Dealing with space sensors can be tricky. First is where are you using your
sensors? Deep space use will give you a better range than in-system use.
The
planetary bodies emit and/or reflect enough radiation that they can mask
anything near them. In deep space there is less interference. A wonderful
example is to look at the stars while in a city, and then to go somewhere
remote, away from the city lights and look at the stars. Without the
interference from a city lighting system you can see stars that you could
never see otherwise.
Of course ships operating in deep space (especially on reconissance or pirate
missions) will probably be "Running Silent" or on "Emm.Con.". This would
entail minimising or controlling all emissions: magnetic, radar, engines,
ect., closing all windows (light emissions) and generally making onesself fade
into the surrounding blackness. While standard procedure for military ships,
even civilian ships might use this technique between jumps to avoid being
raided. So "Running Silent" might in theory negate the bonuses to sensor
operations in deep space.
As far as how well we watch our own solar system: Yes we do have very good
data about other planets, we even have reliable information about what some of
them (mostly the gas giants) are composed of. But this kind of data takes
months to gather. A spectral analysis must be averaged againtst time, the
combined orbits of the observer and the observed, rotation speeds, eclipses,
ect. to compensate for a host of possible errors, the least of which not being
the infamous doppler shift. If you want to see something the size of a fleet
carrier, in time to do something about it, you are limited to the distance
between the earth and the moon. This kind of detection is only practical for
ground and space stations, a moving ship causes too much distortion, mostly in
parallax, to warrant having those kinds of sensors, unless it is a dedicated
science vessel, which usually would end up in geosynchronous orbit anyways.
As far as sensor "Evading": Very few modern astrophysical sensors are
directional. Radar is a commonly used device, then with the radar detection
the optical, IR, and Thermal cameras can be trained on the target. We have the
technology now, that would be practical to mount on a starship to have a
contstantly rotating camera array creating a "Photo Mosaic", updating each
time the camera passes. Multiple array's of cameras with overlapping fields of
view may even be able to give a real time 3D view of the surrounding space
(either with the computer alerting the sensor operator to potential targets in
a specific area on a normal screen, or projecting a holographic representation
around the bridge with a HUD overlay on it, depending on your preferred level
of cinematism).
Then there's the manuver itself. I assume that space combat occours at the 1
inch = 1 kilometer scale. That makes the average table 60 kilometers by 40
kilometers across (30 mile by 20 mile) a respectable distance for space
combat, and more than most space sci-fi shows give themselves. Trying to
"Jink" off even an obsolete directional sensor at these ranges is nearly
impossible. Remember, the father away an object is the less you can see it's
movement. at initial detection range (60km by my scale) in order to "Jink" off
of a directional sensor which may have an arc of 45 degrees from center (a
rotating sensor turret would have your ship in the center of the field) you
would have to apply 120 points of thrust (60 accel. 60 decel.), through port
and starboard manuvering thrusters, in one to ten seconds (common time
intervals for RPGs and wargames). This would be the equivalent of being hit by
a asteroid traveling at 21,600 kph to 216,000 kph, twice! This
"delta-V"
will quickly reduce your entire crew to a thin paste of the color of their
insides. Any slower and the detecting ship can calmly track your position as
normal. Even trying to blur your image with such a jink will involve sudden
manuvering acclelleration/decelleration in excess of 1,000 kph /sec.
This will be enough to injure even power armored marines, much less the light
to medium flexible spacesuits the crew will be wearing. If your ranges are
longer (which I see being discussed on the group), this requires an even
faster delta-V with more traumatic consequences.
> On Mon, 26 Apr 1999, djwj wrote:
> Then there's the manuver itself. I assume that space combat occours at
interesting; i assume 1 MU (ie inch) = 1000 km. consider that the orbital
radii in MT are on the order of tens of MU.
there have been extensive discussions about combat at extreme ranges, ie
lightseconds; mostly this centres on the fact that the radar echo takes
several seconds to get back, and your laser takes a few more to get out, so
you have a minimum error envelope of several seconds' worth of acceleration.
people have described a turn's fire as putting out a hail of shots covering
the envelope, in the hope that maybe one will hit.
in contrast, a range of 30 mu in my system is 30 million metres, or 0.1
lightseconds. this isn't too bad.
> one to ten seconds (common time
the consensus is, i think, 1 turn = 15 minutes.
there is an equation.
s length of a move unit (m) f fraction of the turn over which you burn drives
a acceleration of 1 thrust point when burning (m/s^2)
t length of a turn (s)
s = fat^2
or:
f = s/at^2
a = s/ft^2
t = (s/fa)^(1/2)
the mechanics of FT suggest that f << 1, ie f is quite small. in fact, this
equation is wrong, but it's accurate for small f, and i can't figure out the
fully correct version.
if you put in s = 1000 km, t = 1000 s (16m40s), f = 0.1, you get a = 10
m/s2, or ~1 earth gravity, which is nice.
if you want s = 1000 m, t = 10 s and f = 0.1, you get a = 100 m/s^2, or
10 G. this means you have scouts pulling 80 G, though. this is ok if you have
inertial compensators or some such, but your post indicates that you are
thinking more realistically.
anyway, you pays your money and you takes your choice.
Tom
> Thomas Anderson wrote:
> > one to ten seconds (common time
Ahem. The total time you burn your thrusters is f * t, so you get
s = a * (ft)^2
> or:
Should be:
f = sqrt(s/a) / t
a = s/(ft)^2
t = sqrt(s/a) / f
> if you put in s = 1000 km, t = 1000 s (16m40s), f = 0.1, you get a =
I get a = 1000000 / (1000 * 0.1)^2 = 1000000 / 10000 = 100 m/s^2 ~ 10
g. If you instead assume f ~ 1, a drops to a comfortable ~ 0.1 g.
s = 1000 m, t = 10 s, f = 1 gives a = 10 m/s^2 ~1g, which makes this
scale fit nicely with the atmosphere interface rules in the scenario on
MT p. 39 (where the planetary radius is "infinite" - ie, very large -
compared to the gaming area). With f = 0.1, you're back at the somewhat
uncomfortable a ~ 10g.
'Course, if you assume f = 1 you need more complicated vector movement rules
to stay realistic <G>
Best wishes,
> On Mon, 26 Apr 1999, Oerjan Ohlson wrote:
> Thomas Anderson wrote:
Ahem. The total time you spend travelling is t. if you burn at a for ft, then
you get v = aft. if you then travel at that speed for some time u,
you travel s = uv = uaft. although u = (1-f)t, for very small f, u = t,
so s = aft^2.
> 'Course, if you assume f = 1 you need more complicated vector movement
that's the thing; the mechanics clearly describe an impulse-type drive.
i think it's fairly simple to fix the rules though; it's just a pain keeping
track of two velocities every turn. of course, those who want realistic
physics can pay the price. having just played BFG, even vanilla cinematic
is quite realistic enough for me :-).
it's actually possible to construct an equation which does not assume very
small f, and i believe it is illuminating to do so.
if you consider the turn to have two phases, boost and coast, then
s1 distance covered in boost s2 distance covered in coast
s = s1 + s2
s1 = vft/2
s2 = v(1-f)t
v = aft
s1 = a(ft)^2/2
= at^2 * (f^2/2)
s2 = af(1-f)t^2
= at^2 * (f - f^2)
s = at^2 * ((f^2/2) + (f - f^2))
define
k = (f^2/2) + (f - f^2)
so
f = 1 - (1 - 2k)^(1/2)
and
s = kat^2
k = s/at^2
a = s/kt^2
t = (s/ka)^(1/2)
ie, there is a fiddle factor of ((f^2/2) + (f - f^2)) applied to the
simple at^2.
solving for f, i put in s = 1000000 m, a = 10 m/s^2, t = 1000s, and i
get k = 0.1, which gives f = 0.1055728, plus some more decimal places.
unless i'm being absurdly boneheaded today, that's right, isn't it?
and now, GZG-L will return to your scheduled programming for tonight.
Tom
G'day guys,
> Dealing with space sensors can be tricky. First is where are you using
In answer to the question its in system. Derek had done up some sensor rules
for the a campaign we're heading into and then someone said you'd be able to
see ships coming for ages and that stumped him as all the material he was
working off kept giving him fairly minute ranges in comparison to system size
(e.g Basic sensor's extreme range is 150" passive, 600" active
and.ESM 720" - double that for enhanced and double the enhanced ranges
for superior).
As to the scale we're using. 1" = 1000km and 1 turn = 15mins.
I know that was a fat lot of good with regard to advancing the actual debate,
but I thought it might help to put the original question in perspective.
Just one more thing (which is purely out of my own curiosity) if sensor ranges
are so small that you'd only see a fleet coming if it was as close as the moon
etc, how do the fleet find each other to fight? Just wander around until they
fall over something? And I'm not trying to take the mick here (well not
completely), I am seriously curious.
Thanks
Beth
> Just one more thing (which is purely out of my own curiosity) if sensor
A) The defending squadron stays fairly close to the object it is defending
(which makes tactical sense, otherwise you find out that you're defending
against a feint and you're waaaay out here. Meanwhile, back at the
ranch...)
B) I assume that sensor range means "range at which you can achieve a firm
firing solution." You might double it again, or more, to get the maximum
"there's something out there, don't know exactly what, captain, but I'm
picking up traces" range.
G'day Jerry,
> Actually, MT is kind of weird in which it postulates a larger active
Well I don't know anything about real sensors, but in all the other
sci-fi
books/games we've got they have their passive < then their active (not
so much an explanation as an excuse I guess, sorry). Derek also just checked
out his his Harpoon 4 sonar annex and as a rule the sonar systems with both
active and passive modes have an active range greater than there passive
range, so hopefully we haven't stuffed up too badly. Basically the way we
thought about it was if you're standing in the dark you don't recieve a lot
passive info (i.e. not much light so don't see much), but if you start
swinging a torch around (i.e. actively looking then you're more likely to
see stuff that's further away) - once again hope we didn't screw up too
bad.
> And Beth, what's the difference between passive
Well we looked at it along these lines:
Passive: Just looking for any hint they're there (i.e. looking for
light/heat etc)
Active: Ping someone and work off the radiation reflected back to you
ESM: When you're looking for someone else's ping - so don't detect enemy
ships, but do detect the active sensor scans used by the enemy. Bit like that
torch thing again you can see a torch yonks away, but you can't
see/hear/feel who's using it etc.
> So that gives half a light second passive, 2 light seconds active,
And what does that mean? Good Hmmm, bad hmmm, or just hmmmm I 'd rather be
thinking about something else at lunch?;)
> I think Laser had a point
Does that make him a laser pointer (as in the things you use in
seminars) -
OK very sick but I've been at work WAY TOOO long already today.
Cheers
Beth
Well off the top of my head, an active radar ping fade out is, relative to
the range to the target, proportional to 1/r*r*r*r. Passively listening
to
enemy pings is proportional to 1/r*r. So passive should have the range
advantage, but the target has to be broadcasting/pinging.
I'd say the FT/MT sensor ranges better represent listening passively for
non-sensor emissions within 36" and then actively pinging obvious
targets within 54"; ie. active and passive is apples and oranges.
Oh yeah, I forgot to mention that passively listening for others' pings, you
don't know what power they broadcasted at or their precise time of emission,
so you can't always guess range accurately.
And once you get into reflections, multi-path, inaccuracies of bearing
reading in your passive array, etc., you may be only looking for an indication
of where to point the guns, not a firing solution.
> On Wed, 28 Apr 1999, Jerry Han wrote:
> Beth Fulton wrote:
active
> > and.ESM 720" - double that for enhanced and double the enhanced
FT/MT really has two layers of sensors; it has long-range and
short-range.
short range sensors are our friends the active and passive scanners, which can
be used on ships on the table to identify them, etc.
long range sensors are the things which tell you there is even something there
to scan.
thus, when you start out and there are only bogey markters on the table,
your long-range sensors have done their job and figured out that there
are enemy ships out there, and got their position and velocity. they have also
probably got some ghosts, drones, etc.
when you get a bit closer and start pinging away with active scanners, and
looking out with passives, then those are your short-range
high-resolution
instruments: their job is to gather detailed information on the target.
> > I know that was a fat lot of good with regard to advancing the
except that then you open yourself up to the boom'n'zoom attack... i think
interception is the way to go (defender boosts out, then turns round and
matches velocity with the attacker so that the relative closing speed is
fairly small).
> And also the
that's basically what i am saying too.
Tom
> -----Original Message-----
You've summed it up very well, I think. The rub is to abstract this into an
easy to use, but reasonably realistic sensor rules.
Some aspects to capture: * long range jump detection (measured in AU?) "Sir,
four ships have jumped in system outside the designated
civilian/merchant jump zone. Should we send a sortie to investigate?"
* long range plot (500MU-1k MU?)
"Sir, the four bogeys have just come into max sensor range. They are on
course 136, speed 40MU/turn and accelerating."
* mid range plot (100MU-500MU?)
"Sir, Bogey Alpha is 160 MASS, Baker is 80 MASS, Charlie and Delta are 40 MASS
each. Emissions indicate they are most likely FSE.
* combat range (0-100MU?)
"Sir, Captain Bridgeworth's task force has engaged the enemy. I confirm that
Alpha is a Bonaparte, most likely VFE Ceasar. Baker is a Jerez, very
likely VFE Cadiz with that quirky ZC-1800 drive. Charlie and Delta
appear to be 2 Triestes. Their signatures are not in our database at this
time. Recording.
Throw in some ECM/cloaking and drones/weasels and you're in business.
Or something like that.
<snip>
> that's basically what i am saying too.
> Thomas Anderson wrote:
> > > s = fat^2
Doh! You're right, of course. The error you get in s by approximating u
~ t is roughly f/2%.
> > 'Course, if you assume f = 1 you need more complicated vector
It is quite simple. If the thruster pushes go on throughout the entire
turn the ship ends up exactly half-way between the "coasting end point"
and the point where the FTFB Vector rules would put it, but the new movement
vector is calculated between the starting point and the point FTFB specifies.
No more to keep track of than now, but it takes a bit longer to execute each
move.
Of course this "half-distance move" is slightly off if the ship has to
spend time turning, but with 15-minute turns the time required to turn
the ship around should be small enough that the error is <<1 mu. I
usually can't move my ships with half-mm precision :-7
Later,
> On Tue, 27 Apr 1999, Oerjan Ohlson wrote:
> Thomas Anderson wrote:
aah, right, i was thinking of fixing cinematic, for some reason. this
would involve applying your acceleration twice - once to get the speed
to use this turn and one for next turn.
looking at what you wrote, i see what you meant. yes, that would be better; in
fact, when i tried to write my own vector rules, that's how they worked. since
i haven't seen FB's vector rules, i have been assuming they worked like mine.
evidently they don't.
> No more to keep track of than now, but it takes a bit
in my system, you need to do:
- call ship position P
- plot initial velocity vector from P; call the end Q
- plot acceleration vector from Q; call the end R
- measure a vector from P to R; this is the new velocity vector
- place the ship halfway between Q and R, facing R
this assumes a ship turns instantly, points in one direction the whole time
and burns for the whole turn.
i don't know how it's done in FB; i assume the last step is replaced by "place
the ship at R, facing in the direction Q>R".
anyway, it's not a great addition.
> Of course this "half-distance move" is slightly off if the ship has to
i tried to figure out how it should work if the ship turns over the course of
the turns, but the maths rapidly develops a bad case of trigonometry
which i can't cure :-).
the thing about instant turns is that it follows that all ships should be
allowed unlimited turning (at the start of the move), which isn't terribly
good for gameplay.
Tom
> Thomas Anderson wrote:
> aah, right, i was thinking of fixing cinematic, for some reason. this
OK, I see what you mean. The distance along the real trajectory moved
is still (initial velocity + half the difference between initial and
end velocity), which is pretty easy to figure out. The "mid-move turn"
should be somewhere else than in the middle of the move though, since the
turning radius increases with speed in Cinematic <g>
OTOH, Cinematic is... very strange in many respects, so I'm not too
sure I'd want to try fixing it :-/
> looking at what you wrote, i see what you meant. yes, that would be
They are very similar to those posted by Jon T. and Mike E. to the UFTWWWP,
though <g> A few small adjustments, that's all.
[snip]
> i don't know how it's done in FB; i assume the last step is replaced
Drop the part after the last comma and you're there - you can rotate at
any point during the turn, including at the end of the move.
> > Of course this "half-distance move" is slightly off if the ship has
Well.. if you burn your drives *during* the turn, things get complicated very
fast. As long as you turn them down while rotating the
ship, the half-way point should work IIRC. 'Twas some time since I did
the maths on this, though.
> the thing about instant turns is that it follows that all ships
But it is the way the FB rules work... and, well - I've seen lots of
people turn their ships in the wrong way anyway <g>
Unless you go with turn lenghts considerably shorter than 5 minutes or accel.
rates of 1 Thrust << 1g, you'll have problems getting away from
the almost-instant turns.
Regards,
> On Tue, 27 Apr 1999, Oerjan Ohlson wrote:
> Thomas Anderson wrote:
aaaaah! of course. so FB vector movement is time-taking burns and
instant turns combined in any order you want. basically, you can repeatedly
apply my simple vector movement over the duration of one turn, optionally
finishing with a turn and a zero-length burn. ingenious. i take my hat
off
once more to St St St Jon :-).
> > the thing about instant turns is that it follows that all ships
i suppose in vector, turning doesn't have the same effect on your course as in
cinematic, so it's not so bad. and as you say, the more options you
give players, the more ways your opponents have to mess up :-).
Tom
> Beth Fulton wrote:
active
> and.ESM 720" - double that for enhanced and double the enhanced ranges
Actually, MT is kind of weird in which it postulates a larger active range
than passive range. Can anybody speak of unclassified projects
(8-) where this is true? I always thought that your passive always
exceeds your active. And Beth, what's the difference between passive and ESM,
aren't they just two sides of the same coin?
> As to the scale we're using. 1" = 1000km and 1 turn = 15mins.
So that gives half a light second passive, 2 light seconds active, 2.4 light
seconds using 'ESM.' Hmmmm.
> I know that was a fat lot of good with regard to advancing the actual
I think Laser had a point that, in these circumstances, defending fleets
will tend to stay close to the object they're protecting. And also the
point about the difference between 'firing solution' and 'contact detected but
not localized.' This once again depends on the sensors you're using, and how
the physics of the universe work. For example, I've always assumed that, no
matter how good your technology, you can't hide a jump signature, as long as
you've got a line of sight to any point of the envelope. It throws so much odd
EM radiation and exotic stuff out, that the only way to miss it is if
something nice and massive like a star or a planet were in the way.
Just some pennies worth.
J.
> Beth Fulton wrote:
Howdy Beth.
> Derek also just checked
Hmmm. I guess it's because I'm equating to ESM and passive; I remember reading
that you can read a radar pulse (or a sonar pulse) from a much greater
distance then the generating source can pick it up (assuming no quirky stuff
like line of sight, thermal layers, that sort of thing.)
But the idea of passive tracking (i.e. sticking your eye to a telescope)
and ESM (i.e. sticking your ear to a giant RDF set) corrects that problem.
> >So that gives half a light second passive, 2 light seconds active,
1 am over here. (8-) 3 am now; as I mentioned in the other post, I just
watched the Dallas/Edmonton Hockey Game. Gah.
Actually, I'm just thinking what it means in terms of 'real-life',
reaction times, that sort of thing. Nothing in particular.
> >I think Laser had a point
Signs you've been playing a little too much Full Thrust, me thinks.
(8-)
J.
> On Mon, 26 Apr 1999, djwj wrote:
> Dealing with space sensors can be tricky. First is where are you using
I assume you mean it's difficult to locate a ship in close orbit around a
planet, right? You being in close orbit around a planet won't really have much
effect on your seeing. Your analogy of getting out of the city is true, but
keep in mind that the reason you want to get out of the city is that the city
lights scatter in the atmosphere and wipe out your seeing. Being in orbit
nicely avoids that problem. And really, even when trying to
find things near a planet, the planet doesn't have -that- much of an
effect. The reason you can't see the small Jovian moons is more because of the
great distance and their small size than because of any interference from
Jupiter (which is mainly in radio anyway).
> As far as how well we watch our own solar system: Yes we do have very
Not so! Doppler shift is exactly -how- we determine planetary orbits!
Give me a single doppler reading (which gives me velocity and position at a
given time) and I can give you all six orbital elements for the body. The
rotation rate of Mercury, for example, can also be measured with doppler
radar. Spectral analysis (which my wife does for a living) can take a few
weeks and isn't terribly difficult, actually.
> If you want to see something the size of a fleet carrier, in time to
I agree detection over distance is hard, but not that parallax is a bad
thing - in fact that's probably the only way you'll get a good distance
measurement without going to active sensors.
> As far as sensor "Evading": Very few modern astrophysical sensors are
Hmm. -All- astronomical sensors are directional if you have three of
them...
> Then there's the manuver itself. I assume that space combat occours at
At these ranges (even shorter than Solar Thrust's 80 km, I'm impressed!), I'd
have to agree. It's pretty much impossible to miss with a laser at less than
30,000 km, assuming you have a good targetting solution in the first place.
Keep in mind though that most FT'ers use a range much greater than a few km's,
though.
TTYL..