Solar Wind

Echus_Chasma · 2002-12-22 17:18:51

Does Solar Wind actually push you if you are in space or is it just a flow of particles?

Auqakah · 2002-12-22 17:33:32

It can only be utilized for forward motion if you deploy a sail composed of an ultra-light material (far lighter than air). NASA's JPL is working on such a material as we speak.

Echus_Chasma · 2002-12-22 18:26:34

Interesting, do you happen to have any links or anything so I could get info on solar sails?

Josh Cryer · 2002-12-23 14:07:43

Indeed, the solar wind is very very weak compared to mere sunlight.

Check these sites out: http://cspar181.uah.edu/RbS/HTML/PHY00/ … 0/img0.htm
http://cspar181.uah.edu/RbS/]http://csp … h.edu/RbS/ (click on the dusty magsail page)

They're down at the momment, but they explain it quite well (and propose a very cool solution to exploiting both the solar wind, and sunlight).

Echus_Chasma · 2002-12-23 14:56:51

Thank you both.

Echus_Chasma · 2002-12-25 20:55:54

The Planetary Society are building and going to send a solar-sail ship into space.
Look at this:
http://www.planetary.org/solarsail/]htt … solarsail/

sethmckiness · 2003-09-20 11:08:25

I'll skip how to get back to Earth the fastest way by light sail, until I find out if the above argument proves to be true or not.

If feasible, couldn't one tack back to Earth. Sailboats use tacking to move into the wind, so wouldn't that be possible for a light sail craft?

Spider-Man · 2003-09-20 13:47:44

Since my last post re. "space sailing" in December 2002, quite a lot of discussion has been posted outside of the Mars Society under that title. The main thrust of the discussion was to reject Gold's denial of the feasibility of using light for propulsion. Well, after sifting through the arguments, I was left with the following conclusions: (1) Light propulsion not only is feasible, but practical--even essential--to interplanetary space travel, at our present state of development. (2) The faster the reflective sail moves away from the Sun, the more the amount of thrust from the light, as evidenced by increasing Doppler-shift towards the red of the reflected light. So (3) contrary to inverse-square-law reduction of the amount of light with distance from the Sun, might not the increasing effectiveness-of-light-with-velocity phenomenon of (2) compensate for the inverse-square-law thrust drop-off? If true: Initially going closer to the Sun, to gain additional speed before heading out to rendezvous with Mars, might be the fastest way by light-sail. (I'm posting this to find out if the above argument proves to be true or not.)

Umm... I really don't think so, Dick. Light's velocity is as constant as anything, and so, the closer a lightship approaches that speed, the more and more returns diminish, to say nothing of the inverse square law of radiation. Could you explain this evidence from the Doppler shift, as you say? I'm rather curious as to what you mean.

Spider-Man · 2003-09-21 12:17:03

That is really, very intriguing, Dick... Let me think about this...

If you have any websites or links, by the way, I'd love to see them.

Inspired by your seemingly revolutionary thoughts, I took to researching the photoelectric effect in detail. As we know, the photoelectric effect is that, when light hits a metal surface, the surface emits electrons. This is where I was always confused; I could never comprehend how photons, which have no inertia, could act like particles of mass when they hit an object.

Just to explain it for the heck of it, "Newtonian" propulsion is based off of Newton's work with the laws of motion, more notably in the third and most famous law, which Newton wrote: "Actio est reactio." Translated, that comes out (perversely) as "for every action, there is a an equal and opposite reaction". Essentially, if one is sitting in a little cart, and he throws tennis balls from the cart towards the rear, he will move forward. But this only happens by virtue of the tennis balls having mass.

Photons have no mass. Therefore, reflected photons should not cause any motion to occur, and not change the net momentum of the system.
Indeed, it's not the photons, but the electrons which push the object when they are excited away by the light hitting the metal surface. The light just causes the electrons, which do have mass, to fly off the surface, the action which causes the reaction of the metal surface to move forward.

So that means we don't want a mirror at all! we want something solidly black that will absorb the light, energizing the electrons so they fly off. If the surface is reflective, the electrons won't fly away, but jump back to their previous energy states, and in the process give off the photons we see as reflected light, providing no velocity for the sail.

Egad, Dick, how neat! That's so fascinating...thanks.

However, the Doppler-shift idea is not quite sound. I see exactly where your coming from, that red-shifted light would seem to be giving up more of its energy into the sail, allowing more electrons to be emitted; but in fact that's not the case. Because the light would be reaching the solar sail at lower frequencies as the sail moved away from the sun, the sail would not be receiving as much energy as it did when it was still. Receiving less energy means that its electrons would be excited less, and that it would in fact give off fewer electrons. Therefore, the faster a solar sail moves away from the sun, the less its ability to accelerate, not greater, as nice as that would be.

Another, more serious problem is that of the loss of electrons. Physicists must forget that it isn't truly "light pressure", light reflecting off a mirror which causes the movement away from the reflection and in the direction of luminal incidence ? it's a confusion that is derived from the work in 1901 by Russian scientist Peter N. Lebedev, where he used mirrors suspended in a vacuum and turned them by shining light on them (that they were mirrors was accidental; it was the metal in the mirror which caused the propulsion when electrons were excited off the surface by the light).
The main problem is that, over time, the solar sail would lose significant numbers of electrons. Its surface would be totally ionized, positively, leaving no free electrons left to be excited off the surface. The remaining electrons would take enormous amounts of energy to free, there being no balance of other electrons to allow a few to escape.
The photoelectric effect works for photovoltaic solar panels because powering with electricity is not a simple absorption of electrons, but a continuous circuit of electrons moving in a loop. The electrons, once they are excited off the panel and move into the wire, are replaced by electrons from the negative end of the wire, only to be excited by more sunlight to continue the circuit indefinitely.

Indeed, a system using a metal surface as a sail and a laser, or other light source, could work in Earth's atmosphere. But in space, there is virtually no matter at all, especially no electrons to replenish those lost by the solar sail, the sail would eventually fail to produce electrons, and be "dead". This, I think, is the main case against light propulsion.

Spider-Man · 2003-09-21 19:30:38

(1) I just read everything I could "Google" re. Solar Sails, Light Sails and Space Sails. Not once did I find any explaination of "sailing in space" that treated the reflection of light in terms of the Photoelectric Effect!

Heh, well, they should, because light doesn't have the ability to impart any inertia into a sytem, by the simple virtue that is has no inertia. This is probably the source of error.
Incidentally, though Dr. Zubrin clearly was unfamiliar with the quantum mechanics, he did cite both Peter Lebenev and Albert Einstein as contributors to proving the photoelectric effect in his dissertation on "Light Sails" in his book Entering Space.

I'm not able to interpret what we're attempting to confirm or deny, in such terms. My presentation and (tentative) conclusions used the same terminology as the above sources. So, what can I to do but request you do the same, if you will, please.

My pleasure: http://www.colorado.edu/physics/2000/qu … ctric.html

(2) I can't fault your conclusion that the sail experiences redshifted light the instant motion is imparted. But the reflected light would be again redshifted, so the Sun sees double the redshift due to the velocity away from it--not so?

I have difficulty understanding your diction at times... "the Sun sees"..? I don't know what that means, exactly. The "loss of energy" referring to light from the sun, energy itself, was also very confusing until I deciphered it.
Nevertheless, if you are saying that the reflected light would be redshifted twice as much as the incident light hitting the sail, that would be correct.

To repeat from my previous post: My interest is to establish that, if propulsive force increases with velocity (as "they" are saying in the above sources) won't this have the effect of countering the decreasing force due to inverse square law fall-off?

No. Simply, propulsive force would not increase with velocity. Light, or any radiation, even a matter stream, would still impart the most force to an object when that object would be at its nearest to the source.
The source of this idea, as really neat as I find it to be, is based on inverted logic; that is, the light having less energy (redshift) is the goal, instead of the light giving up more energy. It's assuming the negative, that light that has less energy, that is red, must have given that energy to the sail, which of course is not true.

Shaun Barrett · 2003-09-21 21:15:00

This discussion seems surreal!
I've never heard of light sailing being explained in terms of the photo-electric effect either. There may be some initial force on the sail due to the liberation of electrons from the surface but, if the surface gradually accumulates a resultant positive charge, then electrons will cease to be emitted.

The whole point of the matter is that photons have momentum. (We've been through all this in another thread at New Mars, though I can't remember where just now.)
Photons can and do impart momentum when they reflect from a surface, even though their rest-mass is zero.
I firmly believe Professor Gold will be proven wrong quite shortly when The Planetary Society's solar sail craft, Cosmos 1, is launched.

This business of a solar sail getting more energy out of a photon the faster it's moving away from the light source, smacks of the legendary 'free lunch'!

Think of this in terms of frames of reference. From the solar sail's frame of reference in Dicktice's scenario, it is sitting still and the Sun is receding at a certain speed. This is a perfectly sound way of understanding the scenario, since all frames of reference are equally valid and all things are relative (see Einstein's theories).
If the Sun is receding at a particular velocity at a given moment, light from the Sun is red-shifted. This is a known fact and is seen in the red-shift of far-flung galaxies as they race away from us.
Thus, the photons reaching the sail from the receding Sun are of a longer wavelength (the reason they're redder) and, therefore, a lower frequency.
At the same moment, from our frame of reference, stationary relative to the Sun (for the sake of argument we'll ignore Earth's orbital path), the light reflected from the solar sail is red-shifted by an identical amount because the sail is receding from us at the same speed as the Sun appears to be receding from the viewpoint of the sail!
In other words, there is no significant differential between the wavelength of the photons arriving at or leaving the reflective surface of the sail. There doesn't have to be!
The reason the sail moves is not because of the photo-electric effect and it isn't because of some perceived difference in the wavelength of the arriving and departing photons. It moves because photons have momentum, which they impart to the sail when they are absorbed by it, and doubly so if they are reflected in the opposite direction by it.

Spider-Man · 2003-09-21 22:26:41

This discussion seems surreal!
I've never heard of light sailing being explained in terms of the photo-electric effect either. There may be some initial force on the sail due to the liberation of electrons from the surface but, if the surface gradually accumulates a resultant positive charge, then electrons will cease to be emitted.
The whole point of the matter is that photons have momentum. (We've been through all this in another thread at New Mars, though I can't remember where just now.)

Oh really? Well that's fantastic then. Nevermind.

Photons can and do impart momentum when they reflect from a surface, even though their rest-mass is zero.

Okay, I can live with that.

I firmly believe Professor Gold will be proven wrong quite shortly when The Planetary Society's solar sail craft, Cosmos 1, is launched.

When's that?

This business of a solar sail getting more energy out of a photon the faster it's moving away from the light source, smacks of the legendary 'free lunch'!
Think of this in terms of frames of reference. From the solar sail's frame of reference in Dicktice's scenario, it is sitting still and the Sun is receding at a certain speed. This is a perfectly sound way of understanding the scenario, since all frames of reference are equally valid and all things are relative (see Einstein's theories).

Relativity is inherently self-contradictory. It says, as you note, that all individual observers virtually, indeed, truly have the justification of seeing themselves as stationary and everything else moving around them.
Well then, let's have two astronauts floating in space. From Astronaut Jayne's perspective, Astronaut Kyle is moving towards her at 10 km/s. From Kyle's perspective, Jayne is moving towards him at 10 km/s. So therefore, without any point of refences like a planet or even stars, both observers are right.
But wait a minute ? Relativity also states that motion will cause time dilation; that is, something that is moving will have a slowed perception of time, and everything else will appear to move faster around it. With Kyle and Jayne, which one appears to be moving slower? which one faster? Indeed, only one of them can actually be moving relative to space itself. But that's not possibible under the guiding principle of Relativity which makes it relativity, the math that composes its very foundation.
Relativity is inherently flawed and contradictory.

If the Sun is receding at a particular velocity at a given moment, light from the Sun is red-shifted. This is a known fact and is seen in the red-shift of far-flung galaxies as they race away from us.
Thus, the photons reaching the sail from the receding Sun are of a longer wavelength (the reason they're redder) and, therefore, a lower frequency.
At the same moment, from our frame of reference, stationary relative to the Sun (for the sake of argument we'll ignore Earth's orbital path), the light reflected from the solar sail is red-shifted by an identical amount because the sail is receding from us at the same speed as the Sun appears to be receding from the viewpoint of the sail!

Aye... so...?

In other words, there is no significant differential between the wavelength of the photons arriving at or leaving the reflective surface of the sail. There doesn't have to be!

*Shrugs.* I fail to see why this is an issue.

The reason the sail moves is not because of the photo-electric effect and it isn't because of some perceived difference in the wavelength of the arriving and departing photons. It moves because photons have momentum, which they impart to the sail when they are absorbed by it, and doubly so if they are reflected in the opposite direction by it.

Excellent. Ad astra, Cosmos 1.

dicktice · 2003-09-22 08:45:58

Shaun/Spider:
My purpose all along, has been to follow the arguments opposing Gold's supposition (that Solar sailing won't work) to their 'free lunch" conclusion.
They avoid just how Sunlight imparts momentum to the sail, inferring simply from the amount of redshift of the reflected light (compared with the incident light) the velocity of the sail away from the Sun. For a non-moving sail with perfect reflection, no redshift in the reflected light indicates no motion, according to Gold. Give the sail a boost to start it moving radially, the amount of redshift of the reflected light indicates the velocity.
The amount of redshift of the reflected light (goes the argument) also iindicates the amount of energy given up by the incident light in imparting motion to the sail.
As the redshift increases with increasing velocity (the "free lunch" argument concludes) the energy given up by the light must be increasing as well.
The dilemma stems from mixing-up redshift due to energy loss and redshift due to Doppler effect. Aside from that, I'm convinced by what I've read under the topics of so-called space/solar/light sailing, that photo propulsion will work.
I've deleted all of my forgoing posts on this subject. Sorry to have been such a drag.

sethmckiness · 2003-09-22 09:36:47

As the redshift increases with increasing velocity, the energy given up by the light must be increasing as well

So, by saying that the reduction in movement of a photon(frequency reduction, ie red-shift)Will change this angular sine wave momentum into forward momentum it imparts on the sail. Is that what you are trying to say? The more a particle would shift in frequency the more angular momentum it would lose resulting in further forward momentum gained. (I may be misusing Angular momentum but don't know the proper way to put the movement of a particle through a sine wave)

dicktice · 2003-09-22 19:44:24

Sorry, Seth: I just rewrote my post, which makes your reply invalid. Sorry, as I concluded, for wasting your time.

Shaun Barrett · 2003-09-22 20:08:04

Hi SpiderMan!
It appears my last post wasn't very clear, for which I apologise. I'm not sure how else to explain what I see as the situation regarding the mechanism by which a solar sail 'sails'.
Suffice it to say, my personal understanding is that the photo-electric effect isn't a significant contributor.
As to the relevance of examining the purported difference in wavelength of the sunlight arriving at and leaving the sail (you shrugged and expressed puzzlement at this), this is crucial to answering Dicktice's query. Some theoreticians are asking where the energy is coming from to push the sail. They have concluded that this energy is coming from the difference in wavelength, the red-shift, of the reflected light bouncing off the sail as it recedes from the Sun. They appear to be saying that 'regular' photons from the Sun hit the sail but that red-shifted, or lower energy, photons are reflected back. This difference in energy is where the push comes from.
They even take this argument further by maintaining that a sail which is perfectly stationary relative to the Sun, won't move. The push, which they say results from the differential in photon wavelength, doesn't happen until something else gets the sail moving in the first place.
Then they take it still further by deducing that the faster the sail goes, the bigger the wavelength differential, and the faster the sail goes ... and then the wavelength differential is still bigger, so the push is greater and the sail goes even faster!! (Sounds like a 'free lunch' to me.)

I dispute this. I maintain there is no significant difference in the wavelength of the incident and reflected light at the sail's surface. I justify this argument by appealing to Einstein's concept of relativity to assert that the red-shift is just as applicable to photons reaching the sail as to those reflected back from it.
But then, if there's no energy differential in the wavelength (or thus frequency) of the photons, where does the push on the sail come from? It comes from the change in momentum of the photons.
Dicktice once asked me to explain the detailed mechanism whereby a photon arriving at a highly reflective surface has its momentum reversed and flies backwards along its original path, thus imparting twice its original momentum to the sail. I couldn't answer him and I still can't! An excellent knowledge of quantum mechanics is required for that and I haven't the background for it, unfortunately.

Anyhow, I hope I've at least clarified my position somewhat(?). Apologies again if my previous post was too vague.

SpiderMan, you asked about the launch of Cosmos 1. It looks like it will be in early 2004 now, following a delay designed to allow more testing. If you're interested, there's a news update at this site.
Being a longstanding member of The Planetary Society myself, and having donated money towards making this thing happen, I'm very excited about it and looking forward to the launch.

Spider-Man · 2003-09-22 21:42:58

I've deleted all of my forgoing posts on this subject. Sorry to have been such a drag.

Deleted them??? Why in God's name would you delete them? They were good posts, friend; there's absolutely no reason to delete anything on this board; only absolute vulgarity should be self-censored, but this...?! Heavens, put them back if you still can.

You didn't waste anyone's time. I think that you deleted your own good posts was terrible.

Some theoreticians are asking where the energy is coming from to push the sail. They have concluded that this energy is coming from the difference in wavelength, the red-shift, of the reflected light bouncing off the sail as it recedes from the Sun. They appear to be saying that 'regular' photons from the Sun hit the sail but that red-shifted, or lower energy, photons are reflected back. This difference in energy is where the push comes from.

Ohhhh....! Now I get it! Cool! that's fascinating. I see now.

Yes, you've completely clarified yourself; thank you for informing me on all this.

dicktice · 2003-09-23 13:30:29

Nope, Spider, I was right to delete something I hadn't researched properly. Shaun restated the source of contention and (being a Planetary Society member) is better qualified. I was merely propagating misunderstanding. But Prof. Gold's contention is being opposed (1) by the redshift scenario described by Shaun, which simply adds to the confusion, and (2) using his mistaken conclusion re. the Crookes radiometer's rotation in the "wrong" direction to judge his ability to theorize. (He didn't evacuate the bulb sufficiently.) Shaun's argument opposing Gold, at least doesn't lead to a "free lunch" conclusion.
I might add that, Shaun's having a vested (i.e. financial) interest in the successful theoretical result of the Planetary Society's upcoming experiment, of course, can't have influenced in any way, I'm sure, the complete impartiality of his opposition to Robert Gold's conclusion as to its being...I believe the expression used was "dead in the water." (I miss maverics like Fred Hoyle--he and Gold were such a pair!)

Shaun Barrett · 2003-09-24 19:55:09

Hi Dicktice!
Your second-last post:-

I might add that, Shaun's having a vested (i.e. financial) interest in the successful theoretical result of the Planetary Society's upcoming experiment, of course can't have influenced in any way, I'm sure, the complete impartiality of his opposition to Robert Gold's conclusion as to its being...I believe the expression used was "dead in the water."

Ha ha !! :laugh:

Why, Dicktice, how could you say such a thing when you know my commitment to absolute impartiality in all things?! Go and wash your mouth out, you .. you .. cynical doubting Thomas, you!!

On a less jocular note, I fully understand your difficulties regarding the transfer of momentum from photons to solar sails (or anything else, I suppose, for that matter). As I've said, I can't give you a quantum mechanical, step-by-step explanation for it, since I'm essentially as much in the dark as you are as far as the mathematical theory goes.
I satisfy myself as to the practicalities of it all by imagining that photons have mass, which allows for a more intuitive understanding of how they can push on a sail. Let's say that you are floating, stationary, in the middle of one of the compartments of the ISS. Someone yells: "Catch!" and throws a heavy metal cannonball toward you at 2 m/s. You catch the cannonball and notice both you and it are moving backwards towards the compartment wall at 10cm/sec. You and the cannonball now share the original momentum of the cannonball, including its direction because momentum is a vector quantity. This scenario, in my simple mind, serves as an analogy for a photon hitting a matt black solar sail, being absorbed by it, and giving the sail a tiny bit of momentum in the same direction.
Now imagine that instead of just catching the cannonball, you catch it and immediately throw it back where it came from at the same speed, exactly 2 m/s. You now find you are floating backwards at 20 cm/s, having imparted the original momentum back to the cannonball again, but in the reverse direction. (Actually you'll be going very slightly faster than 20 cm/s because you've divested yourself of the mass of the cannonball, allowing the momentum to act on a slightly lesser mass, your body alone ... but that's a minor technicality and we can ignore it for these purposes.) This new scenario serves me as an analogy for a photon reflecting back from a mirror-like solar sail, giving it twice as much momentum as the absorbed photon did.

This mental picture is no doubt full of flaws and you may not find it helpful at all but it seems to help me understand, in everyday terms, how solar sailing works ( and it will work ... I've put money into it so it has to work!!! )
Any comments?

Euler · 2003-09-24 23:16:19

To understand solar sails, it helps to understand how photons work. Photons do have momentum. The energy of a photon is given by E= vh where v is the frequency of the photon and h is Plank's constant. Since the momentum, p, of a particle is given by p=E(kinetic)/velocity, and the photons travel at c, the momentum of a photon is given by p=vh/c.

How can a photon have momentum if it doesn?t have mass? The truth is that photons don't have rest mass. However, photons are never at rest. In relativity, when an object speeds up, its mass increases. If it were able to travel at c, the object's mass would be multiplied by infinity. So what happens when you multiply the photons 0 mass by infinity? 0*infinity gives you undefined, which is not very helpful. You can, however, use E=mc^2 to find the mass for a photon of a given energy. So photons can be thought of as particles with mass=vhc^2 and speed c.

When dealing with solar sails, it is usually easier to think in terms of momentum rather than kinetic energy. If a photon hits the sail and is absorbed, its momentum is given to the solar sail. If a photon hits the sail and is reflected in the opposite direction, twice the photon's momentum is given to the sail. If a photon hits the sail from a direction that is not normal to the sail, the photon gives the sail a momentum of 2*sin(angle between photon path and sail plane)*photon momentum, with a direction normal to the sail.

This still works in terms of energy, though it is less intuitive because the reference frame must always be considered. If the sail is not moving with respect to the sun, then they are in the same reference frame. In this case, when the photon hits the sail it bounces back with nearly the same kinetic energy that it had before it reflected. It does accelerate the sail some, but the kinetic energy is proportional to the square of the velocity, and since the velocity is so low there is much less change in kinetic energy for the same amount of change in momentum.

If the ship is traveling away from the sun at high speed, then in its reference frame the photons are redshifted and have less momentum and energy. In the ships reference frame, the photons transfer twice their (reduced) momentum to the sail, but since the ship is at rest in its own reference frame, the photons do not impart any energy. From the sun's reference frame, the (full strength)photons hit the sail and give their momentum plus the momentum of the (reduced energy)reflected photons to the sail. Since the ship has a high velocity, the slight increase in velocity increases the kinetic energy significantly, which accounts for the energy lost by the photons in this reference frame.

So the faster the ship travels away from the sun, the less momentum it receives from each photon because the photons are redshifted in its reference frame and have less momentum. The photons are also redshifted slightly by having to escape the sun's gravity well. However, both of these effects would be slight and much less important than the inverse square law that limits the light's intensity.

Hopefully this made some sense, if not I will try and make it clearer.

dicktice · 2003-10-08 09:52:02

Gee thanks, Euler. Very impressive. Where are you coming from, experience-wise?. That clears up a lot of fuzzy thinking, on my part at least! I'll do a printout, to place under my pillow (just kidding). Hopefully with this to refer to, the rest of us (Shaun, Spiderman, et al) can progress with our Solar sailing scenarios. . . .

Euler · 2003-10-09 22:26:36

Gee thanks, Euler. Very impressive. Where are you coming from, experience-wise?. That clears up a lot of fuzzy thinking, on my part at least! I'll do a printout, to place under my pillow (just kidding). Hopefully with this to refer to, the rest of us (Shaun, Spiderman, et al) can progress with our Solar sailing scenarios. . . .

Right now I am a junior in college working towards a math major with a physics minor. I plan on continuing with college after completing my bachelors degree and eventually becoming a mathematician or physicist.

Euler · 2003-10-11 02:26:31

I do not believe that professor Gold?s claim has any validity, and frankly I am surprised that such a notable physicist would make such a claim. As I have said, the motionless mirror would accelerate at roughly the same rate that a moving mirror would accelerate at (for velocities not close to c, at least). It works just like any other elastic collision.

Professor Gold seems to be mixing up kinetic energy and momentum. He seems to think that the acceleration of the spacecraft is proportional to the amount of work done by photons (as evidenced by the redshift). This logic is faulty. Work (energy) is equal to force times distance. Because the stationary mirror is not moving relative to the sun, there is no change in distance, and therefore no work done. However, there is still a force acting on the sail and therefore it will still accelerate.

The pressure of sunlight has been measured and it is significant enough that it is already a factor when computing the trajectories of interplanetary spacecraft. I see no theoretical obstacles preventing solar sails from working.

Euler · 2003-10-11 17:21:38

Now Euler, about "the speed of gravity" controversy--are you willing to take that on. Be great if you did.

I will try to sort out the speed of gravity thing. However, it seems to be a lot more complex than the solar sail controversy, so I may not be able to come up with convincing evidence for either side.

John B · 2003-12-29 05:58:19

There needs to be a full scale design contract let on a low temp ( less than 1100 C )1200 megawatt interplanetary space reactor /turbo-generator coupled to a extreme high current both electron and proton operated combination klystron/linac with targeted exhaust velocities o 10e6 M/sec and exhaust masses of 10 g/sec. This would give a 50 metric ton vehicle an acceleration of about 1/5 G or about 2m/sec/sec, with a reaction propellant usage of 36 kilograms of H2 per hour. Note waste energy would be 100 to 200 megawatts and some of that would be used for internal spacecraft functions Nuclear plant thermal efficiencies would be increased to 90% in this model from the current less than 70%. If that is not possible increase the total reactor thermal output to 1500 megawatts and waste heat to 500 megawatts. That burn would make most Mars trips a twelve day cruise with just 60 hours combined acceleration and deceleration "burn time" and a reaction mass usage one way of 2.4 metric tons H2. Robot cargo ships would make the trip one way taking ten times as long with 500 ton total masses and then their reactors would be converted to surface power units. Best thing yet is that if we only achieve 50 percent of the power throughput goals the whole thing is still practical and very doable using technology that has been theoretically demonstrated today. The other thing is that the reactor radiation shielding only needs to be a 2 meter thick water tank between the crew section and the power plant and propulsion section and that the robot ships will make the flight first. you will note that this is about twice the thrust that you get per unit kilowatt than a current ion engine but the main accelerator klystron proton linac uses acceleration grids only in the preliminary low energy proton klystron stages and the target-less linac uses power only as a function of its own impedance, which using superconductors on the surface of its acceleration cavities would be quite high ( today?s commercial linacs use polished copper and have impedances in the 50 thousand ohm range. The throughput impedance on the DS1's ion drive is about 600 ohms. The high voltages and low ( comparative) frequency of this linac would enable the drift tube diameters to be quite large so that there would be no beam interaction with the accelerating current other than electrostatic. The proton klystron front end of the accelerator would be very long (50 M) because of the 1000 to one difference in the charge to mass ratio of a proton compared to an electron. and the frequency would be much lower because the initial electrostatic gun would be accelerating those protons to a much lower initial velocity, and because the system could accept virtually no out of phase beam losses both for efficiency reasons and power dissipation ones. The main source of power for the linac portion would come from the concurrent electron klystrons needed to neutralize the beam, and they of course would have no collectors just well designed Pulsed acceleration grids.and possibly quadrapole focusing magnets instead of annular windings. all current carrying surfaces would either be gold or superconductor plated and the reactor fluid waste heat and the hot side of the cryo-pumps would cool by the use of conventional space radiators, The design is doable.. all we need is for some Varian or Stanford engineer to crunch the numbers and come up with the exact specs --JJB

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#1 2002-12-22 17:18:51

Re: Solar Wind

#2 2002-12-22 17:33:32

Re: Solar Wind

#3 2002-12-22 18:26:34

Re: Solar Wind

#4 2002-12-23 14:07:43

Re: Solar Wind

#5 2002-12-23 14:56:51

Re: Solar Wind

#6 2002-12-25 20:55:54

Re: Solar Wind

#7 2003-09-20 11:08:25

Re: Solar Wind

#8 2003-09-20 13:47:44

Re: Solar Wind

#9 2003-09-21 12:17:03

Re: Solar Wind

#10 2003-09-21 19:30:38

Re: Solar Wind

#11 2003-09-21 21:15:00

Re: Solar Wind

#12 2003-09-21 22:26:41

Re: Solar Wind

#13 2003-09-22 08:45:58

Re: Solar Wind

#14 2003-09-22 09:36:47

Re: Solar Wind

#15 2003-09-22 19:44:24

Re: Solar Wind

#16 2003-09-22 20:08:04

Re: Solar Wind

#17 2003-09-22 21:42:58

Re: Solar Wind

#18 2003-09-23 13:30:29

Re: Solar Wind

#19 2003-09-24 19:55:09

Re: Solar Wind

#20 2003-09-24 23:16:19

Re: Solar Wind

#21 2003-10-08 09:52:02

Re: Solar Wind

#22 2003-10-09 22:26:36

Re: Solar Wind

#23 2003-10-11 02:26:31

Re: Solar Wind

#24 2003-10-11 17:21:38

Re: Solar Wind

#25 2003-12-29 05:58:19

Re: Solar Wind

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