Special Correspondent

CHENNAI: ISRO will study Chandrayaan-1’s orbit for a day or two before commanding to eject on November 14 or 15 the 29-kg Moon Impact Probe (MIP), a box-like instrument on top of the spacecraft. The probe will crash-land on the Moon’s surface. Since the MIP is painted with the Indian flag on its sides, it will symbolically register the Indian presence on the Moon.

On Saturday (November 8), ISRO accomplished with aplomb the most crucial and critical manoeuvre of safely inserting Chandrayaan-1 into the lunar orbit with an aposelene of 7,502 km and a periselene of 504 km.

This was achieved by retro-firing the engine for 817 seconds, which pushed the spacecraft in the opposite direction of its journey, reduced its velocity and inserted it into the lunar orbit.

S. Satish, Director, Publications and Public Relations, ISRO, said: “The ISRO team was very cautious in executing this critical manoeuvre because we did not want to jeopardise the mission. This is a precious mission for us. Contingency plans were in place in case the liquid apogee motor (LAM) engine on board Chandrayaan-1 did not fire. Then, we would have used other thrusters on board the spacecraft to fire… There have been dynamic changes in our manoeuvres to reach the Moon.”

S. Ramakrishnan, Director (Projects), Vikram Sarabhai Space Centre, Thiruvananthapuram, said the orbit reduction under way now was the reverse of what ISRO did in approaching the Moon.

After the Polar Satellite Launch Vehicle (PSLV-C11) put Chandrayaan-1 in an elliptical orbit with an apogee of 22,866 km and a perigee of 256 km around the earth on October 22, ISRO performed four manoeuvres by firing the LAM to keep increasing this ellipticity.

On November 4, the spacecraft reached the vicinity of the Moon with an apogee of 3,80,000 km. The Moon is 3,84,000 km away from the earth. Then the crucial manoeuvre of inserting the spacecraft into the lunar orbit of 7,502 km by 504 km took place on November 8 and it was captured by the Moon’s gravity.

“We are now reducing the Chandrayaan’s orbit to come closer to the Moon,” Mr. Ramakrishnan said. On November 9, the LAM was fired and the spacecraft’s orbit around the Moon was further reduced to 7,502 km by 200 km. “The Moon’s gravity is not well characterised. It is not symmetrical like that of the earth. The Moon’s gravity is not well understood. So there will be uncertainties. When we fire the engine to reduce the spacecraft’s orbit, depending on the response, we have to do further corrections,” he said.

Mr. Ramakrishnan was confident that the remaining two manoeuvres would succeed because Chandrayaan-1 was already “in a stable orbit and it cannot vanish anywhere.”

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