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  #1  
Old September 3rd, 2010, 11:14 AM
Traveller_without_a_home Traveller_without_a_home is offline
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Default HEPlaR maneuver drive design, fuel and travel times...

Greetings one and all!

Iím currently running through TNE ship design for a new game Iíve recently started. Somebody kindly sent me a spreadsheet before, but I thought Iíd give it a go by hand also, to see if my figures match up with those generated through the sheet.

Iím having a little difficulty in getting the rules for HEPlaR maneuver drives to work, specifically in relation to how G-Turns, G-Hours, and how to calculate fuel requirements etc...

Maybe Iím just being a bit think, but I was wondering if anyone would be so kind as to just provide a few examples so I can get my head around it all!!!

And whilst Iím at it, does anyone have any variant of equations of motion that can be used with the Light Second in system travel as presented in TNE? It makes more sense for a space faring culture to use LS rather than km, but Iíd like a little more realism in determining travel times than just minutes per LS; what about time taken to accelerate and decelerate, and the coasting time in between?

Thanks for your help everyone, much appreciated!!!
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Old September 3rd, 2010, 11:42 AM
BraselC5048 BraselC5048 is offline
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First off, I certently want to help, but I'm not fermilar with the system myself. After reading it, it seems to me that it's a pretty clunky system. I'd recomend scapping the interplanatary travel times system, and using a different method.
This equation should caculate the travel times, although you'll need a caculator.
It works for cases when the ship accelerates, coasts, then decelerates.

T = ((D - (A * t^2)) / (A * t)) + (2*t)

where
T = transit time (seconds)
D = distance (meters)
A = acceleration (m/s2)
t = duration of acceleration phase (seconds), just the acceleration phase only, NOT the acceleration+deceleration phase.
Note that the coast duration time is of course = T - (2*t)
( the symbol * means multipcation)

Some conversions are nessicary. Take the distance in light-seconds from the table (p. 226-227), and multiply it by 300,000,000 for distance in meters.
Each G-hour is 10 m/s2 for 3600 seconds. The t in the equation is for the acceleration alone, so you'll need to have enough fuel for twice t if you want to stop at your destanation.

For very shot trips, without coasting, the equation is

T = 2 * sqrt[ D/A ]

where
T = transit time (seconds)
D = distance (meters)
A = acceleration (m/s2)

Note the the total travel time can't exceed the the amount of time the ship can mantain the acceleration used for that particular trip, since the ship is constantly using its maneuver drive.
If you want examples of how to use the system as written, could somebody else help with that?
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Old September 3rd, 2010, 01:58 PM
Traveller_without_a_home Traveller_without_a_home is offline
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Hi again!

Thanks very much for these equations! I shall save them for posterity, they should be very useful!

BTW, Iíve had another bash at the rules for designing HEPlaR drives, and working out fuel/G-Turn issues... I think Iíve got it sorted out now, but I donít think it was explained very well in the RAW; a few examples should have been included for the mathematically challenged!!!

Thanks again. I may post my ship design on here when Iím finished with it!
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Old September 3rd, 2010, 02:26 PM
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This is great timing, thanks. I had asked a similar question over on the Mongoose forums regarding computing travel times using Mongoose Traveller "reaction drives".

MGT reaction drives have statistics such as "4G with 2 hours of fuel", or "1G with 4 hours of fuel" etc. MGT travel tables are similar to CT (ex: 4G takes 106 minutes from typical surface to moon). These are based upon constant acceleration. Reaction drives in MGT would quickly run out of fuel when attempting interplanetary travel, so couldn't use constant accelaration to midpoint then de-acceleration after turn around.

It seems your equation is exactly what I was looking for! Something to compute travel times with coasting in the middle, a.i. a 4G craft with 2 hours of fuel could accelerate for 1 hour, coast at whatever speed obtained, then de-accelerate for 1 hour at the end of the trip.

Question. A = Acceleration m/s2. So 1 G = 10m/s2, 4G = 40m/s2, etc?
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Last edited by Sturn; September 3rd, 2010 at 02:32 PM..
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Old September 3rd, 2010, 07:50 PM
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Quote:
Originally Posted by BraselC5048 View Post
T = ((D - (A * t^2)) / (A * t)) + (2*t)

T = transit time (seconds)
D = distance (meters)
A = acceleration (m/s2)
t = duration of acceleration phase (seconds)
If the equation above is correct, I made a simple spreadsheet that allows entering distance in kilometers, G-rating of craft, and hours of fuel burnt to give trip times.

Reaction Drive Trip Times

I may work on it later to look a little fancier and output tables for various drive ratings and burn times.

I made it with OpenOffice, but converted to Excel, tell me if something doesn't work right. It's non-glamorous, just type in the values (calculations hidden on sheet 2).

The calculations may fail if you enter a burn time that is less then the total trip time. A.i. you decide to burn 2 hours of fuel, but your trip would only take 1 hour anyway - you can constantly accelerate no need to coast.
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Old September 4th, 2010, 05:06 AM
Traveller_without_a_home Traveller_without_a_home is offline
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Thanks Sturn, that's brilliant!!!
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Old September 4th, 2010, 01:31 PM
BraselC5048 BraselC5048 is offline
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The equations weren't mine, I got them from the Atomic Rockets site. Glad I could help.
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