BENGALURU: In a major milestone,
on Wedneaday said it has integrated the Chandrayaan-3 spacecraft with the launch vehicle —
The space agency is looking at a mid-July launch (between July 12 and 19) window for India’s third lunar mission, and a second attempt at soft-landing equipment on Moon.
While the mission will carry a lander (
) and rover (
), it won’t carry an orbiter, which has been replaced by a propulsion module.
After its failed landing attempt in September 2019, Isro has carried out several changes on the lander.
This time around, Vikram will have stronger legs than in its previous avatar to enable withstanding landing at greater velocities than earlier, while Isro has also made several other changes learning from the failures of Chandrayaan-2.
TOI had reported about changes being made to the lander, including the strengthening of the legs, earlier.
Isro chairman, S
, told TOI: “There are a lot of improvements on the lander. Basically, what were the deficiencies we were trying to overcome? One is the lander legs, which we expected could have withstood a higher velocity [during Chandrayaan-2]. So how much can we increase the velocity tolerance in the available structure? We have enhanced the landing velocity to 3m/second from 2m/second. That means even at 3m/sec, the lander will not crash or break [its legs].”
Another scientist who was part of Chanrayaan-2 explained: “A landing/touchdown velocity of about 2m/second is ideal and safe. And it is good that the tolerance will be for 3m/second, which means in case the best situation is not there, the lander will still do its job.”
The second change, Somanath said, was the addition of more fuel to the lander to handle more disruptions and have the “ability to come back” so there’s more cushion to handle the mission.
“Third, we have added a new sensor called the laser doppler velocity metre, which will look at the lunar terrain. And through laser source sounding, we will be able to get components of three velocity vectors. We will be able to add this to the other instruments available, thereby creating redundancy in measurement,” Somanath said.
Isro has also improved the software to have more tolerance to failures like engine disruptions, thrust disruptions, sensor failures, etc, while also removing the central or fifth engine, which was added last minute during Chandrayaan-2.
“Five engines were OK with the earlier mass of the lander but now we’ve enhanced the mass by nearly 200kg. Also, given its weight now, we have to necessarily fire a minimum of two engines to do the landing, and cannot land with a single engine. Therefore, the central engine has been removed,” Somanath said.
He added that the space agency has extended solar panels and more panel area to generate power. Vikram will be able to generate power even if it lands in a different orientation and is not facing the Sun.
Chandrayaan-3 is scheduled for launch between July 12 and 19. And on selection of the final date and the time needed to reach Moon thereafter, Somanath said: “It will take around 45 days. It cannot be shortened because it depends on the commencement day of the landing. We want the lander to land at the location the day of the Moon starts so we get the full 15 days to work. That’s how the date is being chosen.”
But the major part of the preparations, he said, was dedicated to testing. “The whole of the last two years went for testing and not changes. The amount of tests we’ve done is much more than what was done during Chandrayaan-2. This is in terms of autonomous flights, helicopter flights, crane-mode landing simulation tests, drop tests, software simulation testbeds which were newly made to evaluate potential failures and recovery options etc,” he said.