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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.
