January 23, 2014
‘Space Cop’ Mini-Satellites Set To Patrol Interstellar Traffic Beat
redOrbit Staff & Wire Reports - Your Universe Online
Researchers from the Lawrence Livermore National Laboratory (LLNL) in California have developed and tested a series of ground-based mini-satellites that will be used to help control traffic in space.These so-called “space cops” were used by the LLNL team to capture a series of six images over a 60-hour period to prove that they can be used to alter the orbit of other probes traveling in low-earth orbit. The plan is to use the satellite network to help prevent increasingly-common collisions of satellites and space debris.
“Eventually our satellite will be orbiting and making the same sort of observations to help prevent satellite-on-satellite and satellite-on-debris collisions in space,” explained Lance Simms, a computational engineer at LLNL and the lead author of a paper appearing in a future edition of the Journal of Small Satellites.
According to Sharon Gaudin of Computerworld, potential collisions between non-operational satellites and other bits of space junk are becoming an increasing area of concern for probe operators. For example, last spring, NASA’s Fermi Gamma-ray Space Telescope had a near-miss with a defunct 3000-pound Cold War era Soviet spy satellite.
Without an “eleventh-hour maneuver” completed by engineers with the US space agency, “the two objects, which are speeding around the Earth at thousands of miles an hour in perpendicular orbits, were expected to come within 700 feet of each other,” she added. “A collision would have led to further problems since NASA calculated that, with a speed relative to Fermi's of 27,000 mph, a collision would have released as much energy as two-and-a-half tons of high explosives, destroying both spacecraft and further littering Earth's orbit with dangerous debris.”
The LLNL’s Space-Based Telescopes for Actionable Refinement of Ephemeris (STARE) mission is an effort to prevent these types of collision scares. STARE will consist of a constellation of low-earth orbit nano-satellites designed in order to refine the orbits of satellites and space debris to less than 100 meters.
Project leader Wim de Vries and the rest of the STARE team have used the ground-based satellite to refine the orbit of the NORAD 27006 satellite based on four observations made during the first 24 hours of its flight. In addition, they predicted its trajectory to within less than 50 meters over the next 36 hours, the researchers explained.
“By refining the trajectory of NORAD 27006 with their ground-based payload, the team believes they will be able to do the same thing for other satellites and debris once their payload is orbiting earth,” the team told LLNL's Anne M Stark in a statement. “The tools and analysis used to capture the images of NORAD 27006 and refine its orbit are the same ones that will be used during the STARE mission.”
“Accurately predicting the location of a satellite in low earth orbit at any given time is difficult mainly because of the uncertainty in the quantities needed for the equations of motion,” the researchers added. “These uncertainties and the incompleteness of the equations of motion lead to a quickly growing error in the position and velocity of any satellite being tracked in low earth orbit.”
In order to account for those errors, the Space Surveillance Network (SSN) needs to repeatedly observe all of the approximately 20,000 objects it tracks. However, since the positional uncertainty of an object is roughly one kilometer, there are approximately 10,000 false alarms for each anticipated collision.
“With these large uncertainties and high false alarm rates, satellite operators are rarely motivated to move their assets after a collision warning is issued,” the researchers said, adding that while the STARE mission is looking to reduce that margin of uncertainly to “100 meters or smaller,” the LLNL team was “able to reduce the uncertainty to 50 meters, well below the 100-meter goal.”
Image 2 (below): From left to right: Brian Bauman, Vincent Riot, Darrell Carter, Lance Simms and Wim De Vries have developed and tested land-based mini-satellites that eventually will be used in space to help control traffic in space. Photo by Julie Russell/LLNL