ISRO has stated that the powered descent, a crucial step for achieving a gentle touchdown on the Moon’s surface, is anticipated to commence around 5:45 pm on Wednesday
As India eagerly anticipates the achievement of ISRO’s ambitious Chandrayaan-3, its third lunar mission, scheduled for a historic landing on Wednesday evening, a senior official has said that the planned touchdown might be delayed to August 27 if the health parameters of the Lander Module (LM) are found to be “abnormal” during the crucial stages leading up to the final descent.
The country stands on the cusp of becoming only the fourth nation to successfully master the technique of soft-landing on moon after the US, China and erstwhile USSR. Chandrayaan 3’s successful landing will make India the first to successfully reach the unexplored southern pole of Earth’s solitary natural satellite.
The LM comprising the lander (Vikram) and the rover (Pragyan), is scheduled to make a touchdown near the south polar region of the Moon at 6:04 pm on Wednesday.
The module is set to undergo internal evaluations and will patiently await the break of dawn at the predetermined landing location. ISRO has stated that the powered descent, a crucial step for achieving a gentle touchdown on the Moon’s surface, is anticipated to commence around 5:45 pm on Wednesday.
ISRO TO POSSIBLY POSTPONE CHANDRAYAAN 3 LANDING TO AUGUST 27
ISRO’s Space Applications Centre Director Nilesh Desai had said, ”If any health parameter (of the lander module) is found abnormal on August 23, then we will delay the landing by four days to August 27.”
’17 MINUTES OF TERROR’ AND FINAL DECENT
The critical phase of a soft landing has earned the moniker “17 minutes of terror,” a sentiment echoed by ISRO officials. During this period, the entire process operates autonomously, as the lander must execute precise engine firings, manage fuel consumption, and conduct scans of the lunar surface to identify potential obstacles, hills, or craters before its final descent.
Once all parameters are assessed and the decision to proceed with the landing is made, ISRO will transmit the necessary commands from its Indian Deep Space Network (IDSN) at Byalalu to the Lander Module (LM), a couple of hours before the designated touchdown time.
According to ISRO experts, during the descent, at approximately 30 km altitude, the lander initiates the powered braking phase by engaging its four thruster engines through “retro firing.” This controlled maneuver reduces the speed gradually, ensuring a safe lunar surface contact while accounting for the Moon’s gravitational force.
Detailing the process further, officials highlighted that upon reaching around 6.8 km altitude, only two engines remain active, while the other two are deactivated. These two engines provide reverse thrust, facilitating a controlled descent. As the lander nears an altitude of 150-100 meters, its sensors and cameras come into play, conducting a surface scan to identify obstacles. Subsequently, it continues its descent for a soft landing.
MOST CRITICAL STAGE OF CHANDRAYAAN 3 MOON LANDING
ISRO Chairman S Somanath had recently said the most critical part of the landing will be the process of reducing the velocity of the lander from 30 km height to the final landing, and the ability to reorient the spacecraft from horizontal to vertical direction. ”This is the trick we have to play here,” he said.
Instead of a success-based design in Chandrayaan-2, the space agency opted for a failure-based design in Chandrayaan-3, focused on what all can fail and how to protect it and ensure a successful landing, the ISRO chief said.
After the soft-landing, the rover will descend from the lander’s belly, onto the Moon’s surface, using one of its side panels, which will act as a ramp. On landing the lander may have to face the challenge of lunar dust due to firing of onboard engines close to lunar surface.
The lander and rover will have a mission life of one lunar day (about 14 earth days) to study the surroundings there. However, ISRO officials do not rule out the possibility of them coming to life for another lunar day.
The lander has the capability to soft-land at a specified lunar site and deploy the rover which will carry out in-situ chemical analysis of the lunar surface during the course of its mobility. Both have scientific payloads to carry out experiments on the lunar surface.
MISSION ON SCHEDULE: ISRO
“The mission is on schedule. Systems are undergoing regular checks. Smooth sailing is continuing. The Mission Operations Complex (MOX) is buzzed with energy & excitement!” ISRO said on Tuesday, also sharing visuals of the moon captured by cameras on the lander.
Chandrayaan-3 is a follow up of Chandrayaan-2, driven by objectives to demonstrate secure and gentle lunar surface landing, enable lunar roving, and carry out on-site scientific experiments.
Chandrayaan-2 faced a setback during its lunar phase, as its lander ‘Vikram’ encountered anomalies in the braking system and crashed into the Moon’s surface just minutes before its intended touchdown on September 7, 2019. The maiden Chandrayaan mission took place in 2008.
The Rs 600 crore lunar mission, Chandrayaan 3 was launched on July 14 via the Launch Vehicle Mark-III (LVM-3) rocket. Its 41-day journey led it towards the vicinity of the lunar south pole.
Following the second and final deboosting maneuver on August 20, the Lander Module (LM) now orbits the Moon at dimensions of 25 km x 134 km.
This soft landing attempt takes place in the aftermath of Russia’s Luna-25 spacecraft crash, caused by loss of control, as it impacted the Moon’s surface.
Lunar South Pole
The polar regions of the moon boast an entirely distinctive terrain due to their unique environment and the associated challenges, which have resulted in their remaining largely unexplored. Previous spacecraft missions that reached the Moon have predominantly landed within the equatorial region, just a few degrees north or south of the lunar equator.
Exploration of the Moon’s south pole region holds particular significance due to the potential presence of water in areas that are perpetually shrouded in shadow.
Among the LM’s payloads is RAMBHA-LP, designed to measure the density of plasma ions and electrons in the vicinity of the lunar surface and monitor their fluctuations. ChaSTE (Chandra’s Surface Thermo Physical Experiment) seeks to analyze the thermal properties of the lunar surface near the polar region. Additionally, ILSA (Instrument for Lunar Seismic Activity) will be employed to gauge seismic activity around the landing site and delve into the lunar crust and mantle’s structure.
Upon achieving a soft landing, the rover will descend from the lander module and engage in an examination of the lunar surface through its array of payloads. The APXS (Alpha Particle X-Ray Spectrometer) will facilitate the derivation of the chemical composition, enabling the inference of mineralogical makeup and thereby advancing our comprehension of the lunar surface.
Two-way Communication with Chandrayaan 2
Prior to its anticipated lunar landing, Chandrayaan-3’s Lander Module (LM) has successfully established a dual communication link with Chandrayaan-2’s orbiter, which continues its orbit around the Moon. This achievement offers ground controllers increased communication channels for interacting with the LM.
The separation of Chandrayaan-3’s LM from the Propulsion Module (PM) occurred successfully on August 17, precisely 35 days after the satellite’s launch on July 14.
Meanwhile, the PM, responsible for escorting the LM from launch vehicle injection until the separation orbit, will persist in its current orbit for an extended duration, possibly spanning months or even years, as confirmed by the space agency.
Furthermore, the PM carries an added scientific payload known as SHAPE (Spectro-polarimetry of Habitable Planet Earth) which will allow scientists to make potential discoveries of smaller planets through reflected light, offering insights into a range of Exo-planets that could potentially harbor habitable conditions or even life.
MAPPING CHANDRAYAAN 3’S TRAJECTORY
After its launch on July 14, Chandrayaan-3 accomplished its entry into lunar orbit on August 5. Subsequent to this milestone, a series of orbit reduction maneuvers took place on August 6, 9, 14, and 16. These maneuvers were a prelude to the eventual separation of both modules on August 17.
In the weeks following the July 14 launch, ISRO executed over five strategic maneuvers that progressively positioned the Chandrayaan-3 spacecraft into increasingly distant orbits from Earth.
A significant turning point arrived on August 1 with a pivotal slingshot maneuver. In this maneuver, the spacecraft was deftly directed away from Earth’s orbit and effectively propelled towards the Moon. This trans-lunar injection marked the spacecraft’s departure from Earth’s orbit, initiating its trajectory towards the vicinity of the moon.
