Amateur skywatchers intercept X-37B mini shuttle

After an intense search, a crew of amateur satellite sleuths has spotted the U.S. Air Force's second X-37B space plane – a robotic spacecraft that launched into orbit March 5.

The mission of the unmanned X-37B space plane, which is known officially as the Orbital Test Vehicle 2 (OTV-2), is shrouded in secrecy. The Boeing-built spacecraft is believed to be involved in reconnaissance — perhaps testing powerful sensors for a new generation of spy satellites. It looks much like a small version of NASA's space shuttles and blasted off from the Space Launch Complex 41 at Cape Canaveral Air Force Station in Florida.

While its mission is secret, the OTV-2 itself has attracted the eyes of dedicated skywatchers hoping to spot it in orbit just as they saw its predecessor – the first X-37B spacecraft, OTV-1 – during the OTV-1's months-long flight last year.

A new video, recorded by amateur Canadian skywatcher Kevin Fetterof Brockville, Ontario, shows the OTV-2 as a bright point of light soaring across the night sky. [Video: Skywatcher Spots Second X-37B Space Plane]

Fetter was successful in getting video of the OTV-2 gliding past the binary star Eta Serpentis on March 24. The OTV-2 and the star can easily be seen with the naked eye, shining at a magnitude 3 on the scale astronomers use to measure the brightness of sky objects (with the lowest numbers representing the greatest brightness).

Many satellites and spacecraft are regularly tracked by skywatchers. The International Space Station, for example, can appear to the unaided eye to outshine Venus and the brightest star in the sky, Sirius, under optimum viewing conditions. [Photos: Spotting Spaceships From Earth]

But to find satellites and spacecraft in orbit, skywatchers need to know ahead of time where to look. The secretive nature of the OTV-2's mission for the U.S. military made that task very difficult.

Once the OTV-2 launched, satellite watchers started scanning the skies for a glimpse of it. Skywatcher Ted Molczan of Toronto developed a set of orbital elements based chiefly on last year's OTV-1 flight to help prospective observers in the search.

And days after the launch, on March 9, Molczan announced that OTV-2 had been sighted by satellite tracker Greg Roberts of Cape Town, South Africa. Roberts spotted the spacecraft "in difficult observing conditions," Molczan reported.

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