Many critical components of Chandrayaan-1 were developed at city’s ISRO centreWhen PSLV-C11 blasts off on October 22 from Sriharikota in Andhra Pradesh with Chandrayaan-1, India’s first lunar mission, on board will be the dreams and efforts of a clutch of scientists from Ahmedabad’s Indian Space Research Organisation (ISRO).  Several highly critical components for the mission were developed at ISRO, Ahmedabad.

The mission will last about two years and aim to unravel the mysteries of the moon, which still remains much of an enigma for the scientific community.

Questions relating to the origin and evolution of the moon, the presence of water, the mineralogical composition and the quantification of helium-3 (a clean fuel for the future nuclear fusion reactors) still pose a puzzle to the scientists, and ISRO envisages finding answers to these questions. For this, Chandrayaan-1 will use its high resolution remote sensing sensors to view the moon in the visible, near infrared, microwave and X-ray regions of the electromagnetic spectrum.

Chandrayaan-1 will carry 11 payloads (scientific instruments). Of these, five are India’s very own, three are from the European Space Agency (ESA), two are from NASA and one is from Bulgaria.

The Indian payloads include the Terrain Mapping Camera, Hyperspectral Imager, High Energy X-ray Spectrometer, Lunar Laser Ranging Instrument (LLRI) and a 29 kg Moon Impact Probe (MIP).

While the LLRI will provide the necessary data for determining the accurate altitude of Chandrayaan-1 spacecraft above the lunar surface, the MIP will pave way for future soft landing missions on the moon by demonstrating the technologies required for landing a probe at the desired location.

Among the equipment developed at Ahmedabad is the Terrain Mapping Camera (TMC). This will completely map the topography of the moon with a resolution of 5 metres. It can image a strip of the lunar surface about 20 km wide and will work in the visible region of the electromagnetic spectrum, capturing black and white stereo images. The data from the TMC along with the one collected by the Lunar Laser Ranging Instrument will help scientists map the lunar gravitational field as well.

Another is the Hyperspectral Imager (HySI), also built by ISRO’s Space Application Centre, Ahmedabad. This will help map minerals on the lunar surface along with the mineralogical composition of the moon’s interior. This imager, with a resolution of 80 metres and operating in the visible and near infrared regions of the electromagnetic spectrum, can image a strip about 20 km wide.

The High Energy X-ray Spectrometer (HEX), jointly built by the Physical Research Laboratory, Ahmedabad and ISRO’s Satellite Centre at Bangalore is another key equipment, which will identify polar regions covered by thick water-ice deposits. It will also identify regions of high uranium and thorium concentrations on the moon. Incidentally, this is the first planetary experiment relating to spectral studies of X-ray energies, and is hoped to throw light on the evolution and origin of the moon.

The spacecraft, which will weigh about 1,400 kg at launch and about 590 kg in the lunar orbit, is cuboid in shape with a solar panel generating a maximum of 700 watts, projecting from one of its sides. Alternately, it also has a 36 Ampere-Hour (Ah) lithium-ion battery. To attain the escape velocity and travel towards moon, the spacecraft has a Liquid Apogee Motor (LAM).

The 44.4 m tall launch vehicle also has strap-on motors (PSOM-XL) for achieving higher payload capabilities. The vehicle will use solid and liquid propulsion systems alternately in four stages.

It will begin its journey by reaching a highly elliptical initial orbit (IO) with a perigee (nearest point to earth) of 250 km and an apogee (farthest) of 23,000 km. After circling the earth in its IO for a while, the LAM will fire to lift the spacecraft to an orbit of apogee 3,87,000 km. In this orbit, the spacecraft will make one complete revolution around the earth in about 11 days. Subsequently, the orbit will finally be lowered to the intended 100 km height from the lunar surface. Later on, the MIP will be ejected from the spacecraft to hit the lunar surface, beginning the operational phase of the mission, which will last two years.

Gaurav Sharma

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