NASA says it's using off-the-shelf technology -- a smartphone -- to make the most inexpensive, easiest-to-build satellites in the history of space exploration.

Researchers at NASA's Ames Research Center at Moffett Field, Calif., are developing three PhoneSats, each of which will be 4 inches square and will weigh less than 4 pounds, NASA said on its Web site.

Extensive use of commercial-off-the-shelf components, including an unmodified, consumer-grade smartphone -- an HTC Nexus One running Android -- will keep the price of the micro-satellites at $3,500, NASA said.

The Nexus One acts as the satellite's onboard computer while sensors determine the orientation of the spacecraft so the smartphone's camera can be used for Earth observations, engineers said.

PhoneSat's mission will be a simple one, they said; survive a launch and to stay alive in space for a short period of time, sending back digital imagery of Earth and space via its camera, while also sending back information about the satellite's health.

The program is intended to allow engineers to see what capabilities commercial technologies can provide rather than trying to custom-design technology solutions to meet set requirements, NASA said.