It costs a lot to get to space—in 2001 it cost as much to put something in low Earth orbit ($22,000 per kilogram [$10,000 per pound]) as it did in 1957. Anyone who wants to do things in space (e.g., such as experimenters and scientists) has a cost hurdle to overcome that is not encountered in any other area of human endeavor.

Low Earth orbit (LEO) is a few hundreds miles up. To get to LEO, it takes 30,000 feet per second of velocity change; the total energy needed to get to the Moon is about 45,000 feet per second. LEO is therefore two-thirds of the way to the Moon.

Two factors make the step from Earth to LEO hard. First is Earth's atmosphere, which causes drag and aerodynamic heating. Second is the gravity gradient, or the change in the force of gravity as one moves...