On Feb 23, 10:16 pm, IsaacKuo <mech...@[EMAIL PROTECTED]
> wrote:
> On Feb 23, 8:42 pm, "dwight.thi...@[EMAIL PROTECTED]
"
>
> <dwight.thi...@[EMAIL PROTECTED]
> wrote:
> > On Feb 23, 8:17 pm, IsaacKuo <mech...@[EMAIL PROTECTED]
> wrote:
> > > On Feb 23, 7:56 pm, "dwight.thi...@[EMAIL PROTECTED]
"
> > > <dwight.thi...@[EMAIL PROTECTED]
> wrote:
> > > > 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.
>
> I generally don't assume the existence of magic technologies,
> even if it's entirely plausible that some sort of science which
> today would seem magical will be developed.
Really? What's magical about this technology? What makes it so
difficult? Your whim? Going in the other direction:
http://www.sciencedaily.com/releases/2008/01/080122154610.htm
A material, in the beginning of 2008 mind you, that is better than
99.9% absorbtive.
Don't try to force the issue with lame rhetorical tricks like 'magic',
m'kay?
> > 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.
>
> Maybe there will be clever designs or new science which gives
> us neat broadband highly reflective mirrors. Maybe not. I don't
> assume the existence of them.
And yet, you _do_ assume clever designs or new science which allows a
massive manned presence in space. As I said, swallowing camels,
straining at gnats.
> > 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.)
>
> What other advances do you think I'm assuming? I tend to be
> rather conservative in my speculations on future space
> technology. The only specific "toy" you mentioned was
> nuclear thermal rockets, which I generally do NOT assume
> will be used very much, if at all.
You're not? No extremely high exhaust velocities? No scaled-up mass
drivers? No closed-loop life-support? And so on and so forth. No,
you don't get to say it's a minor adaptation of off-the-shelf stuff we
have now.
> I don't like the general economics and technological
> developmental path of nuclear thermal rockets, compared
> to solar electric. Solar electric is already a mature technology,
> and capable of outperforming nuclear thermal. Nuclear
> thermal has never even flown once. Solar electric costs
> less, it performs better, it doesn't have political problems,
> and it's already flown. The basic technology of solar electric
> has extensive civilian terrestrial applications, which means
> lots of R&D money and effort to make it even better. In
> contrast, the sort of nuclear reactors suitable for nuclear
> thermal have no civilian applications and practically no
> terrestrial military applications. And what's the potential
> eventual payoff? A drive system which underperforms
> compared to cheaper solar electric. So no, I don't anticipate
> nuclear thermal drives.
But you are assuming lots of R&D for solar electric; it's just a
matter of throwing money at the problem?
> This is representative of my approach to future technology
> speculations--I like to be conservative. If something exists
> today, works well, and has great potential for continued
> development, then I like it. If not, then I'll need some
> convincing.
You've got it backwards - you need to convince me that it works well,
first. You don't get to decide this by fiat. And the fact of the
matter is, what you're positing _is_ advanced technology, technology
we don't have yet, technology you're assuming is not terribly hard to
develop.
Your priors seem rather arbitrary to me.
> > > 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?
>
> Because I don't feel like looking them up or redoing them. You
> don't like that? Well, deal with it. I simply don't feel like going
> through the effort.
Pardon me for not just taking your word for it, but I don't; it's
entirely possible you made unjustified assumptions, did some bad
arithmetic, etc.
> > > 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.
>
> That's the design which I had worked on before, and rejected
> it on the grounds that the amount of active cooling required
> exceeded the amount of power available. Well, I didn't
> "reject" it, exactly, I just wrestled with the numbers until I
> got something which worked about as well as I could make
> it (a 60 degree cone).
>
> If you have nothing more to say, then color me completely
> and utterly unconvinced.
Shrug. You're the one telling me that stealth in space is not
possible. It falls upon _you_ to convince _me_ that this is the
case. Not the other way around. Note that at this point, what I've
contributed, basically, is pointing out that John's bit 'wisdom' was
just plain wrong. I am most certainly not trying to convince you that
it is possible. In fact, my position is that we simply don't know
enough to tell yet, because the question turns upon many factors, some
of the economic, which are not amenable to prediction.
> > > 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.
>
> We used gravitational assists and started off from a nice fast
> moving Earth, and the only way to get somewhere fast was
> a one way flyby. If you want to get around in the outer solar
> system, you need to provide all of the delta-v, and you need
> 4x the delta-v to do a return journey.
>
> Also, consider that Neptune if five times further away from
> the Sun than Jupiter. If you want to get from Neptune to
> Uranus, it will take decades even with a high performance
> drive.
I'm curious as to why you would want to get from Neptune to Uranus.
Your assumptions seem to paint a rather inconsistent picture of the
future. With what you've said so far, it doesn't seem likely that
there would be much reason for doing this, and so gravitational
assists from the inner system seem to be a perfectly fine way to get
out there.
> > > > 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?
>
> I don't care for your tone. Are you interested in convincing
> anyone of your argument or are you more interested in just
> insulting others?
No. And I don't care if you don't care for my tone; in fact, you seem
to think that after you make an assertion, that I have to work to
convince you that it isn't so.
That's not how it works. You've got to justify, defend, persuade,
etc.
Needless to say, I find your presumptions and tone annoying, freighted
as it is with these rather obnoxious presumptions.
For example, all of a sudden you're talking about 'active' sensors,
and I have no idea what they are; the only thing I can think of is
radar. And radar is notoriously power-hungry and has (on the scale of
interplanetary distances) a rather short range. So when you say
something like a highly reflective mirror is 'magic technology', but
that these 'active sensors' are practically off-the-shelf, I think I
am fully justified in pointing out that you're denying one (in my
opinion) rather modest advance, but have no problems waving around
your own favorites which seem (at least to me) way more advanced.
Iow, you just can't drag in a deux ex machina, not explain it, and
think that settles everything.
> The relevant active sensors involved would be UV wavelength
> lidar. I've had discussions about active sensors on sfconsim-l,
> and it's an interesting interplay between beam size and
> photon energy. More energetic photons can be focused
> more narrowly, but for a given beam power there are fewer
> photons so your get less of a return. Also, low energy
> photons can be stealthed against, by directing reflections at
> off angles. It seems the ideal photon energy would be
> somewhere in the UV range, which is low enough to get
> a decent return signal but difficult or impossible to stealth
> against (Thomson backscatter).
>
> Now, if I feel like it I'll do the math for a specific long range
> sensor design.
>
> The basic design is straightforward enough. You'd have a
> free electron laser ship in formation with a fresnel lens
> drone several thousand km away. The fresnel lens may
> have a radius of perhaps 100m or maybe 1km. The lens
> both focuses the outgoing laser beam and focuses the
> return only a germanium based detector. It only takes
> one or two photons for a detection. From here, it's a
> matter of math. That's effort, and frankly I don't feel
> like doing that effort if it's for the benefit of a rude bastard.
Now stop right there!
To call me rude for being skeptical, to call positing a highly-
reflective mirror 'magic technology' . . . and then go on to blithely
describe fresnel lenses with a radius of hundreds of meters (up to
one kilometer!) as not such a big deal is - I'm sorry to say again -
swallowing camels and straining at gnats.
> > > 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?
>
> They're too far away to be "evaded" in any meaningful
> way.
>
> You could perhaps shoot missiles at them, but it'll
> take years for the missiles to reach them, during which
> time the enemy is going to be launching replacement
> sensor drones.
>
> You could perhaps shoot long range interplanetary
> X-ray lasers at them, which could be a significant
> strategy. However, if the enemy also has
> interplanetary X-ray lasers, the enemy will be using
> them to shoot at your lasers; your lasers are "wasting"
> firepower on sensor drones while the enemy is withering
> away your own firepower.
Long range interplanetary X-ray lasers. Nope. Just standard tech
here, nothing to see folks, just move along.
Again, pardon me for being skeptical.
I'm not sure you're aware of how wild this really sounds.
Let's take a real-life comparison:
Darn. Can't find it. Maybe you can; it was about the relatively
recent solar sail project that was canceled. Henry Spencer was in on
that one, but my google-fu can't seem to locate it.
If we can't even do halfway decent testing of something as mundane as
solar sails, and you're talking about about fresnel lenses (In Space!)
hundreds of meters across, interplanetary x-ray lasers capable of
shooting down hostile objects . . . and then go on to describe highly
reflective mirrors as 'magic', well, I don't think we live in the same
universe.
And, one last time: I'm not trying to convince you of anything.
You're asserting that stealth in space is 'impossible'; I'm playing
the good skeptic, and have already pointed out some flaws.
Nothing more.
> Spoofing is a more interesting possibility, but it's
> going to be an interesting challenge to try and fool
> all of the sensor drones simultaneously in any way
> cheaper than just doing the real thing. For example,
> suppose you want to fool them into thinking that a
> warship is being launched in some direction. You
> want some sort of flare which matches the signature
> of the drive, and accelerates the same amount as
> the drive. If the enemy only had one or two sensor
> drones, then maybe you could do something cheap
> and clever by pointing lasers at them. But if the
> enemy has dozens or hundreds or thousands of
> drones, it may be cheapest just to slap a real space
> drive onto a cheap rock and fly it just like a "real"
> warship.
>
> Isaac Kuo
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