Author Topic: Full diameter shortened ITS as FH replacement?  (Read 9477 times)

Online Robotbeat

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Re: Full diameter shorted ITS as FH replacement?
« Reply #20 on: 10/10/2016 04:18 AM »
By the way, that maneuver has already been (subsonically, partially) tested by the DC-X swan-dive test:


That's what should be striking about SpaceX's architecture. Nothing is particularly technically questionable except the raw scale and performance. And performance is not critical except you need more refueling flights.
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Offline KelvinZero

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Re: Full diameter shorted ITS as FH replacement?
« Reply #21 on: 10/10/2016 08:21 AM »
It seems so sensible, if you assume 2 stage with SSTO just a nice-to-have. I wonder if the shuttle could have been this.

Online envy887

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Re: Full diameter shorted ITS as FH replacement?
« Reply #22 on: 10/10/2016 01:04 PM »
It seems so sensible, if you assume 2 stage with SSTO just a nice-to-have. I wonder if the shuttle could have been this.

Shuttle didn't have the materials and manufacturing technology that make insane engine performance and mass fractions possible. The key to ITS is the Raptor engine, composite tanks, and lightweight heatshield.

Offline Paul451

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Re: Full diameter shorted ITS as FH replacement?
« Reply #23 on: 10/10/2016 03:09 PM »
That's what should be striking about SpaceX's architecture. Nothing is particularly technically questionable except the raw scale and performance.

Until they fly, all we'll hear from critics is how unrealistic it is.

And after they fly, all we'll hear is how SpaceX hasn't really done anything new.

I wonder if the shuttle could have been this.
Shuttle didn't have the materials and manufacturing technology that make insane engine performance and mass fractions possible.

Although, by the standards of the day, everything about the Shuttle was insane, so far beyond the state of the art. A 130 tonne to LEO spaceplane? Having never developed an orbital spaceplane before? With no preliminary versions? Crewed on its first launch? On a declining budget and shrinking workforce? Ouch. That's what made it so expensive and fragile.

(And why SDLV's (from Shuttle-C to SLS) were always such a dumb idea. If they'd started with Shuttle-C and then added a crew component... mmmaybe. But going the other way? No.)

Offline KelvinZero

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Re: Full diameter shorted ITS as FH replacement?
« Reply #24 on: 10/10/2016 09:46 PM »
It seems so sensible, if you assume 2 stage with SSTO just a nice-to-have. I wonder if the shuttle could have been this.

Shuttle didn't have the materials and manufacturing technology that make insane engine performance and mass fractions possible. The key to ITS is the Raptor engine, composite tanks, and lightweight heatshield.
I probably shouldn't drag this to a shuttle debate, although this does sort of look like a shuttle replacement rather than a FH replacement...

...but my point was that the insane performance claims are not that important. For a SSTO, sure, but im talking about a conventional TSTO. The design just seems to have insane margins. I don't care about 500 tons to orbit. The shuttle only did about 30 and didn't weigh that different. You can evolve this. If you eke more performance out of the rockets later, great. If power doesn't match your requirements you can stretch the booster a bit, add some more engines. You really want more cross range? You could consider a winged version later  like dreamchaser and stretch your booster again or lower your cargo. You are not trapped.

To me the shuttle just looks so so complicated. So difficult. Two solids in balance with the shuttle main engine. Maximum surface area shared between solids and hydrogen tank and wings so that if anything goes wrong with one of them it is bound to hit one of the others.

I know I am just an arm chair rocket scientist but a TSTO just seems so much more straightforward that it should also be cheaper to develop.. and be fully reusable. Or at least you can land it and consider reuse.


Offline Lumina

Re: Full diameter shorted ITS as FH replacement?
« Reply #25 on: 10/13/2016 12:37 AM »
I didn't see mention of a shorter block 0. Were you just referring to what is being discussed on this thread?

Yes, I should have been clearer on that. Neither the "block 0" terminology nor the concept come from anything SpaceX has said. It's only a thought experiment!

But what if the first Ship they build doesn't have quite the performance capability they currently say the final version will have? Wouldn't it then be interesting to supplement its capabilities with a minimalist, reusable version of the Booster? That would allow them to fly fully reusable missions to Earth-orbit....

Then they could develop and fly a Tanker to validate their plan for on-orbit "refilling."

My guess is that the Ship is first on the timeline because out of the two parts it will need the most testing and because a real flight-tested Ship would be an amazing marketing tool to get a country or a billionaire to pay SpaceX in advance to commission the construction of a city on Mars and to charter some flights. These advance payments can then take SpaceX all the way.

Offline sdsds

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Re: Full diameter shorted ITS as FH replacement?
« Reply #26 on: 10/13/2016 05:43 AM »
the Ship is first on the timeline because out of the two parts it will need the most testing

That's a good way to say it! Another way is to say it has the most uncertainty. By doing it first, they "buy down" risk.
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Offline uhuznaa

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Re: Full diameter shorted ITS as FH replacement?
« Reply #27 on: 10/13/2016 10:43 AM »
It seems so sensible, if you assume 2 stage with SSTO just a nice-to-have. I wonder if the shuttle could have been this.

Shuttle didn't have the materials and manufacturing technology that make insane engine performance and mass fractions possible. The key to ITS is the Raptor engine, composite tanks, and lightweight heatshield.
I probably shouldn't drag this to a shuttle debate, although this does sort of look like a shuttle replacement rather than a FH replacement...

...but my point was that the insane performance claims are not that important. For a SSTO, sure, but im talking about a conventional TSTO. The design just seems to have insane margins. I don't care about 500 tons to orbit. The shuttle only did about 30 and didn't weigh that different. You can evolve this. If you eke more performance out of the rockets later, great. If power doesn't match your requirements you can stretch the booster a bit, add some more engines. You really want more cross range? You could consider a winged version later  like dreamchaser and stretch your booster again or lower your cargo. You are not trapped.

To me the shuttle just looks so so complicated. So difficult. Two solids in balance with the shuttle main engine. Maximum surface area shared between solids and hydrogen tank and wings so that if anything goes wrong with one of them it is bound to hit one of the others.

I know I am just an arm chair rocket scientist but a TSTO just seems so much more straightforward that it should also be cheaper to develop.. and be fully reusable. Or at least you can land it and consider reuse.


If there would have been a shuttle 2.0 in the 90ies and NASA wouldn't have been obsessed with it landing like an airplane and the military wouldn't have diluted it with insane cross range requirements, a fully reusable TSTO shuttle would easily (for rocket science values of "easy") have been possible. Integrating the second stage propellant tanks and spacecraft would have the been the natural choice then and a big first stage instead of the SRBs as well as hydrocarbons instead of LH2 too.

In fact scaled down to 60 tons of payload or so and with 30 tons of this going into more pedestrian mass fractions ITS would make a great TSTO reusable shuttle with no need for composite tanks.

But in fact this would have never happened, because this would have been a totally different craft that would have just been a bad fit for the usual porky suspects.

Anyway, if you look at ITS at a scale more familiar for launch vehicles, there's nothing crazy about it, it's an eminently sane and straight design as soon as you accept powered vertical landings so you can do away with wings. The scale and the mass fractions to arrive at the payloads SpaceX wants though are a bit crazy.

Offline Paul451

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Re: Full diameter shorted ITS as FH replacement?
« Reply #28 on: 10/13/2016 09:08 PM »
Minor aside:

"Full diameter shorted ITS as FH replacement?"

Can the thread creator or a suitably empowered mod change the thread name to "shortened"? It makes my eye twitch every time I see it.

Offline KelvinZero

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Re: Full diameter shorted ITS as FH replacement?
« Reply #29 on: 10/14/2016 04:08 AM »
Minor aside:

"Full diameter shorted ITS as FH replacement?"

Can the thread creator or a suitably empowered mod change the thread name to "shortened"? It makes my eye twitch every time I see it.
Done :) Verbing weirds language.

Offline Manabu

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Re: Full diameter shortened ITS as FH replacement?
« Reply #30 on: 10/17/2016 05:39 PM »
21 means just dropping the outer ring of engines of ITS booster. More compatibility with it.

In ITS booster there is 1 center engine, 6 other around it. And 14 on the next ring. This makes 21.
I think it would still mean a complete redesign of the thrust structure, as the outer ring engines were the best located to transfer the thrust to the outer walls of the booster, that ultimately supports the BFS on top. F9 first stage was able to fly with only the center engine, but it never carried significant load on top while doing that.

If you want to partially populate the booster stage, a 5-6-10 or 5-0-16 arrangement, from center to outer, is probably better. If the booster turns off some engines during ascent, then the best would be to remove those, as the thrust structure would already be projected to function w/o those.

However

I'm not sure if all this design effort and lose of commonality is better than just sending the bigger version with larger margins to reduce risk and maintence costs. The total capital cost if you keep the second stage the way it is wouldn't drop that much. The booster is the thing projected to be re-used a thousand of times in the first place. SpaceX only needs to make one booster by launchpad it expects to use and use it until it becomes obsolete or explodes. Even this reduced version's total mass/thrust would still be way too high for other launch pads unmodified.

I only see real merit in a mini-BFR if it is much smaller, around Falcon Heavy payload in fact. This would need a new vehicle from ground up. And that can be left to SpaceX competitors, like ESA and Blue Origin.
« Last Edit: 10/17/2016 05:40 PM by Manabu »

Offline Patchouli

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Re: Full diameter shortened ITS as FH replacement?
« Reply #31 on: 10/17/2016 06:06 PM »

Although, by the standards of the day, everything about the Shuttle was insane, so far beyond the state of the art. A 130 tonne to LEO spaceplane? Having never developed an orbital spaceplane before? With no preliminary versions? Crewed on its first launch? On a declining budget and shrinking workforce? Ouch. That's what made it so expensive and fragile.

(And why SDLV's (from Shuttle-C to SLS) were always such a dumb idea. If they'd started with Shuttle-C and then added a crew component... mmmaybe. But going the other way? No.)

The Shuttle didn't explore any new territory in terms of payload as the Apollo stack with S-IVB could weigh up to 140tons.
As far as aerodynamics and materials they had the Dyna-Soar,ASSET,and PRIME programs to draw experience from.
The two hardest parts of the development of the shuttle were the TPS and SSME which caused numerous delays.

« Last Edit: 10/17/2016 06:08 PM by Patchouli »

Offline Jim

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Re: Full diameter shortened ITS as FH replacement?
« Reply #32 on: 10/17/2016 06:20 PM »

On a declining budget and shrinking workforce? Ouch. That's what made it so expensive and fragile

(And why SDLV's (from Shuttle-C to SLS) were always such a dumb idea. If they'd started with Shuttle-C and then added a crew component... mmmaybe. But going the other way? No.)


wrong.  Not one thing in that post is true.


« Last Edit: 10/17/2016 06:22 PM by Jim »

Offline Jim

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Re: Full diameter shortened ITS as FH replacement?
« Reply #33 on: 10/17/2016 06:23 PM »
the military wouldn't have diluted it with insane cross range requirements,

That has been proven wrong so many times.

Offline Jim

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Re: Full diameter shortened ITS as FH replacement?
« Reply #34 on: 10/17/2016 06:25 PM »
Integrating the second stage propellant tanks and spacecraft would have the been the natural choice then and a big first stage instead of the SRBs as well as hydrocarbons instead of LH2 too.


And that is wrong too. 

Offline Jim

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Re: Full diameter shortened ITS as FH replacement?
« Reply #35 on: 10/17/2016 06:27 PM »
And everybody stop talking as though ITS is a given.  A reusable first stage has yet to fly.  And even if it does, 1, 2 or 3 times stills doesn't prove the effort.

Offline sdsds

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Re: Full diameter shortened ITS as FH replacement?
« Reply #36 on: 10/17/2016 08:15 PM »
On the topic of a fully reusable vehicle for FH-like payloads....

I once pitched a design to my manager and he said something like, "With enough effort you could probably get it to work that way." Implicitly he was saying, "There's likely a better way to get the same result."

It depends though on how you measure whether the two results are the same. It turns out his approach was quicker and simpler. Mine would have provided capabilities on which we could have built lots of other nifty things.

Maybe a fully reusable vehicle for FH-like payloads is rather like that....
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Online envy887

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Re: Full diameter shortened ITS as FH replacement?
« Reply #37 on: 10/17/2016 08:41 PM »
And everybody stop talking as though ITS is a given.  A reusable first stage has yet to fly.  And even if it does, 1, 2 or 3 times stills doesn't prove the effort.

Maybe a little OT, but how much money do you think SpaceX has spent on efforts that only benefit reuse? Half of what it cost then to develop F9v1.0? Just as much?

Online rakaydos

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Re: Full diameter shortened ITS as FH replacement?
« Reply #38 on: 10/18/2016 10:55 PM »
And everybody stop talking as though ITS is a given.  A reusable first stage has yet to fly.  And even if it does, 1, 2 or 3 times stills doesn't prove the effort.
New Shepard.

Offline Jim

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Re: Full diameter shortened ITS as FH replacement?
« Reply #39 on: 10/19/2016 12:03 AM »
And everybody stop talking as though ITS is a given.  A reusable first stage has yet to fly.  And even if it does, 1, 2 or 3 times stills doesn't prove the effort.
New Shepard.

it didn't go to orbit

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