The U.S. Air Force released a final request for proposals May 11 from companies capable of launching small and medium-sized satellites to low Earth orbit.

The Orbital/Suborbital Program-3 (OSP-3) solicitation, posted on the Federal Business Opportunities website, offers an opportunity for new entrants into the market for launching military payloads. The service intends to award up to six indefinite-delivery, indefinite-quantity contracts over a five-year period with a combined cost ceiling of $900 million, Air Force spokeswoman Maj. Tracy Bunko wrote in a May 18 email.

Contract awards are expected to begin in early fall.

The OSP-3 mission set is split into two lanes, according to the solicitation. One is for launching payloads weighing up to 1,800 kilograms into low Earth orbit or on long-range suborbital missions; the other is for bigger satellites, weighing as much as 9,000 kilograms, into low Earth orbit.

The solicitation includes launches of the civilian Deep Space Climate Observatory in 2014 and the Space Test Program-2 satellite in 2015. Both missions have been set aside for new market entrants, meaning United Launch Alliance, which launches the vast majority of U.S. government payloads, is not eligible to compete.