Mission Shakti: The US military tracks objects in space to predict the collision risk for the ISS and for satellites. Mission Shakti: The US military tracks objects in space to predict the collision risk for the ISS and for satellites.

The debris created by the anti-satellite test carried out by India last week had increased the risk to the International Space Station, the head of US space agency, National Aeronautics and Space Administration (NASA), has said. But he acknowledged that this risk was comparatively small and would “dissipate” with time.

The International Space Station, or ISS, is the world’s only permanent facility in space, and has always been manned by one or more astronauts for the last two decades. The ISS serves as a platform to carry out a variety of experiments in space, especially those that require zero gravity, and also for testing new space systems and technologies.

Speaking at a town hall on Monday, Jim Bridenstine, the NASA administrator, in a response to a specific question from a colleague on the impact of the Indian test, said that the risk to the ISS (due to possible collision with space debris) had gone up by 44 per cent after the Indian anti-satellite test, though he added that both the ISS and the astronauts were safe.

“Here is what we know about the most recent direct ascent anti-satellite test done by India. We know that we have identified 400 pieces of orbital debris from that one event. That is what has been identified. Now, all of it cannot be tracked. What we are tracking right now, objects big enough to track and we are talking about objects 10 cm or bigger … about 60 pieces have been tracked. They have got tracking numbers… Out of those 60, we know that 24 of them are going above the apogee of ISS. That is a terrible terrible thing… to create an event that creates debris that goes above the apogee of ISS,” Bridenstine said.

Apogee is that point in the parabolic path of a spacecraft around the earth that is furthest from the earth’s surface. The ISS has an apogee of 408 km, and a perigee (closest point from earth) of 403 km. India had said its anti-satellite test had targeted a satellite that was orbiting at an altitude of about 300 km from earth’s surface. After the hit, the fragments of the satellite fly in all directions.

Explained Why space debris, anti-sat tests are dangerous The International Space Station is at constant risk of collision from space debris, and once in a while needs to navigate away in order to avoid collisions. Since it was established in 1999, it has had to make such delivery avoidance manouevres 25 times, the last one in 2015. Anti-satellite missile tests are a threat to peaceful activities in the space. The NASA, as Bridenstine puts it, is “charged with enabling more activities in space than we have ever seen before for the purposes of benefiting the human condition”. All of those activities are placed at risk when such space debris is generated. “When one country does it, other countries feel like they have to do it as well — it is unacceptable,” he says.

Bridenstine said NASA’s analysis showed that the threat to ISS from possible collisions had increased but did not specify how close to the ISS had the fragments of the Indian satellite been detected.

“We are learning more and more every hour that goes by about this orbital debris that has been created from this anti-satellite test. Where we were last week, from an assessment that comes from NASA experts … was that the risk to the ISS was increased by 44 per cent. The risk, and I am talking about small debris impact to the ISS… risk went up 44 per cent over a period of ten days,” he said.

The Indian government has not given any estimate of the number of pieces of space debris created by the hit, or whether it posed any threat to ISS or any other satellite in space. ISRO chairman K Sivan told The Indian Express that neither ISRO nor any other agency in India had the capability or the resources to track space debris. “We depend on our international partners like NASA for information on space debris for our launches and other operations,” he said.

An official source in the Defence Research and Development Organisation (DRDO) said it was unlikely that the debris from the test could pose any real threat to the ISS or any other satellite.

EXPLAINED | Space debris from Indian satellite: NASA’s worry, and why risk is low

“Our theoretical studies had shown that the debris that was likely to result from the test would not pose any threat to any existing space infrastructure. If you listen to the comments of the NASA administrator carefully, he too acknowledges the fact that debris from the Indian satellite will dissipate very soon. That is what we also expect. We expect all the debris from the test to either decay or fall down to earth’s atmosphere within a maximum period of 45 days. The bigger pieces should start decaying much earlier. We don’t think there is any real threat of collisions from these pieces,” the source said.

Another source in DRDO said at the time of the test, the position of ISS in its orbit was such that it was very far away from the Indian satellite. “At the time of the ASAT (anti-satellite test) interception, the ISS, which goes around the earth in its orbit, was located over North Atlantic Ocean, north of French Guiana over South America, while our own mission was over Bay of Bengal off the Odisha coast,” he said. The source added that it was still possible for some pieces to get near to the ISS subsequently, but this did reduce the chances of any real threat of collisions.

Bridenstine did, in fact, mention that while the debris from Indian test was likely to dissipate soon, a similar test by the Chinese in 2007 had created a much more serious and persistent threat to the ISS.

“The good thing is that it (the debris from Indian satellite) is low enough in earth orbit that over time this will all dissipate. You go back in time, 2007, (the) direct ascent anti-satellite test by the Chinese, a lot of the debris is still in the orbit,” he said.

Also read | The ABC of India’s anti-satellite missile test

Bridenstine also emphasised that no harm was likely to the space station or the astronauts on board.

“While the risk went up 44 per cent, our astronauts are still safe. The ISS is still safe. If we need to manoeuvre it, we will. But probability of that, I think, is low. But at the end of the day we have to clear also that these activities are not sustainable or compatible with the human space flight,” he said.

The ISS is at constant risk of collision from space debris, and once in a while needs to navigate away in order to avoid collisions. Since it was established in 1999, it has had to make such delivery avoidance manouevres 25 times, the last one in 2015.

Bridenstine said anti-satellite missile tests were a threat to peaceful activities in the space.

“We are charged with commercialising LEO. We are charged with enabling more activities in space than we have ever seen before, for the purposes of benefiting the human condition… all of those activities are placed at risk when this kind of events happen. And when one country does it, other countries feel like they have to do it as well… It is unacceptable,” Bridenstine said.

“We need to be clear with everyone in the world, that we are the only agency in the federal government that has human lives at stake here. And it is not acceptable for us to allow people to create orbital debris fields that put at risk our people,” he said.

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