Anti naval Rakurai strikes

I strongly doubt that the OBS, current or former, is a high mass/low velocity system. Rather, I suspect that it's a low-moderate mass/variable velocity system - and that it usually operates at moderate to higher velocities, depending on just how big a bang is desired.



@Louis - if the ship you want to target is engaged in combat with friendly units, you're not going to be shooting KEWs from orbit at them. You're just not - after all, you had plenty of time to drop rocks on them before your ships got anywhere near them. And, if you are going to take a shot at a ship or ships engaged with friendlies, you're only going to do it if you've got an extremely high velocity/extremely low mass projectile available.

This describes what happened at the battle of Midway when a bomb (100 or 500LB) hit near the stern of the Japanese carrier Akagi:

Although Akagi sustained only one direct hit (almost certainly dropped by Lieutenant Commander Best), it proved to be a fatal blow; the bomb struck the edge of the mid-ship deck elevator and penetrated to the upper hangar deck, where it exploded among the armed and fueled aircraft in the vicinity. Nagumo's chief of staff, Ryunosuke Kusake, recorded "a terrific fire... bodies all over the place... Planes stood tail up, belching livid flames and jet-black smoke, making it impossible to bring the fires under control. Another bomb exploded underwater very close astern; the resulting geyser bent the flight deck upward "in grotesque configurations" and caused crucial rudder damage.

https://en.wikipedia.org/wiki/Battle_of_Midway

If a small bomb can do that, what can a very large rock do if it hits the water near a ship?

Keith_w wrote:This describes what happened at the battle of Midway when a bomb (100 or 500LB) hit near the stern of the Japanese carrier Akagi:

Although Akagi sustained only one direct hit (almost certainly dropped by Lieutenant Commander Best), it proved to be a fatal blow; the bomb struck the edge of the mid-ship deck elevator and penetrated to the upper hangar deck, where it exploded among the armed and fueled aircraft in the vicinity. Nagumo's chief of staff, Ryunosuke Kusake, recorded "a terrific fire... bodies all over the place... Planes stood tail up, belching livid flames and jet-black smoke, making it impossible to bring the fires under control. Another bomb exploded underwater very close astern; the resulting geyser bent the flight deck upward "in grotesque configurations" and caused crucial rudder damage.

https://en.wikipedia.org/wiki/Battle_of_Midway

If a small bomb can do that, what can a very large rock do if it hits the water near a ship?

The better example would be "Crossroad's" test "Baker" in 1946. On the megaton scale, of course.

Simply speaking - the kiloton-scale surface blast would destroy all wooden ships in the range of 500 meters from ground zero and dismast them at range of about the kilometer. The KH's would probably survive (but most of its crew would be killed or disabled by overpressure) close to 250 meters from ground zero.

OrlandoNative wrote:Exactly. Unless the velocity is extremely high, the water will splash. As far as wave action goes in deep water, remember tsunamis. They are barely detectable in deep water; the destructive wave occurs when the energy reaches *shallow* water.

No, they wouldn't. The actual calculation in 1980th showed, than even the multimegaton-scale blasts are incapable of creating the equivalent of tsunami wave. Simply speaking - the problem is the influenced area. The underwater earthquakes that produce tsunami waves worked on much greater area than nuclear blasts. Water aren't very compressive; in therm of nucelar explosion it would react as a solid object. The shokwave would be transmitted, but the actual splash would be pretty limited.

Ah, an engineering topic for my first post. Love scifi engineering. So a couple of things.

1 - The strikes on Alexandria were definitely in the high kiloton, low megaton range and penetrated pretty far into the earth. That indicates a lot of mass, as well as velocity. (Low mass, High V gets you Tunguska; high mass, medium to high V gets you Yucatan)

2 - High Frontier, and tactical KKV's, are tungsten 'telephone poles' which gets you tons of tnt yield by just dropping from orbit. Grav acceleration to a decent percent of light speed can get you into the kt range. (~V^2) But the penetrator must survive the atmosphere and penetrate into the earth to cause the damage seen around Armageddon Reef.

3 - The references are to "rocks", not KKV's. So the "rocks" must be pretty large to cause the damage seen.

4 - Pacific nuke tests showed that kTrange surface or near subsurface nukes did not cause large waves. In fact the Independence (CV-22) survived 560 yards from ground zero of a 23-kiloton air blast of a fission weapon, then survived 1390 yards from a 23kT underwater blast. (Note that the Saratoga (CV-3) was 400 yards from the underwater blast and did sink afterwards.)

So what does this all mean for using the Rakurai against naval targets on Safehold?

Well, considering the damage done to Alexandria, its pretty clear that the ammo is very large rocks at medium to high speeds - meaning also that some acceleration is involved. This would create a large thermal pulse that would definitely fire up wooden ships, and then a large wave (tsunami) that would probably take care of a very large area.

Now as for tricking the system into firing, hey, that's how you experimentally determine the thresholds. Just bring a ECM device into the middle of an enemy fleet and increase the ECM emissions until the Rakurai fires.

Killing two birds with one stone...

A good analysis!

CRC wrote:Now as for tricking the system into firing, hey, that's how you experimentally determine the thresholds. Just bring a ECM device into the middle of an enemy fleet and increase the ECM emissions until the Rakurai fires.

Killing two birds with one stone...

The problem is, that we didn't knew, what would actually happen if the Rakurai would saw something suspicious. It MAY just fire at this - but quite probably, that there are some dcecision-making scheme, that would be immediately activated. The tactical AI, for example, or even the Archangel personality from storage - to analyse the situation and actually decide, would the strike solve the problem?

Please keep in mind that the current OBS and the one used by Langhorne to destroy Alexandria are two different animals, according to the Pearls of Weber. The original was built in the Hamilcar, then launched and fired the very same day, so it was a relatively crude system.

The current OBS (which we have an account of being used) has the capability of being much more selective - which probably means it's a relativistic device (or six devices) that "drop the bar" meaning they use relatively low mass and high speed to accomplish the amount of damage desired.

So it isn't dropping rocks anymore. It's firing precisely manufactured ammunition at variable relativistic speeds. Merlin has figured that out, which probably has him even more worried about waking up something that might decided to use it, since a single shot could destroy Tellesberg, for example. Slow down the velocity and it would be effective in taking out smaller targets with less collateral damage, but it's deadly!

And yeah, we all daydream about getting it to fire on the Temple, but it's a pretty good bet that the Temple is the one target on Safehold it won't fire on. Bummer.