"We have been engaging Orbital over the past few months and have them under a study contract through early next year with specific design deliverables," Stratolaunch chief executive Gary Wentz wrote in a Nov. 28 email. "They are currently evaluating several alternative configurations that appear promising. We expect more information to be available in the February 2013 timeframe."

 

What those configurations were, neither Stratolaunch nor Orbital would say. Huntsville, Ala.-based Stratolaunch had been banking on using a liquid-fueled booster from SpaceX. Orbital specializes in solid-fueled rockets. The first stage of the liquid-fueled Taurus 2 rocket Orbital expects to debut in 2013 relies on a Ukranian-supplied first stage powered by a rebadged Russian engine. While the company has extensive experience with air-launched systems, it has not built one with the payload-carrying capacity that Stratolaunch seeks.