Burn Time Calculator

[pincushionman]

KSP BURN TIME CALCULATOR

Have you ever set up a really precise maneuver node, with a very aggressive burn, only for your stage to run out of fuel seconds before you need it to, leaving you stranded?

I have. It's frustrating.

This tool can help. Well, kind of. It can't fix a poorly-designed craft, but it can give you a quick idea of whether you can complete your maneuver on the fuel you have, or if you need to back off and re-think your maneuver.

DOWNLOAD LINK (current version 1.2)

This file is hosted by mediafire. The link will open a new window to "preview" the file, but it looks very bad and I don't know if it's "editable" or not when you do it. There should be a "download" button somewhere on the page for you.

Versions 1.0 through 1.2 were created in Microsoft Excel 365. I believe, however, it will be compatible for all versions of Excel 2007 or later. This file contains no macros or user-defined functions.

WHAT IT DOES

Give the tool the atmosphere condition, the number and types of engines on your current stage, and the tanks they have to draw from, and it will give you the number of seconds of burn you have left in the stage, to compare against the estimated burn time given to you in the maneuver editor:

If you're looking for more detailed information about your ship's performance (like the delta-v it carries), you'll need to look elsewhere for that. The maneuver editor obviously takes that into account, as do other tools like cybutek's Kerbal Engineer. Delta-v estimation is outside the scope of this tool.

ASSUMPTIONS USED

This tool uses the following assumptions:

• All engines in a stage are able to equally draw from the same "pool" of liquid fuel. Likewise, any tanks you have listed will feed into that "pool". If your real craft has engines independently drawing from their own fuel reserves, this spreadsheet will not model that behavior unless the engine-and-tank "sets" are identical to one another. However, you can use it to model each set individually and find out which ones need more fuel supplies added or removed to get all the engines on a particular stage to burn for the appropriate length of time.
  
• All tanks are assumed to carry the proper fuel-to-oxidizer ratio.
  
• The acceleration used as the basis for the weight specific impulse (at KSL) is assumed to be 9.81 m/s², the same as that on Earth.
  
• Fuel units shown in-game are simply "units"; these units are assumed to be liters.
  
• The density of liquid fuel is not specified on-screen in the game. The value used in the spreadsheet was chosen to match the listed maximum fuel flow for the LV-T45 engine (5.7281 /s). This results in a density of 11.122 kg/unit (again, assumed to be liters). This is more than ten times the density of kerosene (most real-world jet fuels), or more than one hundred fifty times the density of liquid hydrogen. Unless the mathematics in the spreadsheet are wrong or "unit" is not equivalent to liter, the density listed on the "liquid fuel" page of the wiki is incorrect. I cannot claim with 100% certainty that the math is correct. Any comments regarding this are appreciated.
  

OTHER USAGE NOTES

Other details to consider when using this tool:

• Up to four different engines may be selected, and up to ten instances of each engine may be added to the configuration. The same applies to tanks.
  
• This tool will allow you to model the behavior of configurations which are downright ridiculous (e.g. a Rockomax Mainsail drawing from a single Probodobodyne Oscar-B tank) or absolutely impossible (e.g. TEN (10) Rockomax Mainsails and TEN Rockomax Skippers drawing from a single Probodobodyne Oscar-B tank). Take the results with a grain of salt!
  
• All engines shown are listed in the order in which they are shown under the "Propulsion" tab of the VAB/SPH.
  
• Use of this tool for rockets still in the atmosphere may not be very useful; especially since the atmosphere condition can change drastically very quickly, you are probably better off using other tools to estimate in-atmosphere performance. But the option is there.
  
• The throttle setting at the top of the calculation sheet can give you the actual burn time for your configuration; however note the maneuver editor will assume full-throttle burns if you wish to compare to that.
  
• As of version 1.2, thrust limiters can be applied to engine clusters, and tank clusters can have fuel amounts assigned, a la part tweakables.
  
• The "instructions" sheet shows the math used to come to the result, but doesn't completely describe the effects of multiple engines or tanks. If you can follow the math you should be smart enough to work out how that actually plays into it.
  
• The "Tests-Checks" sheet shows the results when the shown configurations were built and burned in-game.
  
• The engines and tanks in this spreadsheet are from the base game, KW Rocketry v.2.6c, and Firespitter 6. These are simply the mods I had installed at the time of spreadsheet creation, and I figured I may as well include them. Other engines and tanks can easily be added.
  
• Non-conventional engine technologies like monopropellant engines and ion thrust are not considered, as RCS is not commonly used for standard maneuvers and ion drive is highly reliant on management of other resources besides throttle and fuel supply. Jet engines are also not included.
  

LICENSE

This tool is available under the BSD 2-Clause License.

Copyright (c) 2014, Daniel A. Bender
All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

VERSION HISTORY

• version 1.0 - not released prior to this thread - initial release. NOTE - no license listed - link removed to comply with forum rules
  
• version 1.1 - 2014-Jun-22 - corrected an error on the equation display on "instructions" sheet; added "versions" and "license" sheets NOTE - link removed because Creative Commons license is unsuited to software use
  
• version 1.2 - 2014-Aug-16 - changed to BSD 2-Clause License; added thrust limiter and fuel tweak options; updated KW Rocketry part entries
  

Edited August 17, 2014 by pincushionman
update

[Pecan]

Nice utility :-)

Probably add ons > add on releases and projects showcase > tools and applications

[pincushionman]

Updated to version 1.2: re-released under BSD 2-Clause License; added thrust limiter and fuel assignment options; updated KW Rocketry entries to version 2.6.

Am asking moderators to move this to Forum->Add-ons->Add-on Releases and Projects Showcase->Tools and Applications sub-forum.