What gives me hope for a space elevator is that the technologies we need to make one would have plenty of non-space application. We’re not going to develop large-scale manufacture of carbon nanofiber to build a space elevator. But we might develop it to build a suspension bridge, or a fishing line, or a golf club. And once we have it, developed for some other application, then we can use it for an elevator.
Actually, the most pressing near-term use for carbon nanotube long fiber might be as a near-room temperature superconducting conduit. If the properties can be developed in useful lengths it would provide a way to significantly reduce line losses (which are small with high voltage DC but still represent a tremendous economic loss) as well as making transmission systems more robust and scaleable which may be necessary to support an electric vehicle-based transportation infrastructure.
But building a space elevator or a skyhook isn’t just a matter of having a material with a suitable material strength. There are a whole host of potential issues, not the least of which is that such a structure has to be constructed from the top down; that is, at least the initial cable material has to be lofted in geostationary orbit and then constructed downward under tension until it can be anchored at the equator (most likely on a floating platform that would give some latitude for movement and reduce the hazard of a breakaway payload will threaten inhabited territory). There are also the problems of avoiding or deflecting orbital debris, how to stabilize the structure against destructive resonance, and so forth, none of which are straightforward problems.
And while it is justifiably assumed that the costs of transportation to orbit using a space elevator would drop dramatically—not only because of the inherent efficiency of an elevator versus rocket propulsion but also because the majority of the energy going up gets recovered on the way down—the actual economic case for the initial capital investment has not been assuredly demonstrated. This would be a megastructure vastly larger and more expensive than any other ever attempted, and recouping the costs would require a space manufacturing or resource infrastructure essentially ready to go or already in place. Perhaps the nations of the world would come together to cobble up the tens or hundreds of billions of dollars to construct such a structure and agree to make it available to all parties without political restrictions but that seems unlikely, and such a structure would be uniquely vulnerable to attack requiring a large constant military presence to protect against attack.
So building and maintaining a useable space elevator (or skyhook, or other orbital transfer megastructure) is not just a matter of having the necessary material strength, but invovles a whole host of other technology, political, and security issues that would need to be addressed in order to be viable.
Stranger
Take everything Elon says with a grain of salt, but I believe Elon Musk said on a conference call this week that the cost of a launch on a re-flown Falcon 9 Block 5 is $50 million. I think that means lifting up to 18,240 kg to LEO in a re-usable configuration. If my memory and math are right (both dubious assumptions), that would be $1,243.41 per pound to LEO (if you could max out the payload capacity on a $50M launch). Obviously it’s a bit difficult to find exactly 40,212 lbs of stuff you want to send to LEO at once, and as the payload drops away from that best-case-scenario, the price-per-pound is going to go up.
It is not a question of “can”, but a question of whether there will ever be a market to demand the development of it.
We can take oil out of the ground miles beneath the ocean, ship it half way round the world, and expose to an amazing refining process, for aq couple of bucks a gallon, because consumers want us to. But who would have expected that?
This is a little tangential, but in the interest of fighting ignorance, I have to take issue with the statement above. 1) As far as I can tell, the evidence for intrinsic superconductivity in carbon nanotubes (CNTs) relies mostly on inferential measurements rather than direct evidence of the fundamental unique properties like perfect diamagnetism, Josephson tunneling, or flux quantization*; 2) the best data is at lower temperatures than the current best results for ceramic superconductors; 3)the theory predicting extremely high superconductivity in CNTs is not, so far, predictive enough or precise in duplicating existing experimental data to the extent necessary; and 4) the 1D nature of the claimed effect will most likely prevent reaching zero DC resistance at any reasonable current, which means it very likely won’t beat good copper for energy efficiency.
While the mechanical properties of CNTs are very far away from those needed for the space elevator, they are closer to, and more firmly in hand, for that application than the superconducting properties necessary for any practical application of CNTs depending on superconductivity.
*Resistance drops of many orders of magnitude have been seen in many non-superconductors (never, never trust resistance data alone). Increased diamagnetism can also be observed in some materials and the 1D nature of the CNTs makes it unlikely that the signatures of the true Meissner effect can be observed even if there is superconductivity in the CNT strands. Making SQUIDs is probably the best way of observing something that can’t be duplicated with normal materials.