New Mars Forums

Dear God I hope Drexleresque nanotech isn't required, because we aren't having that... ever.  I would put good money on current and future impossibility of machine-phase matter or any other such nonsense.  Drexler is a smart guy, no doubt, but he doesn't know ^#(@ about chemistry.

I wouldn't worry to much about lighting strikes though.  The conductivity of the cable is not necessarily a nano scale phenominon, at least not when you are comparing the macro-cable to macro-lighting.  Proper-construction could insure that the cable was non-conductive to lightining strikes.  Ancoring the cable in a calm area and a system of lighting rods could also help.

As for mono-atomic oxygen I wouldn't worry to much about the corrosive effect.  It's very sparse and so could not eataway at the cable to quickly in any event.

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I think it's important to point out that the Macro-scopic cable can (and should) have very diffrent properties then a Microscopic nanotube.  The cable can encoporate diffrent materials into it's structure and can utilise diffrent typse of nanotubes to achive diffrent effects along it's length and cumutivly.

I suppose it depends upon what you mean by manuvering.  If you mean simply changing the orientation of the vessle such as what the shuttles Reaction Control System (RCS) do, then no ion engines are probably not the best choice.  Changing the facing and attitude of a spacecraft, even a large one such as an Orion takes a very small Delta V,  <1m/s.  Which is insignifigant when compared to the total Delta-V requirment of most space-mission ESPECIALY those that an Orion type vessle would undertake.  Thus other qualities of the engine become more important than it's ISP.  Specificly it's specific power or thrust/weight ratio and the specific power of it's fuel.  Chemical engines far out-perform ion engines in these respects, and that is why it is what all (to my knowledge) satilites and spacecraft have used them.  Although some satilites requirments for this sort of manuvering are so low that it can be handled entirely with gyroscopes.  Perhace an ion RCS would make sense on a VERY large spacestation of some sort,.  They could be used to help spin it up and what not which could take a fair amount of energy as well as more conventional manuvers, be we are talking 2001 Space-Oddessy sized staions here.  You would want to rock such a boat to fast either.

For minor (and not so minor) corrections in orbit inclination and what not, ion engines are a good choice, although probably not for a vessle the size of Orion.  These sorts of manuvers (which are handled by the space shuttles OMS) take considerably more delta-V.  Generaly >1m/s on up to escape velocity for the planet.  Most Orion type vessles are so large that it is probably worthwhile to fire off a couple nukes to achive any major changes in it's orbit.  Other more minor changes probably should be made as it is probably more worthwhile to bring any smaller objects to it rather than the other way around.  Also even with the larger Delta-V requirments of these manuverse most satilites still don't do enough of them for an ion engine to make any sense.

But for a satilites/probe that has to make alot of manuvers (such as one exploring some of the outer-system) or for a tug (which likewise has to make lots of orbit adjustments.  An ion engine is a good choice.  The only place I could see an Orion using one would be if you had an ion-tug drag the vessle away from the planet before firing up it's engines due to enviromental concurnes.

Well I'm not quite so pesimistic.  I think a one-man one-way mission is quite possible.  Although if you want the person to stay their indefiently so resupply is going to be needed.  It's not just a matter of chemical degredation (although that is a part) it's a matter of mechanical failure.  The moving parts on your fan's/pumps and what not will eventualy fail.  It's no so much a matter of if, it's a matter of when.  The rest of the components likewise have limited lifetimes, the Rovers, your powersource, tankage, whatever.  They can be made tough, but they can't be made unbreakable.

So some resupply is going to be necessary.  You would want some anyways just incase some no-predictable accident happened, such as a pressure loss in your Greenhouse, killing all your plants, or whatever.

But I think the more important question is why?  That one person would probably have to spend the vast majority of his time doing maintance and what not necessary to his survival.  He would have little time to do any science.  Also the sanity of anyone who wants to sign up for such a suicide mission must be called into question.  Suicide is not a sane/logical course of action, and we definetly want our first man on mars to be both sane and logical.

Cyclic ozone shows alot of promise, but it's still quite aways out.  I do remember reading a paper that that detecting the presences fo cyclic ozone, proving that the theoritcal molecule may indeed be possible.  But we are still along way from producing it ourselves, much less on the scale necessary to put a rocket in orbit.  Which, I might add, are to very diffrent things.

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My favorite idea for a TSTO concept is to have the carrier plane to be similar to the shuttle external tank.  That is, the vehicles main rocket engines are actualy placed on the second stage, with the primary stage serving primarily as a large fuel tank.  Operation would be something like this:

#1.  TSTO craft takes off underpower from the main stages air-breathing turbojet engines.  If practicle these might be fuled by liquid hydrogen to eliminate the need for tankage for more conventional jet fuel.  It then accelerates and rises to the out edge of their envelope.
#2.  At this point the secound stage's rocket engines take over, with their fuel provided primarily the large tanks on the first stage.
#3.  At the appropriet time at the edge of space the two stages seperate, with the first stage returning to earth to make an un-manned powered landing with it's conventional engines, and the second stage continuing untill it reaches escape velocity, powered by it's rocket engines and fueld from it's own (smaller) tank.

This scheme alows a TSTO to orbit craft to get most of the benifits of staging without having to carry along extra engines.  Unfortunatly it subjects the first stage to hypersonic flight and possibly a mild re-entery.  And it doesn't necessarily make the turn-around time any better.

Hmm... alot of points to respond to her.

#1.  Alternitive law of electromagnetisim (Dook)
What you propose might be intresting, but all expermintal evidence points to electromagnetic wavelengths existing along a spectrum (a line) not a circle.  Wavelengths increase with a limit at positive infinity, and decrease with a limit at zero.  In any case even if it was not so, it's not mathmaticaly possible to progress from beyond positive infinity back around to zero or negative infinity.  And again there is no conclusive evidence of negative energy even existing.

#2.  Gravity waves (Dook)
Indeed we should be able to detect the Gravitational "waves" produced by massive objects, or objects traveling at very high speeds.  Their presences has been proven  indirectly at least, by measurment the orbits of binary pulsars and the like.  The problem here is that Gravity is such a weak force it takes extreamly massive/fast moving objects to create effects that are detectible, and thankfully such objects are far from our Earth.  So far all direct attempts at detecting it have been failures.  It is currently an open question as to the speed at which these "waves" propigate from their source, but most reaserach points to their speed being very close if not equal to C.  Even if they did travel FTL, utilising them would be difficult given the massive energies necessary in creating detectible waves at great distances.  Of course this is the part of GR that is in most conflict with Quantum mechanics and research is still progressing.

#3.  Zero Point Energy
The concept of zero point energy arrises from the uncertian principle.  If we accuratly measure the energy inside a volume to be zero, then the uncertianty in it's position must be infinite, placing it outside the box.  To avoid this paradox quantum mechanics dictaes that this energy must be greater than zero, hence zero point energy.  This energy is NOT negative as that would create a whole new paradox.  There is some slim hope that energy may be extracted from this phenominon, but I wouldn't hold my breath.  Likely it will take as much or more energy to extract the energy as you get.  Local imbalances in this force may be the cause of some effects such as the Casmir effects.

#4.  Virtual Particles
Virtual particles are temporary stages in the interaction of elementry particles.  They generaly can be thought of as a means of transmiting the information of these interactions.  Quantum Mechanics predicts a field of these anti-particles swarming across our universe.  In order to perserve the baryon number these particles always come in particle anti-particle pairs.  In some cases these two particles can be seperated and become "real" however this always requires the expenditue of at least an equal amount of energy.  And again the imbalances in this force may be the cause of some effects such as the Casmir effects.

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It's very important to note that all of this stuff is on the forfront of Quantum and Theoritcal physics, and our models and understanding of it may change.  However there are quite a few things that probably will NOT change. 
No FTL travel.  Special Realitivity has gobs of experimental evidence backing it up and so it's postiulates are not likely to fall.  The nature of the grandfather paradox's this creates isn't likely to go away either.
Concervation of Energy.  Another concept with even more backing behind it.  We are not likely to get energy from nothing (or from ZPE or Virtual Particles or anything else).  The laws of thermodynamics are pretty solid.

That said, work in Quantum, Theoritcal, and even String Physics may shake things up alot on the sub-atomic scale.  General Realtivity may even be disproven or replaced in a general sense.  But I agree with most respected physicits and doubt there will be any major shake ups to the above two vital principles.

To be honest I'm not sure I'm completely understanding all that you are trying to say but I'll reply to the points I understand.

#1.  Causality not necessary.
I don't know how you can claim this, causality, the principle that things happen in response to things that cause them is absolutly vital to a logial understanding of the universe.  Causality is litteraly the undminning of not just science and physics, but logic in general going all the way back to Aristotal.  I'm not sure how you could have a any sort of ration system without it.  I mean how can you analyse a universe in which the effects (the things that you measure) actualy create the cause.  A universe in which the future creates the past?  In any case it certianly does not match our emperical understanding of the universe.

#2.  Casmir effect is negative energy.
Many people are confused by this, but it simply is not true.  The Casimir effect is caused by presure diferentual of the virtual particle-anti-particle pairs bettwen two plates.  The plates restrict the wavelengths of the virtual particles inbettwen them, allowing greater amounts of energy to be built up on the outside.  This creats a pressure imbalance which creates the attractive force.  Some have called this "negative energy" but it is not so.

I've read the paper before, and while it's a nice thought experiment, it doesn't change the cold hard facts of the real world.

#1.  Information CANNOT be transmited FTL.  Why?  Because if it also causes some information to be transmited backwards in time to some observers, causing causality violations.  Note that these observers are not necessarily limited to those actualy traveling FTL.  Warp bubbles and what not cannot overcome this effect because it is an effect of the universe at large, not just some subset with a "bubble."  Put bluntly any FTL travel causes the possibility for someobservers to recive a message before it was actualy sent.  And I don't know about you, but in my universe CAUSE must always precced EFFECT.  See my previous post for a worked out example.

#2.  A warp drive must invoke "exotic matter" and "negative energy" in order to work.  There is just one problem.  These things do not exist.  There is no theoretical support for their existance and absolutly no experimental or emperical evidence of their existance.  Part of the problem here is applying mathmatical concepts to our real world.  Once must remember that while math provides a great modle for our universe it is NOT our universe.  Mathmatical constructs such as imaginary numbers, negative numbers, irrational numbers and so on simply do not exist in the physical universe where in the end everything must be finaly measured and counted somewhere.  You can't give me -1 apples, and you find me a string sqrt(-1) inches long.

#3. Even if for some reason such a device was possible, the energy necessary to construct it would be huge!  I have seen some estimations indicating it would need 10 times as much energy as present in the entire universe.  So not only is the warp drive impossible it's inpracticle as well.

I realy don't know why I am bothering to reply to this junk anyways, I should just ignore you and turn my attention to serious discusions about Mars.

Not supprisingly we have discussed this before to.  The disscusion was here.

Even if we do some handwaving and create things such as "exotic matter" and "negative energy" it still does not overcome the fundemental problem with FTL in our relativistic universe, the problem of causality violation and pardox.

All FTL methods of communicaton/travel can cause the grandfather paradox when the situation is right.

An exert describing how and why.

"We can describe this effect by idealizing FTL to be "instantaneous", and describing how the more familar time dilation implies this effect. But remember, the same points apply to any FTL speed, you just have more messy arithmetic to grind through.

Consider a duel with tachyon pistols. Two duelists, A and B, are to stand back to back, then start out at 0.866 lightspeed for 8 seconds, turn, and fire. Tachyon pistol rounds move so fast, they are instantaneous for all practical purposes.

So, the duelists both set out --- at 0.866 lightspeed each relative to the other, so that the time dilation factor is 2 between them. Duelist A counts off 8 lightseconds, turns, and fires. Now, according to A (since in relativity all inertial frames are equally valid) B's the one who's moving, so B's clock is ticking at half-speed. Thus, the tachyon round hits B in the back as B's clock ticks 4 seconds.

Now B (according to relativity) has every right to consider A as moving, and thus, A is the one with the slowed clock. So, as B is hit in the back at tick 4, in outrage at A's firing before 8 seconds are up, B manages to turn and fire before being overcome by his fatal wound. And since in B's frame of reference it's A's clock that ticks slow, B's round hits A, striking A dead instantly, at A's second tick; a full six seconds before A fired the original round. A classic grandfather paradox.

Note, this is NOT a matter of when light gets to an observer, it is NOT an optical illusion. It is due to the fact that, in SR, the question of what occurs at the "same time as" something else is observer dependent.

As A fired that first shot at tick 8, the bullet effectively teleported from A's gun to B's back instantly --- instantly according to A. But for B, who was moving at 0.866 lightspeed WRT A, B was hit in the back by the bullet 4 seconds BEFORE the bullet was fired. And again note, this is NOT due to the optical illusion of lightspeed delay in viewing A's turn-and-shoot; the light form that event wouldn't reach B until MUCH later, not tick 4."

As you can see the problems with causality and simultaneity at a distance don't specificly lie with the FTL travel, but the rest of the universe. Any FTL situation could cause a grandfather paradox similar to the one above.

I should first apologise, I didn't read this forum as throughly as I should have, or I would have seen that some of my suggestions had already been listed.  I still think the images help provide a vivid visual example of what might be involved (even if the astronaut is a wolf).

While I agree with the utility of a secondary, more traditional airlock.  The ability to do away with it could save vital space and mass.  While this would be nice for the Hab, it could prove even more vital for a Rover.  The rover is very constrained in tems of the mass and space it has avaliable, much more so than the Hab is.  The is also limited in the amount of  power it can provide to it's equipment.  High powered vacume pumps and air-filters might not be possible.  Some designs forgo an airlock entirely and simply depressurise the entire Rover, venting the air into space.  Indeed space may be so tight on the Rover that the simple ability to store the suite outside may be of some benifit.

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I like the doggy door concept, but it strikes me as less than foolproof, and an airlock has to be foolproof.  It might be acceptable on the Rover where loss of cabin pressure isn't necessarily a total disaster.

There's no need to throw around personal insults, they are not conductive to good debate.

Again the main issue with you proposition is the issue of specific power.  Nuclear reactors offer excelent specific power.  Much better than any solar option and competitive with most chemical sources of energy, but of course far superior when you consider the lifetime of a nuclear source.  However, they still fall short of what is required to power a energy hungry VASIMR engine.  They simply mass to much.  The specific power, or the amount of energy per unit of mass is CRITICAL to the performance of any space reactor.  You haven't given any details as to how this reactor performs in this crucial catagory, and I am hard pressed to belive that this liquid sodium cooled reactor could achive performance radicaly diffrent than that of any others.

The other issue I'm not sure if you are clear on is the issue of cooling.  As I'm sure you know there are only three ways to transfer heat, Conduction, Convection, and Radiation.  Terrestrial reactors rely primarily upon conduction and convection to disipate there heat.  This is because the Earth is full of matter with high specific heats.  Terrestrial reactors are litteraly swimming in it.  So it is fairly easy to dump the heat off to the enviroment, even if the temperature gradiate is not as great.  Space on the otherhand is as vacuum, so there is nothing to dump the heat off in.  Space, despite it's often very cold temperature is a very effective insulator.  The only way to lose the heat is to radiate it away.  The number of coolent loops betwen the reactor and any turbine doesn't change this fact.

Again.  What matters here is MASS.  How much the reactor weighs.  As far as I know no reactor to date, be it cooled by water, heavy water, sodium, or even CO2 achives quite the specific power necessary to make a realy outstanding VASMIR type system possible.  Some sort of next generation system, be it fusion, GCNR, or perhapce lead cooled reactor will be necessary.

You leave out one of the most CRUCIAL issues for any space reactor it's Mass.  I'm not sure what figures you have been looking at, but a brief Googling of the subject led me to a Los Almos paper about a reactor similar to the one you are discussing.  It produces 50-MW electric but masses 250 Metric tons.  This gives a power to weight ratio of 200W/Kg.  Good, but hardly spectacular, and there was no indication that this reactor was desigend for space use, with the heavy and bulky radiators necessary.  I'm curious as to what figures you are looking at that make you so happy.

Another issue is the use of MHD as a means of power conversion.  MagnetoHydroDynamics is still in it infancy and typicaly has a much lower efficency typicaly only 10-20%, much lower than that of a turbine.  However a MHD system may weigh less then a turbine, making it more attractive for a space based system.

Despite it's cold temperature, the rarified atmosphere probably acts as fairly effective  insulation.  So heat dispation may be a \n issue for a green house/hot house.