GSLV: lessons for ISRO

By Our Science Correspondent

BANGALORE, APRIL 14. The aborting of the maiden launch of the Geosynchronous Satellite Launch Vehicle (GSLV) has come as a providential wake-up call to the Indian Space Research Organisation. With no damage to the rocket hardware or the launch facilities, the GSLV launch has been rescheduled for April 18.

At the first attempt on March 28, the launch was automatically aborted after one of the GSLV's four strap-on motors failed to produce the required level of thrust. Later it was found that ``defective plumbing'' in one of the propellant lines was to blame.

The ISRO has also identified the slip-up which occurred during manufacture when the propellant pipeline had to be bent. But more worrying is the fact that a defective part got past the quality control measures carried out at various stages during manufacture and engine assembly.

Indigenous manufacture

The Vikas engine, based on the French Viking engine developed for Europe's Ariane launcher, is used in the Polar Satellite Launch Vehicle (PSLV) as well as the GSLV. The ISRO has farmed out the manufacture of the engine to three Indian companies: Machine Tools Aids & Reconditioning of Hyderabad, Godrej and Kerala Hitech Industries Limited (Keltec) based in Thiruvananthapuram. The final assembly of the engines and the stages is, however, carried out by the ISRO.

Up to now, the Vikas engine has flown only in the PSLVs, five of which have been launched since 1993. The PSLV requires only one Vikas engine (for its second stage).

The GSLV, on the other hand, needs five such engines: one for each of the four strap-ons and one for the second stage. So, as the ISRO starts launching GSLVs, the demand for the Vikas engines will grow. The problem with ``defective plumbing'' has shown that the ISRO's quality control system needs to be urgently strengthened and improved.

The ISRO chairman, Dr. K. Kasturirangan, told The Hindu that the entire gamut of quality control measures at the manufacturers' plants as well as those carried out by the ISRO before accepting these engines and during their assembly was being thoroughly reviewed and tightened. Where necessary, further tests would be introduced.

The ISRO has been remarkably fortunate that the problem with the engine manifested itself early enough for the launch to be aborted at the last moment. Arianespace was not so lucky when it lost a rocket in 1990 because a piece of cloth was left in the pipeline of a Viking engine.

The GSLV is the first Indian launch vehicle whose launch could be aborted after its engines had been ignited. All ISRO's previous launch vehicles used stages filled with solid propellants for lift-off. Unlike liquid engines, solid stages cannot be shut down once they are ignited. In the GSLV, the four liquid strap-ons are fired about four and a half seconds before lift-off. Their performance is checked before the automated launch system gives the command for the solid first stage to be ignited.

Global precedents

At the very first launch of an Ariane rocket in December 1979, the flight was aborted shortly before lift-off. The problem was traced to a faulty sensor and the rocket was successfully launched a couple of days later. According to information with the ISRO, there are over 20 instances recorded when other countries have aborted launches less than a minute before lift- off. In 15 of these cases the abort occurred within six seconds of lift-off and in three cases the engines are known to have been ignited.

The GSLV launch abort has shown that the ISRO's computerised launch system is able to detect a problem and successfully halt the launch even at the last moment. All subsequent operations for securing the launch vehicle and launch pad, worked out in advance, also went like clockwork.

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