Author Topic: Sea Dragon - Would it Work?  (Read 33542 times)

Offline kraisee

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Re: Sea Dragon - Would it Work?
« Reply #20 on: 05/27/2018 02:01 am »
$3.72m becomes an issue if you're designing the system to have a high flight rate. If you're flying no more than once a month, it would probably be quite workable. If you're aiming to create a system able to fly more than once a week, or perhaps daily, then (just like airlines) the prop costs begin to dominate your annual cost profiles.

Like everything in this business, it all depend on what your core requirements actually are, and how does your business model support those choices and how is it affected by changes down-stream.

There's no question that SpaceX have found an excellent solution that promises to revolutionise launch prices. But I still see room for definite improvement beyond BFR. I'm quite sure there are ways to get LEO prices down to a third of BFR's promised levels, probably even lower - though not from a BDB solution :)

Ross.
« Last Edit: 05/27/2018 02:02 am by kraisee »
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Offline pacojoe

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Re: Sea Dragon - Would it Work?
« Reply #21 on: 05/27/2018 04:09 pm »
There's no question that SpaceX have found an excellent solution that promises to revolutionise launch prices. But I still see room for definite improvement beyond BFR. I'm quite sure there are ways to get LEO prices down to a third of BFR's promised levels, probably even lower - though not from a BDB solution :)

How would you do that?

Offline kraisee

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Re: Sea Dragon - Would it Work?
« Reply #22 on: 05/27/2018 08:29 pm »
That, I'm going to hold close for a while ;)

Ross.
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Offline Archibald

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Re: Sea Dragon - Would it Work?
« Reply #23 on: 06/02/2018 11:16 am »
Quote
There's no question that SpaceX have found an excellent solution that promises to revolutionise launch prices. But I still see room for definite improvement beyond BFR. I'm quite sure there are ways to get LEO prices down to a third of BFR's promised levels, probably even lower - though not from a BDB solution

Sure, Falcon 9 is a much improved rocket but it remains, at core, a classic two stage rocket as flown since the dawn of the space age (hint, Saturn I / Saturn IB). Musk was pragmatic and took a low risk tech approach, then "improved" it step by step. Low cost expendable (same engines on both stage gas generator kerosene), streamlined / mass production, then reusability.  All three contribute to lower launch cost.
« Last Edit: 06/02/2018 11:17 am by Archibald »
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Offline Paul451

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Re: Sea Dragon - Would it Work?
« Reply #24 on: 07/20/2018 10:32 pm »
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.

Que?

SeaDragon was meant to be built from ship-steel, in a ship-yard, by ship-makers. That was kind of its whole party piece. (Also, 8 mm is not 4 inches, it's more like 5/16ths.)

Offline Lar

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Re: Sea Dragon - Would it Work?
« Reply #25 on: 07/21/2018 04:46 pm »
That, I'm going to hold close for a while ;)

Ross.

Go bigger, go more frequently... but same tech. That would be my guess.   However I'm not a rocket scientist. Ross is.
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Offline tocnaza

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Re: Sea Dragon - Would it Work?
« Reply #26 on: 09/06/2018 06:31 pm »
Great design, Ross!

Offline floss

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Re: Sea Dragon - Would it Work?
« Reply #27 on: 09/29/2018 12:42 pm »
I want one to launch off the west coast of Ireland so I can ban French fishing boats from destroying the marine ecosystem . 

Offline tdperk

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Re: Sea Dragon - Would it Work?
« Reply #28 on: 09/29/2018 07:27 pm »
That, I'm going to hold close for a while ;)

Ross.

Not having any resources to do it myself, I have no reason to keep any ideas to myself.

A) Either bust or license the patent for pistonless pump engines from Flometrics (I think their idea is actually already thoroughly public domain and their patent derivative, but IANAL), and keep the engine costs far lower while keeping them reusable.

B)  More asparagus staging with prop transfer from the outset.  Goal is to have all stage elements identical and recoverable but any last (3rd?) stage, the required dV of which is to be as low as possible.

C)  Develop two engine sizes, one as large as possible/practical for each stage element and one intended to be well in a throttle range for landing close to empty stage element and to provide retro-propulsive braking and re-entry mitigation, the smaller of them to be the sole 3rd stage engine.

Chief reason none of that means anything is, BFR system will be fully operable by the time any such thing could be developed.  It would be a decent way to compete with the F9 family.

Only way to compete with SpaceX now is to go for a scale/tech which makes BFR non-competitive for the scale of payload you intend to service or, is so much less expensive to develop operate that BFR has no payloads because you take them.  Looks like BFR will be competitive with even current smallsat launchers.

So to any who undertake it, good luck with that.

Offline Lar

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Re: Sea Dragon - Would it Work?
« Reply #29 on: 09/30/2018 03:16 pm »
Yeah, the clock is ticking on this... any proposed competitor needs to beat BFS out of the gate unless it is way less costly.

I like your proposal, though.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
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Offline speedevil

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Re: Sea Dragon - Would it Work?
« Reply #30 on: 10/01/2018 09:37 am »
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
He's flat out stated it can be well under $1M cost to launch in the long term. (passenger transit, 'cheaper than an economy flight' can't be significantly over a million for a profitable service, meaning cost to launch must be considerably less to be profitable).

$7M is - assuming $1M launch site service costs - reusing BFR 25 times or so.

He's also stated they are actively working on second stage recovery of F9, and may be able to fully reusably launch for $6m in '2-3 years' (6 months ago).

Big dumb boosters had a window in the 70s-00's or so.
(if people could work out a payload for them).
That window is closing, because if reusable launchers hit, they begin to violate the entire precept.
'Fuel is cheap'.
With reusable launchers that efficiently use fuel, it can become a non-negligible fraction of the cost, so using ten times more in the aims of simplicity may not be an option, as it leaves you nothing for structure.


Offline Refleks

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Re: Sea Dragon - Would it Work?
« Reply #31 on: 12/31/2018 02:34 am »
Ultimately I think the whole concept hinges on the engine and whether or not combustion instability is a problem on those scales.   Some very smart people seem to think it's a showstopper while other's believe that it won't be an issue, in contrast to the problems encountered with the Saturn.

Some excerpts from another discussion:
Quote
The main problem I'd expect to see would be combustion instability -- conventional wisdom says that's a bigger problem in large chambers than small ones, and this is certainly a large chamber. This Q/A discusses that problem.

However, the original Aerojet-General proposal suggests that the resonant frequencies of such a large chamber would be so low that feedback instability wouldn't be sustained:

    With regard to combustion stability, an analysis on the basis of sensitive time lag theory (perhaps the best theory so far developed) indicates that the Sea Dragon thrust chamber will operate well outside the region of combustion instability. One of the primary advantages of sea based development testing is that it permits early experimental evaluation of combustion stability on a full scale basis without an exorbitant outlay for facilities.

In other words "we don't think it's a problem, but, hey, at least if one of those engines blows up in the ocean it won't hurt anything."

Quote
Truax wasn't concerned with combustion stability because the engine was going to be a pintle injector type. He believed the natural combustion stability of the pintle injector would allow enormous engines to be highly stable at a variety of pressures. (Variable pressure was a key part of his design, because it allowed a much simpler and sloppier system in which pressure started high and slowly dwindled down as the tanks emptied.)

TRW (who built the rockets for the Apollo lander) later validated his belief. In that paper they point out that pintle injectors have demonstrated stable combustion with motors varying in scale by 50,000:1. So, Truax was probably right.

From here:
https://space.stackexchange.com/questions/16816/how-realistic-would-the-sea-dragon-engine-be-to-produce-given-todays-technology

https://space.stackexchange.com/questions/955/why-do-pressure-fed-engines-have-combustion-instabilities

_____


Ultimately, we won't know for sure unless someone builds and tests the engine (and the infrastructure to do so), and then it opens up a whole world of possibilities if successful.

The second biggest issue is many rightly saying there's no need for a 500t class booster.  From a commercial perspective, currently, they're not wrong... but that's also very short sighted view if we are to be in space long term with a future outside of LEO.  While there may not be direct commercial applications at present, it enables a whole host of future activities that commercial applications might leverage.  There is a place, IMO, for a booster of that class for especially heavy or oversized payloads and I can think of uses for the first 20-25 launches off the top of my head...  it's a niche capability to be sure, but if the economies of scale can get the margins down to, say, Saturn V or Shuttle costs-per-launch (which are of course quite expensive by today's standards) it would be quite viable for the performance.

That being said, something that isn't directly profitable (without a for-sure ROI) but takes us in a direction we should be headed, puts it squarely in the relm of Government / NASA funding.  It would complement things like Starship/BFR, New Glenn quite well IMO, but unfortunately there's no interest in shifting away from the current job's program, which makes a kind of sense from the lens of a politician -- current NASA rocket programs keeps the engineers employed for the foreseeable future without having to modify infrastructure, which is considered a tacit success.  Whether or not we get a functioning rocket out of it at some point that has a competitive niche with commercial alternatives is either incidental or irrelevant depending on how cynical we are about the state of Government run programs.

If private companies are to pursue the capability, they would have to be extremely careful about it.  Even SpaceX didn't go straight to BFR/Starship, and it wasn't just because of the crawl/walk/run philosophy of learning how to stick propulsive landings -- it was to build a sustainable and profitable foundation through which they could continue to fund bigger and better projects via things like Falcon 9 / Heavy (and if needed in the future, Falcon 1).  Most startups seem to drive straight towards what they want, and I suspect that's why many fail.

I'm definitely a proponent and would really like to see if an engine of that scale is feasible (or even a half scale / 12m engine).... but unless someone has a real vision and is a whiz at gofundme/kickstarter or maybe won that billion dollar lottery this year... I don't really see it happening anytime soon.
« Last Edit: 12/31/2018 02:41 am by Refleks »

Offline pacojoe

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Re: Sea Dragon - Would it Work?
« Reply #32 on: 04/11/2020 10:05 am »
I wonder how much it would cost to build and test a one-third scale Sea Dragon engine prototype. If nothing else, you'd get a nice big explosion out of it.

Offline Aeneas

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Re: Sea Dragon - Would it Work?
« Reply #33 on: 05/18/2020 12:16 pm »
I wonder how much it would cost to build and test a one-third scale Sea Dragon engine prototype. If nothing else, you'd get a nice big explosion out of it.

Would definitely generate some clicks on Youtube...^^

Offline zeds

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Re: Sea Dragon - Would it Work?
« Reply #34 on: 05/21/2020 02:43 pm »
how would the sea dragon launching impact the marine life around it? and if it does impact the marine life in a negative way, how can we fix or mitigate that?

Offline TrevorMonty

Re: Sea Dragon - Would it Work?
« Reply #35 on: 05/22/2020 04:49 am »
how would the sea dragon launching impact the marine life around it? and if it does impact the marine life in a negative way, how can we fix or mitigate that?
Likely kill every fish and whale with in few kms radius.

Offline slavvy

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Re: Sea Dragon - Would it Work?
« Reply #36 on: 05/22/2020 07:23 am »
Launch it from some dead water body, such as a salt lake or a heavily poluted lake. Does anyone know of suitable candidates?

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Offline Paul451

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Re: Sea Dragon - Would it Work?
« Reply #37 on: 05/22/2020 12:03 pm »
Launch it from some dead water body, such as a salt lake or a heavily poluted lake. Does anyone know of suitable candidates?

Dead Sea, Salton Sea, Aral Sea?

Offline Eer

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Re: Sea Dragon - Would it Work?
« Reply #38 on: 05/22/2020 01:51 pm »
How about the dead zone in Gulf of Mexico, or does that not extend from the dead floor to the surface?
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Offline Aeneas

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Re: Sea Dragon - Would it Work?
« Reply #39 on: 05/23/2020 07:12 pm »
how would the sea dragon launching impact the marine life around it? and if it does impact the marine life in a negative way, how can we fix or mitigate that?

Maybe devices producing different annoying sounds for animals to scare them away.

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