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Comment by zlsa | Hacker News Reader

They've already done it[0], and it was a complete success until a propellant pressure issue resulted in lower than needed thrust, and a hard impact on the pad.

[0]: https://www.youtube.com/watch?v=_qwLHlVjRyw

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It oriented almost perfectly. I'm truly amazed at what SpaceX has accomplished so far. Just need to stick that landing a few dozen more times. It's quite a reorientation.

Curious why does it need to wait so long to reorient? I thought it was going to crash and in last few hundred feet, it flipped! Can it orient straight - way up in the air like Falcon boosters?

Reorienting requires the use of main engines. You want to relight them only once, to ensure that the header tanks and the "downcomer" remain full. Additionally you want to burn off as much speed as possible with the bellyflop, so flipping vertical as late as possible. All combined this means combining the landing burn with the flip is best, as close to landing as possible.

It has a cute nickname, “Suicide Burn”.

Why is it efficient? [https://www.reddit.com/r/KerbalSpaceProgram/comments/2z534g/...]

Guessing we won't be using constant altitude landings in real life?

It actuallyoriented perfectly, but due to the flip, fuel pressure was lost leading an oxygen rich exhaust eating away the engine (becoming what's known as engine rich exhaust) before it was able to complete the landing burn. They should just have to fix the fuel pressure problem to have a complete success.

I'm very dumb so I'm asking: is "engine rich exhaust" a real term?

What do you mean by "real term"?

Real rocket science teams really use phrases like this, including this one. Is it a joke? Yeah, kind of. Is it what they would say if they had no sense of humour? No, probably not. Is it still a thing the experts actually say to actually talk about what's going on? Yeah, it is.

a few more examples:

"Rapid Unscheduled Disassembly" : explosive destruction of the rocket

"Lithobraking" : it's like aerobraking, but with less aero and more litho

Wow, that's surely one of the most amazing feats of human achievement I've ever witnessed - incredible!

On landing video, I see only 2 engines turn on instead of 3 - why is that? Was one engine malfunctioning, or was it the result of low pressure?

The rocket weighs quite a bit less at the end, having used most of its fuel, so only two engines are needed to land. The engines cannot be throttled down more than ~50% (as all rocket engines), so a third one would add too much thrust.

Falcon 9 does the same, relighting 3 engines (out of 9 total) for the boostback burn, 3 for the entry burn and then just 1 for landing.

For that flight the engines are even too powerful for the ascent (it wasn't fully fueled, I think) and as soon as they couldn't throttle any lower, an engine was turned off instead.

Thanks for the explanation! it this also the reason why Raptor is (relatively compared to like F-1) small and BFR uses so many of them?

That, and for redundancy. I've heard it's designed so that even if a significant number of engines malfunction, others can be used to compensate.

A complete resounding success until it burst into flames!

> “a hard impact on the pad.”

It’s called a RUD: Rapid Unscheduled Disassembly

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