ST Team
Wednesday, November 5, 2008
The wee hours of October 22, 2008, marked a historic moment for the entire nation. A large crowd had gathered at the Satish Dhawan Space Centre at Sriharikota to cheer the launch of India's maiden lunar mission—Chandrayaan-1. An indigenous project of the Indian Space Research Organization (ISRO), the mission has catapulted the country into the league of a select group of nations that already have sojourn with the Earth’s natural satellite-the Moon.

Launched using the PSLV-C11 rocket, an upgraded version of ISRO's Polar Satellite Launch Vehicle, Chandrayaan-1 carried 11 payloads, five entirely designed and developed in India, three from European Space Agency (ESA), one from Bulgaria and two from the U.S., that would explore the moon. The mission aims to undertake remote sensing of the moon in the visible, near infrared, microwave and X-ray regions of the electromagnetic spectrum. Along with the preparation of a three-dimensional atlas of the lunar surface, identification of future landing sites and exploration of the moon from close range are also envisaged.

Though Chandrayaan is world's 68th lunar mission, Indian space scientists have italised several key messages with its launch. For once, compared to other space-faring nations, ISRO's missions have proved to be cost-effective and technologically far more effective. Chandrayaan cost ISRO $80 million.

Challenges behind the project Chandrayaan is not just any other satellite. "One of the many challenges in building the spacecraft was to accommodate the six overseas pre-built payloads. The spacecraft had to be designed accordingly," says Chandrayaan Project Director Mylswamy Annadurai.

Five years ago it was decided that Chandrayaan would be carried on a PSLV. At that time PSLV was ISRO's tried and tested rocket, while the heavier Geosynchronous Satellite Launch Vehicle (GSLV) was still in its infancy. PSLV can carry a payload of around 1,500 kg for geostationary transfer orbit (GTO). So Annadurai and his team knew the maximum permissible weight of the satellite. The thumb rule is that a rocket can carry around one percent of its total liftoff weight as luggage. That was one boundary within which the team had to work.

The next was the communications challenge. According to Annadurai, the INSAT satellites cannot be put in lunar orbit. "The communication to and from the satellite will be very difficult. The moon satellite will be orbiting at 3,86,000 km from the earth - over ten times the distance at which communication satellites orbit."

As a result, ISRO's satellite centre had to develop far more advanced communication sensors to receive and transmit signals. Chandrayaan will be orbiting just 100 km above the lunar surface. So the extreme climate near the moon was another challenge that Annadurai's team had to take into account. "Communication satellites while in orbit are manoeuvred to maintain equilibrium between the hot and cold climes up above the earth," he explained. "In a moon orbit the satellite will be exposed to high heat and thermally it needed a different design."

While the on-board motors of INSAT satellites are fired for a maximum of one week to lift it to the intended orbit around the earth, Chandrayaan will have to travel 18 days or more to reach the lunar orbit. So the buzzword for Annadurai's team was maximum possible miniaturization of components to reduce weight.

Future Plans
After the tremendous success of Chandrayaan -1, the scientists at ISRO are now in the process of developing Chnadrayaan-2, an unmanned probe that will land on moon next year. By 2015, ISRO has envisaged a launch of a two person manned mission to the moon using India's second rocket—the Geosynchronous Satellite Launch Vehicle (GSLV). "The manned mission will be an indigenous effort. However we are not averse to cooperating with any other space agency," says Madhavan Nair, Chairman, ISRO.

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