Space Voyage #1

[Janus]

Originally Posted by TheBigDog

The center cylinder is the nuclear fuel plus the liquid fuel used for trim controls and fueling the probes and shuttles. It is meant to last for 100 years of full throttle, plus multiple missions for the smaller craft, so it is big. I am not sure if the proportions are correct. The yellow section is the nuclear rocket that propels the ship.

I hate to rain on your parade, but for your fuel to last 100 yrs at full throttle:

The ISP of a nuclear rocket theoretically can be between 10,000 and 1,000,000 sec.

Using the highest value, and applying a thrust of only 1/1000 g, you would need a mass ratio (fuel to empty ship) of 23. Meaning you would need 23 kg of fuel for every kg of ship.

At a thrust of 1/100 g, the mass ratio jumps up to 5 x 10^13! Meaning that for every kg of ship you would need an amount of fuel equal to 1/36 the mass of the Martian moon Deimos.

[TheBigDog]

Originally Posted by TheFaithfulStone

Stone signing up.

Umm... PR. Incase you meet any aliens and need to convince them to buy some cheeseburgers or something.

Oh yeah, and battle-bot building.

TFS

My deepest gratitude to you TFS! Imagine me, such a devout capitalist neglecting the angle of marketing western culture to alien cultures! We will need a good supply of blue jeans for barter. You can be our both marketing cheif and head of war-mongering.

I of course know that you have far more to add to our trip as well and am glad you have decided to join us!

Welcome aboard The Prophesy!

Bill

[TheBigDog]

Originally Posted by Janus

I hate to rain on your parade, but for your fuel to last 100 yrs at full throttle:

The ISP of a nuclear rocket theoretically can be between 10,000 and 1,000,000 sec.

Using the highest value, and applying a thrust of only 1/1000 g, you would need a mass ratio (fuel to empty ship) of 23. Meaning you would need 23 kg of fuel for every kg of ship.

At a thrust of 1/100 g, the mass ratio jumps up to 5 x 10^13! Meaning that for every kg of ship you would need an amount of fuel equal to 1/36 the mass of the Martian moon Deimos.

No rain, no worries. I am hardly a rocket scientist, so there is plenty of room for error in my calculations. For the purposes of our current mission we are fine with the fuel that our ship can carry. 100 was a bit extreme, but my intension is to suggest a ship that would not require refueling during its functional lifetime. If that is not plausible, then perhaps we can work out a more realistic number. Here is some information about our main tank and rocket...

The main tank is 200 meters long and 33 meters in diameter. The lowest 1/3 holds the nuclear fuel, and so also has thinker walls for shielding the radiation from the fuel. So the inner tank that holds the fuel is 31 meters in diameter by 63 meters in length. This is completely filled with enriched nuclear fuel made from nuclear waste that can be pumped into the pulse engine to produce a rapid series of small nuclear detonations that happen in the rocket exhaust area. I will take a leap in saying that each explosion utilizes one milliliter of fuel. At maximum thrust (rate of firing of the rocket) we can maintain 1G of accelleration. Of course as the fuel is depleted the rate of firing would need to be lower to maintain this thrust limit. The ends are ball shaped, so it has a volume of ... 47298.77179 cubic meters, or 47,298,771,790 milliliters. With 47.3 billion pulses at our disposal we can run for a good long time, even if it is not 100 years. I do not have the knowledge to calculate the amount of energy that will be released by the firing of each pulse of 1 ml of fuel. Perhaps there is a crew member who could help fill in that blank for me?

Janus, are you interested in joining our crew? You are welcome to join in the fun.

Bill

[TheBigDog]

Originally Posted by GAHD

Seems you need a maintenance officer. What happens when the windings short or the micro fastball hits?

It is always comforting to know that Gahd is on your side! Welcome aboard. You are our interplanetary handyman. What grade of duct tape are you bringing to patch holes caused by very small rocks? I am sure you could offer some other services as well.

Welcome aboard The Prophesy!

Bill

[TheBigDog]

Pyrotex, I know you have some expertise in this area. Would you be interested in designing our command and control computer systems? What platform would you develop them on, and what resources would you be needing?

Do I have a volunteer for working out our onboard communicaitons system? We just sticking with 802.11G and VoIP? Or is there something else that we should be considering?

Until tomorrow!

(t-28)

Bill

[Jay-qu]

Originally Posted by TheBigDog

I do not have the knowledge to calculate the amount of energy that will be released by the firing of each pulse of 1 ml of fuel. Perhaps there is a crew member who could help fill in that blank for me?

Resident Astrophysicist at you service
I would first need to know the presise composition of the fuel to do the calculations, sir.

[Janus]

Originally Posted by TheBigDog

No rain, no worries. I am hardly a rocket scientist, so there is plenty of room for error in my calculations. For the purposes of our current mission we are fine with the fuel that our ship can carry. 100 was a bit extreme, but my intension is to suggest a ship that would not require refueling during its functional lifetime. If that is not plausible, then perhaps we can work out a more realistic number. Here is some information about our main tank and rocket...

The main tank is 200 meters long and 33 meters in diameter. The lowest 1/3 holds the nuclear fuel, and so also has thinker walls for shielding the radiation from the fuel. So the inner tank that holds the fuel is 31 meters in diameter by 63 meters in length. This is completely filled with enriched nuclear fuel made from nuclear waste that can be pumped into the pulse engine to produce a rapid series of small nuclear detonations that happen in the rocket exhaust area. I will take a leap in saying that each explosion utilizes one milliliter of fuel. At maximum thrust (rate of firing of the rocket) we can maintain 1G of accelleration. Of course as the fuel is depleted the rate of firing would need to be lower to maintain this thrust limit. The ends are ball shaped, so it has a volume of ... 47298.77179 cubic meters, or 47,298,771,790 milliliters. With 47.3 billion pulses at our disposal we can run for a good long time, even if it is not 100 years. I do not have the knowledge to calculate the amount of energy that will be released by the firing of each pulse of 1 ml of fuel. Perhaps there is a crew member who could help fill in that blank for me?

Janus, are you interested in joining our crew? You are welcome to join in the fun.

Bill

Sure, I'll play along, But I have a few sugestions.
1g acceleration is a tad unrealistic. Not that you couldn't produce such a thrust, it is just that for a reasonable mass ratio it won't last very long. For example, a 23/1 mass ratio would last a little over a month.
On the other hand, if you drop your thrust down to 1/100 g, that same mass ration will last you 10 yrs. 1/100 g may not seem much, but at that thrust level you can still cross the diameter of Neptune's orbit in a little more than 7 mo. That's boosting halfway and braking for the other half.

These numbers are based on the maximum theoretical ISP for a nuclear pulse rocket, as calculated by people who are rocket scientists.(The ISP, or "specific impulse", is a measure of how efficient the rocket is in using fuel/reaction mass to produce delta v.)

You also won't be able to completely fill your "fuel tank" with fuel. If you try and cram fuel that is enriched enough to undergo a nuclear detonation together in a single large mass, you ship will go "poof" and. Some of that space is going to have to used up by some type of damping material (like the control rods in a nuclear reactor.) I'll have some more thoughts on this later (such as maybe utilizing that damping material as reaction mass for the ship.).
I've got some more thoughts but I'll get to them later.

[Janus]

One more thing I want to mention. It is about the design of the ship shown in the diagram. I noticed that the indivdual modules of the "wheel" section are flat and don't curve. In this configuration anyone standing at either end will find the floor tilted at about 15°, with the center of the module "uphill". It would be better if they curved.

[TheBigDog]

Who could ask for a better crew than this. I am surrounded by geniouses!

Welcome aboard the Prophesy, Janus. You are offered the role of our Nuclear Propulsion Engineer (unless you prefer a different title). Along with our resident Astrophysicist - JQ - I am sure we will have discovered the plausible limits of our propulsion system and fuel supply in no time. I am open to all suggestions for how our main engine and fuel tank should best be configured, and I will concede that the Prophesy is probably more of an RV than a Ferrari. So the lower extended thrust is probably appropriate. Although I will reserve the right to keep the potential of 1G accelleration for emergencies (at the cost of fuel economy).

So...

Suggestion: Our tank is filled with spent nuclear fuel that is a single step from being turned back into enriched uranium. This way the whole tank can be filled with the stuff, but in a fairly stable way. As the fuel is brought to the engine it is enriched in line before passing into the engine.
Question: Is that plausible? (By the way, one way we are financing this whole affair is by having the govenrment pay us to dispose of the nuclear waste that we are using as fuel)

Originally Posted by Jay-qu

Resident Astrophysicist at you service
I would first need to know the presise composition of the fuel to do the calculations, sir.

Consider the fuel to be the most energetic enriched uranium. What is the highest amount of energy that we can expect from a ml of that stuff, and what percentage of that energy can ce convert into motive power of the ship? The higher we can get these number the better off we are.

And in answer to your question Janus, The sections are straight. There will be a weird effect near the ends as the gravity will be a bit angular. But we will get used to it. I have them straight because a banana doesn't fly straight. These are assembled on the ground and lauched as completed units. It will add character to the experience. Ever been to "the mystery spot"?

(t-27)

Bill

[Pyrotex]

Originally Posted by TheBigDog

...Consider the fuel to be the most energetic enriched uranium. What is the highest amount of energy that we can expect from a ml of that stuff, and what percentage of that energy can ce convert into motive power of the ship?...

The Hiroshima bomb converted 1 gm of matter into energy (~10 kiloton); the total mass of U235 (the hot stuff) was around 20 kilograms. So, efficiency was 1/20,000 -- very approx.

That was a critical mass bomb. The Nagasaki bomb was a tamper & implosion squeeze bomb. Efficiency was considerably higher (I don't know). Let's say, around 1/10,000. Not bad. If we can convert 0.01% of our nuclear waste into energy, then:

Every metric tonne of waste will convert 100 gm into energy: equivalent to 1 megaton explosive power. Check my E=mc^2 math, but I think that is 10^11 Joule of energy.

If that is released over 10^5 seconds, then we get 1 megawatt of power (Joules/sec) That's about 30 hours at 1 megawatt propulsion power.

Assume the total ship is 10^6 tons. That power will accelerate it at 1 m/s/s.
Now, G (on Earth) is about 10 m/s/s. So we got 1/10 G for 30 hours.

that acceleration will give us a final velocity (burning 1 tonne of nukwaste)
of: 10^5 m/sec. Or 100 kilometers per second. That is 61 miles/sec.

That is 219,000 MPH. that is nearly ten times Earth's escape velocity and seven times faster than the fastest probe we have ever launched.

And this is, in non-metric units, "hauling ass". And all from burning just one metric tonne of waste over a period of 30 hours. Any complaints????? Please, somebody check the math just in case I missed a decimal point.