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From: Dale.Amon@FAS.RI.CMU.EDU
Newsgroups: net.space
Subject: Laser Launch
Message-ID: <8601170304.AA18252@s1-b.arpa>
Date: Thu, 16-Jan-86 20:23:07 EST
Article-I.D.: s1-b.8601170304.AA18252
Posted: Thu Jan 16 20:23:07 1986
Date-Received: Sat, 18-Jan-86 00:59:12 EST
Sender: usenet@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 42

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.