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