ISRO will launch the IRNSS-1H satellite aboard the PSLV at 7 pm today: All you need to know and where to watch

The Indian Space Research Organisation (ISRO) will be launching the IRNSS-1H satellite via its PSLV launch platform at 7.00 pm on 31 August from the Satish Dhawan Space Centre in Sriharikota.

The launch will be the 41st launch of the PSLV. This mission has been dubbed PSLV-C39. The rocket will be taking the IRNSS-1H satellite to sub-Geosynchronous Transfer Orbit (sub-GTO) and will be launched in its XL configuration with six strap-on boosters.

Once placed in orbit, the satellite will fire its Liquid Apogee Motor (LAM) and begin a series of manoeuvres to place it into the required geosynchronous orbit. According to ISRO’s mission briefing ( PDF ), the PSLV-C39 will involve a rocket with a lift-off mass of 321 tonnes.

It will take approximately 19.5 minutes to place the satellite into sub-GTO. At the point of separation, the launch vehicle will be travelling at a speed of 9,597.74 m/s.

IRNSS-1H will join a cluster of satellites that make up the Indian Regional Navigational Satellite System and India’s Navigation Indian Constellation (NavIC) platform. NavIC aims to provide navigation and ranging information to users. This is very similar in function the US’ GPS system.

The satellite’s payload will operate in the L5 and S bands and accurate timing data will be provided by rubidium atomic clocks, which are necessary for accurate navigational information. Incidentally, ISRO is launching the IRNSS-1H as a backup for the IRNSS-1A satellite, which lost all three of its rubidium atomic clocks. One atomic clock each on two other satellites that make up IRNSS also failed.

According to an earlier report , ISRO will continue to use IRNSS-1A as it is still partially functional. Each satellite houses three rubidium atomic clocks for the sake of redundancy, so the loss of a single atomic clock each on two different satellites isn’t much of a concern, says ISRO.

Despite ISRO’s claims, however, the failure of the rubidium atomic clocks is cause for some concern as four rubidium clocks in the GNSS (Global Navigation Satellite System) maintained by the ESA (European Space Agency) have also failed. In the ESA’s case, BetaNews reports that the failed clocks “all seem to have a consistent signature, linked to probable short circuits, and possibly a particular test procedure performed on the ground.”

In the case of the GNSS, only the redundant atomic clocks have failed, meaning that the entire constellation is still functional.

The countdown for the PSLV-C39/IRNSS-1H mission has already begun . The launch can be streamed live from ISRO’s website from 6.25 pm on 31 August.

We will also be running a live blog of the event at the same time, so do tune in for up-to-the-minute updates on the launch.