Mars orbiter spacecraft must be set off between 2.38 p.m. and 2.43 p.m. today

The Mars orbiter spacecraft has just five minutes for getting launched on Tuesday — or it slips into the next day.

It must be set off between 2.38 p.m. and 2.43 p.m.

And the mission has an overall deadline, until November 19, this year. The next best time is not for another 26 months.

“We are on the threshold of a complex mission. If there is a hold during automatic launch sequence there then we will not have it on that day. We can have a maximum of only five minutes. Each day, the launch time advances by 6-9 minutes. We hope that it will make it [on Tuesday],” K. Radhakrishnan, chairman, Indian Space Research Organisation (ISRO) told The Hindu recently.

ISRO scientists, having missed the earlier date of October because a tracking ship reached its watch post near Fiji late, have their calendar laid out for each of the remaining days.

“There is just one opportunity in a day. For each lift-off time, we need to have a new steering programme ready, a new trajectory design, and all this has been done,” he said.

“In earlier missions we worried about only one trajectory and made only a minor change in the steering programme. This total trajectory design is for each lift-off time, which is one big challenge for the Polar Satellite Launch Vehicle (PSLV).”

The flight on the four-stage PSLV-C25 lasts 43 minutes, more than double the time taken for its routine launches which need about 20 minutes, with a long coasting for the last stage.

Mr. Radhakrishnan said now they were concentrating on the launch on Tuesday and then on December 1, when the spacecraft should be put in the trajectory to Mars. Post-lunch, it will be a series of post-midnight exercises for scientists tracking the spacecraft from ISRO Telemetry, Tracking and Command Network (ISTRAC). On Thursday morning, ISTRAC in Bangalore will start increasing its elliptical orbit in phases by firing its motors six times.

Dr. Radhakrishnan said the first orbit raising exercise was crucial and would happen on Thursday at 1.15 a.m.

The remaining orbit expansions would all be done around 2 a.m. on November 8, 9, 11 and 16, until the spacecraft’s apogee (farthest point from Earth in its elliptical orbit) reaches 1.92 lakh km.

The sixth and last Earth-bound manoeuvre is slated for December 1 at 12.42 a.m.

The trickiest time will be in September 2014, when the spacecraft will be near Mars. The scientists have to slow down the spacecraft and bring it into an elliptical orbit going around Mars.

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