Missile Guidance and Sentinels

Talking here about missile guidance in 2300AD space combat.

To start with lets examine missiles in the real world. Early missiles were beam riders. They literally were told where to go by a radar beam. When this was the only method of guidance of course there was little point in anti-ship missiles, which is why they appeared much later than SAMs. Indeed early conceptions of a surface to surface missile were using the beam riding SAMs line of sight, preferably with a nuclear warhead ("special weapons", British Sea Slug and Sea Dart armed ships carried 10 "special weapons" each).

Anti-ship missiles in the 1960's were TV or ARM targeting, except if you bought Russian - they'd cracked the problem a decade before the west, your put a radar on the missile. The radars were fairly small and limited by the available power and extremely small dish size, so you only used it in the terminal phase of the attack and used inertial guidance and gave mid course updates (Active Radar Homing, ARH). The west copied the Russians and fielded their own weapons in the shape of Exocet (France), Sea Eagle (UK) and Harpoon (US).

Surface to air missiles simply couldn't fit the radar systems in them (until recently that is, the Anglo-French Aster and American SM-6 have their own radars). Hence modern missiles have Semi-active Radar Homing guidance systems. That is they don't beam ride, flying a preprogrammed (and updatable) course, but have no radar seeker of their own. They need the target illuminated by a targeting rader on the ship (or another ship). The illuminator need not be painting the target the for the whole of the SAMs flight, but it does need to be illuminated for a considerable period of time for the missile to acquire it and change energy state to intercept.

Modern surface ships usually have more than one illuminator, but not all illuminators can bear on all targets due to parts of the ship being in the way. The typical arrangement is two, one fore and one aft, giving the ability to engage two targets simultaneously to broadsides. Some examples are:

British T-42 DD: 2 illuminators, one fore, one aft (originally designed with 1, but the RN argued for a second doubling capability for a 4% increase in overall cost). T-82 had the same arrangement. The superbly designed T-43 had 4 illuminators for Sea Dart (2 fore, 2 aft) capable of engaging all 4 in broadsides, plus another 2 for Sea Wolf. If built she would have been the most capable air defence ship in the world, including US Aegis types.

US Ticonderoga has 4 illuminators, but due to their placement she can engage with 2 forward, 2 aft, or 3 broadsides. The Burke has 3, but due to better placement only drops one forward, and can still engage 3 targets in broadsides. The Japanese and Korean Burke copies have the same arrangement, but the Norwegian, Spanish and Australian Aegis ships only have two illuminators in the normal one fore, one aft configuration.

The French Cassard has 2 illuminators, both aft, and so can't engage targets directly forward. This is the same arrangement as the now retired Suffren and George Leyges. The modern mark of the Mascura has ARH, and so is independent of the illuminators (as is Aster on modern French ships and the T-45).

The Russian Slava has a single director for it main SAMs, located aft but well away from clutter, giving a fairly wide arc (Kara is the same but more cluttered). The reason for the single illuminator is that the main anti-ship missiles have their own illuminator forward. The Kirov is big enough to have a fore and aft illuminator for the SS-N-6, whilst the Udaloy's SS-N-9 have smaller illuminators allowing for the fore and aft arrangement, although the aft illuminator is much less cluttered than in a western ship.

Now, in 2300AD we never think of starship missile communicators/ directors, and indeed they are zero hull items. The targeting is just assumed to be done by TTA's. In fact a missile director is going to need to be a fairly substancial item, a fairly tight beam radar capable of illuminating a target upto a light minute away. What's more the things will have arcs.

Of course, some 2300AD missiles have sensors. Tosh. How the hell is a 30 sq meter passive array (which is already far too small) fit in a 0.7 sq. m missile nose? Sure, you could fit one, but the proviso would be 1/50th the range of shipboard sensor (range scales linearly to receiver area). Of course if they're reduced to range-0 sensors (the odd nature of the 2300AD sensor system) they're still useful when attacking larger signature targets (like Kafers), since they'd acquire 6 or 7 hexes from the target, and should be able to guide themselves in, but the kicker is none of the missiles in service have the processors to make sense of the data, these being multi-ton mass computers back on the starship.

Ultimately, a true Autonomous Kill Vehicle (hattip to Transhuman Space) could be built. However, the thing needs tons and tons of computational systems. A human fighter gets away with 4 tons of control equipment, and adding another 1 ton targeting computer gives us 5 tons. Adding this to a conventional 10 ton anti-ship missile still gives a useful turn of speed (about warp 6). However, not the problem, not enough hull for a sensor.

Invasion absolutely states that non-warping equivalents of these weapons exist (Sentinels), stating that all autonomous weapons suffer a -3 penalty to hit. Now this may be the true reason why AKVs don't exist, except of course it was good enough for a sentinel mine. An additional 5 or 10 million for a stutterwarp is less preposterous than blowing up a 5 million livre passive array with the det warhead.

A less preposterous sentinel might be a automated vehicle (warping or non-warping) controlling a constellation of weapons (submunitions, automated fixed weapons and even warp equipped missiles, it has the sensor range). Of course, this opens the door to AI warships, which may have been why GDW didn't dwell on the fact. The sentinel (and armed robot freighter in SotFA) have let this genie out of the bottle though. Go nuts.