Stratolaunch Systems has partnered with Orbital ATK Inc. to use the company’s rockets to launch satellites into space, the companies announced Thursday. The arrangement is similar to a previous supplier relationship between the companies that ended last year. The Stratolaunch flight system uses a large airplane to take a rocket to high altitude and releasing it to fly into space. Stratolaunch was founded in 2011 by billionaire Paul Allen to launch satellite-carrying rockets into orbit as a lower cost, more convenient alternative to ground-launched rockets. Under the new agreement, Orbital ATK, in Dulles, Va., will supply to Stratolaunch its Pegasus XL rockets to take small satellites weighing up to 1,000 pounds into low earth orbit. Stratolaunch’s launch airplane, called Roc, is being built at the Mojave Air & Space Port in Antelope Valley by Scaled Composites, a subsidiary of Northrop Grumman Corp. When completed, Roc will be the largest aircraft in the world with a wingspan of 385 feet. Chief Executive Jean Floyd said that Stratolaunch is energized by the evolved partnership with Orbital ATK. “Orbital ATK is the world’s most experienced air-launch service provider, and we are proud to leverage that expertise and progressive approach in pursuit of our shared goal of convenient and affordable commercial access to low Earth orbit,” Floyd said in a prepared statement. Stratolaunch had previously announced a partnership with Orbital ATK two years ago on the launch rocket. Then last year the company began looking at other options when the original Orbital proposal did not match revenue expectations. Scott Lehr, president of Orbital ATK’s Flight Systems Group, called the latest collaboration a first step toward a long-term partnership with Stratolaunch.