updated 8/27/2010 4:58:20 AM ET 2010-08-27T08:58:20

Seasoned skywatchers in North American may have several chances to spot the U.S. Air Force's secretive X-37B space plane fly overhead with the help of a smart phone app that helps track satellites.

The Simple Satellite Tracker app gives a one-week advance schedule of flybys, and also alerts users to when spacecraft will appear with a countdown clock and a direction guide.

This week, the robotic X-37B space plane and the International Space Station are expected to make a series of good passes over some North American cities and towns, according to Tony Phillips of the website, which offers the app for the iPhone and Android phones.

Other app features include using GPS to find the user's location, flyby alarms that the user can set, and detailed information about each tracked object.

The reusable X-37B launched on April 22 aboard an Atlas 5 tocket, and has the capability to stay up in orbit for around 270 days, Air Force officials have said.

A satellite sleuth in Ontario, Canada has already caught the mysterious space plane on video back in May. [ Video: X-37B space plane spotted.]

But the X-37B space plane's return date depends upon how well it performs its unknown tests in orbit, according to Gary Payton, Air Force deputy undersecretary of space programs, before the mission launched.

Called the Orbital Test Vehicle 1, the debut X-37B space plane was built by Boeing in Seal Beach, Calif., and weighs about 11,000 pounds (about 5,000 kg). It is about 29 feet (9 meters) long and has a wingspan of just over 14 feet (4 meters) across.

For comparison, the International Space Station which is also making passes over North America this week is the largest structure ever built by humans in space. It has a backbone-like main truss that is more than 300 feet (91.4 meters) long, making it nearly as long as a football field.

The space station can easily be seen from the Earth by the unaided eye on clear nights and can rival the planet Venus in brightness depending on observing conditions.

This X-37B graphic illustrates some details of the space plane and its relative size. The spacecraft is also equipped with a payload bay the size of a pickup truck bed.

The end of the first X-37B space mission could involve a test of its automated landing system during its scheduled wheels down runway landing at Vandenberg Air Force Base in California.

U.S. Air Force officers have remained mostly tightlipped about the X-37B, except for denying that the vehicle represents a weapon.

Outside experts agree that the space plane most likely represents an orbital spy rather than a space weapon.'s Simple Satellite Tracker:

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