skaterzero807

Yes, I haven't run simulations for elliptical mainly because getting the longitude of periapsis lined up would probably be a pain, as well as timing the SOI exit to result in the correct transfer orbit at the right time to intercept the target. Also, cantab, you bring up a good point about sending all that fuel to Tylo and back. I might look into optimizing this based on minimizing the amount of fuel required on each journey and back, or even to minimize the difference in fuel amounts so you can visit everywhere with the same craft.

And here is the post on my results for those interested: http://forum.kerbalspaceprogram.com/threads/90322-Optimal-Jool-Space-Station-Orbit

I recently set out to answer a question I had about where to put a space station around Jool in order to minimize dV requirements for future craft and wanted to share my results since it was not something I could reason out. The goal was to minimize dV required to rendezvous with the station, then get into circular orbits around Laythe, Vall and Tylo while returning after each trip for refueling/science processing. The cost includes getting from an aerobraking Jool orbit to the station orbit, then getting to a circular orbit around each target and returning to the station. No landing/takeoff was considered since it would be the same regardless of where the station was located. Anyway, the short answer is to put your station in a low Laythe orbit (55-60 km). This solution requires more dV to get to Vall and Tylo, but is worth it because coming back from Vall and Tylo is cheap with aerobraking. Also going to Laythe is very cheap when you are already there . More info on my project page. Here is the plot of total dV vs. location for anyone interested: A few interesting things to note about this plot: 1. DO NOT aerobrake around Jool to get into low Jool orbit. It costs way more to get to the moons than you will save aerobraking at Jool to return. 2. Getting inside an SOI decreases the dV required to travel around. If you don't want to visit Laythe the next best place to be is inside Vall's SOI. 3. Being close to an atmosphere-less body is not good unless you plan on making many trips to that body.

Just for anyone who is interested, I figured out how to get around this problem. Here is a picture of the orbits to hopefully explain better: The main problem was coming from assuming we would transfer to Vall using the dashed cyan orbit. The speed leaving the SOI would have to be smaller than physically possible so calculators might show a negative burn. Anyway, the way to get around it is: 1. Solve for the slowest speed you could leave the SOI from your orbit 2. If the speed you would need to go is slower than this minimum speed, then solve for the flight-path angle (or zenith angle, whichever you prefer, see http://www.braeunig.us/space/orbmech.htm) required so that leaving at the minimum speed and that angle, you will have your desired apoapsis (or periapsis if going toward a target lower). This involves solving a quadratic function for cos(theta) (or sin(theta) using zenith angle). 3. From the known flight-path angle and speed just before leaving the SOI, you can calculate the speed and flight-path angle after leaving by adding the velocity vectors. 4. Given the altitude, speed and flight-path angle just outside the SOI, you know your new trajectory (blue solid orbit) 5. The delta-V in this case is simply the delta-V required to lift your apoapsis to the SOI. From there, you are moving at the minimum allowable speed and if the point of exit is correct, you will exit with the right speed and direction to make it to your target at apoapsis (or periapsis if going lower) I won't go into the mathy details but this would at least give you an idea of how to do it. I may end up doing a small article on this once I have a definitive answer of where to put a space station in Jool orbit to minimize future trips' delta-V.

I've been using a band's album logo since their music is good background while playing: Highly recommend their music, you can listen at http://spaces.bandcamp.com/

Ok, thanks Mr Shifty. I think that explains it pretty well. I guess to do a transfer to Vall would require you to leave the SOI moving at ~648 m/s but in a direction such that when added as a vector to Laythe's motion would result in an orbit (no longer Hohmann) that brings you to apoapsis at Vall. I'll have to see if I can formulate this as a solvable equation to fix my code so I can simulate realistic dV's from these high orbits.

I have been doing some delta-v calculations for where to put a Joolian system station, but I ran into an issue when calculating dV requirements from Laythe orbit to Vall or Tylo. Even the calculator at ksp.olex.biz seems to agree with the issue: some ejection burns are negative. For example, a 3000 km circular orbit around Laythe has orbital velocity = sqrt(mu/3e6) ~ 800 m/s. For a transfer to Vall at Laythe's altitude, you need to exit the SOI at about 350 m/s moving prograde so Laythe's velocity (~3200 m/s) adds and you end up at Vall's orbit at apoapsis. To be going 350ish m/s exiting the SOI you need to slow down by about 400 m/s, but we all know slowing down your circular orbit won't get you closer to the SOI. So it is obvious we would want to increase our speed, a positive ejection burn to escape, but this seems to indicate we will be moving too fast when leaving. So my question is, why are there negative ejection burns? Is it just a poor assumption of scalar addition of velocity upon leaving the SOI? Or do we just have to burn positive to escape Laythe then slow down to bring the apoapsis to Vall's orbit? When I have more time, I'll have to launch a test probe and play with maneuver nodes to see what the deal is but maybe someone knows already. Thanks in advance.