Chandrayaan-3: As Vikram prepares for deboosting, here’s how it separated from spacecraft on Thursday | India News – Times of India
The de-boost manoeuvres — first one scheduled for 4pm today (August 18) — will eventually see Vikramreach an orbit where the Perilune (closest point to Moon) is expected to be 30km and Apolune (farthest point from Moon) around 100km.
An exact orbit may not be achieved, but those margins would be accounted for inIsro’s planning.
Once the 30km x 100km orbit has been achieved, the most critical part of the landing, the process of reducing the velocity of the lander from 30km height to the final landing will begin. Vikram’s orientation would be changed from horizontal to vertical and a successful final descent, would see the lander soft-land on Moon on August 23.
But first, how did Vikram separate yesterday?
After the integrated spacecraft — propulsion module and landing module together — was stabilised in an orbit ideal for separation, Isro would have loaded the sequence of commands for the separation, which would have been autonomously executed by the onboard systems.
The cylindrical structure on top of the orbiter, the extension of the fuel tank, is where the lander with the rover inside it, was sitting. Both these modules were held together by clamps with two bolts.
Isro chairman S Somanath confirmed to TOI that the mechanism employed for separation on Thursday was the same as Chandrayaan-2. That is, two halves of a metal flat spring held the two modules. The springs were pre-loaded using two bolts. The bolts were sheared, releasing the lander.
On the reason behind employing this mechanism, a scientist associated with the previous lunar mission said it was simple, reliable and had extensive flight history.
Former Isro chairman K Sivan said: “If the same mechanism as Chandrayaan-2 was employed, then the systems are released by operation of a pyrotechnic bolt cutter to cut the bolts that hold the clamp. This system has high strength and stiffness when clamped and releases quickly, typically in less than 50 milliseconds, when command is given.”
SHAPE(ing) Future
The propulsion module, whose primary job of carrying the lander and rover from the injection orbit to the lunar orbit from where separation was to be done, also carries the Spectro-polarimetry of Habitable Planetary Earth (SHAPE).
SHAPE will look at Earth from Moon to study the former’s habitable planet-like features and use this information to explore exoplanets in the future. While there was no immediate confirmation on whether Isro has made SHAPE operational as yet — scientific instruments need to be turned on through commands — the propulsion module, subsequent to lander separation, is designed to operate for a three-six months.
However, depending on how much fuel the module is left with and the health of the instruments on SHAPE, could see its life get extended. Indicating this, Isro on Thursday said: “Meanwhile, the propulsion module continues its journey in the current orbit for months/years. The SHAPE payload would perform a spectroscopic study of the Earth’s atmosphere and measure variations in polarisation from the clouds on Earth to accumulate signatures of Exoplanets that would qualify for our habitability!”
