On Feb 23, 11:20 pm, "dwight.thi...@[EMAIL PROTECTED]
"
<dwight.thi...@[EMAIL PROTECTED]
> wrote:
> On Feb 23, 10:16 pm, IsaacKuo <mech...@[EMAIL PROTECTED]
> wrote:
> > On Feb 23, 8:42 pm, "dwight.thi...@[EMAIL PROTECTED]
"
> > > 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:
I don't know whether it's magical. It's beyond our current
knowledge, which makes it unknown. You claim that
it's easy. I make no such assumption. It might be easy,
or it might be difficult, or it might be impossible.
> 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.
So what?
> > > 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.
No, I don't.
> > > 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, I'm not.
> No extremely high exhaust velocities?
No. Current exhaust velocities of ion drives are more or
less ideal. Increasing the exhaust velocity would decrease
efficiency, reduce acceleration, and increase trip times.
> No scaled-up mass drivers?
No. I don't care for mass driver technology for space
applications. It requires large amounts of initial
investment and R&D, and the payloads are small
and must be robust enough to survive high
accelerations. Traditional rocket drives require
propellant, but the payloads can be larger and
they don't need to survive high accelerations.
> No closed-loop life-support?
We currently live in a closed-loop life-support
biosphere, so that's a proof of concept. I
accept that as a baseline for what sort of
minimum investment might be required for
off-world colonization. That's a truly MASSIVE
investment. On sfconsim-l, I worked out a
conservative baseline design which would
be 18km in diameter and 1.5E12 tons. Just
for the habitat. I accept that much smaller
may be possible, depending on technological
advancement and/or willingness for less
than total self-sufficiency. I do not ASSUME
it, though.
> 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.
So, the only choices are between off-the-shelf
stuff we have today, and everything you deem
must be possible. Riiiight.
> > 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?
At this point, yes. Because the technology is sufficiently
mature, we're at a point where a significant amount of
improvement is indeed just a matter of throwing money
at the problem. There's a limit to how far we can predict
the improvement, of course.
> > 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.
I don't need to convince you anything. More and more,
it seems clear that you are just going to believe whatever
you want and no one can convince you to budge in
the slightest.
It's crazy that you insist I'm "swallowing camels" by
assuming the existence of lots of crazy advanced
technology. You don't know what I assume. And
even when I explicitly tell you what I assume, you're
still arguing the point. This is ridiculous.
> > > > 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.
Sure. But that doesn't change the fact that I don't feel like
redoing the math right now. And you're not providing me
with anything to change my mood.
> > > > 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.
What you specifically said was this:
"Sigh. The anti-stealth people were wrong. Period. They
misunderstood a bit of basic physical law."
You're saying that we misunderstood some basic physical
law. When pressed to specify which basic physical law
was misunderstood, you said this:
"The one where Schilling insisted that the radiator had to scale in
inverse proportion to directionality. It doesn't. I gave a proof
(two actually) of why this wasn't so, and consulted with someone in
the physics department who actually knows a little thermodynamics. He
said it was a new one on him. In fact, I had a thread about just this
not too long ago. "
Okay, but it wasn't clear to me what you meant by
"scale in inverse proportion to directionality" nor the
particular relevance with this "basic" physical law
and the difficulties of stealth in space.
> 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.
No, it seems your position is that the anti-stealth people
are wrong. Not that "we simply don't know". That
we're wrong.
> > > > 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.
Because you are in orbit around Neptune and you'd like to
get to something in orbit around Uranus. Why, specifically?
I don't know, it could be a religious war, or something.
Entire wars can be fought over stupid things.
> 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.
Sure, it can be a fine way to get around. It'll still take
decades to get from Neptune to Uranus.
> > > 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.
"No" is a strange way to answer the question I asked.
> That's not how it works. You've got to justify, defend, persuade,
> etc.
If I were all that interested in convincing you of my
statements, then that's perfectly true. But I'm not that
interested in convincing you of my statements. If I
were, then I'd go through the effort to put up all of
the relevant math. But as I've stated several times
already, I just don't feel like it.
Obviously, if I have a desire to convince you of my
arguments, this desire isn't strong enough to overcome
my laziness to doing all of the relevant math.
But why should I even bother? You haven't shown
the slightest good faith by justifying anything of your
own statements.
> 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.
You think that something which no one has the faintest
idea how to make and which could easily be utterly
impossible is a "rather modest advance".
You think that radar, an existing technology which we
know can be scaled up to interplanetary scales (we've
essentially used it on interplanetary scales already),
is way more advanced. It may be extremely expensive
and not worth it because there are better alternatives,
but it's something which we could do simply by throwing
money at the problem. (Retrofit a huge ass transmitter
on Arecibo or something like that.)
Okay, you are perfectly free to feel that way. I differ
from that opinion. I'm not going to bother convincing
you otherwise. And I'll tell you right now that you're
wasting your time if you try to convince me otherwise.
BTW, I never claimed any of the technologies I'm
assuming are "off-the-shelf".
> > 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.
The difference is, I actually have an idea how to go
and build the thing. Hand me a billion dollars and
I'll get to work. You, in contrast, don't have the
slightest clue how to make a broadband highly
reflective mirror, nor do you even know if it's possible.
As for the UV laser system--I haven't described to
you the specifics and the many really annoying aspects.
I have, however, worked out the big ones to myself.
The design of the free electron laser in particular
has a whole slew of non-obvious technical issues
which only become clear when you hammer down
specific designs and work out various formulas.
The optics side of things is less speculative. There's
current research into the "eyeglass" telescope
configuration, which involves a large diameter
fresnel lens drone spaced far away from the
main sensor array drone. This includes foldable
fresnel lenses which have been tested in the
lab, although not flown yet. It's likely that one of
the next generation of space based telescopes
will use such a configuration, perhaps with the
primary mission of directly imaging exoplanets.
> > > > 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.
Note that I said "perhaps". You're the one claiming
that you could maybe do something to the deep space
sensor drones. I'm being helpful to your cause by
pondering the POSSIBILITY of using extremely long
range interplanetary X-ray weapons lasers.
That said, I actually have an idea of how to go
about making long range X-ray weapons lasers.
The technological challenges are VERY daunting.
There are a lot of aspects to the designs which
I've worked out, but it's easily possible that there
are some important deal-killers I haven't considered.
But at least I have a good idea of a direction to
go with the design.
You haven't even got step one.
> 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.
Obviously not. You think something which you haven't even
worked out the first detail on is a "rather modest advance".
It could easily be something which is utterly physically
impossible, but it's nevertheless a "rather modest advance".
I have a preference for speculating on technology which
I can at least understand the basics of.
> 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.
Personally I do indeed think stealth in space is more or
less "impossible". However, my idea of the sorts of
sensors involved are rather different from John
Schilling's. His basic concept involves what I feel is a
rather optimistic assumption of tracking everything all
the time. Maybe the numbers add up, but my gut doesn't
like it. Rather than settle on just one particular sensor
system, I instead pondered the possibilities of different
sensor systems.
In particular, boring old radar is just too good a sensor
system, at least at short range, to discard. Even with
fancy uber-sensitive passive sensors and UV lidar
around, I suspect plain old radar will be used extensively.
And it seems that something which is good at reflecting
sunlight into a narrow cone (to avoid passive detection)
will tend to show up on radar pretty well. That's my
old argument against "stealth in space" from the '90s.
Since then, I've considered different sensor systems
and radar doesn't seem to be as important a component.
Still, radar can be very useful, especially for civilian
purposes.
Isaac Kuo
|
