- Preparations have begun for the launch of Chandrayaan-1, India’s moon mission, with the stacking of the stages of the Polar Satellite Launch Vehicle (PSLV-C11) under way at Sriharikota in Andhra Pradesh from July 21. Simultaneously, the Chandrayaan-1 spacecraft, with its 11 payloads from India and abroad, has been assembled fully at the ISRO Satellite Centre (ISAC), Bangalore. A 32-metre-diameter dish antenna is ready at Byalalu village near Bangalore to track the spacecraft during its 3,84,400 km journey to the moon. If the campaign goes as planned, the PSLV-C11, which is a more powerful version and is called PSLV-XL, will put Chandrayaan-1 in orbit on September 19.
Top officials of the Indian Space Research Organisation said: “We have started stacking the PSLV at Sriharikota for the Chandrayaan-1 mission. We are now building the first stage. The launch campaign has begun. We are moving the various stages from the Vikram Sarabhai Space Centre (VSSC) in Thiruvananthapuram and the Liquid Propulsion Systems Centre at Mahendragiri in Tamil Nadu to Sriharikota.”
- M. Annadurai, Project Director, Chandrayaan-1, called it “a national mission with international participation and India as the captain.” He said from Bangalore, “All the 11 payloads of the spacecraft have been integrated fully. The next milestone is to go for the thermo-vacuum tests.” These entail the creation of space-like vacuum in a big chamber at the ISAC. Mr. Annadurai said: “The fully integrated Chandrayaan-1 will be subjected to tests in the vacuum-like space environment. It will go through tests in minus 120 degrees Celsius and searing hot temperatures.”
After the thermo-vaccum tests, it would go through vibration tests to test its integrity. The spacecraft would later be moved to Sriharikota, he said.
The PSLV-XL is a more powerful vehicle than the normal PSLV. It is suffixed with XL because its strap-on booster motors are extra long.
- S. Ramakrishnan, Director (Projects), VSSC, said: “A PSLV has six strap-on motors. A normal strap-on will use nine tonnes of solid propellants. But XL will have 12 tonnes of propellants in each strap-on. We have also extended the length of the strap-ons from ten metres to 13.5 metres. That is why it is called XL – extra long.”
The PSLV-XL is a four-stage vehicle with a weight of 316 tonnes and a height of 44.4 metres. Chandrayaan-1 will weigh 1,304 kg on the earth but 590 kg when it orbits the moon at an altitude of 100 km.
The PSLV-XL would put Chandrayaan-1 in a long, elliptical orbit with an apogee of 22,000 km and a perigee of 200 km.
- Mr. Ramakrishnan explained how Chandrayaan-1 would reach the moon from this transfer orbit: “You fire the apogee kick motor [on board the spacecraft] to extend the ellipsis from 22,000 km to about half a million km. That is how it reaches the vicinity of the moon. Once it nears the moon, Chandrayaan-1’s velocity is reduced by rotating the spacecraft in the opposite direction. It is called retro-firing. Its velocity is reduced so that the moon’s gravity will capture Chandrayaan-1 and it will be in moon’s orbit.”
From an altitude of 100 km above the moon’s surface, Chandrayaan-1’s payloads will be used to investigate the moon’s minerals and chemical properties, detect the presence of water, if any, on the lunar surface, map the moon’s surface and look for clues on its origin and evolution.
One of Chandrayaan-1 payloads called Moon Impact Probe (MIP) will be ejected after the spacecraft reaches the lunar orbit.