Dr. Keith Gendreau, Physicist, Goddard Space Flight Center, Greenbelt, MD
- Thursday, 31 January 2008
Dr. Gendreau: Well, it’s not a discovery; it’s a concept, and you know it’s achievable. At first I was just trying to get our technology in place for the Black Hole Imager, but then it occurred to me, in the past year or two, that there are actually some advantages to doing communication in x-ray.
Basically, the advantages are all driven by the fact that the wavelength is very small, so if you can use diffraction-limited x-ray optics – and it’s tough, but if you can – then you have something that is more like a laser than a laser really is. In other words, when you have laser communications, you’re thinking a laser beam, right? Well, the laser beam actually diverges, and if you’re going over very long distances – say from the Moon to the Earth – and your beam started off being about a foot across, in about the time it gets to the Earth it’s going to diffract because of the diffraction – lambda divided by 1-foot times the distance between the Earth and the Moon – and you’ll find that your spot is not a foot across when it hits the Earth, it’s a kilometer across or more!
If you did that in x-ray, the beam would be very tight. So what that means is you’re beaming your information exactly where you want it to go; you’re not spreading your power all over the place. The upshot is that as you go to very long distances; if you can use diffraction-limited x-ray optics, you would transmit more information per unit power that you put into the system. So you can potentially beat laser-based communications if you can get all the other technical things taken care of later on. So this is a future thing.
NTB: Two of the organizations showing early interest in this new technology are the military and, of course, NASA. What are some of the potential applications they might have for it?
Dr. Gendreau: The beam is so tight that there are no side lobes, so you don’t have anyone listening in. You would know, because they would interrupt your beam. That’s one reason why you go to laser com.
There are some other applications. Actually, just take that application where you’re taking the fact that the beam is very tight. In the future, say 50 or 100 years from now, if you want to have a high-speed data link between Mars and Earth, then this might be the energy-efficient way to transmit information over that distance. You would do it from orbiting spacecraft around Mars to orbiting spacecraft around the Earth, and do the long leg using X-com, and then you would use conventional communication techniques to go from planet surface to orbit. The idea is that with the beam being so tight, you can spend less energy transmitting a gigabit per second or more, or a hundred gigabits per second. That’s a NASA application, way out in the future.