CubeSats on Space Patrol
November 2013's issue of Sky & Telescope features CubeSats, the low-cost nanosatellites that have piggy-backed on commercial launches for more than a decade. Here's one example, a constellation of miniature telescopes that will track space debris to a level not currently possible from the ground.
On September 13, 2012, an Atlas 5 rocket lofted a miniature telescope into low-Earth orbit, along with 10 other nanosatellites known as CubeSats that hitched a ride with the larger main payload. But one of these CubeSats had a different mission than the rest. Rather than look at the stars or back down at Earth, this satellite planned to look at junk. Space junk, to be precise.
Engineers at Lawrence Livermore National Laboratory and the Naval Postgraduate School built the tiny, GPS-enabled telescope, which is composed of three stacked Rubik’s Cube-sized boxes. Despite a small budget and basic parts, this CubeSat aims to pinpoint space-junk trajectories, besting the accuracy of ground-based tracking tools by a factor of 100.
The Space Surveillance Network, a global network of more than two-dozen ground-based optical telescopes and radar stations operated by the U.S. Joint Space Operations Center (JSOC) keeps tabs on every satellite and spacecraft in Earth orbit.
The system also tracks 20,000 pieces of space debris bigger than a baseball, each of which could cripple a satellite. Every day, JSOC issues alerts about potential collisions to space agencies and satellite operators. But trajectories of orbiting objects are difficult to track from the ground because they’re often accurate only to within a kilometer. Operators know that 9,999 out of 10,000 collision warnings are false alarms, so most are ignored.
“We want to lower the alarm notification from once per month to once per lifetime of the satellite,” says lead project scientist Vincent Riot (Lawrence Livermore National Laboratory). “[Commercial] satellites only have so much fuel onboard, and you don’t want to waste it” by moving them unless it’s essential.
The new miniature observatory, dubbed STARE (Space-Based Telescope for Actionable Refinement of Ephemeris), has two cameras: one takes pictures of stars to figure out the instrument’s position and orientation and the other snaps pictures of space junk. There’s always dark sky in space, so the telescope has virtually unlimited time to spot junk, and it can observe single objects several times each day. More observations lead to better predictions about whether a particular satellite is in harm’s way.
So far just one STARE CubeSat has launched; another two are scheduled to fly this fall. Riot and his colleagues calculate that a constellation of 18 of these orbiting observatories, to be launched one or two at a time and costing $30 million total, could survey the entire sky. Even though each CubeSat will last just a year or two, the cost of routinely replacing the microsatellites is dwarfed by the price tag for the launch of a conventional satellite, which typically costs several hundred million dollars.
Riot doesn’t expect his miniature creations to replace JSOC’s surveillance network, but he hopes the STARE satellites will add another layer of protection against catastrophic collisions between billion-dollar satellites and minimize the proliferation of junk in space.
Chris Palmer is a recent graduate of the Science Communication Program at the University of California, Santa Cruz. He begins a year-long health communications fellowship at the National Cancer Institute this fall.