I was 8 when Armstrong and Aldrin set foot on the moon. It was exciting. My daughter is 18 and has never witnessed anything of the same order of excitement. The human genome project was comparable in some ways but lacked the Buzz.
There is excitement about going back now. We will, and on to Mars. We can do space so much more safely now than back in the 60s. Commercial companies are pioneering space tourism and later on will pioneer the mining bits. But the excitement recently is over the space elevator. The idea is that a cable can stretch all the way from the surface out into space, balanced by gravity, and used as a means to cart stuff back and forth instead of having to use rockets, making it easier, less expensive and less dangerous.
It will happen eventually on Earth. We need to make new materials that are strong enough. Carbon nanotube cables and other fancy materials will be needed that we can’t make long and strong enough yet. But the moon has lower gravity so it is much easier there and will likely happen earlier.
There are plenty of web articles about space elevators already so I don’t need to repeat everything here. But a space elevator is supported from above, a regular building is supported from below. How can we build one very tall from the ground?
I recently issued a report on 2045 construction that among other things also discussed spaceports up to 30km tall:
A 30km tall spaceport on Earth could make use of atmospheric buoyancy for the lower end which of course we wouldn’t get on the moon for the spaceport coming home, but we also wouldn’t get wind on the moon to add stresses. On the moon gravity is less so the structure could be much taller. On the moon a graphene structure could form as much as the bottom 150-200km of the climb. It might offer a nice synergy. The diagram above shows some of the possible structure for the columns, biomimetically inspired by plant stems, though this is just one suggestions, and there are very many ways they could be designed.
This could be enhanced by filling columns with graphene foam:
Since I wrote that, carbon foams have been made and they are 6 times lighter than air.
So how about a 30km tall building? Using multilayered columns using rolled up or rippled graphene and nanotubes, in various patterned cross sections, it should be possible to make strong threads, ribbons and membranes, interwoven to make columns and arrange them into an extremely tall pyramid.
This could be used to make super-tall structures for science and tourism or spaceports, or a home for celebrities, well out of sight of the Paparazzi.
Think of a structure like the wood and bark of a tree, with the many tubular fine structures. Engineering can take the ideas nature gives us and optimise them using synthetic materials. Graphene and carbon nanotubes will become routine architectural materials in due course. Many mesh designs and composites will be possible, and layering these to make threads, columns, cross members with various micro-structures will enable extremely strong columns to be made. If the outer layer is coated to withstand vacuum, then it will be possible to make the columns strong enough to withstand atmospheric pressure, but with an overall density the same as the surrounding air or less. Pressure is of course less of an issue higher up, so higher parts of the columns can therefore be lighter still.
We should be able to make zero weight structures in the lower atmosphere, and still have atmospheric buoyancy supporting some of the weight as altitude increases. Once buoyancy fails, the structure will have to be supported by the structure below, limiting the final achievable height. Optimising the structures to give just enough strength at the various heights, with optimised mesh structure and maximal use of buoyancy, will enable the tallest possible structures. Very tall structures indeed could be made.
So, think of making such a structure, with three columns in a triangular cross-section meeting at 43 degrees at the top (I recall once calculating that is the optimal angle for the strongest A frame in terms of load-bearing to weight ratio, though it ignores buoyancy effects, so ‘needs more work’.
30km tall structures would not be ideal for large scale habitation, since much of the strength in the structure would be to support the upper parts of the structure itself and whatever platform loading is needed. But for a celebrity home, small military observation base or a decent sized lab, it might be fine. The idea may be perfect for pressurised platforms at the top for scientific research, environmental monitoring, telescopes, space launches, tourism and so on. The extreme difference in temperature may have energy production uses too.
Getting the first 30km off the ground without needing any rocket fuel would greatly reduce space development costs, not to mention carbon and high altitude water emissions.
A simple addition to this would be to add balloons to the columns at various points to add extra buoyancy, but they cannot give much extra lift once the atmosphere is too thin so probably wouldn’t make much difference.
Nevertheless, the physics limits are pretty good. 30km is a reasonably achievable goal for a 2045 spaceport, but given the known strength of graphene and carbon nanotubes, a 600km tall building on Earth would be the limit, and that is higher than the Hubble telescope!