Countdown for moon mission begins

The countdown began on Monday for Chandrayaan-1, India’s unmanned moon mission, at Sriharikota spaceport with Indian Space Research Organisation (Isro) gearing up for Wednesday’s much-awaited launch.

“The countdown started at 5.20 am on Monday. The 52-hour countdown has been optimised to 49 hours,” said Isro spokesperson S Satish over telephone from Satish Dhawan Space Centre-SHAR in Sriharikota. “Propellant filling and management of the second stage of PSLV-C11 is in progress.”

Chandrayaan-1 spacecraft is slated to be launched onboard India’s home-grown rocket PSLV-C11 at 6.20 am on Wednesday.

The launch of Chandrayaan-1 will take place from the second launch pad at SDSC, SHAR, Sriharikota in the Nellore district of Andhra Pradesh, about 100 km north of Chennai.

Chandrayaan-1 spacecraft begins its journey from earth onboard PSLV-C11 and first would reach a highly elliptical Initial Orbit (10).

In the 10, the perigee (nearest point to earth) is about 250 km and apogee (farthest point from the earth) is about 23,000 km.

After circling the Earth in its 10 for a while, Chandrayaan-1 spacecraft is taken into two more elliptical orbits whose apogees lie still higher at 37,00 km and 73,000 km, respectively. This is done at opportune moments by firing the spacecraft’s Liquid Apogee Motor (LAM) when the spacecraft is near perigee.

Subsequently, LAM is fired again to take Chandrayaan-1 spacecraft to an extremely high elliptical orbit whose apogee lies at about 387,000 km.

In this orbit, the spacecraft makes one complete revolution around the Earth in about 11 days. During its second revolution around the Earth in this orbit, the spacecraft will approach the Moon’s North pole at a safe distance of about a few hundred kilometres since the Moon would have arrived there in its journey round the Earth.

Once the Chandrayaan-1 reaches the vicinity of the Moon, the spacecraft is oriented in a particular way and its LAM is again fired.

This slows down the spacecraft sufficiently to enable the gravity of the moon to capture it into an elliptical orbit.

Following this, the height of the spacecraft’s orbit around the moon is reduced in steps. After a careful and detailed observation of perturbations in its intermediate orbits around the moon, the height of Chandrayaan-1 spacecraft’s orbit will be finally lowered to its intended 100 km height from the lunar surface. “Chandrayaan-1 is expected to settle into this orbit of 100 km height from the lunar surface around November 8,” Satish said.