11082017, 07:04 PM  #11  
Join Date: Feb 2005
Location: Berkeley, CA

Re: Question regarding GURPS SPACESHIPS formulas
Quote:
Orbital velocity is roughly 30 km/s * sqrt( 2/r  1/a ), where r is your actual distance from the sun and a is your semimajor axis. The semimajor axis of a transfer orbit is equal to (r1+r2)/2. Thus, for an Earth to Mars, we get: Earth orbital velocity: r = a = 1, v = 30 km/s Mars orbital velocity: r = a = 1.52; v = 24.3 km/s Transfer orbit at Earth: r = 1, a = 1.26, v = 33 km/s. DeltaV at Earth: 3 km/s Transfer orbit at Mars: r = 1.52, a = 1.52, v = 21.7 km/s. DeltaV at Mars: 2.6 km/s. Now, for the orbital insertion effect, the velocity required is sqrt( escape velocity ^ 2 + transfer velocity ^2 )  current orbital velocity (if in orbit). Thus, Earth Surface>Mars Transfer requires total sqrt( 11.2^2 + 3^2 ) = 11.6 km/s, Earth Low Orbit requires 11.67.9 = 3.7 km/s. Earth Transfer>Mars Surface is sqrt( 5^2 + 2.6^2 ) = 5.6 km/s, Earth Transfer>Mars Low Orbit is 5.6  3.5 = 2.1 km/s. The orbital period of your transfer orbit is SMA^3/2 or 1.41 years in this case, a transfer takes half a period. The interval between solutions is y1*y2 / abs(y1y2) = 1.88/0.88 = 2.14 years. All of this can be done in a spreadsheet. 

11082017, 08:21 PM  #12  
Join Date: Apr 2015
Location: Pennsylvania

Re: Question regarding GURPS SPACESHIPS formulas
Quote:
Long story short, yes you can create a spreadsheet that will approximate a transfer orbit, but does a game really need that level of detail? 

11082017, 08:31 PM  #13  
Join Date: Aug 2007

Re: Question regarding GURPS SPACESHIPS formulas
Quote:
A gameworld nation's railroad system is usually not something even the most detailoriented among us try and simulate precisely. Normally the PC's are told "The train goes from city X to city Y and it will take Z units of time.". This is the way really, really hard science spaceships work too.
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Fred Brackin 

11092017, 04:58 PM  #14  
Wielder of Smart Pants
Join Date: Aug 2004
Location: Ventura CA

Re: Question regarding GURPS SPACESHIPS formulas
Quote:


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