High Speed Projectiles ...

Tony Hayes:

>I've been reading the posts on hurling various things at other things
>as an attack, interesting but problematic.  There seem to be two
>classes of objects to be thrown, kg sized at moderate velocities (10's
>of km/sec) and gm sized at fractional light velocities (10,000's of
>km/sec).  There would then be two classes of targets, ships and
>planets (space stations are so small compared to planets that they
>will be treated as ships).

Actually, there are *four* classes:
1. Large & slow (asteroid?)
	mass: million of tons and up
	speed: 1-50 km/sec
	delivery system: requires installing ship class drives on a
		suitable "rock" and using *lots* of fuel
	detection: easily detected by a medium tech level civilization
		(but *we* would be in trouble!)
	defense: difficult to destroy, you tend to get a *nasty* meteor
		shower. Deflection is easier *if* time permits.
		Atmosphere is not a defense!

2. medium and fast (ship?)
	mass: hundreds of tons
	speed: 50-500 km/sec
	delivery system: Requires an expendable ship, and a lot of
		fuel. Maybe drop tanks and an AI?
	detection: normal
	defense: somewhat more difficult than against a normal ship

3. small and fast
	mass: tens of kg
	speed: 10-100 kn/sec
	delivery system: Requires a mass driver we could build *now*.
		And which would fit in a medium size ship
		(disassembled). You set it up on a convenient asteriod
		or build extra bracing and attach it to a comet
		nucleues (free fuel!)
	detection: *very* difficult. An 8 kg steel projectile occupies
		approximately one liter. that's a ridiculously small
		cross section for most detector systems. And this thing
		will be at ambient temperature, and could easily have
		an anti-radar coating.
	defense: unlikely. This will hit as hard as a large missile.
		And the odds of a *natural* impact in this range is so
		rare that non-military vessels and installations won't
		be armored against it.  (note that in the (low* end of
		this speed range a *paint flake* blasted a 1-cm pit
		into a shuttle window). Planetary atmosphere should be
		a decent defense, but not guaranteed. (They'd be like
		an artillery barrage if they hit the ground intact,
		which *is* doable!)

4. very small and oh-my-god!
	mass: grams
	speed: 1000+ km/sec
	delivery system: requires one *hell* of a mass driver or
		railgun, but possibly doable even now. Maybe
		installable in a large ship.
	detection: impossible in any practical sense.
	defense: impossible in any practical sense. Atmosphere is a
		defense except for projectiles at a high fraction of
		c. They will not only cause blast effects, but massive
		radiation problems. (at above 1/10th c this is
		effectively one *big* cosmic ray, and will generate a
		shower of secondaries that will be lethal on the
		surface!)

Adrian Hurt:
>Just how much acceleration can a good mass-driver deliver?  If the
ship is
>on the order of 100's of metres long and the mass-driver is spinally
mounted
>(so it is as long as the ship), then the acceleration needed is on the
order
>of 10**11 m/s**2.

I don't have any figures handy. I *may* try bothering a casual
acquaintance at Lawrence Livermore Labs who has worked on railguns and
massdrivers. I've seen an (unused) test projectile. A 1 cm x 1 cm x
.4 cm  block of glass reinforced by some sort of fibers (boron?). They
don't use steel because it *flows* at these accelerations... (If I
remember something from an unrelated bit of trivia properly, this means
they must be doing better than 10^7 gs, as a 10^7 g centrifuge exists
and is built of steel...)

I *think* they were getting 10-100 kn/s out of something less than 10
meters long. And dangerous velocities out of a *one* meter unit.

Any materials sciense folks out there care to look up what pressure it
takes to make steel flow noticeably in *milliseconds*?

The real trick is that a railgun *eats* power. All that kinetic energy
has to be fed into the gun as power. On the other hand, it's very
eficient at making the conversion.

> From: [email removed]
> Subject: (2694) High Speed Projectiles
>
> Scout Ship has accel of 2 G's.  As such it will reach 1/10 speed of light
> in (oops don't have my calculator...)  approx 5 days (?)  at which point
> you toss your one cubic centimeter lead pellets out the airlock.
>
> No big deal.

  The first question in this case is, when the map (MegaTraveller) and the
terrain (physics) don't agree, do we follow the map or the terrain? Personally
I prefer the terrain.

  The trouble is that the scoutship is taking a shortcut through a big hole in
the rules, since the kinetic energy contained in the scoutship at 0.1c is about
1/14th of the *total* energy contained in the mass of the ship (!).
  To supply that amount of energy in five days the ships powerplant has to have
an effect of 2,812,500,000 MW which is a little large in a 1350m3 hull. With a
powerplant on 1000 MW it would take the ship 38,520 years to reach 0.1c and the
fuelvolume for that endurance is also a little large for a 1350m3 hull:)
  [I apologize to the physicists union for quacking on their turf:)]

- - -bertil-
- - --
"Med ett sjyst ja"rnro"r sla^r man va"rlden med ha"pnad!"

In TML message (2694) High Speed Projectiles, Scott Kellog writes:

>Time to go over the 1/10C projectile again...
>
>Scout Ship has accel of 2 G's.  As such it will reach 1/10 speed of
light
>in (oops don't have my calculator...)  approx 5 days (?)  at which
point
>you toss your one cubic centimeter lead pellets out the airlock.

...

>If you use a 1 G Free trader multiply the time reqired by 2.  A damn
cheap
>doomsday weapon if you ask me.

velocity = acceleration * time.

1 g = 9.8 m/s^2
c   = 3e8 m/s

thus at 1 g it takes a bit over 354 *days* to reach c (ignoring
relativistic effects). A good "rule of thumb" is that c is 1 g for 1
year.

So 1/10th c takes 35 days at 1 g, 18 days at 2 g. This is noticeably
above the "one week at full thrust" "rule" I recall from original
Traveller. Also note that you will need *double* this, as you have to
slow down *sometime*! Doesn't MegaTrav have a "one month's fuel" figure
used in designs? Looks like you need *at least* a 3 g ship to do it.

Oh yes, at this speed your tau factor is .995 :-)

to reach 1/10th c
accel	time 		distance
1	35 days		4.6e10 km
2	18 days		2.3e10 km
3	12 days		1.5e10 km
4	 9 days		1.1e10 km
5	 7 days		9.2e09 km
6	 6 days 	7.7e09 km

> From: Adrian Hurt [email removed]
> Subject: (2689) Re: High Speed Projectiles

> Just how much acceleration can a good mass-driver deliver?  If the ship is
> on the order of 100's of metres long and the mass-driver is spinally mounted
> (so it is as long as the ship), then the acceleration needed is on the order
> of 10**11 m/s**2.

  The maximum velocity of a projectile launched with a MD designed according to
the 3G system is about 129km/s, and the projectile in this case is a 2mm light-
weight sphere.
  The reason behind this that the mimimum diameter of the projectile increase
with increasing energy of the projectile, but the energy required for a certain
speed increase faster...

  I'll look at how speeds that can be reached if one stack several accelerators
after eachother and assume that the energy add is equal for each accelerator,
but I'm lost without a spreadsheet right now:)

  As for what material to make the projectiles of, why not take some junk
artifacts of monadium? If it is as indestructible as it is described to be, it
shouldn't suffer from ablation at high speeds.

- - -bertil-
- - --
"That's the best use of Fighting Ships of the Shattered Imperium that *I've*
 ever seen!" - Me to a player who'd just used it to flatten a mosquito:)

Some interesting, non-traveller foo-

If you have velocity dumpers or matter energy converters in your
(likely) nontraveller games, tau factor becomes VERY interesting...

In case you didn't know, tau is multiplied to time to get relativistic
time (though I seem to recall actual lags only occur during acceleration
or something... relativity is more complicated than it appears), mass
and length are multiplied by the inverse.

tau = sqrroot (1- velocity^2/c^2)

I find it very useful to use percent of light^2 instead of
velocity^2/c^2, since it's the same thing.

A fun little rule... tau factor of .5 (mass and length doubled, time
halved) corresponds to 86.6% light speed... so if you convert 1/2 of a
mass to energy and dump it in the other 1/2, that's it's speed.

(with energy equal to that 1/2 mass x c^2! Whee!)

- - -Me
[Pooh Bear incarnate.]

[email removed] writes:
> Some people say they miss High Guard.  I miss Book 2.  they didn't even try
> to guess what a power plant could put out so conservation of energy wasn't
> a factor.  (sigh)

Nor did High Guard, as far as I remember.  It gave the output of a power plant,
and the requiremts of various power-consuming systems, in terms of Energy
Points (which should tell you something about the physics knowledge of the
authors :-) .  It was Striker which dealt with MW, and as it gave MW-rated
equivalents of ship-borne weapons, one could convert Energy Points into MW.

> As to the point of flying blind.

Blind, as in you can't see the target.  Not blind, as in you can't see what's
in front of you.  (Avoiding what's in front of you when your speed is about
3*10**7 m/s and your acceleration is about 20 m/s**2 is a problem, though.)

>		      You don't need to be in sensor range if your target is
> in a fixed orbit or on the ground.  Just plug in that intercept course and
> let her rip.

Which was what I said.  If the target is something fixed, e.g. a planet, then
you might hit it.  If the target is capable of acceleration (e.g. a ship) then
it probably won't be there when you arrive, because it will have its own
reasons for leaving.  (_When_ you arrive?  More like _if_ you arrive!)

> The Japanese had quite a few people get in the cockpit of a Kamikazie (sp?)

But a Kamikaze had a chance of getting to the target, and it was there that
he intended to die.  Flying a spaceship at 0.1c, you won't hit the target.
You won't be hit by the target's defences.  You'll hit a few particles of dust
on the way, and turn into a few particles of dust yourself.

- - --
 "Keyboard?  How quaint!" - M. Scott

 Adrian Hurt			     |	JANET:  [email removed]
 UUCP: ..!ukc!cs.hw.ac.uk!adrian     |  ARPA:   [email removed]

Boy, when I start something I really start something...

Ok, now I see where Bertil is coming from:  use a % of the ship's mass
in the equation E=Mc^2.

Right.  The ship has 1/200th the energy required to reach .1C.  I see your
point.  But your analysis of how an object accelerates is a bit off.
As the ship accelerates it burns off hydrogen:  This is negigible.
As the ship accelerates it encounters relativity:  This also is negligible
at .1C (@ .1C you only encounter a distortion of 0.5%)
	(@ .5C you only encounter a distortion of 13%)
So Basically we have an object under a constant acceleration 2G.
(Sorry guys but you can leave Einstein at home, this is strictly Newton's
turf.)
Now, Newton's second Law F=MA (no trouble here... mass stays approximately
constant, force stays constant, Acceleration should stay constant.)

after 18 days acceleration we hit .1C and see that KE=1/2*MV^2 and there you
are with the .1kton of TNT per gram kinetic energy figure I mentioned
that started this free for all.

Ooops!  Insufficent potential energy in the ship's fuel to reach that figure.
Well, If the ship has only 1/200 the energy then it can only reach 1/200
the kinetic energy of .1C.  Buy some quick envelope calculations, that
means that the ship can only accelerate at 2G's for 2.1213 days.  There is
no unknown deceleration force.  The ship doesn't run until it reaches
a certain speed and then have it's acceletation die off slowly,  It runs
until it's Kinetic energy equals it's potential energy and then
the engines thrust stops.  You are now going ballistic.

So, we come out with a new endurance for the scoutship:  2 days.
that is the point at which all it's potential energy will be used up.

If we accept that then scoutships will never get anywhere.

Ok, look.  We already know that traveller drives by definition (reactionless)
violate conservation of energy.  Any and all ships using what ever drive
you like (fusion flame, grav, thruster) that are designed in the trav
system will violate conservation of energy because they were written by
and designed by someone who never thought of this idea and never thought
anyone else ever would.  We have gone off the board.  Here there be Dragons.
But if we impose conservation of energy then all the trav engines will come
tumbling down like the house of cards they are.

You can't say "conservation of energy applies here, but not over there."
If conservation of energy holds at .1 C then it holds for lower speeds as
well.  so Dur=2.  In order for trav to work Dur should be more than that.

About flying blind... (ie insuffiecent time for collision avoidance @ .1C)
Well, as I said before... "Fred, you knew the job was dangerous when you
took it" - SuperChicken.  I think that while space is not exactly totally
clean, outside the eccliptic plane of the solar system you'd have a better
chance.  On the other hand.  Space is Big.  You can't believe just how
mindbogglingly big it really is.  You may think it's a long way down to...

Sorry.  (Too much Douglas Adams)

Well sure there's a chance you won't make it to the target.  But imagine the
thrill of hitting .1c and getting that tite "Fastest Being alive"
heck even postumously it sounds COOL!  Put that on your tombstone.
(oops nothing left to interr...)  I know a few Vargr who would try it...

And if you are really nervous, that's what auto pilots are for.  Dig?

By the way, this really is metaphysics aien't it?  After all here we are
arguing about when we can and can't violate conservation of energy.

I am reminded of a line I once read and hated...
Changing the laws of physics is one of my hobbies.

I still hate it.

Scott S. Kellogg

Minor point: Reactionless drives don't HAVE to violate physics.

In my games, there is 'accelerationless drive', which really isn't. It
accelerates all atoms at the same rate, however, so only the atoms
suffer any stress. (which limits the acceleration, but not by much)

For reactionless drive, something like setting up a standing gravity
wave... whatever. There's a difference between adding fantasy to
physics, and replacing physics with fantasy...

- - -Me
[Pooh Bear incarnate.]

[email removed] writes:
>
> About flying blind... (ie insuffiecent time for collision avoidance @ .1C)
> Well, as I said before... "Fred, you knew the job was dangerous when you
> took it" - SuperChicken.

Which is why I said I wouldn't take it.  :-)

> Well sure there's a chance you won't make it to the target.  But imagine the
> thrill of hitting .1c and getting that tite "Fastest Being alive"

There's little, if any, chance that you will make it to the target.  There
might be a chance of hitting .1c before you hit a dust particle.

> And if you are really nervous, that's what auto pilots are for.  Dig?

So now you intend to sacrifice (or at least, risk a very high probability of
sacrificing) a whole ship.  Even without worrying about a crew, that's a lot
more expensive than, say, a couple of nuclear missiles.

- - --
 "Keyboard?  How quaint!" - M. Scott

 Adrian Hurt			     |	JANET:  [email removed]
 UUCP: ..!ukc!cs.hw.ac.uk!adrian     |  ARPA:   [email removed]