10032017, 04:19 AM  #1 
Join Date: Feb 2006
Location: Not in your time zone:D

[Spaceships] simply fuel math...
RAW Super Fusion Torch, 50G 450mps but, if you allow use of an SM4 section to get only 0.5G, how far will that tank of fuel take you  45,000mps?
This is either one of those math things so simple you can't believe your own answer or it's Costello's rent arrears and I'm the landlord:/ I mean, I can't believe my own answer so, I need someone else to either say "Yup, it's really that simple." or swat me upside the head and show me the actual math that proves it's really all rocket science. TQ in antici...
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10032017, 04:23 AM  #2  
Join Date: Jun 2006

Re: [Spaceships] simply fuel math...
Quote:
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 MA Lloyd Last edited by malloyd; 10032017 at 04:27 AM. 

10032017, 05:31 AM  #3 
Join Date: Sep 2008
Location: near London, UK

Re: [Spaceships] simply fuel math...
Looked at from a different angle, adding more engines doesn't get you any less deltaV from the single fuel tank, so removing fractions of an engine shouldn't get you any more.
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10032017, 06:00 AM  #4 
Join Date: Aug 2004
Location: Binghamton, NY, USA. Near the river Styx in the 5th Circle.

Re: [Spaceships] simply fuel math...
DeltaV  the change in velocity  is a measure of engine efficiency and does not change with engine size (at least, not on the scale of engines mounted on spaceships). A larger engine uses fuel just as efficiently as a smaller engine does.
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Eric B. Smith GURPS Data File Coordinator GURPSLand The future keeps telling us what the past was about. You make the past mean different things by what you do with the time that comes after. 
10032017, 06:35 AM  #5 
Join Date: Feb 2006
Location: Not in your time zone:D

Re: [Spaceships] simply fuel math...
Thank you, all.
Brain off day. I think part of my scribbled notes were what if you "super" the rocket and scale from there and then I've wandered off into Lalaland:D
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"Sanity is a bourgeois meme." Exegeek PS sorry I'm a Parthian shootist: shiftwork + out of = not here when you are:/ 
10032017, 08:47 PM  #6 
Join Date: Aug 2004
Location: Buffalo, New York

Re: [Spaceships] simply fuel math...
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 DeltaV increase (page 17 of the First GURPS SPACEBOOKS rules)? It states that if you have 6 to 8 tanks, multiply your deltaV 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 deltaV that a normal SM9 tank would have. No question there. But what happens to the DeltaV 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? 
10032017, 09:16 PM  #7  
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 deltaV comes out the same.
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(B) Assuming I was using the bythebook deltaV 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; 10032017 at 09:21 PM. 

10032017, 10:54 PM  #8  
Join Date: Jan 2014

Re: [Spaceships] simply fuel math...
Quote:
Aside: The multipliers given in the book exist to approximate the rocket equation's effect on Delta V (i.e. higher proportion of propellant, higher delta V). However, they do seem to error on the low (but occasionally the high). For example, 19 tanks would have a multiplier of 3.15 according to my equations, but it gets a multiplier of three. On the other hand, 6 tanks should have a multiplier of 1.18 according to my equations, but it gets a multiplier of 1.2. 

10032017, 11:27 PM  #9  
Join Date: Jul 2008

Re: [Spaceships] simply fuel math...
Quote:
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I don't know any 3e, so there is no chance that I am talking about 3e rules by accident. 

10032017, 11:43 PM  #10  
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Join Date: Sep 2004
Location: Southeast NC

Re: [Spaceships] simply fuel math...
Quote:
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