On 8 Jun 2020 at 17:48, xxxxxx@gmail.com wrote:
> Now, space is different.
>
> No hiding in space (your thermal gives you away and you can be found
> by visuals tracking transits). Not a lot of cover.
It's possible to reduce your IR emmission in several ways, but most
are *highly* directional. You may appear to be as cold as the 3K
background from some direction, but in others your signature will be
*greatly* enhanced.
Yes, but here's the rub: You also have an multi-spectral signature. Heat isn't your only way of being spotted.
And more importantly: Against multiple spaced out sensors, your camouflage will fail. And it can't last for long anyway due to the problem of dispensing with or storing the heat.
If you eject it, then the heated ejecta will be visible. If you sit on it, your ship will get hotter.
It's not practical long-duration stealth and commuting around systems takes some time if you aren't jumping or having super drives...
The two methods that don't have this flaw have major flaws of their
own.
"Storing" the heat by dumping it into a "cold sink" is not possible
for an extended time (hours at most).
Well, you *could* try hiding in an iceball/comet, but that too has
drawbacks. Pretty much the same drawbacks as the second method.
Well, that can work, but there's also the fact you can't *manouver* without being noticed and to figure out a ballistic approach that could cover your foes moves and leave you in good position no matter what they do... that's a feat.
The second method is a *huge shell (balloon) around the ship. This
spread the same amount of energy over a *much* larger area, thius
reducing the signature to something plausible for a natural body.
It does, but it's own existence may be betrayed to other sensors.
And again, likely if you manouver, you are detected.
Trouble with that is that if it's a known system, all the bodies that
size will have been recorded and a "new" body, especiall well inside
the system is going to be *very* suspicious.
Esp if heading on trajectories near major points of interest.
Worse, you are stuck moving at a plausible speed for a natural body.
Which means it'll take you months, if not years to get where you want
to be.
Yes.
Lol... one strategy is hide, power down, use low berths... see how everything comes back to low berths? ;)
> A big ship might be a big target, but at long distances, the size of
> targets may matter less (it's a fraction of a degree of angle to
> adjust) and for guided munitions, they aren't getting small enough to
> dodge those.
Dodging works differently in space, regardless of the weapon.
For guided munitions, it's a matter of max accel *and* total
available delta-V.
Assuming the drive isn't reactionless and/or power isn't small, cheap, and available and easily to hand.
If the ship has a higher accel, the odds of being
able to hit it are essentially nil unless the muntions are very
stealthy and lying in wait for the ship to come to them.
I kind of assume a missie designer designs most of the time for higher accel than a ship. That's not 100% of the cases, but I'd imagine 80%+.
And if you lie in wait, that's more mine than missile.
If the munitions have a higher accel, they have a *small* chance. It
all depends on agility *and* delta-V. Doesn't matter if you have a
higher accel if you run out of fuel before you can hit the target.
In a non-reactionless thruster scenario or a situation where energy supply is limited by heavy fuel (vs. zero point energy or whatever).
> Aiming lasers beyond 10K km probably requires gravitic lensing (hence
> we need gravity control).
Actually the limit is not *aiming* (though that's a major problem)
but beam focus
You are more explicit - that's what I consider part of aiming. If you can't get focus, your aim is meaningless.
The size of the beam aperture sets a distance at
which the beam will start spreading badly no matter *what* you do.
Yes, and that was covered in some detail in Brilliant Lances for TNE.
Well, at least until you get beam densities so high the the photons
start to auto-collimate due to their mutual gravitational attraction.
But a beam that strong would have no trouble slicing a *planet* in
half.
Ah, Death Star! ;)
> I'm assuming that railguns and the like over 500 or 1000 km probably
> require amazing predictive gunnery software to hit with because of
> travel time.
This is where we get into the fundamental principles of evasion in
space.
First you've got "tracking lag". Tracking is either using direct
emission from the ship, or reflected radar/lidar pulses. Both travel
at lightspeed.
Or a passive visual solution. Or a passive thermal solution. Or some energy detection.
But yes, lightspeed is a boundary, but beyond that, the impulse of kinetics suggests more limited ranges that something like a laser or particle beam.
So at 300,000 km, your tracking info is one second old. At 300 km.
it's one *millisecond* old. So that's "tracking lag".
Yep. And you get a data point on your PPI (past-position-indicator) display and a probability cone of where the ship might be going based on the characteristics you expect from it.
In reality the lag will be longer due to things like signal
processing (ie how long does it take the sensor hardware & software
to turn the incoming signals to usable targetting info)j
That might be nanoseconds depending on your gear at a high enough tech level.
Second you've got "time of flight". That's how long it takes the
beam, missile or projectile to get from your ship to where you expect
the target to be.
Yep, another lag. So your firing solution has to factor in:
- Where the ship was last seen (with error bars)
- The velocity the ship has last appeared to have (with error bars)
- The predictive estimates of where it could go (given ballistic course or following existing acceleration, or if it did every sort of jink and manouver that it cold) - with error bars
- Then a probabilistic estimate of where one should saturate with fire that incorporates all of that and tries to guess where to fire
Add the two together and you've got total lag. Which is also how much
time the target has to evade.
Yes, of course it could fail to do that, but one has to expect manouver very regularly if there isn't a really tight delta-V issue. Without that, ships should almost always be jinking around in combat.
This is where a seemingly complex problem can be *drastically*
simplified. Rather than using *your* frame of reference, use the
frame of reference of the target.
Treat it as stationary in its frame of reference. In yours, it's
moving at a *constant* velocity on a particular heading. Yes, we
ignore acceleration for the moment.
By doing this, any evasion becomes acceleration from "at rest".
That's very easy to figure.
Easy to figure, but if the vessel being targeted is highly manouverable, it can cover a lot of potential area and be perhaps a very small target in that envelope.
For now, we'll assume the ship can apply its full accel in any
direction (ie we ignore how long it may take to rotate the ship to
get the main drive pointing in the right direction)
Sure, that's the simple case.
Real physics and inertia and momentum tend to significantly affect that simplification though.
So, for a laser, at 300,000 km, the ship has *two* seconds to evade
(one sec of tracking lag, plus 1 sec of flight time for the laser
pulses).
Plus processing if one is being realistic.
And if humans want in that loop, that's another 2 seconds minimum.
Also you haven't mentioned errors in location, speed, vector, etc. for your target.
We aren't counting detection time of the incoming pulses,
because the ship may be evading anyway, and they can detect the
pulses before they get there anyway. (for that matter, it's fairly
likely that they won't detect pulses that *miss* either)
so if the ship has 1 g of accel (we'll use 10 m/s^2 to make the math
simpler) in 2 seconds it can shift its center of mass by 20 meters
(d=0.5*a*t^2)
If the ship has a radius greater than that, you are pretty much
guaranteed a hit. If it's max dimension is onl 10 meters, there's a
fairly good chance you'll miss.
With a single shot, if your weapon is not pulsing across an area of space at a fast rate in some pattern.
Particle beams travel a *lot* slower than light speed. So there's a
lot more "time of flight" lag. and for railguns, any feasible launch
velocity pretty much guarantees a miss at long ranges.
Yes, that's pretty much what I figure.
Realistic space combat ranges in settings without magic power or reactionless drives and no inertia or momentum will tend to be short.
But given the dynamics of acceleration and vectors in meeting engagements, it can really make for low odds passes or it requires the two combatants to want to get close. If your reach (with accuracy) is low, then your odds of actually engaging effectively is a lot lower.
At shorter ranges the evasion time gets shorter.
also note that
"jinking" as it is normally understoood is pretty useless. To
actually move your center of mass enough from your predicted location
requires *seconds* of thrust on a bearing.
Under real physics as we know them, yes.
If, for instance, anti-grav cancels the properties of mass to create inertia, the manouvering might be dizzying.
More seconds the bigger
the ship is (and it gets a lot worse when you include time to change
the ship's orientation)
Depends on your setting for sure. Real physics as we understand them sure seems to agree with you.
For lasers, if the beam can stay focused that far out, you are in
trouble at a light second or more if your ship is at all large.
Assuming no clouds of ablative gas, or ice armour, or reflective mirrors leading your ship in as a shield, etc.
There's lots of conditions that can fuzzy up this simple case.
For particle beams the "oh shit" distance is a *lot* shorter.
Missiles, shorter still. And for railguns, you might as well not
bother unless you are stupid close.
I figure that's in the hundreds of kms. Maybe a thousand or two but not more.
Now flip this around and consider *defensive* fire.
Nothing you can do about lasers except use sand.
Water clouds can suck out energy and also cause dispersion. This was the basics of Knight Hawks' Masking Screen. Note: Ballistic, cannot manouver with you.
Which quits covering
you if you change course or speed.
Yes. Same with water. Or an asteroid you are following unless you've stuck engines on it.
Ditto for particle beams.
I thought the idea with C-PaWS was that a sufficient field could deflect the charged particle stream? (That sounds hard albeit in terms of getting the field up, strong enough and where and when you want it).
Missiles you can try using your missiles, railguns and lasers on.
Or sand. Or even kinetic ERA (reactive armour) if you are expecting contact hits.
And
the closer they get the less effectively they can dodge. Unless your
point defense is overwhelmed, or you are stupid close they aren't
very likely to get thru.
Flooding PDS is one thing, but also creating enough debris from destroyed muntions on the incoming trajectories has a likellihood of buggering up point-dense targeting for subsequent waves.
Railgun rounds are hard to spot (but give a very significant EM
signature when they are fired).
Yes, but only at close ranges because of the cubic fall-off. But with railguns having short ranges, flight times will also be short so the spot might not do you a huge amount of good unless there is a really fast defensive system that can do something dramatic in short time frames.
Worse, lasers and particle beams may
not be very effective. You have to *destroy* the rounds. Even if you
melt them they are gonna hit and do damage.
Maybe. If you graze them, the sublimation of some of the round may alter the trajectory enough to miss. Similarly, some sloped armour panels may work well for directing a lot of the force away from the innards of the ship via deflection.
Missiles are easier. If you knock out the electronics or drive/fuel
tanks, they can no longer manuever and can thus be ignored unless
they are still headed at you and are too close to dodge.
Assuming they are not in-line and packing a bomb-pumped laser or the like.
> Smaller ships jink easier. Saturation of cones from rapid fire guns
> may be one way to generate hits, but individual damage will be less
> than a single heavy penetrator but they will hit more readily.
At typical Traveller velocities, very few rounds are going to act as
"pentrators". At 3 km/sec relative velocity (5 minutes at 1 g) a
round will flash into plasma on impact releasing the enery of an
equal mass of TNT.
Yes, but it is mass-limited. Penetration in this case may mean 'bigger explosion which vaporizes deeper into the ship'.
Not only would that make an impressive crater in the armor if it
didn't blast a hole in it, but it'd also cause massive spalling on
the inner surface.
That's somewhat dependent on armour design but sure. You and I see eye to eye on how the physics works in favour of more, lighter, faster projectiles.
If it does blow thru the armor, you'll have a multi thousand degree
jet of plama moving inwards at hundreds of km/sec.
Which seems bad, but I'm sure having a laser shot through your hull is as bad. And a c-beam could be considerably worse for other reasons.
As you can see the rules for hypervelocity projecftiles are *way*
different from anything we are used to currently.
There's the issue though: Lasers just emit light. So they need to generate X numbers of joules that they can turn into photon streams.
For railguns, the energy required to massively accelerate a vast stream of light projectiles is pretty high to get those high velocities. The range limits and the amount of power needed for a lot of railguns may limit their use, whereas lasers may be more useful for the range alone.
> If you do have a heavily armoured large ship, you may be able to take
> some of the small stuff without too much damage. Fighters and ships
> may have (at least near term) delta-V constraints which will
> drastically limit battle plans, manouvering, and the ability of
> missiles, fighter, and other small craft (drones, etc) to speed
> towards an enemy that is manouvering and have enough fuel left to do
> final attack runs. Most battles will tend to look like jousts.
> Adjusting to change and pass again or pursue is a lot of delta V.
Keep in mind the sort of attack runs Babylon 5's fighters made. Since
orientaion has nother to do with velocity, when they could make
"close" passes on enemy ships, they'd just rotate the fighter to keep
the guns pointed at the enemy ship as they made a pass.
Sure. But if they have a lot of V built up, they'll be out of effective range quickly for projectile or plasma weapons. And ship sized lasers may or may not fit on fighters in some settings.
Then it was
decelerate to a stop (far passt the target and accelerate back to the
battle for another pass.
Yes, passes happen, but the second one will likely be slower (or long delayed otherwise) - catching back up for another pass, esp if the other guy decides to not turn to come back, is going to be a long climb that burns a lot of delta V.
Unless by some remarkable coincidence both sides have nearly the same
velocity (speed *and* direction) that's how most battles will go.
Yep.
Fire at the enemy as you aproach, keep firing as you pass by (or
*thru* the enemy formation) and keep firing until you are out of
range.
Yep.
Orbits, facilities, and so on or converging tracks (rare) could change that.
Going back for another pass pretty much requires either mutual
consent *or* that one side has vastly superior acceleration.
Yep.
And in case you missed it above, "sneak" attacks are moderately easy.
With
lasers you won't even know you are being fired upon unless there's
*very* near
miss or you sensors are looking *closely* at the firing ship at the
right time.
Or you've got a medium in the space around you that will fluoresce when a laser burns through. That'd be one way, but it has the same issues as Masking Screens or other methods that require you not to manouver.
Particle beams are a lot "noiser" and likely to be detected unless
they miss by
a lot.
Missiles, probably fairly easy to spot.
If a ship can stealth, I suppose ballistically tracking missiles could do that.
Of course, if your enemy keeps steadily steaming on the same vector, they are pretty dense.
Railgun or other dumb projectile weapon, you are unlikey to detect
the projectiles. Though there may be a firing signature (EM pulse in
the case of railgun, gas in case of conventional guns)
And you may hear the bangs when they hit solidly or glance off.
So if done right your first clue you are being attacked might be
lasers or projectiles blowing holes in the hull.
If you didn't see the other guy coming half a system away.
One of my buddies is a space sensor scientists and he says the sensors can detect fractional Ks off the background radiation and future compute capacities will allow full sky scans with full resolution in multiple frequencies in real time. The tricks to slip past detection at great range will be few and limited.
--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com
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