DDE

Fission fragment rocket for DRA5 mission

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https://ntrs.nasa.gov/search.jsp?R=20140008733

Props to @nyrath, as always.

TL;DR 'Afterbuner' design with hydrogen injection into the exhaust of a dusty plasma reactor results in Isp=32000 sec, allowing for a single-stage trip from Earth to Mars orbit and back, hence a high degree of reusability.

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32,000 Isp sounds fantastic, but how much radioactive exhaust products (and how long lived) is that going to leave behind it?

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With an exhaust velocity of many times the solar system escape velocity, I wouldn't think you need to be too concerned about the exhaust (as long as you are careful to point it away from anything you don't want to spray with radioactivity).

Edited by Brotoro
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18 minutes ago, Brotoro said:

With an exhaust velocity of many times the solar system escape velocity, I wouldn't think you need to be too concerned about the exhaust (as long as you are careful to point it away from anything you don't want to spray with radioactivity).

Not so bad then. Just be careful where you point that thing.

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Wow, oil moderator, 90 tons empty. I wonder if having an oil moderator will allow it to be changed out, give it a longer lifespan? Thrust is fairly reasonable too, although maybe not for the size of the engine and craft.

Also, those radiators...

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It takes 36 SLS launches to build. At $1 billion per launch and 1 launch per year, that should keep NASA busy for a while...

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Well, its no Daedalus, but I like it. 

Seen a lot of these proposals, with nice CGIs of exotic nuclear engines. Its about time someone actually tried building one.

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6 hours ago, Nibb31 said:

It takes 36 SLS launches to build. At $1 billion per launch and 1 launch per year, that should keep NASA busy for a while...

When they compare the size of the radiators (and thus the whole spacecraft) to aircraft carriers you know it is going to be expensive.

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6 hours ago, Nibb31 said:

It takes 36 SLS launches to build. At $1 billion per launch and 1 launch per year, that should keep NASA busy for a while...

Or you could build it with twice that many FH/NG launches for <1/3 of that price per launch and a dozen launches per year.

Edited by _Augustus_
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1 hour ago, _Augustus_ said:

Or you could build it with twice that many FH/NG launches for <1/3 of that price per launch and a dozen launches per year.

Let's see those fly before making plans.

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13 minutes ago, Nibb31 said:

Let's see those fly before making plans.

Couldn't the same be said of SLS?

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19 minutes ago, Ignath said:

Couldn't the same be said of SLS?

Absolutely.

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1 hour ago, wumpus said:

When they compare the size of the radiators (and thus the whole spacecraft) to aircraft carriers you know it is going to be expensive.

Where was it that I saw the idea that submarines make fantastic pre-built spacecraft, requiring relatively little re-engineering, if a little on the over-built side?

They are airtight, with robust air-locked access ports. Thick steel hull reduces radiation exposure on long trips (probably a good place to shave off some mass tho). Life support, crew accomodation, water, food and hygiene facilities are all already self-contained.

And the big bonus - there is a fully plumbed in, high-power nuclear reactor already installed, ready to rock with your fancy space engine.

......and if you like, space and facilities for nuclear missiles....or I guess "mission equipment" or somesuch...

****

I did hear that concept somewhere, but as I am writing it, I realise that a submarine depends almost entirely on being submerged in seawater for the cooling of its reactor. I dread to think what would happen to the inside of a nuclear submarine floating in space, even on minimum power!

Also I think crew fresh water supplies are refreshed from seawater, but that is relatively trivial.

****

Anyhoo, seeing the comparison to an aircraft carrier didnt make me think it would be expensive, it made me think "Oh, so we've actually built on this scale before. Quite a lot."

If it was 10x the size of an aircraft carrier I'd be all like 0_O

But on the order of the same size? I know we are building this thing in space, but it masses a fraction of a carrier. We are doing engineering in this scale already.

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7 minutes ago, p1t1o said:

Where was it that I saw the idea that submarines make fantastic pre-built spacecraft, requiring relatively little re-engineering, if a little on the over-built side?

Probably in a stupid forum or blog post.

A pressure vessel designed to hold high pressure outside is very different from a pressure vessel designed to keep the high pressure inside. Also weight requirements are slightly different between ships and spacecraft.

 

Edited by Nibb31
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8 minutes ago, Nibb31 said:

Also weight requirements are slightly different between ships and spacecraft.

Hey, we'll just put it into orbit with multiple Skylon launches, NBD.

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10 minutes ago, Nibb31 said:

Also weight requirements are slightly different between ships and spacecraft.

 

I feel like having a submarine, which needs to have a density roughly that of Water, and the Tsiolkovsky equation just wouldn't mix, for a manned vehicle.

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18 minutes ago, Nibb31 said:

Probably in a stupid forum or blog post.

A pressure vessel designed to hold high pressure outside is very different from a pressure vessel designed to keep the high pressure inside. Also weight requirements are slightly different between ships and spacecraft.

 

I will literally eat my hat if a submarine cant handle the pressure environment of space! Keeping 50 atmosphere outside is for sure easier than keeping 1 atmosphere inside.

But yeah they are a little on the heavy side.

Oh I found this:

http://www.projectrho.com/SSC/submarine.html

"This does raise an interesting possibility. There is actually a tradition in science fiction of converting submarines into spacecraft. The earliest instance I could find was an article by the legendary John W. Campbell. He was convinced that if the so called "Dean Drive" space-drive could be made operational, mounting it in a Skate class submarine would make an instant spaceship (as long as you attached a huge tank of water to the coolant intake. Well, maybe it isn't quite that simple.). There are plenty of weird spacedrives lying around."

 

But anyway, this is a little OT.

 

**edit**

7 minutes ago, regex said:

Hey, we'll just put it into orbit with multiple Skylon launches, NBD.

Precisely correct! In my opinion, large-scale spacefaring requires a money-less society, so if cost is not an issue, neither are several hundred skylon launches!

Edited by p1t1o
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26 minutes ago, p1t1o said:

Where was it that I saw the idea that submarines make fantastic pre-built spacecraft, requiring relatively little re-engineering, if a little on the over-built side?

They are airtight, with robust air-locked access ports. Thick steel hull reduces radiation exposure on long trips (probably a good place to shave off some mass tho). Life support, crew accomodation, water, food and hygiene facilities are all already self-contained.

And the big bonus - there is a fully plumbed in, high-power nuclear reactor already installed, ready to rock with your fancy space engine.


We got bored one patrol and started thinking about exactly what would be required to convert the 'Hog* into a spaceship - and found something surprising (though it shouldn't have been in retrospect):  The reactor** (and pretty much all of the rest of the important and desirable machinery onboard) absolutely depends on the presence of gravity to operate correctly.  To convert her into a spaceship would require significant engineering and rebuilding.


* SSBN-655 - the USS Henry L. Stimson, known to her crew (for reasons lost in the mists of time) as the Henry Hogbody or simply the Hog.

** Because of the pressurizer.

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6 minutes ago, DerekL1963 said:


We got bored one patrol and started thinking about exactly what would be required to convert the 'Hog* into a spaceship - and found something surprising (though it shouldn't have been in retrospect):  The reactor** (and pretty much all of the rest of the important and desirable machinery onboard) absolutely depends on the presence of gravity to operate correctly.  To convert her into a spaceship would require significant engineering and rebuilding.


* SSBN-655 - the USS Henry L. Stimson, known to her crew (for reasons lost in the mists of time) as the Henry Hogbody or simply the Hog.

** Because of the pressurizer.

I dont see the problem. Just strap several together in a cylinder and spin it. Simples.

Just kidding! Very interesting point you made.

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22 minutes ago, DerekL1963 said:


We got bored one patrol and started thinking about exactly what would be required to convert the 'Hog* into a spaceship - and found something surprising (though it shouldn't have been in retrospect):  The reactor** (and pretty much all of the rest of the important and desirable machinery onboard) absolutely depends on the presence of gravity to operate correctly.

Any idea exactly how much gravity?  Does it need 1g, or would it work at less?

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43 minutes ago, 1101 said:

Any idea exactly how much gravity?  Does it need 1g, or would it work at less?

No idea honestly.

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If you're throwing something as heavy as a submarine into space, better break out the pig iron and plutonium.

And while FH/NG would be able to handle most of the components of the fission fragment rocket stack, they might balk at the 110-tonne main engine assembly.

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3 hours ago, p1t1o said:

I did hear that concept somewhere, but as I am writing it, I realise that a submarine depends almost entirely on being submerged in seawater for the cooling of its reactor. I dread to think what would happen to the inside of a nuclear submarine floating in space, even on minimum power!

Also I think crew fresh water supplies are refreshed from seawater, but that is relatively trivial.

Nuclear powered submarines also make oxygen from seawater. 

https://www.ussnautilus.org/education/pdf/stemlessons/harris _How-Do-Submariners-Breathe-Underwater.pdf

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