The semi-classified X-37B robot spaceplane hasn't received much attention, despite the fact that it is on its fourth flight in space. At least, that's the official story. Launched in May 2015, the latest mission seems even more covert than the three previous launches. Absolutely no images of the spaceplane were released before launch. That's a big change from the past, when we saw high-resolution images of the vehicle before launch and after landing.

Nobody knows when X-37B is coming home. It's even possible that the US Air Force, which owns the small vehicle, has not set a firm date. But we can consider what will happen when it does. This analyst will speculate that no images or video of X-37B will be released after its landing. Again, that would be a departure from previous trends, but consistent with the "no photography" policy of this flight.

Why is X-37B so camera-shy this time around? The reason could be that the spacecraft currently in orbit isn't the same type of X-37B that we already know, or is an entirely different vehicle. This has been the subject of previous articles by this analyst in SpaceDaily.

But what could it be? It's sometimes convenient to match rumours of other spacecraft and tie them to known launches, but that doesn't seem to be working this time. We really don't know what this spacecraft is. We don't even have any good theories about what has been changed. The payload fairing used on this flight is identical to previous missions, so whatever it is, it can't be too much larger than the standard X-37B.

One possible configuration could be a slightly "stretched" X-37B with larger wings, a larger fuselage and a larger payload bay. This could not only allow more gear to fly inside the spacecraft. It could be an intermediate step towards the development of a new operational spacecraft.

Tentative plans for a crew-carrying spacecraft dubbed "X-37C" have been drawn and openly discussed. As the name implies, its design would evolve from the basic X-37 spacecraft platform. The vehicle currently in orbit could be dubbed the "X-37-B2", assuming this theory is correct. If the title is also correct, we could speculate on potential "Bananas in Pajamas" jokes being told behind closed doors. (Readers who don't get the joke should Google the title of this show.)

Official news on the mission has been absent for quite some time. We were told about the successful performance of an experimental Hall thruster on board the spacecraft, but that was it. This information seems credible, but we wonder what else is happening while the vehicle is in orbit. There was also talk of a NASA materials test array, but no imagery of this was ever released. That's pretty strange for NASA, considering the way that other materials experiments have been openly discussed.

Consider another theory. Perhaps the NASA materials test story is just a smokescreen for something else. It wouldn't be the first time that NASA has been used as a civilian cover for more covert operations. Remember the U-2 spy plane piloted by Gary Powers that was shot down over the Soviet Union?

The initial cover story issued by the US government suggested that the plane was on a civilian scientific mission for NASA. The odds are not in favour of this theory, but it cannot be discounted. If NASA wishes to dispel speculation, it should provide more information or images of the samples. We were shown a clear image of the Hall thruster. Why not the NASA payload?

The fourth mission of X-37B (assuming it is really an X-37B) is approaching its one year mark. We can probably expect it to remain in orbit for longer than that, but it isn't clear how long it will stay in space. The current record for an X-37B mission is 675 days, set by the last flight. Will this mission go further? Perhaps we have a two-year mission in the works!

Normally, our understanding of classified programs gets better over time. With X-37B, it is really the opposite. The mysteries are deepening. The latest flight is probably stranger than of its predecessors, and shows no sign of revealing any more of its secrets.

Dr Morris Jones is an Australian space analyst who has written for spacedaily.com since 1999. Email morrisjonesNOSPAMhotmail.com. Replace NOSPAM with @ to send email. Dr Jones will answer media inquiries.