According to ISRO, this is the heaviest commercial luggage carried by a PSLV rocket to date.

The Indian space agency on Wednesday morning began the countdown for the July 10 rocket launch that would carry five British satellites.

According to Indian Space Research Organisation (ISRO), the 62 hours and 30 minutes countdown for the July 10th night launch of rocket Polar Satellite Launch Vehicle (PSLV) XL variant began at 7.28 a.m. on Wednesday.

The rocket is scheduled to blast off at 9.58 p.m. on July 10 from the first launch pad with five satellites together weighing around 1,440 kg, for an undisclosed fee.

Since 1999, India to date has launched 40 satellites of other countries and the successful launch of the five British satellites would take the tally to 45.

The 44.4 metre tall and 320 tonne PSLV is a four stage/engine rocket with six strap-on motors for addition thrust during the initial phase of the flight.

The first and third stages are powered by solid fuel and are cast ready while the second and fourth stages are powered by liquid fuel which will be filled during the countdown.

Apart from fuelling up the engines, all the systems would be checked and rechecked during the countdown.

According to ISRO, this is the heaviest commercial luggage carried by a PSLV rocket to date.

Of the five British satellites, three are identical DMC3 optical earth observation satellites weighing 447 kg. These will be put into a 647km sun-synchronous orbit.

Of the other two satellites, CBNT-1 weighs 91 kg and also is an optical earth observation technology demonstration microsatellite, while the remaining De-OrbitSail weighs 7 kg. This is an experimental nano-satellite for demonstration of large thin membrane sail-and-drag deorbiting.

The total duration of the launch — from the rocket’s blast off to the fifth satellite separation — will be around 19 minutes 16 seconds.

The three DMC3 and the CBNT-1 satellites were built by Surrey Satellite Technology Ltd. The De-OrbitSail was built by Surrey Space Centre.

According to ISRO, accommodating the three DMC3 satellites (each with a height of about three metres within the existing payload fairing or the heat shield of the PSLV) was a challenge. Thus, a circular L-adaptor and a triangular Multiple Satellite Adapter-Version 2 (MSA-V2) were newly designed and realised by ISRO for this specific purpose.

France’s SPOT 7 satellite weighing 714 kg was the heaviest single foreign satellite carried by a PSLV rocket untill now. It was launched on June 30, 2014.