New Mars Forums

Well in that case, where's my freakin' flying car!? 
I look at our war on cancer, AIDS, hunger, attempt to build an economical SST, LEO booster and I see a LOT of proposed engineering projects that never panned out.  It's easy to get lulled by Moore's law in semiconductors to think the same will apply to other fields.  However, Moore's law only works when you havea clearly defined engineering path to follow - in this case progresively shorter lithography wavelengths.

With CNT's, the formation mechanism is sort of understood and it doesn't look good, I'm afraid.  The problem is that youre trying to build flawless polymers.  The probability of a polymer getting longer without a flaw decreases exponentially with length.  Basically, if anything happens to the iron catalyst such as impurities or temperature changes or mechanical disturbances, the tube is killed.  The problem is that all of the nanotube synthesis schemes rely upon relatively high temperature synthesis where everything is kinetic in nature.  If we could find a way to get enzymes or simple organic precursors to make nanotubes, we'd be in business since then we could do things like error correcting, etc.  However, it's just not possible at the 200+C that anyone does the synthesis at.

Now, if someone were able to figure out a way to join nanotubes at the ends, we might just be able to do this.  It would require a supply of nanotubes of all the same diameter and chirality.  It mightbe possible to do this but the costs would be stupid staggering.  I mean just stupid. 

The big problem is that the elevator cable is so damn long and has to be so perfect.  One or the other is possibly feasible but both at the same time is really difficult.  The problem is that most other engineering projects can do just fine with the low quality tubes and so the massive effort to improve the CNTs has little economic incentive other than the elevator.  If the elevator requirements were just half as high as they are, I'd say that it's feasible.  However, the 100 GPa just requires such perfect material that I'm not terribly hopeful.

I can't rule out some major breakthrough busting the doors open but it would require a minor miracle in present day synthesis or a completely new synthesis method.

SHOCK!  No pipeline?  Who are you and what have you done with ERRORIST!? 

OK, this is something that's a bit more practical.  I actually wouldn't bother with trying to accelerate the hydrogen.  If you're pushing a spaceship, all you have to do is shine a light out the back.  Since light has momentum, it will push you forward.   Now, all the stuff I mentioned about light being a very weak propulsive force still applies.

HOWEVER, this is actually the basis for a proposed propulsion system called a nuclear photonic drive.  Basically, it's a nuclear powered flashlight.  You have a nuclear reactor or some other endless power supply and use it to drive a super-powerful light source pointing out the back of your spaceship.

You have to have insanely powerful lights to make this work and have any sort of decent thrust.  On the other hand, though, the drive doesn't use any fuel.  Also, it uses light as the propulsive medium so you have excellent Isp values. 

Here's a wikipedia [http://en.wikipedia.org/wiki/Nuclear_photonic_rocket]link.

The drive would run until your reactor ran out of fuel which could be decades later.  This is the single best spacecraft propulsion system ever devised.  You only get a few pounds of thrust so you can't use it to get off the Earth but it would be an ideal drive for travelling to other star systems.

You wouldn't want to use a laser since lasers are VERY inefficient.  The most efficient way would actually probably be to just run the reactor core REALLY hot on the back of the spaceship at the focus of a parabolic mirror.  This way all of the visible and IR photons that are sent out as waste heat are used as thrust.  You approach efficiencies approaching 100% this way.  One problem is that the the reactor will slowly boil away at those temperatures.  However, if you use high temp ceramics and design the reactor so that it doesn't start boiling away down to the reactor core until the reactor is depleted anyway, this is not a problem.

The best part is that we could build this with present technology.

Well, it depends on how concentrated the beam is, how well the wavelength coupled to H2 absorbtion, how long you hit the atoms with the light and so on. 

For individual atoms, using a laser is a very inefficient way to push them around.  In fact, with a regular gas, you'll just heat the gas up.  This is because the atoms will bounce off each other and soon, their velocity vectors become randomized.  You'll only get significant velocity if the gas is extremely thin.  By thin, I mean molecular flow regime which starts at about 1 billionth atmospheric pressure. 

So, to answer the question you were about to ask, a laser would push hydrogen up your pipeline - but very poorly and only if you had pretty much no hydrogen in it.  You'd get more H2 to orbit if you built a ladder and had a guy carry buckets of the stuff up to orbit by hand.

The O2 and kerosene were stored in seperate tanks like O2 and H2.  A premixed mixture of oxidizer and fuel would be insanely dangerous.  A mixture of fertilizer and fuel oil is a much less energetic fuel/oxidier mix and we all got to see what even that did in OK city.  Plus, kerosine would probably solidify at liquid O2 temperatures.  The two were mixed either right before or in the engine combustion chamber.  IIRC, the liquid O2 was sent through tubes in the engine cones to keep them from melting and to preheat and pressurize the O2.

The golden color most definately from the kerosene. (most likely more highly purified than camp stove stuff but basically the same)  O2/H2 burns hotter and cleaner so it gives this tiny little blue flame.  The Shuttle main engines generate thrust levels comparable to the F-1s, IIRC but you can barely see the flame.  O2/H2 is a much better fuel but you're right, the gold kerosene glow was much better looking.

I know that at least one X-prize competitor is using O2/kerosene since kerosene is much cheaper and easier to handle than H2.

I dunno, I've seen how well regular voice recognition works and I'd be terrified if my life depended upon it.  I remember an old roomate got some free voice recognition softwre with a sound card.  It was one of the better commercial packages at the time (Somthing-or-other-Dragon or something was the name).  I just remember hearing him in his room saying:
"Emergency."
"Undo...Undo"
"Emmmmergency"
"Undo...Undo...UNDO"
"EmergEEEncy"
"Undo...undo"
"EEEmergencYYY"
"Undo...Undo...Undo...UNDO!!"
And so on for about 10 minutes.

Later, after he'd finally programmed the dumb thing, my other roomate anda friend were testing it out.  I can't remeber what someone said but the program interpreted it as "Robber the condom."  The resulting laughter caused the program to write a long paragraph of "Whom"s....

The situation I was thinking of is the future where we're launching large numbers of rockets off to Mars on a regular basis.  That justifies the fixed orbital inclination.  If the launcher costs $10 billion to manufacture and $100 million a year to run, saves 20% of the $500 million a launch per rocket costs, it could end up being a net money saver in a decade.

A space elevator would be the best bet but read one of my messages on the boards here to see what I think of the probability of that happening anythine soon...

I think that this sort of tech is most useful in exploring the moons of Mars.  It's a way to land on an object with minimal gravity where the probe is likely to float away unless anchored down.
I'd love to see a probed investigate the moons of Mars directly.  There's all sorts of potential uses for the moons that would be made possible by a better understanding of them.

I think that the prolems of building on the PAcific ocean and dealing with the foothills are child's play compared to building a precision, large structure on a mountain.  I've done mountain climing in the past and it is NOT a friendly environment to anything more involved than a hut or a gondola tower.  The Andes do seem more promising.  I suppose that a 50 degree launch angle might even be possible for some of those peaks.

Assuming that we can build the track in that kind of envorinment and the first avalance doesn't wipe the track away, what sort of numbers are we looking at?

Well, since we've pretty far into the future with being able to build this mega track, lets assume that we can go supersonic.  Soem of those Andean peaks can top 23,000 feet.  Let's assume you get a launch angle of 50 degrees at a launch velocity of mach 3.  You've got a vertical velocity of about 785 m/s which is about 10% of the total delta V needed.  I'd say that this might be worth using.  You've still got to carry a lot of weight to space but it wil help. 

Assuming an H2/O2 launcher and ignoring air drag, this launcher give you about an 23% increase in the cargo capacity of the rocket.  Not stupendous but measureable.  To double your launcher capacity, you've got to have atotal vertical velocity of 2420 m/s or 5413 mph.  At a launch angle of 50 dergrees, you need to lob that rocket at mach 9.5.

I don't think the equations I'm using take things like staging into account properly so you could probably improve those numbers quitea bit.

However, it remains that a maglev launcher is an incremental launch improver.  It won't give you 10-fold decrease in launch cost.  THe differences will be measure in percent.  It may well be a vialbe option someday but I think that we need to have a much more crowded launch schedule to justify the contruction of something like this.

It depends on what wavelength of the light is.  Hydrogen will only absorb light of certain, specific frequencies.  (hence why spectroscopy works).  The absorbtion of a single photon will give some momentum to a hydrogen atom.  The higher the frequency, the greater the momentum transferred.  I don't have any numbers handy but it won't be much.  You need a LOT of light to be able to generate any meaningful light.  That's why you can't use a flashlight to fly around. 

Solar sails can generate thrust by using light.  The best situation is to use a reflective surface. Basically, reflective materials like metas have loosly bound electrons that kinda of float around like an electron gas, not particularly bound to one atom.  (it's why metals are conductive)  When light hits, the elecrical component causes a reciprocal oscillation in the electron dentisity that basically causes the photon to 'bounce' off.  It's kind of like a rope that's attatched to a wall with a spring - if you give the rope a twitch to send a wave down its length, the wave will bounce back off the spring.

In this fashion, the photons are bounced backwards.  So not only do you get the momentum of the light hitting the object, you also get the momentum of the photon being redirected in the oposite direction - you've just doubled your thrust.  Even so, at the Earth's distance from the sun, a sail with an area of a square kilometer generates about 1 kg of thrust.  It's pretty weak.  The big problem with solar sails, is that in order to get enough thrust, you need a HUGE sail and the mass of the sail adds so much weight to a spacecraft that it takes forever to get anywhere.

Actually, that answer isn't really correct.  The polarization of light has nothing to do with how wide it is and its ability to pass through a given space. 

Polarization occurs because light can be thought of as an oscillating electric field at a right angle to an oscillating magnetic field.  In linearly polarized light, both the electric and magnetic component are also ata right angle to the direction of travel.  (imagine two sine waves at right angles to each other - the long axis of the travel is the direction the light is going.)

Polarizing materials have a net imbalance in how easily they intereact with an oscillating magnetic field.  This is due to the crystal structure.  Most crystalline materials exhibit this behavior to some extent.  Materials that act as polarizing filters simply exhibit this property to a greater extent. When light hits a polarizing filter, the electric field interacts with the material depending upon the angle it hits at.

As far as the 'size' of light, it's a poorly phrased question.  elementary particles don't really have a size as we know it.  a photon has a size of 0.  A light wave in the visible range has a size of about half a micron.  The currently accepted model (which is likely to be at least partially wrong) is that the wave nature of light is in the form of a probability wave that takes on the form of a photon when it interacts with another particle.  The probability wave simply is the proability distribution of where that interaction is likely to take place.

I'm almost afraid to ask, but why do you think that the books are wrong?  It's an established fact that photons have mass, otherwise they couldn't transfer momentum.  They have no rest mass which is fine since they never stand still.

I'm glad to see the Navy getting on board here.  They have the best safety record in the world with nuke reactors.  I know a guy that was in the nuke program when he was in the Navy - the school has something like a 95% dropout rate.  They're pretty unforgiving to candidates and toss anyone who shows the slightest sign of not being competent.