Probably just an orbit change - this time, anyway...
Once in orbit, the X-37B - unlike the space shuttle - can deploy a solar array for power, permitting it to stay in space for up to 270 days according to its US Air Force operators. It has large fuel tanks and a capable rocket motor of its own, indicating that manoeuvres in orbit are a major part of its mission.
Perhaps still more intriguingly, the X-37B's shuttle-like wings mean that it has "cross-range" capability on re-entry: that is it doesn't have to land at a location directly under its orbital track as re-entry commences. Rather, it can plunge into the atmosphere and use its wings to fly itself down to somewhere well to one side of where its orbit would have taken it.
The space shuttle was purposely built with "cross range" wings - rather than alternative designs such as stub wings or a lifting body which would have perhaps offered greater payload - so that it could carry out cunning spy-sat missions from the US military spacefield at Vandenberg airforce base in California. The idea was that military shuttle missions would lift off from Vandenberg, orbit the Earth just once on a high spysat-type angle, then re-enter to land.
The Earth having turned as the shuttle flew around it, the returning spaceplane would normally find itself descending from orbit above the Pacific rather than California. But the cross-range capability would mean that it could bend its track and reach Vandenberg nonetheless.
The fact that the shuttle could get up and down in one orbit would mean that it would be very hard for anyone to know where it had been or what it had done, as it would pass over mainly uninhabited regions and only once at that: any spysat dropped off on a "Mission 3A" profile might have eluded detection for some time - perhaps forever if it were subsequently scooped up on an equally clandestine "Mission 3B" one-orbit shuttle hop.
In the event, the increasing size of spy satellites and the Shuttles' difficulty in hoisting such big payloads on high-angle orbits* meant that these missions were never flown. But it seems at least possible that the X-37B is intended to make some interesting uses of its cross-range wings and its capable orbital manoeuvring system. A second X-37B is already under construction, too.
As a "black" military project the X-37B would normally be much less well-known, but the project has been funded at different times by different agencies - including NASA - during its genesis before disappearing into the black budget under the auspices of the US Air Force Rapid Capabilities Office. Details of its modern-day mission have never been released, though Air Force spokespersons like to speak of it as though it were mainly a trial for reusable spacecraft concepts. It may indeed be intended primarily for rapid servicing and deployment of smaller space hardware such as the new TacSat and System F6 platforms.
Nonetheless, the little spaceplane's orbital manoeuvring and cross-range landing capabilities would also lend themselves to various kinds of sneaky orbital trickery: close observation/electronic-intelligence runs past other nations' spy satellites, for instance, might be accomplished without anyone knowing in some circumstances. Active electronic meddling might even take place in future: though such is strictly forbidden by international treaty, the US is known to be taking precautions against such deniable attacks being made against its own satellites.
That kind of thing almost certainly won't be going on now, on the X-37B fleet's maiden flight. It may never happen at all. But the fact remains that even Molczan and his keen-eyed colleagues don't know where the X-37B was for over a fortnight earlier this month. ®
*A launch into equatorial orbit made from close to the Equator gets a valuable helping hand from the Earth's rotation. However a spy sat needs to be in a high-angle orbit so that more of the planet will pass beneath its track. The north-south portion of its orbital velocity must be supplied entirely by the launch system, meaning that such a launch becomes harder work as the angle increases.