Missiles and fusion rockets, etc
In reply to #5588 Missiles by Leonard Erickson
Sorry if the following is disorganized, but stuff is coming rather frequently, and I wanted to get *something* out while it was still topical. Also, I've missed *at least* one issue <sigh>. [email removed] (Derek Wildstar) writes: Subject: Missiles and Drives and Such >[email removed] (Leonard Erickson) writes: >> I can just about *guarantee* that detonating velocity is *far* below >> closing velocity. Which means that shaped charges are useles, as the >> missile impact will be moving faster than the detonation of the >> explosive. This kills HEAP and doesn't help HE much either. >I'm afraid that I'm no expert on explosives, but presumably the timing >of the detonation can be arranged to work out anyway. The penetration >mechanism of a HEAP charge is the jet of hot gas generated. To make it >work at high speeds, you need to have a proximity fuse that will set off >the warhead the right amount of time before impact, right? Nope. The jet moves at or perhaps *somewhat* faster than the detonation velocity. The problem is that the missile is moving faster than the jet can progate! (Yes, the jet's speed *does* add to that of the missile. but not significantly) The effects of the missile acting as a penetrator overwhelm it. (Why do you suppose those HEAP pentration curves flatten out?!) > And I'm willing to bet that velocity #2 is below closing velocity in > most cases as well. Which again makes HE a waste of time! Not quite. KEAP is kind of useless agains a ground target - it has lots of energy, but doesn't deliver it in the most useful form. So HE will be around as a ground attach missile that just happens to have a secondary anti-ship role. I was *specificly* discussing ship-to-ship combat. And as Bertil points out, you can always choose *not* to detonate the explosive, after all - it's still got it's kinetic energy. Yes, but it doesn't deliver as efficiently as something more solid would. Now as to the fusion rockets... Going with 20,000 km/s exhaust velocity and 480 gm/s fuel comsumption I come up with the following: Assuming 1 gram per cubic *meter* as the density of the exhaust (a figure that is probably *way* too low), a simple calculation gives a jet diameter of 5.5 *millimeters*. That much energy in that small an area is *not* going to slowed by any atmosphere on the mainworld charts. I also *seriously* doubt that it'll be slowed by rock. Not for the first few meters anyway. As I noted long ago, a fusion rocket exhaust will cheerfully bore a hole in whatever you land on. And with such a small diameter, landing legs aren't neaerly the problem that has been assumed. So what if you've got a puddle of boiling rock a few meters across? Especially since it may be subsurface. About the virus: Someone was wondering how a current day network could be immune from infection as someone else had claimed. It's actually quite simple. With most (if not all) LAN software out there, only the *supervisor* has write access to the directories containing the globally available executables (files in your *personal* directory are your own problem). A user *cannot* change them NOR CAN A VIRUS RUNNING ON HIS SYSTEM. This is because all access to the servers drives is by means of sending *commands* that are executed by the software running on the server. The server checks to see if you are allowed to use the commands *before* it executes them. We had several viruses get loose on a Novell LAN. They *only* infected the directories of a few people that had given each other *write* access to their directories. And several hard drives got infected when someone would log on from the infected accounts. But the rate of spread was slow. Now if the supervisor equivalent accounts had logged in from an infected machine, things could have been messy. But that's *why* you are careful about such things. If we can safeguard things that well at this TL, I rather doubt that later TLs will allow the sort of stupidity required for the Virus to spread. Bertil Jonell [email removed] writes: Subject: Re: Missiles Date: Wed, 9 Jun 1993 12:17:35 +0200 (MET DST) >> From: [email removed] (Leonard Erickson) >> Subject: Missiles >> I can just about *guarantee* that detonating velocity is *far* below >> closing velocity. Which means that shaped charges are useles, as the >> missile impact will be moving faster than the detonation of the >> explosive. This kills HEAP and doesn't help HE much either. > Wildstar adressed this. And I re-addressed it above. >> And if they punch through, they'll either create one *hell* of a shock >> wave in the atmosphere of the ship, or keep punching holes in anything >> that gets in their way until they are slowed to bullet velocities, or >> have completely vaporized. > Are you sure that they are capable of penetrating? If your data is correct >(and I have no reason to doubt it) it would seem that any missile sized >object would vaporize into plasma (along with a part of the hull) when it >hits. So the effect on the hull would be a crater and the effect inside the >ship a fireball and spalls flying around. No penetration of missile parts. There's a relationship between size/mass & velocity that basicly says if it is big enough and fast enough, then as the leading part vaporizes, the rest punches on through the plasma. That's what the meteorite protection schemes are based on. The small stuf vaporizes on impact with the foil shield. The bigger stuff punches through, losing a portion of its mass. >> Your several inches of armor could result in *more* damage than an >> *unarmored* vessel would recieve, simply because more of the projectiles >> KE would be transferred to the vessel! > You need a minimum level of armour to get the radiation down to manageble >levels. >> For a 5 ton projectile, > > Too heavy. Abolute maximum 2 tons (for 1 ton of warhead and one ton of >structure) I'd say. I picked it because the missiles are suipposedly *7* tons according to postings here. I allowed 2 tons for fuel and whatnot. >> V (g-hr) (m/sec) KE(ergs) (% of BC) kilotons diameter(meters) >> 1 3.528e3 3.112e19 .04 .7 kT 91 >> >> These figures should give an idea of just what sort of forces we are >> discussing. No *possible* chemical explosive will even be noticed in >> this sort of energy release. > Having 1000kg of HE in the missile means that you have a cheap (yes, >militarily speaking exposives are cheap) 1 ton lump of something that won't >work worse than any other 1 ton lump, but will work better in an atmosphere. Actually, it *will* work worse that something denser will. It's too easy to vaporize the explosive. :-) > 1 gturn is aprox mach 50. I'd like to see a missile designed for space >pull mach 50 in an atmosphere:) I assume they are designed for space since >most situations occur in space and protection against mach 50 would increase >the cost significantly. > (This also limits the use of KE missiles against ground targets) But we have designs on the drawing boards *now* for orbit to ground KE weapons (project Thor was one about 15 years back). You have to design a bit differently, but it is easily done. I *do* agree that you can't use space-to-space munitions as space-to-ground munitions. >> BTW, for a 5 *gram* projectile, we get 1 millionth the energy, or >> 1/100th the diameter. So change the diameters above to cm. Which means >> that 5 gm projectile (a BB) at the veocity give by a mere 1 g for 1 >> hour, will blast a 91 cm crater in solid rock. And likely do something >> similar im armor. How many 5 gm BBs can a 7 ton missile carry and how >> large a volume will they fill at "optimum" dispersal? > The cannister missile I did used 15000 10mm 10g tungsten spheres, since >I estimated that that would weigh the same as the laser/detonation warhead. > > (Btw: I'll check the crater sizes against the tEoNW, since they look a >little large for the kilotonnage even at optimum depth of burst:) Please do. Though I expect that they are within a factor of 2 which ios *more* than adequate. :-) BTW, that Sprint missile Wildstar mentions had accelerations in the *hundreds* of Gs. I see no reason why they can't build that sort of acceleration into missiles at TL 15. And with a fusion rocket, you could get a reasonable duration without outrageous amounts of fuel. Try dodging a 200 g missile sometime. :-) (Heck, a Sprint could ruin your whole day even if you *were* a TL15 wonder. :-) More on landing a fusion rocket.... Just either land on CG, or run the drive at something *incredibly* inefficient using the plasma to heat something else (LH2? Air?) which gets dumped out secondary nozzles at some horribly "low" Isp like 400-1000 (a fusion version of NERVA). That explains the need for an areodynamic shape, as you *can't* just ride down the jet without wasting *lots* of fuel (this isn't as importnat if you are using "air" as the working fluid). "clearing the throat" of the big jet would likely make anybody in the vicinity *real* unhappy. :-) BTW, the fusion drive *doesn't* have to be continous. It could be pulsed fusion, though that doesn't match well with the high Isp. Want a *real* nightmare? Under the old rules at the *high* tech levels, there was a mention of "photon rockets" or some such. This is a *very* high Isp drive. It's also dangerous as hell, because it amounts to having a laser as your drive. Sit down and figure out the energy density required of a laser that can drive a ship at 6 gs. Then figure out what happens to anything that gets in the way. :-) - -- uucp: [email removed] Internet: [email removed]