“As per our current estimates whatever remains of the structure – [fairing], satellite and the rocket’s fourth stage – will fall into the sea.”
The Indian navigation satellite IRNSS 1H, stuck inside a rocket’s payload fairing and both of which are now tumbling about in space, is expected to reenter Earth’s atmosphere in a couple of months.
However, there may not be any impact on the ground, a senior official of the Indian space agency said.
“The satellite tracking stations are getting intermittent signals from IRNSS-1H. The fuel on-board the satellite has been depleted by firing the motors whenever there was a signal. The satellite-heat shield assembly is tumbling in space,” K. Sivan, director of the Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram, told IANS on September 5.
“The whole thing is expected to re-enter the earth’s atmosphere between 40-60 days. But the days could vary as the structure is tumbling,” he added. The centre is part of the Indian Space Research Organisation (ISRO).
On August 31, the payload fairing – a protective encasement holding the rocket’s payload as part of its fourth stage –of the PSLV C39 did not open up 19.5 minutes after the vehicle was launched from ISRO’s spaceport in Sriharikota, Andhra Pradesh. As a result, the 1H satellite was trapped and could not be placed in orbit.
When asked whether the whole structure would hit the ground and go on to be a ‘mini-Skylab’, Sivan said, “As per our current estimates whatever remains of the structure – [fairing], satellite and the rocket’s fourth stage – will fall into the sea.” Skylab was the US’s first space station. It fell back to Earth in 1979. It weighed around 77 tonnes and the event is remembered as a major incident.
According to Sivan, the speed at which the rocket crosses the atmosphere on its way up is much less than the speed at which the fairing and the satellite would be coming down at. “The rocket crossed the atmosphere at a speed of around one km per second. On the other hand, the heat shield housing the satellite is expected to re-enter the atmosphere at a speed of eight to nine km per second,” Sivan said. “At this speed of re-entry, the whole structure is expected to get burnt.”
Earth’s gravitational pull increases the speed of the object that is falling towards it from the space. This hikes the heat generated due to friction between the fairing’s material and the atmosphere, resulting in combustion. As a result, how much damage the impact will do will depend on the combination of mass and velocity.
According to a space expert, the fairing-satellite combo is currently in an elliptical orbit around Earth such that their perigee (nearest point to Earth in the orbit) is 164 km and apogee (farthest point), 6,500 km. The original flight plan had pegged the satellite’s perigee and apogee at 284 km and 20,650 km respectively.
Another expert, who wished to remain unnamed, said, “The perigee will come down in course of time. Once the perigee touches 100 km, the rate of PSLV’s [fairing]-satellite assembly’s fall towards Earth will be faster.” He added that ISRO would also calculate the ground trace – the probable point of impact – then: “The exact spot where the satellite housed inside the heat shield will fall will be known around 36 hours before the actual impact.”
Sivan said that ISRO is also tracking the assembly through its stations as well as through the multi-object tracking radar in Sriharikota – alongside a lot of other free space debris.