At 100 kilometers per second, any object - be it a depleted-uranium slug, a carton of skim milk, or a throw pillow - packs kinetic energy equal to 5 gigajoules per kg, equivalent to 1195 kg of TNT, rather more than a ton of bang. In space the bang will be soundless, but it will still hurt.
(Someone in the back raises their hand to ask, '100 km/s relative to what?' For purpose of this discussion the answer is 'relative to whatever it hits.' And you should have figured that out on your own.)
This is the basis for kinetic weapons in space warfare. To regular readers of this blog it is no news; in particular I discussed kinetics in two segments of this series of posts. (Though the specific form of killer bus I described in the second post is a bad idea.)
I bring kinetics up again because they were long my weapon of preference for space warfare, for at least three distinct reasons, distinct in addressing different aspects of the overall problem:
1 - Missiles in space have effectively unlimited range, more than even Ravening Beams of Death.
2 - If you have the space technology to put large numbers of people in space, you pretty definitionally have the capability to throw lots of luggage, and throw it fast.
3 - There is reasonable scope for tactical maneuver in kinetics-dominant space combat, something that (it seems to me) is much harder to get in laser combat.
You may note that these three justifications are ranked by increasing meta-ness. The first is a general consequence of space speeds. The second hints at future history.
Any spacefaring society on a grand enough scale to have grand space battles has put generations or centuries of major effort into its overall space technology, whether its past has been peaceful or warlike. Long range lasers probably have more limited and mainly military applications. (Extensive use of laser propulsion does change this equation.) As a point of comparison, in the 19th century military technology tended to adopt new civil technologies, rather than being a primary driving force in itself.
The third point is most shamelessly meta. The people who fight wars are not concerned to make them interesting; that is only of concern to people inventing them in order to write about them.
Thus my picture of kinetic space warfare was kinetic in style as well as in weaponry. My starting point was the observation that if two ships are armed with similar-performance missiles, the more maneuverable ship has a crucial advantage. It can (at least in principle) maneuver to evade an enemy's missile, while the more sluggish enemy ship cannot quite evade its own missile.
Multi-ship tactics also look potentially complex - and therefore interesting. Ships maneuver like (3-D, vector) polo ponies to line up shots at opponents while avoiding the enemy's shots. The worst position a ship can be in is dynamically surrounded, so that a burn that carries it away from one enemy's missile envelope takes it right into another's.
The second worst position a ship can be in is to make a burn that accidentally carries it out of the fight at the point of decision, allowing the enemy to defeat its consorts in detail.
Lasers, in my vision, were purely secondary and defensive, intended for last ditch defense against incomings. There was a serious question in my mind whether a defensive laser armament was even worth carrying - the extra mass of a laser battery would mean reduced missile firepower, more sluggish performance, or both.
In this thumbnail description it sounds much like space fighters dogfighting, though the scale of the thing was such that battles would unfold over hours or days, even weeks.
I have not put any numbers to all this, except for the ones I gave at the very beginning, implying combat encounter speeds on order of 100 km/s. When I first came up with this image of space battles my assumptions were EXTREMELY operatic, as in photon drives with multi-g accelerations. Eventually I worked my way down to mere fusion torches in the low terawatt range.
A variety of holes, of various gauge, can be punched or burned through this vision of space combat, but it still represents one variation on the theme of what we all want for story purposes, Cool Space Battles.
I eventually abandoned this conception. Not because the propulsion was still operatic even in its later, more modest forms - any setting where you have space battles at all, other than near-Earth encounters in a primarily terrestrial war, is at least demi-operatic. But I came to suspect that the laser assumptions I was making were conservative out of all proportion to the propulsion assumption, yielding the equivalent of ships with gas turbine engines and smoothbore muzzle loaders.
By no means is that certain to be the case. Lasers and space propulsion are not inherently linked technologies (though under some assumptions they would be). And there is plenty of experience to show that battle performance of weapons often falls short of bench test performance, sometimes dramatically so. But I came to feel that it was special pleading to assume as much, and ended up with laserstars, as I have described them in prior installments of this series.
At some future point I might change my mind again.
Discuss. (Gentlemen, you can't fight in here! This is the War Room!)
The somewhat retro image is from Atomic Rockets - read also the discussion on the linked page.