Imagine this: A wedge-shaped aircraft attached to a supersonic jet engine is hurtling along an electrified track, carrying a pod or spacecraft destined for orbit.
Sound farfetched? It may not be.
A team of engineers from NASA's Kennedy Space Center in Florida and some of the agency's other field centers are looking into this and other novel launch systems based on cutting-edge technologies.
Scramjet sky launch pads
One early proposal calls for mounting the launching aircraft on scramjets, which are air-breathing jet engines driven by supersonic combustion.
The aircraft would fly up to Mach 10, using the scramjets and wings to lift it to the upper reaches of the atmosphere, and then a small payload canister or space capsule similar to a rocket's second stage would fire off the back of the aircraft and into orbit.
After the high-altitude launch, the mother aircraft would return to land on the runway where its trip began.
The launch system would require some advancements of existing technologies, but it wouldn't need any brand-new technologies to work, said Stan Starr, branch chief of the Applied Physics Laboratory at Kennedy Space Center.
"All of these are technology components that have already been developed or studied," Starr said in a statement. "We're just proposing to mature these technologies to a useful level, well past the level they've already been taken."
Riding rails to space
The scramjet launcher project could form the foundation of a future Advanced Space Launch System, with elements spread across different NASA centers to make it work, agency officials said.
At the Kennedy Space Center, a 2-mile (3.2-kilometer) test-launch track could be installed between NASA's huge Vehicle Assembly Building where shuttles are assembled for launch and Launch Pad 39A, from where orbiters blast off.
But there are some challenges. To launch on an electrified track, for instance, the track would have to withstand at least 10 times the speeds commonly seen on tracks used for roller coasters, NASA scientists said. Roller coasters typically run about 60 mph (100 kph), they added.
NASA scientists also are looking into other methods of powering a track-launched vehicle.
A study into a rail launcher that uses gas propulsion is under way, with Starr's team applying for more funding through NASA's innovative-technology program to pursue it.
Engineers with NASA's Marshall Space Flight Center in Huntsville, Ala., have tested a prototype track-based system that uses magnetic levitation to accelerate vehicles to launch speeds.
As for aircraft launching from a rail, there are some real-world tests for designers to draw on. NASA's X-43A, or Hyper-X, program and the U.S. Air Force's recent X-51 scramjet tests have shown that scramjets can achieve remarkable speeds.
In late May, the Air Force's X-51A Waverider scramjet test vehicle set a world record for the longest hypersonic flight. The vehicle flew faster than Mach 5 for more than three minutes, compared with the previous record of 12 seconds by NASA's X-43A craft in 2004.
Commercial scramjet launches ahead?
Scramjet vehicles could be used as a basis for a commercial launch program if a company decided to take advantage of the basic research NASA performed along the way, Starr said.
Starr and his engineering team propose a 10-year plan that would begin with launching a drone similar to those used in the ongoing Air Force tests. More-advanced models would then follow, with the goal of developing a vehicle that can launch a small satellite into orbit.
The Advanced Space Launch System is not geared to replace NASA's retiring space shuttle fleet, or any other manned spacecraft program, Starr said. But if the early unmanned launches were successful, the system could eventually be adapted to carry astronauts, he said.
"It's not very often you get to work on a major technology revolution," Starr said.