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Old 04-10-2013, 02:35 PM   #471
Marasmusine
 
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Default Re: GURPS Spaceships Design Spreadsheet

Thanks for the quick reply. Yes, I twigged what was happening with delta-v after my first post... 2 engines, 1 fuel tank doesn't mean that each engine gets "half a tank" each, therefore half the dV :) I sat and visualized in my head what was happening, then saw that although the ship accelerates faster and uses up fuel faster, the total change in velocity of course stays the same. My initial confusion came from misreading the rules - the engine entries say "each fuel tank of hydrogen gives a delta-v of X" and I thought that meant "per engine". If I had seen the example under Fuel Tanks first ("a spacecraft that is using any number of TL9 nuclear thermal rocket engines..." that would have helped.

The setting I have will have the possibility of the player having to put together a spacecraft from whatever scrap or second-hand parts are available. They might want a higher G by adding another engine, but are forced to mix different hydrogen-reacting engines together. Why pick another engine over an extra fuel tank? Am I right in saying that this would be better for travelling a shorter distance faster? Sorry if that's a bit off-topic since it's not specifically about the spreadsheet.
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Old 04-10-2013, 02:58 PM   #472
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Default Re: GURPS Spaceships Design Spreadsheet

Quote:
Originally Posted by Marasmusine View Post
Why pick another engine over an extra fuel tank? Am I right in saying that this would be better for travelling a shorter distance faster?
Not really. A higher acceleration means that, well, you can accelerate faster. The delta-V is still a measure of the fastest speed the engine can attain. If one engine has 0.5G acceleration and a delta-V of 0.45 and another has 0.05G acceleration and a delta-V of 0.8 the second engine can accelerate to 0.8 mps - 0.8 miles per second - which is (obviously) faster than the 0.45 mps the first engine is capable of attaining.

The difference is that the first engine has a higher acceleration, meaning it can accelerate to 0.45 mps in less time than the second engine can, but at that point it's out of fuel. The second engine may take longer to reach 0.45 mps, but it still has considerable fuel reserves and can continue accelerating to reach it's maximum speed of 0.8 mps.

Also keep in mind that delta-V is a measure of change in velocity, not just top speed. If you're going somewhere like another planet you normally have to accelerate to start going there, coast for a long while, then decelerate to stop at your destination. This means that you will usually use ~1/2 of your delta-V to accelerate and the other ~1/2 to decelerate, and spend most of your journey in between coasting. Since you're spending most of your time coasting the engine with the higher delta-V, not the higher acceleration, is far more efficient for the journey. For instance, to go from Earth to Mars at their closest pass is still 49,000,000 miles. Even at 0.8 miles per second that's going to take a considerable amount of time (~700 days), almost all of it spent coasting with the engines off. Even Earth to the Moon is ~239,000 miles, which is 3.45 days at 0.8 mps. Most engines have only a few minutes of fuel, however the really efficient ones might have a few weeks worth of fuel.

Higher acceleration only becomes more efficient when you have to escape from a gravity well - take off from a planet - because if you don't have enough acceleration you simply cannot take off from the planet. Higher acceleration is also useful in combat - efficiency be damned, the important thing here is that you can either catch up to or run away from your enemy in the shortest amount of time.
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Last edited by ericbsmith; 04-10-2013 at 03:24 PM.
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Old 04-10-2013, 03:24 PM   #473
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Default Re: GURPS Spaceships Design Spreadsheet

Quote:
Originally Posted by Marasmusine View Post
Am I right in saying that this would be better for travelling a shorter distance faster?
Yes under specialized conditions; basically, if you can't burn all your fuel in your flight time, more drive modules will help. It is rare for multiple drive modules to be valuable for non-atmospheric craft, however.
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Old 04-10-2013, 04:06 PM   #474
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Default Re: GURPS Spaceships Design Spreadsheet

Eric, thanks for your help, you are an excellent human. I promise this is my last dumb observation :) My initial thought about higher G being better for shorter distances I see is only relevant if there's little or no coasting time, but it looks like I really overestimated how much burn-time even TL 9 engines can get!

I've just played with the formula for "continuous acceleration with reaction drives", For a short distance, say 0.001 AU with NLB:
At 0.05G, the ship would need 10 dV (thats 13 hydrogen fuel tanks!) getting there in 9 hours
Adding another engine, 0.1G, increases the dV to 14.82 (19 fuel tanks) at 7 hours.
It needs less tanks than this once you factor in the bonus for having more than 6 tanks, but still.
With a fusion rocket, 1 engine (0.005 G), only needs 3.3 dV (less than 1 tank), taking 30 hours.
Adding another fusion rocket, it still only needs 1 tank, journey drops to 21 hours.
So for these very short journeys - moving between moons or perhaps asteroids - turning on another engine can help (unless I've messed up the calculation) - but for anything interplanetary you stick to one engine!
For my earlier example craft with 1 NLB and 1 NTR (again, because that's all that might be available), the default would be to only run the NLB for travel, and the player has the option of turning on the NTR for combat.
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Old 04-10-2013, 04:36 PM   #475
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Default Re: GURPS Spaceships Design Spreadsheet

Overall your numbers sound about right, though I'm not doing any of the math to check them.
Quote:
Originally Posted by Marasmusine View Post
So for these very short journeys - moving between moons or perhaps asteroids - turning on another engine can help (unless I've messed up the calculation) - but for anything interplanetary you stick to one engine!
Don't forget to take into account the cost of the fuel. Hydrogen is a cheap fuel, but even then burning up an entire fuel tank can cost thousands of dollars. Outside of combat it still may be worth it to take the extra day of travel time over burning the extra fuel (of course, being PCs, you probably have them chasing criminals or saving the galaxy or some such, where time is of the essence - in which case putting them over a barrel to refill their fuel tank at the end of the adventure is just another plot hook to use :-)
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Last edited by ericbsmith; 04-11-2013 at 02:40 AM.
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Old 04-14-2013, 09:15 PM   #476
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Default Re: GURPS Spaceships Design Spreadsheet

Version 2.0 Release Candidate 5

-Crush Depth is now displayed in Atmospheres of pressure, with a secondary display of feet of water on Earth

-Fixed some issues with effective SM, specifically dealing with the Armor and Volume rules from Pyramid 3/34
-Fixed issue with setting custom Ship Length in OpenOffice
-Fixed compatibility issue with OpenOffice v3.2 Portable
-Many other minor bug fixes.

Excel 2000
http://gurpsland.no-ip.org/zip/SpaceshipsV2.zip (2.08MB)
http://gurpsland.no-ip.org/zip/SpaceshipsV2.7z (903KB)

Excel 2007
http://gurpsland.no-ip.org/zip/SpaceshipsV2-2007.zip (2.74MB)
http://gurpsland.no-ip.org/zip/SpaceshipsV2-2007.7z (2.64MB)

OpenOffice 3.2.0/3.3.0/LiberOffice 4
http://gurpsland.no-ip.org/zip/SpaceshipsV2-Ooo.zip (2.00MB)
http://gurpsland.no-ip.org/zip/SpaceshipsV2-Ooo.7z (1.75MB)
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Old 04-14-2013, 09:19 PM   #477
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Default Re: GURPS Spaceships Design Spreadsheet

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Originally Posted by ericbsmith View Post
Version 2.0 Release Candidate 5
Great to see you're still updating this!
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Old 05-06-2013, 10:27 PM   #478
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Default Re: GURPS Spaceships Design Spreadsheet

I've been banging away on this for the last three weeks and it's reached a point I feel pretty good about releasing it. This release represents some pretty significant changes to the sheet, especially to the Weapon Systems section, but also throughout the sheet so there's a lot of possibilities for bugs to have crept in.

Version 2.0 Release Candidate 6
  • Added Ship Classification and Size section to the Design Switches and Features section
  • Added Control Room Crew Breakdown section to the Design Switches and Features section
  • Added Auxiliary Craft section to the Spacecraft Design Table section
  • The De-rated Power Plant options has now been folded into Options 1. If you import a ship in Excel using the Macros it will automatically be converted to the new format.
  • Rework of the Quantity field used throughout the spreadsheet (in Open Spaces, Habitats, Weapons, as well as the new Auxiliary Craft and Crew Breakdown sections). The Quantity in the drop-down menu will now show you the maximum number of systems that you may install, and the field will remain grey while there are systems installable, but will turn white when you can no longer install more items in that location.
  • Added an alternate Troop Strength calculation (see below)
  • Complete rewrite of the back-end code for Weapon Mounts.
  • Error code (cells turning black) within the Weapons section is much smarter, giving you a better idea of what has caused the error.
  • Weapon Batteries are now assigned to specific Mounts instead of being assigned generally to Front, Center, or Rear. If you import a ship in Excel using the Macros the sheet cannot guess at where the weapons should be assigned, so it will assign all of them to section [0]. You will need to manually reassign them to the correct location.
  • Addition of seven new Weapon Battery sizes (see below(
  • Peripheral Weapon Mounts changed to SM+15 (they became redundant with the new mounts)
  • New system: Weapon Battery - Mixed Mount
  • In Excel, made the Load Ship and Delete Ship Macro a little smarter; if you select a cell containing a valid ship name it will automatically be selected in the Load or Delete dialog (this can be useful to load an Auxiliary Craft, for instance). Similarly the Save Ship dialog will now remember which Save Sheet the ship was loaded from and offer to save it back to there by default.
  • Numerous bug fixes and improved functionality

Weapon Batteries and Weapon Systems
  • Complete rewrite of the back-end code for Weapon Mounts. This became necessary to accommodate all the other changes and additions that were made, and may lead to some bugs.
  • Addition of seven new Weapon Battery sizes:
    • Quaternary (SM+8 & 100 Mounts)
    • Quinary (SM+9 & 300 Mounts)
    • Senary (SM+10 & 1,000 Mounts)
    • Septenary (SM+11 & 3,000 Mounts)
    • Octonary (SM+12 & 10,000 Mounts)
    • Nonary (SM+13 & 30,000 Mounts)
    • Denary (SM+14 & 100,000 Mounts)
  • Weapon Batteries are now assigned to specific Mounts instead of being assigned generally to Front, Center, or Rear. This allows for tracking of the number of mounts left in a specific Weapon Battery system.
  • Peripheral Weapon Mounts changed to SM+15 (they became redundant at SM+8 to +14 with the new mounts)
  • New system: Weapon Battery - Mixed Mount. This is a build-your-own Mixed Weapon Battery. It acts similarly to Smaller SM Systems, in that you can install three sub-systems. Each sub-system can consist of either one block of the same sized mount or two separate mount sizes. Each pair of mounts has a default number of mounts, however in the System Options section under Options 3 you can specify the number of mounts that the first weapon in the pair will have, which will adjust the number of mounts in the second of the pair accordingly. With this you can create virtually any combination of two to six different sizes of Weapon Mount.


Ship Classification and Size
These entries allow you to specify a Ship Class, Size, Mission Description, and Type. None of these fields are mandatory, but they can allow you to specify information about the Ship's Class while keeping a different name for the Ship itself. e.g. you can specify a Constitution-Class Heavy Exploration Cruiser while naming the ship itself the U.S.S. Enterprise.
  • Class Name can be text, however -Class will be appended to whatever you enter here.
  • Size specifies a general class size, e.g. Heavy, Medium, or Light.
  • Description is a descriptive word about the ship's intended Mission role, such as Exploration, Mining, etc.
  • Type specifies the general type of ship, such as Destroyer, Cruiser, Starbase, etc.
Note: Several of these fields use drop-down menus. While other menus in this spreadsheet limit what you may enter in the box, these menus are different. In addition to the examples given in the menu you may also enter any text you wish - so be creative in describing them.


Control Room Crew Breakdown
This section allows you to specify the roles that the Control Room personnel will fulfill.
Note: These fields use drop-down menus. While other menus in this spreadsheet limit what you may enter in the box, these menus are different. In addition to the examples given in the menu you may also enter any text you wish - so be creative in describing the positions.

Auxiliary Craft
Allows you to specify the Auxiliary Craft that will fill a Hangar Bay, Upper Stage, or Vehicle Dock. You can select any Craft from the Saved Ships or Official Ships spreadsheets. In the OpenOffice version of the sheet there is a new WorkSheet called Auxiliary Craft where you can manually enter the basic details of a Ship so that it will be assignable through the menus.

Alternate Troop Strength
In the Mass Combat rules from Pyramid 3/30: Spaceships for calculating Troop Strength there is a significant bias towards smaller Spaceships. The base multiplier for TS is dDR + dST/dHP, but these values scale roughly with ship length, not with increasing size/mass/firepower. It gives larger ships a significantly lower TS and than smaller craft. As one example the two TL 12^ spaceships the Mirage Star Fighter (SM+4) has a calculated TS of 257,400 while the Intrepid-Class Frontier Cruiser (SM+12) has a TS of 2,640,000 - just over x10 the TS for a ship massing x10,000 times as much. This may be appropriate for a strictly realistic game (where a million dollar missile can easily take out a billion dollar naval ship) but it does not fit the expectation in most Sci-Fi universes.
To help correct this discrepancy the Alternate Troop Strength option multiplies the final TS by dHP/150, effectively scaling TS with ship surface area (rather than length). This has the effect giving the SM+4 ship a TS 1/10th the current while multiplying a SM+12's TS by 2, so now in the above example the TS of the two ships are 25,740 and 5,280,000 - a difference of about x200 the TS.
Code:
	SM:	+4	+5		+6		+7		+8		+9		+10		+11		+12		+13		+14		+15	
TS Multiplier:	x0.1	x0.1333		x0.2		x0.3333		x0.4667		x0.6667		x1		x1.3333		x2		x3.3333		x4.6667		x6.6667
Excel 2000
http://gurpsland.no-ip.org/zip/SpaceshipsV2.zip (2.67MB)
http://gurpsland.no-ip.org/zip/SpaceshipsV2.7z (1.20MB)

Excel 2007
http://gurpsland.no-ip.org/zip/SpaceshipsV2-2007.zip (3.42MB)
http://gurpsland.no-ip.org/zip/SpaceshipsV2-2007.7z (3.30MB)

OpenOffice 3.2.0/3.3.0/LiberOffice 4
http://gurpsland.no-ip.org/zip/SpaceshipsV2-Ooo.zip (2.10MB)
http://gurpsland.no-ip.org/zip/SpaceshipsV2-Ooo.7z (2.51MB)
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Last edited by ericbsmith; 05-07-2013 at 12:06 PM.
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Old 05-06-2013, 10:37 PM   #479
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Default Re: GURPS Spaceships Design Spreadsheet

Excel 2007 links don't seem to work.
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Old 05-06-2013, 10:50 PM   #480
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Default Re: GURPS Spaceships Design Spreadsheet

EDIT: Corrected the issue, the links should now work fine.
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Last edited by ericbsmith; 05-06-2013 at 11:46 PM.
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