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Comment by m0llusk | Hacker News Reader

If anything they seem to have overcorrected for this. This landing path stopped with a near hover at around 800m, then a prolonged hover at 150m while the lander scoped the situation, then an extremely slow descent that allowed for corrections the whole way down. Very impressive.

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Yes, it was a very conservative landing trajectory. But it is very, very difficult to get a hoverslam right the first time, or the second, or the third...

I did like seeing the live images captured during descent, I also hope those get made into a video and posted online.

Looking forward to the rover deployment too.

This doesn't seem to have been a hoverslam, though -- the probe was hovering at, I think, 150 meters for quite some time, and then maintained a steady and slow rate of descent while still under power.

Yes, Chandrayaan-3 definitely did not performance a hoverslam, the landing was much more conservative than that. With a hoverslam, everything has to go exactly right. A valve that is slightly sticky can be enough to wreak everything.

If they have the fuel available, may as well be very conservative. Either burn the fuel on descent or have it sit in the tank forever on the lunar surface.

Possibly the lander had a choice to be more careful/picky if the remaining fuel permitted. (Just as Armstrong did.)

Also incredibly inefficient.

A lot of things in the world trade inefficiencies for safety.

I was surprised they had the propulsion budget for it.

It helps a lot that the Moon's gravity is about 1/6th of Earth's.

Not only was the Chandrayaan 3 budget lesser than that of Chandrayaan 2, as a meme doing the rounds point out, it was lesser than the budgets of some Hollywood blockbusters like Interstellar. So yeah, safe to say they could have had the budget for more if necessary.

I don't think they're referring to literal money, but rather that the lander had enough fuel.

"Fuel budget", "mass budget", "payload budget", even "delta-v budget" are common terms in spaceflight and refer to how much of a valuable thing a spacecraft can carry given some pesky laws of physics [1], nothing to do with money (except insofar as more money would let you build a bigger spacecraft…)

[1] https://www.kallmorris.com/columns/tyranny-of-the-rocket-equ...

This is one reason why low cost and efficiency are just a nice-to-have when it comes to to space exploration. Moreso the farther you go. A unique mission like a lunar polar landing should be conservatively engineered, where that is possible, on the first try. Early optimization and space exploration don't mix.

First make it work, then make it right, last make it efficient.

It's a lot more efficient than having to send a fourth rocket.

What numerator and denominator are you using to calculate the efficiency of an unmanned lunar soft landing mission?

The most efficient landing - high impulse reverse gravity turn suicide burn vs. what they did - hovering mid-space two or three times, slowly inching toward ground while fighting gravity.

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