Re: Gurps traveller refuelling question

On 27 Mar 2006 07:08:50 -0800, "Cray74@xxxxxxxxx" <Cray74@xxxxxxxxx>
wrote:

The Sophist wrote:
Are you sure? I recall doing some math on this at one point, and while
of course the energy output of a fusion reaction is immense, I recall
the amount of energy needed for such extended periods of multi-g
acceleration was also pretty immense.

Alright...

Assuming 100% of all fusion rocket energy goes into thrust (chemical
rockets get into the high 90s, so it's a reasonable rounding option),
each pound of thrust of a high-efficiency rocket engine (specific
impulse 1 million) requires 24 megajoules of energy per second.

At an Isp of 1 million, reaction mass consumption is 1 millionth of a
pound per second per pound of thrust (1E-6 pounds/second/pound-thrust).

On the other hand, each pound (mass) of fuel converted to energy in a
fusion engine (~1% efficiency) will release 4.08E14 joules. If the
rocket is about 100% efficient at getting released energy into thrust
(like chemical rockets), then to meet the 24 megajoule/second energy
demand per pound of thrust, you'll need 5.88E-8 pounds of fuel per
second.

In other words, reaction mass consumption is 17 times higher than fuel
consumption for a fusion engine with a specific impulse of 1,000,000.
You'll run out of reaction mass before you run out of fuel.

Still, running a few rocket equations for the amount of reaction mass
needed to actually "tool around at multiples of 1g for months," it does
seem like ridiculous ratios of reaction mass to dry weight are needed.
Though that's not actually what's happening in Traveller hyperdrives,
is it?

Mike Miller

mike this is nice and all but traveller ships use a reactionless drive
starting at tl 9 or so. they aren't throwing mass away to make the
ship go which leaves fusing it pretty much as the explanation for
where the h2 goes.
.

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