Space Elevator Likely to Remain Science Fiction

The space elevator is absolutely dependent on a strong tether cable, currently aimed at 100,000 km long, but it could be shortened considerably with a larger mass as the counter-weight. Carbon nanotubes are meant to be the way forward, providing the huge strengths needed for such a cable, but this is problematic and it will be exceedingly difficult to achieve the needed length and consistency.

Therefore, let’s consider how to complete the project if the tether were already built and installed in place. The following steps would be necessary, in my opinion, to complete a functional prototype elevator system:

  1. Determine the minimum useful size and fully loaded weight of the elevator that could serve its purpose in transporting objects into geostationary orbit. Coordinate this weight with the tether design team to make sure they provide sufficient counter-weight force and a long enough tether cable to support the fully loaded elevator.

  2. Carefully select an electric motor for the purpose of lifting the elevator up the tether cable.

  3. Design a set of rollers, driven by the motor, that will clamp on the tether cable and carry the elevator upward at a speed of at least 65 MPH.

  4. Combining steps 1-3, build a prototype elevator model, using the electric motor and rollers and operating with a conventional speed controller on a lithium ion battery, matching total weight to the design value. The elevator would be installed on the tether cable. With all the proper measurement devices turned on, accelerate the model to 65 MPH. With the speed steady at 65 MPH, record the voltage and current readings at the motor. These values need to be known to proceed with the design.

  5. Now, the photocells can be selected which respond to the given laser frequency and matched to produce the needed voltage and current to drive the model at 65 MPH.

  6. Next, the lasers have to be selected, with adequate energy to induce enough electrical power in the photocells. Multiple lasers could be used, in any number of locations and timing could be staged during the ascent. In addition, the total power needed by all the lasers used to transmit power to the elevator has to be manageable. If it takes the entire output of Hoover dam to drive all the lasers for the two week trip, the power cost would be astronomical.

Thus, if any team were to follow this series of steps and if all the necessary components were to become available, and if the laser transmission of energy worked all the way up the tether to the geostationary point, then the project would be successful. That is a lot of “ifs,” and it gets much, much worse before it gets any better.

To this date, both the photocells and the lasers are exceedingly short of the requirements of the minimum-sized practical space elevator. Tests that I have read about, using laser transmitted energy, reveal weights lifted well below 100 pounds and speeds of lifting are well below 10 MPH. This is miserably incompetent to even consider for the space elevator, since that speed would take 2,170 hours to reach orbit altitude, or 12.9 weeks. That’s three months, and for just 100 pounds total, leaving very little, if anything, for payload. Therefore, they are still much more than an order of magnitude away from any practical space elevator prototype.

Now to consider what gets even worse yet, and these are really big “show stoppers:”

In the first place, all clouds will interrupt the laser beams and stop the elevator in its tracks. So, extensive weather reporting would have to be done before launching any ascent that may be stopped in the middle of the tether at any time by clouds. With extended storms, anyone riding in the elevator could be marooned long enough to be threatened by running out of oxygen. This problem is a major limit on the use of the space elevator.

In the second place, it’s impossible to predict what effect lightning strikes on the tether would have. Perhaps some sort of damping circuit could be placed between the tether cable and earth ground, to absorb lightning energy while limiting current through the tether. The present choices of tether material are conductive to electricity, although even non-conductors could become conductive under stormy conditions when wet and dirty from the weather. This factor will always have to be dealt with, and the failure to consider it could well lead to a catastrophic lightning strike that could simply burn the tether cable in two. That would allow the counter-weight to drag the upper portion of the tether (probably with the elevator on it) out into space.

All sorts of wave motions would be imparted to the tether cable by several known forces: (1) all weather and trade winds in earth’s atmosphere surrounding the tether; (2) side force of the elevator on the tether in a westward direction to accelerate the elevator in its eastward rotation of the earth, from 1,040 MPH at ground to 6,680 MPH at the geostationary orbit point; (3) natural resonances of the tether cable, excited by all forces, that could generate other modes of traveling waves along the cable, (4) random motions of the elevator itself, traveling up the tether, which may even go into rotational instabilities that twist the tether cable. All in all, the resultant chaotic motions of the tether cable and elevator would make any steady contact of the laser beams with the photocells virtually impossible beyond a few miles from ground level. Thus, for almost the entire trip, the unpredictable motions of the elevator, along with ripples in the tether repeatedly blocking the laser beams, would so frequently block the laser transmission of energy that the motor would hardly run at all. This is an insurmountable problem, since there is no known way to stabilize either the tether cable or the elevator to prevent this constant interference with the laser power connection.

Worse yet, every laser strike on the tether cable would have the potential to damage it, since high power lasers are being used here. It would only be a matter of time, and it could happen during the progress of the very first ascent, that the repeated laser strikes and damaged areas of the tether cable could result in some section being hit badly enough to develop serious burns and weak spots. As a result, the tether could be weakened all the way to the failure point and break in two. That, of course, would cause the counter-weight to drag the truncated tether and elevator further out into space. If passengers were aboard the elevator in those conditions, a timely shuttle launch would be needed to rescue any of them alive. A similar situation would occur if the tether cable were not severed, but sufficiently damaged as to cause splintering of parts of it to break loose and jam the roller mechanism and stop the elevator. Being stuck in mid-transit would be just as bad as open space, with no way to go all the way up or down.

Finally, the tether cable would be extremely vulnerable to any terrorist attack whatsoever, from any means, bomb in the elevator, attack aircraft shooting the tether in two, any aircraft severing the tether with a wing contact, etc. The only practical way to protect the tether cable is to make the ground termination in a military base. Then, all commercial and private aircraft would be forbidden to fly in the military airspace surrounding the tether. Also, the base would normally be protected by radar tracking of any approaching flying object, with the means to shoot down whatever threatened the base or the cable.

Bottom line: Given all the extreme hazards and the absolute impossibility of smooth operations, I doubt that the space elevator project will ever “get off the ground,” so to speak, in any useful manner that could put anything substantial into geostationary orbit.

    –EngrGene


EngrGene obtained his BSEE from Cal Poly College [Now University] in Pomona, California in June, 1967. Commercial experience includes 13 years of electronic design for EECO in Santa Ana, California, which involved magnetic core memories and tape readers plus special projects. He spent 6 years at Magnavox in Torrance, California working on various electronic systems and components for special military projects, including a military facsimile unit and also worked on electronic hardware of the GPS system in early stages of its development for military use. He retired in 1991.

8 thoughts on “Space Elevator Likely to Remain Science Fiction”

  1. Of course, the real reason a space elevator will never take off, is because of concerns about the release of space-elevator music.

  2. For a good introduction to the modern space elevator concepts, problems, and potential solutions you could do worse than reading the seminal work based on the 3 year NIAC study:
    http://www.amazon.com/exec/obidos/tg/detail/-/0974651710/qid=1127317678/sr=8-1/ref=sr_8_xs_ap_i1_xgl
    14/104-9846044-7466339?v=glance&s=books&n=507846

    Most of the things mentioned in this article are covered in the book and potential solutions to the problems proposed.

    The current thinking has moved on somewhat from this book and it may be that the wikipedia article (http://en.wikipedia.org/wiki/Space_elevator) is the best first place to go to for information and links to up to date information (gasp)

    The project is a very large undertaking but the Liftport Space Elevator roadmap (download the 7 page pdf from http://www.liftport.com/papers/SE_Roadmap_v1beta.pdf)gives what many consider a realistic timeline for a single company strategy of getting there (assuming the money is there for the basic research).

    Liftport as a company is struggling so they may not be able to follow their own roadmap but I’m sure others will follow along behind them.

    At the moment the big thing is the space elevator conferences for sharing theoretical knowledge and the space elevator games for proving the technology. In the coming games, competitors will be trying to climb a 1km high cable at 5m/s or making a cable 2m in length that weighs 2g and can hold 1 ton. See http://www.spaceward.org/elevator2010 for details.

    Its a significant first step, and while it is only the first step and there is a long way to go I must disagree and say that I think the space elevator is not going to remain science fiction but probably be built in the first half of this century and almost certainly by the end of the century (barring civilisation destroying events of course :-)

  3. Thankfully, for all the Luddites who say ‘it can’t be done’, there is always a creative engineer who figures out a way to do it anyway.

    What you should do mate, is go and join the creationists and leave all the hard thinking up to those who can couple their imagination to a desire to achieve something in the world.

  4. Quite amazing how one little post can upset one little individual quite so much. Yes, engineers have achieved huge feats, but I’m inclined to agree with the author that hanging a 50,000 kilometer cable from a big rock in space and shinning up it is a little far fetched with current technologies, even if nanotubes really are very, very strong.

  5. I too think it will ever prove to be quite impractical though perhaps possible.  Besides, at 65 mph we are talking a 343 hour trip.  ;-)

  6. ..is that the author assumed one specific technological approach – an elevator driven by ground-based lasers – and made arguments against it (some specious), then pretended that there isn’t any other way to get the job done.

    How about using a EM wavelength that isn’t blocked by clouds and isn’t in danger of ablating the elevator or tether?

    A mass is needed at the end of the tether, so why not make it a solar farm and beam the energy down? I’m fond of this idea for several reasons, including the fact that the elevator spends most of its time out of the atmosphere and an beam-source out of the atmosphere would be much easier to aim.

    Some of the security concerns are laughable too. Putting mass up the elevator will still be a very expensive proposition, and the contents of each load will be very closely inspected not just for weight concerns but also for any objects that might harm the elevator, intentionally or not.
    Would an aircraft wing sever the tether or would the tether sever the wing? Given the assertion that the tether will wave and twist, just how easy would it be to shoot the tether?

    I’m not saying the space elevator will be an easy project, and ultimately it might not work, but it certainly will never work if we listen to an elderly electrical engineer who’s incapable of thinking outside of the box.

  7. No need to get personal barakn. The author being elderly or an electrical engineer should not enter into the discussion. He could just as easily argue that your or my opinion is not valid on the basis of our being younger and in another discipline.

    One of my concerns about a space elevator is that there wouldn’t just be one. If they turn out to be viable all nations will want one, perhaps one in each city. How will this mesh with air traffic control if there are dozens of tethers whipping around across the globe?

    By the way, what was the rationale for this endeavor in the first place? To preclude the need for shuttle type spacecraft and allow us to exploit near space more effectively? Wouldn’t it be easier to simply a new type of reusable craft that is not based on decades old missile technology?

  8. Correction:  As determined by the simulator program developed after posting this article, the elevator starting at 10 MPH at ground level would get to 130 MPH at 8,880 miles up and reach orbital height after 2.2 weeks under ideal conditions (except as delayed by any or all of the interferences cited).
    I let that article go too soon without realizing I hadn’t considered diminishing gravity on ascending elevator.  :-)    –EngrGene

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