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BDB construction on the pad?

Posted by: malenfant - Wed Jul 26, 2006 7:40 pm
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BDB construction on the pad? 
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Post BDB construction on the pad?   Posted on: Wed Jul 26, 2006 7:40 pm
As much as I like the idea of sea dragon I can't quite believe the thing is workable. To me the logistics of towing it out to sea, fuelling it, erecting it and servicing it in a choppy ocean just don't seem feasible. So I was thinking about how else you could build and operate a booster of that size.

Transport of major components over land would be impossible so I got to wondering if any serious work has been done on building a sea dragon sized booster on the pad itself. More accurately in a semi enclosed underground silo.

I envisage a cylindrical shaft maybe 2-3 times the boosters diameter and somewhat deeper than it. the shaft would be intercepted by 3 large radial flame trenches. Together they would make up a large proportion of the circumferance of the shaft. I can't give any more thought than that to the dimensions because I imagine they would largely be determined by acoustic and exhaust dispersal factors and that sort of study is beyond me.

Removable door structures and a retractable roof would seal the flame trenches and central shaft to provide an enclosed construction site. Large items could be brought down the flame trenches or craned in from above. The lower portion of the complex could be flooded for launch if necessary.

You would need to find a nice remote site with suitable geology for the construction, but given that, I suspect only the central shaft and the adjoining portions of flame trench would even need to be clad in concrete. the outer parts of the trenches could just be cut into the rock and a roadway laid.

Obviously it's a huge engineering task to design a structure that can be both shelter, gantry and assembly jig for the booster but I can't see a show stopper yet. Not apart from "who's going to build?" it, anyhow

Has anything like this been seriously studied? Maybe the acoustic loads in that semi enclosed space are the killer?


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Post    Posted on: Mon Jul 31, 2006 8:09 am
Building a permanent launch site reduces the launch flexibility. You can only make certain orbits, and only when the local weather is good and the downrange area is clear. Noise pollution would be a huge problem and the construction cost would be enormous.

Towing a 7000 ton tube with 2 or 3 sea-going tugs, erecting the rocket by flooding its ballast tanks, and connecting a couple of hoses to a LOX tank (or plant) on a support ship to load 11,000 tons of LOX, is all pretty simple and inexpensive by comparison.

Choppy seas don't matter much on this scale, and you would mostly be launching near the equator, where, tropical storms excepted, the seas are mostly calm. Sea Launch do this with a mobile launch platform.


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Post    Posted on: Mon Jul 31, 2006 12:36 pm
WannabeSpaceCadet wrote:
Building a permanent launch site reduces the launch flexibility. You can only make certain orbits...


Fair point. I'll be honest and say I am viewing this booster as a lunar colonisation vehicle only.

WannabeSpaceCadet wrote:
and only when the local weather is good and the downrange area is clear. Noise pollution would be a huge problem...


Yeah well this and the above are major factors. That leaves me looking for a geologically stable desert region on or near the equator situated on the western shore of a major ocean. Hmmm...

The low launch rate would mean the downrange area wouldn't have to be cleared very often though.

WannabeSpaceCadet wrote:
and the construction cost would be enormous.


True enough. But intuitively I don't believe the chalenges of launching it at sea are as easily solved as you imply

WannabeSpaceCadet wrote:
Towing a 7000 ton tube with 2 or 3 sea-going tugs, erecting the rocket by flooding its ballast tanks, and connecting a couple of hoses to a LOX tank (or plant) on a support ship to load 11,000 tons of LOX, is all pretty simple and inexpensive by comparison.


I think that's a slightly dissingenious description of sea dragon.

You're talking about setting asside a shipyard to build it and hiring a nimitz class aircraft carrier, not just for every launch but for every scrub as well. what happens if you have some valve or guidance box that's below the water level fail while at sea? even a pressure fed engine has quite a bit of associated plumbing and mechanics. The costs of a scrubbed launch and return to dry dock would be huge. I just can't believe that this makes sense to anyone except the US navy. You need to have the support facilities just hanging around doing nothing most of the time.

I notice there is no mention of fueling the LOX/LH2 upper stage. That element seems particularly far fetched to me to begin with. Figuring out a way to insulate the LH2 tank that will allow it to also be submerged and dealing with the boil off problems whilst afloat and upended in a tropical ocean are huge design chalenges that seem comparable to a combined construction/launch site. I remember seeing a discussin of this in another thread.

You raise some good practical considerations about choice of launch site and the practicalities of launching at sea but I'm still not sold on the financial arguments vs a sea launched system. I thought of some additional costs in that you would only be able to build one at a time and your launch rate would be a little over the total construction and launch time for a single booster. There's no opportunity to use production line methods so some of the workforce will be idle for long periods.

My gut feeling is that there has to be some killer technical problem with this concept that we haven't seen yet. Understand that I am not trying to propose some system that some us government agency would want or be able to implement in the near future. I'm just into evaluating the concept in an abstract sense.


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Post    Posted on: Tue Aug 01, 2006 2:37 am
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I thought of some additional costs in that you would only be able to build one at a time and your launch rate would be a little over the total construction and launch time for a single booster. There's no opportunity to use production line methods so some of the workforce will be idle for long periods.


Most of these problems have already been faced and solved by regular ship builders. Most of the point of the Sea Dragon was to treat it like a ship rather than an aircraft.

If you need to have several in production to keep specialists in operation then you build a second or third dry-dock.

The Sea Dragon attempts to get around a lot of issues, like available orbits, by just being excessively big. Be big and inefficient thus cheaper than exponentially reducing returns of chasing efficiency in small craft.

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Post    Posted on: Tue Aug 01, 2006 9:26 am
idiom wrote:
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I thought of some additional costs in that you would only be able to build one at a time and your launch rate would be a little over the total construction and launch time for a single booster. There's no opportunity to use production line methods so some of the workforce will be idle for long periods.


Most of these problems have already been faced and solved by regular ship builders. Most of the point of the Sea Dragon was to treat it like a ship rather than an aircraft.

If you need to have several in production to keep specialists in operation then you build a second or third dry-dock.

The Sea Dragon attempts to get around a lot of issues, like available orbits, by just being excessively big. Be big and inefficient thus cheaper than exponentially reducing returns of chasing efficiency in small craft.


Actually I was raising the workforce issue as a problem with the land launch scenario. For sure it would be easier to aquire a couple more dry docks than to build several of these gargantuan construction/ launch facilities I have in mind.

I totally agree with the concept of being big and inefficient. My main contention here is that it seems to me that there are fewer unsolved technical problems with building and launching this sized booster from a silo than with the sea launch scenario. Problems like how you insulate and top up the LH2 tank and how you service the thing if problems arise once out in the deep ocean. Solving complex design problems like that has got to be more expensive than diging holes or welding steel plate.

It strikes me that viwing it as a ship is probably as simplistic and flawed an idea as viewing it as an aircraft. It's actually something completely different to either.


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Post    Posted on: Tue Aug 01, 2006 11:55 am
As Publiusr likes to say, the sea dragon is more of a bluecollar approach. If you have an engineering difficulty as a shipwright you add steel until the problem is solved. :)

In terms of insulation and transport/service at sea, a semi-submersible second hull seems the best choice to me. That is build a conventional ships hull around the Sea Dragon. This would improve towability and onsite servicing. It would still avoid the complexity of being a full gantry by submersing and floating out from under the Sea Dragon. This would be a fairly straight foward operation to reverse in the event of a scrub.

Its overkill and inelgant but it would side step most show stoppers.

I am still not happy with the use of H2. I would prefer Methane. And I am not to sure about attitude control of such a beast with an ungimballed engine. I think the H2 adds more complexity than it saves in size. The attitude control could easily undo the simplicity of the system also. Also tankage of Hydrogen is a lot harder than other fuels.

A Vertical Silo would be big, but its not that big. It wouldn't be too much bigger than a dry dock either. By flooding the silo before filling the tanks you would change the load bearing equations too much either.

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Post    Posted on: Tue Aug 01, 2006 2:00 pm
idiom wrote:
The Sea Dragon attempts to get around a lot of issues, like available orbits, by just being excessively big.
I don't see how size has anything at all to do with orbit availability. Small or large, any rocket has exactly the same orbit availability issues to deal with.


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Post    Posted on: Tue Aug 01, 2006 3:52 pm
campbelp2002 wrote:
idiom wrote:
The Sea Dragon attempts to get around a lot of issues, like available orbits, by just being excessively big.
I don't see how size has anything at all to do with orbit availability. Small or large, any rocket has exactly the same orbit availability issues to deal with.


You can put any payload into any given orbit from any location given sufficient lifting capacity. I think what he means is that if you can drive the cost per unit mass right down then who gives a damn how inefficient it is to achieve certain orbits? you just suck it up because it's cheaper than moving these behemoths around on the ground.

idiom wrote:
"A Vertical Silo would be big, but its not that big. It wouldn't be too much bigger than a dry dock either. By flooding the silo before filling the tanks you would change the load bearing equations too much either."


heheh, I wasn't thinking about flooding the whole silo, just flooding the bottom to provide a sound supression system like on saturn and the shuttle. I don't even know if you'd need that for a really rugged, heavy design. Is sea dragon really so far along that this is worth doing to preserve the integrity of the design? all along I have been assuming a full redesign, just keeping the basic concept (build heavy, single large pressure fed egine, lox kerosene first stage) - Could you really transfer the whole design? I don't know much about fluid dynamics but surely there is a lot of difference between launching in a highly confined body of water and launching in the open ocean? I would have thought that would be enough to invalidate the design to begin with. Heheh, Interesting Idea, I don't think I would ever have considered it.


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Post    Posted on: Tue Aug 01, 2006 9:23 pm
I meant that the design has enough Delta V to afford a large amount of orbital adjustments that would be considered hideouly expensive on any other design. Launching to an equitorial orbit from the south pole might cut down on final payload, but its still going to more than even the Saturn V ever lifted and much cheaper to boot.

When I talk about 'keeping the design' I mean the principles not the blue prints.

With the silo you describe really big ole flame trenches, I am thinking these might be enough to allow it to take off. Mind you might need to divert a river to flood the whole thing. Its not a lot of rock, but it is a whole lot of water to move around.

As the plans are pretty much unavailable you would go with a full redesign but you would stick with the dimesnsions and the ideas of basically chaining pressure vessels together. With an thrust chamber that is Sixty Feet across you should get pretty high temperature and pressure available because you have so very little surface area to volume. It should be a lot easier to cool and so forth.

Having the thrust of that thing even slightly off center would be an attitude control nightmare, however the sheer size means the accuracy tolerances come down quite a bit too.

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Post    Posted on: Tue Aug 01, 2006 9:29 pm
idiom wrote:
but its still going to more than even the Saturn V ever lifted and much cheaper to boot.
How cheap is cheap? How many millions of dollars do you think it will cost? I mean all costs starting from scratch, including whatever infrastructure you need, through launching the first one?


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Post    Posted on: Tue Aug 01, 2006 10:12 pm
http://en.wikipedia.org/wiki/Sea_Dragon_%28Rocket%29

Quote:
Payload costs were estimated to be between $59 to $600 per kg,


Yeah well I don't believe that, even in 1962 dollars, but if it's even in the same region then it means you can afford to be very inefficient indeed.

The problem, as you say, is the initial investment. Once the infrastructure is paid for the cost savings are very real.


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Post    Posted on: Wed Aug 02, 2006 1:52 am
I forgot about the LH2, but that and the 2nd stage LOX would be above the water-line in the launch position, which is when you would fill it.

A CVN is not needed, you fill it with RP-1 before leaving port, then load the LOX & LH2 from (probably separate) tankers at the launch site.

You build these like WW2 liberty ships. Assembly line, no frills.

I like the idea of the SSTO version with the plug nozzle. That would probably just use LOX / RP-1.


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Post    Posted on: Wed Aug 02, 2006 11:58 pm
Aerojet wanted to lease the infrastructure... Using regular shipyards and sea-going tugs. This way you could move the operation around fairly easily, you could shut down the operation and restart it. Their quote to Nasa included using pre-existing engine test stands and borrowing time at other facilities. This avoids the traditional Nasa layout of everything getting its own facility that invariably gets destroyed if a program is paused or cancelled.

Dont forget the lower stage is fairly short burn and should survive pretty handily to go around again. There is not a lot that can happen to it as it is a lot simple and far more robust than an SSME. The attitude control for the first stage is in the second stage so the first stage is dead simple.

Upgrades the first stage with an aerospike would be an interesting step. It would be about ten feet in diameter at the throat so it might have enough structure to avoid the wiggling that plauges smaller aerospikes.

EDIT: No I am talking out a hole in my head. The first stage engine is gimballed. The gimbal plate is a foot thick! Big jolly actuators too.

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Post    Posted on: Thu Aug 03, 2006 1:09 pm
idiom wrote:
Upgrades the first stage with an aerospike would be an interesting step.
This sounds like a step away from the simplicity that you are counting on to reduce cost. The big dumb booster is supposed to be all proven technology I thought.


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Post    Posted on: Thu Aug 03, 2006 8:55 pm
Just simple and cheap technology. The 1960's Sea Dragon included one of the first expanding nozzels proposed on the Second Stage.

It also had an awesome Flare thing on the first stage. Basically a torus back near the engine inflated to a diameter of 300 feet. a heat resistant mesh ran up to mid-ships. During re-entry the size of the flare stopped it getting to much above 100C. The First stage was slowed to, iirc, 300ft/sec at impact. Internal pressurisation allowed it to survive intact at this speed.

A parachute would have been 2700 ft in diameter. It was apparently ruled out because the first stage has a neutral stability and will tumble as it re-enters.

So not all proven, but easily tested in small scale. For example the water launch is now considered proven but had never even been tried before the Sea Dragon proposal.

An aerospike might not be worth it on the first stage actually, because the burn time is so short and the regime so even. But it is something to look at.

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