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Approaching an unprecedented landing near the South Pole of the Moon on Sept. 7, Chandrayaan-2 performed another maneuver to lower orbit Wednesday morning.
What is the lowering of orbit? Why is it important?
When first injected into lunar orbit, Chandrayaan-2 circled the moon in an oval orbit that moved it away from the moon's surface for quite a long time. Isro wants the spacecraft to be on a circular orbit 100 km above the lunar surface, so that it is always at this distance and that its instruments can observe and image the moon so constant for a year. A staged lowering of the orbit is necessary for Chandrayaan-2 to position itself in this circular orbit. Currently, the spacecraft is in an orbit of 179 km by 1,412 km. It will enter the desired 100 km / 100 km orbit with an additional maneuver by 1 September.
What happens after that?
The satellite will launch the first Indian lunar lander Vikram on 2 September, in anticipation of its long-awaited descent and landing on 7 September, leaving only the orbiter component of the spacecraft in orbit. The orbiter will continue to communicate with the LG and help it to determine the final landing site on the moon thanks to its onboard high resolution Orbiter (OHRC) camera. This is essential because the landing site will have to be flat, inclined at 12 degrees maximum. Images taken by the OHRC will be relayed from the orbiter to the Isro earth station to analyze whether the site can land or not. For images to be clear and accurate, the OHRC will capture the landing site in two orbits. The covered area will be a 12 km by 3 km strip, with a ground resolution of 0.32 meters.
What is the "terrifying 15 minutes" of the Chandrayaan-2 mission so often cited?
A day after Vikram, the Pragyaan rover in the belly, disengages from the spacecraft, he will undergo a short "retro-orbit" maneuver to ensure normality. On September 3, the probe will descend gradually into a lunar orbit of 35 km by 97 km. Vikram's settings will be checked and rechecked for the next three days, for final descent. This final descent, which begins about 30-35 km above the lunar surface, is what Isro's president, K Sivan, described as "the most terrifying 15 minutes" of the mission.
What will happen on September 7th?
The final motorized descent of the LG will begin precisely at 7:40 am on September 7th. After descending to an altitude of about 400 m, Vikram will hover over the moon's surface for 12 seconds. The goal: a last look at the landing site.
Lunar dust will not affect Vikram?
All engines on board Vikram will be triggered to reduce its speed so that the touchdown is safe and smooth. The mission team chose to reach the last 10 meters of descent in 25 seconds. However, landing with multiple engines running could trigger moon dust. Isro's plan to avoid dust is as follows: at a height of 13 meters, the four land thrusters of the lander will be extinguished. Only the engine in the center will be lit so that the dust is dispersed horizontally, thus freeing the site for landing.
What about the Pragyaan rover?
About three hours and fifteen minutes after Vikram's arrival, Pragyaan will leave the belly of the landing gear and deploy his solar panels. In a lunar day, equivalent to 14 Earth days, Pragyaan will cover a distance of about 500 m. Speed: one centimeter per second.
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