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Pearls of Weber

A collection of posts by David Weber containing background information for his stories, collected and generously made available Joe Buckley.

Off-bore missile targeting

Just exactly how does "off-bore" missile fire work? You originally specified a "120-degree" off-bore capability for the Shrike. These days, you seem to be specifying a greater capability. Would you care to explain?

OK. The original Shrike's capability to fire across a total 240-degree arc from its single bow-mounted tube was basically a hardware fix to the missile itself. The Shrike faced a particularly demanding requirement if it was going to use its bow-mounted launcher against targets in what would normally have been a broadside firing aspect. The problem was the width of its wedge, since the missile had to get clear of the wedge before it could bring its own drive up. For a target in the traditional field of fire of a bow chaser, that wasn't any particular problem, since the launcher kicked the missile out at a very high rate of acceleration and into the broadest aspect of the wedge. Because the throat of an impeller wedge is so much "deeper" then any other aspect of it, and because the Shrike's missiles were smaller than standard destroyer missiles (with correspondingly somewhat smaller wedges of their own) they could fire up their drives sooner, and then angle across the front of the wedge. To fire into the traditional broadside arcs, however, was a much trickier proposition, and the solution adopted was to build the Shrike's missiles with somewhat extended drive endurance (which cost both money and mass penalty on a per-missile basis) and to improve the fire control capability and the missile telemetry capability of the Shrike. The result was a missile which launched as if against a target directly in front of the LAC, accelerated well clear of the firing vessel's wedge, and then tracked back to find and engage the target which was "behind it."

This capability was available, initially, only to the Shrike, because it depended (at least in its initial incarnation) on the fact that the missile was being fired out of the throat of the wedge, where the wedge geometry worked for it. A missile fired out of a broadside tube, on the other hand, first had to clear the sidewall (10 km or so from the side of the ship), then clear the entire width of the impeller wedge (up to another 150 km, for a superdreadnought), and then reorient, kill its forward momentum away from its target, establish its telemetry link to its mothership when it was probably passing either above the roof or under the floor of the impeller wedge, and then acquire its target and attack normally.

The possibility of a missile doing this had been discussed as a theoretical consideration for a long, long time. At the time that it first came up for serious debate, however, the missiles available were much cruder, with far less capable drive systems and poorer fire control, driven by poorer shipboard fire control and communications ability, all of which equated to a considerably shorter effective missile range (remember the relatively short range at which Nike engaged in Edward Saganami's last battle). Frankly, the technology wasn't up to handling this sort of a maneuver without the loss of a significant percentage of the missile's total range and an unacceptably high rate of "lost" missiles which simply wandered away without ever "seeing" their target or being reacquired by the telemetry links of the ships which fired them.

As I'm sure you'll recall, I have referred several times to the fact that prior to Honor Harrington's time, naval technology and tactics had plateaued (or, if you prefer, stagnated) for several centuries. (This is what is so likely to turn around and invite the Solarian League on the butt, since they haven't UN-plateaued even now.) Increases in capability had been incremental (at best), and many of the limitations which might have been overcome by application of new technology had simply been accepted as "the way things were." What happened with the Manticorans was that once they had provided the Shrike with off-bore capability, the lightbulb suddenly went on, and they decided that there shouldn't be any inherent reason why they couldn't do sort of the same thing for other missile tubes. The real key to make it work, however, was yet another application of the Ghost Rider mindset. Essentially, what the RMN has done is to take the tethered decoys which have been part of the standard naval war-fighting toolbox for a long, long time, and enormously improve their capabilities. This is another offshoot of the miniaturization they've been pursuing for quite some time as part of the entire Ghost Rider approach. A Manty "tethered decoy" is considerably larger than the tethered decoys deployed by other navies, because it is also much more than a simple defensive EW platform. Instead, Manty "tethered decoys" are full spectrum communications platforms, sensor platforms, and defensive platforms (remember what the Jessica Epps did to the Andermani recon drone that had sneaked in on her, for example). When a broadside missile is launched even directly away from its eventual target, it is monitored and controlled on a continuous timesharing basis using the deployed "tethered decoys" as relays even while it is passing across the communications barrier of the firing ship's wedge. The improvements in missile drives -- in acceleration, endurance, numbers of drives, etc. -- and onboard seekers and improved maneuvering computers, coupled with the ability to keep the missiles under shipboard control throughout the rather complex maneuver required to fire them 180° away from their targets and still have them find those targets, is what permits the sort of fire Hexapuma turned out in Shadow of Saganami. It's also one reason that the Roland-class ships have their missile tubes arranged the way they do. It's much simpler to execute this type of maneuver out of the bow or stern aspects of an impeller wedge than it is out of a broadside firing arc, and destroyers' "tethered decoys" tend to be smaller and less capable than those of cruisers and capital ships. The Roland could have been designed around this type of firing technique, but since there were already some pretty compelling reasons to group the missile tubes the way they had, BuShips made a virtue out of necessity and was able to provide full broadside fire for all missile tubes with considerably less onboard and captive platform mass and volume.

One big reason why it took so long for anyone to develop this sort of an approach was that, first, the technique for firing double broadsides by spinning the ship on its long axis was developed long ago, to permit a similar weight of fire (if at a lower rate of fire) within the limitations of the then available technology and missile drives. That technique had been around so long and was so well established, that it really didn't occur to anyone that they needed to find a better way to do something they could already do. Secondly, there was the problem of adequately controlling the numbers of missiles which double broadsides implied. Prior to the development of missile pods, ships simply didn't have the control links to allow them to control outsized broadsides' worth of missiles. Once the sheer numbers of missiles which had to be controlled in a pod environment became apparent to the RMN's designers and the analysts in BuWeaps, it was obvious that a massive upgrade in fire control ability was necessary. And once that upgrade was made available -- not an easy task, and yet one more of the huge number of projects bundled under the "Ghost Rider" label -- it was also available for controlling off-bore double broadsides. So what we actually have here in the case of a ship like Hexapuma is the convergence of several different technological projects and capabilities, coupled with a mindset which has acquired the habit of asking that incredibly irritating question "Why not?" about restrictions which "everybody knows" simply can't be worked around.