sicarius

Also, even if the planets weren't on rails, it would be impossible. I believe Scott Manley made a video talking about what mind boggling amounts of fuel that would be needed to move something "tiny" (I believe he used Gilly as his example). .

A few months ago I intentionally hit two probes. Sent one into a retrograde orbit and another into the opposite. I felt quite a bit of accomplishment when I got two small objects moving at +4 km/s relative velocity to hit each other . Never been able to do it again though and no accidental collisions that I can think of.

First of all, I believe you did get the correct delta-v for your crew module so your math is right. Considering your lander, it doesn't have nearly enough delta-v. Unfortunately, I usually don't make tiny craft like that, so the only advise I can think of is to 1) strap a couple more tanks on (this may exceed your weight limit) and 2) ditch the lights and land on the day side and use only three landing legs to reduce unnecessary weight.

To address your main problem, when I flew it the center orange tank wasn't draining from the external tanks, so it could be a bug. Off-topic, I would suggest dropping the srbs as their own stage because right now they run out before the liquid boosters, meaning you have to carry the srbs until your liquid boosters run out. EDIT: while what Johnno says is true, because your core tank ignites after you drop your boosters, I believe presence of fuel lines shouldn't affect fuel flow, in other words, they don't do anything