Author Topic: Mini-Super Heavy (BFR) ship F9 Second Stage  (Read 53319 times)

Online FutureSpaceTourist

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Mini-Super Heavy (BFR) ship F9 Second Stage
« on: 11/07/2018 06:34 pm »
https://twitter.com/elonmusk/status/1060253333116473344

https://twitter.com/elonmusk/status/1060253755315118080

Edit to add Elon's subsequent tweets, as posted later in this thread:

https://twitter.com/elonmusk/status/1060265065276825601

Looks like it's strictly a tech demonstrator, unless we come full-circle back to parachutes  ::)

No landing, confirmed
Quote
No, weíre building a BFR dev ship to do supersonic through landing tests in Boca Chica, Texas
https://twitter.com/elonmusk/status/1060282495541727234

« Last Edit: 11/25/2018 01:02 pm by Chris Bergin »

Offline acsawdey

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Re: Mini-BFR F9 Second Stage
« Reply #1 on: 11/07/2018 06:35 pm »
So, does that mean that the "Raptor upper stage" question is on-topic here?

Offline meekGee

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Re: Mini-BFR F9 Second Stage
« Reply #2 on: 11/07/2018 06:37 pm »
Beat me by a minute.

Oh how many times has this been predicted here and shot down by the know-it-alls?

Classic SpaceX.  Find a way to use your existing engine within a working framework so you can move forward without starting everything from scratch.  Just like moving Merlin from F1 to F9.

I'll add (again) my private guess that this will also be a dedicated reusable StarLink deployer upper stage.
« Last Edit: 11/07/2018 06:38 pm by meekGee »
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Re: Mini-BFR F9 Second Stage
« Reply #3 on: 11/07/2018 06:38 pm »
I think this is about the results of the reusable F9 2nd stage development program that Elon has been talking about for a long time. So not literally a shrinked BFS with Raptor, but a recoverable F9 2nd stage.
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Offline RDMM2081

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Re: Mini-BFR F9 Second Stage
« Reply #4 on: 11/07/2018 06:42 pm »
Possible reasons to mention it in relation to BFS:
 - Composite tankage
 - Advanced TPS
 - Methalox / Raptor
 - EDL profile
 - Landing legs?
 - Fins?

Offline happyflower

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Re: Mini-BFR F9 Second Stage
« Reply #5 on: 11/07/2018 06:42 pm »
So this means that the current F9 second stage will get mini control surfaces and a tri-pod to land on?

Online FutureSpaceTourist

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Re: Mini-BFR F9 Second Stage
« Reply #6 on: 11/07/2018 06:43 pm »
Yes not clear the extent to which this is about proving BFS tech, or improving F9 performance/re-use.

As this is SpaceX Iíll hazard itís both.

Online RotoSequence

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Re: Mini-BFR F9 Second Stage
« Reply #7 on: 11/07/2018 06:44 pm »
I wonder what implications this has for BFR. Is this decision motivated by finance-affected development timelines?
« Last Edit: 11/07/2018 06:44 pm by RotoSequence »

Offline wannamoonbase

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Re: Mini-BFR F9 Second Stage
« Reply #8 on: 11/07/2018 06:45 pm »
I think this is about the results of the reusable F9 2nd stage development program that Elon has been talking about for a long time. So not literally a shrinked BFS with Raptor, but a recoverable F9 2nd stage.

Or a second stage with no purpose other than getting to orbit and back to test vehicle shape, stability, reentry and landing.

I like the idea of a raptor powered second stage with some payload capacity. 

What pad do they mod, because they will have to mod a pad even if it stays RP1.

Extremely interesting news.
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Offline RobLynn

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Re: Mini-BFR F9 Second Stage
« Reply #9 on: 11/07/2018 06:46 pm »
I wonder what implications this has for BFR. Is this decision motivated by finance-affected development timelines?
I think more likely by their need for large number of starlink launches before BFR is anywhere near ready.
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Online Lars-J

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Re: Mini-BFR F9 Second Stage
« Reply #10 on: 11/07/2018 06:46 pm »
My gut feeling is that this is will be a limited BFS technology test bed. I'm not sure if such a stage (with payload bay?) will deliver much useful payload to LEO.

Offline speedevil

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Re: Mini-BFR F9 Second Stage
« Reply #11 on: 11/07/2018 06:47 pm »
Yes not clear the extent to which this is about proving BFS tech, or improving F9 performance/re-use.

As this is SpaceX Iíll hazard itís both.

The comment in March about 'fully reusable F9, all-in cost of $5-6M in 2-3 years' seems relevant.

Fuel transfer would help lots of applications in the same way it would with BFR, even if it is in fact kerosene.
A mini BFS, launched on FH perhaps, could do a hell of a lot.


Online Lars-J

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Re: Mini-BFR F9 Second Stage
« Reply #12 on: 11/07/2018 06:48 pm »
I wonder what implications this has for BFR. Is this decision motivated by finance-affected development timelines?
I think more likely by their need for large number of starlink launches before BFR is anywhere near ready.

Which this won't help them with. A reusable F9 upper stage (with integrated payload bay) will drastically reduce the payload capability for both mass and volume. It might make more sense if used on FH.
« Last Edit: 11/07/2018 06:49 pm by Lars-J »

Offline butters

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Re: Mini-BFR F9 Second Stage
« Reply #13 on: 11/07/2018 06:50 pm »
Neither Merlin nor Raptor is going to be useful for propulsive landing of any F9-class upper stage. It would have to be dedicated landing thrusters regardless. So might as well stick with MVac, right? There would be nothing "Raptory" about the entry sequence, it would just be a validation of aerodynamic models.

Offline meekGee

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Re: Mini-BFR F9 Second Stage
« Reply #14 on: 11/07/2018 06:53 pm »
To state the obvious, even before adding speculations about things Musk didn't say, SpaceX will get:

- A low risk test-bed for flying Raptors (and methalox)
- A reusable upper stage
- A high-energy upper stage that's better matched to the later F9s and FH
- BFS technology test bed

EDIT: Actually, yes, he didn't say it is Raptor powered.  That's only an assumption at this point.
« Last Edit: 11/07/2018 06:55 pm by meekGee »
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Offline speedevil

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Re: Mini-BFR F9 Second Stage
« Reply #15 on: 11/07/2018 06:55 pm »
Neither Merlin nor Raptor is going to be useful for propulsive landing of any F9-class upper stage. It would have to be dedicated landing thrusters regardless. So might as well stick with MVac, right? There would be nothing "Raptory" about the entry sequence, it would just be a validation of aerodynamic models.

It could land just fine on the nominal RCS thrusters of BFS, which are optimised for 'lowest impulse bit'.

A test of TPS, BFS RCS, some aero properties, some reuse, as well as a second redundant string for starlink launches would make a whole heap of sense.

A 'mini' BFS, which fit inside the main BFS would have obvious interesting applications for high energy payloads, so it's not as if it's entirely useless in the best timeline, in which BFS works fine.

~130 tons or so wet, raptor engine, oversized 'RCS' to cope with landing and when G gets too large to throttle the raptor.
« Last Edit: 11/07/2018 07:08 pm by speedevil »

Online lrk

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Re: Mini-BFR F9 Second Stage
« Reply #16 on: 11/07/2018 06:55 pm »
What pad do they mod, because they will have to mod a pad even if it stays RP1.

Not really, if it stays the same height and diameter, and any fins/protuberances don't interfere with the T/E. 

Also I strongly suspect that it will use parachutes for landing, maybe a parafoil like they use for fairings.  Adding superdracos is an option, but that would be more work for not a lot of additional progress towards the actual BFR. 

Offline Bubbinski

Re: Mini-BFR ship F9 Second Stage
« Reply #17 on: 11/07/2018 06:57 pm »
Iíd thought the Falcon 9 design was now frozen....very interesting. If a pad has to be modified, which one of the existing SpaceX pads would it be?

I'll even excitedly look forward to "flags and footprints" and suborbital missions. Just fly...somewhere.

Offline Star One

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Re: Mini-BFR ship F9 Second Stage
« Reply #18 on: 11/07/2018 07:02 pm »
I think this is about the results of the reusable F9 2nd stage development program that Elon has been talking about for a long time. So not literally a shrinked BFS with Raptor, but a recoverable F9 2nd stage.

The Twitter thread this comment was posted into by Elon disagrees with you favouring instead a mini-BFS for technological development of the full size vehicle.

Offline Bynaus

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Re: Mini-BFR ship F9 Second Stage
« Reply #19 on: 11/07/2018 07:03 pm »
1) Elon tweets about a mini-BFS. 2) NSF explodes... :D
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