# Humans Not Meant for Space



## Arwena (Jul 16, 2009)

Interference suggested a new thread on this question. It came from a thought on Monday's 40th anniversary of the moon landing. Many thought then that a new human era had begun, but we haven't made any progress. In fact, no human being has traveled beyond low earth orbit since 1972. Some have suggested that human beings simply are not "equipped" for travel beyond their home planet. They after all have to take their (rather delicate) home environment with them. Without the protection of a thick atmosphere, they'd be subject to lethal radiation. Psychologically, they would be separated from a social environment and would eventually go mad. (of course, we occasionally go mad here.) I would hope that this is not true, and that someday, further in the future than we'd hope, we will boldly go where no one has gone before. Maybe part of the problem is that space travel presents more difficulties than we imagined, that there are no destinations in our immediate area of space (the solar system) that are desirable or would justify the huge expense involved. Interstellar travel presents challenges that we have yet no idea of how to overcome. At any rate, Whenever it is said (by those anonymous people who say such things) that something is impossible, I tend to be skeptical of"impossibility"


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## Interference (Jul 16, 2009)

Personally, my view as things stand is that we're going to need to leave the planet quite soon. In favour of this proposition are the destruction of human-life-supporting conditions and the rise in population.

Against is our human frailty, in all its guises.

Whether all of us (or the extant population at the time) or only an elite few will be involved is worthy of some attention, and Asimov has done this, I think, quite well.  So a partial answer to this is certainly "some humans are meant for space travel, others have to tend the farm".

But perhaps even more excitingly is the question of what form space travel will have to take in order for us to embark on it.  Star Gates may be best option, given distances and all the dangers inherent therein.  But how likely are Star Gates?  Will it necessitate planting a receiver on one planet at a time?  Probably, but then advance terraforming would also be a necessity, surely, if we are to colonise that planet eventually.

Suddenly the question is getting to be quite vast.

Ideally, we should all be allowed to visit other worlds, not just a few elite militarists.  How achievable is that?  If we weren't dependent on the mechanics of space flight, we might all stand a better chance, but now we're getting into the territory of psychic projection and Remote Viewing, which is (probably) safer and allows the traveller to explore worlds which are completely hostile to physical human life.  Now, perhaps, the question becomes "can we equip ourselves as individuals for space exploration".

Exploration is in our natures, I think, though quite how this anthropological defect sits so well alongside our nesting instincts I'm not entirely sure, so one day we will get there, I'm sure.  It will be interesting for those of us still around at the time what method is employed in the end to make it comfortable and convenient for us, like the jet brought opposite sides of the world together.


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## chrispenycate (Jul 16, 2009)

Humans are not "made" for polar exploration or high mountains, either. Or living in close proximity in cities. We have a tradition of modifying the environment to suit us, rather than adapting to it. This has generally involved technology, our speciality as a species.

 Certainly, this has caused problems in the past, and doubtless will do so in the future, but it renders irrelevant what we evolved for, specifically.


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## Pyan (Jul 17, 2009)

Humans aren't meant to live in Los Angeles, or any other major city, if it comes to that - they'd die of thirst if the water system packed up...

As Chris says, the thing about our species is that, uniquely, it adapts the eviroment it lives in, and not _vice versa_. Space will be no exception.


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## Nik (Jul 17, 2009)

Well, if you consider our kin can endure life as hunter-gatherers in the Outback, on the tundra, in rain-forests crawling with nasties, in cities crawling with nasties etc etc.

Pole to pole, apex to trench, albeit with lots of tech, plus that 10% death-zone on Everest...

Ocean crossing was hard, what with storms and scurvy.

Um, IIRC, one factor that frightened US politicians about 'extended Apollo' was the solar flare / CME that missed toasting a crew by a few days. #13 got lucky. A crew puking with radiation sickness might not have endured. 

As for accidents-- Apollo 1, the pad-fire, set the project back a year, but probably saved it. The Shuttle's lessons don't seem to have been learned by NASA beyond 'run away', which is why the 'Plan B' team may get the franchise.

FWIW, all the expendable launch folk will be looking over their shoulders at Alan Bond's Sabre engined Skylon. That would reduce NASA to 'heavy lift' supplier until a four-engined S2 comes along. After that, NASA are infrastructure, museum and theme-park...

IIRC, opening the solar system needs nuclear power. Treaty prohibitions on fission reactors probably mean we're waiting on fusion. At the rate ITER etc are going, the polywell approach may arrive sooner and safer...

But, where a fission reactor relies on lots of dumb mass for shielding, a fusion reactor uses magnetic and electrical fields. IIRC, there's enough circulating power in either ITER or polywell that 'bending' the charged solar wind flux comes easy. That still leaves neutrals and photons, but a fusion-powered rocket has a much more generous mass budget...

As regards bone loss etc, there have been some developments that *may* lead to pharmaceutical prevention.

Sure, we're not 'meant' for space. We'll go anyway. Besides, we gotta be off-world when the next Toba blows...


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## Xelebes (Jul 17, 2009)

To prevent bone loss, you only need sufficiently wide and rotating craft to simulate Earth's gravity.


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## Nik (Jul 17, 2009)

Wow ! I wonder if Circus-Circus will grab the Lunar & Martian franchises !!


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## Parson (Jul 17, 2009)

Nik said:


> Well, if you consider our kin can endure life as hunter-gatherers in the Outback, on the tundra, in rain-forests crawling with nasties, in cities crawling with nasties etc etc.
> 
> Pole to pole, apex to trench, albeit with lots of tech, plus that 10% death-zone on Everest...
> 
> ...



Nik,

A lot of good thought here, and for me a lot of gobbly gook. What pray tell does IIRC mean? and CME? and FWIW? and ITER? or Toba? 

Am I showing my lack of technical science backgroud?

The real reason we have not pursued further space exploration in my opinion is that there does not seem to be anything tangible to gain, except insight that intrigues scientists but leaves the majority of the population wondering what the big fuss is about.


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## Interference (Jul 17, 2009)

For what it's worth, I got FWIW, but I forgot what IIRC is, which is why I'm going here next ...

ITER, though, is probably International Thermonuclear Experimental Reactor, and of course it was the Certified Marketing Executive that missed toasting a crew by a few days, naturally 

Toba is a musical brass instrument.


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## Ursa major (Jul 17, 2009)

IIRC - If I Recall Correctly

CME - Coronal Mass Ejection (Coronal mass ejection - Wikipedia, the free encyclopedia)

FWIW - For What It's Worth

ITER - International Thermonuclear Experimental Reactor (ITER - Wikipedia, the free encyclopedia)

Toba - see Toba catastrophe theory - Wikipedia, the free encyclopedia




EDIT: I also use http://www.acronymfinder.com/, for what it's worth. (Sometimes there are pages and pages of possible expansions of an acronym, so you sometimes have to have a vague idea of what you're looking for.)


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## skeptical (Jul 18, 2009)

For acronyms, just put the acronym into google and it will give you the answer really rapidly.    I make good use of google.   I cheat at crosswords....

As far as the question of  "are humans OK for space?" - the answer is no and yes.   No, we are not adapted to space, but, yes, we will overcome that problem as we have overcome heaps of others.

We will do this partly by building environments in space that suit us, such as advanced radiation shielding (magnetic fields?) and rotation for artificial gravity.   And no.  We will not use star gates.   That is an SF concept, not one of science.

We will also use genetic modification to make us better equipped for space dwelling.   There are organisms on Earth, for example, that have fantastic DNA repair mechanisms, that can survive massive doses of radiation.   There is no theoretical reason why we cannot genetically engineer our own bodies to give us superior DNA repair, and allow us to survive the doses of cosmic radiation that space travel will entail.  Of course, this is 100 years plus in the future.

With sufficient development in genetic engineering, I see no theoretical barrier to stop us creating humans that can even take a deep breath and stay in hard vacuum for 10 minutes.  Similarly, it may prove easier to engineer people who can tolerate micro-gravity for long periods, rather than use artificial gravity from rotation.

In another 100 years, we may have a new sub-species of human able to survive the stresses of space travel far better than us 2009 inferior types.

I do not think that space travel is ever likely to provide a solution to over-population.   However, I do not think such a solution is required.   The United Nations demographers point out that population growth is slowing, and that the world will probably peak at around 9 billion in another few decades.  (  www.un.org/popin  ).   

A simple calculation shows that advanced agricultural methods (hydroponics) can feed 9 billion while using only the amount of land that occupies the northernmost one quarter of Australia - so I think 9 billion is something our species can adapt to.

At the same time, I think our long term destiny lies in space.   Even though IMHO  (try this in google), only a tiny percentage of that 9 billion will ever leave the Earth's gravity well, those that do will, in the long run (thousands of years) be the parents of most of humankind in the even longer run (tens of thousands).


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## Granfalloon (Jul 18, 2009)

Well, If you must know the answer - It's Money. Space travel is very expensive and doesn't seem to get as much funding as say, er... War on Iraq.  It may be that until man (America?)  stops wasting his money on other things, more money would be available for space exploration. The issue I have with it when you look at the big picture - our priorities are screwed up. We can't even feed the hungry people in the world, and we spend so much of our $ on military. \


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## skeptical (Jul 18, 2009)

Granfalloon

You are correct.  However, I still have hope for the future.   War is not the same today as it was mid 20th Century and earlier, and I believe things are moving in the right direction.   It is not widely publicised, but the number per million humans dying each year from war has dropped dramatically.   Instead of massive destructive wars like WWII, we now have such things as terrorism and counter-terrorism, plus minor wars.   Even the idiotic Iraq war is minor by standards of 60 years ago.

If humanity can learn to stop spending $$$ and lives on stupid wars, we might be able to invest in space.   I think the real essential step is not moon or Mars colonies, but the building of the first space elevator, which will make the rest possible.   However, that will cost $1 trillion plus.

This should happen within 100 years, and should herald the beginnings of the great expansion into space.  If a space elevator is run way beyond the stationary orbit zone, and its carriages are carried out to its terminus and released, they will flick into space with great speed - giving them a tremendous start to a journey to the moon or the planets, and eventually, the stars.


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## Urlik (Jul 18, 2009)

skeptical said:


> If a space elevator is run way beyond the stationary orbit zone, and its carriages are carried out to its terminus and released, they will flick into space with great speed - giving them a tremendous start to a journey to the moon or the planets, and eventually, the stars.


 
if it continues beyond the optimum geostionary orbit zone then it will put too much strain on the structure.

and releasing the carriages defeats the benefits of an elevator.
the upward bound carriages carry prefabricated parts to build huge colony ships in space and the downward bound carriages carry raw materials mined from the moon or asteroids. the mass travelling down is used to help lift the mass travelling up so that the cost of getting materials into orbit is far less than it is today (possibly even free if enough materials are mined and is in excess of the mass to be lifted to orbit).

if a ship is built in orbit it doesn't need a boost from the elevatoer either. it has already bypassed the costly stage of escaping from Earth's gravity.


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## Parson (Jul 18, 2009)

Thanks for all the acronym help! I have now bookmarked acronymfinderand I may not have to ask such questions again.

I agree that true space utilization does not begin until after a "sky hook" is built. But I would still maintain that we are going to have to have a "good" reason to do so, or else the majority of the population will see it as taking food or more likely conveniences from them. In the more democratic world which may be shaping up this could be the death knell for any serious space utilization.


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## skeptical (Jul 19, 2009)

Urlik

I may not have explained the point well enough.   A space elevator *must *extent well beyond the geostationary orbit point.   If not, the weight of the cable or ribbon below that point will fall due to Earth's gravity, dragging the whole lot back to Earth, disastrously.   Most proposals I have seen have suggested a counter-weight, hanging off the cable or ribbon, well out past the geostationary point.    This is subject to centrifugal action, holding the whole structure taut.

However, it has always been my own opinion that a counter-weight is not needed.   The cable or ribbon itself can act as counter weight if it goes far enough out.

Also, simply building a space vehicle at the geostationary point has always seemed to me to be a waste.   This is because it then has to accelerate, wasting reaction mass, to get to Mars, or the moon or whatever.   On the other hand, if it is moved to the outer end of the cable, it will already have the velocity to leave Earth orbit, just by the velocity imparted by the cable.  No reaction mass is required.   If released from the end of the cable at the correct (computer calculated) moment, it will fly at great speed towards its destination.

Incidentally, for your information, the geostationary point is 36,000 kms out from Earth, and without a counterweight, the space elevator would need to be a little more than double that length.  Say 75,000 kms long.  A space vessel released from that point would have a tangential velocity of about 3 km per second - easily enough to achieve escape at that micro-gravity.


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## Karn Maeshalanadae (Jul 19, 2009)

Humans not meant for space. I believe Chris has already made the argument-humans aren't naturally meant for anything we've done.

Space life? Possible. Uncomfortable for a while, but hey, we haven't been around for a million years by being horseshoe crabs, now have we?

I find it to be an interesting concept. More room in space, but....how do we get farming soil?  Shipments at first, but that would take away from the Earth, other planets are too far-not to mention perhaps not made for Earthling plants-and I'm not entirely sure how fertile moon or asteroid soil would be.....


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## Urlik (Jul 19, 2009)

skepical,
it makes no sense to build the ships on earth's surface and use the space elevator to launch them.
the ships would have to be small to be lifted by the cable compared to craft built in orbit from prefabricated parts.
the amount of energy required to leave orbit is minuscule in comparison to the amount needed to get from the surface up into orbit (just look at how much of the Apollo rocket was needed to get such a small payload into orbit compared to how much was needed to get from an Earth orbit to a Lunar orbit and back again)

the benefit of the elevator is that resources mined from asteroids and the moon going down the elevator to the Earth help lift prefabricated parts and fuel into orbit so getting there is almost free.
the minuscule amount of fuel needed to leave orbit is negligible (and hardly cost anything to get into orbit in the first place)


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## skeptical (Jul 19, 2009)

Urlik
I did not say the ships would be built on the Earth's surface, though I suspect that a lot of prefabrication would occur there.

No, the place to build ships is at the geostationary point, where there is apparent zero gravity.   However, the *launching* point would be at the end of the tether.  It would be relatively easy to attach the completed ships to a magneto-levitation cart that rode the cable.   The entire ship would then travel to the end of the cable for release.   The acceleration to 3 km per second is thus achieved using electricity, not reaction mass.

In fact, if a sufficiently effective magnetic acceleration system could be designed, the vessel would leave the end of the cable at a lot more than 3 km per second.   It might even be possible to accelerate a ship to sufficient speed to coast all the way to Mars, or even leave the sun's gravity well altogether, conserving its reaction mass for deceleration.

It would even be possible to part build and launch vessels, and have the various parts launched in such a way as to meet, and complete final joining into one big ship at a point en route to final destination. 

Mars, at closest pass to the Earth, is about 60 million km away.  At 3 km per second, it would take just under 2 years to cover this distance.  So extra launching velocity from magnetic acceleration would be very desirable.  My own feeling is that to accelerate from geostationary orbit (36,000 km out) to the end of the tether (75,000 km out) gives plenty of scope for massive velocity increase. 

We need to remember that a space elevator will probably not happen for another 100 years.   By then, magnetic levitation and magnetic acceleration technology should be massively advanced over what we have today.   Humanity should also have cracked nuclear fusion, meaning unlimited cheap energy.   With all that enhanced technology, acceleration to a velocity way more than 3 km per second should be achievable.


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## chrispenycate (Jul 19, 2009)

skeptical said:


> Urlik
> 
> I may not have explained the point well enough.   A space elevator *must *extent well beyond the geostationary orbit point.   If not, the weight of the cable or ribbon below that point will fall due to Earth's gravity, dragging the whole lot back to Earth, disastrously.   Most proposals I have seen have suggested a counter-weight, hanging off the cable or ribbon, well out past the geostationary point.    This is subject to centrifugal action, holding the whole structure taut.
> 
> ...



The centre of gravity of the system must be precisely in geostationary orbit. thus, there must be as much mass outside the geostationary stable point as hanging down ti Earth. If you put a big enough counterweight at the precise point, it tends to damp out minor variances in the tension like a capsule climbing the tower (although it would probably be a good idea to send a counterbalance capsule down), or a hurricane. If you have too much mass outside the counterweight, just as if you have too little, the structure winds itself round the equator like a thread round a bobbin, and several megatonnes of extremely energy-rich matter crash down the entire length of the tropics.

Certainly it would be possible to monitor the position of the tower at all times, and continuously correct for minor variations, but this would require near continuous expenditure of reaction mass, and make a ridiculously tempting target for some ambitious terrorist. A big lump of passive matter is less sophisticated, perhaps, but avoids a computer error being able to cause the biggest disaster in human history; even evacuating the tropics (fun) I'd expect a death toll in the hundreds of millions.


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## skeptical (Jul 20, 2009)

The space elevator must be able to withstand impacts by micrometeorite or space debris.   This is the reason I suggest it may take the form of a ribbon.   A wide enough ribbon will still hold together after tiny and ultra-high velocity projectiles fly through it.

Imagine a space elevator with a total length of twice 36,000 kms, which uses a cable rather than a ribbon.   And then a large space object cuts through the cable higher than the geo-stationary point!   All of a sudden the space station plus more than 36,000 kms of cable starts to fall to Earth.  There is net angular momentum, which means it would not all fall to the same spot.   Instead, 36,000 kms of massive thrashing cable would encircle the globe.   It would be a disaster on a scale unprecedented since the KT asteroid struck!

Obviously, a wide ribbon structure, resistant to cutting by meteors and space debris is essential.

I do have one question, though.  Does anyone have any idea how the ribbon could be placed so it does not move by twisting and contorting, with waves running up and down its length?   It is normally an inevitability with ultra long cables or ribbons.  Any unevenness of the movement of any part of it will trigger such contortions.


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## Parson (Jul 20, 2009)

All proving that there is a lot more difficulty to a space elevator than simply the materials necessary to extend from earth to space, something we presently do not have. All of this leaves me skeptical of Skeptical's 100 year estimate.


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## Pyan (Jul 20, 2009)

Oh, I don't know, Parson. Try looking at it another way, and compare the transportation systems and vehicles we have now to those of 1908...


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## skeptical (Jul 20, 2009)

Yet another space elevator difficulty.
There is a zone above the Earth where, due to the magnetic fields of our planet, radiation is concentrated to a point where it will rapidly become lethal.

With the space shuttle and similar vehicles, this is not a problem, since they pass the lethal zone so quickly, and little damage is done.   However, what of a space elevator carriage, which would appear to travel much more slowly?   The passengers would be exposed to seriously damaging radiation.

My own feeling is that we will need magnetic levitation to get the carriage moving fast enough.   It would have to be damn fast anyway, bearing in mind that it has to travel 36,000 kms to the geostationary point.  However, what if humanity develops the technology for a space elevator, but fails to develop magnetic levitation and high speed levitation transports to the same degree?

I see all these difficulties as engineering problems rather than basic science, and hence potentially solveable.   However, we should not kid ourselves that a working space elevator will be easy.


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## Urlik (Jul 20, 2009)

the van allen belts wouldn't be such a problem as the carriages could be shielded (unlike conventional rockets) as the mass of shielding on the upward bound carriages would be countered by the mass of shielding on the downward bound carriages


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## skeptical (Jul 20, 2009)

Re radiation shielding

There was an article on this in Scientific American a few years back.   The best shielding is conferred by water or some other compound with lots of hydrogen atoms.   With water, a thickness of 3 metres (10 feet) is required to give adequate shielding effect.   I rather doubt that the operators of the space elevator will want to have their carriages lifting walls three metres thick with the massive amount of weight that entails.

There has been proposed an alternative shielding system using magnetic fields to divert charged particles away from the vehicle.   Whether this is achievable remains to be seen.


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## Ursa major (Jul 20, 2009)

skeptical said:


> I rather doubt that the operators of the space elevator will want to have their carriages lifting walls three metres thick with the massive amount of weight that entails.


 
If, as Urlik has said, a carriage going up is balanced by one coming down, the weight of the water is not that a big problem.


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## chrispenycate (Jul 20, 2009)

If you built a superconducting Faraday shield incoming charged particles (the only ones to be trapped in the Van Allen belts) would cause eddy currents producing a force proportional to, and in the opposite direction to, the velocity of the particle, and the square of its distance. While this couldn't stop incoming particle it could slow them to manageable energies.


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## skeptical (Jul 21, 2009)

Urlik

How do you plan to use a descending vehicle to balance one that is ascending. With a 36,000 km long cable?????

chris

The SciAm article I read had no such simple solution. They proposed a magnetic system, but admitted that such technology does not yet exist. Perhaps in 100 years???

To me, the obvious solution to this problem, given 100 years to develop a better system, is high speed magnetic levitation technology.   We will need this anyway, to get people to their destination in a reasonable time frame.   Imagine rising the space elevator at 100 km per hour?   To get to the geostationary destination would take 15 days.   Not, in my opinion, acceptable.   However, raise your speed to 1000 km per hour - very possible with maglev - and you get there in 1.5 days.

The reality is that such a journey would start slow, as you moved through atmosphere for the first 100 km, and then accelerated as you moved into vacuum, and as gravity declined.   Maximum speed with an advanced maglev system, in vacuum, and with a somewhat reduced gravity, could be many thousands of km per hour.   Decelerating again could use EM braking, and generate electricity.


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## chrispenycate (Jul 21, 2009)

So, what would stray fields from your acceleration coils do to the Van Allen belts? Accelerate them with the capsule or create turbulent regions.

And "magnetic _levitation_" is for horizontal rails, not vertical ones; what you are creating is a vertical linear accelerator, possibly with magnetic bearings. I will assume that some form of mechanical brake in the event of power failure.

And how do you power the coils, anyway? Thirty six megametres of electric wire is going to introduce serious power losses unless that cable was superconducting, particularly as it has to be relatively high frequency alternating current, and quarter-wave transmission is practically guaranteed.


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## skeptical (Jul 21, 2009)

Chris

Those are good questions.   I am not an engineer, so I probably cannot really answer them.  I will give it a shot anyway.  I am arrogant enough to pontificate from ignorance.   If it comes out idiotic, I am sure you will correct me.

1.   Effects on the radiation belts.   I would hope this would be irrelevent.   If you went quickly enough, as with today's space shuttle, the radiation should not be a serious import.

2. Your correction on maglev is warranted.  Yes, magnetic bearings, and a vertical lifting force.   I am insufficently expert to detail how this might be structured, but I can see no theoretical barrier given some advanced and clever engineering.

3.  Mechanical brakes would pose a difficulty at the speeds we are discussing.   If the vehicle was ascending, gravity would slow it.   If falling, perhaps a parachute system might be appropriate.  Once the movement was slowed sufficiently, a mechanical brake might finish the job.  Alternatively,  perhaps the vehicle might have a generator on board able to generate a magnetic brake.

4.  Power losses.   A good point.   Yes, superconducting may be the answer, especially with another 100 years technological progress.  I wonder also if it is possible for the vehicle to supply the power needed?   Either the vehicle could have a generator on board (nuclear??) or else receive power by microwave beam.   If coils in the ribbon were activated by induction from the vehicle, would that be sufficient?

Incidentally, I hope no-one takes the 100 year estimate too seriously.  I have read estimates of 20 years, 50 years, and 100 years from different sources.  I think 20 is ridiculously optimistic.   100 years should do it.  However, it will not matter, from our viewpoint if it takes 1000.  We are none of us going to see it anyway, and even 1000 years is infinitesimal compared to biological, geological or astronomical time.   It is only one tenth of the time span since humans learned agriculture, so it is not a real major even in terms of human history.

I sometimes like to speculate on the future of humanity.  When I do, I like to think in time spans of thousands of years or more.   This changes things quite considerably.  Predictions over decades are inevitably inaccurate.   Predictions over long time spans at least means no-one can prove me wrong!


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## ktabic (Jul 21, 2009)

skeptical said:


> With water, a thickness of 3 metres (10 feet) is required to give adequate shielding effect.   I rather doubt that the operators of the space elevator will want to have their carriages lifting walls three metres thick with the massive amount of weight that entails.



Well that could be a problem except:



skeptical said:


> Imagine rising the space elevator at 100 km per hour? To get to the geostationary destination would take 15 days.



People without water die in about three days. So you need to provide water. And if the shielding can also be used as the water supply, you are solving two problems at once. The passengers will also need other stuff, like food, oxygen, space to move around in, entertainment, bathrooms. 15 days in a carriage with no showers? That is going to stink.



skeptical said:


> Not, in my opinion, acceptable. However, raise your speed to 1000 km per hour - very possible with maglev - and you get there in 1.5 days.



But at a higher cost, both financially and energy. The reason for building a space elevator is to make launching stuff into space cheap. It's not worth making small carriages (except for special purposes), since you are trying to reduce costs of getting stuff into orbit, so you go large. The more stuff you can move at once, the cheaper it becomes. But large increases energy costs, and fast increases energy costs. Which is what you are trying to avoid in the first place.


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## Parson (Jul 21, 2009)

pyan said:


> Oh, I don't know, Parson. Try looking at it another way, and compare the transportation systems and vehicles we have now to those of 1908...



Point taken. However, at least in transportation, we are not looking at a quantum leap in technology. The cars and planes and yes, even rockets we had in 1908 ran on basically the same principles we use now. AND there was a tremendous economic engine driving the production of the incremental increases which have added up quite nicely in the 100 years. At this point there is no economic or philosopical engine driving a sky hook so incremental increases in the technology needed will be much slower, and to move a "big rock" in to tether it to takes the kind of thrusters which need that "quantum leap."


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## AE35Unit (Jul 21, 2009)

Someone on another forum is arguing that our lack of progress is due to the Van Allen Belt:


> I`d like to think the landing was real, chances are that it is, but a few things have always niggled at me since i was a kid
> 1. From the moment Kennedy made his "putting a man on the moon" speech,the technology required was astounding and unheard of, yet it took less the 10 years to do
> 2. The *Van Allen belt ! !* even todays shuttle expeditions steer well clear of it, due to its massive radioactivity. To pass through it you`d need lead shielding at least 3ft thick, at the time of the Apollo mission the radiation was it its highest for decades ! !
> 
> ...



Just how much of a brake to progress in Space travel is down to the Van Allen Belt? And isn't there more than one?


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## skeptical (Jul 24, 2009)

Interesting article in _New Scientist_

Scramjets promise space travel for all - space - 22 July 2009 - New Scientist

This discusses the intermediate between current space shuttle type technology and the space elevator.  It may be possible to design a space craft that takes off from an airport on standard jet engines, accelerates to speed and switches to scramjet engines which might make mach 10, and achieve very high altitude, before finally switching to rocket engines to achieve orbit.

Since carrying oxidiser for rockets is enormously expensive in weight (80% of the fuel load of the shuttle), and since jets and scramjets use atmospheric air, this approach will both cut the weight of the spacecraft, and its cost per launch, but also increase payload.  Perhaps a flight into orbit may be affordable for the ordinary person within our lifetimes.


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## chrispenycate (Jul 24, 2009)

Not, I fear, within my lifetime.

The main advantage of a jet over a rocket is reaction mass; the rocket has to carry everything it must expel for conservation of momentum, the jet collects it from its environment. The minor losses due to extra friction and changeover from jet to rocket operation should be easily compensated for by this difference, even if I would like to apply the first takeoff thrust with a linear accelerator to conserve all possible fuel for high altitudes, where it is most effective (yes, you're right, I like linear accelerators)

Have you considered laser launchers? Nor reuseable craft, no, and possibly not for passengers, but possibly a good way of getting enough mass up to geostationary to start the counterweight.

Oh, and on the tower, I've got up to:



skeptical said:


> Chris
> 
> Those are good questions.   I am not an engineer, so I probably cannot really answer them.  I will give it a shot anyway.  I am arrogant enough to pontificate from ignorance.   If it comes out idiotic, I am sure you will correct me.



I, on the other hand, am a bit of an engineer (you noticed?) and actually knew Laithwaite, the father of magnetic drive technology. So yes, there is no real problem in adapting to vertical operation; I'm just so used to splitting nits (should that be picking hairs?) that I pointed it out. I'm now preparing my paper on "the long-term effects if ionising radiation on the stability of molecular bonds in carbon monofilaments". Slightly more seriously, would we need to protect the entire cable (all right, ribbon, whatever. It we're planning to send up capsules the size of ocean liners, which is fine by me, the difference is irrelevant, anyway; it's a tower) from radiation to prevent it from degenerating over the centuries?

It might appear that I am negative towards the project. Not at all; I am a pessimistic follower of St Murphy, as any engineer should be. When you have enumerated all the ways in which a project can go wrong, it's obsolete, so we'd best start now; a century or two might not be enough. But you can't build half a suspension bridge, or half an orbital tower; the thing is built once, and forever, with no real hope of demolishing it, nor repairing errors. (sorry that last was for the elevator, not the bridge)  

Power source in the capsule? Well, yes, you could turn it inside out, I suppose, although one of its principal advantages (along with a total lack of moving parts; very Clarkeian) was that all the drive was external, saving weight and complexity. And microwave energy is not an efficient way of powering a linear accelerator- oh, possible, of course, but involving three transformations of energy (microwave to HF electricity, rectified and smoothed then converted into polyphase AC for the drive) and the multigigawatt maser beam is as dangerous as the rockets it replaces; how much would it spread over thirty-six million metres? If aimed down from solar generating panels on the counterwieght, how many birds would be microwave cooked, how many humans have to be evacuated from the danger zone?

Besides, when we are slowing, we want to recuperate those terrajoules of kinetic energy, and use it to power the capsules going the other way, and it is now being captured (due to our inverting the drive structure) inside the capsule. Bad idea, really; batteries that powerful may be invented in the next century, but I don't really want the energy of an atomic bomb in there with me.

Perhaps reading too much SF has oversensitised me to catastrophe scenarios, but we're looking at lots of energy here. If, on the descent, the tower stops pulling energy out of the capsule (braking, if you like, but using the energy, not wasting it as heat) it's going to hit the atmosphere at damn near escape velocity. I think you can write off parachutes as a way of slowing it: a meteor with magnetic bearings. The energy released on impact will be closer to Bikini quantities than Hiroshima, and it will definitely sever the cable/ribbon/tower, leaving the loose end free to wander through the atmosphere; this must not be allowed to happen. Even if mechanical braking reduces the passengers to mush, they were doomed anyway (except in an adventure film).

, which is not all I intended to write, but I'm rather work-intensive these days (nice; I like my work)


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## skeptical (Jul 24, 2009)

Chris

You have some interesting ideas.
I am something of an optimist in relation to human development, in that I think our species is highly innovative and can come up with an amazing array of solutions to problems.

I do not deny the problems, as shown by my earlier posts, in which I detailed some of them.   However, I believe we can, with time and sufficient money and ingenuity, overcome such.

You stated :
_"But you can't build half a suspension bridge, or half an orbital tower; the thing is built once, and forever, with no real hope of demolishing it, nor repairing errors."_

I disagree.    Once the first space elevator is built, the next is going to take a fraction of the effort and money.   The biggest problem is to get that first 75,000 km cable to the geostationary orbit point.   However, once the first space elevator is complete, the cable can winch up its replacements.

Why do you think we would stop at one space elevator?   Once we have the first, relative to the progenitor, it would be easy to set up a second, a third, a hundredth (given enough time).   If the first shows signs of age, simply wind it up again, and attach an ion drive engine to carry it off into deep space, or recycle its bits.  By that time, hopefully, we will have plenty of replacements.

Arthur C. Clarke postulated a structure he called _Ring City_.   A massive tube running right around the Earth, with a thousand space elevators descending to the equator.    That is what I call vision!


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## Urlik (Jul 24, 2009)

skeptical said:


> Arthur C. Clarke postulated a structure he called _Ring City_. A massive tube running right around the Earth, with a thousand space elevators descending to the equator. That is what I call vision!


 
an equatorial ring would be an enormous undertaking but may be easier to construct than a single space elevator.

building a ring of geostationary space stations in orbit above the equator is well within our current technology. connecting them together to form a ring would be a major task but still within the scope of current technology.

putting the actual elevators in place would be the hardest part and would require timing down to the nano second but would still be possible


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## chrispenycate (Jul 24, 2009)

Build more, certainly; mend or demolish a damaged one? The environment is not propitious. I suspect you have to detach the base and cut off small (perhaps 100 M) segments from the bottom up, as the thing drifts into a higher orbit, unrestrained by tension.

Hmm, I don't think anyone's written a story about demolishing a space elevator… (Brain starts to hum gently.)


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## Arwena (Jul 24, 2009)

With all the problems to be solved, would it be safe to say, then, that real space exploration is a third millenium thing - but well into the third millenium.  It is probably something inevitable, though.


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## chrispenycate (Jul 24, 2009)

Arwena said:


> With all the problems to be solved, would it be safe to say, then, that real space exploration is a third millenium thing - but well into the third millenium.  It is probably something inevitable, though.



Real space exploration has already started; something isn't unreal simply because it hasn't got very far yet. The exploration of the Earth didn't start with Columbus, but some long forgotten African leaving his own little patch of Rift Valley (It could be argued it started with unicellular life spreading from its point of origin, and all since then has been rediscovery, but they weren't leaving very detailed maps).

And the inevitability depends on the survival, and progress, of the human race. Which is not in any way certain.



			
				Urlik said:
			
		

> building a ring of geostationary space stations in orbit above the equator is well within our current technology. connecting them together to form a ring would be a major task but still within the scope of current technology.
> 
> putting the actual elevators in place would be the hardest part and would require timing down to the nano second but would still be possible



Why timing? Since any point on the ring is geostationary, it is not moving relative to the Earth's surface. Obviously, you'd have to build out at the same speed (masswise) as you built in towards the planet; but as long as any point on the ring had its centre of gravity geostationary, it would never tend to move, so wouldn't need tying down.

But with present day technology? Even putting an optimistic percentage of the world's gross industrial production into space development it would take a hundred thousand years to get enough mass off Earth to start building it; far better to build one tower and haul up the mass for the others (better still , collect bits that are already disconnected, asteroids and comets and lumps of planetary rings and nudge them into place, all the while firing off lumps from the moon). We need a lot of mass; even two hundred thousand kilometres of wire would be impressively heavy, and we want to be able to live on this. Not to mention that each ascending capsule is going to pull down on the structure, slowing it down a fraction, so some appreciable percentage of the lifted matter is going to have to be expelled as extremely high speed to maintain stability.


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## Urlik (Jul 24, 2009)

I would guess that if there was a fixed ring in a geostationary orbit, if you connected a tether at one point it could cause the ring to become unstable.
so it would probably require tethers to be connected simultaniously on opposite sides of the planet to prevent the instability.
once tethers are in place, they may act like the spokes of a bicycle wheel and help stabilise the ring


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## skeptical (Jul 24, 2009)

Just a point of correction.
There is no need in a space elevator to 'balance' loads going up with loads going down.

What you would do is extend a little more of the ribbon outwards - away from Earth - than the ribbon downwards.   This to ensure that the centrifugal action was a little stronger than the downward pull of gravity.   This would ensure that the whole structure was held taut.   You could then haul stuff upwards to your hearts content without having to haul the other way to balance it.

Like a lead sinker on the end of a line being swung around your head.  If an ant crawls down the line towards your head, it will not pull the weight down at all.  The centrifugal action holds the line taut.


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## chrispenycate (Jul 24, 2009)

skeptical said:


> Just a point of correction.
> There is no need in a space elevator to 'balance' loads going up with loads going down.
> 
> What you would do is extend a little more of the ribbon outwards - away from Earth - than the ribbon downwards.   This to ensure that the centrifugal action was a little stronger than the downward pull of gravity.   This would ensure that the whole structure was held taut.   You could then haul stuff upwards to your hearts content without having to haul the other way to balance it.
> ...


 
Do the maths. If the centre of gravity is appreciably off the geostationary orbit, outside or inside, it will pull the tower steadily ahead or behind the attachment point. If you don't want it to slowly pull round and down, you'll have to keep expelling reaction mass to keep it upright; not something we really want.

Besides, we're close to the limits of materials science here (beyond the present limits) so a few more tonnes of tension might turn out to be the camel's straw.


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## skeptical (Jul 25, 2009)

Sorry Chris.  Not quite correct.
The whole idea is to get the entire space elevator to pull upwards.   That is countered by securing it at the bottom.   I am not talking of anything massive.  Just a slight pull up,   (compared to the whole system, a few thousand tonnes is slight!) to keep the whole system taut.  This is easily achieved by having more ribbon out from the geostationary point than in, and by having the bottom of the ribbon extremely well secured to massive foundations.


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## Pyan (Jul 25, 2009)

chrispenycate said:


> Hmm, I don't think anyone's written a story about demolishing a space elevator… (Brain starts to hum gently.)



IIRC, RAH describes what happens should one fail, in _Friday_...


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## chrispenycate (Jul 25, 2009)

pyan said:


> IIRC, RAH describes what happens should one fail, in _Friday_...



And there's another one in "Blue Mars". But I'm thinking of planned demolition of an obsolete structure seventy kilometres in – length? Height? Maximum dimension, anyway. Like getting rid of skyscrapers in Chicago, but this one doesn't merely scrape the sky, it goes through it to the other side. And I think I've worked out how to do it, too. Velikovsky would love it.


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## skeptical (Jul 25, 2009)

Demolishing a space elevator.

In one sense - easy. The bulk of the elevator is 75,000 km roughly of flexible ribbon. Giant scale to be sure. To remove a ribbon, you wind it up. This ribbon would have to be wound on a giant size spool - easy to build in microgravity given the use of the elevator to lift the prefabricated spool.

The spool might be a skeletal structure of 10 km diameter. Actually, there woud have to be two spools which counter-rotate to wind in both ends of the ribbon. 

Once the entire elevator is wound in, getting rid of it is done by attaching a couple of ion drive engines and accelerating it, albeit very slowly, out of orbit till it can fly off to wherever the powers that be dictate it should go.

An alternative method would be to release it at the Earth base. Since the centre of gravity is outside the geostationary point, it will move to a higher orbit - with the trailing end well up from Earth ground level. Then the giant ion drive motors have to accelerate the whole thing to a safe distance. However, this method involves two 36,000 km long trailing ribbons that might be a space hazard. Would we be able to keep it more than that distance from anyone or anything of importance?


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## Ursa major (Jul 25, 2009)

Rather than simply release the elevator and hope it drifts out of harm's way, should something at the outer end be "pulling" on it? (One might, I suppose, use those ion drives from the off, rather than use them later.) I imagine that no one would want to be near** the bottom of the elevator when it's being removed, so it's only one extra hazard***.





** - I'm not going to provide a definition of 'near' in this context.

*** - I'm not going to define the scale of the hazard.


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## Arwena (Jul 26, 2009)

Another problem of space travel - you've got to have someplace to go.  Earth exploration - you don't have to   carry your whole environment with you, tohugh some people go to places that are simply impossible to live - Antarctica, anyone?  No place in the solar system worth going to!


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## skeptical (Jul 26, 2009)

Arwena

There are a number of luminaries, such as professors Stephen Hawking and James Lovelock, who believe fervently that humanity has to seed itself away from planet Earth to prevent the entire species being wiped out in a sufficiently bad disaster.

My own feeling is that this does not have to be on a planet, though undoubtedly some will stay planet bound.   I envisage the majority of humanity living in space, in giant habitats or cities, rotating for gravity, and moving from one resource to another.  Such a structure could, in theory, be almost totally independent - just mining space rock for metals and raw materials, and taking in water from comets, planetary rings, asteroids etc.

A lot of the SF fans contirbuting here will have heard of Dyson spheres.  What you may not have figured is that the best and safest form of Dyson sphere is successive rings of rotating space cities in orbit, rather than a continuous chunk of matter.   It also means the dwellers therein have a chance of escape should the proverbial hit the fan.  If energy is by then available from nuclear fusion from deuterium, such a city does not even have to be close to the star it orbits for energy.

Even though Earth water is only 0.015% deuterium (as weight percentage of the hydrogen only fraction), there is enough energy there in theory for 1 tonne of water to equal 8 tonnes of crude oil.  Assuming water in space has the same deuterium, there is enough in our own solar system to provide humanity with energy for untold billions of years.
I also think that the unexpected will happen, because it always does, and unknown benefits will fall upon all of humanity once enough is known about the environment away from our world.


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## Granfalloon (Jul 27, 2009)

It is rather interesting to me that members will argue over a single concept for several pages when there are several other contenders out there. The most promising one IMO is this:

MagBeam Propulsion - To Mars And Back In 90 Days: Science Fiction in the News

The beauty of this system is that it eliminates the incredibly high masses of fuel, fuel convertors, or hardware of any kind that would be necessary in most applications. 

NASA is planning a trip to Mars in roughly 20 years from now, but I suspect that competing technologies may confuse the issue. (who decides what technology to use, or what combinations and proportions thereof?)

One thing is for certain - we cannot rely on escape from the planet as a way to save "humanity". Ever heard the expression "Wherever you go, there you are."? If we expect to get away from the problems we have, we are just going to bring our problems with us. We must first solve the issues we have with pollution by creating clean, renewable energy. We must solve the "over-population" crisis with a policy of equality in education for the entire planet, and we must build a world co-operative system that eliminates the need for wars and/or terrorism. _Ha ha!_ Pipe dreams you say! Maybe, but can you say that my point is not valid? You don't think it is achievable? If it isn't, we are doomed to take our "issues" into space with us.


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## skeptical (Jul 27, 2009)

To Granfalloon

Couple of points.

First :  Your magbeam does nothing to fix the major problem, which is getting clear of Earth's gravity well.   Or the second major problem, which is to get up and down through the gravity well of Mars.

Nor is it necessarily the best approach to the journey from Earth to Mars and back.   There is a theoretically possible orbit - very eccentric - that will carry a space craft across Earth's orbit, to Mars orbit, and back.   There is one long transit period and one shorter.  The shorter takes six months from Earth to Mars and the reverse as well.   

One of the proposed methods for long term, regular, travel between Earth and Mars is to throw a 'space castle' into this orbit.   It will be big and heavy, rotating for artificial gravity, and carrying a thick shell of water or polyethylene for protection against cosmic radiation.   It needs to be accelerated into orbit just the once, and will thereafter continue that orbit indefinitely.

Of course, it is still necessary to accelerate to meet the space castle, and decelerate when leaving it.   But only a small and cramped space craft is needed for the acceleration/deceleration phases.   And the long journey is done in comfort on board a very big habitat.  

Obviously, this will not be how the first people get to Mars.   It will be a solution for later, more regular voyages, since it will take an awful lot of energy and acceleration to get the big clunker into that orbit.  It might take 20 years of acceleration using ion drive motors.  Or possibly your magbeam system.

On the problems of planet Earth.   I think it goes without saying that the problems on planet Earth will remain there.   We do not solve all our problems by getting a relatively few people into space.   However, those in space are our species insurance policy.   If something happens to destroy the population on Earth, there are still people in space.  Examples might include asteroid strike, nuclear war, gamma ray burster not too far from Sol (if our space colonists are far enough away in another solar system, they would survive), war using genetically modified viruses etc.

This is a long term insurance policy, since we are unlikely to have self sustaining colonies off Earth for some hundreds of years, and around other solar systems for some thousands.  However, some people think it is important to work towards that goal, even if it takes a long time.   After all, in biological time, 10,000 years is just a blink of an eye.

On the very long time scale, our sun will swell and overheat the Earth enough to make it uninhabitable in a few hundred million years, and swallow it completely in about 4 to 5 billion.  Hopefully, well before then, humanity will be all through the Milky Way galaxy.


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## AE35Unit (Jul 27, 2009)

Can anyone explain to me exactly why one needs to travel at the escape velocity in order to get into space? Is it not possible,once high enough,to push throu the atmosphere,and what would happen if it was tried?


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## skeptical (Jul 28, 2009)

AE

It is theoretically quite possible to get to space without accelerating to escape velocity.  For example : if the space elevator existed, with a 75,000 km ribbon out into space, you could climb that ribbon as slowly as you liked.   Of course, you would be accelerated by the ribbon, since it rotates around the Earth at once each 24 hours.  In fact, you would have kinetic energy 'put into' you equivalent to escape velocity, with that energy taken from the rotational momentum of the Earth.  By the time you reached the end of the tether, you would be travelling at almost 3 km per second tangential to the Earth.  If you let go the tether at that point, you would be flicked out into deep space.

However, for normal space travel, you need an energy input equivalent to acceleration to escape velocity.   For example :  if you used enough energy to simply climb to 100 km on a rocket, you would then fall back to Earth.   To orbit at 100 kms, you need 'sideways' speed sufficient to avoid that fall.  To get that speed, guess what velocity is required?


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## Granfalloon (Jul 28, 2009)

skeptical said:


> To Granfalloon
> 
> Couple of points.
> 
> First :  Your magbeam does nothing to fix the major problem, which is getting clear of Earth's gravity well.   Or the second major problem, which is to get up and down through the gravity well of Mars.



Granted, but since we've already proved we can do that, It would simply (I say simply, not easily) be a matter of getting the propulsion beams into orbit.

And how do you know that the Mag beam cannot be used to get a craft to escape velocity? Do you have the research to back up a statement like that? 
(I don't have any proof that it would, I'm just curious) 




skeptical said:


> On the problems of planet Earth. I think it goes without saying that the problems on planet Earth will remain there.   We do not solve all our problems by getting a relatively few people into space.   However, those in space are our species insurance policy.   If something happens to destroy the population on Earth, there are still people in space.  Examples might include asteroid strike, nuclear war, gamma ray burster not too far from Sol (if our space colonists are far enough away in another solar system, they would survive), war using genetically modified viruses etc.


If the scenario plays out the way it has been described previously in this thread (i.e. only the elite or military being the ones to survive), I'm sorry to say that I don't believe they are the best candidates to carry on the species. I actually consider those folks to be the least evolved mentally, emotionally and spiritually. They would need to take a few geeks with them to have any hope of long term survival. 



skeptical said:


> This is a long term insurance policy, since we are unlikely to have self sustaining colonies off Earth for some hundreds of years, and around other solar systems for some thousands.  However, some people think it is important to work towards that goal, even if it takes a long time.   After all, in biological time, 10,000 years is just a blink of an eye.



I suspect there are plenty of intelligent life forms who are well aware of our existence. Well aware enough to stay well away from us for now. I don't think there is as much need for an "insurance policy" as there is a need for humanity to mature to the point that it can handle the responsibility of the technology they are toying with. 



skeptical said:


> On the very long time scale, our sun will swell and overheat the Earth enough to make it uninhabitable in a few hundred million years, and swallow it completely in about 4 to 5 billion.  Hopefully, well before then, humanity will be all through the Milky Way galaxy.



Hopefully by that time, we'll be hanging tight with the sentient folks who escaped from Beetleguise.


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## skeptical (Jul 28, 2009)

Granfalloon

Re Magbeam.   I just read the reference.   No suggestion of using it to lift people off the Earth.   In fact, it is logical to assume it cannot, since gaining orbit is the most difficult part of the whole exercise, and needs immense thrust.   There are all sorts of ways of accelerating away from Earth, once in space, ranging from standard rockets, to ion drive, to laser thrusters, to solar sails etc.   However, no-one has yet come up with a practical and safe method of lifting into orbit apart from brute force rockets.   Perhaps in the future we may be able to do so, but not yet.

On your idea of advanced aliens waiting for us - I have my doubts.   However, that is a topic for another thread, perhaps under the title of 'the Fermi Paradox" (google it).


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## chrispenycate (Jul 28, 2009)

Like the magbeam, but there are a couple of minor difficulties they have glossed over, (or actually ignored, in that article)

Action and reaction are equal and opposite, so while the plasma generator is pushing the spacecraft forward, it is pushing itself back with equal or slightly greater force. If you reuse it for a number of missions, it's not only going to need to be minimum an order of magnitude more massive than the craft it's propelling, it's going to have to spend half its time firing backwards, to maintain station. And it needs reaction mass. Even if the plasma does come out considerably faster than any chemical reaction can provide, it's still a long way from light speed, and there are no reletavistic advantages to be gained. So, capturing and compressing solar wind, or regular fuel tankers hauling it in from somewhere? Linearly accelerated packets of lunar regolith (you can make plasma from anything) aimed close, and caught in nets?

While the plasma generator will only work in fairly hard vacuum, you could lift spaceplanes into orbit with a tangential beam through the upper atmosphere giving them the final boost. You could definitely use it to power the tugs pulling mass from LEO to geostationary, taking over from the laser launcher at the top of its trajectory or keeping the ferris wheel spinning (I had a look at the "into orbit" problems quite a long time ago, in this:

http://www.sffchronicles.co.uk/forum/35007-the-first-step-into-orbit.html

post, meaning to follow it up with in system drives and ultimately interstellar technology, but ultimately there was little enough interest it didn't seem worth going on.


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## AE35Unit (Jul 28, 2009)

skeptical said:


> However, for normal space travel, you need an energy input equivalent to acceleration to escape velocity.   For example :  if you used enough energy to simply climb to 100 km on a rocket, you would then fall back to Earth.   To orbit at 100 kms, you need 'sideways' speed sufficient to avoid that fall.  To get that speed, guess what velocity is required?



But I still don't see why? You're at the thin barrier between earth and space,just give a little push and you're thru!


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## chrispenycate (Jul 28, 2009)

AE35Unit said:


> Can anyone explain to me exactly why one needs to travel at the escape velocity in order to get into space? Is it not possible,once high enough,to push throu the atmosphere,and what would happen if it was tried?



 Look, you accept the law of conservation of energy, right? Escape velocity (actually "escape speed" would be more accurate; the direction vector is reasonably irrelevant. As long as it's not straight towards the planet) is the speed that would be attained by an object falling from infinity to a point on the planet's surface, assuming there wasn't any atmosphere to confuse things. All potential energy converted to kinetic. So, to escape from Earth's gravitational pull, we need this much kinetic energy to convert into potential.

Often people say "out of the Earth's gravitational field" for the astronauts spacewalking round Hubble, or the international space station. Of course they aren't. Earth's field continues a lot further than that, holding the moon in place, making measurable perturbations in the orbit of Mars… Technically, it extends to the limits of the universe, but it's below noise level before we leave the confines of the solar system, dropping off as the square of the distance. Those astronauts are omitting falling down to the planet because they have a secondary vector sideways so the planet is no longer there when they fall on it (frequently inaccurately referred to as "centrifugal force"), which velocity they share with all the objects around them, in comfortable stability. This doesn't give them enough energy to climb out of the 'gravity well', just to avoid falling any further down. The sum of their kinetic energy and potential energy for any stable situation is a constant, and to get any further out – say a quick trip round the moon – you have to add more kinetic energy, which means more momentum, which means more reaction mass.

TANSTAAFL


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## AE35Unit (Jul 28, 2009)

An object falling from infinity? Scratches head. 
Incidentally they were discussing the atmosphere on QI last night,and they quoted a french authority that say the earth's atmosphere ends at 60 miles or thereabouts. 
One of the contestants said 'Why not just have a ladder going straight up,climb up and walk off?' I was waiting for Stephen Fry to mention the Space Elevator concept but he didn't.


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## Interference (Jul 28, 2009)

Seems to me the first, greatest expenditure of resources could be used to put a platform up there in geo-stationary orbit, then they could just lower a stairway any time they needed to bring up supplies or personnel.

I'd buy a stairway to heaven, wouldn't you?


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## AE35Unit (Jul 28, 2009)

If there's a bustle in your hedgerow then yea


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## skeptical (Jul 28, 2009)

AE

If you climbed a 60 mile high ladder and stepped off, you would fall straight back down to Earth, and end up as raspberry jam.

To orbit at 60 miles high, you need both altitude and sideways velocity.   You will still be falling, but if your velocity sideways is fast enough, you will move out as far as you fall.   That makes the orbit.  

Incidentally, there is no point at which we can firmly say the Earth's atmosphere ends.  It thins gradually until the number of molecules per cubic centimetre is the same as in space.   The point at which that happens is very fuzzy.   However, at 60 miles, it is thin enough to be *almost* equivalent to space.


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## AE35Unit (Jul 29, 2009)

But once you're in Space you can just hang there,neither falling nor climbing. So (un)technically you should able to fly to altitude,punch thru the last layer of atmosphere and then come to a stop. What i'm saying is what is stopping a ship from leaving the atmosphere at normal speeds? Think of it another way. Lets say you get a machine that can hover on the spot,like a helicopter does. It hovers at the edge of space. You do an EVA and walk into space.


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## skeptical (Jul 29, 2009)

AE

In space, you are still subject to the gravity of the Earth. This means you are falling, since you are not supported. If you have no serious sideways motion, you will just fall back to Earth. Satellites orbit because they have substantial sideways motion. For example, a satellite in geostationary orbit, 36,000 kms up, will be moving sideways at 3 km per second. It is falling, but the sideways motion carries it further from the Earth, which exactly compensates for the fall.

If you climb a 60 mile (100 km) high ladder and step off, you have very little sideways motion, and will fall without anything to compensate for the fall. Thus, you will crash to the ground and be smashed to slush.

On the other hand, if the ladder was 36,000 kms high, it would end at the geostationary point. Since the top of the ladder is moving sideways, going around the Earth every 24 hours, then if you step off, you too will be moving sideways at the rate of once every 24 hours - or at 3 kms per second. This sideways motion is enough to compensate for the rate of fall, and you will stay in place relative to the Earth. This is the principle of the space elevator.


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## Urlik (Jul 29, 2009)

chrispenycate said:


> TANSTAAFL


 
Chris, are you using the "typo" version?

There Ain't No Such Thing As A Free L*a*unch


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## chrispenycate (Jul 29, 2009)

AE35Unit said:


> But once you're in Space you can just hang there,neither falling nor climbing.


 Aha, there's the misconception. No. If you are anywhere near a largish mass, say a planet or a star, you experience a force. If there is no compensatory force, Newton informs us you will undergo an acceleration. Since this force is not transmitted by atmosphere, it makes no difference whether you are in 'space' (Meaning drift. You can no more get out of space than you can escape time. Vacuum would be more accurate) or three metres above sea level. Everything in Earth orbit is falling all the time.

However, if two things are falling at the same speed, they have no tendency to separate, so if one of them is an observer, the other appears motionless; possibly even a truth, as no frame of reference can be taken as an absolute; while the planet is attracting you at how ever many metres per second per second it does (at that height it won't be all that much less than the 9.8 at sea level) you're accelerating the Earth with the same absolute force (but a considerably smaller delta v, as it's a bit more massive). 

When you're on your ship going to Jupiter, and you get out to replace the broken bit of your communications gear, you're belting along at a rate of knots (if they use knots to measure speed in space, which I doubt) but you can still spacewalk the length of your vessel, because you both start with the same velocity. Actually, the ship has a gravitational pull, too, but it's so much less massive than a planet the attraction is less than the barmaid in the Orangerie. The only time you'll tend to separate is when firing the engines, or (slightly) tidal effects when you slingshot round Jupiter due to your differing centres of gravity.

Free fall means falling freely, not freedom from falling, and that great big vacuum out there doesn't give you many clues as to whether you're undergoing acceleration or not, until you hit something.


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## AE35Unit (Jul 29, 2009)

Ah of course. Any body in Space creates its own gravity field. And so being close to Earth you are still drawn to it and need to 'escape'. Only if you're away from any large rotating body can you hang motionless,where there is no up and down.


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## Parson (Jul 29, 2009)

AE35Unit said:


> Ah of course. Any body in Space creates its own gravity field. And so being close to Earth you are still drawn to it and need to 'escape'. Only if you're away from any large rotating body can you hang motionless,where there is no up and down.



Motionless? Relative to what? Everything in the universe is in motion.


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## Granfalloon (Jul 29, 2009)

Right. Several things. First, I was not aware that AE was made of raspberry jam. I'll bet Hannibal would enjoy _him_ for lunch.  

Second, Chris has a way of "thinking out loud" so that when he says stuff like "you have an object falling from infinity" what he means is that gravitational fields extend out forever (technically) from a point roughly at the center of that mass. (The bigger the mass, the bigger the field). That is the (equal and opposite) force one must overcome when exiting Earth's gravitational field.  

Also, just as the "velocity" (in technical terms velocity includes a direction or "vector" as well as a speed.) increases as the square of the distance (9.83 meters/sec/sec) once again we are actually gaining in speed (when falling) which is called acceleration (as Newton discovered by dropping an apple on his head  ) Every second an object falls (ignoring air friction) it gains another 9.83 meters of speed. So, now, take that in reverse and try to fly up and away (No one has mentioned fortified helium balloons yet), and as the saying goes "the faster you go, the behind-er you get". 

Also, by the way, I rather liked Skeptical's example about the satellite:


> For example, a satellite in geostationary orbit, 36,000 kms up, will be moving sideways at 3 km per second. It is falling, but the sideways motion carries it further from the Earth, which exactly compensates for the fall.



Another way to look at that is like having a circular escalator that goes around the planet. For each drop toward Earth, you must then thrust away from the intersection of the circle that defines your orbit by the same amount so that you keep a constant altitude.

The question is, where is the end of the circle? And does anyone know how Einstein came to the conclusion that if one started at any random point in the universe and kept going forever, they would end up right where they started?

"The truth will come to you at last, when we are one and one is all."

- Some British rock group.


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## AE35Unit (Jul 29, 2009)

Gravity extends from the centre of an object FOREVER? There must be an awful lot of gravity up there!


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## chrispenycate (Jul 29, 2009)

Why should it stop? There's no way of making a Faraday shield against gravity or, as far as we know, reflecting it back. If it diminishes as the square of the distance, as seems fairly adequately proved, then it never reaches zero. 

The only possible (and unproven) exception I have seen for this is a black hole; if gravity propagates at the speed of light, to satisfy Bert E., then possibly some gravity can't radiate from a black hole, folded back in by itself. There's still plenty left, and doing the measurements to prove this sounds rather hazardous. And nobody has caught, or even mathematically proved the existence of a graviton, yet.



			
				Grandfaloon said:
			
		

> Chris has a way of "thinking out loud" so that when he says stuff like "you have an object falling from infinity" what he means is that gravitational fields extend out forever (technically) from a point roughly at the center of that mass.


 Politely saying that Chrispy spends a fair portion of his time totally incomprehensible, and requires a translator. Mathematicians have no problems with thought experiments that strip the atmosphere off the Earth and sand down mountains to get a millimetrically smooth surface ; physicists (and the inhabitants of the planet) are a bit less convinced whereas the engineers would prefer to cool the whole thing down to less than a degree Kelvin, so the solidified atmosphere will smooth out the surface…


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## AE35Unit (Jul 29, 2009)

See i always equate a gravitic field to be like a magnetic field. It has a definite influence but beyond a certain point it fades to nothing. Its finite.


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## Granfalloon (Jul 29, 2009)

Apologies Chris. No Harm meant by that statement (thinking out loud etc.) It's actually a compliment in disguise because I've read a lot of your posts, and I can see very well that you are impressively learned. Plus, I have the same tendency, and therefore tend to recognize it.


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## chrispenycate (Jul 29, 2009)

AE35Unit said:


> See i always equate a gravitic field to be like a magnetic field. It has a definite influence but beyond a certain point it fades to nothing. Its finite.



A magnetic generator has two poles (north, and south) which, at a sufficient distance, cancel each other out. If a magnetic monopole did exist, it would spread out just like gravity.

Similarly, electrostatic imbalance – an excess or deficiency of electrons – tends to even out over a fairly small distance, a light year or two, so that is self cancelling on a cosmic scale.

Gravity seems to just keep on going.

Still, they're worried that there isn't enough of it (or that they can't explain enough of it away) so they're inventing intangible, undetectable dark matter (with its own dark energy) to boost their theories…


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## AE35Unit (Jul 29, 2009)

Well i guess it makes sense. After all the sun is 93 million miles from us yet it influences us strongly. Plus it keeps the other planets travelling round and round in their orbits


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## Arwena (Sep 3, 2009)

To return to an old topic, I came upon an old _Discover _magazine(November 2007), which said: "1. Nearly every astronaut experiences some space sickness, caused by the wildly confusing information reaching their inner ears.  In addition to nausea, symptoms include headaches and trouble locating your own limbs.  Just like college, really.  2. And those are the least of your worries.  In weightlessness, fluids shift upwards, causing nasal congestion and a puffy face; bones lose calcium, forming kidney stones; and muscles atrophy, slowing the bowels and shrinking the heart."  I suppose you could still survive, though the puffy face seems the worst affliction.


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## Interference (Sep 3, 2009)

Definitely.  Lord save us all from The Puffy Face


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## Hilarious Joke (Sep 3, 2009)

Rofl!!!


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## Granfalloon (Sep 3, 2009)

Don't they have a cream for that? My wife has a closet full of facial creams. Surely _one_ of them must help with that. 

Don't forget that all of this can be overcome by creating artificial gravity. Just read a few of Arthur C. Clarke's Novels (2001, 2010, or Rendezvous with Rama) and you'll get very well written descriptions of artificial gravity. Here's one article about how they are approaching it these days:

SPACE.com -- Artificial Gravity: A New Spin on an Old Idea


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## Interference (Sep 3, 2009)

I think that's what's keeping long space missions in check for so long.  Until they come up with a cost-effective and efficient means of creating earth-like conditions in flight, we probably won't be going anywhere for a while.


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## Nik (Sep 3, 2009)

Um, was watching a program on history of ISS, when they showed a clip of SkyLab. There was ample volume in that for the crew to jog around the internal circumference, do somersaults etc...

(Wasn't spun, they just did 'wall of death' stuff... )

Okay, it was 'only' the 'repurposed' third stage of a Saturn or something, but it sure puts the ISS to shame...

Two issues here: Even with a Skylab-sized spun habitat for fractional g-alike *plus* several hours a 'day' of vigorous work-outs, there's still the issue of transit time. At the moment, any trip to eg Mars is at risk from solar storms. A hardened 'storm cellar' will help, but two or three 'ordinary' storms, or one 'whopper', will push the crew to the limit...

( They'd better carry spare bone-marrow, be blood-group exchange compatible. IIRC, there's been NO mention of this by NASA/ESA etc... )

Moon, Mars or asteroid, a base must be 'dug in' by several metres to shield a CME effectively. Having a Martian lava-tube handy could save the ground crew's life. Of course, the orbiting team could be fried...

Which is why, reluctantly, if you want to go out beyond low-orbit, you really, really need nuclear power. It shortens the transfer time, improving the odds. It hauls a fair radiation shield along 'for free'. It improves your chances many-fold...

---

One head-scratcher over gravity: Assuming it stays inverse-square over cosmological distances, doesn't go MOND where space/time is approx. flat...

IIRC, gravity as 'space warp' or 'gravitons' must still propagate at c-speed. But, over vast distances, everything moves meanwhile. Surely there's a vector offset ?? Even if gravitons are 'entangled' ?? I know there's a different, proven frame-dragging effect under high spin...

I'm thinking of the c+ illusion seen with some quasars due to their wobble swinging their polar emission like a searchlight beam...

My head hurts...


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## Interference (Sep 3, 2009)

Mine, too - now .... cheers, Nik


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## Arwena (Sep 4, 2009)

Artificial gravity.  Now there's an idea.  How do they do that in Star Trek???  Maybe the installation of a mini-black hole???


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## Interference (Sep 4, 2009)

Can something infinitely dense and infinitely small have a mini version of itself? I know what you're going to say.  Alan Titchmarsh's daughter, but that's not what I meant and you know it.


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## Parson (Sep 4, 2009)

Arwena said:


> Artificial gravity.  Now there's an idea.  How do they do that in Star Trek???  Maybe the installation of a mini-black hole???



Actually they suppose that the acceleration provides the effect of gravity. The problem they are dealing with is too much gravity and inertia. For that they have anti-gravity and inertial dampeners. But no mention of how this is done, simply because no one has the least clue.


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## Nik (Sep 4, 2009)

*Space-bending*

Um, in current theory, your mini black-hole can be any mass from atomic upwards. This is why those protestors were trying to get CERN to shut down the Big Ring...

As for using a modest black-hole to impart artificial gravity, it would have to mass the same as a fair sized asteroid or small planet. Hauling that around would be tricky. Of course, you may turn the idea on its head, use the black hole for propulsion and have that 'pull' the ship along with you and your fuel aboard...

IIRC, idea was very well explored by Charles Sheffield in his 'Engineer' series of short stories...
Hasty google...
McAndrew. Chronicles etc.

Um, hypothetically, if you can warp space to push/pull a spacecraft, local use to keep food on your plate and coffee in your mug seems reasonable...

In my 'Convention' tales, this trick is generally used to reduce local gravity so 'Spacers' may live on planet surface. Problem is you must have an array of 'poles' to approximate a 'level playing field'. Keeping them all happy, balanced and in tune could be problematic...

FWIW, I hand-waved such 'Poles' as 'Phased Arrays of Ambient Super-Conducting Distributed Tunnel Diodes'. Happens they're usually deposited on mono-isotopic diamond slabs about the size and weight as a large marble pastry-rolling block. By the time you add a labyrinthine cooling system and appropriate connections, mountings etc, you're talking suit-case size per. Given limited dissipation and to provide redundancy, you would run many in parallel to emulate 'mega-poles'. Then, you would 'phase' such groups as:

'One Pole, null-g.
 Three thrust, five fly,
 Earth, Moon and Mars,
 Nine go to the stars !'


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## Ursa major (Sep 4, 2009)

Parson said:


> Actually they suppose that the acceleration provides the effect of gravity. The problem they are dealing with is too much gravity and inertia. For that they have anti-gravity and inertial dampeners. But no mention of how this is done, simply because no one has the least clue.


 
The Chief Engineer knows more than enough about it. (So much so, that if the Enterprise's mechanism - whatever it is - is required to work well beyond its design parameters, it will take only a few hours for this to be arranged. Just like the warp drives, in fact.)


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## Granfalloon (Sep 8, 2009)

Arwena said:


> Artificial gravity.  Now there's an idea.  How do they do that in Star Trek???  Maybe the installation of a mini-black hole???



All I know is that it would never work properly without an ample supply of Di-Lithium Crystals. 

As the captain and the crew floated randomly about the bridge, Captain Kirk was heard to yell into his shirt button thingy, "Scotty, Scotty, what's wrong... with the ship?!!!" 

The reply came back -
"I doen't uenderstaand it Coaptan, the Di-Liethium crystols joost queet on mea sirr."


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## skeptical (Sep 15, 2009)

In Star Trek they talk of 'gravity plating'.   Sadly, today's physics has no way, even in theory, of achieving this.   The simplest method of achieving a gravity equivalent, for a trip to Mars for example, is to send two pods, tethered together, and spinning around their centre of mass.  

Personally, I like the idea of adding one more.   The centre mass contains the motors, fuel etc, and is at zero G.   Then, there are two other capsules on either side of the centre one, at the end of tubes.   The whole system is spinning with the outer living capsules having a gravity equivalent, and the centre capsule having none.  Astronauts live in the outer capsules, but can crawl down the joining tubes to check the engines, or to continue to the other living pod to have a beer with their buddies.

The point made earlier about radiation is valid.   In fact, normal background cosmic radiation is enough to cause a very high rate of cancer for any astronaut that might make a return trip to Mars.   On top of this, a solar flare may kill them outright.   However, the high risk will not, I predict, prevent people volunteering to go to Mars.  Unless we get a technological break through, putting shielding on a Mars craft would be too massy, making it impractical.


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## matt-browne-sfw (Sep 15, 2009)

Eventually go mad in space? Holodeck technology isn't so far away. Seriously. 3d-television, head-mounted displays, virtual reality... space psychologists should take this development into account.


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## Sparrow (Sep 15, 2009)

> The point made earlier about radiation is valid. In fact, normal background cosmic radiation is enough to cause a very high rate of cancer for any astronaut that might make a return trip to Mars. On top of this, a solar flare may kill them outright. However, the high risk will not, I predict, prevent people volunteering to go to Mars. Unless we get a technological break through, putting shielding on a Mars craft would be too massy, making it impractical.




Radiation, and Cosmic Radiation in particular do more than just cause cancers in humans, it mutates and kills neural stem cells.  The worry is that astronauts will lose mental capacity on a long space journey.
They might even go insane...

Just look at the before and after photos of NASA Astronaut Lisa Nowak...
http://www.denverpost.com/sitemap/ci_5167528

... and that was after just one week in space.


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## skeptical (Sep 16, 2009)

Sparrow.
Very funny!

Radiation is a real problem, and will cause harm to long term astronauts.   However, that will not be enought to prevent people going to Mars.

Of course, any Mars colony will have to be underground.   It takes about 10 metres of dirt overhead to cut radiation on Mars down to Earth normal levels.

My own view is that, long term, we will need to genetically engineer people to be more radiation tolerant.  Genes for more effective DNA repair have been identified in animals and bacteria that are much more radiation tolerant than we are.  Suitable gene insertion should be able to create a radiation tolerant _Homo sapiens._

Perhaps in 100 years or so, people will be less irrational about the idea of improving our species genetically.  Tolerance to higher radiation will benefit everyone, since it will also confer greater resistance to cancer.


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## Sparrow (Sep 16, 2009)

In the distant future I wouldn't be surprised if they bioengineer astronauts and perhaps even have a decades long breeding program for men and women tailor made for deep space missions.  That's another thing NASA never talks about.  Just try to get funding passed for experiments in genetic tinkering for the purposes of altering God's Creation.

As it stands now, we can hardly have proper stem cell research without a hullabaloo from certain religious groups.


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