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Old 03-18-2017, 05:32 PM   #861
ericbsmith
 
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Default Re: GURPS Spaceships Design Spreadsheet

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Some fuel usage issues:[*]The fuel usage duration calculation for reaction engines seems to assume constant thrust rather than constant acceleration. This means at engine burnout the actual acceleration = a × 20/(20 - number of tanks used up) where a = nominal acceleration. Fuel duration for constant acceleration = ΔV × K/a hours where K=0.045 for liftoff and 0.0455 for space. There should be an engine (or ship) option as to which is constant.
This is a direct result of the way that the rules calculate the amount of fuel for calculating delta-V; the rules essentially multiply the amount of fuel available based on the number of tanks installed; by extension, the duration is multiplied by the same factor. This results in the duration being calculated by the first method. The second method may be possible, but would take some work to do.

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[*]If the ship has more than one reaction engine that use the same fuel tanks, ΔV and duration for each engine is calculated using the entire fuel supply. Could you set up a "fuel profile" entry like the "power profile" entry that could assign a fixed amount of fuel to each engine's use?
It is true that duration and delta-V is calculated as if all appropriate fuel tanks are assigned to each engine (or the set of identical engines). Again, while it may be possible to set up a fuel profile, this would take a bit of work. The biggest issue here is that the number of tanks, and thus the delta-V tank multiplier, ends up needing to get calculated for each profile based on which tanks are assigned to which engines. That gets messy and complicated; not impossible, but messy and complicated.


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“who'd still like an answer to his question about collapsible tanks
I don't see why you couldn't pump fuel the from the collapsible tanks into main tanks while using the fuel from the main tanks. The main reason for the limitation is to prevent a ship from using only collapsible tanks, as the standard fuel tanks also include the pump machinery and fuel lines to the engines while the collapsible tanks are meant to be just the tank itself, set up in a cargo bay.
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Old 03-19-2017, 01:49 PM   #862
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Default Re: GURPS Spaceships Design Spreadsheet

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Originally Posted by ericbsmith View Post
This is a direct result of the way that the rules calculate the amount of fuel for calculating delta-V; the rules essentially multiply the amount of fuel available based on the number of tanks installed; by extension, the duration is multiplied by the same factor. This results in the duration being calculated by the first method. The second method may be possible, but would take some work to do.
I suppose it depends on whether you calculate ΔV before or after fuel endurance. This might require a ship or campaign option as to which calc is preferred.

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It is true that duration and delta-V is calculated as if all appropriate fuel tanks are assigned to each engine (or the set of identical engines). Again, while it may be possible to set up a fuel profile, this would take a bit of work. The biggest issue here is that the number of tanks, and thus the delta-V tank multiplier, ends up needing to get calculated for each profile based on which tanks are assigned to which engines. That gets messy and complicated; not impossible, but messy and complicated.
I didn't really expect this one, since it would require a significant structural change. I just wanted to put it on the wish list for future consideration during a major rewrite.

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I don't see why you couldn't pump fuel the from the collapsible tanks into main tanks while using the fuel from the main tanks. The main reason for the limitation is to prevent a ship from using only collapsible tanks, as the standard fuel tanks also include the pump machinery and fuel lines to the engines while the collapsible tanks are meant to be just the tank itself, set up in a cargo bay.
THANK YOU! My first Mars Trans-Orbital Taxi had two hard tanks (LH2 and CH4) for VASMIR and NTR(RR) drives, and 8 collapsible methane tanks in the middle and rear cargo holds for Mars launch. My rationale was the Earth/Mars trade imbalance during the early years: 165 tons imports vs. 45 tons exports. (Also, reducing the ship's effective mass by 45% on takeoff extends the LH2 tank's ΔV by 81%. ;) )

Dalton “now to figure out the 3e->4e fuel cost paradox” Spence
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Old 03-20-2017, 11:34 AM   #863
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Default Re: GURPS Spaceships Design Spreadsheet

More wish list stuff:
  1. Campaign options to define non-standard operating environments. Examples:
    1. Local gravity. Could affect liftoff and ground movement.
    2. Solar irradiance. Affects solar power systems.
    3. Atmosphere molecular weight* and temperature (°K). Affects gasbag lift. (See below.)
  2. A "hot air gasbag" system that uses 1PP to heat the gas inside and thus increase the lift. Option: List of lifting gasses used to inflate gasbag. Each has its own lift potential. Default to Earth air.
I'm considering a Martian Blimp design and discovered that the higher Mol. Wt. of the Martian atmosphere would increase gasbag lift by 53%. (Assuming H₂ is used; CH₄ would have about the same lift on Mars that H₂ does on Earth).

Dalton “*who really didn't know Mol. Wt. was measured in 'daltons' ;)” Spence
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Old 03-20-2017, 07:36 PM   #864
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Default Re: GURPS Spaceships Design Spreadsheet

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More wish list stuff:
  1. Campaign options to define non-standard operating environments. Examples:
    1. Local gravity. Could affect liftoff and ground movement.
    2. Solar irradiance. Affects solar power systems.
    3. Atmosphere molecular weight* and temperature (°K). Affects gasbag lift. (See below.)
  2. A "hot air gasbag" system that uses 1PP to heat the gas inside and thus increase the lift. Option: List of lifting gasses used to inflate gasbag. Each has its own lift potential. Default to Earth air.
There are no rules for 1a, 1c, and 2, nor am I sure where to start in making such rules. 1b doesn't actually have rules, but the Luminosity and inverse square of distance won't be hard to calculate so is something I may do something with.
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Old 03-20-2017, 07:40 PM   #865
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Default Re: GURPS Spaceships Design Spreadsheet

Version 2.0 Release Candidate 20
-If you delete a Ship System the sheet will now automatically delete all System Options associated with that system.
-If you select the Ship Orientation to be Building and then select a ship system to be Underground then all systems in Hull Sections below that system will also be set to Underground (that is, if you make one Front/Upper system Underground then all Center and Rear/Bottom systems will be set to Underground; if you select any Center system to be Underground then all Rear/Bottom systems will be set to Underground).

-Added two new buttons to the System Options section. Copy Options and Paste Options.
--When you select any cell within row in the System Options section and click Copy Options that system's options will be used when pasting; note that even if you change the options after you click Copy Options the sheet will use whatever options are most current.
--If you select a row and click Paste Options the sheet will:
---Check to see if the System names match; if so it will paste the Options into that system
---If the System name is blank it will paste the System name and all the Options into that row
--If you select a range of rows and click Paste Options the sheet will go through each row, as above, and paste the System Name and Options as appropriate.
---This will automatically skip Core systems if two Core systems are already installed.
---Multi-Row Pasting does not work on Sub-Systems (Smaller SM, Reconfigurable Systems, and Mixed Mount Weapon Batteries). You can still select one row at a time and Paste the System/Options into it.
---Pasting may allow you to paste Systems or Options into sections of the ship where they are disallowed. If so this will generally generate an appropriate error.

You can download the spreadsheet here:

Excel 2000 (RC20)
http://gurpsland.no-ip.org/zip/SpaceshipsV2.zip (5.1 MB)
http://gurpsland.no-ip.org/zip/SpaceshipsV2.7z (~2.5 MB)

Excel 2007 (RC20)
http://gurpsland.no-ip.org/zip/SpaceshipsV2-2007.zip (~6.3 MB)
http://gurpsland.no-ip.org/zip/SpaceshipsV2-2007.7z (~6.2 MB)

OpenOffice 3.3.0 (RC9)
http://gurpsland.no-ip.org/zip/SpaceshipsV2-Ooo.zip (~2.1 MB)
http://gurpsland.no-ip.org/zip/SpaceshipsV2-Ooo.7z (~1.9 MB)
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Last edited by ericbsmith; 03-22-2017 at 08:02 AM.
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Old 03-21-2017, 02:18 PM   #866
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Default Re: GURPS Spaceships Design Spreadsheet

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Originally Posted by ericbsmith View Post
There are no rules for 1a, 1c, and 2, nor am I sure where to start in making such rules. 1b doesn't actually have rules, but the Luminosity and inverse square of distance won't be hard to calculate so is something I may do something with.
Well, I've had some thoughts on gasbags, so you might want to reconsider 1c and 2. As to 1b, the calculation you are talking about requires two numbers rather than one, and I really wasn't talking about a complete planetary definition; just some external constants that would affect vehicle performance (now we are using the spreadsheet to design more than spaceships ;) ).

Dalton “still working on his Martian blimp” Spence
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Old 03-22-2017, 07:41 AM   #867
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Default Re: GURPS Spaceships Design Spreadsheet

So, it's been some time since I last checked here, so, I would like to know if it is possible to add the function to design "spaceships" SMALLER than SM+3, for use by smaller SM characters, or as unmanned drones?

I am sorry if someone has asked this already, or if it is already included on the latest versions.
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Old 03-27-2017, 10:51 AM   #868
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Default Re: GURPS Spaceships Design Spreadsheet

I just tried to add some "Steerage Cargo: Partial" to my SM+5 habitat slots with RC20, and it wasn't there. What's happening?

Dalton “working on his own 'Mars Mission' designs” Spence
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Old 03-27-2017, 01:55 PM   #869
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Default Re: GURPS Spaceships Design Spreadsheet

Could someone please tell me where the "Hydroponics Bay" habitat came from? I checked all the Spaceships books, the optional rules and all the connected Pyramid editions I have, and the few times the word 'hydroponics' came up was in indirect references. I even searched the forum for references, but I didn't see any Habitat definition. What is the source of the "4 person production,1 staff" per cabin formula? And why doesn't it reduce the demand for food (by subtracting the production from the life support requirements)?

Dalton “and shouldn't the same go for open spaces?” Spence

EDIT: And why could I add it to my ERV but not my Mars Lander?

Last edited by DaltonS; 03-27-2017 at 02:21 PM. Reason: Fustrated at weird internal filters!
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Old 03-27-2017, 10:06 PM   #870
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Default Re: GURPS Spaceships Design Spreadsheet

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I just tried to add some "Steerage Cargo: Partial" to my SM+5 habitat slots with RC20, and it wasn't there. What's happening?
Quote:
Originally Posted by DaltonS View Post
Could someone please tell me where the "Hydroponics Bay" habitat came from?

EDIT: And why could I add it to my ERV but not my Mars Lander?
Both are from my Unofficial Rules, and you need that option selected in the Campaign Options to use them.

I don't recall where I got the stats for the Hydroponics Bay from; I think I cribbed the basic stats from another book, or maybe based them on a similarly sized "Open Space." I don't honestly recall.
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