Nyrath

Re: Hard sci-fi adventures?

This is one of those topics that eventually comes up whenever there's long discussion of the effectiveness of various firearms. The hydrostatic shock concept seems very popular still' date=' even though AFAIK it's been disproven. Is it back again? (As in, what's "recent"?)[/quote']

I just knew that the thread was doomed once somebody mentioned "hydrostatic shock."

 

There have been some flamewars on the topic that have gone on for years.

Re: Hard sci-fi adventures?

IMO that isn't as far fetched as one might think. There were a few old scifi series from the 50-60's I remember reading that had the sword returning because of spacers. I wish I could recall more' date=' like and author or title, but one story (series?) had the a short sword based on the gladius as the prevalent primary weapon on starships.[/quote']

It was also popularized in the ancient RPG "Traveller." The weapon of choice for boarding actions on a starship was a cutlass.

Re: Hard sci-fi adventures?

The hydrostatic shock and near-complete transfer of energy into that area of the target...

ohno...he said the "H-S" phrase...

Re: Hard sci-fi adventures?

There's a scene in Risen Empire where what at first appears to be a space battle turns out to be an encounter between microscopic remote controlled listening devices' date=' (bugs), and microscopic drones intended to destroy such devices.[/quote']

I remember that scene! You are correct, that would make a nifty scenario.

 

Imagine the epic journey across the dirty floor, trying to reach a critical component. Watch out for the cockroaches and the Ship's Cat.

 

Imagine a variant that was based on the ancient movie "Fantastic Voyage." Our Heroes are miniaturized to microbe size, and are injected into the patient. Instead of minature people, they could be teleoperated virtual reality microscopic drones, like the ones in Risen Empire.

Re: Hard sci-fi adventures?

This is where the concept of the flechette gun comes from. It is a gun that shoots projectiles that move fast enough to shred flesh' date=' but are too small to pierce bulkheads or damage ships systems.[/quote']

 

Mike Van Pelt says that if protecting the spacecraft from clumsy shots has priority, frangible rounds may be the answer. These have been suggested for use by armed airline pilots, who also worry about the damage done by stray rounds. The Glasser Safety Slug was invented back in the 1970's, the current state of the art is the MagSafe. The good news is that they affect human targets far more effectively than spacecraft hulls. The bad news is that the penetration is reduced to a point where the space pirate's arms can offer their torso significant protection. And if the pirate is wearing body armor your handgun has become almost worthless. To make it worse, certain types of space suits are almost as good as body armor.

 

Nightcrawler points out that revolvers might be popular in free fall, since other weapons eject their spent cartridges. Hot brass flying around the compartment could cause all sorts of problems. A cartridge floating inside a control panel and shorting out a critical component could ruin your entire day.

Re: Hard sci-fi adventures?

Projectile weapons inside a space ship are problematic at best. That's why a lot of stories use energy weapons' date=' on the theory that they are less destructive in the terms of hull breaches and ricochet damage.[/quote']

Well, as it turns out, holes in the hull will let air leak, but it will be some time before it becomes a problem

 

whooshTime = ( gaspFactor * vol) / holeArea

where

gaspFactor = 1.4 for 80% pressure, 4.3 for 50% pressure, 29 for 1% pressure.

whooshTime = time for cabin pressure to drop to specified fraction of initial value (seconds)

vol = volume of air in the cabin (yards^3)

holeArea = area of the breach (inch^2)

 

It will be the better part of an hour before the pressure drop from a single bullet hole becomes a problem.

 

James Borham has another often overlooked concern: Speaking of bangs, one thing that virtually every sci-fi writer ignores is the fact that any boarding party is going to need hearing protection. Loud noises (like gunshots) are bad for ones hearing, and narrow metal corridors make great echo chambers, increasing the effect. A modern SWAT team uses suppressed weapons not for stealth, but to protect their own hearing. Anyone firing a weapon on-board a starship is going to have the exact same problem, only many times worse.

 

http://www.projectrho.com/rocket/rocket3l.html

Re: Hard sci-fi adventures?

The US Army is developing something called the Active Denial System, which is basically a pain ray used for crowd dispersal.

I always thought it would be a nifty thing to install in the corridor outside the control room of your starship, to provide a rude surprise to space pirates.

Re: Rail gun damage?

Yes but I assume torch ships with acceleration to mid point flip and slow down. Which makes bullets in the samr bracket again they don't get the extra G's but on the other end they do speed up towards planets and other massive bodies.

Yes, this is true if you and the enemy are engaging around a stationary point. Say if force Alfa is trying to enter Mars orbit to drop bombs, while force Bravo is in orbit around Mars trying to defend it.

But if force Alfa is at the midpoint flip in between Earth and Mars, and is intercepted at that point by force Bravo also doing a midpoint flip, the relative velocities between the two will be very high indeed.

Re: Rail gun damage?

If it's a spaceship weapon (which I think is how the thread started)' date=' it's worth pointing out that the relative velocities of hostile spaceships are likely to be several km/s. That contribution to impact velocity is rather greater than the ~1 km/s that is contributed by the weapon itself.[/quote']

Indeed it will.

 

And for those who didn't look closely, the important word is relative.

 

If the enemy cruiser Sky Trash is sitting "stationary", and you fire a railgun shell through it at 3 kilometers per second, it will do X amount of damage.

 

If the railgun shell is sitting "stationary", and the Sky Trash is flying at 3 kilometers per second and hit the shell, it will do an identical X amount of damage.

 

The key is that in both cases the relative velocity between the shell and the Sky Trash is 3 kilometers per second.

Re: Rail gun damage?

since it's based on hexes per segment it should be logarithmic in function by the nature of movement.

Yes, I see. That will work.

Re: Rail gun damage?

3200 / 5 = 640 d6 of dammage

I haven't checked the math, but did you take into account the fact that damage dice in the Hero system is on a logarithmic scale, not a linear one? I don't know, I'm asking.

Re: Rail gun damage?

So, if we posit that for mass driver weapons, then the maximum effective range is about 2-3 seconds travel time. An effective system would take into account all the possible vector shifts a target could make in that time, and bracket them with multiple mass drivers...so let's say an effective system has 20-40 "barrels" bracketing a fire zone in order to maximize chances to hit.

 

I remember reading somewhere that the practical speed limit for a mass driver is probably around 150km/sec. Applying that to the scenario gives an effective range of 300-500 km perhaps. At those velocities the projectiles could be fairly small, say in the 20-30mm range.

Well, as it just so happens, I was playing around with creating an equation to express the effects of weapon flight lag.

http://www.projectrho.com/rocket/rocket3y.html#dodging

H = Cm / (0.7854 * a^2 * ((Dm / 299,792,458) + (Dm / Wv))^4)

H = maximum percent chance to hit target given light-speed lag (0.0 - 1.0 with 1.0 = 100%)

Cm = target ship's mean cross section (m2, for a purely convex object this is approximately 1/4 of the surface area)

a = target's acceleration (m/s, where 9.81 = 1 g)

Dm = range to target (m)

Wv = weapon velocity (m/s)

To use it in this case, you have to know the mean cross section of the target ship, and its acceleration (to figure how much it can dodge), as well as the range to the target and the velocity of the shot.

If the individual shot was a 30 mm sphere composed of depleted uranium traveling at 150 km/s, it would have about, ummmm, {works with slide rule} 2.5 x 10^10 joules. This is about the same as 6 tons of TNT, a bit more than an average lightning bolt, and about three times the Oklahoma City bombing. Yes, that will do.

30 mm sphere = about 114 cubic centimeters

depleted uranium = about 10.1 grams per cubic centimeter

mass of sphere = about 2.2 kilograms

Kinetic energy = 0.5 * mass * velocity^2

Kinetic energy = 0.5 * 2.2kg * 150000m/s^2

Kinetic energy = 24,750,000,000 joules = 2.5 x 10^10 joules

Look it up on the boom chart

Re: Rail gun damage?

I'm still wondering if coilguns aren't a better option' date=' as IIRC they don't involve sending a current through the projectile[/quote']

Yes, every expert I've talked to say coilguns are superior. It's just that they are orders of magnitude harder to make.

 

The arc you strike with a railgun causes severe rail erosion. In current models you have to replace the rails after a few shots. On the other hand, we have close to weapons grade railguns now.

 

Coilguns have no such erosion. However, since each coil has to reverse its polarity as the projectile passes by, you need power switches capable of handling huge power loads. They are still trying to invent a switch suitable for a weapons grade coilgun, currently available switches are not good enough.

 

Coilguns will still have waste heat because of the second law of thermodynamics, but probably not anywhere near the waste from a railgun.

Re: Rail gun damage?

Not meaning to offend you' date=' Nyrath, but where the heck are you getting [i']any[/i] of your ideas from? I mean, don't get me wrong, your math is great, but this 'causes an explosion' crap is, well, crap; the primary side effect of modern-day mass accelerators -- railguns -- is a short-range EMP burst out the front end due to the electromagnetic acceleration of a slug of steel. No continuing electrical explosion; that isn't how the damn thing works. No 'red-hot slug'; it's a piece of steel suspended in and sent down a tube by computer-controlled electromagnets that takes it from 0 to a zillion m/s in the time it takes to sneeze.

Well, maybe I was being overly dramatic , but have you seen these images?

http://thetension.blogspot.com/2008/02/us-navy-demonstrates-worlds-most.html

Keep in mind that we are talking about railguns, not coilguns. With railguns, the rails strike an arc with the sabot. A tremendous amount of head is generated. So much so that the rails have to be replace after a few shots due to severe erosion.

Does this affect the ship/base? Yes; the back-thrust from accelerating a 50g piece of metal to Mach 25 is considerable' date=' and yes, it [i']may[/i] not do much more to a 250 tonne ship than nudge it off-course, but the firing still has to be taken into account -- like A-10 Warthog pilots have to, especially if you're going for broke. But if it's a ship, then the ship's thrusters are already set to move around 250 tonnes; adjusting for weapons-fire is going to be computed into the ship's piloting equations.

I don't think you understand. In theory you can use a spray can of underarm deodorant as a ship thruster, it will just take a few days to change the ship's orientation a few degrees. By the same token, a thruster rated to move a 250 tonne ship might still take a day or so to stop your ship from spinning like a top due to the last railgun firing.

It all depends upon the specifics: how massive is the railgun round, how fast is it moving, how many rounds are expended, how massive is the ship, and how much thrust the attitude jets can produce.

The question of whether or not the target ship can dodge' date=' however, requires a bit of forethought.[/quote']

It does not have to. If you are under fire from an enemy, you do random evasive maneuvers just on general principles. You don't sit quietly until you see the shot.

 

 

First' date=' does the target know they've been fired upon?[/quote']

Yes. There is no way to hide the firing of the slug. I take it you've never read the page on my website explaining why the experts I've consulted have concluded that there ain't no stealth in space. If nothing else, the weapon turret will light up like a strobe light in the infrared spectrum due to waste heat.

 

Second' date=' how long does it take the slug to get from Attacker to Target? Third, if #1 is 'no', can they detect the round, however big it is, in time to pilot the ship out of the way? In space, once the round is fired, it's going to go down that line for quite a while, until/unless something happens, e.g. gravity effects, etc. Presuming a low-space-tech environment (which I think we are, since we're still using mass weapons), I'd imagine multiple 'likely trajectory' shots instead of just one round getting spat out. "At the speed they're going now, they can only go in these directions. Lay fire down on this path; they'll likely get hit by at least [i']one[/i] of 'em ..."

 

The people I know who have made space combat simulations see such weapons more as a way to create "terrain" in space. You fire wads of shots in certain directions to herd your target the way you want it to go (usually in front of your main guns). The railgun shots deny certain vectors to the target (at least if they want to avoid being hit), so they are forced to move where you want.

Re: Rail gun damage?

Do those military spy sats take video from orbit at 5cm resolution? And will there be enough people or computer power on board a ship to watch for moving objects effectively a few pixels in size' date=' over the entire field of view?[/quote']

If they wanted to take video, I see no reason why not. And even if there was a technical reason that orbital video at 5 cm resolution is not currently feasible, I'm sure it will be possible by the time there are interplanetary warships. After all, a mere fifty years ago any kind of satellite at all was beyond the state of the art. What will the state of the art be fifty years from now?

 

Enough computing power? I think so. There are computers currently available today that are the size of a pack of cigarettes. You could have a room full of these, and have twenty or thirty watching each of the enemy's gun turrets.

Re: Rail gun damage?

Just how big do we expect the projectiles to be? I keep thinking of something smaller than a roll of dimes' date=' based on what I've read. Is a projectile that small going to be noticed at a range of, oh, 100 km?[/quote']

Yes.

 

For one thing, it will be glowing red-hot, so it will show up on an infrared scan like a sore thumb.

 

For another thing, military spy satellites have a resolution of down to about 5 centimeters. From orbit.

 

And for a third thing, the target will be able to see your gun turrets, so they just have to keep a sharp eye on the gun muzzles, watching to see if anything emerges.

Re: Rail gun damage?

If your target doesn't realize you've fired' date=' he might not dodge the shot. [/quote']

Yes, but that will take some doing with a railgun. You insert the round encased in a sabot into the railgun. It strikes an arc with the highly charged rails, making a huge electrical explosion and showers of sparks. This explosion travels down the rails as the round accelerates.

 

If you want to hide this from the target, the railgun has to be inside of your ship. So the traveling explosion also happens inside of your ship.

 

And there is no good way to keep the target from noticing the red-hot railgun round streaking out of the gun muzzle and heading to a point right between your eyes.

 

As for the recoil issue' date=' as you say, F=MA. Isn't the ratio of mass between the projectile and the firing ship then an important issue? As most imaginable railgun or coilgun projectiles are miniscule in relation to the firing ship, shouldn't that offset a lot of the acceleration?[/quote']

 

Yes. If the mass difference is great enough, the ship will not undergo much acceleration. Unless the railgun round is traveling at hypervelocity. Then all bets are off.

 

Keep in mind that there is a ship propulsion system called a "mass driver", which is basically using a railgun for rocket propulsion.

 

If you want to calculate it:

 

As = (Mr * Ar) / Ms

where:

As = acceleration ship experiences (meters per second)

Mr = mass of railgun round (kilograms)

Ar = acceleration railgun round experiences (meters per second)

Ms= mass of ship (kilograms)

 

example:

The space dreadnaught Obnoxious has a mass of 13,500,000 kilograms (the same as a Russian Oscar class submarine), and its railgun fires 18 kilogram rounds.

 

If the rounds travel at 6000 meters per second (about the upper limit of current railgun technology), they will make the Obnoxious recoil at a speed of 8 millimeters per second, or a pathetic 0.0008 g.

It will strike the target with a force of 3.2 x 10^8 joules, about the same as a Battleship Iowa 16 inch shell with 54 kg high explosive charge (according to the Boom table).

 

However, if the rounds travel at 14% the speed of light (where relativity becomes a factor), each round will make the Obnoxious recoil at a speed of 56 meters per second, or a whopping 5.7 gs!!

It will strike the target with a force of 1.6 x 10^16 joules, about 3.5 megatons, or the same as the Barringer Meteor Crater

Re: Rail gun damage?

Recoil: There is recoil when a railgun is fired. In space' date=' where there is no friction, it can affect the ship's trajectory (remember, firing an autocannon deorbited an Almaz station). My solution: Fire thrusters to counteract the recoil at the same time the guns are fired.[/quote']

 

Those would have to be pretty huge thrusters. They have to basically put out the same amount of energy that the railgun round contains.

 

Newton's second law say that F = ma, i.e., momentum is mass times acceleration. If a railgun round of mass x is accelerated at rate a, it will contain xa momentum, which will shove the firing ship with that much force. The thruster will have to emit the same amount of force in the opposite direction to counteract this.

 

Which means you really don't want to in the thruster's exhaust plume.

 

Range: Railguns would be less effective at long range. If the target is able to move under its own power' date=' it can "dodge" the shells. My solution: The guns will be linked to a tactical computer that is constantly updating the target's trajectory and making the necessary corrections.[/quote']

 

This is a problem with all non-seeking weapons, be they cannons, railguns, laser batteries, or particle-beam weapons. And there is no real solution, short of time travel or telepathy.

 

Your target has a certain area that represents its possible future locations. The area is determined by the time-of-flight of your weapon from you to the target, the target's initial trajectory, and the target's engines (how much can it change its trajectory within the time-of-flight).

 

If this area is larger than the target silhouette, you probably will never hit the target.

 

Possible solutions include making your weapon home in on the target (despite the target's attempts to jam the homing mechanism), and area-effect warheads. Both of which work poorly with railguns.

Re: Stars that pass in the night

http://www.exitmundi.nl/Gliese710.htm

Re: New Moon in One of Saturn's Rings

A third of a mile wide? That's not a moon' date=' thats a lump in the ring.[/quote']

According to astronomical comedian and raving looney Richard C. Hoagland, that must be the "Blivit in the B-Ring". This was in the Dec 1982 and Jan 1983 issues of ANALOG magazine.

 

Executive summary: there was a currently unexplainable gap in Saturn's B ring, so it obviously must be an alien black hole, or something exotic. Obviously.

Re: Echoes of a Forgotton Empire

I am not insanely wealthy that I can afford Photoshop at ~$900 plus whatever the cost is for Lunarcell.

You were not reading me closely enough.

I said "Rich people with no talent can use..."

I was not referring to you, since anybody with eyes can see that you have got the talent!

Re: Echoes of a Forgotton Empire

Rich people with no talent can use (the hideously expensive) Adobe Photoshop with the Lunarcell plug-in to instantly make hordes of alien planets.

I think that The Gimp freeware program can use Adobe plug-ins, but I'm not sure.

Re: Echoes of a Forgotton Empire

Are those the "too small" images attaches to your post? Because when I open them up completely' date=' they're bigger than my screen.[/quote']

Well, you must have your screen resolution set rather low. On a 1280 x 1024 monitor, the images are about three-quarters of the screen.

 

But if these are meant to be printed, the determining factor is not how big they look on the screen, but the dots-per-inch setting the printer uses. This can be more than 300, which would make the planet images very small indeed on the printed page.

Re: New Moon in One of Saturn's Rings

No' date=' that won't be necessary. As soon as it repairs it’s FTL drive it will leave again…..[/quote']

heh.

 

Or maybe it won't leave. As I recall, this is similar to the start of the novel Footfall. Which, by the way, would make a nifty campaign.

Re: SN 1987A + 22 years

We do have some scanty evidence of prior supernovae

Evidence of Supernovae Found in Ice Core Sample

http://www.universetoday.com/2009/02/23/evidence-of-supernovae-found-in-ice-core-sample/