StarDestroyer.Net BBS

Since I'm snowed in and can't go to work today, I'm taking the this time to get caught up on some stuff, including my old calcs. One of the things I'm doing is figuring total fuel load for various ships. This requires I know what the typical crusing speed is. Now the Mandal diagrams say .4 C for an ISD. I remember a discussion on this, but not the outcome, is that a valid source making that a god number?

Its official by the rules outlined by Sue Rostini. Its a sanctioned source, and it isn't contradicted by higher canon. That is, it was made within the copyright laws of LFL, and is part of SW.

Whether you can use the Mandal blueprints to make any decisions about ISDs is another matter entirely, since the name contradicts canon, and even disregarding that (which makes it a different ship) all the other stats are wrong for the ISD.

Keep in mind upper limits of 10^6 Gs for ISDs from Marvel.

Well assuming that the 40% of C cruising speed is correct, and the ejecta flies out at 99% of C, that means proportionally 2/3rds of an ISDs mass is fuel for its engines.

Which also mens it only gets ~ 9 hours & 45 minutes of acceleration time before it has to refuel. Which doesn't work. Perhaps it uses complex mass for ejecta, so that it can "m-load" it at the last minute and get the benefit of alot of fuel without all the mass.

Shit.

If we up the ejecta velocity to higher and higher fractions of C, can't we get almost arbitrarily powerful engines even from a small amount of mass?

Howedar wrote:If we up the ejecta velocity to higher and higher fractions of C, can't we get almost arbitrarily powerful engines even from a small amount of mass?

Doing so for a given mass also alters acceleration. which we already know from the movies. you can fudge it a little, but there is still a limit to it. For example. ejecting it at 99.9 % of C jumps it to ~12000 Gs, which contradicts the "thousnads of Gs" statement from ICS.

Course my calcs contradict ICS ina dozen other spaces, so I'm not sure why I care.

I do not understand. Could there not be half the mass that is ejected faster, so that the thrust is equal?

The Acclamator's reactants are denser than the bulk (eg mass) of the ship by "many orders of magnitude"

Newtonian rocketry equations do not apply under relativistic conditions.

Durandal wrote:Newtonian rocketry equations do not apply under relativistic conditions.

Who're you addressing there?

Connor MacLeod wrote:The Acclamator's reactants are denser than the bulk (eg mass) of the ship by "many orders of magnitude"

Does this suggest, as I am collecting, that the (mass of ship) - (mass of fuel) / (mass of ship) = 1/101 or less? That the fuel isn't 2/3s but 100/101s or more? Where the mass of the ship without the fuel is a hundredth or thousandth or less of that of the fuel?

More or less. I dont know what else "bulk" would refer to. This isnt surprising given that as long ago speculated, the Death Star would require superdense fuel supplies to function as it does (The energy for a single blast of the DS's superlaser requires, assuming 100% efficiency, around 3.8x1021 kg of fuel - especially without noticiably massive fuel bottles! Assuming a completely solid 160 km diameter ball of Uranium-dense material, you're talking around 4e19 kg total - clearly insufficient for the needs of the DS by about 2 orders of magnitude.)

I do suspect its only 100 times (for capital ships at least). 1000 times might be a bit too much except for much larger starships (like the Executor or Eclipse classes, perhaps.) Starfighters no doubt have a much lower "ratio" as well (probably not more than an order of magnitude, I'd bet.)

Durandal wrote:Newtonian rocketry equations do not apply under relativistic conditions.

Good thing I'm using a formula that the explanation showed applied for relativistic rockets then.

Connor MacLeod wrote:The Acclamator's reactants are denser than the bulk (eg mass) of the ship by "many orders of magnitude"

Which still fits, 2/3rds of the ships total mass in a few sphers maybe 100 meters acros is certainly going to be denser by many orders of magnitude.

Howedar wrote:I do not understand. Could there not be half the mass that is ejected faster, so that the thrust is equal?

I don't understand what you are saying here.

Ender wrote:

Durandal wrote:Newtonian rocketry equations do not apply under relativistic conditions.

Good thing I'm using a formula that the explanation showed applied for relativistic rockets then.

Which one?

Ender wrote:

Howedar wrote:I do not understand. Could there not be half the mass that is ejected faster, so that the thrust is equal?

I don't understand what you are saying here.

You are taking a given acceleration for an ISD, and it's max speed, then using that to find the mass of fuel needed to get to top speed. However, this is based on an effective exhaust velocity that you seem to have arbitrarily chosen. If we are willing to accept an exhaust velocity of, say, 99.99999c, the mass of propellant (when at rest) should be vastly less.

Howedar wrote:

Ender wrote:

Howedar wrote:I do not understand. Could there not be half the mass that is ejected faster, so that the thrust is equal?

I don't understand what you are saying here.

You are taking a given acceleration for an ISD, and it's max speed, then using that to find the mass of fuel needed to get to top speed. However, this is based on an effective exhaust velocity that you seem to have arbitrarily chosen. If we are willing to accept an exhaust velocity of, say, 99.99999c, the mass of propellant (when at rest) should be vastly less.

Then you're just needing more energy to accelerate, which must come from the ship and because of E = MC^2, it ends up carrying it anyway (unless one evokes hypermatter and says that the "imaginary" mass portion doesn't contribute to mass as we understand it in the ship's acceleration).

I thought we were doing that already, and considering "fuel" to just be reaction mass.

Ender wrote:Which still fits, 2/3rds of the ships total mass in a few sphers maybe 100 meters acros is certainly going to be denser by many orders of magnitude.

However it wouldn't be true.
I remember discussing this with Saxton, the fuel masses more than the ship itself.

Howedar wrote:

Ender wrote:

Howedar wrote:I do not understand. Could there not be half the mass that is ejected faster, so that the thrust is equal?

I don't understand what you are saying here.

You are taking a given acceleration for an ISD, and it's max speed, then using that to find the mass of fuel needed to get to top speed. However, this is based on an effective exhaust velocity that you seem to have arbitrarily chosen. If we are willing to accept an exhaust velocity of, say, 99.99999c, the mass of propellant (when at rest) should be vastly less.

As the ejecta velocity increases linearly, its kinetic energy increases exponentially. In other words, it takes a lot more energy.

His Divine Shadow wrote:

Ender wrote:Which still fits, 2/3rds of the ships total mass in a few sphers maybe 100 meters acros is certainly going to be denser by many orders of magnitude.

However it wouldn't be true.
I remember discussing this with Saxton, the fuel masses more than the ship itself.

Your math is lacking.

If X is equal to the total mass of the ship, and 2/3X is the mass of the fuel and 1/3X is the mass of the ship alone, then since 2 > 1 my position is still true.


Otherwise you are claiming that A > A+ B when both A and B are positive numbers.

Durandal wrote:

Ender wrote:

Durandal wrote:Newtonian rocketry equations do not apply under relativistic conditions.

Good thing I'm using a formula that the explanation showed applied for relativistic rockets then.

Which one?

http://www.ebtx.com/mars/rocketeq.htm

The part under "Lets Make Calculations" says it is valid for finding fuel:mass ratios.

Ender wrote:Otherwise you are claiming that A > A+ B when both A and B are positive numbers.

As long as the fuel masses more than the ship it's fine by me.
Say the ships structure masses 1 million tons and the fuel masses 49 million tons.

His Divine Shadow wrote:

Ender wrote:Otherwise you are claiming that A > A+ B when both A and B are positive numbers.

As long as the fuel masses more than the ship it's fine by me.
Say the ships structure masses 1 million tons and the fuel masses 49 million tons.

Something like that, yes.