India’s Polar Satellite Launch Vehicle (PSLV-C29) successfully launched six satellites for Singapore on December 16, 2015. This was a fully commercial launch undertaken by the Indian Space Research Organisation (ISRO). The year 2015, particularly its second half, has been the most successful year for ISRO from the commercial point of view. During the last six months, it has successfully undertaken three commercial launches and has launched a total of 17 satellites of foreign countries.
Till date, the Antrix Corporation Limited, the commercial arm of ISRO, has provided launch services for 57 satellites from 20 countries. For the last one-and-a-half decade, ISRO has been launching satellites for foreign vendors beginning with a German satellite in May 1999. Interestingly, more than one-third of the launches have taken place in the last six months. This clearly indicates the maturing of ISRO’s commercial launch programme.
Over the years, PSLV has emerged as one of the most reliable work-horse for ISRO, and the launch of satellites on December 16 was its 31st consecutive successful flight. Few months back, Indian Government had stated in the Lok Sabha that by lunching 45 foreign satellites India has earned about US$ 100 million. Now, with all 57 launches, it is likely that this figure could have reached to approximately US$ 120/125 million. Today, many more international clients are waiting for ISRO to offer them launching facility on payment. Presently, ISRO’s hands are full for minimum next two years with around 15 to 20 satellites lined up for launch for various foreign agencies.
One very important but less discussed aspect of PSLV-C29 launch is the experiment performed by ISRO after it had successfully placed all six satellites into their respective locations. The mission carried out a major experiment to restart the fourth stage engine and this experiment has been declared successful. Development of such capability offers ISRO the flexibility to plan launces in different orbits in a single launch vehicle mission. Till date, ISRO has been launching multiple satellites in a single rocket, but all these satellites were designed for similar orbit positioning.
The PSLV is essentially used for Low Earth orbit (LEO) satellite launches (approximately they could carry 1700 kg payload to 625 km distance up in the space from the earth’s surface). Since its first launch in 1993, PSLV has undergone several modifications based on the need of the mission. Such modifications essentially involved boosting its load carrying capacity by adding six strap-on booster motors. Also, some changes have been made for reconfiguring thrust and efficiency aspects. In November 2013, PSLV was even used to launch India's first interplanetary mission, the Mars Orbiter Mission (MOM). However, with PSLV-C29 mission ISRO for the first time has experimented with the multiple burn fuel stage/rocket engine.
The PSLV mission configuration constitutes four stages using solid and liquid propulsion systems alternately. The first stage carries solid propellant, and the second stage uses the indigenously developed Vikas Engine which carries liquid propellant. The third stage is a solid stage and the fourth stage is a liquid stage with a twin-engine configuration.
With the successful restart and shut off of the fourth stage engine on December 16, ISRO has demonstrated its capabilities with multiple burn fuel stage/rocket engine. This is an arena of critical technology development. The main challenge here is to restart the engine after a short gap. In a routine PSLV launch, after the fourth stage gets activated a very high amount of heat is generated. Hence, the real test is to cool the engine down in the space by shutting it off and restarting it after a short gap.
During the PSLV-C29 mission, the fourth stage got cut-off in around 17 and a half minute, and during about next four minutes six satellites were placed in the orbit at 550 km altitude. Subsequently, the fourth stage got restarted after 67 and a half minute at a lower altitude of 523.09 km, as planned. The engine remained active for a period of four second and altitude went up 524 km and engine was cut-off again. Now, with the success with a multiple burn fuel engine ISRO needs to integrate this technology and undertake an actual multiple orbits-single rocket mission. The first such proposed mission, PSLV-C35, could be launched in December 2016. During this launch, one satellite will be launched at a higher orbit and the other at a slightly lower orbit.
Launching of satellites is a Rocket Science! Every new mission is a technological challenge and it is important to ensure that satellites go into the correct orbit and in the most energy-efficient manner. Cost and time aspects demand that rocket launching agency should be able to exploit innovation potential to the maximum to get maximum dividends from a single mission. India’s Moon and Mars mission have demonstrated that frugal engineering is ISRO’s forte. Now, in the coming few years, it is expected that ISRO would be in a position to put big primary payloads into different orbits by using a single rocket launcher.
Views expressed are of the author and do not necessarily reflect the views of the IDSA or of the Government of India.