Much of the comment thread on Part XIII of this series, The Human Factor, turned into a discussion of 'laserstars.' While a thread of 631 comments (so far) might seem to have given this particular debate the full Rasputin treatment, I am instead going to use it as a pretext for another front page post. (And an arguably wretched pun in the title.)
Laserstars, as the term has come to be used on this blog, are military spacecraft designed to carry and deploy a single powerful weapon laser installation of the maximum practical aperture and power. In their 'ideal' form they would be drones, robotic in the broad sense that includes remote control from a separate command ship (or ground station, etc.).
A couple of provisos are needed. In conceptualizing laserstars I chiefly have in mind classical-style lasers operating broadly in the optical band (IR through UV), whose beams are passed through telescope-style aiming and focusing optics. It is this telescope, more than the individual laser itself, that provides the distinctive feature of a 'laser cannon' - if the available power is more than a single laser can handle you could easily have an entire bank of lasers all firing through the same optical system.
If you have lasers zapping in the far UV or X-ray bands, the aiming optics become quite different. My impression is that the main telescope becomes long and narrow instead of short and wide. In either case, however, the optical system of a laserstar is implicitly too big, relative to the whole spacecraft, to be mounted in some equivalent of a turret. Instead it is 'keel-mounted,' and gross aim is achieved by pointing the entire spacecraft toward the target.
The general argument for all this is that the effective range of a laser is in linear proportion to the aperture of its optical system. Double the telescope aperture and you double the range at which the system can achieve a given spot size and zap intensity.
But a further proviso is that the largest practical laser installation and optical system are in fact large enough that you can only conveniently mount one aboard a spacecraft that is itself of practical size for war service. If it turned out that the most cost-effective size for the spacecraft, with its drive engine and power supply, could carry half a dozen of the 'largest practical' laser optical installations, that is how many it would carry.
Finally, a broader proviso is that a laserstar is not to be regarded as a 'space warship.' It is perhaps more nearly analogous to a railroad gun, deployed to a position where it can make use of its long range firepower while being supported by other spacecraft. In spite of the image at the top of this post, I don't see laserstars primarily engaging in combat in low orbit around a planet, but rather at the outer edge of a planet's strategic envelope, either defending it against attack from elsewhere or maintaining a blocked by cutting off communications with or relief from elsewhere.
In the comment thread previously linked, commenter Tony raised several serious issues with respect to the laserstar concept. These range from the technical to the meta, and I'll discuss what I see as the most critical objections in that order. (The expressions of these issues, however, are mine, not Tony's.)
Precision and the battlefield don't mix. There is a lot of precedent for the general observation that pinpoint accuracy is hard to achieve amid the turmoil of combat. On the other hand, in the contemporary era precision-guided munitions have demonstrated capabilities that would have startled military observers of an earlier era. And laserstars are not a rock & roll weapon, which is why I wouldn't expect to see them in action in (relatively!) crowded planetary space. They are long range artillery for use against targets that must travel through deep space.
Monocultures are vulnerable. This principle of ecology also applies to warfare: Dependence on one weapon generally makes you vulnerable to an enemy who can make use of several. A laserstar by itself is indeed dangerously inflexible. In its 'pure' form it would be deployed only in a constellation containing other spacecraft and weapon systems.
In other situations I would expect to see only partial application of the laserstar concept - for example, I suspect that multi-mission military spacecraft (broadly 'cruisers') would carry a single big keel-mounted laser mirror, for long range zapping power, while also carrying a few smaller mirrors, along with kinetics, for fighting in more chaotic environments.
And, of course, having said this, in any given setting it is plausible that things have worked out otherwise. Laserstars or their like may have no place in the order of battle, for perfectly credible reasons ranging from inability to combine extreme steadiness with extreme power levels, to a power-political environment in which the ability to zap things at 30,000 km has no military significance.
Space armadas have no place in the plausible midfuture anyway. On this point I plead guilty; significant military operations beyond Earth orbital space are an inherently operatic concept, only to be expected when there are substantial human populations, strategic assets, and even polities scattered across space.
This point has a couple of sub-implications. Since we are somewhere beyond the plausible midfuture anyway, techlevels are presumably higher, especially propulsion performance and thus the ability to sling kinetics.
A subtler argument also stems from being beyond the 'plausible midfuture:' A civilization with colonies and space armadas has evidently solved the problem of sending large numbers of people into space - weakening the argument for automated spacecraft as against human crews.
The specific response to these points would be that higher techlevels presumably apply as well to lasers and automation. But really this aspect of the debate takes us into an issue broader than just laserstars, namely the balance of technology and the flavor of technology in space-operatic settings.
I used to have an SF paperback that featured, among other things, a reconditioned World War II heavy cruiser armed with smoothbore muzzle-loaders. This combination was justified by a post-apocalyptic setting, but in general we want our future technologies to have an internally consistent techlevel, or at any rate feel as if they do. What constitutes this internal balance is itself, of course, a matter of speculation.
Also, if you are a regular reader of this blog you probably have a bias toward 'realistic' space technology, in a sense that is as much aesthetic as strictly technical. Roughly, you want spaceships that are broadly recognizable as industrial products - at least descended from the plausible midfuture, even if that era has become the plausible mid-past.
I will deal further with this subject (but not necessarily laserstars) in upcoming posts.
Via Atomic Rockets, this Martin-Marietta concept for an orbital laser ABM platform gives the general impression of a laserstar, but is already notably retro - probably of 1980s vintage. We'll delicately ignore the visible-in-space beam.