I don't ever let that happen. Every mission has at least 1000 delta-v to spare, every colonised planet has a station in orbit over it, every station has a carrier docked to it (a 3 man capsule, rcs, big orange tank and nuclear engine, with something like 9000 delta-v with full fuel), and every base a vehicle capable of getting into a stable orbit and back. Vehicle development is quite another thing...