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Space

Why satellite mega-constellations are a threat to the future of space

A recent Indian anti-satellite test was hazardous, but plans for mass satellite launches by SpaceX and OneWeb could pose even greater risks in orbit.

Mar 29, 2019

When India shot down one of its own satellites with a missile this week, NASA administrator Jim Bridenstine was not impressed. “Creating debris fields intentionally is wrong ... If we wreck space, we’re not getting it back,” he said.

He was referring to the growing problem of space junk: dead satellites, leftover rockets, and debris from previous collisions that threaten operating satellites, human spaceflight, and even the International Space Station.

It’s still too early to have good enough data on the debris cloud from India’s anti-satellite test, and tracking firms will be monitoring the area closely. The Pentagon has its eye on 250 separate pieces at the moment, an official told Reuters. But while it is likely that the collision created a cloud of metal fragments, it happened at a relatively low altitude. The majority will be dragged down into Earth’s atmosphere within months.

And while Bridenstine wasn’t happy about the India test, space debris experts currently have much bigger concerns. Proposed “mega-constellations” of satellites that sit higher up are likely to cause far greater and longer-lasting problems.

Around half of all the debris in space today comes from just two events: a 2007 anti-satellite test by the Chinese government, and an accidental 2009 collision between two satellites.

But there are plans to make low Earth orbit vastly more crowded. For example, satellite startup OneWeb wants to put 900 small satellites into orbit to provide broadband internet connections to places where it’s not currently available. SpaceX, meanwhile, has been granted approval to scatter 12,000 satellites through low Earth and very low Earth orbit. Other firms, such as Telesat and LeoSat, have similar, smaller-scale plans.

This sudden influx of new arrivals has the potential to cause serious problems. In a paper presented at the 69th International Astronautical Congress in Bremen, Germany, last October, Glenn Peterson, a researcher at the Aerospace Corporation, calculated the effect of introducing thousands of satellites for communications, surveillance, and Earth observation into the low Earth orbits where the majority of space junk is located.

If all the mega-constellations launched, Peterson found that current tracking technologies would generate over 67,000 “collision alerts” annually. Operators would then have to choose whether to make hundreds of precautionary satellite maneuvers a day, or risk the small chance of a collision.

In January, synthetic aperture radar imaging startup Capella chose to move its only satellite, Denali, when faced with a possible “conjunction” with a commercial CubeSat. “The probability of a collision went up to 12 percent,” says Capella CEO Payam Banazadeh. “That’s a big risk and we took it very seriously.”

It was the first time Capella had used Denali’s thruster, and the whole process took several days. Future maneuvers would be quicker but would still hit his company’s bottom line—especially if they had to be carried out multiple times a day, says Banazadeh: “Instead of collecting imagery over a certain area, you’re changing your orbit, you’re taking power and resources to make that maneuver, and then you’re taking time to check it out afterwards.”

But if even just one missed alert turned out to be correct, it could be catastrophic.

The 2009 “conjunction” between an Iridium communications satellite and an inactive Russian satellite “could have been predicted, but the probability value did not stand out from many other conjunctions faced by Iridium that day,” writes Peterson in the paper.

No one is suggesting that Iridium chose not to move the satellite in order to save money or extend its operational life, but the orbital environment is only becoming more crowded and more competitive.

“If I am being a good steward of space, it doesn’t mean others will be,” says Banazadeh. “It might take only a few bad actors along the way to make it a lot worse for everyone involved.”

Improved ground-based radar, known as the Space Fence, should be coming soon to the US’s Space Surveillance Network. This should improve the accuracy of predictions about possible collisions. But that technology is a double-edged sword, points out Peterson. Where today’s radars can only reliably track the 20,000-odd pieces of space junk larger than 10 centimeters, tomorrow’s sensors will reveal fragments down to 2 centimeters in size—numbering perhaps 200,000.

Peterson calculates that even if all objects are tracked accurately, the larger constellations will still face several hundred false alerts every year. Some operators might be tempted to risk a low-probability conjunction with something the size of a screw, even if it is traveling at over 30,000 kilometers per hour.

“At the moment, there are no international rules that can be enforced properly, in all the countries and for all the companies,” says Banazadeh. “There is a lot of self-regulation, and self-regulation in space is really, really dangerous.”