StarDestroyer.Net BBS

Inspired by a certain threat at TFN i did a small calculation:

If an ISD spents 300,000 tons of fuel per second at maximum output, this output will be 2.7E25 Watt.

Using the formula:

W = 1/2m*V*V with W= 2.7E25 Watt, m the mass and V the velocity of 30 Km/sec (based on an acceleration of 3,000G)

i get a mass for the ISD (ship and fuel) of 6.0E16 kg.

If an ISD has a volume of 80,000,000 cubic-meters and fourty percent of this volume is solid matter at the density of uranium we get a weight for the ship of 6.096E11 kg.

By this we would get a mass for the fuel of ~ 5.99E13 tons of fuel.

Using a fuel-consumation of 300,000 tons per second as maximum output the fuel would last for 2,315 days or close to six years (coincidentally this fits with the consumables for six years for an ISD according to WEG).


I don't know why, but i think i somewhere made a mistake (either in the calculation or the assumptions i based this on).

FTeik wrote:Inspired by a certain threat at TFN i did a small calculation:

If an ISD spents 300,000 tons of fuel per second at maximum output, this output will be 2.7E25 Watt.

280,000 really, for a 2.57*10^25 watts output.

Using the formula:

W = 1/2m*V*V with W= 2.7E25 Watt, m the mass and V the velocity of 30 Km/sec (based on an acceleration of 3,000G)

Incorrect formula. You need to do a relativistic correction for the ejecta mass moving at near C velocities. m = (((p/v^2)/((1-(v^2/c^2))^0.5))*v)/a
where p is power, m is mass, v is specific impulse in m/s, a is accel in m/s^2, and c is lightspeed.
Or you can do a back of the envelope one using C, where m = p/(c*a), but that is less accurate and lower number.

i get a mass for the ISD (ship and fuel) of 6.0E16 kg.

2.05*10^13 for the first, 2.91*10^12 for the second

If an ISD has a volume of 80,000,000 cubic-meters and fourty percent of this volume is solid matter at the density of uranium we get a weight for the ship of 6.096E11 kg.

Odd assumptions. Whats the basis behind them?

By this we would get a mass for the fuel of ~ 5.99E13 tons of fuel.

Using a fuel-consumation of 300,000 tons per second as maximum output the fuel would last for 2,315 days or close to six years (coincidentally this fits with the consumables for six years for an ISD according to WEG).


I don't know why, but i think i somewhere made a mistake (either in the calculation or the assumptions i based this on).

Yes.

Sigh.

Somehow i knew it. When things get relativistic i'm lost.

FTeik wrote:Sigh.

Somehow i knew it. When things get relativistic i'm lost.

You do know Mike has a quicky tutorial on the main site, right?

Ender wrote:

FTeik wrote:Sigh.

Somehow i knew it. When things get relativistic i'm lost.

You do know Mike has a quicky tutorial on the main site, right?

You mean his "General Science" on his science-page?

Yes, i do.

I saw no problem with the formula for the acceleration, because i assumed the ISD to start at zero - nothing relativistic there or so i thought. The part about the ejection-mass at lightspeed i hadn't considered.

Keep in mind that normal power output is most likely a miniscule fraction of peak power output. An ISD with its hyperdrive system would be a good example of a "bursty" power usage profile.