India's Mars Orbiter Mission

India's Mars Orbiter Mission

Mangalyaan was launched on the Polar Satellite Launch Vehicle, PSLV-XL C25. As its name suggests, it is used to launch satellites into orbit and also launched the Moon probe Chandrayaan.

The PSLV has four stages using solid and liquid propulsion systems alternately. The first stage is one of the largest solid-fuel rocket boosters in the world. Six strap-on motors, four of which are ignited on the ground, augment the first stage thrust while two more are burnt in the air. Each stage burns for several hundred seconds only. A large number of controls make sure that the rocket does not topple and faces the correct direction without rolling. This time, the PSLV carried the Mars Orbiter, which weighs 1350 kg.

The payload

The payload is the object that is launched by the PSLV, that is, the Mars Orbiter. The photo shows the Orbiter undergoing tests before being placed inside the PSLV.

The next photo shows the Orbiter being attached to the fourth stage of the PSLV. You can see the heat shields surrounding the orbiter, ready to be closed, to protect the payload. Once closed, this will form the pointed or top end of the launch vehicle.

The next photo shows the PSLV, with its heat shield closed.

You may have seen that a ball that you throw up always comes back and hits the ground. If you throw it with more velocity, it may reach farther (like a javelin or discus throw) but ultimately it reaches the ground. If a space craft should be launched so that it doesn't land back on the Earth, it should therefore have sufficient velocity. If it has a velocity of at least 11.2 km/s (about 40,300 km/hour), it can escape the Earth's gravitational field, so this velocity is called escape velocity.

Since the escape velocity is so high, it requires a great deal of energy (costly fuel) to impart such a high velocity to a rocket when it is launched. So the fascinating idea behind the launch of the Mars orbiter is that it is first launched similar to a satellite. That is, it is simply put into orbit around the Earth. For this, a much smaller orbital velocity is needed.

Orbital velocity is the velocity needed to balance the two forces: gravity's pull on the satellite and the inertia of the satellite's motion, that is, its tendency to keep going. This is approximately 27,359 kph at an altitude of 242 kilometers.

Once the orbiter is launched as a satellite, this means it is put into elliptical orbit around the Earth. This is marked as stage 1 in the figure. From such an orbit, it is slowly given additional velocity (by burning its fuel in phases) so that it goes in increasingly larger orbits around the Earth. Finally, it is given a push that sends it out of Earth's orbit and into an orbit around the Sun. This is marked as stage 2 in the figure.

Now, Earth, Mars, and the orbiter are all three circling the Sun. The time of launch is calculated so that, at the point when Mangalyaan's orbit crosses that of Mars, Mars is also at that point! This happens after Mangalyaan goes about half an orbit around the Sun, about a year from now. Now that Mangalyaan was shifted successfully from its Earth orbit to its Sun orbit on Dec 1, it will simply keep moving in this orbit until Sep 2014, a journey of nearly eight hundred million km!

This trajectory becomes possible when the relative position of Earth, Mars and Sun form an angle of approximately 44 degree. Such an arrangement recur periodically at intervals of about 780 days or about 2 years.

Once it reaches Mars, it will be moved into an orbit around it. This is marked as stage 3 in the figure.

This is the first time India has launched a probe that has left Earth and its gravitational field, and will circle another planet. The launch itself is therefore an important objective since the complex manouvres required are already challenging. Once the probe reaches Mars, it is carrying a whole lot of scientific instruments that will probe the planet.

The Mars Orbiter Mission carries five scientific payloads to observe the Martian surface, its atmosphere and exosphere extending up to 80,000 km. It will measure quantities that will help us understand the evolution of that planet, not just geologically (its rocks and minerals) but also look for materials that may point to the existence of life forms.

The payloads consist of a camera, two spectrometers, a radiometer and a photometer. Together, they have a weight of about 15 kg.

The Mars Colour Camera (MCC) will be used for optical imaging. Its Thermal Infrared Imaging Spectrometer (TIS) will map the surface composition so that we can find out the minerals that are on this planet. The Methane Sensor for Mars (MSM) will detect the presence of Methane gas. The Mars Exospheric Neutral Composition Analyser (MENCA) will study the composition of Martian upper atmosphere. There is an advanced instrument called the Lyman Alpha Photometer (LAP) that is sensitive to the presence of hydrogen and will check for water on the planet.

The mission will add to the understanding of Mars that we have from other Mars probes, including the ones that have landed on its surface and are probing it.