The Indian Space Research Organization (ISRO) has successfully brought the propulsion module from the Chandrayaan-3 mission back to Earth’s orbit.
While not in the original mission plan, ISRO used the logistical advantages from a near perfect Chandrayaan-3 mission to bring back the module which had been orbiting around the Moon, after travelling nearly 384,000 km.
“In another unique experiment, like the hop experiment on the Vikram Lander, the Propulsion Module (PM) of Chandrayaan-3 was moved from an orbit around Moon to an orbit around Earth,” ISRO announced on Monday (December 10). The module had left Earth’s on August 1.
Ch-3’s Propulsion Module (PM) takes a successful detour!
In another unique experiment, the PM is brought from Lunar orbit to Earth’s orbit.
An orbit-raising maneuver and a Trans-Earth injection maneuver placed PM in an Earth-bound orbit.… pic.twitter.com/qGNBhXrwff
— ISRO (@isro) December 5, 2023
How did ISRO manage this feat? Why is it a big deal? What other ‘suprise’ experiments has the space agency carried out during the Chandrayaan-3 mission?
First, what is this propulsion module? How did it operate?
Unlike Chandrayaan-2, which had a full fledged orbiter with major payloads and communications systems, Chandrayaan-3 featured a lighter propulsion module. For the lander’s communications with Earth, the mission used the Chandrayaan-2 orbiter, which remains functional four years after the 2019 mission.
The only scientific instrument aboard was the Spectro Polarimetry of Habitable Planet Earth (SHAPE) — an experimental payload which studies the signatures that make Earth a habitable planet, in order to possibly identify habitable planets outside the solar system.
After the propulsion module separated from the lander on August 17 — 100 km from the lunar surface, and six days before the scheduled landing — it was supposed to continue orbiting the Moon for six months or more.
“The main function of PM is to carry the LM (lander module) from launch vehicle injection till final lunar 100 km circular polar orbit and separate the LM from PM. Apart from this, the PM also has one scientific payload as a value addition which will be operated post separation of the Lander Module,” ISRO had stated ahead of the mission.
There were no plans to bring the propulsion module back to Earth, with ISRO stating that it simply wanted to operate the SHAPE payload for about three months — “”“”the mission life of the module.
So, how did ISRO manage this feat?
What helped was just how precise and efficient the Chandrayaan-3 Mission had gone thus far.
“The meticulous mission planning of the earth and lunar burn maneuvers and precise injection orbit by launch vehicle resulted in propellant saving,” P Veeramuthuvel, Chandrayaan-3’s project director, told The Indian Express. To be precise, after over a month of operations, the PM continued to hold over 100 kg of fuel.
“It was decided to use the available fuel in the PM to derive additional information for future lunar missions, and demonstrate the mission operation strategies for a sample return mission,” the space agency said on Tuesday.
A mission plan was created to ensure the PM’s return without crashing on to the lunar surface, or entering into a low Earth orbit. “Considering the estimated fuel availability, and the safety to GEO spacecrafts, the optimal Earth return trajectory was designed for October 2023 month,” ISRO said on Tuesday.
How did the return journey go?
ISRO initially performed a maneuver on October 9, to raise the altitude of orbit of the PM around the moon to 5112 km from 150 km (from 2.1 hrs to 7.2 hrs). The Trans-Earth injection (TEI) maneuver was performed on October 13, following which the propulsion module made four Moon fly-bys before leaving the Moon’s sphere of influence on November 10.
“Currently, the propulsion module is orbiting Earth and will cross its first perigee (point closest to Earth) on November 22, at an altitude of 1.54 lakhs km,” the ISRO said.
“The orbit period is nearly 13 days … The perigee and apogee (point farthest from Earth) altitude vary during its trajectory and the predicted minimum perigee altitude is 1.15 lakhs km,” the space agency said, adding that “there are no threats” of the PM flying too close to any operational Earth orbitting satellites.
The SHAPE payload continues to be operated, whenever Earth is in its field of view.
What has ISRO learnt from this ‘surprise’ experiment?
Through these efforts, ISRO has been able to get an idea of “planning and execution of trajectory and maneuvers to return from the Moon to Earth,” aiding the space agency’s work in developing a software module for such a maneuver.
“UR Rao Satellite Centre/ISRO’s flight dynamics team has developed an analysis tool … for this operation which is being validated through the return maneuvers carried out for the Chandrayaan-3 PM,” ISRO said.
The experiment will also aid the planning and execution of a gravity assisted flyby across a planets/celestial bodies, as well as avoid “uncontrolled crashing of the PM on the Moon’s surface at the end of its life” and prevent space debris creation.
What was the other ‘surprise’ experiment carried out during the Chandrayaan-3 mission?
This was Chandrayaan-3’s second surprise experiment, after the previously-mentioned hop experiment carried out by the lander 11 days into its time on the lunar surface.
“On command, it [the lander] fired the engines, elevated itself by about 40 cm, as expected, and landed safely at a distance of 30–40 cm away,” the ISRO said in a statement on September 4. “Importance?: This ‘kick-start’ enthuses future sample return and human missions!” the space agency said.
Although a small jump, the hop experiment indicated ISRO’s capability to get the lander to fire its engines and produce the thrust needed to lift off from the lunar surface. In conjunction with the current experiment, these are seen as key for ISRO’s ambitions conducting the Lunar Sample Return Mission (LSRM) — where a lander take-off from the lunar surface, dock with the orbiter, which will then make a return journey to Earth, all while carrying lunar soil samples.
ISRO is also working on technology for re-entry of space capsules to earth.