A model of Chandrayaan-1 at Sriharikota. File picture

New Delhi, Nov. 4: Spacecraft controllers in Bangalore today pushed Chandrayaan-1 into what they hope will be its final orbit around the earth — one step away from being guided into its first orbit around the moon.

Indian Space Research Organisation (Isro) engineers commanded a thrust engine on the spacecraft to fire for 150 seconds, inserting it into a new orbit that will take it into the lunar neighbourhood, about 380,000km from the earth, in four days.

The next thrust engine firing operation — planned for November 8 — will be among the most crucial manoeuvres of the mission, intended to ease the spacecraft out of its earth-bound orbit and into a lunar orbit.

To achieve this orbit transfer, engineers will need to reduce Chandrayaan-1’s speed as it approaches the moon from about 2km per second to about 1.5km per second. This speed reduction is designed to ensure the spacecraft is retained in an orbit around the moon.

Before activating the thrust engine, engineers will have to change the orientation of the spacecraft.

Isro will have only one chance to make the orbit transfer with ease. If it is missed, the engineers said, a different set of complicated manoeuvres would be required to salvage the mission.

“It will then become difficult,” a senior engineer said.

Chandrayaan-1, launched on October 22, is on its way into a lunar orbit where it is expected to spend the next two years observing the moon, collecting and sending data to Earth via Indian and foreign-made instruments.

During each earlier orbital manoeuvre, the engineers gained experience with controlling the orientation and speed of the spacecraft, one senior engineer said.

“All has gone well so far and we expect a trouble-free orbit transfer.”

Once Chandrayaan-1 is in its first lunar orbit — the nearest point being 500km and the farthest point 750km — engineers plan to reduce its speed several times to guide it into its final orbit only 100km above the lunar surface.