What technology is most likely to take us to the stars??

[aeroeng314]

Whats wrong with journey times of days?

The fact that the journey on a space elevator takes you through the Van Allen radiation belts. Sure the Apollo Astronauts survived it without much trouble, but they were moving at several km/s and did not spend much time there. If we ever do build a space elevator (and we most likely won't, there are much cheaper--though the cost of such EPoUS*es will still be large--alternatives that are possible with current technology) it'll likely only be suitable for cargo since carting up heavy radiation shielding would be wasteful.

Another alternative is to use a space elevator on the moon descending towards Earth through the Earth-Moon L1 point. It would certainly make getting to the moon less costly (since the elevator would extend well past the L1 point) and the structural requirements on the cables are a lot less strict. The moon has no radiation belts and also there's not nearly as much orbital debris (an Earth-based elevator would constantly have to move its base to avoid LEO satellites; there's a lot of them).

 

[JacobEvans]

In my opinion, we need to understand more about the universe that we'd be sailing around in before we head out.

Also, we don't need to go faster than c to feasibly visit some stars. I think the closest star to our own is only 4ly's away, though still a long ways away, THAT would be our first step.

 

[AntiSkill42]

There was the idea of BOOOM BOOOM drive. Take stak of nukes, blow them up behind huge shield, and let the detonation push you forward.
Not very likely to happen but kind of fun...

Problem is surely if we can somehow travel faster than light.
If we can't we're buggered. Multi-generation ships? With humans on them???
-By the time the second generation starts rebelling the whole thing is doomed...

Suspended animation is a interesting possibility. Espacially when this kind of stasis puts your age on "hold".
Then you could divide a crew into 4-5 groups, let one group run the ship -4 groups go into stasis. And then switch every 3 months.

This way crew members would reach a far longer life-span and they might see a new star when they've become too old to reproduce and settle it...

 

[Grimlock]

The fact that the journey on a space elevator takes you through the Van Allen radiation belts. Sure the Apollo Astronauts survived it without much trouble, but they were moving at several km/s and did not spend much time there. If we ever do build a space elevator (and we most likely won't, there are much cheaper--though the cost of such EPoUS*es will still be large--alternatives that are possible with current technology) it'll likely only be suitable for cargo since carting up heavy radiation shielding would be wasteful.

The Van Allen belt isn,´t all THAT dangerous, not to say it should be taken lightly, on no account should ANY kind of radiation that might be harmful to us humans ever be taken lightly.
However the guy the belt is named after said himself that unless you walked around in it unprotected or about a month with the protection the Apollo astronauts had. you wouldn,´t be in any immediate danger from it.

If a space Elevator were to be build (again i think its quite possible that it will) you can bet your ass that it won,´t be unprotected against the radiation out there.

Anyways back on the first topic Generation ships or suspended animation is a possibility, but as i pointed out earlier the problem with such ships is the shear amount of time it will take to reach the other stars.
Yes the ship might be accelerated by solar/laser sails up to the speed of light, but its still 4 years and thats just to the nearest star.

The problem with such colonies is that they would pretty much be on their own, if things go wrong out there they,´re pretty screwed if they can,´t fix it.

I would still say that Warp travel is the most likely way as it would allow us to get to a location fast enough for our colonist to be able to assist.

 

[nasher168]

You have to take into account the experience of the people back home. It would really suck if your friend or child was going into space at the speed of light, and they would never return until you were either really old or dead for thousands of years. You have no communication, no anything. They might as well have died.

 

[aeroeng314]

The Van Allen belt isn,´t all THAT dangerous

My point was mostly that it's an unnecessary risk. There's a lot of legal issues that arise when you intend to subject people to doses of radiation. I just don't think a space elevator on Earth is a good idea. Yeah, it's fun to imagine standing on a boat out in the Pacific ocean where you can see a cable sticking up just beyond the horizon that goes up into the sky with no top, but I just can't see this as being practical. Other things you could do would be mini space elevators that don't connect to the surface, but rather have bottoms at sub-orbital velocity to reduce the requirements of launch vehicles. Another possibility is to have rotating cables whose bottoms are again moving at a sub-orbital velocity (though this time by virtue of their rotation).

Yet another possibility is to build a levitating maglev track. Levitation would be accomplished by having a moving cable magnetically confined within the track. This cable would be moving at a velocity greater than the escape velocity. The extra force required to keep it from escaping would be supplied by the weight of the track. The track itself could be 80-100 km up if you wanted it to be and you could launch vehicles from there. This structure would really only be suitable for very high demand space-flight, though, since it requires a constant power input to keep itself from falling down (the advantage is it can reach ridiculously high launch rates limited only by magnetic heating in the moving cable).

My point is, there are a lot of other things we could do that would avoid these problems.

 

[JacobEvans]

Either way we went.... we'd be forever separated from Earth by time and space.

Does anyone here believe we could do some intergalactic travelin'?

 

[Icefire9atla]

Does anyone here believe we could do some intergalactic travelin'?

Technically, we might be able to go to the Large and Small Megellanic clouds, and Adromeda once it gets close enough.

But really, without going around a million times the speed of light, I don't think that it is feasable.

 

[Ozymandyus]

I'm of the opinion that anything is possible with enough technology. Even if we are never able to go faster than the speed of light, we will undoubtedly be able to get to another galaxy, given a billion years. A ship on autopilot at 90% lightspeed or whatever for a few million years with a bunch of embryos in stasis could set up a colony and then grow up the embryos when it was ready for them.

Such technology is within reach well within a thousand years. All you really need is a well designed computer and a good energy supply, whether through starlight or needing to recharge near various suns or fusion technology. Once you build it theres very little that would stop it, if you made it sturdy and able to avoid space objects and such.

 

[JacobEvans]

Either way, I'm bummed we'll never live to see it

 

[Chirios]

Can't remember where I read it, but I read somewhere that mathematically the stargate version of a wormhole is actually pretty accurate, that due to solving relativity the time elapsed from travel would be equal for those travelling through the wormhole, and those not.

 

[Netheralian]

Spaceelevators <sic> ... I just can't see this as being practical.

Interesting start before making the following claims...

Other things you could do would be mini space elevators that don't connect to the surface, but rather have bottoms at sub-orbital velocity to reduce the requirements of launch vehicles.

If they don't connect to the surface then what is the point? Trying to reach a cable that has zero velocity wrt the inertial reference frame of the earth would actually be harder to reach - not easier. And also your whole objection to a space elevator was Van allen radiation which goes up to 10,000km. So You would have to fly straight up of 10,000 kms and have zero velocity at the top - its easier to go orbital. All you are suggesting is a space station made of a cable.

Another possibility is to have rotating cables whose bottoms are again moving at a sub-orbital velocity (though this time by virtue of their rotation).

How is that going to work. It would not be stable. You would end up with a oscillation in the cable each time it was tangential to the earth. Either that or you need to rotate it really quickly in which case you will just make it harder to dock and increase the stress in the cable - making it even more difficult to build.

Yet another possibility is to build a levitating maglev track. Levitation would be accomplished by having a moving cable magnetically confined within the track. This cable would be moving at a velocity greater than the escape velocity. The extra force required to keep it from escaping would be supplied by the weight of the track. The track itself could be 80-100 km up if you wanted it to be and you could launch vehicles from there. This structure would really only be suitable for very high demand space-flight, though, since it requires a constant power input to keep itself from falling down (the advantage is it can reach ridiculously high launch rates limited only by magnetic heating in the moving cable).

I'm losing confidence that you are an aerospace engineer as you name implies. This looks like pseudo science to me... How did you get it up there? You seem to have build a magic levitation device (why would we even need a space elevator if you could levitate everything - you wouldn't need any launch capability beyond your levitator...)

My point is, there are a lot of other things we could do that would avoid these problems.

So you've invented your own realm of science to avoid some radiation and materials problems with space elevators. Interesting approach.

 

[Desty]

There was the idea of BOOOM BOOOM drive. Take stak of nukes, blow them up behind huge shield, and let the detonation push you forward.
Not very likely to happen but kind of fun...

Actually, that's a great option, and a great way to make use of that pile of crap. The Medusa and Orion projects I think.
I actually produced a 34 pages homework last year on interstellar propulsion. I'm gonna look through my files and post some infos if I find it. I checked and calculated for fuel, ion, fission, fusion, anti-matter and solar / magnetic sails. They really all got their pros and cons, which makes them all fundamentaly useful. But if you want to go interstellar, you can reach the closest star in a couple generations with a controlled continuous fusion reaction (and start breaking midway).

Its quite a fascinating subject actually, especially the maths. There's plenty of info scattered on wikipedia if you search for "rocket propulsion".

 

[aeroeng314]

If they don't connect to the surface then what is the point? Trying to reach a cable that has zero velocity wrt the inertial reference frame of the earth would actually be harder to reach - not easier. And also your whole objection to a space elevator was Van allen radiation which goes up to 10,000km. So You would have to fly straight up of 10,000 kms and have zero velocity at the top - its easier to go orbital. All you are suggesting is a space station made of a cable.

There are many velocities less than orbital velocity that are also bigger than 0. I never said the bottom of the cable would not be moving at 0 velocity w.r.t. the ground. I said it would be moving at a sub-orbital velocity. This reduces the propellant requirements of conventional rockets since now they don't have to actually reach orbital velocity. Yes, it would essentially be a space station that's a cable. You could have a short elevator which could transfer payload delivered by conventional rockets to the other end. Yes, in order to get a significant decrease in the velocity of the bottom of the cable (which would likely only be 200 km in altitude, I don't know why you assumed it'd be above the inner radiation belt; that'd be stupid) a large portion of the cable would have to reside in the inner belt. The reason this approach is better than a full space elevator is because the structural and material requirements are actually realistic. Building a space elevator not only requires that you find a material strong enough to support itself over that length, but that you also get all the necessary materials into orbit in the first place.

How is that going to work. It would not be stable. You would end up with a oscillation in the cable each time it was tangential to the earth. Either that or you need to rotate it really quickly in which case you will just make it harder to dock and increase the stress in the cable - making it even more difficult to build.

Still easier and less expensive than building an actual space elevator. I haven't examined anything about instabilities in the cable. Could you elaborate on this some more? For instance, how fast would the cable have to rotate if it were, say, 400 km long? Would there be a problem if the cable was made more rigid (there's no reason for it to be flexible anyway).

I'm losing confidence that you are an aerospace engineer as you name implies. This looks like pseudo science to me... How did you get it up there? You seem to have build a magic levitation device (why would we even need a space elevator if you could levitate everything - you wouldn't need any launch capability beyond your levitator...)

I apologize for not going into much detail here. The cable is magnetically held within a protective sheath (which would also maintain at least a partial vacuum inside). This whole structure starts out on the ground. The structure itself is a large loop with a base station at each end. The base stations are responsible for turning the cable around and sending it back in the direction it came from. The base stations also deflect the cable upwards. As this is being constructed the cable is spun up to a high velocity on the order of 12 km/s. Since this cable is traveling at greater than orbital (and even escape) velocity, the force of gravity on the cable alone would be insufficient to keep the cable from escaping into space. By this mechanism the cable and sheath can essentially levitate. The magnets have nothing to do with the levitation itself and I'm sorry if I made it sound that way. They are only used for containment of the cable within the sheath. The levitation works by centrifugal force. The moving cable appears to exert a force upwards. I also neglected to mention that there would be cables attaching this structure to the ground to help stabilize it. If anything is still unclear, please let me know.

So you've invented your own realm of science to avoid some radiation and materials problems with space elevators. Interesting approach.

I did no such thing. The mistake I did make was not provided enough information to prevent you from misinterpreting what I said. I feel it's also important that I point out that I never stated that any of these things would be easy or cheap. I only asserted that they would be easier or cheaper than a space elevator which, to be honest, isn't really saying much.

 

[Netheralian]

Still easier and less expensive than building an actual space elevator. I haven't examined anything about instabilities in the cable. Could you elaborate on this some more? For instance, how fast would the cable have to rotate if it were, say, 400 km long? Would there be a problem if the cable was made more rigid (there's no reason for it to be flexible anyway).

You would never get something 400km long to be very rigid - it will be inherently flexible as it will have a low moment of inertia around your principle axis wrt to its length. What would you even want to do with this? Its pretty limited... OK, maybe you have a non orbit velocity to attach to the cable (which would be very difficult to dock with too due to its rotation (i.e. non zero relative velocity to your spacecraft - additional complexity) but then what are you going to do? You can't use it for much as it is in a pretty specific orbit - and it would have to be in orbit which means you couldn't use it to put anything else into different orbits (particularly polar which most spacecraft are). It would have to be in a equatorial orbit with the rotation of the cable such that the drag on the lower end of the cable wasn't causing you any problems. You can't actually do a lot with equatorial orbits (unless you want pictures of the equator). I don't think you are proposing anything simpler here - its could actually be more complex and a whole lot less useful.

The cable is magnetically held within a protective sheath (which would also maintain at least a partial vacuum inside). This whole structure starts out on the ground. The structure itself is a large loop with a base station at each end. The base stations are responsible for turning the cable around and sending it back in the direction it came from. The base stations also deflect the cable upwards. As this is being constructed the cable is spun up to a high velocity on the order of 12 km/s.

How are you possibly going to achieve a cable at 12km/s that is completely frictionless that is inside something and is very long? Especially when you are deflecting cables - i'm not really sure what you mean here still.

Since this cable is traveling at greater than orbital (and even escape) velocity, the force of gravity on the cable alone would be insufficient to keep the cable from escaping into space.

How? The cables centre of mass is stationary wrt the earth - its not at escape velocity at all. You said it was a loop. You have to get the loop centre of mass to orbital velocity, not just its rotational velocity. It just outright won't work...

By this mechanism the cable and sheath can essentially levitate. The magnets have nothing to do with the levitation itself and I'm sorry if I made it sound that way. They are only used for containment of the cable within the sheath. The levitation works by centrifugal force. The moving cable appears to exert a force upwards. I also neglected to mention that there would be cables attaching this structure to the ground to help stabilize it. If anything is still unclear, please let me know.

I think I see what you are trying to get at - you have a big lasso spinning (with its axis perpendicular to the gravity vector) which you use to keep the whole thing up in the air. Is that right? And you can tell me this is less complex than a space elevator? I think you need to rethink this... The energy requirements alone would be phenomenal - you want to keep a massively long (and heavy) cable moving at 12km/s in a 100% frictionless environment. I think you have gone at least an order of magnitude more complex than a space elevator here - probably more. And for what? To get an 80km or so advantage on the earths atmosphere? Thats small change in terms of achieving orbital velocities. And once again you would be stuck to very specific orbits (i.e. only the direction this thing is pointing) as you couldn't possibly move it once it was rotating due to the gyroscopic forces. I think you can pretty much forget it...

 

[aeroeng314]

You would never get something 400km long to be very rigid

You're right, you couldn't. But you can make it a lot less flexible than a cable. What I wanted to know is what effect this would have on the instabilities. You also didn't answer my questions.

OK, maybe you have a non orbit velocity to attach to the cable (which would be very difficult to dock with too due to its rotation (i.e. non zero relative velocity to your spacecraft - additional complexity)

Why are you assuming that the spacecraft isn't traveling at a similar speed to the bottom of the structure? Yes, docking is non-trivial, however there isn't actually a need for an accurate impact docking mechanism. Since the entire structure is rotating, there will be an apparent acceleration at the end points (if the entire thing is 400 km long and rotating such that the ends are moving at 1 km/s w.r.t. the CoM, there's an acceleration of about half a G). I'm not sure I understand your point about the relative velocity. The spacecraft isn't moving at an orbital velocity. You'd send the spacecraft up so that it was going at the same relative velocity.

(particularly polar which most spacecraft are)

I have a really hard time believing that most spacecraft are in polar orbits. If I had to guess I'd wager that most satellites are in geostationary orbits which are equatorial.

It would have to be in a equatorial orbit

Not necessarily, but putting it in another orbit does severely limit launch windows and usefulness, so you're mostly right that it would have to be equatorial (there's just no physical requirement that they need be).

What's funny is your whole argument about equatorial orbits not being useful also applies equally to a space elevator. You're definitely not going to have polar space elevators. So this structure isn't really any less useful than a space elevator like you claim.

You have to get the loop centre of mass to orbital velocity, not just its rotational velocity.

No you don't. If that were true then rotation space stations wouldn't be a way to produce artificial gravity.

How are you possibly going to achieve a cable at 12km/s that is completely frictionless that is inside something and is very long? Especially when you are deflecting cables - i'm not really sure what you mean here still.

I neglected to mention that the cable is actually a ribbon made of iron about 1 cm thick, 5 cm wide and 4000 km long which weighs about 16000 metric tons. The entire motion of this ribbon is controlled magnetically. The ribbon is also not really continuously connected. There are joints located about 1 meter apart to allow the expansion of the ribbon (since it won't be moving at a uniform velocity).

I think I see what you are trying to get at - you have a big lasso spinning (with its axis perpendicular to the gravity vector) which you use to keep the whole thing up in the air.

I don't think I've sufficiently described the shape. Imagine it's less like a circle/lasso and more like the shape a rubber band makes when you stretch it between your fingers. The majority of the loop is traveling parallel to itself (though in opposite directions). The base stations at the two ends are responsible for deflecting the cable in two ways. One way is to turn the cable around 180 degrees and send it back in the other direction. The other way is to deflect the incoming cable so that it is parallel to the ground and, after turning it around, deflect it back upwards away from the ground.

With a 300 MW power input, the spin-up would take about 60 days. Once it's running it would take about 200 MW to keep it running without launching anything.

To get an 80km or so advantage on the earths atmosphere?

More than just the altitude. Launches would have vehicles induce eddy currents in the iron ribbon which induces a magnetic "drag" force between the ribbon and the vehicle (same principle used in magnetic braking systems on amusement park rides). Since the ribbon is moving at 12 km/s the vehicles will be accelerated up to orbital velocity. No rockets needed until apogee (to circularize the orbit). The launching process does rob the ribbon of some kinetic energy and heats it up. The kinetic energy is restored by linear induction motors (which are compensating for other drag losses anyway).

In order to get a cost benefit out of building this, you'd need to have a pretty high demand for space launch, otherwise you're just wasting 200 MW.

And once again you would be stuck to very specific orbits (i.e. only the direction this thing is pointing) as you couldn't possibly move it once it was rotating due to the gyroscopic forces. I think you can pretty much forget it...

Yeah, the thing won't move once it's going, but then neither does a space elevator. Sure, in that case you might be able to get limited motion at the base, but that really doesn't affect your orbit choices. The advantage of something like this is that you don't have to build it at the equator anymore. You could build more than one at different latitudes to achieve different orbit inclinations.

Now, I have a few questions for you about the space elevator.

How much do you think the whole thing would weigh? I'll even let you assume a futuristic material we don't have yet.
What are the electrical properties of this material and how does the magnetic field affect it?
How much would it cost to get all of those materials into geostationary orbit?
How difficult would it be to build an on-orbit manufacturing facility to take the raw materials and construct the cable?
How difficult would it be to move the cable around as it descends to make sure nothing runs into it?
What kind of power transmission system exists for the climbers?
How long does it take for the climbers to reach geostationary altitude?
If this is a long time, what if a climber breaks down somewhere in the middle?
How does the cable move to keep satellites in LEO from running into it?
What kind of impact does particulate space debris have on the cable's integrity?

 

[Netheralian]

What I wanted to know is what effect this would have on the instabilities. You also didn't answer my questions.

A lot - a 400 km long structure is essentially a cable - either that or it is HUGE. You also have a major drag problem - that will make this thing wobble around everywhere and eventually probably destroy itself. Maybe this could be controlled...

Why are you assuming that the spacecraft isn't traveling at a similar speed to the bottom of the structure? ... Since the entire structure is rotating, there will be an apparent acceleration at the end points ... acceleration of about half a G

This is exceedingly non-trival. Not only do you have an apparent acceleration at the end points of the cable, you are also sitting in a very near 1G environment from the earth...

I have a really hard time believing that most spacecraft are in polar orbits. If I had to guess I'd wager that most satellites are in geostationary orbits which are equatorial.

From wikipedia (http://en.wikipedia.org/wiki/Low_Earth_orbit#Human_use) "While a majority of artificial satellites are placed in LEO "

And you can't really do anything from LEO equatorial so most of these are polar (or near polar)

It would have to be in a equatorial orbit

Why i said this was that if you have a rotating space station that is hundreds of kms long that is in a LEO orbit then you have a major drag issue on one part of the extension. Actually you have a major drag issue anyway which you will have to use a shitload of fuel to keep your station there anyway. But I went for equatorial with the rotation such that the relative velocity in the lower section of the station is low hence minimising drag which could induce oscillations in your cable... Or you could alternatively use more thrusters (and more fuel).

What's funny is your whole argument about equatorial orbits not being useful also applies equally to a space elevator. You're definitely not going to have polar space elevators. So this structure isn't really any less useful than a space elevator like you claim.

Actually no - you can easily come off a space elevator and with minimum fuel move into a polar (or any) orbit because you can get most of your energy from dropping from a higher point on the cable. Whereas your problem is you can only spin in 1 direction and hence only go in 1 direction.

I neglected to mention that the cable is actually a ribbon made of iron about 1 cm thick, 5 cm wide and 4000 km long which weighs about 16000 metric tons. The entire motion of this ribbon is controlled magnetically. The ribbon is also not really continuously connected. There are joints located about 1 meter apart to allow the expansion of the ribbon (since it won't be moving at a uniform velocity).

... The majority of the loop is traveling parallel to itself (though in opposite directions). The base stations at the two ends are responsible for deflecting the cable in two ways. One way is to turn the cable around 180 degrees and send it back in the other direction. The other way is to deflect the incoming cable so that it is parallel to the ground and, after turning it around, deflect it back upwards away from the ground.

16,000 tonnes - moving at 12 km/s? With a right angle turn half way - it would destroy itself at your bend. You would also not be able to contain this ribbon with magnetic bearings - the inertial of any section of the cable would be enormous. It would not survive. I don't even have to do any calculations to know it wouldn't survive... Not bothering with the rest for that reason.

You could build more than one at different latitudes to achieve different orbit inclinations.

Actually you would have to build one for almost evey different orbit inclination - depending on your purpose there are a lot.

How much do you think the whole thing would weigh? I'll even let you assume a futuristic material we don't have yet. ...etc

I'm not really going to go into this because there is lots of research now being done on space elevators including research money from NASA. It is a serious effort with a lot of good engineers working on the concept and therefore there isn't any need for me to spend a hours justifying a space elevator to a discussion group. There are plenty of websites around if you care to do some research yourself. Perhaps start with Wikipedia. There is even an anual conference. And we do have a material - at least theoretically. I'm pretty sure it was the invention of Carbon Nano tubes and their theoretical strength that made the project at least partially feasible and hence kicked off the work. Clearly there are no major show stoppers or this would have halted years ago...

Didn't realise this was on Wikipedia (just found it) - estimated capital cost of space elevator as of 2004 was $6.2 billion US. See - http://en.wikipedia.org/wiki/Space_elevator_economics. However some costs go up to $40B but includes 100% contingency. There are design differences between the two costings...

 

[Sam]

I'm picking a synthetic planet build around a fusion reactor.

 

[Pulsar]

Forget about that space elevator stuff, I've found the ultimate solution:

a giant, helium-filled, inflatable tower.

:shock: :shock: :shock:

What drugs were they on when they came up with that???

 

[AntiSkill42]

Maybe on helium.

The idea itself sounds far more workable than a rigid cable elevator of some sort.

A flexible structure, self-lifting nice idea. But the article states that it would be possible to build this with todays technology -I don't think so- and denies that there are nano tubes. Well of course these tubes are expensive but they are availabel.


Are there any calculations if such a long... kind of lever... would affect earths trajectory?