Re: Slow Stealth

On Feb 23, 8:17 pm, IsaacKuo <mech...@xxxxxxxxx> wrote:
On Feb 23, 7:56 pm, "dwight.thi...@xxxxxxxxx"

<dwight.thi...@xxxxxxxxx> wrote:
On Feb 23, 7:41 pm, IsaacKuo <mech...@xxxxxxxxx> wrote:
You can design a radiator to radiate into a cone a bit narrower
than an entire hemisphere, but it is HARD to get a radiator to
radiate into a small cone. The basic design would be a large
actively cooled polished parabolic mirror reflecting light from
a small hot blackbody radiator. Unfortunately, some light
will be absorbed by the mirror, which is why it must be actively
cooled. You're going to be consuming a lot of energy pumping
heat from this large 3K mirror into the small hot radiator.
And that energy consumed adds to the waste heat generated.
What is this HARD you speak of? Some numbers, please? In fact, an
arrangement that covers 1% of the sky or less should be assumed to be
doable. Assume the mirror is 99.99% reflective.

Why would I assume that? The only mirrors we have which are
that reflective are only so reflective at extremely narrow
bandwidths.

Uh-huh. You've an economic power, or powers that can support a huge
space industry. Possibly parts of the solar system off Earth are
permanently manned if not outright colonized. You've got all sort of
toys like nuclear thermal rockets, at the least, but at any rate,
extremely advanced technologies beyond anything we can achieve today.

Yet mirror technology improves not a whit. Even though there is
nothing in the laws of physics that forbid such reflectivities, and
even though such reflectivities have been achieved for certain
wavelengths.

And you think this is realistic? Or do you think, as I do, that this
is swallowing camels and straining at gnats? If not, why suppose all
these other advances, but not advances in optics(and rather
pedestrian advances at that.)

You seem to want to
imply that in doing this calculation the sums converge slowly, but I
don't see you showing your reasoning as to why this is so.

I've done numbers on various "stealth" radiators before, usually
coming from the perspective of trying to design one (i.e. I was
"pro-stealth"). I don't remember the specifics, but basically I
settled on a design with a 60 degree radiation cone. I wanted
to design one with a 15 degree radiation cone, but the numbers
never came anywhere close to adding up.

Instead of saying this, why don't you just show the numbers?

If you have a better design in mind, I'm all ears.

What? A radiator whose output is redirected by an advanced, actively
cooled optics system?
Something along the lines of a paraboloid with the radiating surfaces
at the focus?

There's not a whole lot more to say.

This depends on how patient you are. It could take decades to
get outside the network if you use a highly visible drive to get
outside the net quickly (and thus it's something suspicious to
the enemy). Or if you lob the thing slowly with something like
a planetary mass driver, it could take centuries to get outside
the network.
Again, you're assuming stuff without using any numbers.

Just using basic intuition about how long it takes to get around in
the outer solar system. Even with 300km/s class drives, it takes
decades to get around.

Really? 20th C Earth did that . . . without even 30 km/s exhausts.
Your numbers don't say what you think they do.

But so what?
Why shouldn't these sorts of manuveurings take decades?

Well, if you don't mind the enemy knowing exactly where you
are at all times, because he's suspicious of this rocketship
zooming out beyond the sensor network at high speed and he
tracks it with active sensors...then fine. You could very well
do some "stealthy" maneuver with a heat signature he can't
detect because you're beyond the passive sensor network.
But he's tracking you with active sensors anyway, so your
patience is a wasted effort.

But now you're invoking something else: what are these 'active'
sensors you speak of, how do they work, what is their range and
resolution? Swallowing camels again?

On the other hand, if you'd rather the enemy not noticed,
and stealthily lobbed the ship using a planetary mass
launcher, then it could easily take centuries to get outside
the outer solar system.

This assumes it's even possible to get outside the sensor
net at all. The easiest way to launch the sensor drones is
to just send them out with just enough fuel to accelerate
outward. No deceleration burn when reaching a particular
desired radius from the Sun. Thus, the sensor network just
continuously gets bigger and bigger. Instead of wasting
resources on deceleration burns, you simply periodically
launch more sensor drones to "replace" the ones that get
too far out to be particularly useful.
But, uh, if you're doing that, aren't you kinda showing where those
sensors are? The rules are most definitely, 'assume sensors can
always be perfectly stealthed and never found, while spaceships have
to obey the laws of physics.'

Yes, the enemy knows where the sensor drones are. So what?
It doesn't give the enemy any particular capability to do anything
about it.

It doesn't? They can't be evaded then, or taken out, or spoofed, or a
combination of the three or something else?
.