ISRO plans to do the first of its four small, planned course corrections on the Mars-bound Indian spacecraft at dawn on Wednesday.

The spacecraft, ejected from the earth’s orbit on December 1, was on Monday said to be cruising some 23 lakh km away from earth.

Controllers of its various systems met at tracking centre ISTRAC in the evening to take stock of its situation and plan the operation, called trajectory correction manoeuvre (TCM). Team ISRO calls it fine-tuning of its course.

This TCM is needed as the spacecraft slightly overachieved its parameter, which can happen during operations such as the crucial December 1 manoeuvre, said M. Annadurai, Programme Director of the Mars Orbiter Mission.

Taking stock

Monday’s meeting was to take stock, finalise the duration of firing the smaller thrusters — tentatively for about 40 seconds at 6.30 a.m. on December 11 — and the rest of the TCM-1 strategy.

This time, all eight small 22-Newton thrusters on the spacecraft would be used to minutely slow it down. The activity, as also the three similar remote shots planned next year, would ensure that the spacecraft travelled at a specific speed and kept its date with Mars in September next year, he explained to The Hindu.

Dr. Annadurai said, “We have a fair idea of the trend of its 10-month behaviour, such as its position and velocity.”

On December 1, while steering the spacecraft away from the earth, the trans-Mars injection (TMI) gave it a small extra speed of 2 km a second. Mars, too, is moving at 30 km a second in its own path.

As such the spacecraft’s motion should be occasionally synchronised for its rendezvous with Mars in September 2014, he said.

Currently it was under the predominant influence of Sun’s forces. The signals were coming at a delay of eight seconds each way and this would get longer.

For the December 1 move and the earlier six orbit-raising moves, the ISRO engineers used the larger 440-Newton liquid motor.

The other corrections or TCMs are due next year in April, August and mid-September, the last one 10 days before the spacecraft reaches and begins to orbit Mars.

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