Space Elevator

[roy10]

I may be particulaly dense here but surely the elevator concept using carbon nonotubes is an obvious candidate for a linear motor to propel everything into space? <br />I read about motors to lift cargos but nothing about a linear motor drive. <br />Am I misreading the whole concept?? <br />

 

[nacnud]

No you haven't misread the whole concept but I suspect that a linear motor would be too heavy. The most belivable concept I have come across uses a ground based laser to power an electic motor on the elevator car via photovoltic cells. <br /><br />See ISR for more details.

 

[grooble]

Its better just to build space cannons, the tech already exists and is cheap. You could put 100s of tons into orbit for $'s

 

[nacnud]

Looking at the new constellation architectures for the CEV I'm beginning to think that there would be a good case for building a cannon launch capability.<br /><br />The most interesting designs for the CEV involve refuelling in space but the cost of the propellant is exorbitant making these proposals expensive in the short term compared to single use schemes. Propellant is one of the few things that can survive the acceleration of a gun launch method. I can't se the investment being made in the short term but if I was tasked to look at the CEV development gun launch might become attractive for fuelling Mars expeditions or a permanent moon base.<br />

 

[grooble]

Just pile a load of that firepaste on top of it, it'll be ok <img src="/images/icons/laugh.gif" />

 

[igorsboss]

Cannons and electric railguns were discussed here at SDC shortly before the great forgetting. Here are some reasonable conclusions from that discussion...<br /><br />1) Orbital mechanics says you can't put an object into an orbital trajectory using a cannon alone. The projectile must carry a thruster along with it to correct the trajectory during the flight.<br /><br />2) Cannons are better than electric railguns because it is easier to store and release the requsite energy chemically than electrically.<br /><br />3) Projectiles (from cannons or electric railguns) suffer extreme g-loads as they exit the cannon and encounter the surrounding atmosphere. These loads are so extreme that almost all kinds of cargo (especially humans) would be severely damaged during the first 100 meters or so of the flight.<br /><br />4) It might be feasable to launch small rocket-assisted projectiles from a cannon, designed to carry water ice into orbit. Once in orbit, the water can be converted into H2 and O2 for life support, power storage, and thrust.

 

[nexium]

I agee: To send stuff from Earth's surface to Mars requires a muzzle velosity of about 40,000 miles per hour. This speed even at 29000 feet will vaporize all known materials due to atmosperheic friction heat. Neil

 

[nexium]

<br />~There are a few important difference between this info from NASA(sorta) and from www.liftport.com which I posted about 3 months ago~ <br />The Space Elevator is a thin ribbon, with a cross-section area roughly half that of a pencil, extending from a ship-borne anchor to a counterweight well beyond geo-synchronous orbit. <br />The ribbon is kept taut due to the rotation of the earth (and that of the counterweight around the earth). At its bottom, it pulls up on the anchor with a force of about 20 tons. <br />Electric vehicles, called climbers, ascend the ribbon using electricity generated by solar panels and a ground based booster light beam. <br />In addition to lifting payloads from earth to orbit, the elevator can also release them directly into lunar-injection or earth-escape trajectories. <br />The baseline system weighs about 1500 tons (including counterweight) and can carry up to 15 ton payloads, easily one per day. <br />The ribbon is 62,000 miles long, about 3 feet wide, and is thinner than a sheet of paper. It is made out of a carbon nanotube composite material. <br />The climbers travel at a steady 200 kilometers per hour (120 MPH), do not undergo accelerations and vibrations, can carry large and fragile payloads, and have no propellant stored onboard. <br />Orbital debris are avoided by moving the anchor ship, and the ribbon itself is made resilient to local space debris damage. <br />The elevator can increase its own payload capacity by adding ribbon layers to itself. There is no limit on how large a Space Elevator can be! <br /><br /><br /><br />Frequently Asked Questions <br />Science Fiction or Science Fact? <br />The Space Elevator was first proposed in the 1960's by a Russian engineer (Yuri Artsutanov) as a far-reaching engineering concept. The scientific principles underlying it are well understood and do not require any fictional inventions, except for the super-strong material required for its construct

 

[xfactor]

Whew, long read.<br /><br />I've actually read up on a project like this in Popular Mechanics (maybe its the same?). I'm not especially educated as to the topic of nanotechnology, but I do know the basics of it. It's supposedly a very effective method of producing extremely strong composites and alloys by creating "strings" of atoms on the molecular level.<br /><br />One thing to consider though: gravity is omnipresent in the universe (that we know of, in theory). Even if humans were able to produce an extremely strong "nano-ribbon", once it's put into orbit, it would not only be affected by the gravity of the Earth and the Moon but also by the Sun as well as the other planets of our solar system. The proxigean spring tide is a perfect example if this: when the Moon and Sun are aligned, the gravitational influence on the Earth is extremely strong when compared to the normal gravitational influences Earth succumbs to. Imagine a object in space being affected by such a pull...<br /><br />Result: $200 billion worth of tech sucked into outer space and 6 billion very pissed off people.

 

[chic_y]

Reality Intrudes:<br />Dr. Brad Edwards appears to conveniently ignore the energy that is needed to increase the orbital speed of the elevator and its 'payload' as it is placed into ever larger circles above the Earth while climbing. The westward deflection on the ribbon will mostly add to the now vectored pull on the Earth anchor point in the early portion of the climb - but will gradually transfer that vectored westward pull to the ribbon's top anchor mass.<br /><br />Unless rockets are attached to the elevator to provide the forces required to increase the elevator's orbital speed as the radius of its rotation around the Earth is increased, this ribbon defection from true vertical will continue to increase - as will the westward movement of that anchor mass, as it is also pulled into a somewhat lower orbit.<br /><br />If this were to be only a "sightseeing trip" up and back down (no mass off-loaded) one could argue that the return to Earth trip would restore the energy taken from that anchoring mass at the top of the ribbon - and its former position due to the centrifugal pull on the ribbon - providing that the ribbon stays intact.<br /><br />However, this is not the claimed purpose of this space elevator; not even when I first challenged NASA on this concept in September 2000. The laws of Physics and those of orbital mechanics have not changed.<br /><br />I continue to challenge this, also, in an ongoing blog on Elevator2010.

 

[nexium]

Hi chic_y: The usual explanation is the Earth is pulling on the tether with about 15 tons average. This causes the ribbon to slowly move back to vertical after each launch. The Earth rotation is slowed to provide the energy. I agree this seems suspicious, but can you picture the ribbon tilted far from vertical, if rockets are not used to counteract cummulative West movement?<br />Perhaps you are thinking of a ribbon that is not anchored at Earth's surface. If so, I agree it will drift to the West with each launch, unless the energy is replaced.<br />Can I add my comments to Elevator 2010? If so, What is the Web address? Neil

 

[nexium]

Hi Xfactor: Net gravity is hundreds of times weaker at an altitude of 100,000 kilometers, but the changes can be calculated and compensated for. ie the pull on the anchor point is calculated to increase by 20 extra tons, so we launch a twenty ton climber, which decreases the tension short term by 20 tons. Neil

 

[rocketman5000]

a simple expirement to convince yourself could be to tie a tennis ball to a string and swing it around and allow a washer to slowly slid out the string when it gets to the end it should stop deflecting the string and the string should return to perpindicular to the axis of rotation

 

[chic_y]

Consider the string to be attached to a a point next to the rim of a constantly rotating several ton flywheel (to represent the Earth) with a photcell triggering beam of light interrupter at that same point and the flywheel turning just Just fast enoughto keep the string radially almost straight out from axle center. The photocell would then trigger a strobe flash at that same point in rotation every time around - in a nearly dark room. Your Tennis ball at the end of your string would appear at a constant point in the rotation of that assembly - until that metal washer was released to slide out along that string due to centrifugal force. By the time the washer reached the Tennis ball the ball would have retrograded a few degrees as the result of contributing tangential energy to that washer as it neared the Tennis ball. <br /><br />This would be far more apparent if conducted in the vacuum of space - without the constant lagging of the Tennis ball due to overcomming air resistance during every portion of these revolutions. In space the vectoring of the string would therefor be obvious in the absence of that caused by the air resistance in the above illustration.<br />Chic

 

[mcbethcg]

The outward tension away from the axis of rotation would constantly straighten it back out. The string is "hanging" away from the earth.<br /><br />Look at the opposite situation. At the top of a tall building, we travel slightly faster than we do at the bottom, because we are farther from the earths axis of rotation. If you dangle a string a thousand feet down down from the empire state building, and lowered weights on it, the string would still hang straight down, even though the weights had more velocity at the top of the tower.

 

[chic_y]

Kinetic Energy can be transferred between masses, changed into another form (electricity, light, heat, etc.) and/or absorbed in the process of crushing something - but it does not just disappear - nor just appear. Also, transferring energy only to Gravity, by itself, in space, is not yet proven - at least to my knowledge.<br /><br />The postulated 1000 ft long string from that high up on the Empire State - and then a weight traveling down that string creates and interesting and energized pendulum that would, due to frictional losses of both the string and the weight moving in a hypothetical entirely still air mass, eventually come to rest directly below the above 'standoff' (presumed) string support.<br /><br />The greater vectored tangential speed of the descending weight would, of course, provide the energy for this pendulum motion creation - if the string were not to be anchored at the bottom, also, to thus absorb that energy.<br /><br />Holding such a string out from such a building and lowering it would prove nothing. But without such a solid standoff from a well anchored mass such as that Empire State building at the top end of that string - it too - would be tangentially deflected somewhat, at the beginning, as the weight descended.<br /><br />chic_y

 

[mcbethcg]

No one said the energy would dissappear.<br /><br />In the case of the string going down, the sidewise tendency of the string would transfer energy, through the string sidewise, that would minutely, immeasurably speed up the earth. In the case of an outward moving weight on a space elevator, the opposite is true.<br /><br />This is so obvious to me it freaks me out that you see it differently.

 

[chic_y]

Please, do not try to convince us that any pendulum, once however energized, cannot swing past dead center because by then it will have transferred all of its energy (through its pivot point support structure) to the Earth in those tiny, unmeasurable amounts (...or to Gravity).<br /><br />It is indeed truly unfortunate that - in this age of rapidly increasing Virtual Reality - anyone can be actually freaked out by the real thing (actual reality).<br /><br />Chic

 

[l3p3r]

the force of tension from the mass past geostationary orbit would indeed straighten out the tether over time, but I expect it will take quite a long time-<br /><br />oh i see now... pendulum motion ... no air!!! <img src="/images/icons/smile.gif" /> <br />ok<br />so launch the next payload when the swing is leading the earths rotation, to counter the effects of the previous climb, and so on... sensible?<br /> <div class="Discussion_UserSignature"> </div>

 

[mlorrey]

Actually, you could do it with kevlar, but it would have a hellacious taper. <br /><br />A kevlar tether for the moon would be pretty effective, both in ferrying mass quantities of materials up from the moon (without having to build a big mass driver or wasting precious lunar water on fuel production) for orbital construction, but also to conduct power from L1 solar sats to the lunar surface.<br /><br />Just because something is not possible now does not make it scifi. Most SF is little more than fantasy with technical jargon. The fact is that carbon nanotubes exist, are in production, the technology is advancing, and there are no reasons why long CNT tethers should not be possible.<br /><br />The last segment of a tether that is built is that going from LEO to the surface. By that time, the cost of putting things in GEO will become as cheap as a suborbital launch, so the cost of putting satellites in LEO will be more expensive than a suborbital hop to the low end of the tether and a ride to GEO. Because of this, there will be no market for LEO sats, other than to pay for space junk collectors, and satellite companies will be able to deorbit their LEO sats as their GEO replacements come on line. At that point, the last leg of the tether from LEO to the surface will be completed.

 

[chic_y]

With the following directed back to Neil, regarding the slow but eventual return of the top anchor mass to an essentially vertical spot above the ribbon's Earth level anchor point. I would agree, due to vectored 'tugging' force from the Earth that would eventually overcome the new equilibrium point created after a mass was unloaded from the Space Elevator and it subsequently returned to Earth restoring only partial Kinetic energy to that top anchor mass on the way back down. (Hope you received the personal message re: Elevator2010.org/forum-challenge) <br /><br />However, due to the resultant continually decreasing vector angle of that 'tow' force this could take months, or longer - drastically reducing the usefulness of any Space Elevator.<br /><br />By reeling in some of the ribbon - after each launch of a load and the return to Earth of the elevator - the top mass could be pulled into a lower Earth orbit where its speed would move it Eastward towards the original vertical line above the Earth anchor point. Letting out some of the ribbon again - carefully - could cause the top mass to rise enough to stop its circumnavigation movement at another, but lower, equilibrium point with less outward pull on the ribbon.<br /><br />This could be repeated until the top mass could only support the elevator and the rockets necessary to be sent up for the vectored thrust required to restore the top mass to the original point of equilibrium at its 100,000 Kilometer height and speed, while more ribbon was unwound from the Earth anchor point.<br /><br />While it is still very doubtful that such a multi-equilibrium orbital mechanics process would create anything close to the savings in energy and costs predicted for the Space Elevator, it does not appear that it would violate any laws of Physics. Chic

 

[nexium]

Hi chic_y: I check at the forum more often than my E mail, and have sort of followed your debate with mlorey, and others. My guess is the ribbon is slow to correct and does over shoot considerably unless another climber is launched to partially cancel the over shoot.<br />Winching in and out for various reasons will be done, I think, but a few days after winching out, the average tension of the ribbon increases, then winching in increases tension on the part close to Earth such that it can not tolerate launching another climber which also increases tension just above the climber. My guess is tension transients travel on the ribbon only a few hundred kilometers per hour, but others claim much faster.<br />Winching in some ribbon at the Earth end reduces the average ribbon tension after a few days, perhaps to the point that significant parts of the ribbon are falling toward Earth. Launching another climber pulls down on the ribbon, perhaps causing the entire ribbon to eventually fall. My point is the balance is unstable and we can not risk failure to straighten the ribbon. As long as we are aware of the average tilt of the ribbon, my guess is perfomance is not compromised. Constant monitoring of tension thoughout the ribbon will be esentual to safely make several launches per week, not necessarilly evenly spaced. Neil

 

[barrykirk]

How about a space tether. It doesn't have the material strength requirements of the space elevator and also solves a lot of the other problems of the space elevator. The benefits are quite as great as the pure space elevator concept but they make space access a lot cheaper and easier to achieve.

 

[chic_y]

Hi Neil...Several factors enter in the use of such an elevator IF it could be made to work at all.<br />1. We have no figures on the modulus of elasticity of the Nanotube composite ribbon, and therefore how much it would stretch - even before the breaking point.<br /><br />2. For a 15 ton elevator carrying a load only 10% of its weight (mass) it would take a 176 Horsepower engine to achieve the projected 120 MPH climbing speed - if we discount all forms of friction (and air resistance in the early portion of its climb).<br /><br />3. At 120 MPH or 200 Kilometers per hour, the trip to GEO would take 7 1/2 days --- and another 7 1/2 days to come back down. So instead of 2 per week - we would be faced with more than two weeks per round trip.<br /><br />4. Due to ribbon strength, it would not even be possible to design elevators that could pass each other - or one climb over the other after each slowed down.<br /><br />In my previous example of returning the top mass to a position directly above the bottom anchor by pulling it into a lower orbit, where its kinetic energy would keep its speed the same in that then smaller circle (orbit) - calculations could time the release of more ribbon to raise that top mass in a timely way to have it then in the slightly higher orbit where it would again have equilibrium at that now lower-than-original spot above the bottom anchor point - without overshooting.<br /><br />It would, of course, not have as much upward pull on the ribbon as before because of its transfer of kinetic energy - and the loss of centrifugal force - to the mass that was off-loaded from that elevator trip. Chic <br /><br />As to Barry Kirk's reference to a "Space Tether" - He does not explain the difference between that and the proposed ribbon. Certainly, we hope it is not intended to grip and hold on to outer space.

 

[nexium]

Hi chic_y: 1 Some recent data is available indicating that at extremely high temperatures, The CNT can stretch to more than double it's light load length, so the ribbon may behave like a bungy cord. 2 176 horsepower is likely correct. Dr Edwards estmated that 4 each one megawatt lasers were needed for full speed in the lower atmosphere. Gravity decreases with distance from the the center of Earth and has a very low net from 30,000 to 36,000 kilometers altitude, so power is required mostly for miscellanious friction. 3 No round trips are planned for the first elevator 4 The ribbon can likely be beefed up for SE2 to permit passing, or the climbers can carry short burn rockets which off set most of the stress on the ribbon during the brief passing manuver. If the pass can be sychronised with the passing of a stretch transient, only one climber will need the short burn rocket. Neil