Chandrayaan-3 lunar landing mission poised for launch from India


The Indian Space Research Organisation (ISRO) Chandrayaan-3 lunar lander is set to launch from the Second Launch Pad at the Satish Dhawan Space Centre in Sriharikota, India. This will be India’s second attempt to successfully perform a lunar landing after the Chandrayaan-2 lander failed during its descent.

The launch time for Chandrayaan-3 and its Launch Vehicle Mark 3 (LVM3) rocket is scheduled for Friday, July 14 at 09:05 UTC (2:35 PM local time), though the window for this opportunity lasts until July 19. The LVM3 is India’s medium-lift launcher, capable of flying heavier payloads than the other rockets ISRO has developed.

Chandrayaan-2, launched in 2019, is among the payloads the 43.5-meter-tall LVM3 has flown in its career. The rocket that will fly Chandrayaan-3 is the LVM3-M4, and it will be the seventh LVM3 launch since the rocket’s first flight in late 2014. Additionally, this will be the second LVM3 launch and fifth flight overall for ISRO in 2023.

The LVM3 will be flying on a trajectory with an azimuth of 107 degrees out of Sriharikota, which is on the Bay of Bengal in southeast India. The rocket starts its S200 solid rocket motors at T0 and lifts off the pad via the thrust of just these solid boosters. The L110 core stage, with two Vikas engines using hypergolic propellants, ignites 108.10 seconds into flight.

At 127 seconds into the flight, the solid rocket boosters are jettisoned, and the L110 core stage, the upper stage, and the payload continue on their way to orbit. The five-meter fairing is jettisoned at 194.96 seconds into flight, and the L110 burns until T+305.56 seconds. The cryogenic C25 upper stage, using liquid oxygen and liquid hydrogen as propellants, finishes the journey to orbit.

The C25’s engine will shut down at T+954.42 seconds, with the Chandrayaan-3 Integrated Module (the lander and the Propulsion Module attached together) separating at T+969.42 seconds.

The Chandrayaan-3 mission profile. (Credit: ISRO)

Chandrayaan-3 will be launched into an approximately 170 by 36,500-kilometer elliptical parking orbit inclined 21.3 degrees around Earth. From there, the spacecraft will use a fuel-efficient trajectory to get to the Moon. This trajectory involves an orbit around Earth that gradually increases its apogee for around 17 days until the spacecraft performs a trans-lunar injection burn.

Chandrayaan-3 is expected to reach lunar orbit on Aug. 5 with an on-time launch. Once in orbit, the spacecraft will gradually lower its orbital apogee until the spacecraft enters a 100-kilometer circular lunar orbit. This process will take just under three weeks to accomplish.

The Chandrayaan-3 lander and propulsion module stacked together for flight. (Credit: ISRO)

The Chandrayaan-3 mission will include a lander and a rover, but not an orbiter like Chandrayaan-2. The spacecraft consists of the 1,726-kilogram Vikram lander, the 26-kilogram Pragyan rover, and the 2,148-kilogram Propulsion Module.

The Propulsion Module, equipped with a solar panel generating 758 watts for a 440 Newton hypergolic liquid engine, can not only get the mission to the Moon but also can relay communications from the lander to Earth while in lunar orbit. The module uses an S-band telemetry, tracking, and command antenna to communicate with Earth, and is designed for a three to six-month mission.

The Vikram lander, with the Pragyan rover on board, is scheduled to detach from the Propulsion Module and land on the lunar surface on Aug. 23. The target landing site is in the Moon’s south polar region, near 69.37 south latitude and 32.35 east longitude. The south polar region has received a great deal of interest due to water ice in permanently shadowed craters, and Artemis III is scheduled to land at a location within the region.

Two views of the Integrated Module, which will fly the lander, rover, and Propulsion Module as a unit to the Moon. (Credit: ISRO)

After Vikram detaches from the Propulsion Module, it will use its four engines to deorbit and land on the surface. This lander will have four engines, as opposed to five on the Vikram lander for the failed Chandrayaan-2 landing, and will be equipped with a laser Doppler velocimeter (LDV) to assist in making a successful landing.

In addition to the LDV, the lander for Chandrayaan-3 is equipped with Ka-band and laser altimeters, an accelerometer, star sensors, an inclinometer, a touchdown sensor, and hazard avoidance cameras to be used during the landing process. The four engines, utilizing hypergolic propellant, generate 800 Newtons of thrust each. After Chandrayaan-2’s failure, the landing legs received additional reinforcement.

The Lunar Reconnaissance Orbiter imaged Chandrayaan-2’s crash site from orbit. (Credit: NASA/Goddard/Arizona State University)

The Chandrayaan-2 landing attempt in September 2019 failed due to a software issue. New software was needed after a fifth engine was added to the lander, and there are questions surrounding the testing of that software. The lander hit the surface of the Moon at a much higher speed than allowed for a safe touchdown.

Once the Chandrayaan-3 Vikram lander touches down, assuming all goes well, India will have become the fourth nation to conduct a successful robotic lunar landing on the Moon, after the Soviet Union, the United States, and China.

India, Japan, and Israel have, in the last few years, attempted landings that ended in failure, while the Russian Federation — which inherited most of the infrastructure of the Soviet program — is scheduled to fly the Luna 25 landing mission in August. The Chandrayaan-2, HAKUTO-R, and Beresheet landers have demonstrated the difficulty and hazards that can be encountered during lunar landings.

The science instruments on board the Chandrayaan-3 lander and rover. (Credit: ISRO)

The Vikram lander, measuring 200 by 200 by 116.6 centimeters, features four scientific instruments. The Chandra’s Surface Thermophysical Experiment will measure the lunar surface’s thermal properties, while the Instrument for Lunar Seismic Activity monitors seismic activity near the landing site.

The Radio Anatomy of Moon Bound Hypersensitive ionosphere and Atmosphere (RAMBHA) is a Langmuir probe intended to study the gas and plasma environment on the Moon, and NASA has provided a passive laser retroreflector array for precise measurements of the Moon’s distance from Earth. Similar reflectors have been flown on other missions, including the Apollo crewed lunar landings.

These instruments will utilize the power from the aforementioned side-mounted solar panels, which generate a total of 738 watts. What’s more, the lander will use an X-band antenna to communicate experiment results and spacecraft status to Earth, with the orbiting Propulsion Module serving as a relay and the Chandrayaan-2 orbiter as a backup option.

Illustration showing the Pragyan rover and its components. (Credit: ISRO)

The Pragyan rover, measuring 91.7 by 75 by 39.7 centimeters, will carry an Alpha Particle X-ray Spectrometer (APXS) and a Laser-Induced Breakdown Spectroscope. These experiments will be powered by a solar panel generating 50 watts of power, and the rover will communicate with the Vikram lander using Rx/Tx antennas. The rover will use six wheels on a rocker-bogie wheel drive assembly.

The APXS has been used on other spacecraft in the past, including the Sojourner rover — the first wheeled rover on Mars. The Pragyan rover will also use a rectangular chassis, and will generally resemble Sojourner with the exception of the solar panel moving to the side. Pragyan will be a pathfinder for future rovers much like Sojourner was, and this will be India’s second attempt to fly a rover to the lunar surface. An identical Pragyan rover was destroyed during the Chandrayaan-2 landing failure.

Artist’s impression of Chandrayaan-3 on the lunar surface. (Credit: ISRO)

The mission is scheduled to last 14 Earth days, which is equal to one full lunar day. During this time, Pragyan is targeted to rove 500 meters, and Vikram would be using its instruments to study the local lunar environment. The Propulsion Module will not only relay communications from Vikram but also use its own scientific instrument, the Spectro-polarimetry of Habitable Planet Earth, to study Earth from lunar orbit.

The Chandrayaan-3 mission will become the first mission to ever land in the Moon’s south polar region if it successfully lands before Luna 25, which is also expected to land in the south polar region. The NASA Commercial Lunar Payload Services program is also funding future robotic landers to the south polar region as the world’s space agencies research the possible landings and bases the region’s water ice supplies would allow for in the future.

(Lead image: Chandrayaan-3 and its LVM3 launch vehicle on the pad before launch. Credit: ISRO)

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