable cost-effective means for augmenting the Space Command's Space Surveillance mission.

The Allen Telescope Array (ATA), located at the Hat Creek Radio Observatory, 290 miles northeast of San Francisco, California is a tool with strong potential for use by AFSPC in support of the Department of Defense’s Space Surveillance mission. The ATA is a radio interferometer that is dedicated to cutting-edge astronomical research. This array of antennas is optimized to receive and process a very wide portion of the radio spectrum and can stare at many areas of the sky at once.

AFSPC, through the Space Innovation and Development Center (SIDC), is currently researching the possible use of the ATA to augment the already extensive sensors of the Space Surveillance Network, potentially leveraging the array to help increase space situational awareness. Initial demonstrations show promise for the ATA to track transmitting satellites in Low Earth Orbit, Medium Earth Orbit and, most promising, in Geosynchronous Orbit (GEO), which is home to the most costly, highly-utilized, and vital satellites that orbit the earth. A collision and subsequent debris field in GEO could permanently remove the GEO belt from worldwide use.

AFSPC is working with the SETI Institute, and its partner, the Radio Astronomy Laboratory at the University of California, Berkeley. These partners currently operate the ATA. The effort is to demonstrate the array’s capability of accurately surveying the GEO belt by demonstrating the array’s capability of precisely locating objects in that area, in an effort to avoid a devastating collision in GEO. The ATA may prove to be a viable and sensitive SSN sensor, capable of all-weather, day and night operations, and will hopefully lead to improved space safety.

Questions and Answers -- Use of the Allen Telescope Array for Space Surveillance

Q1. What is the degree to which SETI Institute is collaborating with the Air Force here?
A1. AF Space Command is exploring opportunities in academia and the commercial sector that could provide suitable cost-effective means for augmenting the Space Command's Space Surveillance mission. The Allen Telescope Array (ATA) could be an important tool to support the Department of Defense’s Space Surveillance mission. The significance of this mission has become even more acute with the recent collision of two satellites and the resulting danger posed to the International Space Station, the Hubble Telescope and other satellites in low earth orbit.

Q2. How can the Allen Telescope Array complement the Air Force's existing sensors?
A2. The ATA has numerous unique capabilities for astronomy and SETI research, and because it is the first instrument of its type, some of its capabilities may enhance Air Force daylight space surveillance capabilities.

Q3. What would SETI Institute get from such a collaboration?
A3. If the ATA proves to be a valued contributing sensor, it could provide a potential additional use of the array and, concurrently, an additional source of long term funds to assist in the operations and support cost of sustaining the array.

Q4. What tasks have been done by the ATA for AFSPC?
A4. The initial task completed was an assessment of the capability of the array to accurately track orbiting objects, specifically GPS satellites. The GPS satellite constellation was selected because the location of these satellites in space is well known. Therefore by utilizing this data, the accuracy of the array’s observations could be assessed. The ATA has observed GPS satellites to a relatively high accuracy, and the accuracy is expected to improve as the array’s algorithms for satellite positional determination are refined and as the array’s configuration is extended by the addition of more antennas.

Q5. What do you foresee as some future tasks the ATA may conduct for AFSPC?
A5. Future tasks for the ATA will include demonstrating the capability to track objects besides GPS. Additionally, tasks such as tracking objects during the daylight hours, or with the sun or moon in field of view, will further demonstrate the capabilities of the ATA as a sensor for the SSN. These demonstrations are important because many of the current sensors have difficulty with light-pollution, which hampers observations. If the ATA can demonstrate its capability to precisely locate satellites in all orbits, during day or night, it increases it significance as a SSN sensor, and increases the overall safety of space.

Q6. What are the future plans for the ATA?
A6. The SETI Institute and its partner, UC. Berkeley, plan to increase the size of the array in stages. As the number of array elements increase, the sensitivity and capability of the array also increases. This helps for both scientific and astronomical research, and will also increase the capabilities of the ATA as a SSN sensor.

Q7. What are the plans for securing the funding needed to fill out the antenna array?
A7. The SETI Institute and its partner, UC. Berkeley, have plans to increase the size of the array in stages. Dependent upon the availability of funds, the first expansion to 128 dishes with additional control building and other support components, is expected to cost between $18 -$20M. The next 128 (256 total) is budgeted at an additional $20M ($156K per dish).

Q8. Why is the Air Force interested in using this sensor as opposed to others?
A8. The unique design of the Allen Telescope Array (ATA) is intriguing to the Air Force because it provides a similar sensitivity to a very large dish antenna, but at a cheaper cost for the same collecting area. This is known as a Large-Number Small-Diameter concept, and fits well with the Air Force’s goal of conducting its mission in a fiscally responsible manner.

The AF working with the ATA may be a natural win-win relationship. Specifically, the AF requires additional sensors to observe orbiting objects during the daytime, because many of its Electric-Optical (EO) sensors are affected by light pollution during the day, which limits the observations that can be conducted at that time. The ATA's primary missions, searching for extraterrestrial life and scientific research, are most often conducted at night, because this gives them the best pointing stability and avoids decrease in the strength of narrow band signals due to scattering by the solar wind. Operating the ATA during the daylight hours for the AF allows the array to be more fully utilized while not detracting from its scientific and SETI goals, and may provide the AF with vital daytime observations.

To be utilized as a viable long-term sensor for the SSN, the ATA has to demonstrate many characteristics besides accurately being able to observe orbiting satellites. Its data have to be consistent, timely, precise, sensitive, and have a throughput that makes it worth the cost of a long-term investment by the Air Force. If these factors demonstrate themselves, the ATA may be integrated into the SSN to help to ensure the safety of flight of objects in space.