PSLV-C35 Successfully Puts Satellites Into Different Orbits. Here’s How ISRO Did It.

PSLV-C35 Successfully Puts Satellites Into Different Orbits. Here’s How ISRO Did It.Indian residents photograph the launch of the ISRO PSLV-C35 (ARUN SANKAR/AFP/Getty Images)

The Indian Space Research Organisation (ISRO) on Monday morning (26 September) successfully launched into orbit its own weather satellite, the SCATSAT-1, and seven others – five foreign and two domestic – in a copybook style using its workhorse launch system, the Polar Satellite Launch Vehicle (PSLV). This was PSLV’s longest launch, spread over two hours and 15 minutes.

The Indian space agency, ISRO, put into commercial use its multiple burn technology.

Multiple burn technology

Multiple burn technology is the switching off and on of a rocket’s engine in space, mainly to deliver satellites in two different orbits.

The process involves launching the weather satellite into a 730-km polar sun synchronous orbit, after which the rocket’s fourth stage is shut down. It is then turned on again after a certain stipulated period for a short amount of time before being turned off again. There is another ‘burn’ (i.e., restarting of the engines) late into the flight. And then the satellites are put into different orbits.

This switching off and switching on of the rocket’s fourth stage is called multiple burn technology.

How ISRO did it

After slinging the SCATSAT-1 into its orbit, the rocket’s fourth stage was restarted one hour and 22 minutes into the flight and cut off around 20 seconds later.

Two hours and 11 minutes into the flight, the fourth stage was again restarted to be cut off a minute later. Following that, in three minutes, all the seven satellites were ejected, putting an end to PSLV’s longest mission till date.

The PSLV rocket is a four-stage rocket engine powered alternatively by solid and liquid fuel.

The challenge

On Sunday (25 September), the director of Vikram Sarabhai Space Centre (VSSC), K Sivan, told IANS that the long time gap between cutting off of the engine and restarting it was not an issue.

Sivan said multiple burn technology was first tested by ISRO while flying its PSLV rocket on 16 December 2015, and later, in June 2016, the technology was demonstrated again.

About the challenge, Sivan said:

After cutting off the engine, its condition should be brought to such a stage that it could be restarted again. The next challenge is to controlling the engine and bringing it so as to eject the remaining satellites into a different orbit.

He said the rocket has GPS-aided navigation system so that the data generated by the rocket’s inertial navigation system and the one provided by the former will be blended so as to erase errors and to generate a precise data.

(With inputs from IANS)