New Mars Forums

The 0 energy trajectories are neat but the energy savings to Mars aren't overwhelming - you still have to get to Moon L1 before you can use one.  Plus it's probably too slow for human transfer.  Nonetheless, it's a very good way to increase cargo mission performance and unlike standard orbits, hasn't been worked out in detail yet.

If I get a chance, (unlikely for a few months) I'll try to write up an orbit simulator that would let one play around with various delta Vs.

OK, tons of stuff to reply to...

Rxke: Interesting idea but it would require going dangerously low into the upper atmosphere.  Perhaps you could lower the refrigerator down on a tether but you'd still have a lot of problems with drag even then.  I'll keep the idea in mind, though.

Gennaro - The Mars to LEO SSTO isn't a BAD idea, just not a terribly optimal one.  Another disadvantage of a combined SSTO/interplanetary freighter is that you tie up your SSTO for long periods of time.  One of the advantages of an SSTO is that it's got a short turnaround time.  If your SSTO then spends 5 months puttering off to Earth, you lose that advantage.  Also, SSTOs inherently tend to be small in terms of cargo load.  Because of Mars' smaller gravity well, it might be realistic to expect 20 MT to orbit for an SSTO.  If you want to move decent amounts of cargo from here to Mars, you have to have seperate vehicles.
For example, let's say that we want to move a couple of heavy earth movers(bulldozers, etc), a bunch of H2 stock, a few km^2 of clear plastic sheeting and a polymer production plant to Mars totalling 100 MT.  In return, the Martian colony has a deuterium isolation facility and is going to send 10 MT of the stuff back to Earth(worth about $1 million at present prices), 5 MT of Mars rocks and other samples.  The SSTO can realistically carry, maybe 5 MT back to the surface of MArs with each trip (SSTOs are already riding a fine line to get themselves back down as it is) so the whole process would either take 50 trips or a huge fleet of vehicles.
In contrast, as long as you can accept slow travel, high Isp engines and 0-energy pathways can be used for a freighter to carry all 100 MT of cargo to Mars, pick up the return material and head home.  A couple SSTOs operating on a 1 week turnaround could bring down most of the cargo (except the 2-25 MT earth movers) in about 5 weeks.  The earth movers can be equipped with their own reentry systems.
This analysis doesn't even include the fact that a hybrid SSTO/freighter with two completely seperate engine systems would have much lower performance.  The freighter wom't be availabe for maintainance but it's never under very much stress and therefore can operte for long periods without being worked on.  The Mars SSTOs can be serviced once a week if necessary, not once every 6 months like a hybrid vehicle.

Gennaro/GCNRevenger - the GCNR is a cool idea and I like it as well.  However, it stands that we've never built an operational one and still don't really know how.  Our continuing problems with controlled fusion show that our grasp of high density plasma physics leaves much to be desired.  Many of the problems in GCNR are the same as with fusion.  Until we've got the latter licked, I'm not going to bet the farm on GCNR.

GCNRevenger - I don't think tha NWSR is even worth thinking about in getting to Mars - it's just too dangerous.  It depends on a very carefully controlled rate of flow of the fissible salts through the reaction chamber.  If the rate of flow drops, the critical reaction area moves up into the engine and basically detonates a tactical nuclear warhead there.  If anything caused the fuel flow rate to drop, the engine will blow up.  It's not even clear how one of these things could be safely started or stopped.  Furthermore, if the engine explodes, those fragile boron nitride neutron absorber baffles are going to get shattered - the entire fuel supply could go up in a multi-megaton fireball. 
  That doesn't even begin to deal with the political implications of throwing around huge quantities of radionucleotides out the back of the engine as it runs.  Sure, they might be aimed away from Earth and at greater than solar escape velocity but do you really think that the public and by proxy, the government will let this fly?  I seriously doubt it.
NSWR is a great idea for the exploration of the outer solar system or the nearby stars.  I think its a great idea as long as we don't put people on it or fire it up anywhere within lunar orbit.

I do agree with you on the shortcomings of ETP.  I also just noticed that there might be limitations on the total thrust, regardless of the power available due to limitations in the free electron availability in LEO.  However, a thrust of 10-20 N is entirely possible and realistic.  The power supply only need supply an average power flux of about 1 kW/N thrust.  Since you would have to operate in a perigree thrust/apogee raising mode, the actual constant power supply can be much lower.  Existing solar power systems for high altitude balloons already exist that would make the system work quite well with low mass.  We'll be able to say how well the system works soon.  The ProSEDS mission got delayed because of Columbia but is scheduled to go up soon.  Check out [http://www.tethers.com]www.tethers.com - they're the contractor for that mission.  They're enamored with rotovators ??? but also have a cool product called a terminator tether for deorbiting LEO satellites that they are already offering commercially. 
Of course, ETP is for slow cargo - the thrust is on the same order as an ion engine.  However, for things like heavy equipment, the ability to get a 1.0 mass ratio from LEO to LMO is worth pursuing.

dicktice - kinetic momentum tethers are cool but have limitations.  For one, you've got to catch your payload - this a is a non-trivial problem.  Also, you're limited to stuff of maybe 5 MT, tops.  Beyond that, the counterweight just gets too heavy and the stresses on the tether too high.  To boost a 140 MT Mars mission to Mars with one of these tethers, your counterweight has to weigh 700 metric tons!  Ther e is no way to get this kind of mass to orbit other than 5 heavy lift booster launches and in-orbit assembly.  It would be a much better use of money to just send 5 missions to Mars with that money.  Rotovators do have quite a bit of promise for small sattelites but that's about it.

Oi, I don't even want to think of the effects of the tidal forces on the Earth if Venus were in close orbit with us.  Keep in mind that the oceans of Europa are liquid and Io is basically one big volcano of molten rock because of the tidal forces that come from Jupiter.

I suppose that reflective balloons around Venus would help but it would take a looooooong time to bring the temperature down.  The Venutian atmosphere is basicallt a big blanket that holds onto IR radiation like its going out of style.  The only way to really get it to become stably cool would be for plate tectonics and large quantities of water to be reintroduced.

I'm really suprised tha the SOHO website doesn'ttalk about the near-death experiences it's had.  That satellite's been declared dead at least twice that I can remember.  It's a true testament to the engineers at NASA that it's still operational - it's YEARS past its operational design and a whole slew of 'critical' subsystems broke down years ago.  I'd argue it's the single most impressive peice of remote engineeringthat NASA has ever accomplished.

??? Uhhh.. why did I post duplicate messages earlier?  Did the board hiccup or something?

I think the whole idea of a biological ecosystem working in concert like a single organism in some ways if fairly well accepted in spirit if not in letter.  BTW, Lynn Margulis co-wrote a book a few years back called Five Kingdoms which I own and is quite good.  It basically spends a page or two on each pylum of life - there are hundreds.  The best part is that out of over 400 pages, 4 are devoted to the phylum craniata (chordates including everything from apmphibians up to us).  Almost all of the book is filled with single celled organisms, including some truly bizzare ones. 

A favorite are the Archaeprotista - giant protozoa with no mitochondria and hosts of symbiotic bacteria living inside of them.  It's not clear if the symbiosis is something recently evolved or if these are living fossils of the original proto-eukaryotes.  These are the organisms that digest wood in termite guts amongst other things.  One genus is large enough to see with the naked eye (~200 microns long)!

GCNR, I agree with most of what you said earlier.  Sails, ion engines, rototethers, and solar thermal are all non-starters as far as I'm concerned. 

I think that ETP has potential - the mass of the tether for ETP is trivial as it has to carry very little force as opposed to a rototether.  Getting enough power to run the thing at any appreciable speed is difficult, however.  If there were a way to run a 5 MW nuclear reactor in Earth orbit, you could boost a 140 ton Mars mission to TMI in about 1.5 months IIRC.  The weight involved with ETP would require that it operate in an Earth tug configuration.  There's no reason to take it along as it's not going to work at Mars with no magnetic field there anyways.  While it is a bit slow and requires a seperate drive tech, it has an infinite ISP for all practical concerns, which is nothing to sneeze at.

NTP gives some benefit, basically cutting the fuel fraction of a Mars Direct mission by about 2/3. 

GCNR is promising but the technical concerns of getting it running reliably might put it out of the timeframe of initially getting to mars.  30 - 40 years down the road, it does have the potential to cut fuel fractions to almost nothing.

Orion/NSWR - I think that the probability of anyone letting you fire either of these drives off in LEO can be nicely approximated as 0.

I'm dubious about a Mars to LEO SSTO.  Too many design conflicts between a good SSTO and good interplanetary freighter.  The Martian SSTO would probably use either CH4/O2 or NTR for takeoff and has to be able to withstand aerodynamic forces.  The LEO to LMO freighter probaly uses ion engines (for freight) or something equivalent and has all sorts of big radiators and other ungainly stuff hanging off it.

It just doesn't make much sense to have a heavy, aerodynamic vehicle go interplanetary.  I think that a custom built Mars SSTO could ferry stuff up to LMO where it can be loaded up by a dedicated interplanetary freighter that cycles back and forth.  You'll get much better performance out of both.

Also, we should look at these new 0-energy transit orbits.  I've ben reading a little more about them and it appears that you can use them to go from any L point to any other L point in the solar system for pretty much no delta V.  I think that initially getting to a particular L point from a planetary surface has to be done the old fashioned way but going back down to the planetary surface can be done with a 0 energy trajectory.  Check out the NASA Genesis experiment for an example of such a trajectory.  The example Earth to Mars trajectory actually looks fairly straightforward.  If we use this scheme, it looks as if the only delta V we have to provide is LEO to moon L1.  If we're able to use something like an ETP tug, LEO to Mars surface can be done for essentially free.  140 tons to LEO becomes 140 tons to Mars surface.

True, although one has to wonder about what the definition of a singularity is.  An electron has 0 radius and a finite mass which would seem to imply that it should be a singularity itself. I suspect that we'll have to have a fully developed theory of quantum gravity first before little problems like that are resolved.

High energy cosmic rays (~10^20 eV) have momentums measured in Joules which should have an additional apparent mass of something like 10^10 AMU. When packed into an object as small or smaller than an atomic nucleus it should be well past the point of collapsing into a singularity.  AFAIK, the particle fallout from those high energy collisions don't exhibit behavior consistent with black holes.  Therefore, I'm fairly sure that the apparent mass is incapable of collapsing into a singularity.  However, so few of those high energy events have been observed that it's difficult to say for certain.

I think that you're going to have to be a bit more specific about what you want if people are going to help you.  What's the paper about?  What sort of paper is it? (high school/college)  What sort of information are you looking for?

Once we know that, we can help you.

CM, are you sure those equations are correct?  I believe that the standard convention is for m to equal the rest mass and M to equal relativistic mass.  Therefore your equation should be E=SQRT(((M*a)^2*c^4)+(p^2*c^2)).  Just to make sure we're on the same wavelength, these are the equations and variables that I'm using:

E=Mc^2
Where M is the relativistic or apparent mass.

E=SQRT((m^2*c^4)+(p^2*c^2))
Where m = the invariant or rest mass.

The relativistic correction term you mention (a=SQRT(1-v^2/c^2) is the conversion term between M and m.  eg: M = m/a

I double checked these equations in both the Usenet Physics FAQ and Wikipedia.  If they're in error, please let me know - my physics textboks are in storage so I can't refer to them right now.

According to my memory and the online references I've looked at, this is the relationship between M and m.

m is the rest/invariant mass and is what modern physics refers to when they say mass.  It's used in the equation E=SQRT((m^2*c^4)+(p^2*c^2)).  In this case, m represents the actual physical mass of a particle or the total energy of the particle after kinetic energy is removed.  For example, if you combine an electron and positron, the energy released is equivalent to the rest masses of the two particles.  The SQRT(m^2*c^4) is basically the rest mass of the particle and the SQRT(p^2*c^2) is the kinetic energy portion.

M is the relativistic/apparent mass and is an antiquated term.  However, it is what most physicists refer to as mass when writing popular science texts like The Brief History of Time.  This no doubt is the source of much of the confusion related to layperson comprehension of relativity.  For M, E = Mc^2.  In this case, M represents the total energy of the system, including the kinetic energy.  Basically, M = E.  The whole E=Mc^2 is just a unit conversion equation that really translates to E=E or M=M.  M=E is why relativistic/apparent mass isn't used anymore since it's just another term for energy.

For a photon, m = zero since the physical photon has no actual, physical mass.  However, M is non-zero.  For a photon, M is the kinetic energy or momentum of the particle.  Basically, whether a photon has mass depends on how you define mass.  The actual photon doesn't have mass but its kinetic energy does - sort of.  If you ask a physicist if the kinetic energy has mass, s/he will say no since mass is defined as m.  However, the kinetic energy term which is all that's left in M can still convey momentum and is capable of bending spacetime just like regular old mass does. 

So, it really depends on how you define mass.  If you define it as the physical mass of particle, then mass = m and a photon has no mass.  If you define mass as the ability to impart momentum and bend spacetime, mass = M and photons do have mass.  Personally, I prefer the latter definition just because its easier to wrap my mind around but the overwhelming majority of physicists and textbooks will go with the former.  It's purely a semantic argument, really.  You just have to be careful about which 'mass' you are talking about.

Here's an example:

If you accelerate a particle to nearly the speed of light, does it collapse into a black hole?

No, as you approach the speed of light, M goes to infinity but m remains the same.  m is the actual mass of the particle and it stays the same therefore the particle itself doesn't collapse since it hasn't gotten more massive.  However, the kinetic energy term which is included in M goes to infinity and does gain gravitational energy, at least in theory - I doubt that this effect is measurable with modern instruments, even with high energy cosmic rays.  However, the kinetic energy is not a physical object and therefore can't collapse into a black hole.

I believe that planktonic capture of CO2 in the eventual form of limestone is one of the major carbon sinks on our planet.  Regular old temperate forests can also act as a carbon sink.  This is especially true if you don't allow the wood to rot.  If wood is used as building supplies, the carbon is tied up out of the atmosphere.  (this is not to say that we should start cutting down trees and burying paper in landfills to fight global warming but it *would* help)

The Gaia theory is neat but pretty much no one, not even its creators believe in it anymore.  It's pretty clear that life doesn't modify its environment to suit it unless by chance.  The history of life on this planet is a lot like our own - lurching from one near disaster to another by luck as much as anything else.

For example, plants nearly wiped life on this planet out twice.  The first was when they started making oxygen, converting our atmosphere from a reducing to oxidizing environment and just about killing everything inthe process.  (the original toxic waste dumpers)  The second was when plants developed cellulose which other organisms coudln't break down.  As a result, gigatons of carbon were locked up in dead plants and not recycled to the atmosphere.  There is some tenuous evidence that the Earth actually went into a massive ice age for several million years where the oceans froze to a depth of a mile and the planet did its best Mars impression.  Life would have been largely wiped out had it not been for tectonic activity causing volcanos to start bringing the CO2 levels back up.  Eventually, microbes developed the ability to break down cellulose but an enormous amount of carbon was lost in the meantime.  It's believed that most of our hydrocarbon deposits are the result of that episode and that we're now reintroducing 'missing' carbon that fell out of the biosphere 500 million years ago.

Huzzah, just like Origin, Looking Glass and a bunch of other great studios that made games I loved at one point, Maxis is yet another casualty of EA and it's moronic business practices.  I swear, running good game companies into the ground must be part of their corporate motto..