Amateur astronomers believe they have located the X-37B US military unmanned spaceplane, which was launched into orbit on a classified mission a month ago.

We now know where, but not why or what.

According to the authoritative skygazers' site Heavens-Above, the X-37B is in an orbit angled up 40 degrees from the Equator, meaning that it passes regularly over all nations between southern Europe and South Africa and corresponding portions of south Asia, Australia, Latin America and much of the USA. The little spaceplane is at a height of approximately 400km above Earth.

The X-37B is operated by the US Air Force and its mission, budget and other particulars are classified, or "black". Nonetheless, various facts about the project are known as it began life as a NASA programme.

The X-37B takes off inside a fairing atop a normal disposable launch stack, in this case an Atlas V from Cape Canaveral a month ago. It is much smaller than a space shuttle, but like the shuttle has delta-shaped wings which should offer similar "cross range" abilities during re-entry - that is the X-37B could potentially make a landing somewhere well off its orbital track.

Another difference from the Shuttle is that the little robot wingship has a deployable solar array rather than fuel cells for electric power generation, and the air force has stated that it can remain in orbit for up to 270 days. The planned duration of the current mission hasn't been revealed.

Then the X-37B also has a powerful thruster and substantial propellant tanks, which indicates that it may be intended to change orbit quickly and/or frequently - it will certainly be no surprise if at some point the sky-watchers lose track of it again.

The US air force has refused to discuss the X-37B's mission in any detail, though spokesmen have emphasised its usefulness as a testbed for developing space technologies and also for trying out rapid-response and quick turnarounds with runway-landing spacecraft. A second X-37B has already been ordered.

The secrecy has led to much speculation regarding the little craft: that it may be intended to service or deploy the planned new "fractionated" mini-sat clusters, or as a way of rushing custom spy packages into space in response to emerging crises.

No obvious mission would seem to require the X-37B's delta wings and the cross-range re-entry capability they appear to offer, however. A lifting-body or stub wing design would have been able to carry more payload and still make a runway landing - just not one well off the craft's orbital track.

This has led us here on the Reg space-war desk to wonder whether there might just be plans in some quarters for crafty one-orbit flights like the "Mission 3A/3B" planned for (but never actually executed by) the space shuttle - details here. Such missions would allow the X-37B to escape the notice not just of amateur skywatchers, but also of foreign powers with space-tracking capabilities.

It'll probably be a long time before any details emerge, however. ®