In an interaction with TOI, Isro chairman S Somanathlaid out plans for the complex mission.While Isro has shown it can reignite engines on the lunar surface (needed for spacecraft to ascend and reach a lunar orbit before returning) and bring a spacecraft back to Earth orbit (the PM experiment), it would need to demonstrate docking of systems before attempting sample return.
For this, Isro has in the pipeline Space Docking Experiment (SPADEX). “Sample return mission is much more complex as it’ll have many more manouvres: Collect samples and place them in a canister, return of that unit to the unit that will take off from Moon and reach Moon’s orbit where it needs to dock with a spacecraft that will return to Earth’s orbit. After this, the unit needs to separate and dock to a spacecraft in Earth’s orbit which will eventually make a re-entry,” Somanath told TOI.
Therefore, SPADEX will be a crucial experiment not just for lunar sample return mission but will also give Isro data on space rendezvous technology — where two spacecraft can find each other and remain in the same orbit — advancements in which are critical for a space station and sending humans there and eventually to Moon. The PMO had recently made public a roadmap for Isro, which includes a space station by 2035 and humans on Moon by 2040.
“We are aiming for SPADEX by the end of 2024. The satellite is getting ready,” Somanath said. As part of the experiment, the satellite will launch with two components. It’ll separate into two pieces and then get docked into a single piece. This single unit will then function as a full-fledged satellite.
CH4 Progress & LUPEX
On the progress of Chandrayaan-4 so far, Somanath said: “We’ve identified a team and I’ve reviewed the initial project and overall architecture. Now system-by-system review, technology review and departmental review etc has to be done. It is a long process but the work is on.”
India is also working with Japan on the Lunar Polar Exploration (Lupex) mission, whose main objective is to confirm the presence of water in the polar regions of the moon. As reported by TOI earlier, Isro is yet to submit the final project report for clearance as some issues pertaining to the weight of the lander and rover are being looked into by both sides.
Will Chandrayaan-4 pip Lupex? “I cannot predict as of today. Both are under approval process. Lupex is an international engagement and we need readiness from the other side also while Chandrayaan-4 is our own. I cannot predict which one will be first,” Somanath said.
44-day Return Of PM
Somanath said these future missions have received a shot in the arm from the return of the PM — a 44-day-long journey that saw a series of complex manoeuvres being performed using the 100kg fuel that was left.
The first manoeuvre to raise apolune altitude to 5,112km from 150km was done on October 9. Then, the second manoeuvre plan was revised to target an Earth orbit of 1.8 lakhs x 3.8 lakhs km. The Trans-Earth Injection (TEI) was performed on October 13, 2023. This was followed by four Moon fly-bys before departing Moon’s sphere of influence on November 10 before it reached the intended Earth orbit on November 22.
Currently, PM is around Earth and Somanath said Isro would use the payload — SHAPE (Spectro-polarimetry of HAbitable Planet Earth) — to continue studying habitable planet-like features of Earth every time the planet is visible to the PM.
Watch ISRO brings back Chandrayaan-3 Propulsion Module to Earth’s orbit