Space Missions have been the flavour of the last 1 month – 2 Mars Missions – The Indian Mars Orbital Mission [MOM] – Malgalyaan, The American MAVEN [Mars Atmosphere and Volatile Evolution] Mission and on the heals of it the Chang-e 3 Mission from China to the Moon. While the MAVEN Mission was launched on 18th November its already in its inter planetary journey while the Indian MOM is still orbiting the Earth and is scheduled to start its inter planetary journey only in the wee hours of 1st December despite having being launched about 2 weeks before MAVEN on the 5th of November.
Why did MOM [Mangalyaan] follow a different path than the MAVEN. The answer to this is in the type of launch vehicle used, the amount of fuel used and lift off capability [Launch Mass]. While the MAVEN uses the much larger Atlas V rocket. The blast off launch weight of the Mangalyaan [MOM] is only 1360 kgs and the projectile is powered by the 4 stage PSLV rocket which had been previously used for the Chandrayaan I mission to the Moon in 2008. However the difference come after this stage.
The MAVEN [2500 kgs] is powered by a High Powered Centaur Upper stage engine. Once the MAVEN was fired by the Atlas V rocket it was placed into a low altitude earth orbit by the Centaur. After about 27 mins it fired the engine again and at the periapsis to inject the MAVEN into a interplanetary trajectory towards Mars. NASA effectively used larger rockets and the High Powered Centaur to reduce the complexity of attaining the escape velocity to effectively break out of Earth’s gravity.
ISRO [Indian Space Research Organisation] on the other hand depended upon its proven PSLV technology. The MOM is carrying a much smaller engine than the Centaur on the MAVEN. So what ISRO does is to fire the engine again and again at the periapsis [Nearest point from the Earth]. The ISRO will follow the technique of repeated burns of small duration in what will result in creating higher speeds for the MOM and at the same time lift the apoapsis [farthest point from Earth during the orbit raising procedures] of the MOM.
Why is the orbiter given the thrusts from the engines at the periapsis? The answer is simple. The orbiter is at its highest speeds at the periapsis and any injection of energy will result in a higher velocity which will help the orbiter gather more momentum to eventually break Earth’s Gravity.
Once the Magalyaan leaves the Earth on 1st [as estimated] the craft will follow a similar trajectory to the planet Mars – like a free fall in inter planetary space – often firing the thrusters to ensure course corrections at regular intervals.
Both the missions follow the Hohmann Least Propellant Transfer mechanism. Which means that they will get precisely one opportunity to enter the Gravitational Field of Mars and the lower their orbits in a series of orbit reduction mechanisms to eventually getting captured by the Mars’ Gravity.The Hohmann’s Transfer for a Mars’ Mission comes up every 26 months. Once the MOM reaches Mars on 24th September 2014 it will weight about 1100 kgs since it would have used up some fuel in the process of leaving Earth. The MAVEN will weigh nearly equal to its blast off weight of 2500 kgs and will reach on 22nd September 2014.
ISRO’s $69 million Mission to Mars is based on a shoestring budget compared to the ~$700 million.NASA mission is a great story in itself.
Wish both ISRO and the NASA all the best in their respective Missions!
“Keep Calm and Go to Mars”
The Silly Point 