According to the Space Daily page, NASA is conducting a study into a variation of an old concept that might one day replace conventional rockets as a means of launching payloads into space, using ground based lasers or microwaves.

The idea is that an array of lasers or microwave generators would focus their beams on a single heat exchanger on a space craft. The heat exchanger in turn would heat fuel, likely liquid hydrogen, ejecting the super heated gas out a nozzle, propelling the space craft into low Earth orbit.
The advantage of what scientists call beamed thermal propulsion is that a launch vehicle would not have to be fueled with liquid oxygen to ignite the hydrogen fuel, thus saving mass.
A regular rocket generally launches in two to three stages, sometimes with the assistance of strap on solid rocket boosters, carrying only 3 percent of its mass in useful payload.
A beamed thermal propulsion system would launch a one-stage space craft into low Earth orbit, with a useful payload mass of five to fifteen percent.
The cost savings of such an arrangement are obvious. More payload can be launched into low Earth orbit at one time. The cost of stacking a three stage rocket and the complexity of multiple rocket engines are done away with.
The hardware of such a facility would last about ten thousand hours of constant operation before having to be replaced. A payload could be in low Earth orbit in eight to 10 minutes with a laser system, and three to four minutes using microwave generators.
The new innovation in the NASA study is the idea of doing away with a single, powerful laser or microwave beam, but instead using an array of lasers or microwave generators, all focusing on the one spot on the space craft's heat exchanger.
The cost of building a beamed thermal propulsion system is said to be about the same as developing a new rocket launch system, say in the hundreds of millions to several billion dollar range. But the reduction in launch costs and the increase in reliability might make such an investment worth it.
A beamed thermal propulsion system facility would be about the size of a football field, likely in an area where aircraft do not frequent, likely in a high altitude desert.
The civilian market for such a facility would be endless. Since people wishing to place research, education, or commercial satellites into orbit often have to wait for launch opportunities on existing rockets, a beamed thermal propulsion system would be ideal as it would be available at any time, schedule permitting. The military could use such a facility to launch quick reaction satellites, say for reconnaissance.
Mark R. Whittington is the author of Children of Apollo and The Last Moonwalker. He has written on space subjects for a variety of periodicals, including The Houston Chronicle, The Washington Post, USA Today, the L.A. Times, and The Weekly Standard.
(Source: ContributorNetwork)