An analysis of Chandrayaan-2 lander Vikram’s descent graph has indicated that contact with the lunar probe was lost when it was 400 metres above the surface of the Moon
- Isro lost contact with Chandrayaan-2 lander on Saturday when it attempted landing on the Moon
- The descent graph shows the lander going off course at 2.1 kms and losing contact at 400 metres
- The Chandrayaan-2 orbiter is safe in orbit and will remain operational for the next few years
ontact with the Chandrayaan-2 lander Vikram was likely lost when it was far closer to the lunar surface than what has been assumed. Ever since the Indian Space Research Organisation (Isro) lost contact with the Vikram lander, the popular perception has been that the probe was 2.1 km above the lunar surface when it went silent.
However, in reality, Vikram was likely as close as 400 m to the Moon surface.
The reason for the confusion could be put down to a possible misinterpretation of the statement released by the Indian Space Research Organisation on it losing contact with the Vikram lander. And, the clarity comes from an image of a graph that was following Vikram’s decent on to the Moon.
First, let’s recap what happened on Saturday when the Chandrayaan-2 lander began its descent on to the Moon:
- Vikram began its descent shortly before 1:40 am on Saturday. The probe went through a series of manoeuvres to slow down, lower its altitude and get in position to land near the south pole of the Moon.
- At around 1:50 am, silence began gripping the Isro command centre in Bengaluru and worry began creeping up on the faces of the scientists there, suggesting that something had gone wrong. No updates came in from Isro for the next 20 minutes.
- At 2:18 am, Isro chief K Sivan took to a mike at the control centre and said, “Vikram lander descent was as planned and normal performance was observed up to an altitude of 2.1 km. Subsequently, the communications from the lander to the ground centre was lost. The data is being analysed [sic].”
Now, let’s take a look at this image. The image shows Vikram lander’s descent on to the Moon.
Of the three elliptic lines seen in the image, the centre line corresponds to Vikram’s descent. The red line shows the planned path that Vikram was to take to land on the Moon. The green line is Vikram’s actual path.
Now, for the most part of the landing, the green line perfectly coincides with the red line, indicating that Vikram’s descent was going exactly according to plan.
Between the altitudes of 5 and 3 km, there are variations in Vikram’s actual descent trajectory and the one that was planned. But these seem minor.
Now, at an altitude of 2.1 km, the green line deviates sharply from the red line, suggesting that Vikram had gone off course.
The green line ends in a blip at an altitude of around 400 m.
This suggests that Vikram was in touch with the Isro command centre in Bengaluru till it was 400 m above the lunar surface. That is when the Chandrayaan-2 lander seems to have stopped communicating with Isro.
SO WHY THE CONFUSION?
Since Vikram lost contact on Saturday, it has been widely reported and believed that Vikram lost contact with Isro when it was 2.1 km above the lunar surface. However, the descent graph suggests otherwise.
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