Chuck Bednar for redOrbit.com – Your Universe Online
Cryptography, the practice and study of techniques for secure communication in the presence of third parties, could help prevent collisions among the thousands of commercial and spy satellites currently in orbit around the Earth. It would also maintain privacy, according to experts.
In an article written last month for Scientific American, Brett Hemenway, a research assistant professor with the University of Pennsylvania who focuses on cryptography, and William Welser IV, a space policy expert, explain how it can help avoid potential satellite collisions.
One such collision took place in February 2009, the authors explained, when the US Iridium 33 satellite and the Russian Cosmos 2251 collided and were both destroyed. Telescopes tracking the two probes from the ground indicated that they should have missed one another, but data from instruments on board either of them would have revealed that they were on a collision course.
That information was not used, however, because it was deemed to be top-secret.
“Satellite owners view the locations and trajectories of their on-orbit assets as private,” Welser and Hemenway wrote. Companies fear that sharing the exact positions of their satellites could help the competition determine the full extent of their capabilities, while governments are afraid that revealing such information could compromise their national security, they explained.
Yet even minor collisions could cause millions of dollars worth of damage. Debris can be knocked into the path of other satellites, spacecraft carrying a human crew, or even the International Space Station (ISS), the authors wrote. The 2009 incident served as a warning to officials to find a way to fix the problem, but without revealing too much information.
Adding a third party
“In the current working solution, the world’s four largest satellite communications providers have teamed up with a trusted third party: Analytical Graphics. The company aggregates their orbital data and alerts participants when satellites are at risk,” wrote Hemenway and Welser, adding that the arrangement “requires that all participants maintain mutual trust of the third party.”
Analytical Graphics, also known as AGI, makes commercial modeling and analysis software for the aerospace, defense, and intelligence communities. The company was founded in 1989 and is headquartered in Exton, Pennsylvania, though it also has offices located in Colorado, California, Washington DC, the UK, and Singapore. Its current CEO is Paul Graziani.
As more and more satellites are launched into orbit, and new companies and countries start to launch probes of their own, experts are looking for an easier way to keep track of the locations of different satellites. The belief, Hemenway and Welser said, is that adopting cryptography would eliminate the need for a mutually trusted third party altogether.
“In the 1980s, specialists developed algorithms that allowed many people to jointly compute a function on private data without revealing any number of secrets,” they wrote. “In 2010 DARPA tasked teams of cryptographers to apply this technology to develop so-called secure multiparty computation (MPC) protocols for satellite data sharing.”
“In this method, each participant loads proprietary data into its own software, which then sends messages back and forth according to a publicly specified MPC protocol,” the duo added. “The design of the protocol guarantees that participants can compute a desired output (for example, the probability of collision) but nothing else. And because the protocol design is public, anyone involved can write their own software client,” eliminating the need for mutual trust.
Such a plan is not without drawbacks, however, and foremost among them is speed. The calculations needed to determine the odds of collisions between two orbiting satellite would require intense data crunching that could take 90 seconds when performed on commodity hardware, Welser and Hemenway explained.
“As computing power improves, however, the MPC protocols will become more practical to use,” they added. “Now DARPA’s efforts are wrapping up, and a proof-of-concept algorithm is ready. At present, no one is using the protocols in practice, but cryptographers are looking for adopters of the technology.”
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