When India shot down one of its own satellites with a rocket this week, NASA administrator Jim Bridenstein was not surprised. However, he expressed his displeasure: "It is wrong to intentionally create space debris fields … If we litter space, we will not return it." The problem of space debris is only getting worse: dead satellites, spent rockets, debris from previous collisions - all this threatens working satellites, people in space and even the International Space Station.
It is too early to talk about the debris cloud left over from the Indian test. The Pentagon has an eye on 250 separate units, Reuters reported. However, while the collision likely produced a cloud of metal fragments, it happened at a relatively low altitude. Most of them will fall to Earth within a few months.
How much debris is in orbit?
And while Bridenstine was not happy with the Indian test, space debris experts have a lot more problems. The alleged "mega-constellations" of satellites could lead to much more serious and lasting problems.
About half of all space debris today comes from just two events: the Chinese government's anti-satellite test in 2007 and the accidental collision of two satellites in 2009.
However, there are plans to make low Earth orbit more populous. For example, startup OneWeb wants to launch 900 small satellites into orbit to provide broadband internet connectivity where it is not currently available. At the same time, SpaceX received permission to deploy 12,000 satellites in low and very low Earth orbits. Other companies like Telesat and LeoSat have similar plans.
A sudden influx of recruits can cause serious problems. In a paper presented at the 69th International Astronautical Congress in Bremen last October, Glenn Peterson, a researcher at the Aerospace Corporation, calculated the implications of deploying thousands of satellites for communications, surveillance and reconnaissance into low-earth orbit, where most of the space debris is located.
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If all the mega-constellations are up and running, Peterson estimates that state-of-the-art tracking technologies will generate over 67,000 "collision warnings" annually. Operators will then have to choose between hundreds of satellite warning maneuvers per day, or risking a low probability of collision.
In January, synthetic aperture radar imaging company Capella decided to move its only satellite, Denali, when it faced the possibility of crashing into a commercial Cubsat. “The probability of a collision was around 12%,” says Capella CEO Payam Banazadeh. "This is a big risk and we took it very seriously."
This was the first time Capella had used a Denali engine, and the entire maneuver took several days. Future maneuvers will be faster, but will still require attention - especially if they have to be done multiple times a day, Banazadeh says. "Instead of collecting images in a specific area, you change the orbit, waste time and resources, and then check post facto."
Yet, if even one missed alarm turns out to be correct, the consequences can be disastrous. Nobody imagined that Iridium could beat the satellite and save money, but the orbital environment is becoming more populous and competitive.
Very soon, the United States will have an advanced ground-based radar network known as the Space Fence. It should improve the accuracy of predictions about possible collisions. But this technology is a double-edged sword, Peterson says. Where modern radars can reliably track only 20,000-plus pieces of space debris larger than 10 centimeters, sensors of the future will be able to detect fragments up to 2 centimeters in size, and their number will reach 200,000.
Peterson calculated that even if all objects are tracked accurately, larger constellations will encounter several hundred false alerts each year. Some operators may be tempted to take the risk and go into a close aisle with an unlikely collision, but any "encounter" will be disastrous at 30,000 kilometers per hour.
Ilya Khel