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Comment by dzhiurgis | Hacker News Reader

I doubt they will have any cabin crew and different regulation could potentially mean cheaper operation.

The primary purpose of the cabin crew in an airliner is to handle emergencies. When SHTF, they'll figure out the right course of action, open emergency exits, and get people outside.

I'm not sure if the BFR ship would have any emergency survivability. It looks to me like the sort of thing where the flight goes well or everybody dies. In which case, yes, no need for cabin crew!

(And to be clear, I have nothing against "goes well or everybody dies" as long as the probability of "goes well" is sufficiently high.)

An emergency landing on water followed by everyone exiting the vehicle and using their seat cushion as a flotation device seems like the obvious counterexample. That seems survivable enough (I bet that ship would float better than a 747) but you'd want people on hand to help everyone out.

I can't come up with a scenario where the BFR ship would make an emergency water landing. (Of course, it could just be that I lack knowledge or imagination.) Airliners can do them because they glide, so water landings are a possibility after fuel exhaustion or engine failure. BFR won't glide well enough to land softly, so it would have to be a propulsive water landing. And if you can land propulsively in the water, surely you can land propulsively at the landing pad.

> if you can land propulsively in the water, surely you can land propulsively at the landing pad.

I think if you take off and you immediately find that one of the rocket motors isn't gimballing correctly, or something else looks off with the engines, it might be prudent to abort before building up a lot of velocity. (not to mention aborting before something explodes) It's certainly easier.

Land back at the takeoff point then?

I don't think that's always going to be possible, but yeah, that's probably the first choice.

I imagine the most problematic abort in something like a NY to London flight would be if multiple engines fail several hundred miles out. All kinds of velocity in the wrong direction if you want to fly back, not enough thrust to maintain the proper trajectory towards the target. I think there are bound to be some scenarios where you can do a limping, powered landing (the vehicle probably only needs one or two working engines) but you have to do it downrange.

I'm not sure that the ship would be strong enough to withstand a water landing. It'll come down on its tail, and then it will (I think!) tip over, which will probably smash it to pieces.

Aborts also leave you with too much fuel on board, probably way too much fuel. You could burn it off with the engines, although you'd want to actually use it to reach your origin or destination if possible.

If you abort early, you can still reach the origin. If you abort late, you can still reach the destination on the remaining engines. So the pertinent question is: do these two regimes overlap, or is there a gap, and how big? I don't have the answers, and you may be right that there is one.

The point is with a rocket, if you can't land at your original destination, you probably don't have the capability to safely land anywhere else. Maybe I'm overlooking a scenario you have in mind, but IMO you're looking at two classes of problems:

1) Problem during launch. There's been one successful use of a launch escape system in rocketry history[1], and such a system has never been developed for a shuttle type craft.

2) Problem after entering orbit. Cutting your orbital flight short isn't going to change the fact that you still have to survive re-entry stresses and have a working vertical landing system.

[1](https://en.wikipedia.org/wiki/Launch_escape_system#Usage)

> 1) Problem during launch. There's been one successful use of a launch escape system in rocketry history[1], and such a system has never been developed for a shuttle type craft.

I'm not sure if you're aware, but this is a feature of the latest version of SpaceX's capsules. I'm sure it would exist for their larger vehicles.

edit: although I'm just not sure what you'd do during an abort with all that fuel that larger vehicle holds...

I'm not so sure. The Dragon 2 integrates a launch escape system by using the same engines that are also intended for propulsive landing (which is now probably off the table for good, but that was the idea). The BFR ship won't have near enough TWR when fully loaded for its landing engines to double as launch escape engines, and I see no evidence of any other engines.

The fact that the BFR ship serves as both second stage and capsule combined, whereas the Dragon 2 is just a capsule with a separate second stage to put it into orbit, makes the problem a lot harder. I bet that the system for the BFR will consist of "don't explode."

> which is now probably off the table for good, but that was the idea

Oh, that's interesting. What makes you say so?

Apparently I'm remembering an official statement!

https://spaceflightnow.com/2017/07/19/propulsive-landings-ni...

The reason seems to be a combination of NASA not being interested in propulsive landing (and they're funding most of Dragon 2) and deciding to go all-out on BFR instead of refining Dragon 2 further.

Thanks for sharing, that is news to me! I need to review their inventory at some point when I have a few minutes...

Emergencies are a good point. You can't wave off and try landing again if something is not right. If diversion inflight is even possible then the options would be extremely limited.

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