Author Topic: BFS is an SSTO?  (Read 18645 times)

Offline Lar

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Re: BFS is an SSTO?
« Reply #80 on: 12/17/2017 04:15 PM »
Nevertheless I think BFS would go first, BECAUSE it's harder. At least it would start developing first. Items such as TPS and ECLSS are not required to do meaningful cradle landing tests. So conventional wisdom as I understand it is that we will see development mules, as we did with F9, for landing tests. The F9 difference, though, is that these would appear right away since BFS is not an expendable with a feature being added it is full up reusable from the start.
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Offline Radical_Ignorant

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Re: BFS is an SSTO?
« Reply #81 on: 12/19/2017 08:26 AM »
Hmm... that sounds reasonable and isn't contradictory to what SX said. BFS tests first, but nobody said BFS will be finished first. There is quite a road from having A - testable (hopping) article with the same outer shape to B - final product. Works on booster can start after A and finish before B.

Offline JamesH65

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Re: BFS is an SSTO?
« Reply #82 on: 12/19/2017 09:10 AM »
There's also the cost. BFS is going to be more expensive than BFR, even as am empty shell prototype, so if you want to get your Raptor engines tests going, it's cheaper to do it on the BFR. In case things go wrong...Also the carbon composite structures would be cheaper to test on the BFR.

Offline hkultala

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Re: BFS is an SSTO?
« Reply #83 on: 12/19/2017 09:27 AM »
There's also the cost. BFS is going to be more expensive than BFR, even as am empty shell prototype, so if you want to get your Raptor engines tests going, it's cheaper to do it on the BFR. In case things go wrong...Also the carbon composite structures would be cheaper to test on the BFR.

"why do you think "empty shell prototype" of BFS is more expensive than BFR?

Things that make BFS more expensive are heat shield, multiple engine types, wings, payload bay.

Almost all of these can be omitted from the first "empty shell prototype" which will only do short jumps in atmosphere, like grasshopper
« Last Edit: 12/19/2017 09:28 AM by hkultala »

Offline Radical_Ignorant

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Re: BFS is an SSTO?
« Reply #84 on: 12/19/2017 09:41 AM »
There's also the cost. BFS is going to be more expensive than BFR, even as am empty shell prototype, so if you want to get your Raptor engines tests going, it's cheaper to do it on the BFR. In case things go wrong...Also the carbon composite structures would be cheaper to test on the BFR.

Carbon composite will be more expensive for BFR as they are bigger there than in BFS.

Offline JamesH65

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Re: BFS is an SSTO?
« Reply #85 on: 12/19/2017 11:42 AM »
BFS, as stated above, has a load more stuff on it, but is smaller. You could omit a lot of that stuff in a prototype however.

But why? Why not just make a cheaper to test but much closer to final design BFR (because its much simpler) rather than making an expensive one off BFS prototype that's a long way from final design?

BFR is a long tube with tanks, engines, fins - you cannot get much cheaper to make although I do expect the first version to have testing legs.

Offline envy887

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Re: BFS is an SSTO?
« Reply #86 on: 12/19/2017 01:21 PM »
BFS, as stated above, has a load more stuff on it, but is smaller. You could omit a lot of that stuff in a prototype however.

But why? Why not just make a cheaper to test but much closer to final design BFR (because its much simpler) rather than making an expensive one off BFS prototype that's a long way from final design?

BFR is a long tube with tanks, engines, fins - you cannot get much cheaper to make although I do expect the first version to have testing legs.

A stripped-down BFS is also a (much smaller than BFR) tube with tanks and engines. How is BFR simpler, exactly?

Offline JamesH65

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Re: BFS is an SSTO?
« Reply #87 on: 12/19/2017 02:18 PM »
BFS, as stated above, has a load more stuff on it, but is smaller. You could omit a lot of that stuff in a prototype however.

But why? Why not just make a cheaper to test but much closer to final design BFR (because its much simpler) rather than making an expensive one off BFS prototype that's a long way from final design?

BFR is a long tube with tanks, engines, fins - you cannot get much cheaper to make although I do expect the first version to have testing legs.

A stripped-down BFS is also a (much smaller than BFR) tube with tanks and engines. How is BFR simpler, exactly?

If you strip EVERYTHING out (doors, windows, legs, TPS, any sort of passenger interior, basically just fuel tanks with engines on the bottom) then yes, the BFS is smaller with regard to materials, but about the same complexity. But at that point is a waste of time. Why even build something that stripped down when you can build, for about the same price or a bit more, an actual BFR?

Offline philw1776

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Re: BFS is an SSTO?
« Reply #88 on: 12/19/2017 04:55 PM »
BFR requires LOTS of Raptors.  Not good for early design testing.

Start with 3 sea level Raptor BFS testing with early Block One engines.  If it's like Merlin, the engine design will evolve rapidly.  Easy to upgrade or change out a 3 engine or later 7 engine BFS than say a minimal 16 engine BFR. 
Additionally ONLY the BFS lets you test Rvacs.
Winner BFS.
There's lots of reasons Elon says BFS tested first.
“When it looks more like an alien dreadnought, that’s when you know you’ve won.”

Offline speedevil

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Re: BFS is an SSTO?
« Reply #89 on: 12/19/2017 05:12 PM »
If you strip EVERYTHING out (doors, windows, legs, TPS, any sort of passenger interior, basically just fuel tanks with engines on the bottom) then yes, the BFS is smaller with regard to materials, but about the same complexity. But at that point is a waste of time. Why even build something that stripped down when you can build, for about the same price or a bit more, an actual BFR?

Some of these seem very much BFS block 2 features that could benefit from actually having data from several-many orbital test flights.

For example, the small windows are low risk adds - once you have nice detailed stress and strain and temperature measurements from actual flights.
The passenger interior is not actually going to be usable until you get it certified for passengers, and is not integrated with the vehicle design seemingly.

Same with ECLSS, solar, thermal radiators, BEO comms, fuel transfer, satellite deployment, firefighting, suits. Overweight initial worst-case TPS and landing systems can be fine-tuned in the face of experience, ...

Rather than trying to get it all right at once.

There are arguments for doing it both ways, BFR and BFS first - but depending on assumptions, one or other may look better.

For example - was the '85 ton' 'dry mass' of the BFS shown at IAC for a fully outfitted Mars craft less stores?

If it was, then not fitting that in the initial version gives you an arguable margin for SSTO testing.

If you can do SSTO testing up to a high cycle count in a very short period, that does all sorts of interesting things.

Once you have a hundred launches on the same vehicle, arguments on lack of safety for putting up crew get rather weaker, and you can then shuttle crew up, with full cargo launched on very early BFR with no risk to human life and fewer regulatory hurdles.


Offline JamesH65

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Re: BFS is an SSTO?
« Reply #90 on: 12/20/2017 11:36 AM »
BFR requires LOTS of Raptors.  Not good for early design testing.

Start with 3 sea level Raptor BFS testing with early Block One engines.  If it's like Merlin, the engine design will evolve rapidly.  Easy to upgrade or change out a 3 engine or later 7 engine BFS than say a minimal 16 engine BFR. 
Additionally ONLY the BFS lets you test Rvacs.
Winner BFS.
There's lots of reasons Elon says BFS tested first.

You don't need all the raptors on the prototype of course, since you are not trying to lift the BFS.

I suspect they are going to be built in parallel, simply because you cannot go to Mars unless you have both anyway.

Offline philw1776

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Re: BFS is an SSTO?
« Reply #91 on: 12/20/2017 03:49 PM »
Elon has said the BFS will be built & tested first.  See earlier post for reasons.
“When it looks more like an alien dreadnought, that’s when you know you’ve won.”

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