India's Chandra 3 Probe Grabbed Headlines Today

And we thought the mission of India's Chandrayaan 3 was over; at least I did.  Turns out India's space agency, ISRO, had a surprise for us Monday.

In a surprise announcement made Monday, ISRO announced that it has successfully returned the propulsion module used by the spacecraft into a high orbit around Earth. This experimental phase of the mission, the agency said in a statement, tested key capabilities needed for future lunar missions, including the potential for returning lunar rocks to Earth.

The primary mission of the probe the ISRO refers to as CH-3 was to carry their Vikram lander and Pragyan rover to the moon for their first lunar landing.  That major goal was achieved on August 23rd, and while there were hopes the pair would survive the two week long lunar night, the mission was intended to last one lunar day and did.  

After the landing, the propulsion module portion of Chandra (CH-3 PM) moved to an orbit around the Moon at an altitude of 150 km. There it would carry out a mission called SHAPE a remote sensing mission to observe Earth with a separate, dedicated instrument package.

Here's where things departed from the early plans.  After a month of flying in this orbit, Indian mission operators found that the spacecraft still had a reserve of more than 100 kg of propellant, out of the original nearly 1700 kg of fuel and oxidizer. 

The engineers knew that the SHAPE mission could carry out its observations of Earth's atmosphere from a different orbit. By looking at Earth from a distance, this innovative science experiment seeks to set a benchmark for what to expect from the atmospheric signatures of exoplanets that may be capable of supporting life. So, the Indian engineers reasoned, it would be good to demonstrate the capability of their spacecraft to return to Earth orbit.

"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 Indian space agency said Monday.

On October 9, CH-3 PM raised its lunar orbit from 150 km to 5,112 km, and four days later it burned its engine again to begin exiting lunar orbit and transitioning into Earth orbit.  It reached its perigee on November 22, at an altitude of 154,000 km (95,700 miles).  That's far beyond the geostationary orbit at 22,236 miles, over four times the distance from the surface, and not likely to threaten any operational satellites around Earth.  It's also an orbit from which the SHAPE payload can observe our atmosphere.

CH-3 PM's path from lunar orbit (greenish color) to Earth orbit (yellow).  From ISRO

Ars Technica's Eric Berger takes this as a demonstration that India has replaced Russia as the third most advanced deep-space exploration program in the world, bumping Russia down to #4. India placed a spacecraft into orbit around Mars in 2014, and its Vikram lander succeeded in December after Russia's Luna 25 spacecraft crashed into the Moon in August.  I see his point of view.