Introduction 

Chandrayaan-1 was India’s first unmanned lunar probe. It was launched by the Indian Space Research Organization (ISRO) in 22nd October 2008, and operated until August 2009. Chandrayaan-1 is aimed at chemical, mineralogical and photo-geologic mapping of the moon in visible, near infrared, low energy and high energy X-rays with high spatial resolution.
 
Specifically, the objectives will be to carry out high-resolution three-dimensional mapping of topographic features along with the simultaneous mapping of distribution of minerals such as Si, Al, Mg, Ca, Ilmenites (FeTiO3, which may retain 3He) and elemental chemical species including radioactive nuclides. This mapping could unravel the mysteries about the origin and evolution of the planetary system in general and moon-earth system in particular. 

About Moon
 
Looming at about 384,400 km from the Earth, the Moon is the brightest object in the night sky and only second in brightness to that of the Sun. It has a diameter of 3,476 km and a mass of 7.35x1022 kg with a mean density of only 3.35 g/cc as compared to 5.52 g/cc of that of Earth. It has no atmosphere and degassing from the surface produces only trace gases. The gravitational force on the Moon is only 1/6th of that of Earth, and is not able to retain its atmosphere. The Moon does not have a substantial core of molten iron like Earth and hence has no magnetic field. The Moon undergoes extremes in temperature. It is scorching heat at 110º C during the day and freezing cold at .180º C during night.
 
The Moon.s surface is generally dry, dusty and rocky. The rocky crust is about 60 km thick on the near side that faces the Earth and about 107 km on the far side. Moon.s terrain is divided into two sharply contrasting areas. The rugged and very ancient mountainous .Highlands regions and smooth younger lowland, Maria regions. While Earth.s mountain ranges are formed by movements and coming closer of crust sections pushing against each other (known as plate tectonics), the lunar highlands did not result from an active uplifting process due to crustal dynamics. But its surface has been periodically bombarded with different sizes of meteorites and asteroids. During the initial period of lunar evolution, such giant meteor impacts resulted in the creation of flatlands or lunar basins. The regions not affected by these giant impacts are the lunar highlands.
 
Ancient observers thought that the round and dark areas on the face of the Moon are seas, which they called Maria (Latin word for seas). Maria are not seas at all but relatively flat areas produced by massive flow of lava from earlier period of lunar volcanism. Maria comprises 16 percent of the Moon.s surface and has huge impact basins. They are concentrated in the near side of the Moon. Associated with the Lunar Maria are gravity anomalies called mascons (mass concentrations). A spacecraft would accelerate as it nears the Maria region and decelerate as it moves away due to such gravitational anomalies.
 
The Moon is covered with a gently rolling layer of powdery soil and rock fragments called the regolith, which is made of debris created by the meteor impacts forming the craters. Such craters are the remains of collisions between an asteroid, comet or meteorite and the Moon. The size, mass, speed and angle of the falling object determine the size, shape and complexity of resulting craters. Surface of the Moon is scarred with millions of impact craters and the record has been retained on Moon,s surface.
 
One striking difference between the lunar surface material and that of Earth concerns the most common kinds of rocks. On the Earth the most common rocks are sedimentary because of atmospheric and water erosion of the surface. On the Moon there is no atmosphere and little or no water, and the most common kind of rock is igneous (.fire-formed-rocks.). According to studies, the lunar surface material has the following geological characteristics:
 

• The Maria is mostly composed of dark .basalts which are formed from rapid cooling of molten rocks from massive lava flows. 
• The Highlands rocks are largely Anorthosite, which is a kind of igneous rock that forms when lava cools more slowly than in the case of basalts. 
• Breccias are fragments of different rocks compacted and welded together by meteoric impacts and are found in Maria and Highlands. 
• The Moon has either a very small core rich in iron ore or no core at all.

 
 
Analysis of lunar rock samples indicate that
 

• The rocks are rich in Calcium (Ca), Aluminium (Al) and Titanium (Ti) 
• There is high abundance of Silicon (Si) and Oxygen (O)
• There is a relative abundance of 3He on the Moon, compared with Earth. This may be due to the fact that over the four billion year history of the Moon, several hundred million tons of solar 3He have impacted directly onto the surface of the Moon and got trapped in minerals such as ilmenite (a compound of iron and titanium; FeTiO3).

​The abundance of radioactive elements in rock samples can be used to determine the age of the rocks in a process called radioactive dating. Using such techniques on lunar samples brought back by the Apollo missions, it has been found that the oldest material from the surface of the Moon is almost as old as we believe the Solar system to be that is 5 billion years. Thus the material brought back from the Moon by Apollo missions provides a window on the very early history of our Solar system that would be difficult to find on the Earth, which is geologically active and has consequently obliterated its early geological features.
 
Seismic S waves apparently do not traverse the region below the zone of Moonquakes, suggesting that this material has very low shear strength, possibly containing some liquid.

Origin of Moon
 
The origin of the Moon is still not clearly understood and there have been speculations about its origin how it was formed and how it acquired its present orbit around the Earth. Studies using the chemical, mineralogical, isotopic and chronological data led to postulation of five major theories on the origin of the Moon:
 
The Fission Theory:
 
At some time in the distant past, the Moon had separated from the Earth Perhaps the Earth was not as round then as it is today and that imbalance caused it to split in two.
 
The Capture Theory:
 
The Moon was formed somewhere in the solar system and was later captured by the gravitational field of the Earth.
 
The Co-accretion Theory:
 
The Earth and Moon may have been formed at the same time from solar nebula by co-accretion.
 
The Colliding Planetesimal Theory:
 
Moon condensed from the debris of the interaction of Earth-orbiting and Sun-orbiting planetesimals (very large chunks of rocks like asteroids) early in the history of the solar system.
 
The Giant Impact Theory:

A planetesimal of Mars size had impact with the Earth, early in its history, ejecting large volume of matter from the evolving Earth, which aggregated and formed the Moon.

Why Moon
 
Apart from the scientific interest, the Moon could have economic benefits to mankind. This includes exploitation of the resource potential of the Moon including habitation of the Moon to reap the benefits on a continuous basis. The Moon has abundant resources of oxygen, hydrogen and other solar wind gases trapped in its regolith. Understanding the availability of such resources from the perspective of mineralogy, lithology and regional geology is a prerequisite for efficient human presence on the Moon. Early studies of the lunar regolith showed that there is a relative abundance of Helium-3 (3He) isotope on the Moon compared to that of Earth. 3He can be used as a fusion element and is thus considered as one of the important fuels for power generation in the future. Since 3He has high diffusivity, it normally gets lost from lunar grains. However, the mineral Ilmenite (FeTiO3) is abundant on the Moon and has high retentivity for 3He. The distribution of 3He associated with Fe and Ti can be determined by geochemical mapping since it would have the same distribution as (Fe + Ti). Over the four billion-year history of the Moon, several hundred million tonnes of 3He have impacted the surface of the Moon from the solar wind. The analyses of Apollo and Luna samples showed that over 1 million tonnes of 3He still remain embedded in the surface of the Moon. Even a small fraction of this could provide the world.s electricity for centuries to come. A large number of studies are being carried out to determine the technical feasibility of having a human outpost on the Moon.
 
 
The twenty-first century will mark a significant milestone in the history of human development: the colonization of the Moon! The Moon being the nearest neighbor of Earth and with 1/6 th of the Earth’s gravity offers a unique outpost for planetary exploration. The conditions may be adapted to generate lunar self-sustaining bases for such endeavors. Moon’s far side would provide an excellent site for establishing an astronomical observatory because of the absence of atmosphere and the absence of Earth’s reflected radiation on the far side of Moon.

​Propulsion in a broad sense is the act of changing the motion of a body. Propulsion mechanisms provide a force that moves bodies that are initially at rest, changes a velocity, or overcomes retarding forces when a body is propelled through a medium. Jet propulsion is a means of locomotion whereby a reaction force is imparted to a device by the momentum of ejected matter.

Rocket propulsion is a class of jet propulsion that produces thrust by ejecting stored matter, called the propellant. Duct propulsion is a class of jet propulsion and includes turbojets and ramjets; these engines are also commonly called air-breathing engines. Duct propulsion devices utilize mostly the surrounding medium as the "working fluid", together with some stored fuel.
 
The energy source most useful to rocket propulsion is chemical combustion. Energy can also be supplied by solar radiation and, in the past, also by nuclear reaction. Accordingly, the various propulsion devices can be divided into
 

• Chemical propulsion

 

• Nuclear propulsion

 

• Solar propulsion.

Radiation energy can originate from sources other than the sun, and theoretically can cover the transmission of energy by microwave and laser beams, electromagnetic waves, and electrons, protons, and other particle beams from a transmitter to a flying receiver. Nuclear energy is associated with the transformations of atomic particles within the nucleus of atoms and can be of several types, namely, fission, fusion, and decay of radioactive species. Other energy sources, both internal (in the vehicle) and external, can be considered. The energy form found in the output of a rocket is largely the kinetic energy of the ejected matter; thus the rocket converts the input from the energy source into this form. The ejected mass can be in a solid, liquid, or gaseous state. Often a combination of two or more of these is ejected. At very high temperatures it can also be a plasma, which is an electrically activated gas.
 
DUCT JET PROPULSION 
 
This class, also called air-breathing engines, comprises devices which have a duct to confine the flow of air. They use oxygen from the air to burn fuel stored in the flight vehicle. The class includes turbojets, turbofans, ramjets, and pulsejets.
 
ROCKET PROPULSION

Rocket propulsion systems can be classified according to the type of energy source
 

• Chemical
• Nuclear
• Solar

 
The basic function
 

• Booster stage
• Sustainer 
• Attitude control
• Orbit station keeping, etc. 

The type of vehicle
 

• aircraft
• missile 
• assisted take-off
• Space vehicle, etc. 

Another way is to Classify by the method of producing thrust.

A thermodynamic Expansion of a gas is used in the majority of practical rocket propulsion concepts. The internal energy of the gas is converted into the kinetic energy of the exhaust flow and the thrust is produced by the gas pressure on the surfaces exposed to the gas,
 
This same thermo-dynamic theory and the same generic equipment (nozzle) is used for jet propulsion, rocket propulsion, nuclear propulsion, laser propulsion, solar-thermal propulsion, and some types of electrical propulsion. Totally different methods of producing thrust are used in other types of electric propulsion or by using a pendulum in a gravity gradient.
 
Chemical Rocket Propulsion
The energy from a high-pressure combustion reaction of propellant chemicals, usually a fuel and an oxidizing chemical, permits the heating of reaction product gases to very high temperatures (2500 to 4100°C or 4500 to 7400°F). These gases subsequently are expanded in a nozzle and accelerated to high velocities (1800 to 4300 m/sec or 5900 to 14,100 ft/sec). Since these gas temperatures are about twice the melting point of steel, it is necessary to cool or insulate all the surfaces that are exposed to the hot gases. According to the physical state of the propellant, there are several different classes of chemical rocket propulsion devices. Liquid propellant rocket engines use liquid propellants that are fed under pressure from tanks into a thrust chamber.
​

​​The liquid bipropellant consists of a liquid oxidizer (e.g., liquid oxygen) and a liquid fuel (e.g., kerosene). A monopropellant is a single liquid that contains both oxidizing and fuel species; it decomposes into hot gas when properly catalyzed.

Gas pressure feed systems are used mostly on low thrust, low total energy propulsion systems, such as those used for attitude control of flying vehicles, often with more than one thrust chamber per engine. Pump-fed liquid rocket systems are used typically in applications with larger amounts of propellants and higher thrusts, such as in space launch vehicles.
 
In the thrust chamber the propellants react to form hot gases, which in turn are accelerated and ejected at a high velocity through a supersonic nozzle, thereby imparting momentum to the vehicle. A nozzle has a converging section, a constriction or throat, and a conical or bell-shaped diverging section Gas pressure feed systems are used mostly on low thrust, low total energy propulsion systems, such as those used for attitude control of flying vehicles, often with more than one thrust chamber per engine. Pump-fed liquid rocket systems are used typically in applications with larger amounts of propellants and higher thrusts, such as in space launch vehicles.
 
Some liquid rocket engines permit repetitive operation and can be started and shut off at will. If the thrust chamber is provided with adequate cooling capacity, it is possible to run liquid rockets for periods exceeding 1 hour, dependent only on the propellant supply. A liquid rocket propulsion system requires several precision valves and a complex feed mechanism which includes propellant pumps, turbines, or a propellant-pressurizing device, and a relatively intricate combustion or thrust chamber.

In solid propellant rocket motors the propellant to be burned is contained within the combustion chamber or case. The solid propellant charge is called the grain and it contains all the chemical elements for complete burning. Once ignited, it usually burns smoothly at a predetermined rate on all the exposed internal surfaces of the grain. Initial burning takes place at the internal surfaces of the cylinder perforation and the four slots. The internal cavity grows as propellant is burned and consumed. The resulting hot gas flows through the supersonic nozzle to impart thrust. Once ignited, the motor combustion proceeds in an orderly manner until essentially all the propellant has been consumed. There are no feed systems or valves

Gaseous propellant rocket engines use a stored high-pressure gas, such as air, nitrogen, or helium, as their working fluid or propellant. The stored gas requires relatively heavy tanks. These cold gas engines have been used on many early space vehicles as attitude control systems and some are still used today. Heating the gas by electrical energy or by combustion of certain monopropellants improves the performance and this has often been called warm gas propellant rocket propulsion.
 
Hybrid propellant rocket propulsion systems use both a liquid and a solid propellant. For example, if a liquid oxidizing agent is injected into a combustion chamber filled with solid carbonaceous fuel grain, the chemical reaction produces hot combustion gases.

​There are also chemical rocket propulsion combination systems that have both solid and liquid propellants. One example is a pressurized liquid propellant system that uses a solid propellant to generate hot gases for tank pressurization; flexible diaphragms are necessary to separate the hot gas and the reactive liquid propellant in the tank.