railguns

A question for you propellor heads. At what velocity do you think a decent
railgun projector (ala KV design) would spit out its slugs and how large would
they be?

> Los wrote:

> A question for you propellor heads. At what velocity do you think a

It depends on the precision in your targetting sensors, the size of the target
and the ranges you want to hit at. Assuming the "standard FT
scales" and shotgun-style fire with several (preferrably *lots* of)
projectiles into the target volume each time you fire, aiming to
achieve the MT railgun hit probabilites, 3000 km/s (0.01c) might be
sufficient... How to achieve such velocities is another matter entirely, but
who knows what tech will be available in the future?

At those speeds, the slugs don't need to be very large - the kinetic
energy of a 10-gram slug travelling at 0.01c is IIRC about one kTon,
but don't quote me on that yet since my reference books are at work :-(

> On 15-Sep-99 at 16:44, Oerjan Ohlson (oerjan.ohlson@telia.com) wrote:

> Roger Books wrote:

> > At those speeds, the slugs don't need to be very large - the

Thanks :-) That's the one I didn't have handy at home :-(

> My (probably faulty, if someone could check) old physics says it

Yep, correct. I was an order of magnitude off - in the right direction,
fortunately <g> 10g at.01c relative is about.1 MTon instead, so if it hits
someone is gonna get *hurt*...

Regards,

> Los wrote:

Hard to say. Offhand I'd say they would be spat out at a minimum of twelve
miles per second, and mass enough to do serious damage to a ship.

joules of damage = ( kg projectile) * ( velocity^2)

Ok, with all the other info I've gotten, and by perusing the digests, here's
kind of what you're looking at:

Max engagement range is 36". Equals 36 million meters. Turn length is 7.5
minutes which gives you a turn of 450 seconds. A kton of TNT is equal to
6.31*10^8 joules A nuke (a small one), if my source is correct, produces
around 1*10^10 joules
C=2.99*10^8 m/s

Now, with these numbers you can figure that the absolute minimum speed of a
projectile has to be around 80,000 m/s.  Anything lower and it literally
will not be able to make it from max firing range to the target in one turn.
Since
7.5 minutes is way to long for a time-to-impact for a ballistic weapon
we need to bump it up significantly. So lets take it up to oh around 1 minute
(600,000
m/s).  That's still a long lag, but not too bad.  Ok, now assume a
projectile of 1 gram (itty bitty). So we have

Energy=.5*.001*600,000^2=1.8*10^8 joules, or about 1/3 of a kton of TNT

A 10 gram projectile will be 1.8*10^9 or about 3 kton of TNT

Now just to get silly, let's take our velocity up a bit, say to around 3.6
million m/s.  That gives us a time-to-impact of 10 seconds. We'll use
our 1 gram projectile again.

Energy =.5*.001*3.6 million ^2=6.48*10^9 joules

A 10 gram projectile would be 6.48*10^10, a 100 gram is 6.48*10^11, etc.

Just for reference 3.6 million m/s is equal to about .01 c, so you're
going to see some minor relativistic mass shifts, which will both make it
harder to achieve that velocity, and increase it's mass and consequently its
energy.

The more reasonable 600,000 m/s is a velocity of about .002c which is
still considerable.

Now as far as the practicality of the weapon systems, and the affects of a
very small projectile hitting a container full of atmosphere at VERY high
speed go, I'm not going to speculate.

For personal weapons, the speeds, would be MUCH lower, and the projectiles
could be correspondingly larger.

Bill

Los <los@cris.com> on 09/15/1999 03:36:04 PM

Please respond to gzg-l@CSUA.Berkeley.EDU

  To:          gzg-l@CSUA.Berkeley.EDU

  cc:          (bcc: Bill Brush/InfSys/Revenue)

  Subject      railguns
:

A question for you propellor heads. At what velocity do you think a decent
railgun projector (ala KV design) would spit out its slugs and how large would
they be?

Los

On 16-Sep-99 at 11:44, bbrush@rev.state.ne.us (bbrush@rev.state.ne.us)
wrote:
> Ok, with all the other info I've gotten, and by perusing the digests,
Ok, now
> assume a projectile of 1 gram (itty bitty). So we have

Recoil arresters, absorbers, etc. would be a requirement on this system I
think.
:-)  Of course if they have inertial dampers, then there's no reason
they couldn't use something similar to help reduce recoil. PSB

Bill

Roger Books <books@mail.state.fl.us> on 09/16/1999 11:06:27 AM

Please respond to gzg-l@CSUA.Berkeley.EDU

  To:          gzg-l@CSUA.Berkeley.EDU

  cc:          (bcc: Bill Brush/InfSys/Revenue)

  Subject      Re: railguns
:

Ok, now
> assume a projectile of 1 gram (itty bitty). So we have

Inertial dampers? If you have this technology, why not Inerta impellers
and/or inertia storage.

Quite a while ago, I decided that the PSB for cinematic movement was a
combination of gravity drive for thrust and an Inertia Redirection System for
turns. This is why ships maintain velocity (and inertia) through a turn (even
a 180 degree turn).

Inertial redirectors? Hmmm, so you could conceivably use them to redirect the
force of the recoil in such a way that firing the railguns would increase your
forward velocity. Talk about your odd thoughts.

:-)

Bill

"Bell, Brian K" <Brian_Bell@dscc.dla.mil> on 09/16/1999 11:29:02 AM

Please respond to gzg-l@CSUA.Berkeley.EDU

  To:          "'gzg-l@CSUA.Berkeley.EDU'"
               <gzg-l@CSUA.Berkeley.EDU>

  cc:          (bcc: Bill Brush/InfSys/Revenue)

  Subject      RE: railguns
:

Inertial dampers? If you have this technology, why not Inerta impellers
and/or inertia storage.

Quite a while ago, I decided that the PSB for cinematic movement was a
combination of gravity drive for thrust and an Inertia Redirection System for
turns. This is why ships maintain velocity (and inertia) through a turn (even
a 180 degree turn).

Hm. Now I've checked my books at work, and according to them

1 kTon TNT = 4.18*10^12 J rather than the

1kTon tnt = 6.31*(10**8) J Roger claimed.

I haven't been able to find any independent data for TNT, but I know
that some more modern explosives yield about 8 kJ/g (ie, about 8*10^12
J/kTon) and are supposed to be about twice as powerful as TNT,
mass-wise, so 4.18*10^12 J fits better.

So, third try: the speed necessary to get the equivalent of 1 kTon out
of a hit with a 10g slug is approx. 29 000 km/s, or:roughly .1c. That's
starting to get nasty <g>

Best wishes,

Mostly good thinking, but an important figure in the input data was off by
four orders of magnitude and no consideration was given to the hit
probabilities, so here goes:

> bbrush wrote:

> Max engagement range is 36". Equals 36 million meters.

Max railgun range is 30", but it doesn't matter much for the calculations.

> Turn length is 7.5 minutes which gives you a turn of 450 seconds.

Sorry, no. Not unless modern explosives are more than ten thousand times
stronger than TNT is, and I'm pretty certain they aren't...
otherwise we would've stopped using TNT in non-nuke warheads decades
ago. See my other post for this.

> Now, with these numbers you can figure that the absolute minimum

80 km/s is speed 36... that's about twice the speed of my
slowest-moving capital ships, and slower than my fastest escorts. If
they can survive running into space dust at those speeds, they're not going to
have *that* much problem with small slugs.. and that's quite
apart from the fact that some of my ships can *outrun* those slugs :-/

> Since 7.5 minutes is way to long for a time-to-impact for a ballistic

> weapon we need to bump it up significantly. So lets take it up to oh

> around 1 minute (600,000 m/s). That's still a long lag, but not too

Yes, it is. Assuming the standard scale - Thrust-1 ~ 1 g - a *Thrust-1*
target will be able to get up to about 17 km away from your projected target
point during that minute. Even if you're talking about Renegade
Legion-style Leviathans, a sphere with a 17km radius leaves quite a few
possible true target points  - and the MT railgun has a 17% hit rate at
that range (against all targets, regardless of thrust rating - but
after running these calculations I'm more and more inclined to make
railgun hit numbers dependent on target thrust :-/ ). Anyone care to
figure out how many slugs you'd need to fire to achieve this hit rate?

> Ok, now assume a projectile of 1 gram (itty bitty). So we have

Um... no. Only about 43 kg of TNT... Question for you naval historicians: how
much TNT was there in a 16" naval grenade?

Since there is space dust, micro-meteorites etc out there, my ships
(some of them flying *faster* than this slug, remember) are likely to
suffer similar hits quite often in normal operations - without taking
any noticeable damage from them.

> A 10 gram projectile will be 1.8*10^9 or about 3 kton of TNT

430 kg of TNT.

> Now just to get silly, let's take our velocity up a bit, say to

It isn't silly. It is necessary, unless you want to fire a several thousand
slugs in each shot...

> That gives us a time-to-impact of 10 seconds.

Yes please. Now that thrust-1 target can't move more than about 500
meters away from where you thought it would be, before the slug arrives...
starts looking as if we might actually have at least a
prayer of hitting the target :-)

> We'll use our 1 gram projectile again.

Which is still "only" about 1.5 tons of TNT. Starts getting nasty, but nowhere
close even to a small nuke.

> Just for reference 3.6 million m/s is equal to about .01 c, so you're

The mass increase at.01c is ~0.005%... rather easy to take account
for, I think :-/ The mass shift stays below 5% until above .3 c.

Regards,

Thanks everyone for all the great info!

> On 16-Sep-99 at 17:34, Oerjan Ohlson (oerjan.ohlson@telia.com) wrote:

Well in my defense, having only just joined the list I was unaware that
railguns had been radically, unofficially revamped so I used the stats out of
MT.
 Which
is where I got my max engagement range. As far as the energy yield goes, I was
going by what was presented here, so if it was wrong then naturally all of the
comparisons are going to be wrong.

I don't really see that targeting considerations are germain to the discussion
of slug mass and velocities, which is why I didn't address them. A mass moving
through space is fairly predictable which is what the targeting computers are
for.

There are several factors which are overlooked in the discussion of railguns,
all of which would really render them inadequate in a long range weapon
capacity. Factors like power consumption, projectile material, target
composition, recoil (a really big problem), and a host of other things. Since
Jon gave the KV railguns, that's what we use.

I must say I find it interesting just how big a range of velocities you see
people talk about on this list. Oerjan says his capitals move at V, of 18 and
his escorts of 36. I would think this would take a VERY large table, otherwise
everything would just go screaming off the other side of the table and that
would be the end of the game. Most games I've watched on standard 4x6 or 4x8
tables have velocities of around 8-18, depending heavily on the
nationality and maneuverability of the ship.

JMO, Bill

"Oerjan Ohlson" <oerjan.ohlson@telia.com> on 09/16/99 01:04:36 PM

Please respond to gzg-l@CSUA.Berkeley.EDU

 To:      gzg-l@CSUA.Berkeley.EDU

 cc:      (bcc: Bill Brush/InfSys/Revenue)

 Subject: Re: railguns

Mostly good thinking, but an important figure in the input data was off by
four orders of magnitude and no consideration was given to the hit
probabilities, so here goes:

> bbrush wrote:

> Max engagement range is 36". Equals 36 million meters.

Max railgun range is 30", but it doesn't matter much for the calculations.

> Turn length is 7.5 minutes which gives you a turn of 450 seconds.

Sorry, no. Not unless modern explosives are more than ten thousand times
stronger than TNT is, and I'm pretty certain they aren't...
otherwise we would've stopped using TNT in non-nuke warheads decades
ago. See my other post for this.

> Roger Books wrote:

> > Hm. Now I've checked my books at work, and according to them

No problem at all. My data also comes from the 'net originally - that's
why I had to compare with the other explosives to choose between the
two values :-/

Best wishes,

On 16-Sep-99 at 18:03, bbrush@rev.state.ne.us (bbrush@rev.state.ne.us)
wrote:

> I must say I find it interesting just how big a range of velocities

My speed depends more on what my opponent expects me to do. As soon as the
tactics showed up for dealing with my high speeds I dropped to
lower speeds.  Last game I spent 1/2 the battle stopped, of course I
was playing an SDN against 3 hvy cruisers.

Oh, I lost, two alpha strikes (total of 25 dice rolled) did 3 points damage
against lvl 1 screens, two unopposed SM hits did another 4 more. My opponent
managed to do 11 damage at one point with 3 class 1s, and this was the norm
for the game.

I'm not going to take the time to search the archives, but I believe that
Oerjan is one of those players who uses cm instead of inches. This gives him
about a 2.5 times the game area for the same size table.

---
Brian Bell bkb@beol.net <mailto:bkb@beol.net>
http://members.xoom.com/rlyehable/
---

-----Original Messages-----
bbrush@rev.state.ne.us
Subject: Re: railguns

[snip]
I must say I find it interesting just how big a range of velocities you see
people talk about on this list. Oerjan says his capitals move at V, of 18 and
his escorts of 36. I would think this would take a VERY large table, otherwise
everything would just go screaming off the other side of the table and that
would be the end of the game. Most games I've watched on standard
4x6 or 4x8 tables have velocities of around 8-18, depending heavily on
the nationality and maneuverability of the ship.

Hell even in a regular inches game my ships are honking along pretty nicely
after four or five turns of accell.

Los

> Brian Bell wrote:

> I'm not going to take the time to search the archives, but I believe

> bbrush wrote:

> Well in my defense, having only just joined the list I was unaware

Not sure what you're referring to here, but the MT railgun has a max
range of 30 mu :-/ As I said, it doesn't matter much for the general
discussion.

> I don't really see that targeting considerations are germain to the

> them.

Believe me, unless your projectiles are guided their velocity has *everything*
to do with targetting considerations. If a weapon can't hit its targets, it
doesn't matter how much damage it would have inflicted if it had hit...

My table is 120 x 80 mu; that's equivalent to 10' x 6'8" if you measure in
inches. In Cinematic, maximum practical velocities (without using a floating
board) are roughly 6*Thrust; in Vector, 4*Thrust. I like
Thrust-8 ships :-/

Best wishes,

Oerjan Ohlson oerjan.ohlson@telia.com

"Life is like a sewer. What you get out of it, depends on what you put into
it."
- Hen3ry

Which
> is where I got my max engagement range. As far as the energy yield

> From: "Oerjan Ohlson" <oerjan.ohlson@telia.com>

Just to be pedantic (hey, it's a Friday), it's worth stating that the 4.184
GJ value is the energy released by one _short_ ton (2000lb) of TNT. I'd
guess that by the "current" era in FT time, short and long tons would be as
uncommon as the barleycorn (1/3 inch) is now, and the only ton(ne) would
be 1000kg.

gee, this reminds me of the spinal mounts in FASA RL: Leviathan

----------
From:   Robert Smith[SMTP:rob_m_smith@hotmail.com]
Sent:	Friday, September 17, 1999 8:40 AM
To:     gzg-l@CSUA.Berkeley.EDU
Subject:	Re: railguns
<snip>
....  that the 4.184 GJ value is the energy released by one _short_ ton
(2000lb) of TNT. I'd guess that by the "current" era in FT time, short and
long tons would be as uncommon
as the barleycorn (1/3 inch) is now, and the only ton(ne) would be
1000kg. <end snip>

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