On March 27, India conducted an anti-satellite missile test and successfully destroyed a live satellite sitting 186 miles above the surface, in low Earth orbit (LEO). This means the world’s biggest democracy is also the fourth nation in the world with anti-satellite missile capabilities (after the United States, Russia, and China). The news was not greeted warmly: The Union of Concerned Scientists issued a statement expressing, well, concern about the test as an example of increased militarization of space. Planet Labs, a long-term partner of the Indian Sauce Research Organization (India’s space agency), condemned the test and emphasized that space should be used for “peaceful purposes.”
But the fiercest criticisms came on Monday by none other than NASA administrator Jim Bridenstine, during a meeting with NASA employees for an open Q&A session. Bridenstine called the test and the orbital debris field it left in its wake “unacceptable,” and said “NASA needs to be very clear about what its impact to us is…It’s is not acceptable for us to allow people to create orbital debris fields that put at risk our people…These activities are not sustainable or compatible with human spaceflight.”
At the Q&A session, Bridenstine explained that NASA and the military had assessed the debris field last week, and determined the risk of small debris impacting the ISS was increased by 44 percent, over a period of 10 days. (This came in spite of previous comments from Lieutenant General David Thompson, vice commander of U.S. Air Force Space Command the week before, who said, according to Reuters, that the ISS at that point was not at risk.) Bridenstine said NASA had identified about 400 pieces of orbital debris created by the event (and in all likelihood, there were probably 10 times as many fragments produced). Only about 60 pieces were large enough (at least 10 centimeters in diameter) to be actively tracked.
So what exactly does this “44 percent increase in risk” mean? How did NASA come up with this number, and what sort of danger does this pose to the astronauts on board the space station? NASA declined to comment or make any expert available for questions, but we know that assessing orbital debris threats is not a clear-cut process. The main issue “is that we don’t have precise knowledge of where things are in orbit,” says Raymond Sedwick, a University of Maryland aerospace engineer and the director of the Center for Orbital Debris Education and Research. While the location of operational satellites are obviously known and tracked by whomever is operating the satellite itself, decommissioned satellites and pieces of debris have to be tracked by the Air Force, and depending on the object and whatever sensor is tracking its movements, the estimated location ranges to within a few hundred meters or as wide as a several kilometers.
“If your estimate of the velocity is off, then [the object] is moving faster or slower than you think, so over time it ends up moving more or less than you think,” says Sedwick. At an orbital velocity of, say, 7,500 meters per second, an error of only a few centimeters per second might sound low, but it will cascade over time. After just a single day, the object could be several kilometers away from where you would expect it to be. Compounding this process are factors like atmospheric drag and object orientation. And not all objects are measured every single day. As a result, you can hardly ever know the exact whereabouts of an object at a given moment—you have to rely on broad estimations.
What this means, according to Sedwick, is that threats to the ISS are influenced by uncertainties. You might have a piece of space junk whose closest approach to the ISS is 10 kilometers, and you know its location to within 100 meters. Cool, nothing much to worry about there. But in a different scenario, You might predict an object’s closest approach to the ISS would be 4 kilometers. That should still be safe enough, but the uncertainty of that prediction might be plus or minus 2 kilometers, meaning there is a statistically significant chance the object could get closer than 2 kilometers, and a smaller chance it could be even closer than that. That might be too close to comfort for NASA—especially when human lives are on the line—so it would make sense to boost the ISS to a higher orbit and create more distance between the spacecraft and the debris. (This is a maneuver that happens periodically anyway, since atmospheric drag causes the ISS to fall over time, so the agency would just schedule the boost earlier than usual.)
Here’s where Bridenstine’s “44 percent” value comes in: Prior to India’s anti-satellite test, there were some number of debris objects in the vicinity that presented some kind of statistically significant threat (like what’s described in the second example above). After the test, the number of those objects increased by 44 percent. “44 percent more things to ‘worry’ about,” says Sedwick.
Of main concern after India’s test was that 24 of the 60 trackable objects were beyond the apogee of the ISS (the most distant point of the space station’s orbit). Over time they would be dragged down by gravity and start to threaten the ISS more acutely. “That is a terrible, terrible thing—to create an event that sends debris in an apogee that goes above the International Space Station,” the NASA administrator said.
This is unpleasant to deal with, but it’s highly unlikely going to create an imminent threat to the ISS. Bridenstine followed up to say that all of this would eventually dissipate thanks to the debris field’s presence in LEO. That aftermath doesn’t approach the hazards created by the 2007 Chinese anti-satellite missile test, which resulted in 4,000 trackable fragments and grew the orbital debris catalog by a whopping 36 percent. The administrator noted that NASA and others responsible for space situational awareness for the world were still grappling with the impact of that event, 12 years later, as more than 3,000 of those objects are still in orbit.
That doesn’t even account for the threat of the untrackable debris population. The space station has shielding to protect against debris the size of a bb-gun pellet and smaller, but any astronauts out for a spacewalk will find their spacesuits ripped open if they’re hit. Anything bigger than a marble (including many untrackable pieces of debris smaller than 10 centimeters), moving at thousands of meters per second, could puncture right through the ISS shielding and cause damage.
Part of what perturbed Bridenstine and other space officials is the potential for this event to encourage more anti-satellite tests and create more debris fields to worry about. “When one country does it, then other countries feel like they have to do it as well,” he said. Although those worries are real, they also ignore the fact that countries like the U.S. and Russia paved the way for these weapons during the Cold War. The U.S. intercepted a satellite as recently as 2008, and Russia has conducted five test flights of a new anti-satellite missile in the past four years. The Trump administration’s declaration of a Space Force has only exacerbated concerns over the militarization of Earth’s orbit. An arms race is quickly precipitating.
And right now, there really isn’t any action to remediate orbital debris—only plans to improve our ability to spot it. Sometime this year, we should see the Space Fence come online, an Air Force-backed system that should give the U.S. capability of tracking hundreds of thousands of new pieces of orbital debris, smaller than 10 centimeters.
But increased awareness is just one part of the solution. We need ways to disable satellites that limit destruction and debris. Sedwick says one method might be to spray paint over a spacecraft’s solar arrays—a more difficult task, but one that would at least decommission the craft without creating space shrapnel. Other pie-in-the-sky ideas include a giant space trash collector, which is unrealistic for now, but perhaps feasible later on. Whatever the case, we need a solution sooner rather than later, before we turn our planet’s orbit into a weightless junkyard.