Saturday, November 15, 2008

Tryst with Chandamama

With the successful entry of Chandrayaan-1 into Moon's orbit, India's space exploration has entered a new phase. Narendra Bhandari's book The Mysterious Moon and India's Chandrayaan Mission brings out the motivation behind the venture and explains its scientific aspects. Excerpts:

Lunar landscape showing craters. The crater density is high on bright highlands (left) than dark surfaces
Lunar landscape showing craters. The crater density is high on bright highlands (left) than dark surfaces

A satellite image of Earth and Moon. The Moon is unique as none of the other inner planets, other than the Earth, have permanent large satellites
A satellite image of Earth and Moon. The Moon is unique as none of the other inner planets, other than the Earth, have permanent large satellites

Chandrayaan-1 is ISRO’s first mission to the Moon to carry out high-resolution mapping of the lunar surface and distribution of various chemical elements and minerals
Chandrayaan-1 is ISRO’s first mission to the Moon to carry out high-resolution mapping of the lunar surface and distribution of various chemical elements and minerals

IN recent years, there has been a growing interest in using the Moon as a test bed for equipment and operations required for other planetary missions and a gateway for exploration of other solar system bodies. USA has outlined long term plans of having permanent human presence on the Moon and a Moon-Mars route for exploration of Mars. This will require exploration and utilisation of resources available on the Moon essential for establishing a lunar base. Europe, China and Japan also have ambitious programmes and Italy, Germany, France and some private entrepreneurs are making plans for lunar exploration in the coming decades.

The Indian Space Research Organisation (ISRO), since its inception about half a century ago, had well thought out priorities of development and applications of space technology. Vikram Sarabhai, who defined the vision of ISRO, wanted to use space technology for benefit of the society and national development. This resulted in two sets of satellites, the IRS series, for remote sensing of natural resources and INSAT series devoted to communication, etc. With successful launches of PSLV during the mid-1990s, a fly-by or orbiter mission to Moon and some inner planets appeared feasible but, in view of various national priorities at that time, ISRO started planning about planetary exploration program only around 1999-2000.

The Moon was the obvious choice for exploration in view of its scientific importance described above and considering the constraints imposed by the technical capability of ISRO in terms of launching, communication, satellite and payload technology. Dr K. Kasturirangan, Chairman of ISRO at that time, set up a Moon Mission Task Force with about 20 experts, under chairmanship of Dr George Joseph to define a programme of scientific exploration of the Moon.

The mission

Chandrayaan-1 is a lunar polar orbiter for remote sensing of the Moon from a nominal altitude of about 100 km. One orbit around the Moon will take about 118 minutes and both the poles will be observed during every orbit. The primary objective of this mission is to carry out topographic, chemical, radioactive and mineral mapping of the Moon with a high spatial and spectral resolution. It will collect data for a period of two years and cover the entire surface of the Moon. This information will enable scientists to determine the chemical and mineral distribution not only on the surface but should also enable them to infer relationship of various rock units as a function of depth, providing crucial information on early evolution of the Moon and transport and deposition of volatiles. These studies should also enable better understanding of resources available on Moon.

Chandrayaan-1 was approved in 2003 and was launched on October 22, 2008, it successfully entered the lunar orbit on November 8. The mission required many components such as launch rockets, lunar orbiter craft, remote sensing instruments, deep space communication network for telemetry, tracking and command, data handling systems, etc. The lunar craft uses several components e.g for power generation, propulsion systems for orbit correction, communication systems for data reception and transmission, attitude and orbit control systems, star and Sun sensors, thermal control systems for maintaining appropriate temperature for various instruments, data storage and handling systems etc.

Chandrayaan-1 has 11 payloads. To achieve the goals set for this mission, four baseline payloads were conceived which include Terrain Mapping Camera (TMC) for stereo imaging, Lunar Laser Ranging Instrument (LLRI) for altitude determination and gravity modelling of the Moon, Hyper-Spectral Imager (HySI) for mineral mapping, and a High Energy X-ray spectrometer (HEX) for radioactive mapping. These are the Indian payloads designed by various ISRO laboratories, namely Space Applications Centre, Laboratory of Electro-Optics, ISRO Satellite Centre and Physical Research Laboratory. The mission was further strengthened by international collaboration, which provided multiple techniques for meeting the science goals of Chandrayaan-1.

Five payloads under international participation have been included in Chandrayaan-1 mission. Miniature Imaging Radar Instrument (mini-SAR) and Moon Mineralogy Mapper (M3) are both US payloads. The other international payloads are Infrared camera (SIR-2) from Germany (ESA), and a Radiation Monitor (RADOM) from Bulgaria. The Sub-Atomic Reflecting Analyser (SARA) is a joint payload between Indian and foreign groups from Sweden, Switzerland and Japan, which will measure neutral particles in Moon 's environment.

In addition,Chandrayaan-1 also carries a Moon Impact Probe (MIP) to be released from Chandrayaan-1 lunar craft to impact on Moon. The impactor has some imaging and analytical instruments (e.g. mass spectrometer) and will make observations during its descent before crash landing on the Moon on a predetermined site. The objective of the impact probe is partly technological, preparing for future soft-landing on the Moon. All these instruments make Chandrayaan-1 a comprehensive mission, fully equipped with sensitive instruments to meet its scientific goals.

Deep space network

To communicate with the lunar craft 400,000 km away from Earth, to command it for proper manoeuvres and receive data on performance of the lunar craft as well as the data obtained by various instruments, a robust communication system is required. For this purpose two antennae with 18-m and 32-m diameter, have been erected by ISRO Tracking Centre at Byalalu, near Bangalore. This will form the Indian Deep Space Network, which can also be used in future for other planetary missions. The 18-m antenna is capable of S-band uplink and both X-band and S-band down link. The 32-m antenna is designed to provide uplink as well as receive signals in both X-and S-bands. Both these antennae are equipped with remote control operations from the ISTRAC Net work Centre in Bangalore, which is responsible for all spacecraft operations during various phases of the mission. To continuously remain in contact with the lunar craft, particularly in the initial phases after launch, when the craft may not be in the visibility range of Bangalore, more antennae are required. It is proposed to use the 64-m antenna at Bears Lake, Russia and other European and American Deep Space Net works for some time after the launch.

Several units of ISRO will execute various aspects of the mission. Various instruments have been made at Space Applications Centre, Ahmedabad, Laboratory for Electro-Optics Systems, Bangalore, ISRO Satellite Centre, Bangalore, and Physical Research Laboratory, Ahmedabad, besides the foreign payloads, which have been made in several countries as mentioned above. The lunar craft has been made and integrated with various payloads at the ISRO Satellite Centre (ISAC), at Bangalore. The tracking and control of the satellite will be carried out by the Deep Space Network, ISTRAC, Bangalore, and the mission will be launched from the Satish Dhawan Space Centre, Sriharikota.

Global cooperation

An opportunity for international collaboration and cooperation arises during the Chandrayaan mission because there will be several orbiters around the Moon with overlapping periods of observation. Japan's Selene (now christened Kaguya ) was launched in September 2007 and China sent its Moon orbiter Change 'E -1 in October 2007. They will be in orbit for about a year or possibly longer.

Chandrayaan-1, together with Kaguya, Chang 'E-1, LRO and some other missions, which are being planned, will provide more than three years of continuous observation of the Moon. This may constitute the longest continuous period of study of the Moon and should help us resolve some of the outstanding questions regarding chemical, mineralogical and geological evolution of the lunar surface, Earth-Moon interactions in the remote past, size dependent evolution of the planetary bodies and assessment of lunar resources. This series of missions may enable us to identify suitable sites for a permanent base on the Moon, paving the way for future missions.

Future plans

During the past few years there has been resurgence in planetary exploration programmes with a large number of space missions announced by USA, Europe, Japan, China and Russia for exploration of several planetary bodies of the solar system. Apart from understanding the evolution of the solar system objects, a major thrust is for finding evidence of life (fossil or living) in extra-terrestrial environments. Mars and the icy satellites of Jupiter and Saturn are the most promising bodies for this purpose.

The study and exploration of Moon will continue for a long time because of the various important and complex problems regarding its origin, evolution and Earth-Moon relationship. It is, therefore, desirable to embark on a long-term exploration plan, which should logically include landing and sample return missions.

ISRO has been debating on a landing mission to Moon, Chandrayaan-2. This will enable experiments to be conducted on selected areas on the Moon’s surface. Since the Moon is largely made up of the same elements as Earth, the lunar resources have little commercial implications except that they can be useful on the Moon itself to support a manned base.

The Mysterious Moon and India’s Chandrayaan Mission Abundant solar energy and traces of helium-3, available on Moon, however, may offer opportunities of economic exploitation. Helium-3 is a futuristic resource, considered to be an ideal fuel for fusion and is extremely rare on Earth but available in lunar soil in trace but recoverable quantities.

Apart from the economic aspects, the Moon can be used as a test bed for instruments, to be deployed for exploration of Mars and other planetary missions. Thus, Moon will continue to be an object of study as well as a stepping stone for exploration of other planets. With plans of a large number of missions to Moon and planets, we may be entering an exciting era of planetary exploration.

The author is a senior scientist from Physical Research Laboratory, Ahmedabad. He has done pioneering work in the study of Moon and has been associated with Chandrayaan–1 mission right from its inception.

Excerpted with permission from
The Mysterious Moon and India’s Chandrayaan Mission 
by Narendra Bhandari. Vigyan Prasar. Pages 88. Rs 195