Earlier this month Stratolaunch Systems confirmed one of the worst-kept secrets in the space industry: its new partnership with Orbital Sciences Corporation to develop the launch vehicle for its air-launch system. Since late last year, after Stratolaunch ended its original partnership with SpaceX, Stratolaunch was rumored to be in discussions with Orbital. Earlier this year, when Stratolaunch updated its web site, it showed a redesigned booster that even appeared to have an Orbital logo on it, but there was no official confirmation from either company about a partnership.

“The agreement was finalized after a research period in which Stratolaunch charged Orbital with developing a comprehensive operational concept for its air-launch system, including the unique design of the rocket and operational processes and procedures that will need to be in place to operate the system,” the Stratolaunch release states, but offers no other information about the vehicle that Orbital will develop. The web site does indicate that the rocket, creatively called the Air Launch Vehicle (ALV), “combines proven solid and liquid propellant technology” and “utilizes a proven winged configuration first proven with Orbital’s patented Pegasus air-launch system and makes use of Orbital’s proven MACH avionics system, engineering standards and common vehicle and payload integration processes.” The video above shows what appears to be a mix of solid- and liquid-propellant engines used in the lower and upper stages, respectively, although one should be careful about reading too much into a single video.

“As we move forward, we’re focused a lot on the technical issues right now,” said Jim Halsell, a former astronaut who is currently the technical director of the space division of Dynetics, one of the companies working with Stratolaunch Systems, in a talk at the FAA’s 15th Annual Commercial Space Transportation Conference in Washington, DC, last Thursday. Halsell gave an overview and status update about the Stratolaunch system, including offering a few new details.

The focus for Stratolaunch right now is laying the foundation—figuratively and literally—for its launch system. That includes a groundbreaking last month of a facility at the Mojave Air and Space Port in California to build its gargantuan airplane. “There’s a squadron of earthmoving machines laying the foundation for the manufacturing facility and the tee hangar in which the aircraft will be manufactured,” he said. Halsell also revealed that Stratolaunch has taken delivery of the first of two 747 aircraft, which the company separately announced last week. Those planes will be disassembled so that parts, including their engines and landing gear, can be used for the custom-designed Stratolaunch plane. Halsell added the second 747 would arrive “soon”.

Stratolaunch’s plane, with its dual-fuselage design and giant wingspan, has attracted the most attention. “Our technical challenge, clearly, is to build something as light as possible, empty-weight wise, so as to maximize the payload capability that we can offer,” Halsell said. Scaled Composites is working to make “a design that closes” by the time manufacturing begins this summer on the initial elements of the plane, the wing spar and wing box.

However, he said the designs released in December are still being modified. “Even now, as we’re doing the systems trades and perfecting the carrier aircraft design, I would share with you that it’s going to move away from looking like two 747s that were pasted together, because that was a fairly early—not inappropriate, but more conceptual—design,” he said. The basic elements of the plane, including the dual fuselages and long, straight wing, will remain, though. “Stand by for further refinement of the design, but when you see it, it’ll all make sense.”

One thing Halsell declined to talk about in detail was the business case for the system, including what the company planned to charge for launches. “We can bring our costs into a very competitive range” with a sufficient tempo of launches, he suggested. “We now have something that we believe will be extremely competitive with the medium-launch market.”

He suggested, though, that Paul Allen—who is putting in an initial investment of perhaps several hundred million dollars into Stratolaunch—has reasons beyond simply financial ones for supporting development of this air-launch system. “Our primary investor, Paul Allen, was drawn to this project because he’s at a point in his life where he wants to be involved in projects that not only make good business sense,” Halsell said, “but also, he wants to be involved in furthering mankind’s progress in the space program, especially when it comes to US launch capability.”