A spare satellite, IRNSS 1I, was expected to launch in November 2017, followed by two more spares next year. How the failure of C39 will impact this schedule is not known.
On August 31, the PSLV C39 mission launched by the Indian Space Research Organisation (ISRO) failed. The mission was to launch the IRNSS 1H satellite, slated to be part of the network of seven satellites of the regional navigation system India has been setting up over the last four years. The 1H satellite itself was going to replace the 1A, launched in 2013, after a timekeeping system onboard the latter failed completely last year.
IRNSS stands for the Indian Regional Navigation Satellite System. It consists of a spaceborne network of seven satellites – from 1A (now 1H) through to 1G, all in a geosynchronous orbit. The last satellite of this network was launched in April 2016.
This is only the third failure of a PSLV mission. The first failure was with the PSLV rocket’s first launch in September 1993. In 1997, the rocket failed to reach the orbit it was aiming for. Twenty years later, the C39 mission – also the 41st ISRO mission using the PSLV rocket – has failed. However, the reasons for the failure indicate that the rocket launch itself was successful. It was a procedure to separate the satellite from the rocket that had gone awry.
A trapped satellite
ISRO has initiated an official investigation into the causes of the problem. Such a procedure could take three to six months depending on – as one engineer put it – “how soon the bosses would like it and how difficult it is to ascertain”. At the same time, other space scientists and engineers have been discussing the problem on various forums, trying to narrow it down to specific components.
For example, some analysis focused on the pyro bolts, a set of bolts used on the payload fairing. According to the same engineer (who wished to remain unnamed), these bolts contain a notch and a small amount of an explosive below them. When the explosive goes off, the bolts shear along the notch and separate the satellite’s protective encasement from the rocket’s last stage, a process mediated by the use of a connecting component called a Marman ring. The encasement subsequently comes off as two separate halves.
After the mishap was first reported, ISRO chairman A.S. Kiran Kumar held a news conference where he said that the satellite’s holding mechanism inside the rocket had unclasped, figuratively speaking, like it was supposed to. But “the heat shield did not separate, as a result the satellite is enclosed in the body of the fourth stage. So the mission is unsuccessful,” he said. “We have to check heat shield separation command and whatever happened subsequently and it will be analysed.”
Although the terms ‘heat shield’ and ‘payload fairing’ have been used interchangeably, there is an important difference between them. A heat shield refers to a protective layer attached to a part of the rocket if it plans to reenter Earth’s atmosphere, not when it is flying through it upwards. Atmospheric reentry heats the reentering object to much higher temperatures (the NASA Space Shuttle experienced 1,650º C). The payload fairing is typically the rocket’s nose cone part, a protective encasement (as discussed above) that contains the payload. Once the rocket reaches its designated altitude, the fairing comes apart and leaves the payload to do its thing.
This said: No operational (non-developmental) ISRO flight has involved a rocket reentering Earth’s atmosphere after completing its tasks to deliberately incinerate itself, leaving it floating around in orbit as trash.
Earlier, the rocket’s launch from Sriharikota had been delayed by one minute because mission scientists were trying to avoid a piece of space debris that would likely have been in the rocket’s path. After the rocket had reached the sub-geosynchronous transfer orbit, the satellite separated from the rocket’s fourth stage but couldn’t exit it altogether. Some scientists had suggested that if the payload fairing could be opened partially, the satellite’s motors could be used to propel itself out of its cage, although this would risk damaging its instruments.
It seems no such rescue ops were conducted, and the rocket and its satellite have now been classified as debris – leaving ISRO, and other space agencies, with yet more junk to avoid during future launches. The C39 mission’s official debris designation is 2017-051A, located in a 166 km × 6,556 km orbit inclined at 19.16º.
Three spares left to launch
IRNSS 1H was the first satellite built for ISRO by a private contractor – rather a consortium, lead by the Bengaluru-based Alpha Design Technologies. Early reporting on the incident had been confused, with Reuters going so far as to quote Kumar as saying that the satellite had “imploded” (it hadn’t). The headline of an NDTV article also suggested that the failure could be partly laid at Alpha’s doorstep, causing some consternation among private players.
However, going by Kumar’s preliminary assessment (about the payload fairing), nothing has happened that ought to jilt the private sector or even cast the PSLV’s reliability – of which ISRO has been justifiably proud – in doubt. In a different report, NDTV quoted unnamed ISRO scientists as saying that the incident was “trivial”, and Kumar as saying that the PSLV would not be grounded during the course of the investigation. Note that this time the launch itself was as successful as it has usually been.
With the 1A satellite having gone kaput and the 1H undelivered, the IRNSS – colloquially referred to as ‘India’s GPS’ – remains incomplete. Unlike the American GPS or the Russian GLONASS systems, the IRNSS is not global but regional. According to ISRO, its primary service area is a region that includes India and an area “extending up to 1,500 km from India’s boundary”, over which “it is designed to provide accurate position information service to users in India”. Notwithstanding the failure of the timekeeping systems (in the form of three rubidium atomic clocks onboard), the satellites are expected to have a lifetime of 10 years. Even IRNSS 1A, all of whose clocks failed in 2016, has been broadcasting system messages to the ground station.
The clocks were all made by SpectraTime, a Swiss company. The European counterpart of the GPS, called Galileo, also uses clocks provided by SpectraTime. Eight of them experienced glitches in 2016. The Chinese space agency is another of SpectraTime’s clients.
Back to India: Another spare satellite, IRNSS 1I, was expected to launch in November 2017, followed by two more spares next year. How the failure of C39 will impact this schedule is not known. Moreover, ISRO has three major PSLV-related commitments coming up on its calendar.
The first, according to The Hindu, is a CartoSat 2 series satellite due to be launched in November or December 2017. The second is in late December to launch a lunar rover built by TeamIndus, and another by Team HAKUTO that will be piggybacking on it, as part of the Google Lunar XPrize contest. In a blog post, Rahul Narayan, who is leading TeamIndus’s bid to win the contest, wrote that his team “expects very little impact, if any, on our launch scheduled for the first quarter of 2018. The glitch reported appears limited to a pyro device circuit in the nose-faring [sic] with all other systems working as they should.”
The third commitment is an early-2018 launch of ISRO’s own widely anticipated Moon mission, Chandrayaan 2.
This article was updated at 11:00 pm on September 1, 2017, to update the PSLV’s schedule for 2017 and Rahul Narayan’s comments. Another update was made on September 10 to note that no operational ISRO mission has reentered Earth’s atmosphere deliberately.