But other experts doubt feasibility of plan for tracking near-Earth space rocks
Go tiny or go home. That’s one suggestion for building telescopes to find a city-smashing asteroid before it finds us. A fleet of pint-sized satellites orbiting the sun could track down the majority of asteroids that threaten the Earth, researchers propose online March 29 on arXiv.org. Some experts worry, however, that the plan has holes big enough to drive an asteroid through.
Five miniature observatories evenly spaced just inside the orbit of Venus would let NASA meet its congressional mandate to discover 90 percent of asteroids wider than 140 meters by 2020, says Michael Shao, an astrophysicist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and colleagues. Whereas a single dedicated space telescope would take eight to 10 years and about half a billion dollars to find the same space rocks, Shao contends that his armada could do it in three years for about one-tenth of the cost.
“There’s almost no scientific merit to what they’ve presented,” says astronomer Timothy Spahr, former director of the Minor Planet Center at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. “If somebody was going to come along and solve this problem for one-tenth the price, I would love it,” he says, but a flotilla of teeny telescopes isn’t going to cut it.
Shao proposes mounting telescopes on CubeSats, miniature satellites typically just 10 centimeters on a side (SN: 9/10/11, p. 18). CubeSat technology has come a long way in the last few years, he says, and researchers can now build orbiting observatories with off-the-shelf parts. Image processing algorithms designed to detect quickly moving asteroids can find fainter rocks than standard techniques on larger telescopes, Shao says.
Going to space makes up for some of what’s lost by using smaller telescopes. There’s no moon or weather to worry about and the lack of atmosphere, which blurs images of space, lets the algorithms get more precise positions than from the ground. Moving to a Venus-like orbit lets the fleet whip around the sun faster, allowing the satellites to see more of the sky in less time than they could near Earth.
The claim that CubeSats can do the work of a traditional space telescope for a tenth of the cost sounds a little too good to be true, says Eric Christensen, an astronomer at the University of Arizona in Tucson. “It’s a very interesting idea,” he says. “But they’ve set a very high bar for themselves.”
One of the main challenges, he says, is that the radio links for any satellite leaving Earth orbit can’t keep up with the rate of incoming data; all image processing must be done onboard without human intervention. Christensen is also concerned about how the CubeSats would map out precise orbits of asteroids with limited observations.
Spahr doesn’t see how the minisatellites could detect so many asteroids in three years. “There’s zero percent chance of that happening,” he says. Many of the asteroids are on five- to six-year orbits that keep them far from the sun — and too faint to see — most of the time. He’s also not convinced that the CubeSats would be able to see objects that are as faint as Shao and collaborators say. The algorithms they plan to use are also quite complicated, he says, requiring billions of calculations per image. “You don't do billions of calculations on a spacecraft that’s the size of your chest,” says Spahr.
But Shao is optimistic. Computer simulations show that, on average, the CubeSats can get about 20 observations for each large asteroid, he says. A recent trial run of the new algorithms at Palomar Observatory near San Diego turned up a fainter asteroid with more precise positions than could be done with current techniques. He’s also confident that, given the latest advances in digital circuitry, the CubeSats will be up to the complex computational challenge. Shao’s team is currently forging ahead with tests using a small ground-based telescope that he says will help the researchers figure out how to do this in space.
Everyone does agree on one thing: Current efforts can’t hit the 90 percent detection mark set by Congress for at least another 20 years. “We’re simply not going to do any better unless we throw a ton of money at the problem,” Spahr says. Unfortunately, the congressional mandate did not come with funds. For fiscal year 2014, NASA spent about $40 million on observations of near-Earth objects; a traditional space telescope that could make rapid progress would cost at least 10 times as much.
M. Shao et al. A constellation of CubeSats with synthetic tracking cameras to search for 90% of potentially hazardous near-Earth objects. arXiv:1503.07944. Published online March 29, 2015.
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