How can that make sense? Until they actually get a successful landing they can't be sure they don't have a problem that causes a failure 100% of the time.
Presumably they've tried to estimate that probability and factored it into the 20% probability of not succeeding. (I don't know though, since I haven't seen the calculation.)
But you shouldn't also pretend you have zero information. They hit the barge last time, engineering principles are sound, so those two things alone give you an estimate of "quite likely". Yes, 80% is kind of arbitrary, but it tells you the same story as "quite likely" with an added benefit of being able to plug it into some math that will yield you better results than going with just words.
(Note that I think that starting with a good 50/50 coinflip and revising it based on evidence in this case is reasonable, I just think it's nice to have a reasoned opposing opinion sometimes.)
>But you shouldn't also pretend you have zero information.
If you've never done something before you really have no idea if it's going to work, and in rocket launch everything that occurs after the last failure is a complete unknown in terms of failure modes.
Now, if he'd made successful flyback stages before, or it was a relatively routine thing for the industry he might have a good enough feel to assign a ballpark number. But that's not the situation.
In the link you provided he uses computer failure as an example, where a person who is familiar with computers does have some information - I've owned my current rig for three years and it's never failed. If you told me you thought it has a 50% chance of failure next month I can pretty confidently say that's an overestimate.
But it's useless to pull numbers out of the air for something as complicated as SpaceX is trying to do.
If you have an expectation, you have a probability. Not a numeric one, but a probability nonetheless.
Nobody has ever landed a rocket before. But we don't expect the rocket to turn into an alarm clock or suddenly develop antigravity. In fact, we have quite reasonable expectations on what behaviors the rocket will exhibit. We might, for instance, expect the rocket to crash more than we expect it to land. What else does that say rather than p(crash) > p(land)?
(Of course, this may well come down to "probability as ratio" vs. "probability as anticipation", which is probably a matter of preference.)
I think he's referring to the fact that every time they do one of these they have more experience with everything, therefore with each new launch the chance of failure should be reduced. He said there will be more than one launches until the end of the year. So by then, the chance of success should rise to 80%.
Yes, I do, and that's why I'm laughing at what you wrote. Just how do you arrive at a numeric probability for an event for which you have no way of assessing the likelihood of occurring?
If one had complete clairvoyance and absolute understanding of every element in a system then there would be no estimates, no probabilities, merely outcomes foretold in advance.
For an estimate one needs to gather up what evidence and information is available; make a judgment on how well understood the system is, and its components; determine how predictable the behavior of the system has been in the past; figure out how close what is attempting to be done is to any previous testing or operations; and so on. Then take all of that and make an informed estimate of the likelihood of something occurring.
That's what an estimate is, a statement about how well a system seems to be understood and the probability of some event occurring. An estimate can build in uncertainty in the understanding of the system quite easily, by simply making a more cautious or pessimistic assumption.
SpaceX designed and built these rockets. They've flown them numerous times. They've done test flights exploring landing operations. They've done re-entry flights and landing attempts multiple times. All of these things increase confidence in understanding how the rocket operates under different conditions during landing, making it possible to come up with a reasonably informed estimate of the probability of a successful landing over a given number of attempts.
Perhaps they are wrong, perhaps they have made a key error in their modeling, who knows. That's why these are estimates, because there's always the possibility for unknown variables to affect outcomes. But to say that there is no basis for SpaceX's estimates is patently ridiculous.
I feel like a truer estimate would be "100% chance of success unless some unknown factor causes failure." It's saying that the unknown factor subtracts 20% that makes me go hmmm.
Musk is a mastermind/strategic/INTJ personality. Much of someone skill of someone like this it often from making assumptions based on hunches. It could just be a hunch. And that's totally fine.
As an INTJ, I'm curious why you mentioned that trait in such a sentence. Also, remember: everything you see around you, what you call the world, was built be people no smarter than you.
https://twitter.com/elonmusk/status/588076749562318849