Science Forums 2

[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