Now, the Airborne Launch Assist Space Access isn't going to be launching the really big hardware – it'll be limited to satellites that weigh in under 100 pounds. That shortcoming is far, far exceeded by the ALASA system's ability to put an orbiter into space with just 24 hours notice and for under $1 million.
According to Defense Tech, the satellite would basically be a missile attached to the F-15's underbody and fired into the sky. The fighter would fly to a high altitude before launch, at which point the launch vehicle would use its own rockets to escape the atmosphere.
Development of the system kicked off in 2012, but is properly hitting its stride now. According to Bradford Tousley, the director of DARPA's Tactical Technology Office, a demonstration flight should be completed by the end of the year, and in 2016, 12 orbital tests will be completed. DARPA has released a video simulation of the system below. Check it out.