Artist's rendering of tethered picosats in orbit. Photo: The Aerospace Corp.

Engineers from The Aerospace Corporation have established effective two-way communications with the smallest satellites ever released into orbit.

The two picosatellites measure 4-by-3-by-1 inches and weigh less than one-half pound each. In passes over the ground station at Menlo Park, Calif., Monday evening and Tuesday morning the engineers received data and transmitted commands.

It was determined that the tethered satellites were released Sunday evening from their "mother" satellite, OPAL, built by Stanford University students. OPAL stands for Orbiting Picosat Automated Launcher.

Engineers have commanded the tiny satellites to switch to low-power mode except when they appear over the ground station. This is to conserve power. They are to transmit beacon signals when over the ground station.

The satellites also have been commanded to exercise microelectromechanical systems (MEMS) radio frequency switches designed by Rockwell Science Center, Thousand Oaks, Calif. The switches are the primary mission payload.

Picosatellites, less than one-half pound each, are shown against a coffee mug. Photo: The Aerospace Corp.

The picosatellites were designed and built by The Aerospace Corporation, El Segundo, Calif., under funding from DARPA, the Defense Advanced Research Projects Agency.

The Aerospace Corporation tested and integrated the satellite components and conceived the mission. The picosatellites are considered a link toward slightly larger and more sophisticated nanosatellites envisioned as tiny space workhorses of the future.

Dan Oltrogge, head of The Aerospace Corporation's tracking team, said locating the tiny picosats was like "finding a needle in a haystack."

He credited the U.S. Space Command's Space Surveillance Network based in Colorado Springs with getting a good fix on the satellites. In a tether connecting the two satellites are thin strands of gold to facilitate pickup by radar.

He said the mission so far has been "wildly successful" given its complexities.

These include a new four-stage launch vehicle -- the Air Force's Orbital Suborbital Program Space Launch Vehicle constructed from refurbished Minuteman II rocket motors and Pegasus XL motors -- and the succession of satellite deployments.

OPAL, a university satellite, was released by JAWSAT, the Joint Air Force Academy Weber State University Satellite, and the picosatellites were released from OPAL.