Last year, the US Air Force sent a robotic spaceship into orbit and kept it there for seven months. No one outside the program knows why exactly it was up there, but part of the reason could be that they were testing a replacement vehicle for the space shuttle. It’s just speculation, so don’t go getting too excited just yet.
Nobody’s really sure what the X-37B is for. All we know is that the Air Force sent it up into space, twice, and it stayed there for a long time (months), changing orbits and doing mysterious (and highly classified) things. Evidently it did what it was supposed to do, and did it well enough that the Air Force asked Boeing to build it a second one.
For its part, Boeing is looking even farther ahead, and they’ve drafted designs for an X-37C, which would be just like the X-37B, only about twice the size. This would make it large enough to carry a six person crew capsule in the cargo bay, or in a slightly different configuration, give it a space shuttle-style cockpit and crew area.
While the X-37C might offer many of the same capabilities as the space shuttle (albeit in a much smaller package with a reduced cargo capacity), it would be cheaper, with a faster turnaround, and would launch on top of a rocket system (the Atlas V) that could be used for other cargo, making it much more versatile.
Again, this is all entirely speculation, but we can’t depend on Russia forever, and even with advances in rockets in the private sector, I doubt the Air Force (not even just NASA) will want to depend on SpaceX for outer space travel either.