The landing window for the U.S. military X-37B space plane opens Friday, but officials are mum about the timing of specific opportunities to return the craft to Vandenberg Air Force Base, Calif.

An artist's concept of an X-37 re-entry when the program was under NASA management. Credit: NASA/MSFC

The 29-foot-long winged spaceship, often referred to as a mini-space shuttle, is still scheduled to come home some time between Friday and Monday, the Air Force said Thursday.

The time of landing will depend on weather and technical considerations, and most days feature multiple chances to return to Earth as the craft's orbit passes over Vandenberg.

Although officials are not divulging potential landing times, the X-37B's orbit flies over Vandenberg this weekend in the early morning hours, primarily before sunrise Pacific time.

The X-37B will fall from space and plummet back into the atmosphere, weathering fiery hot temperatures with a shield of thermal blankets and ceramic tiles. The lifting body space plane will be flying on autopilot and touch down on Vandenberg's 15,000-foot-long runway at nearly 300 mph.

Air Force officials can remotely destroy the spacecraft if it there are problems during re-entry and landing.

Breaking silence for the first time in more than seven months, the Air Force issued a press release Tuesday announcing landing of the craft would occur around this weekend.

Lt. Col. Barbara Carson, an Air Force spokesperson based at the Pentagon, said the military will not release any further information on the X-37B's return until after landing. The Air Force plans to hold a teleconference with reporters after landing.

The X-37B, also called the Orbital Test Vehicle, has been in space since launching aboard an Atlas 5 rocket in April from Cape Canaveral, Fla.

The Air Force stopped discussing the progress of the mission a few minutes after liftoff. The space plane's activities in orbit have been classified.

With a wingspan of nearly 15 feet and a height of 9.5 feet, the X-37B is about one-fourth the size of a space shuttle orbiter. Its cargo hold is about the size of a pickup truck bed and can carry several hundred pounds of experiments.

Built by Boeing's Phantom Works division, the craft is powered by a deployable solar panel, which is expected to be stowed back inside the payload bay before landing.

The re-entry, landing and recovery sequence will demonstrate upgraded thermal protection systems, automated computer algorithms and electromechanical flight control surfaces.

The lightweight vehicle was also built with composite structures, instead of traditional aluminum skin used on the space shuttle.

"A new generation of high-temperature wing leading-edge tiles will also debut on the X-37B," said a Boeing fact sheet. "These toughened uni-piece fibrous refractory oxidation-resistant ceramic (TUFROC) tiles replace the carbon carbon wing leading edge segments on the space shuttle. The X-37B will also use toughened uni-piece fibrous insulation (TUFI) impregnated silica tiles, which are significantly more durable than the first generation tiles used by the space shuttle."

NASA, which originally held responsibility for the X-37 program, continues to receive insight into the development, testing and performance of the heat shield, an agency official told Spaceflight Now in April.

Daniel Dumbacher, the former X-37 project manager at NASA's Marshall Space Flight Center, said earlier this year the space plane experiences more severe heating and re-entry environments than the shuttle.

Although the Air Force is not providing details of the X-37B's mission in space, military officials insist the craft's primary objective is demonstrating its capability to launch, operate in orbit and safely return to Earth.