Humanity Creates a Cloud of Space Garbage, Again

With the destruction of the Microsat-R reconnaissance satellite on March 27th, India became the fourth country in history to successfully hit an orbiting satellite with a surface-launched weapon. While Microsat-R was indeed a military satellite, there was no hostile intent; the spacecraft was one of India’s own, launched earlier in the year. This follows the examples of previous anti-satellite (ASAT) weapons tests performed by the United States, Russia, and China, all of which targeted domestic spacecraft.

Yet despite the long history of ASAT weapon development among space-fairing nations, India’s recent test has come under considerable scrutiny. Historically, the peak of such testing was during the 1970’s as part of the Cold War rivalry between the United States and then Soviet Union. Humanity’s utilization of space in that era was limited, and the clouds of debris created by the destruction of the target spacecraft were of limited consequence. But today, with a permanently manned outpost in low Earth orbit and rapid commercial launches, space is simply too congested to risk similar experiments. The international community has strongly condemned the recent test as irresponsible.

For their part, India believes they have the right to develop their own defensive capabilities as other nations have before them, especially in light of their increasingly active space program. Prime Minister Narendra Modi released a statement reiterating that the test was not meant to be a provocative act:

Today’s anti-satellite missile will give a new strength to the country in terms of India’s security and a vision of developed journey. I want to assure the world today that it was not directed against anybody.

India has always been against arms race in space and there has been no change in this policy. This test of today does not violate any kind of international law or treaty agreements. We want to use modern technology for the protection and welfare of 130 million [1.3 Billion] citizens of the country.

Further, the Indian Space Research Organisation (ISRO) rejects claims that the test caused any serious danger to other spacecraft. They maintain that the test was carefully orchestrated to that any debris created would renter the Earth’s atmosphere within a matter of months; an assertion that’s been met with criticism by NASA.

So was the Indian ASAT test, known as Mission Shakti, really a danger to international space interests? How does it differ from the earlier tests carried out by other countries? Perhaps most importantly, why do we seem so fascinated with blowing stuff up in space?

Learning from the 2007 Chinese Anti-Satellite Test

In 2007, China tested an ASAT missile against one of their own weather satellites in a polar orbit at an altitude of approximately 865 kilometers. It was the first time a satellite had been destroyed in orbit since 1985, and to this day represents the largest debris cloud ever created in space. More than 2,000 objects large enough to be tracked by ground radar were created in the impact, in addition to potentially hundreds of thousands of smaller particles which can’t be detected.

Model of satellite destroyed in 2007. Image credit Jakub Hałun.

Due to the high altitude of the impact, the debris field from the Chinese satellite will remain a hazard to navigation for years to come. With little atmospheric drag to slow them down, it’s estimated that some of the smaller pieces might not burn up for centuries. According to a report released by NASA, even relatively large pieces are estimated to remain in orbit until at least 2035. As recently as April 2011, debris from that 2007 ASAT test passed within 6 km of the International Space Station.

So how does this compare to the recent Indian ASAT test? Both weapons used what’s known as a “kinetic kill vehicle”, which is to say that the missile had no explosive payload. Much like the hypersonic weapon systems currently in development, the energy released upon impact is itself enough to destroy or disable the target. Indian authorities were quick to point out that such a weapon theoretically results in a smaller and denser debris cloud than would be created by an explosive warhead, though that came as little consolation during the Chinese test.

The biggest difference between the two events is the altitude at which the target was destroyed. Two weeks ago Microsat-R was flying at only 270 km when the impact occurred, putting the debris cloud fairly low within the Earth’s thermosphere. Objects orbiting within this regime will begin to slow down and lose altitude quickly, burning up once they hit the thicker parts of the atmosphere. Depending on how large the individual pieces are, they should completely burn up within weeks to months. Between the short time the debris will remain in orbit and their relatively low altitude (for comparison, the ISS orbits at an average of 400 km), ISRO officials say the cloud should pose little risk to other spacecraft.

High Flying Fragments

NASA agrees with the IRSOs assessment that the destruction of Microsat-R has resulted in far fewer debris than the 2007 Chinese test. Current estimates from the agency show the impact created around 400 objects which could pose a danger to other spacecraft, with as many as 60 of them large enough to track with radar. They also acknowledge that the majority of these pieces are in a low enough orbit that they should burn up in the near future. But recent statements from NASA Administrator Jim Bridenstine indicate the agency believes these facts don’t completely preclude the possibility of fragments being ejected into a higher orbit.

The issue is perhaps best understood through an animation produced by Analytical Graphics, which illustrates the moment of impact and the resulting debris cloud based on standard breakup model simulations used by the ESA and NASA:

While the majority of debris remain more or less on Microsat-R’s original orbit, some are blown farther out into space. The higher orbit of these fragments not only means they’ll remain in space longer than the ISRO’s estimates, but that they could pose an impact risk for the International Space Station. Administrator Bridenstine stopped short of saying the Station needed to perform any evasive maneuvers, only that the agency determined there was an elevated risk of impact for the two weeks following the satellite’s destruction.

Low Orbit Saber Rattling

India’s ASAT missile

As is often the case, the truth in this matter is likely somewhere in the middle. ISRO’s claim that the destruction of Microsat-R posed no danger to other spacecraft is likely reductive, but at the same time, Administrator Bridenstine’s description of the test as a “terrible thing” is obvious hyperbole. If there was even a chance that the debris posed a credible threat to the International Space Station or the crew members aboard it, evasive maneuvers would have been performed as a matter of course.

It’s unlikely Mission Shakti will have any long term effects on other craft in Earth orbit, and it’s even less likely there will be any punitive measures against India for carrying it out. History is full of nations scrambling to show each other they are on equal technological footing, and the development and successful deployment of an ASAT weapon is a milestone to strive for. India’s test was not in violation of any international law, and was less invasive than previous tests carried out by other countries. Aside from the fact they didn’t notify other countries before launching the weapon, India carried out Mission Shakti in about as responsible a manner as possible.

In the end, the chances of any nation actually shooting down a rival’s satellite is slim to none. The concept of mutually assured destruction (MAD) kept the nuclear weapons in their silos during the Cold War, and the same idea applies here. Shoot down their satellite, and you’re likely endangering one of your own. Make a habit of it, and pretty soon there’s no safe orbits left.

The true purpose of tests such as these is to demonstrate to the world that your country has the ability to destroy fast moving objects traveling at extreme altitudes. Landing a direct hit on an old weather or reconnaissance satellite is the least provocative way to indicate your country can defend itself against incoming ballistic missiles should the need ever arise. It’s an ability all countries hope they will never have to put into practice.