Mangalyaan: The least costly interplanetary mission ever


Article by: Abhinav Tanksale, on 03 April 2022, at 03:00 am Los Angeles time

The Indian space program (ISRO) has set the bar for first time missions with one of their most successful Mars Orbiter Mission (MOM) at a cost of just INR 450 million ($73 million). This figure was a small fraction of what NASA had spent on similar missions, making MOM the least costly mission to ever reach Mars!

From taking a modular approach to project development, to conducting ground tests and long working durations (6-9 hours) from scientists and engineers, the low cost was attributed to utilizing concepts of Physics in an effective way.

So are you excited to know what concepts were responsible for the mission's success? Then let's breakdown and explore the physics behind 'Mangalyaan'.

1) Launch:

India's Mangalyaan weighs less than a thousand pounds and if placed in the back of a pickup truck, it would not even stagger the suspension. This is small when compared to typical satellites that are launched into space. It weighed around 1,350 kg which is lighter than a decent-sized vehicle. 

The key to this was the alternate types of fuel used in order to counter gravity: solid and liquid propulsion systems. When there's an issue with solid engines, they can't be shut off while they burn; otherwise the propellant will escape without generating any thrust. Liquid propulsions on the other hand could be easily controlled throughout their burning process and then turned off once it has achieved maximum speed for its surrounding environment.

The craft took off by India's PSLV C25 rocket utilizing alternate solid and liquid propulsions in four stages. After the 6 main engines were burnt, it was able to gain escape velocity and leave the earth's sphere of influence.

2) Newton's laws and the Slingshot effect:

As we know, Newton's First Law of Motion states that "An object at rest tends to stay at rest, and an object in motion tends to remain in motion." When Mars is at the critical position, the orbiter has been moving away from the earth on a path tangential (or nearly perpendicular) to the earth's orbit for many hours. The fuel needed to change the path was thus minimal.

3) Elliptical orbit and inclination between planets:

The angle between Earth, Mars, and Sun needs to be approximately 44 degrees. This condition occurs at the time interval of 780 days meaning that if the mission had failed to send the satellite on that particular date, it would have postponed to January 2016.

The shortest distance between Earth and Mars is 54.6 Million implying consumption of large amount of fuel. Therefore, Engineers and Scientists came up with the idea of taking the shortest possible route and then decelerate it to match the planet's speed. This was made possible through an elliptical orbit of around 680 Million km which forms a tangent to the Mars and earth's orbit around the sun. 

4) Doppler effect:

Radio signals (including cosmic rays) travel at the speed of light to transmit information from the orbiter. In order to keep their connection live, mission control needs to continually update its position and velocity as it moves farther away. 

The radio wavelength is extended by how fast the network is able to figure out where the signal has traveled, which allows them to track how far along in its projected trajectory the spacecraft has progressed.

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