Secret Star Wars program

[ijuin]

Two points:

First, laser-driven schemes for intersteller travel are bogus.  The law of diffraction means that you have build a laser with a huge aperture in order to focus power on a spacecraft at great distances.

Dr. Robert Forward has the laser beam focused through a one-thousand kilometer diameter Fresnel lens to collimate the beam. Much is made of the issue that the beam will be useless for stopping the Prometheus at Banard's Star if the lens is less than 100% complete by the deadline. The main sail of the Prometheus is likewise 300 kilometers in diameter, making for a bigger target, and the beam is expected to spread somewhat in order to make up for minute targeting errors. Don't assume that the scientists who propose these things have not already crunched the numbers to the limit of current theory.

[DonPMitchell]

So you think that's an engineering posibility?  To build a lens 1000 kilometers in diameter to optical tolerance?  I like Robert Forward's science fiction too, but it is that -- science fiction.

I see this all the time on wikipedia -- science mixed with pseudo-science mixed with science fiction -- antimatter engines, moon-sized lenses, giant lasers in space, alien technology from Roswell.  Every time there is an attempt to have a public discussion about intersteller travel, it is drowned out by bull****.

[ijuin]

The lens would be built out of micron-thin material like the lightsails. Thus, a thousand-km lens would mass tens of thousands of tons, as opposed to the quadrillions of tons of a solid lens. It would be slowly spun to keep it rigid. Forward estimated the construction cost for one as being about ten billion dollars plus the cost of transporting the materials to the assembly site.

[Johno]

Let me put it this way: why would he lie ? Personal gain, you say. You think an officer like him would make up a whole book for a couple of thousand bucks?

I think SOME people would sell your internal organs if the return on investment was good.

Maybe, maybe not.

Alternatively, he could be schizophrenic.  I have a good friend who is convinced that he has done a PhD in Biophysics.  His stories are internally consistent and believable.  Trouble is, during the time he claims to have been at University, I was occasionally visiting him in a hospital.  His memories are nothing more than figments of his imagination (but those of us who know haven't the heart to tell him . . .).

Even if this author's work is internally consistent, that means little - he could still believe what he was saying and that's no proof that it's actually true.

So no, I don't automatically believe anyone just because they write a book.  You'll have to do better than that - a lot better!

[DonPMitchell]

Johno, I've interacted with a number of cranks, and they seem to fall into two catagories:

1. Mildly schizophrenic people.  One guy I knew had a web site about gathering antimatter from comets, so we could build a "star trek" future.  It was unclear how he had arrived at the belief that comets are made from antimatter.

2. Narcissistic Personality Disorder.  These are the bulk of conspiracy nuts.  They believe they have elite knowledge, but without spending the effort to learn real science, math and engineering.  They skip all that tedious study and work and go right to the place where they acquire superior knowledge and deep insight behind the curtain of lies that all the rest of us are fooled by.  You can't reaons with these guys, becaues their egos are huge and completely entangled with their belief system.

[DonPMitchell]

The lens would be built out of micron-thin material like the lightsails. Thus, a thousand-km lens would mass tens of thousands of tons, as opposed to the quadrillions of tons of a solid lens. It would be slowly spun to keep it rigid. Forward estimated the construction cost for one as being about ten billion dollars plus the cost of transporting the materials to the assembly site.

And you're going to stabilize that, under photon pressures, to optical tolerance?  I'm also skeptical that you can cheat the law of diffraction by combining a small-aperture laser with a large secondary objective.  I'd like to see the calculations there.  And by the way, the example I gave was for interplanetary distances.  To build a laser that could focus on intersteller spacecraft would require structures on the order of an AU in diameter.  This is just not a sound concept for space flight.

[Satanic Mechanic]

2. Narcissistic Personality Disorder.  These are the bulk of conspiracy nuts.  They believe they have elite knowledge, but without spending the effort to learn real science, math and engineering.  They skip all that tedious study and work and go right to the place where they acquire superior knowledge and deep insight behind the curtain of lies that all the rest of us are fooled by.  You can't reason with these guys, because their egos are huge and completely entangled with their belief system.

That is a true statement.  They have a science education of a junior high student and they cannot be reasoned with.  In the four years I did research for hybrid and electric vehicles, I probably had around fifty people come up to me with generator-on-a-tire, windmills on cars and wind turbines in cars to generate electricity while driving.  We used to keep a tally on a whiteboard labeled "Generator/Tire". 
Most of the time I would explain to them the First Law of Thermodynamics and I would get a blank stare.  Some walked away happy with my explanation, others have said I was a "stooge" for G.M., corrupted by the teachings of the school or some government agency.  Towards the last year I got tired of explaining it and I would tell these people to go out, build it and show it to me.

SM

[DonPMitchell]

There is a famous story I heard when I was doing gradate physics at Caltech.  A man walked into Dr. Tombrillo's office and said, "I have some new ideas about nuclear physics.  But usually people just throw me out of their office"

"Well, let's hear your idea.", said Prof. Tombrillo

"First, protons are flat.", said the man.

"You're right!", said Tombrillo

"I am?!"

"Yes, I'm going to throw you out of my office now."

[ijuin]

And you're going to stabilize that, under photon pressures, to optical tolerance?  I'm also skeptical that you can cheat the law of diffraction by combining a small-aperture laser with a large secondary objective.  I'd like to see the calculations there.  And by the way, the example I gave was for interplanetary distances.  To build a laser that could focus on intersteller spacecraft would require structures on the order of an AU in diameter.  This is just not a sound concept for space flight.

The initial aperture is a ring of solar-driven emitters surrounding the planet Mercury, which gives us an initial diameter of around 5,000 km. Anyway, read the book, "Rocheworld" by Robert L. Forward for the specific details.

[DonPMitchell]

Dude, you're siting science fiction books.  Forward was half scientist and half nut.  He believed in zero point energy batteries.

[ijuin]

I'm citing Forward's book because that's where all the numbers I was citing originated. If the calculations are wacky, then it's because Forward decided to do an ass pull.

[DonPMitchell]

Well an objective the size of mercury would not be big enough to focus a beam at distances much beyond the solar system.  And even that assumes an impossible level of perfection, because at great distances even the tiniest deviations in the optics will result in a wide dispersal of the radiation.

I'm harsh on these guys, because they present cool ideas without being self critical.  Kepler started out trying to prove that the orbits of planets were based on Platonic solids.  After years of careful calculations with Tycho's astronomical measurements, he gave up that cherished theory and accepted the even more brilliant (and correct) idea that planets travel in elliptical orbits.  Carl Sagan always considered Kepler to be a true hero of science for not just fudging the data to make things support his first idea.

That's what separates the men from the boys in science.  You have to have creative ideas, but then you have to be honest and objective and accept that most of your ideas will be proven wrong.

[DonPMitchell]

(continuing in another message, because this forum software goes nuts when you try to type a long message)

A really sad example of bad science was NIAC.  I've been looking into antimatter, just to try to confirm my impression that it is not a practical idea.  Particle accelerators can generate antimatter at enormous cost and enormous ineffciency.  It's not just an issue of turning energy into mass (m = E/c**2), but for every million 120 GeV protons that go into Fermilab's antiproton target, only 20 antiprotons are generated.  People talk about harvesting antiprotons from the Van Allen belt, when you can calculate that there are only 10 micrograms of Pbar in the whole belt -- and think about the task of sweeping that volume of space!  Then there are unsolved problems of storing it -- nobody can bottle plasma in bulk for more than fractions of a second.  There are the unsolved problems of building an engine that could use antimatter fuel without simply being vaporized.

Some of these laser schemes talk about coating the receiver with a material that will generate thrust by evaporating.  How much fuel supply is that?  What's the exhaust velocity from material just evaporating from being heated?  You don't have to be a PhD to know that's a worthless propulsion concept, and yet more grant money gets sent to those guys.

And yet...millions of dollars were given to people and small companies to develop antimatter and giant lasers.  A whole cabal of these buddies just reviewed each other's proposals and sucked $30 million out of NASA to hand out ot each other for utterly useless work like that.  Frankly, I think there should be a criminal investigation of NIAC.

[Johno]

There is a point I wish to make here, though, Don.

One thing that I have noted is that quality research is an accident that happens when you have enough quantity research.

The problem is that we don't really know what research will lead to breakthroughs, and which will just lead to heartbreak.  Sure, it may seem like the Sociologist's research paper on "The effect of tofu on obese lesbian depressives in an inuit context" is a load of garbage, but it may just lead to some collateral insights that totally revolutionise the way we see depression.

On the other hand, my sister in law did her PhD on the eminently reasonable topic of "Can you find a method to clinically age bruises?", and found the result of her three years (or so) of hard labour was a resounding "Nope!"

Yes, NIAC and co's ideas might be nonsense .  The question is, if they throw enough dollars at it, might it lead to something amazing?

[DonPMitchell]

I was rude, I apologize for that.