Stuck on the Surface of Giants.

I've ignored the plane change and directly went for a elliptical flyby instead.

You really don't have much of a window to attack with the default ships while taking that option, though - the approach speed in that scenario is over 25km/s, and i've had better results with a large manually detonated flak missile instead.

This mission honestly just makes me wonder how the USTA actually uses that depot. I get that it needs to be low to skim the methane, but it seems like the amount of effort to reach it would make trying to get supplies from there a net loss.

Using the default fleet I did a bielliptic maneuver to execute the plane change, fully refueled the combat ship and split it off from the tanker, then spent the next three passes to match orbits and sync up for the intercept.

It wasn't so much a battle as an execution.

I am a horrible person

The way to go is to extend your orbit around Neptune, then make your plane change around the apoapsis. You can save some deltaV to get gold by launch the missiles on a flyby, as the missiles have lots of deltaV

Though, really, who would put a fuel station in a polar orbit?

Got it on my third try. On my first try I forgot to detach the tanker and ended up in a 6km/s flyby with the target. On my second try I've thrusted in a wrong direction and got into a retrograde orbit relative to the target. On my third try I've had enough fuel left in the tanker to return to the starting orbit, and when I entered combat with the target at a nice 400m/s I found I had missiles all along. Damn. It's was a fun mission.

For those questioning the logic of the station, it has all the time in the world to periodically send and receive, there are a million cheap, economic ways to use the moons around neptune to drop onto and leave the skimmer station, thus making it profitable. By putting it polar you also limit the options of intercepts so it's a well defended station merely by location. If the USTA had been smart enough to leave a warship around it or nearby the long shot of a fast intercept with a cheap high delta-v weapon before re-enforcements can save it wouldn't have happened. But there is a lot of risk leaving something too close to Neptune so the economic option was kept. It is a civilian structure after all that just happens to be supplying the military.

Gotta think in terms of Delta-V. There is an easy, low delta-V path to get to and from the station using the surrounding moons for assistance in plane changes and such. But it takes weeks. Large fleets take time to even put together so a large fleet would be seen coming before it was together. A small fleet has to do it, but if it takes the economic path it's open to intercept for at least a month. Getting to the station in a timescale that doesn't get you stopped requires a rather limited number of already nearby ships to make hard, high delta-V burns within a very limited time frame.

The polar orbit is genius for defense and still works for economics. But they didn't station any decent defenses nearby preferring to keep their troops nice and comfy at the colonies. This oversight is what has the station ultimately doomed in the given scenario, the one thing they overlooked... that someone starting from within system would in fact be desperate enough to risk people falling into Neptune for a poorly armed craft to pull it off.