Author Topic: Speculation: SFR (mini-BFR) as fully reusable Falcon Heavy replacement  (Read 192633 times)

Offline Elmar Moelzer

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Cannot see that. The next gen rocket is probably 8 years away before it's reliable.
It took them 10 years to get from founding to supplying cargo to the ISS for the first time. I would assume that they can do develop new tech A LOT faster nowadays than back then. They have more experience, more funding and more people, all the infrastructure in place needed for development and they already have an engine that is pretty far down the development path. I think 4 years is a better estimate with a first flight much earlier than that.

Online Robotbeat

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I think 8-10 years is realistic, but you'll need to start the clock whenever they started testing Raptor components at Stennis or wherever. 2012? 2013?
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Offline tdperk

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I think 8-10 years is realistic, but you'll need to start the clock whenever they started testing Raptor components at Stennis or wherever. 2012? 2013?

Hmm.   I recall being laughed at when i suggested that.

I agree with you.  We may only see the FH fly 8 to 12 times before a fully reusable two-stage MethaLOx stack takes it's place.

Online Robotbeat

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I don't think they'll abandon FH immediately. Even after ITSy flies, they'll need it for legacy customers.
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Offline guckyfan

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I am thinking of crew Dragon. Can they put it on top? They can deploy a cargo Dragon out of the payload bay, but a crew Dragon needs the ability to abort.

Online Robotbeat

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I am thinking of crew Dragon. Can they put it on top? They can deploy a cargo Dragon out of the payload bay, but a crew Dragon needs the ability to abort.
We don't know yet whether ITSy will use Shuttle-like payload bay or if it'll use traditional fairing. Both directions have supporting arguments. For the latter, it should be relatively straightforward to put crew Dragon on top, although ITSy will need to be totally qualified for human spaceflight and integration into Dragon's abort systems. That's expensive, so SpaceX may just keep Falcon 9 and Heavy around for that purpose until the actual (subscale?) BFS is ready (which likely will take longer than ITSy herself).
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline mmeijeri

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Offline sghill

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Bring the thunder!

Offline mmeijeri

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I find the topic fascinating and we've had some more updates since the older posts, so I'd like to see how that would modify the projections people have been making. If we look at Wooster's presentation BFS will have 7 Raptors and be 9m in diameter. Musk has said 9m would be possible with existing tooling. I wonder if a 7 Raptor, 9m Al-Li first stage could be an intermediate step.
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Offline docmordrid

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>
Musk has said 9m would be possible with existing tooling. I wonder if a 7 Raptor, 9m Al-Li first stage could be an intermediate step.

Why do an Al-Li intermediate version when SpaceX already has  the tooling for composites in hand?
« Last Edit: 09/04/2018 09:07 PM by docmordrid »
DM

Offline OneSpeed

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I find the topic fascinating and we've had some more updates since the older posts, so I'd like to see how that would modify the projections people have been making. If we look at Wooster's presentation BFS will have 7 Raptors and be 9m in diameter. Musk has said 9m would be possible with existing tooling. I wonder if a 7 Raptor, 9m Al-Li first stage could be an intermediate step.


If you retain the 9m diameter, the difference would look something like this:

Offline KelvinZero

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I have always liked that idea of a stubby version.. maybe not quite THAT stubby :-)

Maybe the goal could be to keep the upper stage pretty close to the full size, but have a much shorter 1st stage with a lot less engines which is still enough performance for typical F9R missions.

Even when they were aiming for 12 meters I wondered if this was actually a sort of stealth development: Let no one take it seriously, let no one consider it threatened payloads in the range of their launchers, then at the last moment just shorten it and produce a weird stubby rocket that is not at all extravagant for the current market.. while still being able to grow to the promised scale just by stretching and adding engines.

There are just so many engines on the first stage, and they are packed so close together. Cutting that problem in half initially could reduce a lot of price and difficulty during early iterations, and get it paying for its own development quicker.

Offline aero

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How well would the stubby work for point-to-point?
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Offline gin455res

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I find the topic fascinating and we've had some more updates since the older posts, so I'd like to see how that would modify the projections people have been making. If we look at Wooster's presentation BFS will have 7 Raptors and be 9m in diameter. Musk has said 9m would be possible with existing tooling. I wonder if a 7 Raptor, 9m Al-Li first stage could be an intermediate step.

Why did they decide the 1st stage needed to be made of carbon fibre?
« Last Edit: 09/05/2018 08:38 AM by gin455res »

Offline spacenut

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Cutting the number of engines in half on a stubby version booster would put it in the FH and New Glenn range.  It wouldn't help much with payloads to orbit when you already have a rocket to do that.  No need for a stubby version to compete against yourself. 

Offline KelvinZero

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Cutting the number of engines in half on a stubby version booster would put it in the FH and New Glenn range.  It wouldn't help much with payloads to orbit when you already have a rocket to do that.  No need for a stubby version to compete against yourself.
I think that is sort of the point.. and to get rid of F9 and FH when possible. Elon made a big announcement that it could be justified just as a replacement of existing rockets that already have business. It does not need any not-yet proven business model like Mars or point-to-point. It can do everything the current rockets can AND do it cheaper due to 100% reusability.

Online hkultala

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I have always liked that idea of a stubby version.. maybe not quite THAT stubby :-)

Maybe the goal could be to keep the upper stage pretty close to the full size, but have a much shorter 1st stage with a lot less engines which is still enough performance for typical F9R missions.

Making the first stage very small would mean way too much delta-v for the second stage for GTO missions.

The BFR design is already staging quite early compared to many other rockets, as it's optimized to deliver the BFS to LEO while returning the first stage to launch site as effectively as possible.
« Last Edit: 09/05/2018 02:05 PM by hkultala »

Offline mmeijeri

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Why do an Al-Li intermediate version when SpaceX already has  the tooling for composites in hand?

That's a very good question. It might be less risky, and if they can do it with the existing tooling, the cost of such an intermediate step could be acceptable.

Falcon is already a very capable rocket family. If I didn't know SpaceX had Raptor, composite tooling and plans for BFS, I would expect a very different next step than BFS. I'd expect them to go for full reusability first. That might require landing thrusters and legs on top of the upper stage, making the whole vehicle even longer. A wide body shorter Falcon might seem logical. That would also help with wider and longer fairings, which though not essential would be useful, and would eliminate an advantage EELVs/Vulcan have.

Once you know SpaceX do have Raptor, a wide body Raptor vehicle looks like a logical next step. Judging by their competitors I would expect 5m, but given that their first stage is already reusable, having an excessively large vehicle doesn't necessarily make it uneconomical. So if you are going for a wider body, you might as well go for the widest body you can make with your existing tooling, i.e. 9m.

The composites I find hard to judge. They seem risky from a reuse perspective. But first doing either a 5m or 9m Al-Li Raptor vehicle only to immediately follow up with a composite vehicle seems inefficient.
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Online envy887

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I find the topic fascinating and we've had some more updates since the older posts, so I'd like to see how that would modify the projections people have been making. If we look at Wooster's presentation BFS will have 7 Raptors and be 9m in diameter. Musk has said 9m would be possible with existing tooling. I wonder if a 7 Raptor, 9m Al-Li first stage could be an intermediate step.

Why did they decide the 1st stage needed to be made of carbon fibre?

Lower dry mass helps a lot with RTLS. The booster is accelerating through ~7,000 m/s of delta-v.

Offline mmeijeri

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If you retain the 9m diameter, the difference would look something like this:

How does that work? Wouldn't it be similarly sized as the BFS in the other picture, only more Falcon-shaped?
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