FT: Missiles and Gas Tanks

> At 08:51 PM 7/17/97 +0200, Oerjan Ohlson wrote:

> What do you military guys say - can an air-to-air missile run out of

The Standard Missile accelerates up to a set speed on a solid rocket booster
and then uses the airfoils to use that momentum to maneuver. Beyond that I
cannot say....

I don't have a problem with them at all. It depends on what assumptions you
make about scale, power sources, etc. If the missile is trying to impact a
maneuvering target, it will be constantly be burning whatever it uses for fuel
(antimatter, peat moss, whatever) A missile, by definition has limited tankage
for such, as it must carry sensors powerful enough to track a target, a
warhead of sufficient yield to severely damage a target, and thruster arrays
to maneuver with. If you are assuming fractional cee missiles, those are more
properly railguns anyway. As far as fighter endurance goes, the endurance rule
is (like all rules in the game) optional. I can see if a weapon on a fighter
took a great deal of energy to fire how it's batteries might run low for it's
weapons. Just a thought. A great use for missiles BTW is to herd an enemy task
force into a killing zone for Wave guns....

A missile would be easier to maneuver than a ship at the same velocity.
Missiles at higher speeds would have to pull more Gees to maneuver effectively
to engage a target. Missiles, in this discussion I think, are defined as
independently maneuvering seeking weapons as opposed to dumb kinetic energy
rounds. Simple KE rounds would have to have VERY high velocities in order to
engage targets at long range and have any hope of effectively striking the
target. That is not to say you could not use fractional cee mass drivers
lobbing maneuverable rounds at targets. Your rounds would simply need to have
a heckuva drive to get any appreciable vector change to engage a target. But,
then with higher velocities the target has moved less distance. I guess it all
depends on what tech you are simulating after all...

I've got a real problem with this missile thing in FT. You guys talk as if the
missile would "run out of fuel" during its flight. What if the ship that
launched the missile imparts its velocity? Then the missile would only use
"fuel" for course corrections. I think turning missiles during the game is
kind of silly. Just launch, move to target and roll for ECM,
ECCM, Point Defense Systems and caculate damage.   I don't see how they
can
"run out of fuel".   Thats one of the less believable aspects of the
game, besides the limited durability of "fighters".

> On Thu, 17 Jul 1997, Gerald McVicker wrote:

> I've got a real problem with this missile thing in FT. You guys talk

It should do (and does, if you use the Newtonian movement rules on The Page or
elsewhere). However, unless the missiles uses some sort
of main engines - and quite powerful at that - it won't hit very
well, because its trajectory will be very easy to predict - and a
target ship will be able to move out of the way, unless the missile
launcher is _very_ powerful and throws the missile at speeds similar
to railgun slugs. Unless I misunderstood you entirely, your suggestion is
roughly equivalent to trying to hit a jet fighter with
a guided bomb instead of with an air-to-air missile.

What do you military guys say - can an air-to-air missile run out of
fuel? How radical maneuvers is it capable of?

Later,

> On Thu, 17 Jul 1997, Gerald McVicker wrote:

This is very different from an air-to-air missile.   The energy required
to manuver it would be in relation to the mass of the vehicle. "Correct me If
I'm wrong." Therefore a missile would be eaiser to manuver than a ship.
 I
liken it to a naval warship trying to evade an anti-ship missile of
today.
There is NO WAY an aircraft carrier could out-manuver a missile.  So
check for the point defense systems and work out damage if it fails. Besides
an
air-to-air missile needs the fuel and the engine to maintain its
velocity
and its flight.   If you shot a missile out of say a " gravic propulsion
launcher" or some other sci-fi equivalent..it would maintain its
velocity. All the engine would have to do is change its vector of movement.

> I don't have a problem with them at all. It depends on what

Actually a missile, by definition, is "an objcet thrown or projected so as
to strike something at a distance".   A bullet from a gun is a missile,
an arrow from a bow is a missile, and ICBM is a missile. It does NOT have to
have a fuel tank and engines, nor does it have to have a warhead. If the ship
expended the energy to launch the missile on its current velocity, it would
only have to expend small amounts of energy to alter its vector and not its
velocity. The velocity would remain the same after launch. If you could lauch
it fast enough, a small engine probably couldn't add that much
velocity to the object in a short time.   Besides, I liken it to a
battleship trying to dodge or outrun an anti-ship missile today.   You
better have good armor or point defence systems, cause you're not going to get
away. You could launch missiles with differeing velocities, according to the
power of the launcher and NOT the missile, then you could still use them to
herd in the enemy.

> Gerald McVicker writes:

Some stuff that's more or less correct.

> Then he writes:

@:) Besides an air-to-air missile needs the fuel and the engine to
@:) maintain its velocity and its flight. If you shot a missile out
@:) of say a " gravic propulsion launcher" or some other sci-fi
@:) equivalent..it would maintain its velocity. All the engine would @:) have
to do is change its vector of movement.

While we're being pedantic about definitions, velocity is defined (in physics)
as a vector that describes both speed and direction. Changing either one
requires energy. In space, changing direction requires a significant amount of
energy because there's no atmosphere to push on. Of course Full Thrust's
standard movement rules act as though there is something to push on so perhaps
you want to assume your missiles can turn by simply moving their flaps around.

I think the actual reason that FT missiles have fuel limits is that it makes
them easier to live with. Good for FT. Missiles that didn't have to manouver
to hit should probably cause significantly less damage if you want to keep the
overall "balance of power" between the various game weapons and systems.

[using something akin to a cruise missile in my example]

I've had the impression that missiles are launched
out-of-direct-line-of-sight
of the enemy.  The missile has a course set and flys nap-of-earth,
evading
trees, buildings and, possibly, incoming anti-missile missiles.

In FT I would think that a launched missile would have to perform some kind of
evasive actions against rocks, wreckage and anti-missile efforts.  Also,
we are not talking about a surface launcher firing against a surface target.
There is a "volume" of space to figure in that the target is moving through.
Therefore, there must be some kind of expenditure of propellant...?

In high school chemistry I remember first learning about "Finnegan's
Constant".

You have the problem, you know the answer, but you are not sure exactly how to
get from one to the other.  After laying-out the problem, if it does not
come-out to the exact answer you "add Finnegan's Constant" to the
equation to make it work. The teacher didn't buy it... but it has been handy
to have.

FT has a marvelous flexibility so perhaps we could say that the
effort/energy/whatever it would take to reach from Point A to Point B is
three G'zgs. One G'zg is one turn's worth of whatever.

Okay, its a bit weird sounding but it could be a very handy solution to many
problems and discussions.

> At 05:29 PM 7/17/97 -0500, you wrote:
Also, we
> are not talking about a surface launcher firing against a surface
Watch the missile attacks in an anime space battle. They dodge and weave
like no-ones business.  At this tech level it would be easy to point a
defence laser at an incoming target on a constant trajectory. The more jukes
and jives you put in your missile's flight path the better the odds of it
reaching the target. To do this type of manuevering in space would consume an
enormous amount of fuel compared to the payload delivered.(modern missiles are
mostly propulsion and they can use fins to stear.fins arent much good in
space.)

Anyways try playing a few games where the missiles dont run out of fuel. Or
even double the time now. You end up with ppl who start launching their
missiles several boards away, travel at the same speed dumping more and more
missiles out into one giant wave. In SFBs the drone bombardment cruiser with
long range drones is the most powerfull ship in the game by a factor of 10.
"Captain we have 240 contacts coming in at high speed. What do we do?"

"We bite the big one."

These games were never very much fun.

> On Thu, 17 Jul 1997, Gerald McVicker wrote:

> If you shot a missile out of say a " gravic propulsion

Jerry, under newtonian physics the velocity _IS_ a vector. Changing the
direction of travel is done in exactly the same way as increasing the speed,
except for the direction you accelerate in. Changing the vector of movement is
another way to say that you change the velocity.

If you have something that excerts force on you from the "outside" (like

air or water), you can use fins or rudders to change the direction of
travel - but you'll most likely lose momentum when you do this. The
standard FT movement system assumes some sort of similar "friction"; by using
this technique you can indeed let a missile keep its speed and still change
its direction of travel without expending (very much) fuel.

Under the "Realistic Movement" rules (on The Page or elsewhere), you can't.

Later,

A quick reminder on this missile thread. I've seen alot of comparissons to
current naval situations. Let's remember that the missiles and ships are
working in the same medium and under the same conditions (ie., more like ship
vs. torpedo as opposed to ship vs. SSM). Also, distances and detection ranges
are much longer. This gives ships more warning to manuver and deploy counter
measures.

Just adding my $0.02 as it seems the comparrisons on this discussion are
drifting a touch.

Hmmm, sorry folks I missed that question. Ahem; (entering "talking about job
to the civies mode":) The answer is, it depends. Current air to air missles
are solid fueled but are usualy a bit "over fueled" for thier stated ranges.
The AIM9 Sidwinder is a "short range" missle, it's "attack envolope" is @ 9
miles. It's fuel can last longer than that, but I can't give you exact
figures. The AIM 7 Sparrow is rated at medium range @50
miles. All at supersonic (Mach 4+) speeds. The Phonix missle is rated
at @ 124 miles, but is a bit slower, (@Mach 3 or so). The solid rockets burn
at full thrust from just after launch to burn out, contro is by areodynamic
surfaces. These things can turn on a cime as it were, usually in thier own
length. The only thing they have to worry about in radicaal manuvering is how
well they are put together, and thier seeker cone, or how much of the sky they
can see with the
seeker head. Most have an angle of 95-180 deg.  This is why the best
tactic for pilots is to turn into the missle fireing countermeasure. Hopefully
you can fly out of it's seeker aspect before it can manuver, or possiible make
the countermeasures more enticing. (Fat chance, but you do what you can.) As
for running out of fuel, yes they can and do. If they miss, most have a self
destruct charge at the end of the motor burn to destroy the missle. But there
are some, like the Harpoon I belive, and The
Tacit Rainbow, which are powerd by small turbo-jets, very fule
efficiant which gives them incrediable range. (I don't work with either so I'm
going by what I remember from Janes) As for missles in FT, I think they could
easly run out of fule after so long. They are after all trying to hit a
moviing and EVADING target. Unless the range is point blank, in relative
terms, your target iis not going to sit there and let himself be hit. The
engine used for "course corrections" would have to be as powerful as the main
propullsion motor as you are not just "turning" as atmoshperic missles do
using wings, your changing vectors, whiich usually means a lot of honking
thrust. And you have to do it fast to keep the target in "sight" of the seeker
too. Of course I don't see why you can't shoot "over the shoulder" either, as
even missles today are becoming sophisticated enough to be programed to not
begin a lock on till they are scanning a certaiin part of the sky. Any other
Munitions Questions? (Without violating security?:) Randy

With all the discussions about missles and gas tanks I thought I might list a
few of the the simple things I would design into one of MY basic missles.

1. It would hop, jink, and rotate around it axis of flight like a demented
mongoose so that a point defense system would have as hard as possible job to
predict its course.

2. It would drop chaff, flares, and electronic noise makers so that the
targets computers would have a heart attack determining just which radar
return to target with its point defenses.

3. It would have enough sensors ( multiple ie: IR, Millimeter wave, gavetic
meters, etc) to find the target ( you don't think the target isn't doing 1 &
2 ???)

4. It would have enough computing power to do 1, 2, & 3 at the same time.

5. If possible it would it would have a big motor to make the flight time as
short as possible so that the target would have the fewest possible chances to
do anything about my missle.

6. It would have really big warhead so that if it only got close, it would be
enough.

7. Last and not least it would be as small as possible so that I could carry
as many as possible. (also small targets are harder to see!)

If you include ALL the above points in a missles' design you'll soon see why
it will runs its gas tank out in just a few turns. If enough fuel is included
to make it last for say ten turns the size will go up by several factors( and
therefore the number in your magazine goes down), more mass
=
slower vector changes, and the chances are that the point defense will get a
lock on a fat, slow, and more predictable target. The result is you get fewer
missles that are easier to defend against, just so you can launch them a
little further away ( this also gives the target more time to evade the missle
envelope.)

The point is, you reach a point of diminishing returns on the range of a
missle (ie: the gas tank size.) The real (and military) tradeoff is between
range and effectiveness. Besides do you think any approprations committee
would let you build missles which were less likely to hit and many more times
expensive?

> PsyWraith@aol.com wrote:

I agree! Missles and ships are in the same medium...therfore they are subject
to the same laws of physics. Maybe missles should be thought of as very tiny
ships...

> Phillip E. Pournelle wrote:

> >What do you military guys say - can an air-to-air missile run out of

OK, and omitting all classy data (exact ranges, velocities etc)

The Nato Sea Sparrow Missile (RIM-7H) has the following profile:
In the first A seconds, the primary booster accelerates it up to B
m/sec. The sustainer then cuts in at the range of C, where it has enough
energy to tackle a target pulling D gee. The speed changes slowly to E, at a
range of F, when it can tackle a target pulling G gee. Finally, the sustainer
cuts out at a range of H, whereupon the missile decelerates to I at a range of
J, when it only has enough energy to hit a target pulling K gee. After that,
it's deemed to be pretty much inneffective
except against a slow, non-manouvering target.

Source: Raytheon publicity brochure illustration. The actual figurtes depend
on air temperature, pressure, altitude of target etc as well.

As the RIM-7H is basically a modified AIM-7H (ie an Air-to-Air missile)
the same principles apply. The big difference is that at sea-level, the

> Donald Hosford writes:
@:) >
@:) > Let's remember that the missiles and ships are working in the @:) > same
medium and under the same conditions (ie., more like ship @:) > vs. torpedo as
opposed to ship vs. SSM).
@:)
@:) I agree! Missles and ships are in the same medium...therfore they @:) are
subject to the same laws of physics. Maybe missles should be @:) thought of as
very tiny ships...

Perhaps, but even if you compare ships to torpedoes there are significant
differences. Last I heard torpedoes tended to be rocket powered (at least some
of them) which allows them to move much more quickly than ships but with a
very poor range (on the order of a hundred miles was the longest I remember
hearing about). So although ships and torpedoes operate in the same medium,
they use different propulsion methods and therefore operate differently.

Even if you ignore the possibility for different types of propulsion (a near
future FT might have only rocket power available, eg) there are still matters
of efficiency. Missiles, being small and expendable and needing to travel only
a short distance, might be able to use more volatile fuels than a ship that
needs to travel for extended periods and reuse its engines throughout its
lifespan.

> Ok, I can believe this. I've been thinking more and more that it
<snip>

The Rocket powered torpedo is a Russian countermeasure weapon that, while fast
(200mph!) is totally unguided. It is designed to be
snap-fired in the direction of an incoming torpedo in order to get
the launching sub to maneuver and break the control wires on it's wire guided
torp(s).

> Randy Campbell writes:

@:) > Last I heard torpedoes tended to be rocket powered (at least @:) > some
of them)

@:) I'd have to ask about this, but all the torps in the current US = @:)
inventory I know of are "steam turbine powered" propellers.

Ok, I can believe this. I've been thinking more and more that it was an
experimental Soviet torpedo I was thinking of and not standard issue.

@:) Ranges sound about right, but a rocket under water wil burn out = @:)
faster than a miissle engine, due to increased drag.

That's true. They were using a rocket to spin a propeller, though, not to push
the torpedo directly.

@:) > Missiles, being small and expendable and needing to travel only @:) >a
short distance, might be able to use more volatile fuels...
@:)
@:) Again using todays missles for example, volitile fueled munitions @:) is
the LAST THING you want stored in magazines on your war ship.

  I guess that's true.  High-efficiency might have been the phrase I
was actually looking for.

@:) There are currently several hiigh efficaincy liquid fuels @:) availible
for missle engines, but we still use mostly solids due @:) to the stability of
it.

First, don't ICBM's use liquid fuels? And presumably cruise missiles use some
kind of jet fuel. But second, I actually thought solid fuels were more
efficient than liquid fuels, which would explain why they're used, for
example, in the Shuttle SRBs. You can't turn them off is (I thought) the
biggest problem.

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Uh, OK.

First, don't ICBM's use liquid fuels? And presumably cruise missiles use some
kind of jet fuel. But second, I actually thought solid fuels were more
efficient than liquid fuels, which would explain why they're used, for
example, in the Shuttle SRBs. You can't turn them off is (I thought) the
biggest problem.

The Titan II ICBM, and most (all?) of its American predecessors (Titan I,
Atlas, etc.) were liquid fueled. The Minuteman and Peacekeeper
(AKA MX) are solid fueled.  A silo in the middle of no-where is a much
more stable controlled environment than a ship pitching around on the
seas (or space) with a hundreds of crew (the sea/space is a harsh
mistress after all). Having said that I believe the early American
Sub-Lunched Ballistic Missiles (SLBMs) (Polaris and Poseidon) were
liquid fueled, different time I guess.

The Harpoon and Tomahawk both use jet engines and jet fuel, but I imagine jet
fuel is not nearly a volatile as liquid rocket fuel (don't need the oxidizer
right there after all).

In terms of efficiency it is the other way around, liquid rocket fuels
are much more efficient/unit weight.  The Titan II has a much longer
range than it successors (and USSR ICBMs making it relatively safe
strategicly) but the maintenance difficulties with liquid fuels prompted the
US Air Force to switch to solds.

For example I believe the Titan II was the first US ICBM where the fuels could
be stored inside the missiles indefinitely (liquid rocket fuels tend to be
corrosive), previous ICBMs need to be fueled immediately before launch (for
the Atlas this fueling had to be cared out above ground and took 30 minutes!).
I believe part of the reason
for Minuteman's name was that because it was sold fuel the pre-lunch
prep-time was very short (0?).

A couple years ago their was a crisis at a Titan II silo when someone working
on the missile dropped a spanner down the side of the missile, there was a
major worry that the spanner might have pictured the missile's tanks...very,
very bad on a ready for flight liquid fueled missile.

> Last I heard torpedoes tended to be rocket powered (at least some of
I'd have to ask about this, but all the torps in the current US inventory I
know of are "steam turbine powered" propellers. They have a higher velocity
than a ship or sub, but this is due to thrust to wieght ratio. Ranges sound
about right, but a rocket under water wil burn out faster than a miissle
engine, due to increased drag. And due to the seekers on most torps being
acoustic, (sonar) the sound of the motor burn would be a great problem.

> Even if you ignore the possibility for different types of propulsion<

Again using todays missles for example, volitile fueled munitions is the LAST
THING you want stored in magazines on your war ship. There are currently
several hiigh efficaincy liquid fuels availible for missle engines, but we
still use mostly solids due to the stability of it. You can store them safer,
and you haave a much less chance of having them cook off due to a hit on the
ship, (AirCraft, whatever) Randy

-joachim

Joachim Heck - SunSoft <jheck@East.Sun.COM> said;

> First, don't ICBM's use liquid fuels? And presumably cruise

In order; No there are no Liquid ICBM's left in the inventory. Solids
transport and store better, no re-fuel or top off time and ready in
an instant fireing was more important. As for efficiancy, the SRB's are
replacing a morre efficiant fully reusable, but MUCH larger 1st stage that was
planned for the shuttle.
The LH/Lox engines have a much higher ISP, but you see the size
diffrence due to Hydrogens volume requirement. Cruiise missles and some others
use liquid jet fuels, but if we could get away with it they would all be
solids, (and yes they are working hard on solid jet fuel, an air breathing
rocket actually) they are easier to store and have a much longer "shelf life"
than any liquid. Your riight though about not being able to turn them off, but
this is not a problem from a military point of view as we don't want them to
quite short of the target, and if it's still burning on impact so much the
better. Randy "AMMO: Giiving the Enemy the maximum opertuunity to die for his
country"

"John W.F. McClain" <jmcclain@lads.is.lmco.com> said;

> Having said that I believe the early American

Uhmmm, nope not that I can find. The only ones close were the Regulas cruise
missles of the late '50s. Polaris and Posidan were both solids
developed as solids because  of the pproblem of storing fuel/oxidizer
on a sub, not to mention trying to fuel those suckers. (I'm made to understand
that the missles on subs are pretty much inaccesable anyway, basically sealed
in thier tubes)

> The Harpoon and Tomahawk both use jet engines and jet fuel, but I

JP4 or 8 I belive. Pretty much standard jet fuel.

> In terms of efficiency it is the other way around, liquid rocket fuels

Recall, the Titan II was used to launch the Gemini missions, as a two stage to
orbit vehichle, where as the Minute man is ( I belive) a four stage vehicle
with less payload capability.

> For example I believe the Titan II was the first US ICBM where the

The Titan's fuels are worse than most. The Atlas was; Liiquid Oxygen
and RP-1 (Kerosene) where as the Titans was;  N2O4 and Aerozine 50
storable but toxic... and....

> A couple years ago their was a crisis at a Titan II silo when someone

...and the tank was punctured, the bad part was, (I don't think tthey ever
found out for sure) but somthiing came inttoo contact with the fuel cloud. The
Titan fuel and oxidizer were "Hypergolic" they explode on contact. Somthing in
the silo acted like oxidizer, one man waas killed and one badly injured, and
the explosion blew the silo lid right off. The Titan was retired very soon
after this incedent.

Also the solids can be made much more robust due to not having to have liquid
filled tanks. In the case of both the Atlas and Titan, the tanks are actually
structuaraly stiffened by the fuel pressure. Rupture the tank during flight
and the missle falls apart.

Randy

> John W.F. McClain wrote:

No offence, but.... IMHO, discussing what CURRENT missle technology
uses for engines/fuel is ok.  But it disturbs me when peaple seem to
think that all future missle developments will continue to use the SAME
technology used today.  At some point, space/atmo propulsion technology
is going to turn out something that surpasses any liquid/solid fueled
rockets. Manned military spacecraft (the ones of interest to us...) will
allways use the best engine tech available. And when that tech
(whatever it is...) surpasses liquid/solid fueled rockets, the missles
built after that, will (in most cases) switch over to the new technology. Most
of these space battle games are set very far from today, it is safe to say
that most of them will use small ship engines in their missles. (Once you have
a technology, there is no problem to produce a weaker (ie smaller) version.
Missles don't need as much propulsive energy as a ship does. Very easy.