Bengaluru: India’s Chandrayaan-3 is on a mission to explore and study the Moon’s south pole, which is rich in water resources and permanently shadowed craters.
After its lander, Vikram, successfully completes its descent to the Moon, it will remain stationary, and send out a rover, Pragyan, that will move about the surface.
The mission has a total of seven payloads, six of which are ISRO’s while one is NASA’s. Chandrayaan-1 also carried a NASA payload.
The payloads are distributed among the lander, the rover and the propulsion module — four aboard Vikram (lander), two on Pragyan (rover), and one on the propulsion module that carried the craft from the Earth into the Moon’s orbit.
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Vikram’s payloads
The Vikram lander is named for Vikram Sarabhai, considered the ‘father of the Indian space programme’.
Its payloads include RAMBHA or Radio Anatomy of Moon Bound Hypersensitive ionosphere and Atmosphere. RAMBHA is a ‘Langmuir Probe’, which is used to measure properties of charged particles like electrons and ions, as well as their density in plasma. Plasma is the fourth state of matter after solid, liquid, and gas, and exists in the form of superheated gas that has been subjected to an electromagnetic field and carries charged ions and electrons.
It is the most abundant form of matter in the universe.
The Moon is surrounded by plasma from the solar wind. As electrons travel fast in heat, the lunar surface also collects electrons and thus accumulates a negative charge. This environment is also dusty, but the distribution and density of plasma is not uniform.
The plasma in the Moon’s exosphere — its atmosphere — varies constantly under the solar influence, and the mechanics of how it varies over time is what the RAMBHA payload will capture and quantify.
The second Vikram payload is Chandra’s Surface Thermophysical Experiment (ChaSTE). ChaSTE will study the Moon’s thermal conductivity and surface temperature. It will measure the temperature gradient vertically, from within the soil, rising up. It will also attempt to quantify how much heat the surface of the Moon can conduct. It has thermal probes with sensors that will be dug into the lunar soil (known as regolith) to a depth of about 10cm.
The payload called Lunar Seismic Activity (ILSA) will measure seismicity around the landing site. Moonquakes are not unusual. There are no plate tectonics on the Moon, but the Moon is cooling and shrinking, and is constantly subject to tugging by the Earth. This causes release of pressure, sending out energy in the form of quakes, cracking the crust. ILSA will be able to detect minute displacement in the ground, and it will also measure the velocity of lunar quakes.
The Laser Retroreflector Array (LRA), the fourth payload, is NASA’s reflector array that will allow for lunar laser ranging studies. Laser ranging studies are typically the ones that entail pointing a laser at a far away reflector, and measuring how long it takes for the light to bounce back to source. Such experiments help in making more accurate assessments about the speed at which the Moon orbits the Earth, and the distance between them at any given point of the Moon from Earth. It is a passive experiment that will not perform any operations, but findings from the instrument will help refine the understanding of Earth-Moon dynamics.
The Vikram lander also carries aboard the Lander Hazard Detection and Avoidance Camera (LHDAC). While not technically a scientific payload, this camera will be used to identify a safe location for landing, and prevent the craft from ending up unintentionally in craters or on slopes. The camera has captured images already, some of which the ISRO has released.
Pragyan payloads
The Pragyan rover will disembark from the lander on a ramp and will explore the lunar surface while roving on it.
Among its two payloads is the Alpha Particle X-ray Spectrometer (APXS). This instrument will determine the elements present on the Moon’s surface, at the landing site. It uses x-ray fluorescence spectroscopy, where x-ray or alpha particles are bombarded onto the surface to excite it or give it more energy. This is done through the element curium, and can help detect the major elements on the surface of the Moon, including aluminium, calcium, iron, silica, sodium, magnesium, titanium, strontium, yttrium, and zirconium.
The second payload is the Laser Induced Breakdown Spectroscope (LIBS). This payload will calculate the abundance in which these elements are present. The instrument will fire high-power laser pulses at various points on the soil, and the radiation emitted will shed light on the density of an element.
Propulsion-module payload
The propulsion module will be studying the Earth’s atmosphere from the lunar orbit using its lone payload, the Spectro-polarimetry of HAbitable Planet Earth (SHAPE).
It will orbit the moon for a few months (or years), performing spectroscopy and polarisation studies on the Earth’s atmosphere and clouds, to gather biosignatures that could be used to identify habitable exoplanets.
The module was expected to function for about 3 months, but carries 150kg of fuel, which could give it a longer lifespan going into years.
ISRO will livestream the landing of Vikram on Facebook and its YouTube channel. The official telecast will begin at 5.20 pm Wednesday.
(Edited by Sunanda Ranjan)
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