Thursday 26 May 2022
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Mars mission’s trajectory corrected

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The Indian Space Research Organisation (ISRO) reported yesterday via Twitter and Facebook that its Mars Orbiter Mission (MOM) has carried out its second trajectory correction manoeuvre, a 16-second rocket burn amounting to an additional velocity of 1.577 m/s, as ground controllers at the ISRO Tracking, Telemetry and Command Network (ISTRAC), Bengaluru, corrected the trajectory by transmitting via radio commands to the four thrusters of the orbiter to for 16 s from 4:30 pm onwards. The spacecraft is on track for a 24 September arrival at Mars.

Little rocket burns like this one may appear as routine, but there’s nothing commonplace about deep-space operations where the tiniest mistake can lead to the irrecoverable loss of a one-of-a-kind spacecraft. It’s even less routine for India, for whom Mars Orbiter Mission is their very first deep-space operation. Every day that this little spacecraft operates is a step farther into space for India than ever before.

tl tcm01 brIf things had gone wrong, the Rs 450 crore mission launched on 5 November 2013 from Sriharikota could have been lost forever. Nearly 20% of the 51 missions to Mars launched by different countries lost track on the way. Among the factors that could have affected the outcome of the operation is solar wind, which can make inter-planetary spacecraft drift from course. If the firing goes awry, the spacecraft can easily get lost. There can be errors due to wrong thrust or third body attraction as well.

ISRO chairman K Radhakrishnan told NDTV, “It has been executed successfully”. Earlier, he had admitted, “It is not a routine operation. Great precision is required in calculating and correctly firing the four small rocket engines on board the spacecraft in the exact direction.”

There are never any new pictures associated with deep-space rocket burns. There’s nothing nearby to shoot a photo of. But we are providing the readers with some graphics for a better understanding of the spacecraft’s path. The picture on top are two of the great southern-hemisphere radio dishes, both listening to the Mars-bound spacecraft as it performs its little course adjustment.

Spacecraft Optimal Trajectory Design_2.jpgTo optimise spacecraft trajectory in an efficient way, many numerical techniques are investigated such as pseudo-spectral method, genetic or evolution-based algorithm, gradient-based approach, Sequential quadratic programming and continuation or homotopy approach. The adjoining graphic shows a possible trajectory map (maximum radius trajectory with fixed final time).

Different kinds of trajectory correction manoeuvres (TCMs) are carried out en route a Mars mission. If needed during the spacecraft’s final approach to the red planet, a trajectory correction manoeuvre targets the orbiter to its final aim point for Mars orbit insertion on an intended approach trajectory. A TCM is then undertaken to remove any errors from the previous TCMs during cruise. It targets the final aim point for Mars orbit insertion and occurs days prior to that event.

Another type of TCM is kind of an insurance policy for the orbiter. In case the orbiter comes too close to Mars upon arrival, this manoeuvre is used to increase the orbiter’s altitude for the Mars orbit insertion burn. Its commands are then stored on board the orbiter several days in advance. An orbiter sent by National Aeronautics and Space Administration (NASA) has had two burn opportunities: At 24 h and 12 h before the Mars orbit insertion burn. During the last day before arrival, navigators determined whether the orbiter was not too close to Mars. If the orbiter had arrived at Mars on the expected trajectory, the last TCM would not have been needed.

Mangalyaan is currently travelling with a velocity of 28 km/s or about 100,800 km/h. It is now the fastest and farthest ever-traveling Indian object in space. It is so far away that it takes a radio signal almost five minutes to travel from Bangalore to the Mangalyaan.

If the Mars mission manages to reach within 440-560 km of the red planet’s surface after its epic marathon, India will become the third country in the world to achieve such an exacting target on a maiden journey.

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Surajit Dasgupta
Surajit Dasgupta
Co-founder and Editor-in-Chief of Sirf News Surajit Dasgupta has been a science correspondent in The Statesman, senior editor in The Pioneer, special correspondent in Money Life, the first national affairs editor of Swarajya, executive editor of Hindusthan Samachar and desk head of MyNation

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