Space junk problem: Is a solar-sail ship the answer?
- By Kevin McCaney
- Sep 26, 2011
A big reason NASA couldn’t predict exactly when and where its Upper Atmospheric Research Satellite (UARS) would fall to Earth last week was the effect solar activity had on its trajectory.
Heat from the sun can cause the upper levels of the Earth’s atmosphere, the thermosphere, to warm and “puff up,” which creates a drag on satellites, NASA says on its website. And because the effects aren’t consistent, scientists could only estimate the six-ton satellite’s re-entry.
UARS, a 20-year-old climate research satellite that had been out of commission for six years, finally came down, though the time and location is still uncertain. NASA estimates it hit between 11:23 p.m. EDT Sept. 23 and 1:09 a.m. Sept. 24 somewhere in the Pacific Ocean. The trail of debris that didn’t burn up in the atmosphere was probably spread over 500 miles.
NASA’s falling satellite wasn’t always a hunk of junk
But if solar activity can produce unpredictable results, it also can be harnessed, and NASA is planning to test one method that could, among other things, be used to clear orbital paths of the kind of space junk that UARS had become.
The agency recently announced plans to test a large solar sail as part of its an upcoming round of Technology Demonstration Missions aimed at improving space communications, deep space navigation and in-space propulsion capabilities.
Solar sails aren’t new, but this one will be seven times the size of any previously flown, which NASA says will increase its utility for jobs such as deep-space exploration, advanced geostorm warnings and removal of orbital debris.
The sail, expected to be deployed in 2015 or 2016, is being developed by LeGarde Inc., in collaboration with NASA and the National Oceanic and Atmospheric Administration.
Using the sun to provide thrust, the spacecraft would be able to navigate orbital paths and collected debris over a period of years. Future satellites also could have sails built in so that, when they’ve completed their missions, they can be taken out of orbit in an orderly way rather than becoming space junk themselves or falling to Earth and causing “Deep Impact” consternation.
NASA says the sail also would allow solar-storm satellites to be positioned farther from Earth than current such satellites, which would increase warning times of solar storms from 15 minutes to 45 minutes, and the sails could provide propulsion for deep-space probes.
Orbital debris, better known by the catchier name of space junk, is a growing problem in the upper atmosphere. The U.S. Space Surveillance Network tracks about 8,000 working and decommissioned satellites and other objects larger than 4 inches, and there are millions of other bits and pieces floating around.
The biggest problem isn’t that the debris will eventually fall to Earth, since the vast majority of junk would burn up. But with that much congestion, active satellites and spacecraft could collide with other objects. In 2009, a defunct Russian spacecraft crashed into a working Iridium satellite, taking the satellite out of commission and creating more space junk.
NASA, the military and other organizations have considered ways of getting rid of the debris, including using laser guns to slow down orbiting junk so that it would re-enter the atmosphere and burn up.
But a solar-powered space schooner that collects bits as it sails by might be an even more efficient way of cleaning up the litter.
Kevin McCaney is a former editor of Defense Systems and GCN.