Dale.Amon@FAS.RI.CMU.EDU (01/17/86)
A recent issue of Scientific American discussed phase conjugate lasers, and two of the capabilities seemed made to order for a Kantrowitz laser launch system. 1) Self targeting: A small laser need only illuminate the target area, ie the combustion chamber area, and the main laser would follow the target point without having requiring heavy calculation or rapid mechanical tracking. Tracking and feedback would be at the speed of light. Probably a fairly good safety factor also because of the use of basic properties of light rather than relying on complex systems. 2) Ability to put a large number of seperate lasers into precise phase step: This allows a ring of smaller lasers to be used to efficiently deliver power to the rocket combustion chamber. the phase conjugate system corrects for deficiencies in the optics, atmospheric scattering and time delays through each laser, thus allowing multiple beams to arrive at the target point exactly in phase. For those who are not familiar with the laser launch concept, it works as follows. The vehicle has a highly refractive combustion chamber on which powerful laser pulses are directed. The pulses superheat the air contained in the chamber and cause it to expand out the expansion nozzle at high velocity, producing thrust. The vacuum thus formed draws in fresh air between pulses, readying the chamber for the next cycle. As the rocket travels into thinner air, the accelerating rocket rams more air into the chamber. Final injection is by normal thrusters. The advantage of the system is that the 'fuel supply' is left on the ground (the lasers and their power sources) and the propellent mass is picked up along the way (atmospheric gases). Such a system drops the cost per kilo in orbit down to a few $$'s/kg. I have the feeling that the advances in phase conjugate lasers have just solved the most difficult of the engineering problems in this system.
henry@utzoo.UUCP (Henry Spencer) (01/19/86)
> I have the feeling that the advances in phase conjugate lasers have just > solved the most difficult of the engineering problems in [laser launchers] Last I heard, there was near-universal agreement that by far the most difficult engineering problem of the laser launcher was on the receiving end of the beam, not in the beam optics: how to efficiently use the beam energy to heat exhaust mass. Nobody has more than vague notions for the design of the beam receiver, I believe. Incidentally, I believe Kantrowitz's proposals generally envisioned having the vehicle carry the exhaust mass in tanks, rather than scooping up air for the purpose. The extension to using air results in a prettier system with potentially higher performance, but makes the beam-receiver design still harder. A "first generation" system probably would avoid the extra complexity and accept the lower performance. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry
farren@well.UUCP (Mike Farren) (01/20/86)
In article <8601170304.AA18252@s1-b.arpa>, Dale.Amon@FAS.RI.CMU.EDU writes: > A recent issue of Scientific American discussed phase conjugate lasers, and > two of the capabilities seemed made to order for a Kantrowitz laser launch > system. > > [Insert discussion here] > > I have the feeling that the advances in phase conjugate lasers have just > solved the most difficult of the engineering problems in this system. No, but they may have solved some of the theoretical problems. The engineering problems will come up when you try to BUILD one of the things. There's a fairly vast difference between a small lab laser and one of the behemoths needed to make laser launch work. -- Mike Farren uucp: {your favorite backbone site}!hplabs!well!farren Fido: Sci-Fido, Fidonode 125/84, (415)655-0667