Early on Saturday, spacecraft specialists of the Indian Space Research Organisation (ISRO) succeeded again in boosting the apogee of the Mars spacecraft, which had been put into earth-orbit on November 5.

It was the third time that the ISRO Telemetry, Tracking and Command Network (Istrac) at Bangalore had commanded the 440-Newton engine on board the Mars orbiter to fire. The engine promptly swung into action, using its liquid propellants, from 2.10 a.m. At the end of nearly 12 minutes, the spacecraft’s apogee had been raised from 40,186 km to 71,636 km.

The ISRO had already boosted the Mars spacecraft’s orbit twice, first on November 7 and again on November 8. Three more orbit-raising manoeuvres remain — on November 11 and 16, and December 1.

On December 1 — “the D-day”, as ISRO Chairman K. Radhakrishnan called it — the Mars spacecraft will be slung out of its geo-centric (earth-bound) orbit into a helio-centric (sun) orbit, and the spacecraft will cruise around the sun for the next nine months. On September 24, 2014, when the spacecraft is closest to Mars, it will be manoeuvred and captured in the Martian orbit with a peri-apsis of 377 km and apo-apsis of 80,000 km by firing the engine again and reducing the spacecraft’s velocity.

The restart of the spacecraft’s propulsion system after it has hibernated for about 300 days in deep space will be one of the biggest challenges that the ISRO will face in its maiden interplanetary mission. The ISRO has done a series of tests at the Liquid Propulsion Systems Centre (LPSC) in Mahendragiri, Tamil Nadu, to simulate the re-start of the engine in deep space.

There is also provision for mid-course corrections of the spacecraft’s trajectory.

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