What is ‘17 minutes of terror’ for Chandrayaan 3? Senior ISRO official explains

With the Chandrayaan 3 set to make soft landing on the moon's surface in less than 24 hours from now, all eyes are on the final moments when the lander module will touch the south pole of moon. A senior ISRO director has described those crunching moments before landing as “17 minutes of terror”.

India's ambitious moon mission Chandrayaan 3 is smoothly inching towards the moon, expected to make soft landing tomorrow at 6:04 pm. However, the last 17 minutes before the landing could pose a risk to the soft landing.

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Nilesh M Desai, the space application centre (SAC) director of ISRO, while speaking to ANI, described the significance of those 17 minutes. “On August 23, the lander will attempt to land from a height of 30 kilometres. Its estimated velocity will be around 1.68 kilometres per second, which is considered to be a great speed. The moon's gravitational force will pull the lander towards itself”.

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Adding further, Desai said,"We will have to retrofy the thruster engine, so that the lander de-accelerates to 0 when it makes the soft landing. We have installed four thruster engines in the lander module. From an altitude of 30 kilometres, the lander will come down to 7.5 kilometres and then to 6.8 kilometres".

“We will then shut two of the four engines and the remaining engines will be used for landing. We will cary out reverse thrust of the engine. From 30 kilometres, the lander's speed will be less by four times to 350 metres per second at an altitude of 6.8 kilometres”, Desai added.

“From 6.8 kilometres, it will descend to 800 metres and then go on a vertical descent towards the lunar surface. Using the reference data obtained from cameras and sensor, the lander will hover over the surface before deciding on the site where it has to land”, the SAC director added.

“The entire process will take place in 17 minutes and 21 seconds. If the lander moves a bit sideways to land on the suitable site, the maximum site, the time taken will be 17 minutes and 32 seconds. This '17 minutes of terror' is very critical for us”, he added, pointing out that there is absolutely no scope for error.