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10-03-2017, 09:16 PM   #7
Ulzgoroth

Join Date: Jul 2008
Re: [Spaceships] simply fuel math...

While the initial question is well answered, I'd add a thought - the smaller engine will take 100 times as long to burn through the reaction mass...but since it's producing 1/100 times as much acceleration, naturally the delta-V comes out the same.
Quote:
 Originally Posted by hal Ok, piggy backing on this thread... Suppose you decide to design a spaceship with the following in mind: You have a SM 9 ship. A single "reaction Engine" for this ship will produce 3G acceleration. However, using the Swapping out rule from page 5 of Transhuman Space ships... Suppose I decide to use one SM 8 rocket engine to produce 1G extra, allowing for a 4G acceleration? Further suppose that I use the other two modules for Fuel. Those two fuel will be 2/3rds of a fuel tank for a SM 9 ship. So what happens to the Delta-V increase (page 17 of the First GURPS SPACEBOOKS rules)? It states that if you have 6 to 8 tanks, multiply your delta-V by 1.2. If you have 9 to 12, multiply by 1.4 Now, if we have 2/3rds of a tank, we have 2/3rds of the delta-V that a normal SM9 tank would have. No question there. But what happens to the Delta-V multiplier when you're at the "threshold" level between the multiplier values? In other words... if you have 5 and 2/3rds of a tank, does this get the full 1.2 modifier? If you have 8 and 2/3rds of a tank, do you get the full 1.4 multiplier? How would you resolve that issue?
So (A) there's no actual reason to involve the smaller rocket in this, it has no bearing on the question.

(B) Assuming I was using the by-the-book delta-V rule rather than using the rocket equation to smooth it, I'd use it by the book - 5 and 2/3s is not 6 to 8, it is less than 6, so you don't get that multiplier. 8 and 2/3s is slightly more of a problem, but for consistency I'd put it with the lower group rather than the upper group.
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I don't know any 3e, so there is no chance that I am talking about 3e rules by accident.

Last edited by Ulzgoroth; 10-03-2017 at 09:21 PM.