Through the fourth orbit correction on Monday,Isro scientists were planning to raise the apogee (the farthest point from Earth) from 71,623km to about 1 lakh km, but a drop in incremental velocity (35m per second as against 130 per second as planned) resulted in a lower apogee.
Now scientists at the Spacecraft Control Centre in Bangalore will carry out a supplementary orbit-raising exercise at 5am on Tuesday. This means more fuel consumption.
What saved the spacecraft were the redundancies (back-up systems) on board the spacecraft. “When both the primary and redundant coils were energized together, as one of the planned modes, the flow to the liquid engine stopped. The thrust level augmentation logic, as expected, came in and the operation continued using the attitude control thrusters.
This sequence resulted in reduction of incremental velocity,” Isro said in a statement.
Scientists said the spacecraft is in good health to achieve its objectives including the trans-Martian injection on December 1, and the 400-million km cruise to the red planet in 300 days.
“During the orbit-raising operations conducted since November 7, 2013, Isro has been testing and exercising the autonomy functions progressively. The prime and redundant star sensors have been functioning satisfactorily. The primary coil of the solenoid flow control valve was used successfully for the first three orbit-raising operations,” Isro said.
The drawback means the planned simultaneous operation of two coils would not be possible anymore, but if the rest of the operations happen as planned, the spacecraft will reach the Martian orbit on September 24, 2014.
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