An engine underburn in the course of a fourth orbit raising manoeuvre on the Mars-bound Mangalyaan caused a glitch, in ISROs plan to raise the height of the spacecraft from 71,623 km to 100,000 km on Monday. The agency has proposed a supplementary firing of the engine on Tuesday to raise it to the required height from the current 78,276 km apogee.
In an official statement,ISRO said Mondays manoeuvre saw the engine provide a thrust of only 35 metres per second as against an intended 130 metres per second,resulting in the spacecraft being raised only to a height of 78,276 km orbit from the 71,263 km orbit that it acquired during the third orbit raising manoeuvre carried out on Saturday.
The under-performance occurred as ISRO for the first time tested the functioning of backup engine measures on the spacecraft,the statement said.
According to ISRO,the glitch came in the course of energising the primary and redundant coils of the solenoid flow control valve (a valve that regulates the mixture of engine fluids) of the 440 Newton Liquid Engine.
When both primary and redundant coils were energised together,as one of the planned modes,the flow to the Liquid Engine stopped.
Following the stoppage of the engine,a kind of auto pilot (thrust level augmentation logic) which was also under test on Monday came into play. This sequence resulted in reduction of the incremental velocity, ISRO said.
ISRO said the engine shut-off during the fourth orbit raising move did not hit the mission per se,but would prevent parallel use of the primary and redundant coils of the solenoid flow control valve in future. While this parallel mode of operating the two coils is not possible for subsequent operations,they could be operated independently in sequence, ISRO said.
The agency said that during the three successful orbit raising manoeuvres carried out prior to Monday,when the spacecraft was taken from an initial parking orbit of 23,550 km to 28,814 km to 40,186 km and to 71,623 km,only the primary coil of the solenoid flow control valve was used.
The spacecraft is in normal health. A supplementary orbit-raising operation is planned tomorrow (November 12,2013) at 0500 hrs IST to raise the apogee to nearly 1 lakh km, ISRO said.
Former ISRO officials familiar with orbit raising manoeuvres on INSAT spacecraft said there would be no danger to the mission as long as fuel is not lost in the additional moves to raise the orbit.
ISRO hopes to raise the orbit to a height of 200,000 km by November 30 to generate the velocity to slingshot the Mars Orbiter Spacecraft toward Mars on December 1. The agency had initially hoped to carry out six manoeuvres; with Mondays glitch,three more are left to be done.
The 440 Newton Liquid Engine on will also need to fire again after 300 days in space in September 2014 to slow down the spacecraft to enable it to be captured by the gravity of Mars.