ISRO may use standy engine to launch GSLV

Indian space agency ISRO will look at options of using a standby engine for the early launch of its heavy geosynchronous satellite launch vehicle (GSLV) after examining what forced the postponement of the launch Monday, an official said.

"We have a standby for the second stage engine. But first we have to study the problem. If the problem is due to a faulty component, then we have to look at the batch to which the component belonged and have to replace the entire components from that batch," an Indian Space Research Organisation (ISRO) official told IANS preferring anonymity.
He said there was no point in replacing an engine with another faulty one.

According to him, ISRO will look at different options like using a standby engine, replacing the component or correcting the problem.

"If the problem is external, it will be easy to correct. But if it is internal, then the engine may have to be dismantled," he said.

ISRO had called off the launch of its GSLV rocket carrying the communication satellite GSAT-14 after the liquid fuel started leaking like a tap from the rocket's second stage.
The GSLV is a three stage/engine with four strap-on motors hugging the first stage. The first stage is powered by solid fuel while the four strap-on motors and the second stage are powered by liquid fuel. The third is the cryogenic engine powered by liquid hydrogen and liquid oxygen.

"This is the first time we have seen such a fault," said a source close to ISRO.
According to officials, the second stage is identical for ISRO's two rockets - its lighter rocket polar satellite launch vehicle and GSLV.

While GSLV is under the development stage, the PSLV is termed as the space agency's workhorse and used to launch Indian and foreign satellites.

In 2010, ISRO had to postpone a PSLV launch as it found "a marginal drop in the pressure in the second stage of the vehicle during mandatory checks".

At that time the faulty part was inaccessible as the rocket stages had been fully assembled. ISRO had to dismantle the second stage to correct the fault.

In 2013, ISRO had to postpone the launch of its PSLV rocket carrying India's first navigational satellite after it found a problem in one of the electro-hydraulic control actuators in the second stage.

Here again, the fully assembled rocket had to be dismantled to replace the actuator, an assembly of several components.

In both cases, the second stage was not fuelled up and hence did not pose a problem for ISRO.

But the problem in the GSLV supposed to fly Aug 19 is complex as the leaking second stage was fuelled up and the third and critical stage - the cryogenic engine - was being fuelled for its flight.

"Some of the components in the second stage, like sealants, have limited life after fuelling. They might become brittle if not used within a specified period," officials told IANS.

The one comforting factor is that the crucial cryogenic engine is safe and it does not face such limited life component problems, an ISRO official IANS.

According to them, the first task for them is to drain the fuel from the second and third/cryogenic stage.

Following that, the engines will be decontaminated for fuel and traces of fuel.

"Then the rocket will be moved back to the assembly building and a detailed study of the problem will be made and corrective action will be taken," the official said.

However, ISRO officials could not say when the rocket would be ready for launch.

"Advanced countries test their stages several times before it is used in a rocket. In India, owing to vendor constraints, we have to make our rockets operational after a few tests," R.V. Perumal a retired ISRO rocket expert said.