Chandrayaan-3 lunar hop explained: Small jump for Vikram lander, giant leap for ISRO

Chennai

After successfully completing a hectic fortnight of constant work, wouldn't you want to unwind and try something new or extraordinary, as a final and celebratory act? That's kind of what the Indian Space agency ISRO has done with its Chandrayaan-3 craft, that has completed all its scientific and exploratory work near the Lunar south pole. 

The craft performed what is known as a Hop test, where its jumps from its landing site and moves a little sideways and soft-lands again. This is a helicopter-like controlled and meticulously planned vertical take-off and vertical-landing. 

Also read | NASA shares image of India's Vikram lander on Moon spotted by its lunar orbiter

The latest hop test that ISRO has completed successfully is a surprise move by the Indian Space agency and a significant technological leap for the Indian Space programme. This is the first publicly-known vertical take-off and vertical-landing

(VTVL) done by an Indian craft. Notably, ISRO is also working on re-usable rockets that are capable of VTVL.

What is a Hop test? 

Chandrayaan-3 was primarily meant to land on the Lunar surface (using the Vikram Lander) and traverse the Lunar terrain (using the Pragyan rover), while both of them conduct their respective experiments. 

This mission was supposed to be a one-way trip and will be so; land at your destination, conduct studies and remain there for eternity. 

What if ISRO wishes to send back samples from the moon or land humans on the moon? In that case, safe-soft-landing is just half the job. 

In order to commence a return journey from the moon to the earth, one must be able to vertically take-off from the Lunar surface and reach moon's orbit and then fire its engines to head towards earth orbit. 

This hop test is a preliminary step towards understanding what it takes to fire the craft's engines on the Lunar surface and take a small hop towards the side. 

This would provide valuable data for ISRO and validate their existing hardware and software. 

At present, ISRO does not possess the technological means to make a craft take-off vertically from the moon and reach lunar orbit and then facilitate its return to Earth. A hop test offers more confidence, for such technology development in future.  

How far and high was the Hop?

"On command, it (Vikram Lander) fired the engines, elevated itself by about 40 cm as expected and landed safely at a distance of 30 - 40 cm away. Importance?: This 'kick-start' enthuses future sample return and human missions!" ISRO said in a post on X, formerly known as Twitter. 

To put this in perspective, this Hop is similar to a pre-workout warm-up, where one jumps up and lands one feet away from the original spot. This is easy for us to imagine and perform by ourselves on Earth. 

However, when a robotic Lunar craft has to perform the same thing near the Lunar south pole, things get exponentially complicated. 

On the moon, the gravity is barely 1/6th that of Earth. The Lunar terrain is uneven and strewn around with fine Lunar dust, which gets kicked up when an engine is fired on/near the surface and this fine dust (which remains suspended over the site for a few hours) can cause issues for the craft's on-board sensors, cameras and instruments. 

Given the uneven terrain, the craft must be able to take-off, hover and land smoothly and not get toppled over. By executing all this successfully, ISRO has proven the robustness and reliability of their technology. 

When was the first Lunar Hop executed?

NASA Surveyor 6 was the fourth of the Surveyor Lunar craft series to successfully achieve a soft landing on the Moon. 

The primary objectives of the Surveyor program, a series of seven robotic lunar soft-landing flights, were to support the crewed Apollo landings that commenced in 1969. 

On 17th November 1969, the engines of the Surveyor 6 craft were fired for 2.5 seconds, causing Surveyor to lift off the lunar surface 3 to 4 meters and land about 2.4 meters west of its original position. 

This lunar "hop" represented the first powered take-off from the lunar surface and furnished new information on the effects of firing rocket engines on the Moon. 

After Surveyor 6 did the first-ever Lunar hop, the same technology was used in a significantly scaled up manner to conduct multiple lunar sample return missions and Apollo astronaut missions. 

Also watch | Chandrayaan-3 Vikram Lander in hibernation mode for more than 24 hours | India News | WION Dispatch

Therefore, after Surveyor 6, multiple crafts have vertically taken-off from the Lunar surface and headed back to earth. In 2023, ISRO has done its own hop test, perhaps, in preparation for bigger and more sophisticated Lunar exploratory ambitions. 

India's next Lunar Mission is with Japan

The Chandrayaan-3 mission has been a resounding success and ISRO has proven its Lunar soft-landing technology. This would fast-track the proposed ISRO-JAXA Lunar Polar Exploration Mission (LUPEX). 

While the Indian and Japanese space scientists have worked closely in the formative years of ISRO, there has never been a formal joint mission between the two. LUPEX will change that. 

Fundamentally, LUPEX will be like Chandrayaan-3. It will be an uncrewed moon mission and the in-situ experiments would be carried out by the robotic lander and rover combination. 

Speaking to WION prior to the Chandrayaan-3 launch, Ishii Yasuo, Vice President, JAXA had said that the flawless landing of Chandrayaan-3 would be a pre-requisite for the LUPEX mission, as LUPEX would involve an Indian Lunar lander and Japanese rover.

He added that the mission was meant to explore the distribution of water-ice around the Lunar polar region and that Indian and Japanese team were conducting phase-2 studies on the joint mission, which could be launched by a Japanese rocket in 3-4 years.

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