Tuesday, 21 October 2008
Chandrayaan-1: The Course It Takes From Sriharikota To The Lunar World
October 21, 2008
By Syed Akbar
Hyderabad, Oct 20: India's first lunar orbitor, Chandrayaan-1, will travel about 4,00,000 kilometres outside the Earth's atmosphere to capture the "beautiful secrets" of the Moon. But astrophysicists at ISRO will have to wait for at least 18 days to get the first close-up pictures of the lunar terrain from Chandrayaan-1.
Not until November 8, Chandrayaan-1 will reach its designated orbit around the Earth's only natural satellite, at a safe but close distance of 100 km from the Moon. The Polar Satellite Launch Vehicle-C11 blasts off from Sriharikota island in Nellore district in the early morning of October 22 carrying Chandrayaan-1 spacecraft. The PSLV-C11 will leave the spacecraft at a point in space, 250 km from the Earth at its closest (perigee) and 23,000 km at its farthest (apogee).
According to the celestial schedule drawn up by ISRO team, after circling the Earth in its initial orbit for a while, Chandrayaan-1 is taken into two more elliptical orbits whose apogees lie still higher at 37,000 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 the spacecraft to an extremely high elliptical orbit whose apogee lies at about 3,87,000 km," says the ISRO's plan of action.
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," an ISRO release says.
Later, the Moon Impact Probe will be ejected from Chandrayaan-1 spacecraft at the earliest opportunity to hit the lunar surface in a chosen area. Following this, cameras and other scientific instruments are turned on and thoroughly tested. This leads to the operational phase of the mission. This phase lasts about two years during which Chandrayaan-1 spacecraft explores the lunar surface with its array of
instruments that includes cameras, spectrometers and its radar system.
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