48 replies to this topic

[eternaltraveler]

BTW they have pretty much killed the Prometheus project and that was the best chance of a building a nuclear rocket we had.  Now they seem more intersted in blowing things up with nuclear energy than even flying to Mars.


Prometheus, ISS Research Cuts Help Pay for Shuttle and Hubble Repair Bills
http://story.news.ya...bblerepairbills

Why can't they just admit that the shuttle was a bad idea from day 1 and stop flushing money down this toilet. How can they think the shuttle is a good idea?

NASA is disgusting. The last thing of value was putting humans on the moon, and that was almost 40 damn years ago. They have sucked since they lost Von Braun.

It's funny how all of his war crimes were over looked so he could work on our rocket program. He developed the V2 at a forced labor camp. And the V2 was really only used when the war was already lost as a kind of vengance weapon. And he had a big part in aiming them.

[eternaltraveler]

Here is a reference I just found on wikipedia that backs up my position.

http://en.wikipedia....lativistic_mass
Some reasons for abandoning the notion relativistic mass:

-One is forced to make statements like "A photon has no rest mass", which sounds slightly odd because a photon can never be at rest.

-The idea of mass increasing with velocity leads many to believe that the internal structure of a quickly moving object is somehow altered. However, the standard view of relativity is that the internal structure of an object is always unchanged, and that the different quantities measured by different observers for energy and velocity are simply the same reality seen from different points of view.

-The idea of relativistic mass combined with the notion of Lorentz contractions leads some people to the incorrect conclusion that an object traveling fast enough will form a black hole. However, by the very principle of relativity, if an object is not a black hole in one frame (its rest frame) it cannot be a black hole in any other frame either.

-If one wishes to retain the notion that mass measures the "resistance" to acceleration, then mass can no longer be treated as a scalar quantity. This is because it is easier to accelerate something perpendicular to the direction of motion than parallel to the direction of motion. In effect, an object would have more mass in one direction than other.

-The primary reason that most physicists chose to abandon relativistic mass in favor of the rest mass is that rest mass is a Lorentz invariant quantity — it is the same in every reference frame. Strictly speaking, it is the time-like component of a four-vector (the energy-momentum four-vector). A four-vector is a Lorentz invariant quantity, but its individual components are not.

-In the end, the usage of mass, energy, and momentum in place of terms like rest mass and relativistic mass is a matter of semantics. Neither usage is technically wrong. However, that the latter terms are little used in the scientific community is a strong argument in favor of abandoning them altogether. Einstein himself wrote:

“It is not good to introduce the concept of the mass M = m/(1 - v2/c2)1/2 of a body for which no clear definition can be given. It is better to introduce no other mass than ‘the rest mass’ m. Instead of introducing M, it is better to mention the expression for the momentum and energy of a body in motion.” – Einstein, in a 1948 letter to Lincoln Barnett

This precisely echoes the modern sentiment

[eternaltraveler]

This generally mimics the problem of lifting a mass into orbit as the energy requirements for lifting the fuel alone are almost 85% of the fuel capacity of the rocket. Obviously these are apples and oranges but the issue is the same as the amount of energy to go from 80% to 90% C is equivalent to a major percentage of all the energy expended to reach 80% C that is why the formula achieves a demand for infinite energy to reach C. (The math is not done for this example)

That is why something like a ramjet would be required. The ramjet would use the hydrogen spread throughout space as fuel for a fusion rocket. Fuel would not have to be carried on board.

You’re right though. It would require a LOT of energy. (I’ve done my best to come up with a figure later on in this post which is hopefully within a couple orders of magnitude.

However for the sake of argument do the math on that acceleration rate and you will find it isn't much faster in some respects than an elevator. 

Actually a rocket is accelerating at faster than g (by about the rate of an elevator). If it wasn’t it wouldn’t go anywhere. Or rather it is generating the force it would need to accelerate at slightly faster than g if it was unhindered by any gravitational attractions. Earth’s gravity well is a bitch )

From a stationary starting point, after the first hour you are still only doing just a little over the speed of sound at roughly 698 mph. However at this rate you will achieve escape velocity in roughly a little over a day but for the sake of argument lets begin from escape velocity but are you also seeing the problem?

After accelerating at g for one hour you are traveling approximately 22 miles per second. Using chemical energy for this would of course be unreasonable. However nuclear energy certainly wouldn’t be. As I’ve stated in another thread, there is more energy to be had from the tiny uranium impurities used in a fission reactor (assuming you use all of it utilizing a breeder reactor), than you can get by burning the coal.

Nuclear reactions turn a significant portion of their mass into energy. Chemical bonds too have a mass associated with them, however these masses are incredibly small. Deuterium fusing into helium turns ~.6% of it’s mass into energy. 1 gram of deuterium would yield .0064 grams converted into energy. Which is 5.76*10^11th joules. . Assuming an efficiency of 25% (you can pick any other arbitrary number, ion drives currently have much higher efficiencies than this) 1 gram of deuterium would translate into 1.44*10^11th joules of work. 1 gram of deuterium would therefore be able to accelerate a 10,000 kilogram object for about 5 hours or so.

Edit: Whoops, this should be about 5 seconds. Not 5 hours.

I’ve been tinkering with trying to figure out just how much fuel would be required to accelerate to this kind of velocity. It’s simpler to split the travel time in half such that you only worry about the acceleration phase.

The total work done on the vessel would be 2*10^9(lys)*1*10^19(meters per ly)*10000(mass of vessel)*9.8(force)=~2*10^33th joules

Over the course of the voyage ~3.4*10^15 metric tons of deuterium would be required. Of course in free space you are more likely to find plain hydrogen and fuse that into deuterium. The problem with that is the activation energy is significantly higher since there is twice as much electrostatic repulsion per amount of strong nuclear force. And then you kick off a positron as well. The good news is that a mere 3.4*10^15th metric tons of fuel would be easy to find over the course of 2 billion light years.

My math above could be horribly flawed. Anyone is welcome to come up with a better figure for the fuel consumption.

Edited by elrond, 19 May 2005 - 09:49 PM.

[Lazarus Long]

Yes there is no real consensus about Relativistic Mass but I for one would warn that we are not describing the behavior of subatomic particles and we need an adequate theory of Quantum Gravity to describe the types of phenomenon that the ship would experience at relativistic velocity. Some of the data still supports that Special Relativity applies for these kinds of *macroverse* problems.

Because we are dealing with a large mass (a ship/stellar not atomic scale mass/distance) with relatively simplistic models and methods (mass/thrust propulsion, and human/biological occupants not inert mass) I think it prudent to err on the side of caution with our expectations and eliminate by testing rather than assuming what the risks would be.

*****

On a separate note, an elevator going up and experiencing one gee is actually accelerating at 2G. In fact sitting here typing I am experiencing an acceleration of One G: albeit in the wrong direction, it is called gravity.

However it diminishes as a I go up and away from the center of the Earth and coincidentally as a pilot I happen to remember that I can accelerate in a lateral direction on a path that is tangential to the force of gravity and slowly by achieving a significant distance from the stronger gravitational forces, gain momentum and altitude toward escape velocity. )

However we really need to start discussing some alternative propulsion methods as this one is of limited value IMHO as we approach c.

This certainly is true. Shielding would be a problem

Edit: The mechanism of the electromagnetic vortex of the RAM would naturally tend to act as a shield (deflecting charged particles away from living areas and into the reactor, and pretty much everything out there is charged). There would of course be limits to this.

I am glad you liked my idea of the electromagnetic RAM vortex but there are a few things you glossed over.

First, the dangerous cosmic radiation is really not the heavier *particle* (protons, alpha and dispersed H molecules) type needed for thrust, it isn't contributing and needs to still be deflected as it will go right through most physical shields and injure the cells of the occupants.

Second, as you are achieving relativistic v that EM RAM Scoop becomes an obstacle because the effect also induces resistance as friction (drag).

Third, at relativistic v a tiny micro-meteor particle (whether bollide or even ice) the size of a grain of wheat would be drawn into the ship by such a EM RAM and it would not enter as fuel but as FOD (Foreign Object Damage). In fact it would go through the ship like a high velocity round and put a hole through almost anything in its path.

That is it will go through you or slow you down as it imparts its mass/momentum against the trajectory of the ship by getting stopped by physical shielding. The EM RAM at relativistic velocity is both a partial shield against smaller particles and a hazard by attracting slightly larger particles of iron based material toward the ship without being able to really use them and not being able to really deflect ice at all.

These are more reason I recommend higher initial acceleration rates and then using the force field/shield as a deflector at cruise v because this would reduce the relativistic friction and minimize the threat. Anyway the amount of real benefit from the approach you offer is mitigated against the induced relativistic drag and you can scoop more reaction mass and nuclear fuel in one atmospheric skip of a gas giant than you will encounter on the entire voyage through space to your destination.

The upper atmospheric gasses of the gas giants are routinely bombarded by ambient radiation and there is a higher percentage content per volume for deuterium. It is simply a lot easier to design a craft to refuel the way a firefighting aircraft is able to scoop up lake water in principle and to do so at velocities where the full advantages of the shielding are in place because the velocities while significant are not relativistic.

This approach also takes advantage of Hohmann orbits/Gravity assist slingshot trajectories and best utilizes a stellar polar departure/approach path with respect to the plane of the ecliptic so as to dodge some of the worst regions of the Oort cloud during the initial acceleration to relativistic v.

Gravity Assist

Slingshot Trajectories
http://www.esa.int/e...HD_index_0.html

[Lazarus Long]

(elrond)
However you have to keep in mind that when you are on such a vessel it is the universe you are going to apply these equations too. Not the ship you are standing on.

BTW that was the whole point of applying SR as this statement on your part is not true according to SR.

And finally this actually leads back to the appropriate topic of this thread. [lol]

You see the real issue is the need for a much better theory of gravitation whether it is based on QM, GR, both, or an alternative.

As a larger mass approaches relativistic v basic QM is invoked and Newtonian Principles fail. Is the ship accelerating to c and approaching relativistic conditions becoming equivalent to a subatomic particle compressing itself into a Black Hole as v achieves c and mass/density goes to infinity and time stops?

In other words are we coming up against a back-door to the Schwarzschild Limit describing the event horizon of a Black Hole?

Quasinormal modes of black holes


Quasinormal modes of nearly extreme Reissner-Nordström black holes

The ship's mass is not subject to the same conditions under relativistic v as it is in a rest state. It is like being in a giant particle accelerator and don't forget that just as the observed universe appears to contract, and the on-board time passage appears to dilate both are conditions ALWAYS relative to the other.

But more importantly the fact is that you are putting a great amount of energy into the mass of the ship and may be converting some of that energy into relativistic mass as a result of the inverse of E=mc² and as such this not only supports SR but contributes to the dilemma of increasing resistance to acceleration as inertia would increase v as a consequence of the effect and deceleration has to get then rid of that extra mass somehow when it goes to decelerate, which it would encounter as dramatically greater momentum than you are predicting and accounting for.

The plus side is this may represent a kind of stored potential energy to tap.

The down side is that reaction mass propulsion is not the best way to accomplish this.

We need a very different propulsion model than is currently available. I prefer magnetic displacement but I will go into that elsewhere.

Another reason to resolve the dilemmas surrounding gravity is to tap it directly for the famed anti-gravity drive, which for the sake of memetics and fiction I call a Dark Energy Drive (or a DED motor). [":)] [alien] [pirate]

[eternaltraveler]

am glad you liked my idea of the electromagnetic RAM vortex but there are a few things you glossed over.

My original idea was for a bussard ramjet. Here is an overview: http://www.bbc.co.uk...abaster/A600436

Second, as you are achieving relativistic v that EM RAM Scoop becomes an obstacle because the effect also induces resistance as friction (drag).

This is certainly true. I happen to have no idea at what velocity thrust would be canceled out by drag. I suspect it would be rather high . I suppose it wouldn’t be very hard to calculate if you knew the density of the intergalactic medium. You could account for a lot of the drag by just turning the magnetic field down. It wouldn’t become a problem until the relative density of the intergalactic medium was so high that the ship itself had trouble pushing through it.

One potential problem that has been proposed about the ramjet is that accelerating the interstellar hydrogen to the velocity of the ship would create a huge amount of drag. Most of my assumptions were based on not doing this, but initiating the fusion reaction through lateral compression and controlling the direction of thrust with a magnetic field.

These are more reason I recommend higher initial acceleration rates and then using the force field/shield as a deflector at cruise v because this would reduce the relativistic friction and minimize the threat. Anyway the amount of real benefit from the approach you offer is mitigated against the induced relativistic drag and you can scoop more reaction mass and nuclear fuel in one atmospheric skip of a gas giant than you will encounter on the entire voyage through space to your destination.

That’s true, you could get more fuel out of Jupiter than you could out of a tremendous distance of intergalactic medium. And I would recommend doing just that in order to get yourself to a velocity where a ram would function. However you have to keep in mind that for every gram of fuel you carry that’s more fuel you need to push that extra gram. The figure I came up with for the amount of fuel consumption was truly staggering. 3.4*10^15 metric tons. If you had to carry all the fuel you would need from the beginning this amount would look like a tiny drop in the ocean. The whole planet of Jupiter might not be enough.

As a larger mass approaches relativistic v basic QM is invoked and Newtonian Principles fail. Is the ship accelerating to c and approaching relativistic conditions becoming equivalent to a subatomic particle compressing itself into a Black Hole as v achieves c and mass/density goes to infinity and time stops?

Under SR the ship would not collapse into a black hole. This brings us back to the concept of relativistic mass. Relativistic mass is only applied along the axis of travel. This is why relativistic mass is not a good concept. If you pushed the ship laterally it would still behave like it was at rest mass. Relativistic mass is not a real concept. It really isn’t used anymore. The ship would not collapse into a black hole at any percentage of c. I posted a link and quoted above a reference that went over this, it probably got buried in all my blabberings: http://en.wikipedia....lativistic_mass

[eternaltraveler]

pretty picture I made of a ramjet

Attached Files

•  ramjet.jpg   20.96KB   41 downloads

[armrha]

Test.

[Lazarus Long]

(armrha)
test

What are you testing armrha?

Elrond if you read my posts I also mentioned the critique of relativistic mass and referenced the Wiki site.

I addressed the issue when pointing out the importance of how this introduces QM to the problem and also that there is a possible, if not probable fallacy in treating a *ship* like a nuclear particle in order to avoid invoking SR.

Lastly if you look at your model I suggest you reexamine the characteristics the gauss field we can generate as it will look more like an hour glass than a cylinder and there in lays the difficulty.

Also how does that field interface the transient aspects of the space/time continuum since it is being generated in one relativistic condition but impacting material and energy that is in the other?

It suggests various paradoxes and sets up its own category of problems for the transfer of mass/energy in both directions.

There is also the fact that as relativistic space compacts along the line of trajectory, the amount of ambient hydrogen only increases if the relativistic friction from that phenomenon does as well.

TANSTAAFL (There ain't no such thing as a free lunch)

[armrha]

Sorry, Laz. I was testing posting. For some reason, my powerbook won't let me post anything longer then... one word. In any form. Pretty distressing. Anyways, here is what I meant to post:

Ah... yes, I see now, Laz. I need to stop doubting you.

Elrond, it seems the idea of fusing the hydrogen up to iron would be pretty outstanding. That would release a lot of energy, despite diminishing returns. Considering the amount of machinery needed to fuse each set of hydrogem atoms up the chain from hydrogen->helium->carbon->oxygen- >silicon->iron would be pretty exorbant. How would you capture each stage, too, when the initial release of energy is so great? Fusing a kilogram of hydrogen results in ~2.5e15 joules + 1 4HE. Fusing a kilogram of helium only releases about a tenth of that. How much of the initial yield of the hydrogen to helium fusing would be lost in catching the 4HE and preparing it with 3 other 4HE just to yield 1/10th of the initial reaction? I am just not sure if it would be feasible or worth it to continue to fuse the remnants.

Another method, that might provide even more thrust, could be colliding the hydrogen we scoop up with antihydrogen. A kilogram of antihydrogen annihilating a kilogram of hydrogen would net us 1.8e+17 joules. Even with half of that being dissappated into neutrinos, that's still like ~30 times higher yield then the fusion all the way up to iron, provided we don't waste any energy for diminishing returns.

[Lazarus Long]

Ah... yes, I see now, Laz. I need to stop doubting you.

Well there is no reason to go that far, please. [bl:)] [glasses]

Just remember that when you challenge me to be ready to go the distance and examine the full range of fact and detail required for the analysis and then we can all benefit from the process [lol] )

We are in complicated, dangerous and still relatively uncharted waters with this inquiry. We must be very precise and careful about the assumptions, the details are so profoundly complicated enough on their own.

[eternaltraveler]

the details are so profoundly complicated enough on their own

Indeed they are. This discussion is forcing me to think more deeply about these concepts than I have in the past.

When I first mentioned traveling 2 billion light years in 42 years it was a mere mathmatic curiousity. Now I've been thinking of ways that it actually someday might be possible. Sure these approaches might lead to dead ends. But figuring these things out has helped me workout a part of my brain I haven't used since junior high.

[armrha]

I guess we will want any ramscoops to be retractable. Or at least the front portion of the ship should be morphologic and capable to adjust to the medium as we want. We could open it long enough to gather what we need, and then keep it closed to streamline the vessel to increase efficiency during thrust...

I would like to see some figures out what our potential gauss fields would look like. We can probably work up an optimal shape where we can have the ship aero, erm... balancing both minimizing drag and minimum distance to the fuel-gathering posture. If we can make a few rough estimates about the interstellar medium, the efficiency of our ramscoop design, how much fuel would be needed, how much acceleration would be produced, and the neccessary dimensions of the vessel, we could probably make a simple genetic algorithim for testing some variations in shape to figure out the best shape with the minimum of drag during flight configuration and maximum gathering in fueling configuration combined with a minimum distance between the two states.

[armrha]

I wonder how much of fluid dynamics will be applicable in an interstellar medium. It's not really a gas, of course...

[Lazarus Long]

I wonder how much of fluid dynamics will be applicable in an interstellar medium. It's not really a gas, of course...

True but it is a *plasma* at these velocities and the relationship of issues like magnetic fields interacting from a moving body propagating at C while being generated from that body moving at a significant percentage of C, invokes many of the paradox concerns of SR.

For example it creates a trans-temporal concern as you are basically accelerating the captured gas molecules into the ship by such a capture making them go from a resting mass state to a relativistic mass state that is then acted upon within the ship's drive.

[armrha]

That's true, but wouldn't we want to accelerate them as little as possible? The magnetic field capturing them could really just adjust the vectors of the particles as we pass near them, only accelerating it 'slightly', and then colliding it with a antihydrogen molecule or fusing it in-stream, without having to capture, hold, and accelerate it with us. Is that possible? Otherwise, the drag from the the electromagnetic field generates will be pretty severe, depending on the density of the interstellar medium.

[armrha]

Does anyone have any recent reference material on the possibilities of relativistic flight? Are there any journals that deal in applications of present or foreseeable technology in an interstellar environment? Is there any currently foreseeable material that could withstand the friction of refueling in the upper atmosphere of a gas giant, as Laz suggested? A ship like that is going to need a powerful 'sensory' array, what kinds of tools would it need to observe the environment around it? SR says electromagnetic radiation would still be useful at those speeds, so radar could at least give us a split-nanosecond warning before we ran into something that was stationary. What could the ship do in advent of a collision other then just be destroyed? What kind of protective systems would something like this have? Ablative material probably couldn't accelerate even a tiny chunk of something to the speeds where it wouldn't tear straight through the ship. Unless the ablative component was like what we were using to fuel the ship.

After the hull armor, the radiation shielding would have to be pretty intense for the living portion of the ship. I don't have the calculations handy, but several meters of lead or preferably depleted uranium, impregnated with several inch-thick layers of hydrogen (for the neutrons) ought to be adequate radiation shielding for relativisticly energized gamma rays, alpha particles and beta particles, and neutrons. As long as that radiation shielding wouldn't be exposed to the friction of the outside environment and the stresses the external frame will have to go through, it should hold up fine even at those speeds. The living portion of this ship will probably very small in comparison to where we keep the fuel. There is room for improvement, though.

I suppose the rear will have to be tapered to a point, too, to decrease friction during the decelleration phase. Or, what would be simpler? Should the engine move? If it could just climb up the ship, or detach from the ship, push itself ahead, then turn around and reattach, that might be best. I guess after that point, we can't use the ramscoops, as we'd lose a lot of energy in stopping the particle and then shooting it back the other way.

Edit: Actually, no. You'd want to use the ramscoops, as absorbing their velocity would increase our decelleration. You could gather the hydrogen and direct it right into the turned-about anihillation nozzle and hit it with antihydrogen right there, absorbing the full kinetic energy from the impact in the distribution of energy released and making decelleration slightly easier then acceleration.

[Lazarus Long]

(armrha)
Is there any currently foreseeable material that could withstand the friction of refueling in the upper atmosphere of a gas giant, as Laz suggested?

Plenty as the combinations of ceramics and high temp metal alloys are already sufficient on a skim/skip approach that are the currently achievable velocities rather than relativistic ones. At these velocities a magnetic shielding/RAM combined with physical shielding and ceramics can probably handle the stress and heat. Especially after nanotech improves their coatings as well as the cooling characteristics for this process.

Also a side note. The shielding mix you suggest is valid but does not have to be so thick if layered properly and also the hydrogen is available as water storage from the recycling of what is needed for life support and the extraction of the heavy water (deuterium) from that supply can contribute to fuel, which is stored actively in a layer that is a molecular matrix adapted from the currently developing designs for reduced pressure H2 fuel tanks in cars. Some deuterium is manufactured on-board this way from acting as shielding and sufficient water can be obtained in space from capturing cometary water.

Also active shielding works by converting various wavelengths into alternative usable energy like electricity. We see solar cells acting this way and as we are beginning to understand nanocoatings better for stealth they too can be utilized this way by not merely absorbing radiation but converting the photons to usable forms of energy.

But IMHO generally the best way to cope with the impact concern at relativistic v for early programs is to avoid it. Create a deflective shielding model and choose a route through space that is more vacuous. No need to play Titanic.

[Infernity]

http://en.wikipedia....wiki/White_hole

I saw some weird prog on The History Channel about white holes, the Burmuda Triangle and the relation it has to the Dragon Triangle that lies exactly on the other sode of the earth and has many similar phenomenon occuring there...

Couldn't find much info about it on the net yet, does anyone know something of it.

I guess my theory of white holes wasn't too far from the truth.. ?

-Inf.