What are they doing? DARPA has created a new kind of rocket they call the Airborne Launch Assist Space Access program or ALASA. It's designed to be launched from the belly of an airborne F-15. Once launched, the rocket will carry small satellites, weighing about a hundred pounds into low earth orbit. DARPA is planning a proof of concept launch by the end of 2015.
Why are they doing this? Bradford Tousley, director of DARPA's Tactical Technology Office describes it this way: "Currently, small satellites have to hitch a ride into space with bigger, more expensive "prime" payloads. So, I have to wait on somebody else, I have to go through their certification; if there's a hiccup with the prime, I wait. For a whole bunch of reasons, the small satellite, or the small payload market, has not been well serviced to this point." Tousley makes several good points here. Even hitching a ride is hugely expensive and inconvenient. These launches have to be planned years in advance, because, you know, it's a rocket. Nobody's got a warehouse full of these things just sitting around waiting to be pulled out and launched.
But think about the ALASA concept. All you need is a free F-15 and a runway, both of which the military has plenty of. You could take off pretty much any time you wanted, in pretty much any weather you wanted. The F-15 would then climb to the appropriate altitude and release its ALASA rocket, which would take its payload into orbit. The F-15 would then return to base and to prep for the next mission. DARPA's goal is to be able to have a satellite in the air within 24 hours of being ordered. "...we think that by going after this, [the ALASA concept]," Tousley explains, "we'll be able to really change the nature of it," the "it" being launching satellites into space, and if DARPA can pull this off, which certainly seems likely, they will certainly have changed the ease of satellite launches and the cost. Each ALASA launch is projected to cost no more than a million dollars.
After its proof of concept flight later this year, DARPA has planned a series of 12 orbital flights that will begin in early 2016. "The plan right now is, we have 12 [orbital] launches," Tousely said during a presentation he gave last February to the Federal Aviation Administration's Commercial Space Transportation Conference in Washington, D.C. "The first three are fundamentally engineering checkout payloads. The other nine will be various scientific and research development payloads that we're after."
(Sources: space.com, Wikipedia)