In the early hours of September 7, 2019, Indian lunar lander Vikram met its end on the lunar surface, hurtling at 58m per second when it was supposed to be gently descending at 2m per second.
The disappointment left Dr K Sivan, then chairman of Indian space agency ISRO, in tears, prompting a comforting hug from Prime Minister Narendra Modi in the mission control room.
Sreedhara Panicker Somanath, the current head of ISRO, would definitely prefer a pat on the back than a comforting hug at the end of the upcoming ₹615 crore Chandrayaan-3 mission.
Landing (not crashing) on the moon is the central goal of ISRO’s planned third lunar exploration mission, slated for launch on July 14. It’s the most important of the mission’s three technology demonstration elements – reaching lunar orbit, a lander soft landing, and rover gliding and crawling on the moon’s surface.
The previous mission’s lander, Chandrayaan-2, failed due to a software glitch, which has since been fixed. ISRO says other precautions were also taken this time around to ensure a successful landing.
The lander is slightly heavier this time – 1,752 kg, compared to 1,471 kg previously, although it has only four engines instead of the previous five. (These motors are intended to provide upward thrust to the descending lander, in order to slow it down.) The removal of one motor is presumably to compensate for the added weight of the new lander’s stronger legs. Somanath said some redundancies have been built in, to ensure a safe touchdown. The lander has a number of sensors, including an accelerometer, altimeters (Ka-band and laser), Doppler velocimeter, star sensors, inclinometer, touchdown sensor and a suite of cameras to avoid hazards and know the position.
The Chandrayaan-3 lander’s side solar panels are designed to provide more power – 738 W compared to 650 W previously, although this was not a factor in the landing.
Soft landing power
Other than that – and perhaps luck – there is little difference between the Chandrayaan-3 and Chandrayaan-2 landers. A landing on the lunar surface on August 23 or 24 would make India the fourth country to demonstrate a lunar soft landing (after the United States, the former Soviet Union and China).
All of Chandrayaan-3’s science instruments are the same as those of its predecessor – they will probe the lunar regolith to determine what elements are present there by burning mud into a plasma and analyzing plumes; check how heat is conducted on the surface of the moon near the polar region by drilling a probe 10 cm into the ground; and study the gas and plasma environment of the moon. But the main objective of the mission is to master the technology of soft landing.
However, there is a crucial difference compared to an instrument which will not land on the moon but will remain with the “propulsion module”, the vehicle which will take the lander the distance between the earth and the moon. The LVM-3 rocket will take the propulsion module and lander from the Sriharikota launch station into an elliptical Earth orbit of 170 km (closest to Earth) and 36,500 km (farthest from Earth) . At this point, whatever remains of the LVM-3 rocket (the upper stage with a cryogenic engine, after the other parts have fallen into the sea) will bid farewell to the propulsion module and blast off into space. . The propulsion module, after thanking LVM-3 for getting it there, will circle the earth five times in elliptical loops, each larger than the last, before picking up enough speed to launch off. on a month-long trip to the moon.
As it approaches, it will circle the Moon in 5-6 elliptical orbits, getting closer each time, until it reaches 100 km above the lunar surface and clears the lander. At this point, an interesting instrument aboard the propulsion module will come to life – an instrument that was not part of the Chandrayaan-2 mission.
Spectropolarimetry of the Habitable Planet Earth (SHAPE) will examine Earth from the vicinity of the Moon to see what kind of spectrum is generated by light emerging from Earth. Light is affected by the type of gas in an atmosphere, as different elements absorb or deflect different wavelengths of light. So if you know what the Earth’s spectrum looks like, you can look for similar spectra of exoplanets (planets of other stars) – if they match, you might want to believe that the exoplanet might, like Earth, contain life.