Why wasn’t PSLV used for Chandrayaan-2?


  • The launch of Chandrayaan-2, India’s first attempt at landing a spacecraft on the Moon, was aborted less than an hour from liftoff  after scientists detected a technical glitch in the launch vehicle system. The mission vehicle was a GSLV Mk-III rocket, a relatively new acquisition that is critical to ISRO’s future missions.

What makes the new rocket crucial?

  • ISRO intends to use the rocket, a product of over three decades of research and development, for all future deep space exploration missions, including Gaganyaan, India’s first human mission, scheduled to be launched before 2022. The vehicle, which can launch heavier commercial satellites, is also projected to be a big revenue generator for ISRO.
  • However, the mainstay of ISRO’s launches over the last three decades has been the Polar Satellite Launch Vehicle (PSLV), a rocket that has failed on only two of its 48 launches since the early 1990s. Chandrayaan-1 and Mangalyaan too, were launched by PSLV.

Why wasn’t PSLV used for Chandrayaan-2?

  • PSLV has its limitations. It does not have enough power to carry heavier satellites, or to go deeper into space. PSLV can deliver a payload of about 1750 kg to lower Earth orbits, up to an altitude of 600 km from the Earth’s surface. It can go a few hundred kilometres higher in Geostationary Transfer Orbit (GTO), but only with a reduced payload. Chandrayaan-1 weighed 1380 kg, while Mangalyaan had a liftoff mass of 1337 kg.
  • Many of the common commercial satellites used for remote sensing, broadcasting or navigation are well below 1,500 kg, and need to be put into low Earth orbits. PSLV has proved an ideal vehicle to do this — for both Indian and foreign commercial satellites.
  • However, there are satellites that are much heavier — in the range of 4,000-6,000 kg or more — and need to be put into geostationary orbits that are over 30,000 km from Earth. Rockets that carry such massive satellites need to have substantially more power.

And GSLV rockets have that power?

  • GSLV (Geosynchronous Satellite Launch Vehicle) rockets use a different fuel, and have a thrust that is far greater than PSLV’s. They can, therefore, carry heavier payloads and travel deeper into space. Chandrayaan-2, for example, had a total mass close to 4,000 kg.
  • Among ISRO’s GSLV rockets, GSLV Mk-III is the latest and most powerful. It has had two successful flights so far — it carried and deployed the GSAT-19 communication satellite on June 5, 2017 and then, the GSAT-29 communication satellite on November 14 last year. It had an experimental flight in 2014.
  • GSLV Mk-III is powered by a core liquid engine, has two solid boosters that are used to provide the massive thrust required during liftoff, and a cryogenic engine in the upper stage.

What is a cryogenic engine?

  • Cryogenics is the science relating to behaviour of materials at very low temperatures. Cryogenic technology is challenging to master, but essential for a rocket like GSLV Mk-III. Among all rocket fuels, hydrogen is known to provide the greatest thrust. But hydrogen in its natural gaseous form is difficult to handle, and therefore, not used in normal engines in rockets like PSLV. Hydrogen can be used in liquid form, but it turns liquid at a very low temperature — nearly 250°C below zero. To burn this fuel, oxygen too, needs to be in liquid form, and that happens at about 90°C below zero. Creating an atmosphere of such low temperatures in the rocket is difficult — it creates problems for other materials.

When and how did India advance in such technology?

  • The development of the GSLV Mk-III is the story of three decades of hard work on cryogenic technology. The technology was denied to India by the United States in the early 1990s, forcing it to go for indigenisation.
  • ISRO had planned the development of a cryogenic engine back in the mid-1980s, when just a handful of countries — the US, erstwhile USSR, France and Japan — had this technology. To fast-track the development of next-generation launch vehicles — the GSLV programme had already been envisioned — ISRO decided to import a few of these engines. It held discussions with Japan, the US, and France before settling for Russian engines. In 1991, ISRO and the Russian space agency, Glavkosmos, signed an agreement for the supply of two of these engines along with transfer of technology, so that Indian scientists could build these in the future.
  • However, the US, which had lost out on the engine contract, objected to the Russian sale, citing provisions of the Missile Technology Control Regime (MTCR), of which neither India nor Russia was a member. MTCR seeks to control the proliferation of missile technology. Russia, still recovering from the collapse of the USSR, succumbed to US pressure and cancelled the deal in 1993. In an alternative arrangement, Russia was allowed to sell seven, instead of the original two, cryogenic engines, but it could not transfer the technology to India. These Russian engines were used in the initial flights of the first and second generation GSLVs (Mk-I and Mk-II). The last of these was used in the launch of INSAT-4CR in September 2007.
  • After the original Russia deal was cancelled, ISRO got down to developing its own cryogenic technology at the Liquid Propulsion Systems Centre in Thiruvananthapuram. It took more than a decade to build the engines. In 2010, two launches of second generation GSLV rockets, one with a Russian engine and the other developed indigenously, ended in failures.
  • The big success came in December 2014, with the experimental flight of third generation (Mk-III) GSLV, containing an indigenous cryogenic engine. This mission also carried an experimental re-entry payload that ejected after reaching a height of 126 km, and landed safely in the Bay of Bengal.
  • Two more successful launches of GSLV Mk-III followed. Chandrayaan-2 was its biggest and most keenly-awaited launch.

So, what went wrong?

  • ISRO has not yet provided the nature or details of the technical glitch in the rocket. The glitch was observed after every major operation had been completed. One of the last tasks before the launch is the loading of the cryogenic fuel, hydrogen and oxygen. This was completed about a half hour before the countdown was stopped Monday morning. An assessment of the seriousness of the problem could take several days.

How big a setback is this?

  • The immediate impact is on the schedule of Chandrayaan-2. ISRO had said that the current window of opportunity to launch Chandrayaan-2 was available only between July 9 and 16. That opportunity now appears to have been lost. This could potentially delay the mission by several months. ISRO has not said when the next window of opportunity will open.
  • Until ISRO makes public its assessment of the problem, it is not possible to predict the impact on future missions, notably Gaganyaan, which has a tight deadline.
  • However, space launch failures are not unusual. Lunar missions, particularly, have had high failure rate. As many as 52 per cent of all lunar missions have been unsuccessful, the most recent being the case of the Israeli Beresheet Lander, which developed problems after entering the lunar orbit and crash landed on the Moon’s surface.

Source:Indian Express

Leave a Reply