‘Designing Chandrayaan was like writing lyrics to a set tune’

October 19th, 2008 - 1:54 pm ICT by IANS  

ISROChennai, Oct 19 (IANS) While building India’s first moon craft, Chandrayaan project director Mylswamy Annadurai was reminded of his engineering college days when he wrote lyrics to the tunes of his classmates.At that time he used to write poetry - some were published in the college magazine.

“One of the many challenges in building the spacecraft is to accommodate the six overseas pre-built payloads. We had to design the spacecraft accordingly - sort of writing lyrics to a tune,” 50-year-old Annadurai told IANS from the Satish Dhawan Space Centre at Sriharikota, 80 km from here.

The man who will go down in space annals as the designer of India’s first moon orbiter was born in the small village of Kotavadi in Pollachi district of Tamil Nadu. He graduated from the Government College of Engineering, Coimbatore, and did his Masters at PSG College of Technology in the same city.

Now Annadurai is a veteran at the India Space Research Organisation (ISRO), having joined it in 1982.

“ISRO offers the good freedom even to freshers,” he said, citing his own experience when he suggested software modelling of ISRO satellites.

“It is something like a flight simulator. Operators can operate the computer-modelled satellites. Viewing the screen they can take corrective steps before a satellite is actually built and sent up,” he explained.

Over the years Annadurai has worked in different satellite projects - from Indian Remote Sensing (IRS) satellites 1A, 1B and communication satellites Insat 2A to 3E series.

He was mission director for the Insat 2C to 3E satellites and was associate project director for the country’s first education satellite Edusat before being assigned the prestigious Chandrayaan project in 2004.

“But Chandrayaan is not just another satellite,” Annadurai told IANS. “There were many new challenges in building it.”

The challenges started from the launch vehicle itself, as that is what determines the weight of the satellite.

Five years ago it was decided that Chandrayaan would be carried on a Polar Satellite Launch Vehicle (PSLV).

At that time PSLV was ISRO’s tried and tested rocket, while its 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 Annadurai 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 10 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 extrme 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.”

Then there was the question matching the payloads the PSLV will carry in addition to the experimental instruments aboard Chandrayaan. They are from multiple sources - the US, different European countries and ISRO.

The spacecraft had to be designed for them. “In respect of one overseas instrument we had to come up with a slightly different design so that it would perform as expected,” Annadurai said.

Then, to reach the lunar orbit, the satellite’s propulsion system needs high-thrust engines.

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 and his team was maximum possible miniaturisation of components to reduce weight.

The hyper spectral imager that will photograph the lunar surface has been reduced in size and weight, for instance. “The spin-off benefit will be that future satellites can carry smaller equipment,” Annadurai said.

The space bug obviously affects more than one member of the Annadurai family. His son is now studying aerospace engineering in Bangalore. “He is showing interest in space science but it’s too early to say whether he will follow his father’s footsteps.”

Annadurai hasn’t written a poem on Chandrayaan yet.

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