[danielweber]

If order to meet, they would need to match both position and velocity. Meaning whatever history they had gone through, they both had to get to that position-and-vector.

There are some faster and slower paths. More missions to Mars have taken an 8-month-or-so journey because it's easiest and lowest power, and all unmanned cargo are probably going to take that route.

But by using just a bit more energy, you can cut the travel time down to about 6 months.

Most Mars missions involve launching stuff to land on the Mars surface (or maybe in orbit) that would take the slower path while the humans take the faster path.

(If you really want a bigger craft than you can launch from Earth at one time, just link up in LEO.)