Author Topic: Sea Dragon class LV thead  (Read 80053 times)

Online A_M_Swallow

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Re: Sea Dragon class LV thead
« Reply #15 on: 09/10/2007 02:46 PM »
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Christine - 10/9/2007  7:50 AM
The best way to shield from solar protons during a flare in my mind would be to put a giant water filled polyethylene tank on the sun-facing side of your habitat.

That sounds like a description of a fuel tank.   :cool:

Offline khallow

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Re: Sea Dragon class LV thead
« Reply #16 on: 09/11/2007 01:50 AM »
I think it's a terrible idea to ignore the economies of scale from using small LVs launched more frequently. I don't know what the future launch market will look like, but I think it possible for a market of competitive 25t LVs (with heavy commercial activity on the side) to be cheaper and more reliable than a 400+t LV. Perhaps, a mix of launch vehicles with most of the payload covered by the cheapest commercial vehicles (in $ per kg) and the rest by a specialized HLV with a decent launch rate. But I don't see a place for a 400t LV unless it is used a lot (more than a few times a year).
Karl Hallowell

Offline Kaputnik

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Re: Sea Dragon class LV thead
« Reply #17 on: 09/11/2007 12:37 PM »
Payload volume and fairing diameter are one aspect in which multiple small LVs cannot compete with HLLVs. With current technology, fairing diameter represents a major bottleneck in capabilities for a manned Mars mission, because it restricts the size and mass of individual entry vehicles to  the point where manned vehicles become very hard to design.
A pessimist is just an optimist with experience

Offline tnphysics

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Re: Sea Dragon class LV thead
« Reply #18 on: 09/11/2007 08:58 PM »
In principle, why couldn't you make the spacecraft able to withstand launch loads without a fairing?

Offline Kaputnik

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Re: Sea Dragon class LV thead
« Reply #19 on: 09/11/2007 10:06 PM »
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tnphysics - 11/9/2007  9:58 PM

In principle, why couldn't you make the spacecraft able to withstand launch loads without a fairing?

No reason other than that it is usually more mass-efficient to have a disposable fairing than a toughened spacecraft. For an entry vehicle it makes less difference because it needs to be quite sturdy anyway, hence the Shuttle has no fairing.
However doing away with the fairing wouldn't remove the constraint on payload diameter. Increased payload size will adversley affect the centre of pressure, potentially causing guidance problems duirng ascent; it will also increase the aerodynamic drag on the vehicle, reducing performance.
A pessimist is just an optimist with experience

Offline tnphysics

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Re: Sea Dragon class LV thead
« Reply #20 on: 09/12/2007 07:48 PM »
What would be the payload of Sea Dragon be if 3 first stages where clustered together with one upper stage on top in a manner simaler to Atlas V Heavy?

Offline kkattula

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Re: Sea Dragon class LV thead
« Reply #21 on: 09/13/2007 03:45 PM »
Just a WAG but probably over 1000 mt.

Online bad_astra

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Re: Sea Dragon class LV thead
« Reply #22 on: 09/13/2007 04:10 PM »
Unless you're building an Oneal colony from Earth Materials (exactly the opposite of how it should be built, anyway), there is no reason, ever, for a Sea Dragon.

How many launches of this kind of vehicle could be needed by one country in one year? One? Maybe one every 2? You still need standing army to maintain it, it's prep facilities, etc during the off time so you really get no savings from having such a monster. And if you LOSE a Sea Dragon, how many years are you unable to go to space at all because you bet the farm on one LV and killed off the rest of the competition?

What is far more reasonable and robust is a diverse lv's with high flight rates.
"Elon Musk was able to build this in a cave! With a box of scraps!"

Offline Tergenev

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Re: Sea Dragon class LV thead
« Reply #23 on: 09/13/2007 04:43 PM »

kkattula wrote: "Basically, if you take a bunch of smokers, send them to Mars and back over 3 years, (without cigarettes), their life expectancy on return would be higher than if they'd stayed on Earth and continued smoking."

If you take a bunch of smokers and put them into a small aluminum can together on a trip to Mars,  without cigarettes . . .and I guarantee their life expectancy will be no more than 2 weeks. They'll all kill each other!  :laugh:  


Offline renclod

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Re: Sea Dragon class LV thead
« Reply #24 on: 09/14/2007 09:19 AM »
They could grow some stuff in zeegee and delay the fight.  :cool:
Tobacco seeds and seedlings on STS-95 ?

Offline J05H

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Re: Sea Dragon class LV thead
« Reply #25 on: 09/18/2007 07:54 PM »
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Kaputnik - 11/9/2007  6:06 PM
No reason other than that it is usually more mass-efficient to have a disposable fairing than a toughened spacecraft. ... it will also increase the aerodynamic drag on the vehicle, reducing performance.

A possible solution is to split an updated Ultra-heavy Lift Vehicle (ULV) into 2 stages that function together or separate. The bottom stage can be used for harbor-to-harbor ballistic launches. Combined with a standard-sized/interfaced upper stage, it can deliver 250-500t cargo and the upper stage to LEO. The craft can be a LEO-only cargo booster or using the same mold-lines be an interplanetary transport, with additional propellant.

Fuel is your choice, but one possibility is propane or LNG and LOX. Both are available in quantity and Propane/LNG is available on refrigerated ships, which serves the SeaDragon-type operations well.

Offline tnphysics

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Re: Sea Dragon class LV thead
« Reply #26 on: 09/18/2007 11:34 PM »
LNG/LOX stage 1 and LH2/LOX stage 2 is my preference.

Offline khallow

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Re: Sea Dragon class LV thead
« Reply #27 on: 09/19/2007 06:31 PM »
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bad_astra - 13/9/2007  9:10 AM

Unless you're building an Oneal colony from Earth Materials (exactly the opposite of how it should be built, anyway), there is no reason, ever, for a Sea Dragon.

How many launches of this kind of vehicle could be needed by one country in one year? One? Maybe one every 2? You still need standing army to maintain it, it's prep facilities, etc during the off time so you really get no savings from having such a monster. And if you LOSE a Sea Dragon, how many years are you unable to go to space at all because you bet the farm on one LV and killed off the rest of the competition?

What is far more reasonable and robust is a diverse lv's with high flight rates.

I agree. Keep in mind in every mode of transportation, we've seen progressions to larger and larger vehicles just as is occuring in launch vehicles now. Sometimes as in the case of ships, this process has repeated itself many times as new technologies are developed. But there's always a point past which growing larger becomes uneconomical. For example, rather than build larger train engines, multiple smaller engines are used to pull the larger loads. Planes and ships could technically get a lot bigger, but the infrastructure isn't able to handle them.

As I see it, the Sea Dragon is too big for us now. There's no mission that requires it nor can we guarantee a high enough flight rate (a high flight rate being the most important way to lower launch costs) to justify its existence. And as bad astra notes, there are other disadvantages from the lack of diversity.

An area of squandered opportunity is devising techniques that exploit the relatively cheap launch vehicles with smaller payloads but high launch rates and good cost per kilogram. That means orbital assembly and construction techniques, refueling, perhaps even finer grained manufacture techniques. It may be impractical or too unreliable to launch everything via the restricted spaces of these small rockets and later assemble them into larger structures.

But I dislike the impulse to assume that one can make a heavy launch vehicle and then design the mission around that. There are many examples of specialized transportation systems (for example, city subways; airport walkways, shuttles, and light rail; ore conveyance systems in mines, military transportation), but these invaribly are intended to have a lot of traffic. In current heavy LV plans, there's no high volume need.
Karl Hallowell

Offline tnphysics

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Re: Sea Dragon class LV thead
« Reply #28 on: 09/19/2007 11:14 PM »
Sea Dragon was intended to use a "brute force" approach to acheving large payloads.

What about a more clever approach?

Pump-fed reusable LRBs. Pump fed (but no more expensive) reusable core stage. Nuclear upper stage.

Offline MKremer

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Re: Sea Dragon class LV thead
« Reply #29 on: 09/20/2007 05:20 AM »
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tnphysics - 19/9/2007  6:14 PM

Sea Dragon was intended to use a "brute force" approach to acheving large payloads.

What about a more clever approach?

Pump-fed reusable LRBs. Pump fed (but no more expensive) reusable core stage. Nuclear upper stage.

Anyone can speculate about different pie-in-the-sky options till the cows come home. However, real life demands things concerning realistic engineering based on budget constraints, development time limits, testing time limits, and overall construction time limits. (Oh, and not to mention budgets, budgets, budgets, etc.)


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