August 27, 2023
Lunar Soft Landing Success: Future Tasks and Challenges


THE Chandrayaan-3 Mission to make a soft landing on the moon is already a success, whatever happens during the remainder of the lunar day, that is, the next 13 earth days starting yesterday, August 23. Both the Vikram Lander and the Pragyaan Rover, both powered by solar energy available during the lunar daytime this fortnight, will go about their science tasks, gathering data and information and relaying them back to Mission Control in Bengaluru. If all goes well, there will be a wealth of data, enhancing our understanding of the southern polar region of the moon and also adding to the large amounts of information about the origins of the moon and our solar system.

As we know, and as covered in an earlier article in these columns, the various instruments in the lander, rover and one in the still orbiting Propulsion Module (which had carried the lander-rover inside from earth orbit to lunar orbit till separation from the former) roughly a week ago will gather data about the chemical composition of this region of the lunar surface, the very thin atmosphere of the moon, temperature and heat conductivity upto a depth of 10 cm below the surface, vibrations on the lunar surface due to seismic activity and even due to the rover’s movements, and a study of the composition of and around the earth as a marker of what an inhabited planet looks like and which could be used to compare similar composition data from other exo-planets ie, planets outside our solar system. Analyses of this data, or at least most of it, would later be published in peer-reviewed journals as per accepted practice among space-faring nations so that it adds to the cumulative knowledge of humankind.     

Notwithstanding all the above, which are in themselves exciting scientific exercises using purpose-built instruments, the overarching and main objectives of the Chandrayaan-3 Mission, as of the unsuccessful Chandrayaan-2 mission that preceded it, is, as stated on ISRO’s website, to “demonstrate end-to-end capability in safe landing and roving on the lunar surface.” In other words, the successful demonstration of the soft-landing of the Vikram Lander, hopefully with all its instruments intact and functioning as designed, and the deployment of the rover, is the main achievement of the mission and therefore the foundation upon which many future missions would be built. The celebrations witnessed yesterday by people from all walks of life, ignoring for now the over-the-top triumphalism and even jingoism some of which may be forgiven as prompted by the excitement of the moment, will soon subside, and ISRO will have the tough task of carrying the work forward.

This article examines the opportunities this achievement presents to ISRO and to India, and the challenges posed as well, given the capabilities and likely missions of other spacefaring nations.  But before we do that, let us look more closely at what the mission has achieved with regard to its main objectives.


The entire mission, but especially the landing phase, was conducted with admirable calm, precision and confidence. The phase till the spacecraft was inserted into lunar orbit was exactly as designed, as it was in the Chandrayaan 1 and 2 Missions. So ISRO has shown that it has mastered orbital missions, bar the odd mishap that could happen to anyone at any time.

The failure of Luna25 occurred when the initial de-orbiting maneuver was being conducted. The spacecraft was to fire its engines to lower its orbit and get closer to the moon’s surface but, according to the chief of the Russian space agency, Roscosmos,  the engines fired for 127 seconds instead of the planned 84 seconds, departed from the lunar orbit and crashed when ground control could not re-establish contact with it. Only further investigations will establish whether the control systems did not give the correct direction, or whether the engines’ actuators did not respond to these signals correctly.   

With Chandrayaan-3, which had settled into its final 140km x 25km orbit after a few de-orbiting maneuvers, the most impressive part was the powered descent phase when the lander commenced its series of autonomous maneuvers down to the lunar surface, with no further inputs from mission control, which is why the next 20 minutes or so are often described as “twenty minutes of terror.” The telemetry or performance data of the lander’s descent, which were displayed and telecast live by ISRO, showed the craft almost exactly following the planned course in terms of trajectory, horizontal and vertical velocity, altitude above the moon, and phases of descent.

The lander first fired its four engines to start reducing the orbital speed which, at this point, was about 1.7 km/second or about 6,100 kmph, almost all in a tangential or horizontal direction with the lander oriented parallel to the moon’s surface. This reduced the velocity by about 80 per cent, the slower speed resulting in the lander losing altitude at around 61 m/s to about 7.4 km above the moon’s surface. The next phase saw the lander reduce its horizontal velocity further using its 8 thrusters to about 336 kmph, coming down to 6.8 km altitude, still remaining roughly horizontal or parallel to the lunar surface. The lander next descended further to about 1 km altitude, gradually changing its orientation with its legs starting to point downwards, and its horizontal velocity now zero. The lander then hovered at this spot, with its sensors obtaining data pertaining to its landing site and assessing its suitability for landing which it presumably found OK, because it did not move towards an alternative site as it was programmed to do if needed. The lander then descended further to around 150 m, modifying its orientation to be perfectly vertical with legs pointing straight down, hovering again for several seconds, once again to confirm the landing spot, then quickly descended while decreasing its downward velocity to just under 2 m/s or around 7 kmph, and shut off its engines and thrusters after making contact with the moon.

Absolutely perfect!


Needless to say, after the lander crashed in the Chandrayaan-2 mission, this perfection was not achieved easily. After much discussion over the past week or more in the media about the corrective measures taken since Chandrayaan-2, the media last night and this morning have been fulsome in its praise of the entire team at ISRO and its allied agencies or companies, for the extra-ordinary work they had done between the 2019 failure and now to ensure success. Some of the corrective measures taken had been discussed in the earlier articles in these columns, so we will not discuss all of them in detail here except to say no stone seems to have been left unturned.

After rigorous examination of all possible causative and proximate factors contributing to the crash of the lander, various changes had been made to its hardware and software. Many more cold and hot tests of the lander executing its final maneuvers were conducted using helicopters and cranes, not leaving things only to computer simulations. Margins specified for the landing site were widened, from 400m x 400m to 2.5km x 4km, giving the lander greater decision-making freedom to select its landing site. Huge volumes of data and images accumulated by the still-orbiting Chandrayaan-2 orbiter were fed in to the Vikram Lander’s computer and modified algorithms, including identifying craters and rocks of 30 cm or more, so that the lander need to worry only about smaller rocks. The algorithms now allowed the lander to control the thrusters throughout its descent, to hover at two points as we have seen to allow for more considered landing spot decisions, and to descend at a fixed speed if its altimeter fails.

Several physical modifications were also made. Many redundancies were built in, such as having two hazard detection and avoidance cameras and systems, two on-board computers to insure against failure. The lander was also provided a doppler velocimeter to measure speed in three directions, additional fuel to enable more adjustments in speed and location, a larger tank with safeguards against the fuel sloshing around inside (a well-known problem in rockets believed to have been one of the proximate causes in Chandrayaan-2’s crash), larger solar arrays and stronger legs to withstand greater shocks during landing.

Some of these may sound excessive, but clearly ISRO wanted to be doubly sure. It was little wonder that the ISRO team leaders as well as the control room exuded a calm confidence throughout the mission.

After the successful landing, the media has been full of praise for the perseverance, determination and persistence of the ISRO team after the previous crash. However, perhaps the best quality they displayed was thorough and transparent investigation to determine contributory factors for the crash, evidence-based reasoning to get at causes of problems, and systematically addressing each of these issues and more. This epitomizes the scientific method. One wishes there had been more discussion of these processes during the media discussions, instead of much of the adulation and cheer-leading choruses.

NEXT STEPS          

As has been repeated, perhaps too often, India is now in a small group of countries with advanced capabilities in space technologies which would be important in coming decades both nationally and internationally. International collaborations are important, because science would then advance faster and contribute more to humankind as a whole than through narrow nationally-defined missions which, however, would also be required given harsh international realities. India finds itself in a good position with regard to international collaborations in space missions but it needs to evaluate its capabilities, fill gaps and update them in order to make significant contributions to them, and to engage in national endeavours of serious significance.

For this, India needs to develop heavy-life launchers enabling more direct flights to different space destinations and for being able to carry heavier loads of either scientific payloads or crew and support systems. A careful evaluation of costs and benefits of crewed missions is required before India commits itself to multiple, expensive crewed missions with low returns compared to robotic missions that could accomplish more or less the same goals. For the latter, India would require larger and better equipped landers, returnable landers essential of course for crewed missions, and far better rovers.

Most importantly, as an important and leading member of the small club of space-faring nations, India has a big responsibility. Space and other extra-terrestrial bodies should be viewed as a common good for humanity as a whole, not to be exploited for either national or corporate benefit. There has been too much talk in the media, spurred on by jingoist rhetoric, of water, minerals etc on the Moon which could be exploited, mined and so on. India has an opportunity to push for ethical and internationally regulated use of space. It should not fall into the temptation of leveraging its new-found capabilities for self-aggrandisement. Unfortunately, the US-led Artemis Accords which India has joined, and India’s own Space policy which has not been placed in Parliament for legislation, point in an opposite direction. After the success of the landing, the prime minister spoke of the mission being for the benefit of all humanity. If that is to be translated into reality, India needs to steer its space policies and programmes in a suitable, different direction.