While the U.S. Air Force is mum about the orbital whereabouts of its X-37Bmini-space plane, a dedicated band of amateur skywatchershas got its cross-hairs on the spacecraft.
The unpiloted X-37BOrbital Test Vehicle 1 was lofted on April 22 atop an Atlas launcher. It isbeing flown under the auspices of the U.S. Air Force Rapid Capabilities Office.
In U.S. military tracking parlance, when the space plane reached orbit itbecame identified as Catalog Number 36514, 2010-015A, OTV-1 (USA 212). [Video:X-37B space plane spotted.]
From there it entered a cone of silence regarding any on-orbit duties.
But thanks to a worldwide eyes-on-the-sky network of amateurs, thespacecraft is reportedly in a 39.99 degrees inclination, circling the Earth inan orbit 401 kilometers by 422 kilometers. This data may change slightly as thevehicle's orbit is better refined, said Greg Roberts of Cape Town, SouthAfrica, a pioneer in using telescopic video cameras to track spacecraft,chalking up exceptional results over the years.
The Air Force has not said what the robotic ship is for, but analysts saythe X-37Bis likely a spy craft and almost surely not a weapon. [X-37Bspacecraft photos.]
Absolute confidence
Roberts said that those sighting the craft have "absoluteconfidence" in their observations, claiming no chance of it being anythingelse. "The fact that we have now seen it several times confirms that theorbit we have is very close to the real orbit -- perhaps an error of a fewkilometers or so at most," he told SPACE.com.
"One of our North American members got a brief view of what wassuspected to be the space plane under somewhat difficult circumstances beforeit was no longer visible in the evening sky from the United States,"Roberts said.
That single observation was not enough to define the spacecraft'sinclination as the skywatcher used binoculars,Roberts added. Video observers of the sky get "traces" when theyrecord the object of interest, he continued, so it's possible to determine theangle of travel and hence an idea of the inclination.
Roberts said the space plane has been observed over the last week by severalmembers and its orbit is properly tied down. "We now face a spell of aweek to two weeks when there will be no optical visibility until it becomes amorning object in the southern hemisphere and an evening object in the northernhemisphere."
The degree of difficulty in finding the X-37B has been a product of notknowing its inclination and having limited optical visibility due to its loworbiting altitude. Amateur astronomers learn howto spot satellites by tracking spacecraft orbits and finding when they may fly over viewing areas on the ground.
"This means it spends most of its time in Earth's shadow during apass," Roberts said. Also the ship's low inclination and altitude hasmeant that tracking has only been possible from mid-latitude, ruling outobservations by some of the members of the team unless they are in position atvery low elevations.
According to Ted Molczan, a leader in thesatellite sleuthing business based in Toronto, the X-37B search was moderatelychallenging.
"It was the first launch of its kind, so we had only a rough idea ofits altitude, inclination and plane. Its low altitude and inclination put itout of reach of several of our most skilled observers," he told SPACE.com.
Molczan said his role was estimating the range ofpossible orbits in which the space plane might be found, which was the basisfor the searches.
"The object is moderately bright. Based on the limited tracking so far,I estimate that it will reach about magnitude 2.5 when observed at highelevation above the horizon, and well illuminated by the sun. That is similarto the brightest stars of the Big Dipper," Molczansaid.
Nighttime fixation
What's behind the nighttime fixation on the X-37B?
"Well the challenge is finding it without much data to go on,"Roberts responded. "If the data were freely available we would probablynot have bothered with it. I see little sense in tracking objects for whichdata is freely available. It's like re-inventing the wheel. So as long as thereare missions with little or no information, I personally will be interested inthe challenge of finding them."
Roberts said that the sky watching group has a pretty good record. "Ifmemory is correct, we have found and are tracking every single object launchedin the past five years or more. The only objects we are not able to track arethose stationed over areas of the earth where we have no active observers???mainly the central Pacific Ocean area."
Next up on the Roberts "to-do" list is attempting to see ifthe space plane is emitting any radio signals on the frequency bands that he'sable to monitor.
"That is going to be an even bigger challenge," Roberts concluded,"and I'm not really that keen on it as it's like looking for a needle in ahaystack!"
Mystery manifest
Still, even with the ground observations, exactly what's tucked inside theX-37B's cargo hold -- about the size of a pickup truck bed -- remainsa mystery.
The X-37B signals a new way for the Air Force to conduct on-orbitexperiments, said Gary Payton, Air Force deputy under secretary for spaceprograms, during a pre-launch press briefing teleconference last month."Actual on-orbit activities we do classify...for the experimental payloadsthat are on-orbit with the X-37," he noted.
Payton did indicate that there's enough payload room on the mini-spaceshuttle to house a couple of small satellites in the range of a few hundredkilograms each. There is growing speculation that the vehicle is likely totingEarth spying gear for the National Reconnaissance Office.
The reusable X-37B Orbital Test Vehicle 1 was built by Boeing Phantom Works.It is about 29 feet (9 meters) long and has a wingspan of just over 14 feet (4meters) across. It stands just over 9 1/2 feet (3 meters) tall and weighsnearly 11,000 pounds (about 5,000 kg).
Big test ahead
The OTV 1 mission is also designed to test new technologies and develop waysto make space access more routine, affordable and responsive. The OTV is thefirst vehicle since NASA's shuttle orbiter capable of returning experiments toEarth for further inspection and analysis.
A second X-37B is now being fabricated for a test mission scheduled for2011.
X-37B is being operated under the direction of Air Force Space Command's 3rdSpace Experimentation Squadron, a space control unit located at Schriever Air Force Base in Colorado.
Capable of orbiting Earth for up to 270 days, a big test for the X-37Bis ahead: A "do-it-itself" guided entry and wheels down runwaylanding at Vandenberg Air Force Base in California, with Edwards Air Force Baseas an alternate site.
If the incoming space plane strays off its auto-pilot trajectory over thePacific Ocean, the craft is outfitted with a destruct mechanism.
- Top 10 Most Dangerous Space Weapons
- Gallery - The Air Force's X-37B Space Plane
- Video - Secret X-37B Space Plane Revealed in Flight
Leonard David has been reporting on the space industry for more thanfive decades. He is past editor-in-chief of the National Space Society's AdAstra and Space World magazines and has written for SPACE.com since 1999.
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