Brian,
I have to suggest that if your logic for suggesting you'd be detected anywhere
in the system if you went active drive is the 'sector blanking' that prevents
FT ships from shooting out the rear, I must ask:
1) Thrusters can fire without causing this interference. Does this by
inference mean one could manouvre on these without detection? I think you'd
answer no.
2) What is the practical range of IR detection? Bradford made some comments
based off of black body radiation, but didn't say much about what ranges
drives could be detected at. You figure across the system. I have to wonder
about that.
I assume drive ejecta would be directional (the particulate component). The
radiated component might be omni-directional or nearly so. However, I'm
also sure that the further away I go from a spot in space that is radiating,
the less likely I am to detect one of the radiated waves. The volume of space
a wave must travel through grows as the third power of distance from that
source. So presumably the detected density of radiation drops as the square of
distance? If that is true, then if we take Brad's figures as an example of the
sensitivity of IR detection (detect 300K at 1 LS surely, 10 LS probably lost
against the background radiation) and assume that drives emit
more powerful signatures (pick 4800K for a guess - lets say that'd be
doubling the 300K 4 times), then I'd guess they'd be visible at 4^4 times the
original figure... which might be about 256 LS for sure and 2560 LS they'd be
for certain lost to background radiation).
So, if my idea is right, that means you would for certain detect a manouvring
ship out at 76.8 million km (7600 mu at 10,000 km per mu). You'd for sure not
detect it out at more than 750 million km. Assuming drives run that hot. If
your thrusters only ran at 600 degrees Kelvin, you'd only be detectable at 16
LS. This is still a long way.
So it seems that if you could close on a ballistic track with baffling on and
some method of dropping your hull to 150 K, you could probably close to
tactical ranges without detection. If you fire up your (presumably) hot
drives, you get picked up wherever you are, if someone is looking. If you're a
real stealth machine, you might even get under 6 mu, but your ship would be
storing heat at I imagine a high rate... which you would eventually have to
dispose of.
So what this seems to suggest is that comet-tail riders, asteroid
riders, and stealthed ballistic ships could close in on enemies with good
sensor arrays, but anyone just manouvring would be far more visible at huge
distances. I guess it pays to have your patrol ships take a peek at any
strange objects floating through your space - and check for
"hangers-on".....
> So, if my idea is right, that means you would for certain
Assuming drives run
> that hot. If your thrusters only ran at 600 degrees Kelvin,
Compared to what? Not interplanetary distances. (Yes, I know it's a long way
with respect to tactical ranges).
> So it seems that if you could close on a ballistic track with
If you come in on a ballistic track, how far out from your target will you
need to be? If it's a couple AU (Weber) or a
30+AU (Mote in God's Eye--"merchant ships don't need to come
nearer to Earth than Neptune"), you'll either need to have high velocity
before you jump, or you'll need to drift in very, very patiently.
> "Thomas.Barclay" wrote:
Indeed. That's a weakness that I didn't consider. Mostly, I was indicating
that interference as meaning that WHATEVER your drives, they put SOMETHING
out.
> 2) What is the practical range of IR detection? Bradford made some
I'm basing this on an article from rec.arts.sf.science (I believe that's the
NG) that calculated that, with today's infrared telescopes, we could detect
the Space Shuttle's manuvering thrusters firing in the asteroid belt, and the
main engines firing significantly beyond Pluto. I don't have the math or
science training to verify this (although I'm hoping to acquire it before I
graduate), but there seemed to be a consensus that the person who was doing
the calculations knew what they were doing. As for 'future drives' I'm
guessing that they would radiate AT LEAST as much as the space shuttle (they
have to move a larger mass at greater acceleration, at least assuming 1 thrust
= 1g). Also, the best way to increase the efficiency of a drive is to make the
reaction mass hotter (and thus easier to detect), while the best way to
increase the thrust is to increase the mass of propellant used per unit time,
thus also making it easier to detect. Yes, ejecta would be directional, but it
would still be detectable pretty far out.
> So it seems that if you could close on a ballistic track with baffling
hot
> drives, you get picked up wherever you are, if someone is looking. If
Whereas essentially my view is that, given the information above, you'll be
picked up (and your course plotted) as soon as you start manuvering. If you go
ballistic (undetectable or not), your course isn't
changing, so they know where you are ANYWAY (sure, with a VERY low-power
thruster burning VERY far away, you won't be detected, but it'll take you
forever to get anywhere.
> So what this seems to suggest is that comet-tail riders, asteroid
Unfortunately, asteroid-riders would tend to be fairly
detectable. Most asteroids don't get near anything interesting, and even today
people are looking fairly hard at those that do....
> On 20-Apr-00 at 09:53, Brian Quirt (baqrt@mta.ca) wrote:
I'm assuming this was with the caveat that we had to know where to look?
> On Thu, 20 Apr 2000, Brian Quirt wrote:
> As for 'future drives' I'm guessing that they would radiate AT
I would assume that another way to make a drive more efficient is to make the
ejecta more uniformly directed. Sorta like a laser that is invisible until you
blow smoke through them to reflect some of the light.
One of the ideas I like from Gundam is the idea of a particle that makes
communication and detection nearly impossible beyond short distances. So you
know SOMETHING is there because SOMETHING is emitting the particles, but thats
all the information you get. Sorta cheesy, but it does let big mecha be a more
plausible solution to combat situations...
Anyway, my long-winded point is that even if something is directed,
all you have to do is blow a little smoke.:) Regardless, no matter what
detection system you have, someone is going to think up some sort of counter.
On 20-Apr-00 at 10:36, sportyspam@harm.dhs.org (sportyspam@harm.dhs.org)
wrote:
> On Thu, 20 Apr 2000, Brian Quirt wrote:
You know, that does bring up the question of a laser drive. Point the laser to
thrust. If the laser happens to be pointing the right directions you could
pick it up, otherwise you would see nothing, rec.sf notwithstanding. As a
matter of fact if I throw little steel pellets out (accelerating them with an
linac type device) you would never pick them out from earth with passive
systems. (heck, I could cool them to 1K before I accelerate them)
> Roger Books wrote:
a) Laser Drive: Big problem: efficiency. Yes, light has energy. No, it
doesn't have very much. The kind of laser that will give you multiple-g
accelerations will a) consume an INCREDIBLE amount of fuel and b) be VERY bad
news for anyone in its path. I recall a discussion on light
propulsion (inspired by Niven and Pournelle's _The Mote in God's Eye_)
(on another list) where it was calculated that, even for a
non-collimated (spreading) light drive, the intensity required to
produce the necessary thrust would make the drive a better weapon than
ANYTHING else shown in the stories. If your ships are laser propelled,
treat their drive as a Beam-500 or so to anything directly behind them
(or who happens to get in the way when you turn with the drive on). The third
problem is efficiency. Lasers (currently, although that may be changing
slowly) are less than 50% efficient, meaning that for every joule you pump
into movng yourself, you have to absorb a joule of heat. This can get BAD
quickly. As for seeing nothing, sure, if you don't count anything behind the
drive suddenly heating up and melting....
b) Rock drives. Fairly efficient. Require a LOT of reaction mass. NOT very
high thrust. If you cool the rocks to 1K, you have to absorb the resultant
heat yourself. Sure, your rocks will be undetectable, but you'll make up for
it. Also, ISTR that drives based on said principles tend to heat the mass in
the launching process AND put out em radiation. I may be wrong, of course.
> On 20-Apr-00 at 12:01, Brian Quirt (baqrt@mta.ca) wrote:
No, it
> doesn't have very much. The kind of laser that will give you
The Moties drive doesn't count, the laser stayed on the planet. It was used to
heat the reaction mass (ice I believe) on the acceleration end of the ship.
You waste lots of power but the power is coming from the planet where you can
afford the waste.
> b) Rock drives. Fairly efficient. Require a LOT of reaction mass.
NOT
> very high thrust.
They require no more reaction mass than anything else. They can also be very
high thrust, it all depends on how fast you throw them out. When you start
throwing out mass it doesn't matter for acceleration purposes wether it is ice
cold rocks or gas heated by combustion.
> If you cool the rocks to 1K, you have to absorb the
In deap space, far beyond detection range. I kind of like this one. Big
circular accelerator. Before you leave home you spin it up, venting
any excess heat. When you need to accelerate you release particles, they whiz
out the back and you whiz forward (or sideways). Of course the whole thing
would need to be free to spin so we avoid gyro affects.:)
> Sure, your rocks will be undetectable, but
Depends on your process...
I still see your scientific principles as what you believe could work is
scientific even if it requires hand waving, if you don't believe it could work
it isn't scientific.
> Brian Quirt wrote:
Agreed, "better weapon" as in "could slice the Moon in two parts".
According to the knowlegeable Erik Max Francis:
The mometum of a photon is given by
p = E/c,
where E is the energy of the photon, and so the thrust delivered by a stream
of them is
dp/dt = dE/dt/c
or
F = P/c
> Roger Books wrote:
No, it
> > doesn't have very much. The kind of laser that will give you
No, sorry, that isn't what he was talking about. <grin> THE MOTE IN GOD'S EYE,
page 42:
"Of course light pressure could be used for propulsion. In fact, the MacArthur
did exactly that, using hydrogen fusion to generate photons and emitting them
in an enormous spreading cone of light."
It goes on to describe the MacArthur landing on a moon
to re-fuel, with the base using a Langston field on
the landing pad to prevent the drive from burning