Author Topic: Sea Dragon - Would it Work?  (Read 33538 times)

Offline pacojoe

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Sea Dragon - Would it Work?
« on: 03/17/2018 06:19 pm »
From a technical standpoint, would the Sea Dragon rocket work?

TRW validated the design in 1963, but there is still some skepticism of its viability. The most compelling criticism that I've seen is the potential combustion instability of its single massive pressure-fed engine. Robert Truax didn't think it would be a problem.
https://space.stackexchange.com/questions/16816/how-realistic-would-the-sea-dragon-engine-be-to-produce-given-todays-technology

Assuming combustion instability is a problem, would it be possible to mitigate it without overhauling the design of the rocket?

For any who aren't familiar, Sea Dragon is the ultimate "big dumb booster". It's a 500-foot sea-launched rocket designed to lift 550 tons to LEO with simplicity and economies of scale.
https://en.wikipedia.org/wiki/Sea_Dragon_(rocket)

Offline Hominans Kosmos

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Re: Sea Dragon - Would it Work?
« Reply #1 on: 05/06/2018 08:22 am »
https://rippleaerospace.com/

I don't know about not-overhauling, but multi combustion chamber annular aero spike engine would be one way to replace the large combustion chamber instability problem with non-trivial propellant manifold complexity and tight coupling of individual chamber performance with directional control. Gimballed aero spike cluster appears not applicable at the SeaDragon scale.

The obvious alternative is to single large combustion chamber and nozzle is to adapt multiple small bell nozzles as proven for atmospheric flight by SpaceX and Firefly. Possibly fewer miracles required to succeed that way.

Aerospike might be considered a premature optimization.

It would appear the group has recently got into recreating some of the lessons learned by the original Sea Dragon proponent: 


The company's previous you tube content appears to have been removed, but one of their former concept visualizations is presented here in this Norwegian language clip: 


Originally the idea was to leverage the offshore oil and gas industry skillset and infrastructure towards this new opportunity.
« Last Edit: 05/06/2018 08:35 am by Hominans Kosmos »

Offline Archibald

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Re: Sea Dragon - Would it Work?
« Reply #2 on: 05/07/2018 10:49 am »
Bar the combustion instabilities you (rightly) mentions as a major issue, seems Sea Dragon could have worked. Never found another serious issue with the design, bar economic viability, which is an entirely different matter.
Diamant first stage was pretty good, and more importantly, in 1999 Andrew Beal (BA-2) tested a pretty big pressure-fed engine, and it worked well. Still it was small compared to Sea Dragon.

BUT combustion instabilities were one hell of a teething issue with the much smaller F-1, and also with the RD-170 (AFAIK) both exploded, destroyed their test stands and send shards of metal flying miles away.
« Last Edit: 05/07/2018 10:52 am by Archibald »
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Offline Hominans Kosmos

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Re: Sea Dragon - Would it Work?
« Reply #3 on: 05/09/2018 06:10 am »
I've since learned there is a separate thread dedicated to discussing the resurrection attempt venture over at Commercial Space Flight General:

https://forum.nasaspaceflight.com/index.php?topic=45364.0

Roadmap proposing evolving the architecture up to 14 meter diameter has been proposed at some point:


Offline kraisee

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Re: Sea Dragon - Would it Work?
« Reply #4 on: 05/09/2018 05:26 pm »
Ripple's design is almost identical to one I tried to kick-off around 2012 as a followup to DIRECT. The only real difference is we managed to delete the need for the outlier thrusters on the outside of Stage 2.

The biggest issue that we found with this whole approach is that the performance envelope of a 2-stage pressure-fed launcher - when using KeroLox or MethaLOX first stage - is that the whole architecture is limited to LEO missions only. To get to GTO or anywhere else (which is where the initial low hanging fruit customers are) required an additional stage.

That could be solved by switching to HydroLOX for both stages, but the overall vehicle size grows substantially for the equivalent LEO performance, due to the lower density of the S1 fuel. Physically larger doesn't pose much of a problem with the water launch approach though.

If a 3rd stage were to be added later, using HydroLOX throughout, you got an interesting, flexible and pretty low-cost launcher able to deliver better than $500kg to LEO!

A 3-stage Kerosene/Hydrogen Peroxide variant was also feasible (with acceptable GTO performance), offering room-temp propellants, which solves a major headache of working directly in the ocean. But H2O2 production in the quantities we needed was not a low cost option.

Ultimately, these configs essentially use about 2x as much propellant as a more traditional thin-tank turbo-pump fed launcher though. IF you expect the launch business to grow substantially beyond today's market size, at some point the higher cost of the propellants will become a bigger factor in your annual operational costs than the low cost infrastructure can save you. When I was looking at this, the transition point seemed to be somewhere around 30-35 flights per year of a 20-30,000 kg to LEO launcher.

Ross.
« Last Edit: 05/09/2018 05:58 pm by kraisee »
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Offline AncientU

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Re: Sea Dragon - Would it Work?
« Reply #5 on: 05/09/2018 09:38 pm »
Ripple's design is almost identical to one I tried to kick-off around 2012 as a followup to DIRECT. The only real difference is we managed to delete the need for the outlier thrusters on the outside of Stage 2.

The biggest issue that we found with this whole approach is that the performance envelope of a 2-stage pressure-fed launcher - when using KeroLox or MethaLOX first stage - is that the whole architecture is limited to LEO missions only. To get to GTO or anywhere else (which is where the initial low hanging fruit customers are) required an additional stage.

That could be solved by switching to HydroLOX for both stages, but the overall vehicle size grows substantially for the equivalent LEO performance, due to the lower density of the S1 fuel. Physically larger doesn't pose much of a problem with the water launch approach though.

If a 3rd stage were to be added later, using HydroLOX throughout, you got an interesting, flexible and pretty low-cost launcher able to deliver better than $500kg to LEO!

A 3-stage Kerosene/Hydrogen Peroxide variant was also feasible (with acceptable GTO performance), offering room-temp propellants, which solves a major headache of working directly in the ocean. But H2O2 production in the quantities we needed was not a low cost option.

Ultimately, these configs essentially use about 2x as much propellant as a more traditional thin-tank turbo-pump fed launcher though. IF you expect the launch business to grow substantially beyond today's market size, at some point the higher cost of the propellants will become a bigger factor in your annual operational costs than the low cost infrastructure can save you. When I was looking at this, the transition point seemed to be somewhere around 30-35 flights per year of a 20-30,000 kg to LEO launcher.

Ross.

Expendable flights?
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Offline pacojoe

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Re: Sea Dragon - Would it Work?
« Reply #6 on: 05/10/2018 05:02 am »
Ultimately, these configs essentially use about 2x as much propellant as a more traditional thin-tank turbo-pump fed launcher though. IF you expect the launch business to grow substantially beyond today's market size, at some point the higher cost of the propellants will become a bigger factor in your annual operational costs than the low cost infrastructure can save you. When I was looking at this, the transition point seemed to be somewhere around 30-35 flights per year of a 20-30,000 kg to LEO launcher.

That's surprising to me - I thought propellant was usually a tiny fraction of the overall launch cost. The Falcon 9, for example, costs $62 million to launch, but the fuel and oxidizer is only about $200,000 of that.

Offline Archibald

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Re: Sea Dragon - Would it Work?
« Reply #7 on: 05/10/2018 05:12 am »
Quote
The biggest issue that we found with this whole approach is that the performance envelope of a 2-stage pressure-fed launcher - when using KeroLox or MethaLOX first stage - is that the whole architecture is limited to LEO missions only. To get to GTO or anywhere else (which is where the initial low hanging fruit customers are) required an additional stage.

That could be solved by switching to HydroLOX for both stages, but the overall vehicle size grows substantially for the equivalent LEO performance, due to the lower density of the S1 fuel. Physically larger doesn't pose much of a problem with the water launch approach though.

If a 3rd stage were to be added later, using HydroLOX throughout, you got an interesting, flexible and pretty low-cost launcher able to deliver better than $500kg to LEO!

How interesting. Andrew Beal faced similar issues with his BA-2 back in 1999.
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Offline kraisee

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Re: Sea Dragon - Would it Work?
« Reply #8 on: 05/10/2018 05:28 am »
Expendable flights?

Can't say for Ripple, but for mine, both first and second stages were intended to be fully reusable. An optional third stage would have been expendable, but there was a clear upgrade path available that would have made it reusable too. Decision would have come down to demand/flight rate.

And just for clarification, I would not go that direction today. The shape of the industry has changed too much over the last decade and you need to pay a lot more attention to the underlying cost drivers.

Ross.
« Last Edit: 05/10/2018 05:39 am by kraisee »
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Offline kraisee

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Re: Sea Dragon - Would it Work?
« Reply #9 on: 05/10/2018 05:32 am »
How interesting. Andrew Beal faced similar issues with his BA-2 back in 1999.

Yeah, another Sea-Dragon style system, "re-imagined" for land operations.

I studied Beal's work intensively at the time, and IMHO it's only real weaknesses were the high cost of H2O2 production and the high cost for those massive composite tanks. Even with those, he was still on-target to have a very viable GTO sat launcher at a fraction of the cost of Atlas or Delta.

He claimed at the time that he closed because he was cut out of NASA sales, but if he had continued he would have been a few years ahead of everyone when the first COTS contracts came around, and would probably have been flying the BA2 with commercial GEO sats before Elon got Falcon-1 to orbit, so this industry could have been very different.

Ross.
« Last Edit: 05/10/2018 05:37 am by kraisee »
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Offline kraisee

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Re: Sea Dragon - Would it Work?
« Reply #10 on: 05/10/2018 05:47 am »
Ahhh, finally found the file in my archive. Brings back memories!

This was the BIG 2-stage HydroLox beastie. There was to be a ~20 ton interim version first.

Hmmm.   I wondered why Ripple's launch image above looked familiar...  ;)

Enjoy!

Ross.

EDIT: Added link to the 20 ton'er too.
« Last Edit: 05/10/2018 05:58 am by kraisee »
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Offline Archibald

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Re: Sea Dragon - Would it Work?
« Reply #11 on: 05/10/2018 11:59 am »
How interesting. Andrew Beal faced similar issues with his BA-2 back in 1999.

Yeah, another Sea-Dragon style system, "re-imagined" for land operations.

I studied Beal's work intensively at the time, and IMHO it's only real weaknesses were the high cost of H2O2 production and the high cost for those massive composite tanks. Even with those, he was still on-target to have a very viable GTO sat launcher at a fraction of the cost of Atlas or Delta.

He claimed at the time that he closed because he was cut out of NASA sales, but if he had continued he would have been a few years ahead of everyone when the first COTS contracts came around, and would probably have been flying the BA2 with commercial GEO sats before Elon got Falcon-1 to orbit, so this industry could have been very different.

Ross.

Sure. Kistler and Beal are my favorites pre-COTS, pre-SpaceX concepts. Both were workable, reasonable designs. Kistler was quite unlucky (or just silly), they had a vehicle 75% complete right from 1998 but did nothing of it for the next decade, including being kicked out of COTS by OSC.
At least Beal got McGreggor running for SpaceX  ;)
« Last Edit: 05/10/2018 12:00 pm by Archibald »
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Offline chrisking0997

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Re: Sea Dragon - Would it Work?
« Reply #12 on: 05/10/2018 04:32 pm »
these discussions always seem to focus on the rocket...what about the payload?  how do you have umbilicals set up?  any issues with random wave effects (vs known states on a land based rocket)?  problems with making the shroud watertight (or is that already the case)?
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Offline pacojoe

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Re: Sea Dragon - Would it Work?
« Reply #13 on: 05/12/2018 05:00 am »
these discussions always seem to focus on the rocket...what about the payload?  how do you have umbilicals set up?  any issues with random wave effects (vs known states on a land based rocket)?  problems with making the shroud watertight (or is that already the case)?

In the case of Sea Dragon, two of the original concept studies are linked on the Wikipedia page. I've read most of Volume 1; it describes some of what you talk about, although perhaps not in great detail.
http://neverworld.net/truax/Sea_Dragon_Concept_Volume_1.pdf

Umbilicals are discussed in the Vehicle Subsystems section. Wave effects are discussed in the Vehicle Analysis section.

Offline pacojoe

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Re: Sea Dragon - Would it Work?
« Reply #14 on: 05/12/2018 07:02 pm »
Thanks for sharing those designs with us, Ross. Do you know roughly how much the propellant would cost for the full-size Leviathan?

Offline kraisee

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Re: Sea Dragon - Would it Work?
« Reply #15 on: 05/21/2018 11:03 pm »
Sorry, missed your question until now.

From my old notes, the big 140 ton launcher that I linked to above needed about $3.4m of LH2 and about $320K of LOX.

There was another variant with KeroLox S1 and HydroLox S2 - similar to the original Sea Dragon concept - which needed about $1.2m in propellants.

The Jet-A/Hydrogen Peroxide variant needed about $8.9m worth of propellants (plus your own H2O2 production facility!), but there were no boil-off or ocean-freezing issues to deal with.

An all-MethaLox variant would have needed about $1m to fuel it.


Compare that to the BFR's fuel costs at around $200K per flight and you begin to realise how the economic situation today differs quite a bit from when Truax was putting this idea together. His ideas were brilliant, and in his economic environment I believe he was dead on the money.

Today though, is a different situation.   The costs of the extra fuel needed for these BDB's now represents more money than the cost of the materials needed for these big, heavy tanks, not to mention that the costs to develop a turbopump these days would be recouped on the third or fourth flight.


While the cost/performance trade for pressure-fed vs. pump-fed has reversed today, that doesn't discount the principle of launching directly from the water.   I believe its still a very valid approach, it just needs a thorough review of the alternatives and impacts.   I love that sort of thing :)

Ross.
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Offline Sawyers

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Re: Sea Dragon - Would it Work?
« Reply #16 on: 05/24/2018 07:45 am »
Great design, Ross!
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Offline Nomic

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Re: Sea Dragon - Would it Work?
« Reply #17 on: 05/24/2018 11:36 am »
There is a comment in the Q&A Dr Antonio Elias did on here along the lines of big dumb boosters using pressure fed engines at sea level are doomed to economic failure even if they are technically successful. Some of the problems,

-Material costs for the tanks, Sea dragon was meant to use 4" thick aluminium, which they didn't have a method for welding. That much carbon fiber would have a (very) significant cost, glass fiber would be somewhere in between lighter than aluminium, cheaper than carbon fiber, and then there is the tooling needed.

-Tanks (particularly LOX/peroxide) will need cleaning to a similar standard needed for turbo pump powered rockets and there is a lot more tank to clean.

-Pressurisation, helium is expensive, for autogenus metholx relative to a pump fed rocket there is a lot more volume to fill at a higher pressure.

Basically I would argue that BDBs might be slightly cheaper per kg to build and operate, but any advantage will be lost by the 2x mass.

Offline Lars-J

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Re: Sea Dragon - Would it Work?
« Reply #18 on: 05/25/2018 11:32 pm »
The whole pressure-fed "fad" has turned out to be mostly a dud, it seems. (as main LV propulsion)

Turbo-pumps have become easier and easier to build with modern technology. Yet even back in the 60's turbo-pumps were the easy part compared to solving combustion instabilities. And I don't think it ever would have been resolved for Sea Dragon, even if in theory it should be possible.

Offline pacojoe

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Re: Sea Dragon - Would it Work?
« Reply #19 on: 05/27/2018 01:39 am »
From my old notes, the big 140 ton launcher that I linked to above needed about $3.4m of LH2 and about $320K of LOX.

Compare that to the BFR's fuel costs at around $200K per flight and you begin to realise how the economic situation today differs quite a bit from when Truax was putting this idea together. His ideas were brilliant, and in his economic environment I believe he was dead on the money.

Today though, is a different situation.   The costs of the extra fuel needed for these BDB's now represents more money than the cost of the materials needed for these big, heavy tanks, not to mention that the costs to develop a turbopump these days would be recouped on the third or fourth flight.

$3.72 million of propellant for the Leviathan is definitely a lot compared to $200K for the BFR, but it's still only about 6.2 percent of the total launch cost. It seems counter-intuitive that propellant cost would be the difference maker when comparing the Leviathan to a more traditional pump-fed rocket like the BFR. Of course, if Big Dumb Booster concepts fail to significantly reduce costs in other areas, and fail to enhance reusability, then I can definitely see how propellant cost could be a difference maker.

Evidently, Elon Musk has hinted that the cost per launch of the BFR could become as little as $7 million. That's $21.21 per pound to LEO. That number seems insanely optimistic to me, but if SpaceX can achieve anything close to that, we won't need a Sea Dragon or a Leviathan.
https://www.nextbigfuture.com/2017/10/spacex-bfr-to-be-lower-cost-than-falcon-1-at-7-million-per-launch.html

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