On Feb 24, 1:21 am, IsaacKuo <mech...@[EMAIL PROTECTED]
> wrote:
> 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?
Come on, I know you can make the connection. If I had said in
December of '07 that it was possible to make a material that was
99.99% absorptive, you would have (or could have) made exactly the
same claim as the one you are making now with regards to reflectivity.
I think one needs to distinguish between 'magic' that depends on the
violations of supposedly fundamental law, the 'magic' that is an
engineering nightmare, and the 'magic' that is simply unknown. An
easy example would be Edison trying out materials for the filaments of
light bulbs; by your own criteria, he was engaged in 'magical'
speculation.
> > > > 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.
It pains me to say this, but yes you do. You've even given explicit
examples below.
> > > > 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.
Those exhaust velocities are 'extremely high', at least as I judge
them. Your second statement simply does not follow, depending as it
does on a multitude of factors. But then again, I am unsure as to
what you think constitutes an ion drive: is it just the thrusters?
Or something more?
I would also note that while ion drives might - might - qualify for
certain unmanned probes, but the fact of the matter is, they're not
even that far yet:
http://query.nytimes.com/gst/fullpage.html?res=9C02E2D61E38F935A35753C1A96E958260&sec=&spon=&pagewanted=all
And for manned flights? No, that is way speculative. I might add
that in the context of, say, a Mars mission, the sense is that ion
propulsion will increase payloads, not decrease 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.
I CALL FOUL! No way. Closed loop life-support is _very_ advanced
technology. We can't even do it here, on Earth, with even fairly
large mammals, let alone in space, for humans. I know that some
physical-science oriented types tend to be dismissive of these sorts
of issues, but the fact of the matter is, this is an extremely hard
problem. It might, as you say, be eminently solvable, but at this
point we simply don't know. Just as, in fact, we don't know how
difficult it would be to make highly reflective mirrors - that was my
whole point (I'm a bit baffled why you're hung up on this, frankly; I
don't think stealth is dependent upon the development of that
technology. I just picked a number that was easy to work with, namely
0.0001. It could be 0.01, or 0.001, for all I care or know.)
And if you don't have this sort of technology, how do you justify an
extensive manned presence in space? And if you don't have _that_, how
could there be any need for stealth or space wars, ever? You've got
to be consistent.
> > 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.
No, of course not. But you seem to be missing something: the
argument you're attributing to me is actually _your_ argument. I'm
pointing out that you're making assumptions that seem to be arbitrary,
in fact, seem to be driven by the need to assemble a consistent set of
story elements. There is no evidence to suggest the sorts of stories
you wish to tell are in fact feasible.
I don't suppose it would help at this point, but I'm a space-head from
waaay back. I thought that we'd have space stations, a moon base, a
manned mission to Mars by now, with plans on the drawing board for a
Jupiter shot (this was back in the 60's.) I am bitterly disappointed
that none of that has come to pass, and I really, really want there to
be something even so humble as a manned Mars trip before I die.
But such is life. You don't always get the pink pony you wanted -
that really flies.
> > > 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.
You need to talk with other people who are actually in the field. My
impression is that these are very hard problems, and that the money,
even for your scenario, isn't coming in large gobs any time soon.
That's for manned flight 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
Um, no. I am very willing to be convinced. I want to be convinced.
But you're not giving me a lot to go on.
..
> 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.
In fact, you've given me numerous examples of what is, indeed,
advanced technology. Maybe you're getting the impression that it's
not because you're comparing yourself to the types who say that Orion
is 'just a matter of assembling bits of present technology'. But
really, you are.
Let me put it this way: if it's not advanced technology, how come
it's not already in use?
> > > > > 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.
Right. Perhaps I should have been more clear: the anti-stealth types
who base their misconceptions on this misunderstood 'law'. In fact, I
was thinking of the last several go-rounds:
http://groups.google.com/group/rec.arts.sf.written/browse_thread/thread/7f6677c7015a43af/7e7e0f0e5be3ae21?hl=en&q=dwight+thiem+stealth&lnk=ol&
http://james-nicoll.livejournal.com/1130300.html
http://www.projectrho.com/rocket/rocket3w.html#nostealth
_That_ is what I am replying to: that stealth is impossible because of
a (fictitious) natural law. It may be impossible for other reasons,
maybe, but certainly not that one.
> > 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.
See above. I'm just objecting to using misunderstood natural law as a
springboard for some sort of authoritative conclusion.
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