- 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
Contact 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].”
So, that’s how the early hours of Saturday played out as Isro lost contact with the Vikram lander. Remember Sivan’s words confirming that contact had been lost. We’ll be coming back to that.
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.
So, why the confusion?
Well, as we said earlier, the confusion could be a result of a misinterpretation of Isro’s statement on Vikram going silent.
Recall what K Sivan told the tensed Isro control room on Saturday: “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].”
We’ve highlighted the important bits of that statement in bold. Note that Sivan never said that communication with Vikram was lost when it was at an altitude of 2.1 km. What he actually said was “normal performance was observed up to an altitude of 2.1 km” and that communication was lost “subsequently”.
This matches what is seen in the descent graph: Vikram’s is seen descending according to plan up until an altitude of 2.1 km when it sharply goes off course.
Note that there is no official communication from Isro on when and how contact with Vikram was lost. The space agency has been tight-lipped over the matter and has not said anything apart from its original statement and confirming that the Vikram lander has been spotted on the lunar surface.
Ever since losing contact, the Indian Space Research Organisation has been making constant efforts to get in touch the Vikram lander. On Sunday, Isro said it had spotted Vikram on the lunar surface with the help of the Chandrayaan-2 orbiter, which is safe and is in orbit around the Moon.
Time for Isro to re-establish contact with Vikram is running out — Vikram’s mission life — as well as that of the six-wheeled Pragyaan rover — was just 14 days. Isro now has less than 10 days to successfully get in touch with Vikram.
Meanwhile, most of Isro’s second moon mission remains on course thanks to the Chandrayaan-2 orbiter, which is where a majority of the experiments are located. Not only is the orbiter safe, Isro has been able to extend its mission life from the original one year to seven years due to significant fuel savings made by the Chadnrayaan-2 spacecraft on its way to the Moon.
Over the next few years, the Chandrayaan-2 orbiter will continue revolving around the Moon and studying the lunar surface and atmosphere. One of the most significant experiments the orbiter will perform will be to estimate the quantity of iced water present in south polar region of the Moon.