Author Topic: Mini-Super Heavy (BFR) ship F9 Second Stage  (Read 107493 times)

Offline marokrile

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #300 on: 11/12/2018 11:56 am »
Agree, for me the only question remains if they just need sensors data or they will try some parachute or balloon soft touch for material wear tests.

Offline philw1776

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #301 on: 11/12/2018 12:26 pm »
.. They must already have some idea, but they aren’t sure enough to risk a trial with a prototype BFR yet. It’s also not just about money. The loss of a prototype BFR at this stage would create delays whilst a new one was built, something that Musk would not be keen on.
..

You need a BFR first stage to test full speed BFS re-entry. This would create delays, also  :-) 

- BFS hopper:  full scale, sub speed incremental testing, non destructive, grasshopper like.
- Modified F9:  sub scale, full speed, destructive testing, possibly enable F9 upgrades just in case.

Hopefully they'll get enough points to refine mathematical model.

Agreed.
However, an early BFR proto 1st stage could have say 16 engines and get a reduced payload BFS into LEO for all up re-entry tests.
The sub-scale BFS stage 2 F9 approach indicates they don't want the delays you correctly mention.
From the start, way back in 2016, Elon has consistently stated that BFS testing occurs as early as possible and before BFR.  Risk identification & mitigation before too much time & $ is spent.
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Offline speedevil

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #302 on: 11/12/2018 12:33 pm »
You need a BFR first stage to test full speed BFS re-entry. This would create delays, also  :-) 

You don't.
BFS-SSTO is a thing, Elon has repeatedly mentioned that they will be doing SSTO tests of BFS alone, before BFR.
This lets you test the full range of entry conditions up to and including accurate tests of entry of a light vehicle.

It lets you test at nominal overall peak heating of the vehicle at heavier and faster entries - by doing hops with very high apogee that crash into the atmosphere, rather than enter at a shallow angle.

It does not let you test to full fidelity heavy BFS entry, or BFS entry at higher than LEO velocity, as the same heat flux at mach 30 and mach 40 is not the same detailed behaviour over the whole heatshield.
However, you don't need the heatshield to work for >LEO to have a working launcher that is much better than FH.



Offline oiorionsbelt

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #303 on: 11/12/2018 03:39 pm »
On the question of the M1D Vac nozzle being an issue during re-entry.
 Are the concerns because it may interfere with the aerodynamics of re-entry or some other reason?
 Lot's of ideas being floated about about how to get around the issue such as using sea level M1D.
 
 Is it possible SpaceX could discard the nozzle extension after ascent?

 

Offline ThereIWas3

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #304 on: 11/12/2018 03:56 pm »
How BFR lands is very much like F9 - just bigger.  Their models are probably pretty close already.  The hopper tests will deal with the precision landing details.

BFS reentry is a whole new thing so using subscale models on their existing launcher is probably the fastest way to acquire the necessary data.  It is not like a small model in a wind tunnel - it would still be close to 3.7m in diameter.  I would not be surprised if Scaled Composites paid money to SpaceX to get some of that data.
« Last Edit: 11/12/2018 04:56 pm by ThereIWas3 »

Offline Slarty1080

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #305 on: 11/12/2018 03:57 pm »
On the question of the M1D Vac nozzle being an issue during re-entry.
 Are the concerns because it may interfere with the aerodynamics of re-entry or some other reason?
 Lot's of ideas being floated about about how to get around the issue such as using sea level M1D.
 
 Is it possible SpaceX could discard the nozzle extension after ascent?
My concern was that it might not only interfere aerodynamicly but might disintergrate suddenly under extreme heat stress. Such a sudden loss of mass might destabilise the whole stage. But perhaps the payload adaptor is a bigger issue because when it disintergrates in the heat it will fall directly back into the top of the stage.
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Offline Oersted

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #306 on: 11/12/2018 04:25 pm »
Making a precise sub-scale demonstrator used to be a daunting job. I am thinking that in these days of 3D-printing it is much more straightforward. Just reduce the dimensions of existing CAD models. SpaceX is already using a lot of 3D-printing.

Yes, of course physics doesn't allow a reduced scale of all components, I of course know that. But the work should be a good deal easier than it would have been years ago.   

Offline Hobbes-22

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #307 on: 11/12/2018 04:49 pm »
Making a precise sub-scale demonstrator used to be a daunting job. I am thinking that in these days of 3D-printing it is much more straightforward. Just reduce the dimensions of existing CAD models. SpaceX is already using a lot of 3D-printing.

Yes, of course physics doesn't allow a reduced scale of all components, I of course know that. But the work should be a good deal easier than it would have been years ago.

Having enlarged/reduced a bunch of scale model parts, I'd say that's not true unless they've been very clever in the original design. When you scale a part, you soon run into issues with wall thickness: the part becomes too thin to be printed (or when scaling up, way more expensive than necessary).
You can design parts to account for this, but you'd have to do that from the start. Going back and editing existing parts for scaling can run into a full-on redesign.

Offline Lars-J

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #308 on: 11/12/2018 05:41 pm »
Making a precise sub-scale demonstrator used to be a daunting job. I am thinking that in these days of 3D-printing it is much more straightforward. Just reduce the dimensions of existing CAD models. SpaceX is already using a lot of 3D-printing.

Yes, of course physics doesn't allow a reduced scale of all components, I of course know that. But the work should be a good deal easier than it would have been years ago.

Having enlarged/reduced a bunch of scale model parts, I'd say that's not true unless they've been very clever in the original design. When you scale a part, you soon run into issues with wall thickness: the part becomes too thin to be printed (or when scaling up, way more expensive than necessary).
You can design parts to account for this, but you'd have to do that from the start. Going back and editing existing parts for scaling can run into a full-on redesign.

This is not going to be an exact scale model, for your reasons as well as other reasons.

Think of it is a model validation tool. Flying something similar will allow them to validate that it behaves exactly as predicted. Once they know that and adjust the model to match reality, they can predict how the BFS will behave and hopefully not lose a BFS during the testing process.
« Last Edit: 11/12/2018 05:41 pm by Lars-J »

Offline marsbase

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #309 on: 11/12/2018 05:52 pm »
  I would not be surprised if Scaled Composites paid money to SpaceX to get some of that data.
And I would not be surprised if SpaceX refused to sell such data. 

Offline Robotbeat

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #310 on: 11/12/2018 05:54 pm »
It's less like the traditional model validation and wind tunnel testing. It gives them an opportunity to iterate fairly inexpensively and quickly, to gather experience with orbital recovery of an upper stage, something no one else has done (STS etc had too small amount of on-board propellant to really qualify as an upper stage, although they did validate many of the necessary technologies). They can iterate fast enough and cheap enough that the results can actually help guide the fundamental design decisions, instead of just providing a check on analysis and simulation.

Provided it also flies other payloads, like with droneship recovery. Otherwise, they may only be able to afford one or two failures of these test recoveries in a short period of time.
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Offline lrk

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #311 on: 11/13/2018 12:31 am »
How BFR lands is very much like F9 - just bigger.  Their models are probably pretty close already.  The hopper tests will deal with the precision landing details.

BFS reentry is a whole new thing so using subscale models on their existing launcher is probably the fastest way to acquire the necessary data.  It is not like a small model in a wind tunnel - it would still be close to 3.7m in diameter.  I would not be surprised if Scaled Composites paid money to SpaceX to get some of that data.

Why would Scaled Composites be interested in BFR reentry data? 

Offline OxCartMark

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #312 on: 11/13/2018 01:22 am »
  I would not be surprised if Scaled Composites paid money to SpaceX to get some of that data.

Scaled composites' machine never really gets past jogging speed so the info would only be of limited relevance and Scaled has gone with with a fold in half entry scheme which places the difficulty more on the mechanics of the folding structure than it does on entry aerodynamics.
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Offline lrk

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #313 on: 11/13/2018 01:30 am »
  I would not be surprised if Scaled Composites paid money to SpaceX to get some of that data.

Scaled composites' machine never really gets past jogging speed so the info would only be of limited relevance and Scaled has gone with with a fold in half entry scheme which places the difficulty more on the mechanics of the folding structure than it does on entry aerodynamics.

Are you talking about SpaceShipTwo?  That was sold off to Virgin years ago, and is long passed the design stage where such data would be useful. 

Offline jpo234

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #314 on: 11/13/2018 08:19 am »
Fundamentally, this is about as close as we're gonna get to an explicit admission from Spaceflight that they're going to incur a loss because of the drop to 50+ payloads from what was originally advertised as 70-100+ over the last year or two. Rephrased in a few words, Curt Blake is basically saying "not worth the effort or risk".

https://twitter.com/pbdes/status/1062090419683708928

This is where I think the Mini-BFR fits: a smaller payload for a significantly cheaper launch. The Electron price is probably not possible for a F9 based launch (some costs like the pad are fixed), but undercutting the Vega should be possible with S2 reuse.
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Offline gin455res

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #315 on: 11/13/2018 08:55 am »
If the SFS was only designed to launch multiple starlink sized payloads could it get by with a small hatch?

Offline high road

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #316 on: 11/13/2018 09:10 am »
  I would not be surprised if Scaled Composites paid money to SpaceX to get some of that data.
And I would not be surprised if SpaceX refused to sell such data.

To a credible competitor, sure. But even with such data, it's not even remotely likely that Scaled Composites would be able to bring anything to market in a timeframe that would make it a threat to SpaceX's plans. However, it's also unlikely that Scaled Composites would be willing and able to pay enough for such data to make it worthwile for SpaceX to take that risk.

SpaceX isn't the only game in town, but it seems like they will remain the fastest movers while having very audacious designs, with all of their competitors lagging far behind or looking for different market segments.

Offline JamesH65

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #317 on: 11/13/2018 10:18 am »
Whilst I have been pondering for some time the concept of a dedicated reusable starlink satellite dispenser, since they are going to need a LOT of launches,  I'm not sure this is it (in its current suspected form). Strikes me this is just a test bed for bigger things, BFS and possibly a reusable dispenser. It might end up helping with S2 reusability, it might not.

Offline fast

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #318 on: 11/13/2018 02:10 pm »
On the question of the M1D Vac nozzle being an issue during re-entry.
 Are the concerns because it may interfere with the aerodynamics of re-entry or some other reason?
 Lot's of ideas being floated about about how to get around the issue such as using sea level M1D.
 
 Is it possible SpaceX could discard the nozzle extension after ascent?
My concern was that it might not only interfere aerodynamicly but might disintergrate suddenly under extreme heat stress. Such a sudden loss of mass might destabilise the whole stage. But perhaps the payload adaptor is a bigger issue because when it disintergrates in the heat it will fall directly back into the top of the stage.

They can simply cut M1D Vac nozzle shorter as they did before, they dont need full performance for this mission.

Offline Semmel

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Re: Mini-Super Heavy (BFR) ship F9 Second Stage
« Reply #319 on: 11/13/2018 02:24 pm »
On the question of the M1D Vac nozzle being an issue during re-entry.
 Are the concerns because it may interfere with the aerodynamics of re-entry or some other reason?
 Lot's of ideas being floated about about how to get around the issue such as using sea level M1D.
 
 Is it possible SpaceX could discard the nozzle extension after ascent?
My concern was that it might not only interfere aerodynamicly but might disintergrate suddenly under extreme heat stress. Such a sudden loss of mass might destabilise the whole stage. But perhaps the payload adaptor is a bigger issue because when it disintergrates in the heat it will fall directly back into the top of the stage.

They can simply cut M1D Vac nozzle shorter as they did before, they dont need full performance for this mission.


Thats a good point from Slarty1080. The nozzle extension is very thin metal. During reentry and if it is exposed to the stream, it gets hot, soft and then deform and burn off. I have no idea if that is violent or not. But if its within the control authority of the fins, I could totally see SpaceX go for it (what do they get to lose?) anyway and not cut the nozzle extension short. If it works, it works, if its too violent and unbalances the descend, thats valuable data too. As a first attempt, I can totally see them do that. Based on the result, it might change the approach for the next one.

Cutting the nozzle short is a quite invasive change, I would expect them to explore other options before doing that.

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