Second in a sporadic series.
Space is vast and dark, so for diurnal creatures like us it seems like a good place to hide in. But the darkness of space is exactly why it is mostly not a good place to hide: Objects such as spacecraft tend to be bright, if not in visible light then in the infrared. Drive engines are really bright, as is any large power source not perfectly efficient. Thus the popular rule of thumb in haunts like SFConsim-l, that 'everyone sees everything.'
In the rocketpunk era, before automated detectors, this was not so much of a problem. Human lookouts get bored and nod off or goof off; even if conscientious they may slip into a sort of highway hypnosis and miss a faint 'star' drifting across the starfield. Automated scan is annoyingly non-deficient in these respects.
Physics and technology are similarly unfriendly to decoys. For an accelerating decoy to be mistaken for a ship it must have the mass of a ship, or else passive scan will reveal a suspiciously low power backwash. But if the decoy is as big and heavy as a ship, with a drive engine as powerful as a ship's drive, it will be more or less expensive as a ship, and you may as well go the rest of the way and arm the thing.
A great many electrons have been spilled in vain trying to wiggle out of these conundrums. Of course with a sufficiently large array of oscillating hands you can defeat any inconvenient physics; tactical FTL for example, or (less problematic from a causality standpoint) discontinuity fields that space subs can dive into.
For this series of discussions, however, I am ignoring outright magitech and concentrating on plausible midfuture technologies using known physical principles. Yes, 'plausible midfuture' is a slippery phrase (and a topic for a future post), but it gives us something to hang our hat on. The realm of coilguns and fusion drives is at least defined enough for people to know what they disagree about. In this realm the arguments outlined above are pretty robust.
That said, politics is more complicated and difficult than physics, and so is warfare. Targets will go out of their way, perhaps literally, to be unhelpful. 'Stealth' in the currently popular sense of making yourself invisible to tracking tech looks like a nonstarter, but there are many other ways to be stealthy, even in space.
In the comments to Part I of this series, commenter Mark brought up orbital decoys. The relationship between mass and thrust that gives away low-mass accelerating objects does not apply to non-accelerating objects, in orbit for example. Long range scan then reveals only how bright things are, not how heavy.
This generally is an advantage to the defender. We can assume that in a space setting, important planets (or moons, whatever) have a lot of orbital clutter, from major stations to space junk, as well as defensive forces and decoys. It will be hard for an approaching attacker to tell which is what. Even visual imagery may not be helpful, if warcraft are not obviously and outwardly different from civil types (or can be made so). The Beziers solution, blow it all away, may not be practical for a variety of reasons.
For deep space attackers hiding in the clutter is problematic, but there are other forms of stealth and deception. In Heinlein's Between Planets the Venus rebels seize Earth's military-civil orbital station, including its stockpile of nukes, by arriving aboard a scheduled space liner. Better security measures should have foiled this, but you can say that of many successful operations, and it is not hard to come up with scenarios for military raiders approaching on civil orbits.
For major forces this is harder to bring off. Vast space armadas probably won't be mistaken for Hanseatic merchantmen, but there is the opposite ploy of using relatively cheaper civil craft (perhaps obsolescent ones) to bulk up a task force – or simulate one, drawing the other side into a wild goose chase. How this works depends in part on secondary factors that are dealer's (or author's) choice. Drive engines may have a distinct signature that identifies models or even individual ships, but this is by no means a given. Just don't have 'drive signature characteristic of a Vikrant class cruiser' and 'estimated drive power of 2.5 to 7.0 gigawatts' in the same story. (Or at least have a quick explanation for the differing specificity of results.)
All of these deceptions are on the operational scale, but there are also smaller-scale tactical or 'micro-tactical' deceptions. Opaque 'smoke' can throw off precision targeting. The hidden ship presumably can't fire lasers through it, but it can launch missiles through it (at least if some other ship is providing targeting data). A small target-seeker warhead probably does not carry a scan suite equivalent to that carried by a large warcraft, and cheap flare- or chaff-like decoys only need to confuse its sensors for a few second, and create a few meters' worth of error, to turn a hit into a miss.
In space, everyone sees everything. But in war, no one can be quite sure what they are seeing.
Related links: Part I of this series is here. And some of these points grew out of discussion of space piracy here, here, and here.
Update: This post also generated discussion at SFConsim-l, much of it covering different ground from the comment thread. Yahoo Groups has lame threading, but the discussion spins off from my pimping post here.
Monday, June 15, 2009
Second in a sporadic series.