Space Diary
Chandrayaan-2

On July 22, 2019, India launched its second moon mission called Chandrayaan-2. The satellite was launched in space by a launch vehicle called GSLV Mk III that stands for Geosynchronous Satellite Launch Vehicle Mark III. The words "Mark III" means that it is the third improved version. For the meaning of "geosynchronous", see the Box.
First the satellite is put into an elliptical (egg shaped) orbit where the closest point of approach is as small as 230 km above the Earth but the farthest point of the orbit was 45,163 km. Slowly, this was raised by firing more rockets (called orbit-raising burn). Four such burns will bring the orbiter into an orbit from where it can escape Earth's gravity --- this is called trans-lunar injection (TLI).
The TLI procedure was refined and perfected by the Soviet (old Russian) Luna space missions. The orbit burn is done at a time and place so that the satellite will go into a path that will arrive at the moon. Even then all is not yet complete: the satellite has to be slowed down and "captured" by the moon into an orbit around it, so that it becomes a moon to the moon! In fact, when the American Apollo 8 lunar mission was injected with such a TLI, the entire procedure could be seen from the islands of Hawaii. 
In fact, Chandrayaan-2 was visible as a slow, bright, moving objectover Australia immediately after launch. The TLI for Chandrayaan-2 is expected to happen in the month of August.  
It will take seven weeks for Chandrayaan-2 to reach the moon.  It will spend 23 days orbiting the Earth, and 13 days orbiting the moon (decreased from the original 28 days due to delay in the launch).  It is expected that the lander will land on 6th September, 2019.  We have to wait and watch, literally!
The Chandrayaan-2 satellite has three parts: a lunar orbiter, a lander, and a rover. Its main objective is to map the location and amount of water on the moon, if any.

Lunar Orbiter
As the name suggests, the orbiter will orbit the moon at a height (altitude) of about 100 km. It carries five scientific instruments.  Three are new, and two are improved versions of those launched in the earlier Chandrayaan-1 moon mission. The main goal of the orbiter is to observe the lunar surface and so it carries a high resolution camera. It was built so that its batteries would last about one year.

BOX on Geostationary Orbit
A geostationary or geosynchronous orbit is one that circles the Earth in a circular orbit with a time period equal to that of the Earth rotation, and moving in the same direction. This means that it will always be overhead at the same point on Earth. This is convenient if you want to send instructions and signals to the satellite in such an orbit from a fixed point in space (for instance, from the ISRO command station in Sriharikota to the satellite which will remain overhead). So it is "synchronous" with the movement of the Earth. The antennae on the Earth then can be permanently pointed at the satelite. The orbit turns out to be a fixed one, at a height of 35,786 km above Earth. It is difficult to place a satellite so high up in the sky. So it is done in stages.
END of  BOX

Vikram Lander
Lander is the object that will detach from the orbiter and actually land on the moon. It will first descend into an elliptical (egg shaped) orbit of 30 km X 100 km so that it will fly closer to the moon. It has special liquid fuel engines for this task. After a series of check, it will attempt a soft landing on the moon. 
Have you thought about this: Even on Earth, if you are falling, the friction from the air will slow down your fall. There is no atmosphere on the moon and so no braking effect. If you allow the lander to "fall" from the orbiter, it will crash-land, just as the "Moon Impact Probe" from Chandrayaan-1 did. This time, the scientists want the lander to survive the landing without getting damaged or destroyed. For this, the lander will have parachutes to slow the fall. Some landers even have rockets that go in "reverse" and slow the fall. Vikram will have 8 thrusters for attitude control and 5 main engines with liquid fuel. 
It will have several cameras, mainly to check for obstacles in the path of its landing, such as rocky terrain, cliff, etc. It can land on surfaces with sloped up to 12 degrees.
This lander was named after the scientist Vikram Sarabhai, the father of the Indian space programme.
The Pragyan Rover Once the lander has landed safely, it will release the 30 kg small rover that can "rove" or move about on the moon's surface. Operated on solar power, the rover will move on six wheels and is expected to cover about 1/2 km of the moon's surface. It will travel at the incredible speed of 1 cm/s, taking rock samples and doing a chemical analysis of the composition and sending the information back to earth. Since the moon's terrain at the exact spot of landing is unknown, each of the six wheels has an independent electric motor to turn it! So it can go over very bumpy terrain. It also has a "rocker-bogie" suspension system. This means that when the wheels are at different heights, going over different slopes, the main part of the rover (called the chassis) will be more or less kept horizontal and not shaken very much, so as to protect the instruments it carries.
For the rover to move, there are two stereoscopic 3D vision cameras.  These cameras will take 3D images of the immediate surroundings so that an Earth-based team can decide which direction it can safely move without hitting a rock or toppling into a hole. The rover will operate for one lunar day (about 2 Earth weeks) since its electronics will not be able to operate in the intense cold of the lunar night. So for optimum operation, the rover should be brought out just when the day begins. 

Not all eggs in one basket
As you can see, there are many tense moments about the operation, including at the lift-off itself, which happened successfully. In addition to positioning the orbiter in the correct lunar orbit around the moon, and landing the lander safely, the rover should also work well, and at the right time. Because of this, all these three carry different scientific instruments. These are called payloads. The orbiter carries 8, the lander 4, and the rover 2. Many will take detailed photographs and analyse the lunar rock. Some will measure if there are any "moonquakes", that is, it will do seismology. Surface and air measurements will also be done. One of the quirkiest payloads is an NASA laser retro-reflector on the lander that will measure accurately the distance between the lunar surface and the satellites above. Many such reflectors are already there on the Moon, but this is so small that it fits on the palm of your hand! It is a testing arena for future Mars missions where such measurements will be critical.

However, one of the main missions of Chandrayaan-2 is to search for water on the moon. What is the interest in finding this out?

What is the lunar temperature?
The moon is very cold or very hot, going to 125C in the "daytime" (which lasts 13.5 days on the moon!) and -170C at "night". Why is there so much variation, unlike on Earth? This is because the moon does not have an atmosphere. Why? The moon is very small, and has a small mass, just about 1% of the Earth's mass. So its gravity is very small, the value of g on the moon being g=1.6 m/s2. Contrast this with g=9.8 m/s2 on Earth. So the moon cannot hold down the gases that form an atmosphere. Years of being buffetted by the solar wind would have stripped off whatever little atmosphere was present. Another reason is that the moon also does not have a strong magnetic field unlike on Earth. Earth has a liquid core of iron that causes a strong magnetic field to be formed around it, which extends beyond the planet. Lots of charged particles and radiation (from the Sun and outer space) is blocked by this field. This prevents the Earth's atmosphere from being stripped off.
But in the case of the moon, there is no protection from this radiation. Unless you are in a place where sunlight cannot reach: that is, at the lunar poles. Why is this place special? Because if it remains cold all the time over here, it is possible that water (in the form of ice) may be found at these places.

Is there water on the moon?
We know that liquid water cannot survive on the moon and water vapour is decomposed in the strong sunlight since the moon has no atmosphere. Why? See the Box. Since the 1960s, scientists have believed that water ice could survive in cold places on the Moon.  At these places, the sunlight should never fall, so that it remains cold all the year around. Possible locations are deep craters at the Moon's poles. Recently water molecules have been detected in the thin layer of gases above the moon's surface. But it is more likely to find forms of water as in hydrates or hydroxides of lunar minerals.
In 1976 the Soviet Luna 24 probe landed on the moon and showed evidence for water molecules 1-2 m deep under the lunar surface. But it was a small amount: just 0.1% by mass. On Sep 24, 2009, the NASA's Moon Mineralogy Mapper (MMM) spectrometer on Chandrayaan-1 detected signatures of water on the moon surface. This was confirmed by NASA in 2018, whose MMM showed that water ice is indeed present at the Moon poles. If this water is indeed in considerable quantities, it will make long-term lunar habitation by humans possible.
This is why it is planned to land the lander of Chandrayaan-2 at the pole: around 71 degrees south latitude, just north of the South Pole-Aitken basin rim. An alternate site at 68S also has been selected in case the first option does not work out. This basin is the largest, deepest and oldest basin that has been found on the moon. It is rich in minerals such as iron, titanium and silicate rocks.

Woman Power
Many women are part of the panel of instrumental scientists and engineers who were crucial to the development of Chandrayaan-2 project. Many women are in positions of authority as well. They are:
Muthaya Vanitha – Project Director, Chandrayaan-2
Ritu Karidhal – Mission Director, Chandrayaan-2
Chandrakanta Kumar – Deputy Project Director, Chandrayaan-2
We wish them all the best.
--Compiled from several sources; images from ISRo website and Wikipedia.