Hi all
Just thinking about sensors and a game at a higher level than the tabletop FT.
By higher, I mean longer time and distance scale, with more hide and seek.
Brian posted his ideas and I skimmed them, but I'm working on my own so I
thought I'd quiz the list intelligentsia.
Specifically: 1) At what range could one likely detect a starship with good
passive sensors? By that, I mean optical (visible and not visible spectra) and
other similar systems. Something that doesn't rely on "wazoo newtech".
2) How much does the answer to 1 depend on if the ship is thrusting?
3) How much does the answer to 1 depend on if the ship has activated some kind
of active sweep sensors or firecontrols?
4) How much does the answer to 1 depend on mass of the vessel?
5) How much does the answer to 1 depend on
EMCON levels employed? (is silent/black running
of any use in space?)
6) I assume there are three phases to engaging an enemy:
1) gross detection - there's something out
there, even if it is too far away to tell what or how many
2) fine detection - we can tell how many,
perhaps what thrust, what mass, are any emitting
3) lock-on - we have a fire control solution
I assume passive sensors will generally take you through phase 1 and maybe
phase 2, but you definitely need to "go active"
(sensors/firecontrol) to get 3.
7) Does using active sensors increase your ranges for the first phase of
detection? Or are they long enough that your pathetic amount of emitted energy
just has no effect? I am sure active sensors would have some impact in the
second stage, and obviously firecontrol is the third stage.
8) How feasible are recce fighters or stealthed drones or missiles with
sensors and a link back to the ship to extend your active or passive detection
radius? Would communications with such a drone or fighter not become
problematic beyond <insert arbitrary range>? Or if you had to suddenly
manouvre in combat, thus breaking your hard to detect presumably direct laser
link?
9) If I have ECM or an area jammer, I assume that I'm making detection level 1
easier and detection levels 2 and 3 harder. Turning on the jammer systems
would mean people would quickly discover something was emitting out there, but
exactly where (more than a general few mu area) might be significantly more
difficult to pin down than without the jammer. So you'd never use ECM or
Jammers until such time as you thought the enemy already knew you were there
(otherwise why give up your invisibility). Is this right? Or don't I get how
real
EW jammers/ECM work?
This is just some starting points for my thinking. But any input from people
with solid ideas or some sort of domain expertise (or a keen interest) would
be worthwhile.
From: "Thomas Barclay" <kaladorn@fox.nstn.ca>
> 1) At what range could one likely detect a
Reasonable passive sensors: Types:
EM sensors - ie everything from Gamma-rays to
HF radio, including light. We can do this now.
Forward Mass Detectors (not wazoo as such, we just haven't seen the need to
build them yet).
Particle sensors - Mesons, Neutrinos etc.
We can do this now, but the measuring devices are huge (for neutrinos anyway).
I've seen posts on sfconsim-l that lead me to
believe that you can detect anything as low as 24 magnitude by IR Call it a
breadbox with a mirror finish in bright sunlight (not eclipse) near Mars if
I've done my sums right.
> 2) How much does the answer to 1 depend on
Depends too much on the thrust mechanics. If a rocket with a plume, we could
be talking
detection at a range of Light Years if a matter/
antimatter fusion torch. If an inertialess drive, who knows? Maybe nothing. Or
maybe it
emits tau-neutrinos detectable on the other
side of the Galaxy, after a few hundred millenia.
> 3) How much does the answer to 1 depend on
Regardless of the actual technology, whether it's using Electromagnetic or
gravitational waves, or particles, an active sensor must both emit and receive
the reflection. This means that the range to counter-
detect will be (relative receptivity) * distance* X *
Y.
X = 2 if inverse-square propagation, else 1
Y = 2 if linear or inverse-square.
Relative receptivity might be > 10 if it's a good ESM suite, but probably a
lot less than 1 if the opponent is
frequency-hopping randomly.
So anything from half the distance to 100 x the distance, depending. 3x is a
good rule of thumb.
> 4) How much does the answer to 1 depend on
It depends on the mass (if using gravitons, gravitational waves, or measuring
space curvature, which the FMD does). It depends on the mass if what you're
detecting is a power plant, assuming bigger ships require more power. It
depends on
the cross-section otherwise - you'll often see the
term RCS or "Radar Cross Section", which is
a combination of the physical cross-section with
the reflectivity. Anyway, assuming all ships are
homogenous spheres of uniform density, cross-
section is proportional to the 2/3 power of mass.
But differences in reflectivity vs various sensors can
change the cross-section by a factor of 100 or more.
So a stealth aircraft may have a physical cross-section
of 5 square metres, but an effective RCS of 0.01 square metre.
> 5) How much does the answer to 1 depend on
Vs active sensors - marginally. If you're not accelerating,
you might just be a rock. OTOH if you ARE accelerating at 1 g, you're no
asteroid! Vs passive sensors, it depends.. Usually if you're using more energy
to move, or sense, or fire, you're emitting more. Of course if you're firing
Gamma-ray lasers, and the other guy only has Infra-Red
detectors, you won't be detected. But generally, yes, you will stand out
either more or a helluvalot more, the usual case being the latter.
> 6) I assume there are three phases to
This is the distance that we detect asteroids now. Basically, if we get a
radar return from an object that's got an RCS of 100 m^2 at 300,000 km, we
assume it's
a rock, not Elvis coming home in a non-accelerating UFO.
In a military situation, we can't neccessarily make such an assumption.
> 2) fine detection - we can tell how many,
It depends too much on the exact mechanics.
> 3) lock-on - we have a fire control solution
True. Passive sensors generally are Fuzzy though a passive detection may be
enough to fire a seeking
or area-effect weapon. And enough passive sensors
for long enough can be good enough for any shot at short range. Remember your
eye is a passive sensor in daytime. Your eye and a torch is an active obne at
night. At short ranges, you even have coincidence rangefinding, if you have 2
working eyes.
> 7) Does using active sensors increase your
Usually yes. Consider a torch at night.
> Or are
Usually no. But consider IR goggles and an IR torch at night vs someone who's
relying on eyes alone, hence the "usually".
> I am sure
True.
> 8) How feasible are recce fighters or stealthed
It depends.
> 9) If I have ECM or an area jammer, I assume
Actually, you're making detection level 2 easier up to a point. Asteroids and
merchants, and even friendly militaries, don't jam. So we know you're a
confirmed hostile military vessel. What we don't know is whether you're a
single corvette or a whole Task Force of Dreadnaughts.
Though that's Noise Jamming.
There's also Deception Jamming, where you send
out delayed, advanced or frequency-shifted signals
so that one ship appears like many, or it appears to be going at a different
acceleration or direction,
or even (with sufficiently good electronics) phase-
shifted so that it cancels out an incoming pulse and you appear not to be
there.
We know how to do all the above vs EM signals, but not vs gravitons etc.
> Turning on the
True. I can think of no exceptions off the top of my head (Noise jamming that
is).
> So you'd never use ECM or Jammers until such
I'll give you a typical example of what happened in an air defence exercise 15
years ago.
We were on a destroyer. The first indication of
attack was when we detected the I/J band search
radars of the atacking aircraft. As the signal strength increased, then the
bearing became constant, we flashed up our active sensors as we figured we'd
either been detected or were about to be. Shortly thereafter we detected a
Shadowing aircraft which was
guiding the attacking F-111s in, and had detected us
by passive means, but not located us exactly. The Shadower then started using
Confetti (Chaff) and active jamming on that sector, which meant that we
had some difficulty seeing the F-111s on radar. We
knew there were at least 2, from 2 different radars, but there could have been
a dozen.
After we'd fired a bit at the F-111s (simulated launch)
and they'd fired at us (ditto) we were suddenly surprised by a brace of small
Macchi trainers that had
sneaked in on an opposite bearing, wave-hopping so
they were out of line-of-sight from us until they were
within 2km. They'd been guided in by the Shadower, and only popped up to see
us (and allow us to detect them) when there was a real danger that they might
collide with us if they didn't. The waves were very high, sea state 7, just
after a force 10 gale.
So in summary, you have it right, but the devil's in the details. Choose your
PSB carefully and you can get pretty much whatever answer you want.
> But any input from people with solid ideas or
Well, I've designed a few surface combat systems in my time that are on board
a variety of naval vessels. And done bits of submarine combat systems too. ( A
combat system is the computer network that takes data from the sensors, tries
to figure out what it all means, displays the result to the crew, controls the
weaponry, and in advanced cases, makes suggestions on what to do next). And
I'm currently doing spaceflight avionics for a research satellite. So I guess
that I'm probably
qualified. Marginally. :-)
One thing to note: it does you no good to detect something if you can't pick
it out from a zillion other things you're detecting at the same time that are
of no interest to you. As in the traditional needle in a haystack, or rather,
a needle in a stack of pins... So a needle can be detected (on its own) by
eyes during day on a black background at maybe as much as 20 metres, more if
it glints. But put it in a stack of pins,
> Thomas Barclay wrote:
I'm going to take a stab at these. Bear in mind that I do NOT have
professional qualifications in this area, I am operating on a roughly
University-level physics knowledge and my experience from a number of
these discussions in the past. My most frequent source will be a
professional astronomer who posts regularly on sfconsim-l (Bruce
Macintosh)
> Specifically:
This depends on what you're trying to detect, so I'll split it down a bit.
1) If you want to detect heat emmissions alone (just the fact that the
ship is at ~300K (it has a crew) and space isn't), then a ship-mounted
set of telescopes can do a full-sky scan to detect said ship at 1AU
(from the detector) in ~24 hours (using present-day telescopes
(near-infrared)). Using 1000km/MU and 15 minutes/turn, that means that
ships can be detected at 150,000MU within 96 turns, BY HEAT EMISSIONS ALONE.
2) Unless the ship is 100% black (even 99.99% isn't quite good enough) you
will have a comparable range to detect a ship by reflected sunlight (out at
least to Mars orbit, possibly farther), within the same
timescale (again, present-day telescopes).
3) If the ship is using a reaction drive, present-day scopes
could see
it out as far as Pluto orbit. 4 non-ship-mounted scopes could do a
full-sky survey in ~16 hours (64 turns) (roughly 4,500,000 MU). One
ship-mounted scope could do it in 72 hours (288 turns).
These full-sky surveys will take awhile, but for a ship to
actually get very close before being picked up, it would have to be moving at
a rather extreme velocity and have very high thrust.
> 2) How much does the answer to 1 depend on
As above. A considerable change.
> 3) How much does the answer to 1 depend on
I haven't even considered this, because it depends too much on what exactly
the active sensors look like. In any case, due to the inverse square law, you
can detect active sensor use at least twice as far away as the active sensors
can detect you (assuming the same detector, same
cross-section, etc.)
> 4) How much does the answer to 1 depend on
Not much at all. Note that if they have a reaction drive, and use it, you can
get thrust from the drive's spectrum, and the ship's mass from the combination
of thrust and acceleration.
> 5) How much does the answer to 1 depend on
Not really. Keeping your whole ship at 0 degrees centigrade could help, but it
would have to include crew quarters, and that wouldn't be very comfortable.
Even so, the above (1AU) detection would then require the 'scopes of 2 ships
(or, it would require us to make some advances in
technology over present-day telescopes, not impossible over the next 200
or so years).
> 6) I assume there are three phases to
I'm not sure that this quite applies. Now, passive detection from 1 platform
won't get you everything. 1 and part of 2, most likely. However, detection
from more than one platform will get you parallax, which will get you all of 1
and 2, and some of 3 (if they're thrusting, they're a known quantity. If they
stop, they can be hit at an arbitrary range, because now they're ballistic.
Once you see a ship from its thrusters, a dedicated scope can pick it up from
heat alone at the same range).
> I assume passive sensors will generally take you
I'm not sure of this.
> 7) Does using active sensors increase your
No, IMO.
> 8) How feasible are recce fighters or stealthed
Communications might be problematic, depending on laser spread. Thrust would
be bad (the figures for thrust above assumed a space shuttle main engine (not
all THAT powerful, and on a Mass 1 or less ship in FT terms I believe).
> 9) If I have ECM or an area jammer, I assume
This, I don't know about. I don't know much about EM myself.
As for fire control, there were recently an interesting series of
articles posted on sfconsim-l by a person whose job is in that area.
They generated some debate (mostly clarification), but are quite informative.
They're probably in the archives, or I could ask him for permission to post
them here.
> This is just some starting points for my thinking.
Hope I was some help,
ref #1 below Spacecraft Imaged At Long Range Spacewatch imaged the Galileo
Spacecraft on the night of November 28, 1992 as it made its second close flyby
of Earth. It was 8.06 million kilometers from Earth when the following images
were
obtained - a record distance for an observation of a man-made
spacecraft.
http://www.lpl.arizona.edu/spacewatch/other.html
range: 26.87 lightseconds
[quoted original message omitted]
> Thomas Barclay wrote:
> Hi all
I think this was heavily assaulted in a previous thread on sensors that
evolved into an email discussion on Low-Probability-of-Interception
(LPI) radar and the problems of trying to quickly locate an object that
is light-seconds away with active sensors, between Derk Groeneveld and
myself. The subject was Re:[FT] Flashes was: a couple of quick replies. We
indulged in some technical speculations about what could be done.
> Specifically:
Given that SETI has to remember where the Voyager probes are and using 1mu
equal to 1000km but remembering those asteroids that sneak up on us, somewhere
between 450 (radius of the moon's orbit [approx.]) and several hundred
thousand (way past Jupiter). Given that warships will try to avoid detection,
probably a good guess is 1000mu. One of the primary sensors for detection is
infrared, near infrared, and microwaves, because the ship will be radiating
heat against the 5 kelvin background radiation and the contrast between an
object and its background is proportional to the fourth power of the
temperature difference.
> 2) How much does the answer to 1 depend on
It depends on the mechanism for the thrust, but if the thrust plume is
pointing at something, that something will be able to detect the inbound from
a long ways away. For example, if a Bonaparte class is thrusting directly away
from a base, that base could probably detect the drive
plume at a distance of several light-hours. The variation for other
angles would be specific to each class of ship, and could vary widely between
vessels of different sizes, with engines of the same power output.
> 3) How much does the answer to 1 depend on
The simple rule of thumb is that for equal receiver sensitivity, the passive
set can detect the transmissions of the active set at the square of the active
set's range. So the active sensors of a pds (range of 6*10^6 meters) can be
detected at 36 million mu, if the receiving set knows what to look for. Even
if the passive set does not have
fore-knowledge of the pulse modulations and frequency hopping of the
active set, it will still detect the active emitter long before the active
emitter's receiver will detect a return echo.
> 4) How much does the answer to 1 depend on
All other things being equal, the larger vessel will be easier to detect
because it has less surface area per unit volume to radiate away heat, so the
hull surface will be at a higher temperature [see response to 1].
> 5) How much does the answer to 1 depend on
Plenty, but it is harder to do [see responses to 1,2,3]. Ships will have a hot
and a cold side. The cold side will be oriented towards the likely direction
of the opposition, and the hot side will be pointing away. The more ship's
surface that made cold, the hotter the hot surfaces must be. It is likely that
the simple expedient of making the drive nozzles hot, and everything else cold
is used, and an aweful lot
of time is spent coasting towards the target with off-axis thrust to
keep the vector pointing at the target. Screaming in at high speed and
decelerating towards the target will let them know that you are coming once
you get to the turnover point.
Active sensors are only switched on when you know that the opposition has
found you, much like the active sonar of a sub.
> 6) I assume there are three phases to
Just like ASW.
> 1) gross detection - there's something out
At 1000km per mu, the propogation delays of active sensors may actually be too
long to provide useful information, but it will help the passive sensors. At
smaller scales (tens of km per mu), active sensors rule.
> 7) Does using active sensors increase your
Only if your opponent is using them (IMHO).
> 8) How feasible are recce fighters or stealthed
At any significant range (about a light-second) the recce unit needs to
know how the ship will move, in advance, because the time to
re-establish the link will take at least as long as the propogation
delay IF the recce unit can detect the unit that is receiving its
transmissions. However, a picket could detect inbound ships that have just
jumped into the system, FTL to the base and let the defending units know where
to jump to find the (hopefully) still disorganized and scattered inbounds.
An attacking fleet that has just jumped into the system has the terrible
problem that there is no quiet way to let everybody know where everybody else
is. They have to send out omnidirectional signals with a modicum of power, or
risk arriving at the battle in scattered penny packets (this is the one good
reason to use battleriders and tugs, the whole squadron arrives in the same
place, but you may as well spend the extra 9.1% to allow the battleriders to
flee on their own).
Even though the pickets are spaced three or four light-hours apart, you
will still need dozens of them (another valid reason for campaigns to have a
lot of small ships).
> 9) If I have ECM or an area jammer, I assume
You would use EW/ECM for different things, rather than concealing the
existence of a ship, you would obscure what the ship actually was. Stingboats
would pretend to be SDN's, the main battleline would try to emulate a mass of
stingboats. Decoys would pretend to be ships and ships would pretend to be
decoys. Ships would pretend to be heavily damaged after being fired upon,
maybe even detonating a nuke to fake their destruction.
> This is just some starting points for my thinking.
G'day guys,
Sorry this isn't exactly on topic, but thought you might be interested to hear
how effective passive sensors can be (probably old news to many of you, but I
thought it was cool).
This was on the cnn site earlier this week
Cheers
Beth
> [quoted text omitted]
WASHINGTON (AP) -- America's stealth bombers may be in danger of having
their cover blown by a new type of radar that uses cell phone technology,
researchers say.
The Air Force says it's a limited problem and America's unique stealth fleet
is in no danger. Yet U.S. intelligence reports label the radar a serious
threat, and several scientists agree.
"We're talking about radar technology that can pinpoint almost any disturbance
in the atmosphere," said Hugh Brownstone, a physicist at the
Intergon Research Center in New York who has worked for the cell phone giant
Nokia.
"You might not be able to distinguish between a stealth plane and a normal
one, but you might not need to. The point is, you can see the stealth plane as
a blip."
The potential risk comes from the towers used by cell phone companies to
draw in signal patterns. The new technology, called passive radar, watches
signals from common cell phone transmissions. When a plane passes through, it
leaves a hole in the pattern, giving away its location.
Traditional radar -- the kind stealthy B-2 and F-117A bombers can fool
with their angles and radar-absorbing paint -- sends out signals and
waits for them to bounce off large objects in the sky and return.
Some aviation experts suspect the Serbs used a rough version of passive
radar -- plugging computers into their existing air defense system -- to
locate an F-117A Nighthawk stealth bomber, shot down in 1999.
There are more than 100,000 cell phone towers and other sites within the
United States. Industry analysts estimate there are 210,000 sites in Europe.
The rest of the world is unevenly covered, but even the smallest
and poorest nations often have several cell phone towers.
The passive radar system has drawbacks. It can't effectively pinpoint whether
a plane is indeed a stealth plane or some other aircraft, scientists say. It's
also much more difficult to make work.
"The success rate of these systems is just below the success rate of
traditional radar," said Air Force Capt. Eric Knapp.
A major hurdle is the complex math necessary to translate cell phone
signals into easy-to-understand blips that move across a computer
screen. Without the computer programming to make sense of the cell phone
signals, it would be impossible to fire a missile at a plane.
Still, the passive radar technology is basically sound, said Nick Cook, an
aerospace consultant for Jane's Defence Weekly.
"It needs further work, but the theory is there," he said. "Still it would be
some time before I could imagine something like this compromising stealth
technology completely."
John Hansman, professor of aeronautics and astronautics at the Massachusetts
Institute of Technology, said passive radar is still in its "infancy, but is
something that will lead to new stealth research."
"This is another trick that will force stealth researchers to push forward,"
Hansman said.
The British defense contractor Roke Manor Research is in the forefront of
passive-radar technology.
Peter Lloyd, head of research there, said, "We would be utilizing technology
that we already have available. The mobile telephone base stations would not
have to be altered at all. "
His company's Web site claims existing stealth technology already has been
rendered obsolete.
Brownstone believes China, Japan and Russia already have passive radar in
various stages of development. He is concerned that those countries might sell
the technology to smaller countries that are hostile to the United States.
Keeping stealth planes safe from enemy radar has always been a
back-and-forth contest, pitting American ingenuity against developing
concepts in radar.
The F-117A, developed in great secrecy in the 1970s, was not disclosed
until 1988. It saw its first combat in the 1989 invasion of Panama and was a
star of the 1991 Gulf War.
The B-2 bomber, which saw its first combat in NATO airstrikes against
Yugoslavia, uses stealth technologies that are more advanced than the
F-117A's. An even newer version of stealth is used in the F-22 fighter
now in development. No other country has stealth aircraft in active use,
although Russia and others have researched the idea.
Six of the $2 billion B-2s, in their first combat use, flew about 50
secret missions out of a total 30,000 NATO bombing runs over Kosovo in 1999.
They dropped about one of every 10 bombs in the campaign.
> [quoted text omitted]
> Per Varis Casus wrote:
> Spacecraft Imaged At Long Range
Or about 8000 MY in FT terms, at 1000 km per MU.
Thanks very much for this link - it gives us the right
order of magnitude to be looking at.
This is with a 1.8 metre telescope, through an atmosphere,
using late 20th/early 21st century technology.
I think we can agree that detection is marginal, but
definite - and that even basic identification is not possible.
There's an object there. Of about the right size. Where we expect Galileo to
be. Had we not been expecting a spacecraft there, I doubt it would have been
recognised.
Things that would improve performance: 1a) No atmosphere when looking from
spacecraft 1b) Technology 200 year advance 1c) Possibly larger aperture sensor
1d) No terrestrial vibrations (big trucks nearby, earthquakes etc)
Things that would degrade performance
2a) Possibly trillions of similar-sized objects, from decoy
balloons to pieces of wreckage, some of which would be set up to look exactly
like the target. 2b) Lower integration time ( ie less than 3 days) 2c)
Possibly smaller aperture ( must scan entire sky, not just a bit of it) 2d)
Vehicular vibration due to thrust, people moving inside
in microgravity, non-rigid structure, thermal differences etc.
I reckon that 1a,1c,1d are cancelled out by 2c,2d pretty nearly. That leaves
1b vs 2a, 2b. I have no difficulty believing that sufficiently good sensors
could exist in 200 years to actually get a recogniseable image of Galileo at
that distance. To differentiate Galileo from, say, Pioneer 10 which looks
similar would be more difficult. To be able to read the nameplate, which says
"Galileo" rather than "Decoys R Us" is more difficult still.
Had it been spray-painted black, it may not be detectable unless much
closer.
Wrap it in rock-coloured tinfoil, and you'd have a really hard time
telling it from an asteroid.
So I'll just ignore the the problem for now, it's PSB. Maybe they cancel out.
<intellectual honesty mode = OFF> Galileo masses what, a few tonnes? Call it
size 0.02. It's actively emitting telemetry towards Earth, call it the same as
an active search sensor's counter-detection range (2000).
It's civilian (ie no attempt to hide it), so multiply range by 2. (4000) It's
previously detected (ie we expected it to be there), so multiply range by 2
again. (8000) So I'd expect us to be able to detect a spacecraft of about this
size as a faint, fuzzy blob of indeterminate size that can be identified
as a "possibly telemetry-emitting spacecraft" at about 8 million km.
Which we did. QED The System Works, and is a good simulation of reality.
<intellectual honesty mode = ON>
> Beth Fulton wrote:
> Sorry this isn't exactly on topic, but thought you might be interested
-->8--
> The potential risk comes from the towers used by cell phone companies
Unless the aircraft has a low-powered cellphone repeater on board....
For the same reason, a dark ship that is slightly illuminated at night is more
difficult to see than one that isn't.
Yes, it's old news to me, but you're right, the temperature approaches zero
kelvin. Thanks for relaying it. And it illustrates well some of the problems
in detection, and the sophisticated (and sometimes surprising) countermeasures
required.
Sorry, I refused to say "cool" when it was popular in the 60s, I refused again
in the 80s, and I'll be darned if I'll say it in the 00's!