[mlangsdorf]

I realized a way to get there with only 3 stages - instead of making the next stage take up the forward 6 systems of a spacecraft, use a 1/3rd size upper stage that only takes up the first two systems. That means you can devote 16 systems per stage to reaction tanks, and use the more favorable x2 modifier (SS1 p 17). So an SM+13 first stage gets to 60*16*2 1820 mps by itself, launches an SM+11 second stage for deceleration, and deposits a SM+9 survey craft. Not that much of an improvement, but it saves a couple of reaction drive assemblies on the intermediate stages and brings the cost down closer to 6 billion GURPS $ or so.

And yeah, getting back in a problem. In theory, you can add two more stages, but that brings you up to SM+17 for the initial craft, which is 30 million tons and 1,500 yards long. Better hope you find the secret to FTL travel on the other side of the trip and can retrofit it.