Chandrayaan to orbit moon for two years

By Fakir Balaji, Sriharikota (Andhra Pradesh), Oct 12: India's maiden lunar mission, the Chandrayaan-1 spacecraft that launches Oct 22, will orbit about 100 km from the lunar surface for two years, performing remote sensing of the dark side or hidden portion of the moon to unravel its mysteries, scientists working on the project said.

About 500 space scientists are working round-the-clock to launch India's maiden lunar mission next week.

The Chandrayaan-1 spacecraft will be launched on board the Polar Satellite Launch Vehicle (PSLV) C11 from the Satish Dhawan Space Centre (SDSC) here, about 90 km from Chennai and off the Bay of Bengal.

"Preparations are in full swing to send the Chandrayaan spacecraft Oct 22 between 06.15 a.m. and 06.35 a.m. though 06.21 a.m. is the most optimal time for lift-off, as moon is inclined 28 degrees towards earth at the equator," SDSC director M.C. Dathan told IANS at a preview of the historic launch.

With the northeast monsoon a week away from the proposed launch date and weather forecast till Oct 26 being ideal in terms of wind movement and clear skies, scientists of the Indian Space Research Organisation (ISRO) are striving to integrate the 1,380-kg spacecraft with the 316-tonne rocket, fitted with six strap-on motors for the D-Day.

The 45-metre tall, updated version PSLV is the trusted workhorse launch vehicle of the Indian space agency, with a record of 12 consecutive launches since 1994.

The four-stage rocket is equipped with solid and liquid propellants that will fire the strap-on boosters to catapult Chandrayaan into the lunar orbit 18 days after the lift-off, on Nov 8.

"Though the launch window will be kept open Oct 22-26, the actual launch operation will commence Oct 17 (T-5) with formal countdown 50 hours before the lift-off, on Oct 20 at 04.30 a.m. and the final countdown seconds before the rocket is fired by computers into the sky," Dathan said.

As India's first spacecraft mission beyond earth orbit, Chandrayaan is aimed at expanding our knowledge about earth's only natural satellite - moon.

Orbiting about 100 km from the lunar surface, the spacecraft will perform remote sensing of moon for about two years using 11 scientific payloads, including five instruments designed and developed indigenously.

"Moon is the nearest celestial body to earth at a distance of 384,000 km. Formation and evolution of moon are central to understanding the solar system. Though there have been many manned and unmanned lunar explorations, Chandrayaan will be the first spacecraft to explore the dark side or hidden portion of moon and unravel the mystery behind," SDSC deputy director M.S.N. Prasad said at a demo of the lunar mission.

With Chandrayaan, India will join the elite space club comprising the US, Russia, European Space Agency, China and Japan by demonstrating its capability to explore moon with its own spacecraft and launch vehicle.

Shaped like a cuboid, Chandrayaan is powered by a single solar panel generating about 700 watts. A 36 ampere-hour (AH) lithium ion battery supplies power when the solar panel, projecting from one of its sides, is not illuminated by sun.

The spacecraft's dual gimballed antenna will transmit the precious scientific data collected by its instruments to earth.

Within 25 seconds of the lift-off from the second launch pad, the two strap-on motors will fire the rocket to place Chandrayaan into a highly elliptical transfer orbit around earth in the next 110 seconds.

After circling earth in its transfer orbit for a while, the spacecraft will be put into more elliptical orbits by repeatedly firing its liquid apogee motor (LAM) at opportune moments.

The LAM onboard will be fired again to make the spacecraft travel to the vicinity of moon by following a path called lunar transfer trajectory (LTT), whose apogee - farthest point from earth - is at 387,000 km.

"The initial operation, crucial for launching and putting the spacecraft into the elliptical transfer orbit, is programmed to last 1,089 seconds or 18.9 minutes. Over the next 18 days, the spacecraft is made to get into an elliptical lunar orbit with the help of moon's gravity and LAM onboard," Prasad pointed out.

After a detailed observation of the lunar orbit perturbations, the orbital height of Chandrayaan will be finally lowered to its intended 100 km height from the lunar surface.

"Once the spacecraft stabilises in its intended orbit, the moon impact probe will be ejected at the earliest opportunity to hit the lunar surface in a chosen area. Cameras and other scientific instruments are turned on and tested for the operational phase, which is expected to last for two years," Dathan noted.

According to ISRO director S. Satish, the lunar mission is estimated to cost about Rs.3.86 billion (USD 80 million), including Rs.1 billion for the launch vehicle, Rs.1 billion for the Deep Space Network (DSN) near Bangalore to receive the radio signals transmitted by Chandrayaan and Rs.1.86 billion for the spacecraft, sub-systems and other components, including payloads.

"The prime objective of the lunar mission is to expand scientific knowledge about the moon, to upgrade India's technological capability and to provide opportunities for planetary research to Indian scientists," Satish said.