Mission to the moon

Print edition : August 15, 2003

`SOMAYANA 1' - that is the name of the Indian spacecraft that will journey to the moon in about five years, pending formal clearance of the project by the government. It will ride on a Polar Satellite Launch Vehicle (PSLV), which will deploy it at a height of 100 km from the moon. The orbiter or spacecraft will observe the moon from various angles, and beam back pictures on its chemical, physical and physio-chemical characteristics, besides its crater history. The orbiter will also survey the minerals on the moon. The information received is expected to throw light on the origin and evolution of the moon and other bodies of the planetary system, and how life evolved on the earth.

The orbiter will take about five days to reach the moon, which is 3.84 lakh km away, and will have a life of two years. While the Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram, will build the PSLV, the ISRO Satellite Centre (ISAC) in Bangalore will fabricate the orbiter. The mission will cost about Rs.300 crores.

Said Dr. P.S. Goel, Director, ISAC: "It will be a dedicated science mission to map the moon in detail." Mapping the moon will be done with a high accuracy of five-metre resolution, with a stereoscopic camera.

Said G. Madhavan Nair, Director, VSSC: "We have completed the mission design and the interaction with the scientific group. The project report has been submitted to the government. We are awaiting the government's approval." The scientific group, called the National Lunar Study Task Force, is headed by Dr. George Joseph, former Director, Space Applications Centre, Ahmedabad, and consists of ISRO's launch vehicle technologists, satellite engineers and scientists belonging to various disciplines from other institutions. It has gone into the technical and scientific challenges of the mission, and its project report submitted to the government is called `Somayana 1'.

More than receiving information about the moon's history, the mission will provide ISRO a platform to undertake inter-planetary expeditions. Said V. Adimurthy, Deputy Director, VSSC, and a key member of the Task Force: "The moon mission is a stepping stone to other missions. It will be a platform to go to other planets. The energy of the moon can be used to do inter-planetary travel."

One of the objectives of the mission "is to improve our knowledge of the moon's gravity field". For, its gravity field has not been understood fully despite so many missions to study it. Each time the Russians or the Americans sent an orbiter to the moon, they had to revise their earlier data on its gravity field. Besides, in spite of so many missions, many regions of the moon have not been explored. "We, therefore, want to send a modest mission to the moon," said Adimurthy.

There have been more than 60 missions to the moon so far, and the United States, Japan, China and the European Space Agency are planning more. Of the 60 missions, Russia sent 24 Luna missions between 1957 and 1976 and five Zond missions between 1965 and 1970. The U.S.' programmes included the Ranger, Lunar Orbiter, Survey, Clementine and Lunar Prospector missions. The high point of the U.S. programme was that six of its Apollo missions landed human beings on the moon and brought them back to earth. In recent times, the Japanese mission Hiten, launched in 1990, performed a sophisticated circumnavigation and was directed to impact on the far south side of the moon.

If a spirit of scientific curiosity kindled the moon missions of the earlier decades, it is economic reasons that drive lunar missions now. "The moon has an abundance of helium-three. It is going to be the future source of energy. It can be captured. It is rare on earth," said Adimurthy. Although the presence of water on the moon has not been established, the general hypothesis is that it has a large amount of water.

ISRO's orbiter will weigh 1,050 kg in the geo-synchronous transfer orbit but only 523 kg in the lunar orbit. It will carry 80 kg of scientific payload. ISRO will keep 50 to 60 kg of the payload for itself to conduct experiments. The remaining 10 to 20 kg will be available for international cooperation or to academic institutions in the country. ISRO has already received inquiries from several countries to use part of the payload to conduct experiments.

THERE are several scientific and technological challenges to make a spacecraft go round the moon at an altitude of 100 km. The moon's gravity model is not uniformly spread as on the earth and is far more complex. Precise orbit manoeuvring capabilities should be engineered into the orbiter to prevent it from falling.

Navigating the spacecraft, controlling it and communicating with it will be among the technological challenges of the moon mission. So far ISRO scientists' communication with satellites have been limited to giving commands to INSATs when they reach the GTO (36,000 km above the earth). The distance to the moon is of many orders more and ISRO's engineers and scientists must be able to track, command and guide the spacecraft over such a long distance.

There are three ways of reaching the moon. The Russians and the Americans have used the traditional approach: that of sending the spacecraft into a low parking earth orbit and then boosting it to the lunar orbit. A lot of studies have been done recently on the optimal way of going to the moon. The Task Force studied the orbital mechanics and found that there are two or three ways of going to the moon. Said Adimurthy: "We found that instead of going to the circular parking orbit, it is better to go to the elliptical orbit. To achieve 100 km x 100 km lunar polar orbit, the PSLV will inject the orbiter in the elliptical 285 km x 36,000 km GTO. This is the fastest and cheapest way of going to the moon. This is well within the PSLV's capability."

Once in the lunar orbit, the orbiter will come under the influence of the moon's gravity. Retro-firing is then done to make the probe orbit around the moon.

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