A Delta II model 7920 will lift off from Space Launch Complex 2 at Vandenberg Air Force Base, Calif., to boost the telecommunications satellites for Motorola and Iridium LLC into an orbit 345 nautical miles above the Earth. Thrusters will be fired aboard each of the Iridium spacecraft to place them into final orbit.

Because the 66 satellites of the IRIDIUM constellation will be placed in six different orbital planes, the launch site must be directly below the position that the satellites will be placed. The accuracy required for IRIDIUM missions means that engineers must plan to launch the Delta II within a five-second window.

On May 5 a Delta II placed the first five of the 66-satellite IRIDIUM constellation into orbit. That launch was also within a five-second window.

The IRIDIUM system will provide a satellite-based wireless personal communications network permitting any type of telephone transmission to reach its destination virtually anywhere on Earth, at any time.

"The Delta launch team is pleased to have a transportation role in Iridium LLC's plan to revolutionize worldwide communications," said Darryl Van Dorn, director for NASA and Commercial programs. "We look forward to working with IRIDIUM to meet its goal of making worldwide commercial service available by late 1998," he added.

McDonnell Douglas signed a contract with Motorola in 1994 for eight Delta II launches through the year 1998. A year later, the companies signed a separate, but related operations and maintenance contact for five additional Delta II launches between April 1998 and June 2001.