Artistic depiction of Chandrayaan-1. © ISRO

Moon's secrets are set to be unravelled in greater detail with four robotic visitors from Earth simultaneously trying to fathom explore them. India's Chandrayaan-1 (moon vehicle in Hindi) built by its space agency ISRO in Bangalore is one of them.

Perched on the nose of ISRO's Polar Satellite Launch Vehicle (PSLV), at Satish Dhawan Space Centre in Sriharikota Island off the east coast, it is ready to leap toward the Moon any time the week starting October 20. If everything goes well, a week later, the box-shaped Chandrayaan-1 will hold hands with Japan's SELENE and China's Chang'E-1 already circling and photographing the Moon from different orbits. The Lunar Reconnaissance Orbiter (LRO) of the United States is slated to join the Moon party in February 2009.

From 1972 until SELENE's arrival in September 2007 and Chang'E-1's launch the following month, the Moon had just four visitors, that too one at a time: Hiten (1992) of Japan, Clementine (1994), Lunar Prospector (1998) of the US, and Smart-1 (2005) of the European Space Agency. For the first time, 2009 will see Moon's privacy being violated in chorus by a fleet of four alien spacecraft with a formidable array of equipment and cameras.

"As such, possibilities exist for coordinated study," says Narendra Bhandari the founder of ISRO's planetary exploration programme and currently at the Basic Sciences Research Institute in Ahmedabad.

Understanding how the moon evolved is a common objective of all four missions. However the LRO aims beyond this: it plans to map the lunar surface in preparation for human missions to the moon scheduled around 2020. China, whose astronauts staged a spacewalk last month, also has ambitions to set up an outpost on the Moon. Japan is not a novice: it has sent a probe to the Moon before.

However for ISRO, Chandrayaan-1 mission, coming almost exactly five years after approval by the government, symbolizes the initial baby step into the interplanetary space.

Since 1993, ISRO had launched 16 satellite missions — the latest on April 28, 2008 — but Chandrayaan-1 is the first that will leave earth's gravity.

"We have no experience in tracking a spacecraft to distances more than 36,000 km," admits S.K. Shivakumar who is in charge of ISRO's tracking and telemetry network. Moon is ten times farther and so tracking Chandayaan-1 at that distance will be another first for India.

"The mission is a real challenge for us," says Mylswamy Annadurai, project director of Chandrayaan-1. And that is to put it mildly.

The PSLV that will carry Chandrayaan-1 is not as powerful as Japan's H-IIA or China's Long Mrch-3A that sent SELENE and Chang'E-1 to the moon or the Atlas 401 that will lift the LRO on 27 February 2009 from Cape Canaveral in Florida.

"Smaller lifting capacity of PSLV meant lighter payload," Annadurai recently told reporters. Chandrayaan-1 roughly a 1.5 meter cube with a dry weight of 523 kilograms is a pigmy compared to bath-room sized SELENE (2914 kg) or China's Chang E-1 (2,300-kg).

"Development of spacecraft bus itself has thrown several technological challenges" due to space, weight and power constraints, says V. R. Katti of ISRO Satellite Centre (ISAC) in Bangalore where Chandrayaan-1 was assembled and integrated with payloads. So, the emphasis was on miniaturization and use of lighter materials, he says.

What emerged was a spacecraft of the size of a domestic refrigerator crammed with 11 science payloads drawing no more than 700 watts of power. "The real challenge was to accommodate different payloads in specific location/orientation in a small spacecraft," says Katti. The PSLV's limitation on lifting capacity also forced Annadurai's team to add a propulsion system to Chandrayaan-1 enabling it to reach the lunar orbit on its own thereby avoiding an additional stage to PSLV.

The Indian Deep Space Network, established at Bayalu, 40 km from Bangalore, is another challenge successfully overcome. The network's 60-tonne 32-m diameter dish antenna that will track and receive data from Chandrayaan-1 has been tested and is all ready. Built in record time of two years the antenna "is totally an Indian effort", says Shivakumar.

Unlike SELENE or Chang'E-1, Chandrayaan-1 is truly an international venture. Six of its 11 payloads have been contributed by 12 labs from eight countries: UK, USA, Germany, Sweden, Finland, France, Bulgaria and Czechoslovakia.

Artistic depiction of Chandrayaan-1. © ISRO

"This is a national mission with international participation and with India as the captain," Annadurai says. ISRO does not charge for carrying the foreign payloads but expects that data collected by the foreign agencies will be shared with ISRO scientists.

If everything goes as planned, the PSLV will inject Chandrayaan-1into a highly elliptical parking orbit from where the spacecraft will transfer on its own to the lunar orbit over the poles initially at 200 kilometers and finally moving to 100 km. ISRO says it will have enough fuel to give Chandrayaan-1 a life of two years. It will be tracked through a worldwide network of ground stations belonging to ISRO and space agencies of USA, Russia and Brazil.

What will Chandrayaan-1 find on the Moon that other missions have not found?

"It will be the first to use radar to study the moon," says Bhandari. "It is capable of seeing below the surface so we can determine what lies underneath," he said. "And if everything on Chandrayaan works well, one can learn how water gets transported to the poles." Earlier American lunar probes have indicated water may be found in the permanently shaded regions at the poles but no one knows how it gets there. The presence of water-ice can be detected by several of the instruments on board Chandrayaan-1 as well in other three spacecraft.

"We will also have a digital elevation map with 5 meter resolution both on ground and in elevation that will enable us to select potential sites for a future base," Bhandari said. "We will have chemical and mineral maps of the Moon which will be useful in indirectly determining evolution of the Moon."

Bhandari adds that Chandrayaan-1 is a "well designed" mission with powerful remote sensing instruments. "When the results start coming, we will know how important they would be."

Chandrayaan-1 will drop a heavily instrumented impactor on the Moon within the first week of is life and receive data during the 18-minute free fall. Its crash-landing is a precursor to the soft-landing by the rover to be flown by Chandrayaan-2 slated for 2011-12, says ISRO chairman Gopalan Madhavan Nair.

A successful moon mission by ISRO would indeed be a revelation to the world that neither giant rockets nor big budget is needed to go to the moon.

As against SELENE's $480 million Chang'E -1 $187 million and LRO's $491 million ISRO spent on Chandrayaan-1 Rs.3.86 billion (about $76 million). And that includes Rs.1 billion towards establishment of the Deep Space Network that ISRO would need when it launches Chandrayaan-II and after that, perhaps, to Mars.