This NASA Marshall Space Flight Center image shows on-orbit functions for the reusable X-37B space plane, now under the wing of the U.S. Air Force.
A U.S. Air Force robotic space plane continues to maneuver in Earth orbit, according to the latest observations from skywatchers. The reusable space drone has been carrying out tasks using a suite of classified sensors and may be nearing its mission's end, according to comments from Air Force officials.
The spacecraft is the Air Force's X-37B space plane, also known as the Orbital Test Vehicle 1, which launched on its maiden flight on April 22 atop an Atlas 5 rocket.
The winged orbiter's mission has been shrouded in secrecy, but Air Force officials have said it was built for 270-day spaceflights, suggesting that it may be in the flight homestretch and preparing to make an atmospheric re-entry and landing ? all on autopilot. [Video of the X-37B in space]
Official details regarding the space plane's whereabouts, its classified payload and projected landing date are scarce ? more mum than informative.
"Nothing new," said U.S. Air Force Major, Tracy Bunko, a spokeswoman for the mission at the Pentagon?s Air Force press desk.
"The first flight of the X-37B/OTV-1 is ongoing and continues to focus on checking out the on-orbit performance of the vehicle and proving the technologies required for long-duration, re-usable space vehicles with autonomous re-entry and landing capabilities," Bunko told SPACE.com.
Bunko said that after the X-37B test objectives are satisfied, "we look forward to a successful re-entry and recovery at Vandenberg Air Force Base, California."
No landing date has been scheduled, she added.
This SPACE.com X-37B graphic illustrates some details of the space plane, its solar array power plant, and its relative size.
Meanwhile, amateur skywatchers are keeping tabs ? as best they can ? regarding the orbital antics of the mystery space plane. As to what the overall mission is of the vehicle, they too can only guess.
"The shortest and best answer is that I don't know," said space sleuth and veteran skywatcher Ted Molczan, a leader in a network of heads-up amateurs around the world monitoring the actions of the X-37B spacecraft.
Molczan speculates that the spacecraft's orbit appears to provide several landing opportunities each day. Therefore, special pre-landing maneuvers of the space plane are not required.
"It has made four significant maneuvers, including the latest one. All of its previous orbits resulted in ground tracks that nearly repeated after two, three, four or six days," Molczan said. "Ground tracks that nearly repeat after two, three or four days have long been a feature of U.S. imaging reconnaissance satellites, which leads me to suspect that X-37B is carrying experimental sensors for that purpose."
Molczan's theory appears to be backed up by similar thoughts from other veteran space watchers.
"The mission is demonstrating one of the primary uses planned for the X-37B: flying attached sensor payloads so that their performance can be assessed before they are integrated with much more costly free-flying systems," wrote veteran space reporter Craig Covault in the November issue of the magazine Aerospace America, published by the American Institute of Aeronautics and Astronautics.
Room for debate
But exactly how the robotic space plane fits into the U.S. security and space interests today and tomorrow leaves room for debate.
"I just find it a fascinating program because a hypersonic space plane was one of the first space programs I looked at ? 25 years ago," said Joan Johnson-Freese, a faculty member of the U.S. Naval War College in Newport, R.I. and a leading expert on space security issues. "Even then it wasn?t clear what it would be used for, but equally clear that the Air Force really wanted one."
Johnson-Freese told SPACE.com that "obviously, persistence pays off."
"That said, this technology could turn out to be the next GPS-type hardware ? where its uses aren't clear until it becomes operational. Given the few really new types of transportation technology since the space shuttle, it's time for something new and newer, and clearly NASA doesn?t have the resources."
Misunderstanding of physics
Other analysts question the purpose, duties, and usefulness of the vehicle.
"It still seems to me that the enthusiasm for X-37B and its follow-ons grow out of a misunderstanding of the physics of putting things in orbit and maneuvering in space," said David Wright, a senior scientist and co-director of the Global Security Program at the Union of Concerned Scientists, headquartered in Cambridge, Mass.
"This appears to be a case in which trying to make a flexible, one-size-fits-all system makes it suboptimal for essentially all missions," Wright said. "I still haven?t seen an analysis that explains its purpose and shows that it makes sense compared to alternatives."
Wright and UCS colleague, Laura Grego, recently co-wrote "Securing the Skies" ? a report that outlines 10 steps that the U.S. should take to safeguard space.
One step in the outline noted that the U.S. should declare it will not intentionally damage or disable satellites operating in accordance with the Outer Space Treaty, and pledge that it will not be the first country to station dedicated weapons in space. The Obama administration should press other space powers to make the same promise, the report explains.
"I personally think the X-37B space plane is just a new toy for geeks in the military," said Ting Wang[s1] , a postdoctoral associate at Cornell University's Judith Reppy Institute for Peace and Conflict Studies.
Wang said that satellites can do almost all the missions the space plane can do, and they can do it at a much cheaper price. "The only thing the space plane can do, [that] others can't, is to bring down a satellite and repair it."
However, the cost of doing so is questionable, Wang said.
Furthermore, the X-37B is a small vehicle with a payload capacity of roughly 500 pounds (227 kilograms), Wang advised. "It could hardly bring any valuable satellite down to the Earth," he said.
Given that satellite launch costs are so high, and electronic technology is developing so quickly, it likely to be much cheaper just to build a new spacecraft, Wang said.
"Personally, I don't think the unmanned space plane make any sense", until rocket technology has made significant progresses and enables the single-stage-to-orbit and reusable space plane, he added.
Bringing X-37B home
Whatever the case is today for flying the X-37B ? and as its first space test draws to a close ? the next show-and-tell milestone is bringing the bird home.
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 (4 meters) across. It stands just over 9 1/2 feet (3 meters) tall and tips the scales at nearly 11,000 pounds (about 5,000 kg).
The craft?s payload bay is 7 feet (2.1 meters) long by 4 feet (1.2 meters) across.
Given a successful de-orbit engine burn and reentry, the space plane is to wing its way to a California touchdown in autopilot mode. If the incoming space plane strays off its trajectory over the Pacific Ocean, the craft is outfitted with a destruct mechanism.
In preparation for the X-37B?s automated home coming at the Vandenberg Air Force Base in California, workers have readied a runway to enable the robot space plane?s landing.
According to the Santa Maria Times newspaper, a small armada of workers have replaced hundreds of landing strip plates along the flight line's centerline, a task done specially for the space plane.
Edwards Air Force Base, also in California, serves as backup to the Vandenberg landing strip.
The X-37B program is under the banner of the Air Force Rapid Capabilities Office in Washington, D.C., with one job description dedicated to demonstrating a reliable, reusable, unmanned space test platform for the United States Air Force.
The space plane is being operated under the direction of Air Force Space Command?s 3rd Space Experimentation Squadron, a space control unit located at Schriever Air Force Base in Colorado.
A second X-37B ? called Orbital Test Vehicle 2 ? is also in development, headed for a test mission slated for 2011.
- Photos of the X-37B Space Plane, Spotting Spaceships From Earth
- Video: X-37B Space Plane Spotted in Orbit, X-37B Skywatching App
- Air Force's New X-37B Space Plane Likely an Orbital Spy
Leonard David has been reporting on the space industry for more than five decades. He is past editor-in-chief of the National Space Society's Ad Astra and Space World magazines and has written for SPACE.com since 1999.