Isro chairman S Somanath, confirming this to STOI, said: “It has too much fuel, way beyond our expectations.There’s a lot of fuel left as everything was very nominal on the way to Moon and there were no contingencies requiring corrections (for which fuel would have been expended). We’re left with almost all the margin, that’s around 150+kg.” The propulsion module was loaded with 1,696.4 kg of fuel at the time of the launch on July 14, and did all the heavy lifting — five Earth-bound manoeuvres and five lunar-bound manoeuvres before separating from the landing module — between July 15 and August 17.
Each of these manoeuvres that were part of the mission profile and some minor corrections in between would have consumed some fuel. While there’s no break-up of how much fuel each of these operations have consumed, STOI has data from initial calculations — at the end of the first two manoeuvres — done for Chandrayaan-2, which could shed some light given that the mission profile so far has been similar to 2019.
03:38
Chandrayaan-3 Mission: Vikram lander separates successfully, now landing on Moon on August 23
More Time For SHAPE
The Chandrayaan-2 orbiter had carried 1,697kg of propellant, marginally more than the Chandrayaan-3 propulsion module. The orbiter was calculated to have expended more than 657kg of fuel completing the five Earth-bound manoeuvres and the trans-lunar injection (TLI).
In this phase, the Chandrayaan-3 propulsion module is expected to have used up slightly more fuel given that Isro opted to inject the spacecraft into a slightly lower orbit soon after launch for sake of stability. Post LOI, the Chandrayaan-2 orbiter was calculated to need more than 749kg of fuel at the end of the separation manoeuvre. The Chandrayaan-3 propulsion module is expected to have expended a similar amount of fuel or slightly more in this phase.
With 150+kg fuel still left in the module, it could go around Moon for much longer than the initial design estimate of three-six months — Isro says it could be for months/years without specifying a time. This means that the scientific instrument — Spectro-polarimetry of Habitable Planetary Earth (SHAPE) — gets more time to study Earth for its habitable planet-like features from the lunar surface. On whether SHAPE had been turned on for operations, Somanath said that as of late Friday, it was yet to be confirmed.
03:16
ISRO releases breathtaking visuals of the Moon captured by Chandrayaan-3’s Vikram lander
Final De-boost
Meanwhile, the landing module, comprising Vikram and Pragyan (the rover), would have attempted the second deboost manoeuvre after STOI went to print, at 2am Sunday. If it succeeds, Vikram would be all set for the power descent for soft-landing.
“Sunday’s de-boost would be the last operation unless there is a need for some corrections after the manoeuvre. If the de-boost goes as planned, next action would be on August 23, when we attempt landing,” Somanath added. The objective of Sunday’s manoeuvre will be to reduce Vikram’s Perilune to around 30km and Apolune to around 100km from the existing 113km x 157km. During Chandrayaan-2, the second deboost had put the landing module in an orbit of 35km x 101km.Watch Chandrayaan-3: Vikram completes 2nd de-boost, landing on August 23
