Historic voyage

The earth as seen by Chandrayaan-1 from a height of 70,000 km. This image, the second taken by the Terrain Mapping Camera of the spacecraft on October 29, shows Australia's southern coast.-ISRO

Chandrayaan-1 is moving closer to the moon and is expected to enter its lunar orbit on November 15.

IT is a time of reckoning for Indias space scientists as they prepare for the countrys first rendezvous with the earths closest neighbour, the moon. On October 29, the Indian Space Research Organisations (ISRO) spacecraft Chandrayaan-1 was on its way to reaching two-thirds of the 3.84-lakh-kilometre distance to the moon. It is expected to enter its final orbit around the moon on November 15.

That morning, three minutes after the firing of its engine system, Chandrayaan-1 was knifing through space in an orbit around the earth with an apogee of 2.67 lakh km and a perigee of 465 km. In this highly elliptical orbit, the spacecraft takes about six days to go round the earth once. This was the fourth precision manoeuvring of the spacecraft to raise its orbit, but what made the day for the engineers at the Spacecraft Control Centre (SCC) at ISTRAC, ISROs Tracking, Telemetry and Command Network at Peenya in Bangalore, was the fact that they started getting signals from Chandrayaan-1.

The previous manoeuvre, on October 26 morning, had Chandrayaan-1 sailing into deep space and reaching almost half the distance to the moon, achieving an apogee of 1.64 lakh km and a perigee of 348 km.

But it was a dreadful launch day on October 22 at the spaceport at Sriharikota in Andhra Pradesh. Tension ran high at the Mission Control Centre as Team ISRO raced against time to complete the countdown for the lift-off of the Polar Satellite Launch Vehicle PSLV-C11 at 6.22 a.m.

It was a dramatic finale to a long-awaited event. The spindle-shaped island in the Bay of Bengal had been buffeted by rain and thunderstorms for five days. It was in driving rain on October 18 that the 44.4-metre-tall PSLV-C11 was moved to the second launch pad, and there it stood in the open, all 316 tonnes of it and with Chandrayaan-1 mated to it, through rain and storm, until the launch.

As the final 49-hour countdown wound down from 5.22 a.m. on October 20, the weather turned worse. Although the PSLV is a rainproof vehicle and has lifted off twice earlier in pouring rain, what worried the mission team was the lightning and the charged particles in the dark clouds that hung over the island.

Then, the liquid propellant servicing facility on the ground, which remotely fills the second and third stages of the PSLV, sprang a leak. There was no problem with the vehicle itself. An ISRO technician gallantly went to this remote-controlled facility, changed the offending O-ring and plugged the leak.

By then, 10 hours of precious time had been lost in the 49-hour countdown. The launch window was a narrow one just 15 minutes from 6.22 a.m. to 6.37 a.m. Meteorologists had warned ISRO that the outlook for the weather beyond October 22 was bad, with the northeast monsoon setting in. Besides, a moon mission can be launched only on two dates in a month, which depend on the alignment of the earth and the moon.

The ISRO top brass met at around 1.30 a.m. on October 22 and contingency plans were put in place to complete the countdown on time. It was a tough job. Operations such as electrical checks and filling of pressurants and gases, which should be done in a sequence, were executed simultaneously to gain time. Team ISRO was back on track by T minus four hours, that is, four hours before the lift-off, and the weather cleared just in time.

At the appointed time of 6.22 a.m., the brown-and-white PSLV-C11, which is an advanced version of the standard PSLV, sizzled to life and quickly cleared the launch pad. It was visible only briefly as it vaulted into the sky on towering columns of flame and smoke before it disappeared into the thick, dark clouds blanketing the sky. A deep, thunderous roar from the six strap-on motors of the PSLV-C11, which are more powerful than those on the standard PSLV, reverberated for a few minutes.

It turned out to be a precision flight, with the strap-on motors, which form the zero stage, and the four core stages igniting on time and jettisoning themselves away. The heat shield around Chandrayaan-1 split in two and fell into the Bay of Bengal after its task of protecting the spacecraft during the vehicles ascent into the atmosphere had been achieved.

Eighteen minutes and 20 seconds into a flawless flight, the rockets fourth stage injected Chandrayaan-1 into its initial orbit, with an apogee of 22,866 km and a perigee of 256 km. Soon the spacecrafts solar panel, which supplies power to it, opened like an accordion, and the mission team at Sriharikota erupted into cheers. This was the first time an Indian spacecraft was going beyond the earths orbit, deep into space towards the moon.

Soon after the spacecraft went into its initial orbit, ground stations at Sriharikota, Lucknow, Thiruvananthapuram, Port Blair, Hawaii in the U.S., Biak in Indonesia and Brunei started tracking it. In the afternoon, 40 km from Bangalore, at Byalalu village, two bowl-shaped antennae with diameters of 32 m and 18 m, practically the eyes and ears of the mission, started tracking Chandrayaan-1.

This is the beginning of our long journey to the moon, declared an exultant G. Madhavan Nair, ISRO Chairman. It is a historic moment for India. We have opened a new chapter [in the history of ISROs space exploration programme], he said, adding: Everything went perfectly. It was a remarkable performance by the launch vehicle. What we have started is a remarkable journey for an Indian spacecraft to go to the moon and try to unravel the mysteries of the moon. The first leg, and perhaps the most difficult part, has been accomplished successfully.

The PSLVs fourth stage had catapulted Chandrayaan-1 into orbit, giving it sufficient velocity and attitude, and the spacecraft was now going round the earth with an apogee of 22,866 km and a perigee of 256 km. Said Madhavan Nair: The spacecrafts propulsion system would be fired in stages in the coming days for Chandrayaan-1 to perform sophisticated manoeuvres. Its trajectory would then be precisely calculated and it would be inserted into the final orbit at an altitude of 100 km around the moon.

M. Annadurai, project director, Chandrayaan-1, made a similar observation: We have just delivered the spacecraft into orbit. We have a long way to go in time and space before it goes into its final lunar orbit on November 15.

M.Y.S. Prasad, Associate Director, Satish Dhawan Space Centre, Sriharikota, who was also director of range operations for the mission, was ecstatic. He said, It was a thrilling experience. In spite of all the delays that accrued, we managed the mission well, to the satisfaction of the launch vehicle team and the spacecraft team.

At his post-launch press conference at Sriharikota, Madhavan Nair said: This mission had a lot of dramatic moments after we came to the launch complex. We were working against all odds. What we faced in the last five days was really an ordeal. The SHAR [Sriharikota High Altitude Range] team has done a remarkable job. We were racing against time. Last evening [October 21], we lost 10 hours of the countdown. We lost all hope of the countdown this morning. But the rain kept away at the last moment and we just made it at 6.22 a.m. Working against all odds, Team ISRO won the day.

Chandrayaan-1, built by the ISRO Satellite Centre (ISAC) in Bangalore, has the most comprehensive set of 11 scientific instruments to fly on board a moon mission. It will put a total map of the entire surface of the moon in the hands of the scientists in India and abroad. The spacecraft has a novel combination of remote-sensing and communication capabilities.

Chandrayaan-1s instruments are unique for the spectrum of their coverage, which will provide information on the minerals and chemicals in lunar soil, the moons hills, valleys and craters, possible confirmation of water-ice in the permanently shadowed South Pole of the moon, and the presence of helium-3. The information that the instruments gather will provide clues on the origin and evolution of the moon and thereby provide insights into the origin of the earth itself.

Annadurai, the driving force behind the integration of the 11 scientific instruments into the spacecraft, said: Chandrayaan-1 is configured with a judicious combination of flight heritage and mission-specific newer systems. The Indian mission to the moon should be seen beyond the scientific results it produces. Studies have shown that the moon could serve as a source of economic benefit to mankind and be of strategic importance.

However, Chandrayaan-1s journey to the moon is fraught with uncertainties because this is the first time an Indian spacecraft is going beyond the earths gravity deep into space. When the spacecraft escapes the earths gravitational field, the influence of the moon will be considerable. The suns interference will be there. Besides, the moons gravitational field is one of the biggest unknown factors. The spacecrafts antenna, which will radio the information gathered by the instruments to the ground, should always be pointing to the earth. ISRO will face all these problems for the first time.

While the first manoeuvre to raise Chandrayaan-1s orbit by firing its onboard engine went off without a hitch on October 23, the second manoeuvre the next day had a little hiccup. The packet of commands sent from the SCC did not go home at all. ISROs radio engineers were in a quandary: Did the commands not reach the spacecraft at all or did the spacecraft not register them after they reached it? We are used to giving commands to the INSATs [Indian National Satellites], which are geostationary satellites, when they are in their apogee. But for Chandrayaan-1, we have to give commands when it is in its perigee. We are not experienced in this, said an ISRO engineer.

T.K. Alex, Director, ISAC, said: Finding the spacecrafts position in orbit and the direction in which the spacecraft is pointing are the most important challenges in accomplishing this mission. The direction of Chandrayaan-1 is found out by using its star-tracker and gyroscope, which were both developed by ISRO laboratories. The star-tracker images the sky and gets its direction from 10 stars in the sky. The positions of the bright stars are kept in the memory of the spacecrafts computer by a technique called pattern-imaging. Thus, the star cluster is identified, and the precise direction of the spacecraft is automatically stored in Chandrayaan-1s computer.

The spacecrafts position in orbit is found out by a chain of ground stations spread all over the globe. The most important part is for Chandrayaan-1 to reach the moon at the precise time and with precise velocity when the moon is exactly at the desired place, Alex said. Once Chandrayaan-1 reaches the vicinity of the moon, its velocity is reduced. Its altitude is brought down in stages until it is inserted into the lunar orbit at an altitude of 100 km. Commands will then be radioed from the SCC to the Moon Impact Probe (MIP), an India-built instrument on which the Indian tricolour has been painted, to eject and crash-land on the moons surface. The remaining 10 instruments will be switched on later, one by one.

S. Ramakrishnan, Director (Projects), Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram, said: This is Indias first planetary mission. Success in the Chandrayaan-1 mission will give us the confidence to plan more such missions. We will command respect in the international community and we can be partners in such international programmes.