Bengaluru: When the sun set on the lunar South Pole Thursday, its shadows also marked an end to Chandrayaan-2’s lander Vikram which has come to the end of its lifespan.
The South Pole’s 14 earth-day-long lunar night has brought a permanent standstill to all efforts of photographing and establishing communication with the lander. The lunar night is also the time when surface temperatures plunge to minus 180 degrees Celsius.
The designated landing spot of Vikram (70.9°S, 22.7°E) had come under darkness between 2.30 pm and 3.30 pm Thursday. The lander (as well as the rover housed within it) will not survive since it is powered by solar energy. It wouldn’t have survived by this time even if it had performed a successful landing earlier.
Vikram lander had attempted a touchdown on the lunar surface during the early hours of 7 September but lost communication with earth, moments before it was to land. While ISRO still hasn’t said anything concrete about the structural integrity of the lander, unofficial reports claim that it was spotted in an “inverted position” or “tilted” in its designated spot. There were also reports of closed-door meetings where engineers were asked to “move on”.
Images of the lander had been captured by the orbiter belonging to the same Chandrayaan-2 mission earlier but no details about it has been revealed by the ISRO. Official statements only mentioned that the orbiter was attempting to communicate with the lander.
#Chandrayaan2 Orbiter continues to perform scheduled science experiments to complete satisfaction. More details on https://t.co/Tr9Gx4RUHQ
Meanwhile, the National committee of academicians and ISRO experts is analysing the cause of communication loss with #VikramLander
— ISRO (@isro) September 19, 2019
Why wasn’t NASA able to see Vikram
NASA’s lunar orbiter, called the Lunar Reconnaissance Orbiter (LRO), has been active since 2009 around the moon. It is also in a polar orbit like Chandrayaan-2, but at a much lower altitude of 50km from the lunar surface compared to ISRO’s orbiter which is currently at a 100km orbit. LRO has gathered information by completely mapping the lunar surface and contributed to the creation of 3D maps which will be crucial when humans return to the moon.
It had flown over the designated landing spot of Vikram on 17 September, but NASA officials have said that the orbiter failed to spot the spacecraft. The LRO’s camera was quite powerful and was able to image the landing site of Apollo 11, including capturing the magnificent footsteps of the first astronauts that walked on the moon’s surface and their landing module. While it could capture footsteps, the LRO wasn’t able to photograph the lander or its debris field due to lack of light.
By 17 September, the sun in the moon’s South Pole region was already starting to set in its 24-hour equivalent cycle of 29 days. Being low on the horizon, the sun was casting longer shadows and blocking light. Given that the lunar surface is dotted with so many craters, finding where exactly the Vikram had possibly crashed was difficult for scientists on semi-dark pixelated images.
It is also likely that the lander had ended up crashing far from its designated spot, in which case it was not in the LRO camera’s field of view. The NASA orbiter will fly over the Vikram landing site on 14 October again when the area will have light.
NASA would release the images but only after processing them first and comparing them previous image of the site to the new ones. This is precisely what NASA did when LRO had captured images of Israel’s Beresheet lander, which also crashed while attempting to land on the moon earlier this year.
Information from crash images
Images of a hard impact can provide many clues. The debris around the actual vehicle can indicate the angle at which it fell as well as its speed. Clear images can of course reveal what the status and position of the lander still is. Some questions that would eventually be answered are whether it is in one piece, whether it crashed at the spot it was supposed to or away from it, and whether it is in an inverted position or leaning slightly.
Scientists can also figure out what direction the antenna was pointing to and if the lander still was in one piece to be able to communicate again. If it is, then the question would arise why the lander couldn’t respond at all. But, of course only in the unlikely scenario that it is in a single piece.
What is perhaps more likely is that clear images will enable scientists to see displacement of lunar soil (called regolith) at the crash site.
Lunar regolith is a fine and powdery. When Chandrayaan-1, India’s previous lunar orbiter mission, released an impact probe that intentionally crashed on the lunar surface around the same region a decade ago, it had displaced the regolith and exposed white, water ice under it. This directly contributed to the discovery and confirmation of water ice on the moon.
Similarly, Vikram would have displaced the regolith as well when it hit the surface. This would enable Chandrayaan-2’s orbiter to analyse and study the water ice using its two payloads called the Imaging Infrared Spectrometer (IIRS) and the Dual Frequency Synthetic Aperture Radar (DFSAR).
The IIRS is an infrared imager that can perform a full mineralogical mapping of the moon. It’s purpose is to map water ice by looking for signs of both H20 as well as hydroxyl (OH). The DFSAR will also perform lunar mapping in the process of measuring the thickness of the crust. It will calculate how thick the regolith is, quantity of water ice at different spots and measure the thickness of ice layers.
Ice is common on astronomical bodies and is made of many frozen gases. But water ice is special since water is a biomarker. In liquid form, water greatly increases the chances of habitability of a celestial body.
In the case of the moon, it’s a great resource that can be utilised if and when humans build settlements there. It can be used for consumption, and can be split into hydrogen and oxygen for fuel and respiration respectively.
Results expected from the mission
ISRO has officially said that the expected lifespan of the orbiter has been extended from one year to seven years. The orbiter also has ample fuel and apart from IIRS and DFSAR, it has six other instruments on board that are expected to provide science results.
The Orbiter High Resolution Camera (OHRC) photographs the same location twice on different orbits and from different angles, creating digital elevated models of the lunar terrain. This is the highest resolution camera currently orbiting the moon and has captured the first images of Vikram’s landing site. A Terrain Mapping Camera (TMC2) will map the entire lunar surface in 3D resolution. Both these cameras help boost preparations for future missions.
The Solar X-ray Monitor (XSM), which observes X-rays from the sun’s corona and works in conjunction with the Chandrayaan-2’s Large Area Soft X-ray Spectrometer (CLASS), measures emitted x-rays from regolith elements like silicon, iron and magnesium when these are activated by the sun’s rays.
The Chandrayaan-2’s Atmospheric Compositional Explorer 2 (CHACE-2) will continue the work of CHACE-1 — which was present on the first mission’s impactor and had studied the composition and variation of the wispy lunar exosphere. The Dual Frequency Radio Science (DFRS) experiment will study the evolution of electrons in the ionosphere of the moon by transmitting radio signals.
Can the lander be salvaged
The short answer is – not really. But as with most things in science, it is impossible to say for certain.
The darker it gets on the moon, the colder it is. Since the moon has no atmosphere (the thin floating gases make up its ionosphere and exosphere), there is no temperature regulation on the lunar surface. The part that’s exposed to sunlight can reach daytime temperatures of over 100 degrees Celsius, whereas it can be as cold as -173 degrees Celsius at night.
This cold environment will remain for at least 10 to 12 days during the lunar night on the South Pole.
Because the moon is “tidally locked” to earth – meaning that its period of rotation on its own axis is equal to its period of revolution around the earth – one lunar day is 29 earth-days long. This is also the reason why we always see the same side of the moon from the earth’s surface.
The 14 days of darkness would not provide power to solar panels and so many days of freezing temperatures will also freeze-up circuits as well as the spacecraft’s hull. Freezing can make them brittle and susceptible to breakage due to shrinkage and expansion under sunlight. Any unlikely moisture would also cause damage. Vikram and Pragyan (the rover), which was supposed to move 500m on the lunar surface — were not built to withstand the night time temperatures.
However, ISRO did clarify that communication attempts would be made after the lunar night. But this was much before the attempted landing. In the current scenario, it looks unlikely.
Already in works is the next lunar mission – Chandrayaan-3 (also called SELENE-R) – in conjunction with the Japanese space agency JAXA. Japan will provide the launch vehicle and a surface exploration rover while India will provide a lander. It will be a polar exploration mission.
It was initially proposed as a sample return mission in 2008, but that was when Chandrayaan-2 was expected to launch in 2013. Currently, it is slated for launch in 2024.
Apart from this, ISRO has two other confirmed missions, and three more unconfirmed ones. Aditya-L1, set to launch in two years, will study the sun’s corona from near the earth. It will be at the L1 Lagrangian point, one of the five points between the sun and the earth (or any two-body systems) where the gravitational pull of both bodies act in such a way that a spacecraft or space rocks can remain in stable ‘halo orbits’, i.e. orbiting around an empty point in space.
The X-ray Polarimeter Satellite or XpoSat, to be launched next year, will study the polarisation of x-ray sources in the universe. This will help us understand the magnetic field strength and distribution around common x-ray sources like pulsars, galactic nuclei, supernovae, etc.
Other unconfirmed missions include Mangalyaan-2, India’s second orbiter, to be sent to Mars to perform more sophisticated science experiments than the first demonstrator. It is expected to launch in 2022.
There is also a planned mission to Venus, unofficially titled Shukrayaan-1, set to launch in 2023. This will also be an orbiter, as landing on the hottest planet in the solar system is risky due to its average surface temperatures of 460 degrees C.
In 2028, again there will be the Exoworlds mission, which will study exoplanets or planets outside the solar system.
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