The unmanned air force space plane C37B will land sometime this weekend at the airbase on California's central coast.
Since launching in April, space enthusiasts have speculated about the ultimate purpose of the X37B, which resembles a small space shuttle.
The air force has only said the space plane is a test platform for unspecified experiments.
Hundreds of millions of dollars have been spent on the X37 program, but the current total hasn't been released.
