Re: Root cause
Ach, away with ye - this woman wasn't offended by it!
back to the main subject - It always puzzles me when something perfectly normal and not unexpected happens relating to rocketry and then folk come along and state that they don't believe it, or the explanation given, when they clearly don't understand what's involved. The phrase 'It's not exactly rocket science!' came about to describe something simple because rocketry, whilst conceptually simple is, in practice, very difficult indeed.
Using Kerbal Space Program, I've found that despite my understanding of the math, I just cannot reliably land on the Mun , the game's Luna-analogue, unless my lander is hideously over-engineered with plenty of fuel. Even on Minmus, and after many many hours of practice, i can't pull off a good suicide burn every time, and that's got about 1/20 G surface gravity as against Munar/Lunar 1/6G. Oh, I can make a good landing evey time, but I tend to waste a fair bit of fuel.
In real life you don't get to carry large amounts of excess fuel. Doing so makes your ship inefficient and able to carry less payload. Launches to geostationary transfer orbits put the first stage of a Falcon 9 right at the limits of what it can handle. Under those circumstances, it doesnt take more than a few metres out in position (in any axis) or a fraction of a second off in time to make the difference between a landing and a crash. If the thurst goes asymetric at any point due to oxidiaer depletion, it's almost cetainly game over, unless this happens within centimtres of the deck.
I'm frankly stunned that SpaceX have done so well thus far with their booster recoveries, and utterly delighted about it too. It's been an annus mirabilis in that sense since the first landing.
As for Sabre - looks tome like a perfectly usable technology, and the testing has been going well, so far as I can see, if slowly. Can't use 'em on VTOL ships as they are intended to boost ships horizontally through the air as they climb, creating oxidiser from the air as they go, then just keep on going on internal tanked oxidiser once the air gets too thin.
I just hope there's some young lass out there wanting to go knock lumps off rocks on Mars by the time she's 40 that gets her wish realised. My deams were dashed by the lack of activity after Apollo, but I'd still be dead chuffed to see some youngster get to do what i hoped I might. I really REALLY want to know what's going on geologically in Noctis Labrynthus and the upper end of Coprates, and Hellas and the polar regions too, for that matter. :-}