WASHINGTON – The U.S. Air Force released on Aug. 19 a draft solicitation that sets up a competition between SpaceX and United Launch Alliance to launch a multipurpose experimental satellite in late 2018 that’s equipped to detect nuclear detonations for the Pentagon and carry out a laser communications demonstration for NASA.

Known as Space Test Program Satellite (STPSat)-6, the Orbital ATK-built spacecraft will host up to eight payloads. The satellite’s primary payload is the Space and Atmospheric Burst Reporting System (SABRS),  which is designed to complement nuclear detonation detectors aboard current GPS spacecraft. STPSat-6 will also be carrying a Laser Communications Relay Demonstration payload built by NASA’s Goddard Space Flight Center. That payload originally was scheduled to launch aboard a Space Systems/Loral satellite in 2019, but NASA opted for the Defense Department satellite citing less risk and common technology interests.

The Air Force said in late July that STPSat-6 will be built on an Orbital ATK A-500 satellite bus another U.S. government agency bought for a different geosynchronous mission but transferred to the Space Test Program after deciding it didn’t need it.

Orbital ATK’s A-500 bus, which it refers to as its High End Modular Bus, can accommodate 200-500 kilograms of payloads and is intended for missions lasting 2-7 years. The Air Force said it has room for up to six hosted payloads in addition to the SABRS and Laster Communications Relay Demonstration payloads.

In an effort to re-introduce competition to the national security launch industry, the Air Force has said it plans to award nine competitively bid launch contracts before the end of 2018. By releasing the draft request for proposal, the STPSat-6 launch appears to be the third of those missions. Six of the nine missions are expected to be GPS-3 satellites.

SpaceX won the first competitively bid contract in more than a decade in April to launch the GPS 3-2 satellite in 2018 for $82.7 million. Earlier this month, the Air Force released a formal request for proposals for the second competitive mission, the GPS 3-3 satellite. That satellite is expected to launch in 2019.

Mike Gruss covers military space issues, including the U.S. Air Force and Missile Defense Agency, for SpaceNews. He is a graduate of Miami University in Oxford, Ohio.