Some months ago, Dr. Brad Edwards made an appearance at the ideacity forum in Toronto and gave a talk on Space Elevators. You can view the video here – it’s not long, less than 20 minutes. I always enjoy hearing Dr. Edwards speak about the Space Elevator, but I do have a couple of issues with his presentation.
To listen to the talk, one would think that the idea of a Space Elevator was first explored in science fiction. He did not mention either Yuri Artsutanov or Jerome Pearson, the first engineers who came up with the modern-day idea of a Space Elevator and who, in the vernacular of the field, “ran the numbers” (especially Jerome Pearson). Both of them did so long before Sir Arthur C. Clarke popularized the idea in his book The Fountains of Paradise (both authors, by the way, corresponded with Sir Arthur about space elevators). There can be no disputing Dr. Edwards contribution towards the effort to build a Space Elevator; he (and Eric Westling) wrote THE book on space elevators, but he wasn’t the first person to describe what a real space elevator might look like.
According to his talk, we now have the carbon nanotubes necessary to build a space elevator. Oh, if only that were true. I wish, I wish, I wish… Yes, there have been carbon nanotubes built which are 55 cm long and yes, there have been carbon nanotubes which have tested out at 200 GPa, but not at the same time. And, even if you can get CNTs to grow to this length and have perfect (no defects) structure, they’re still not going be aligned – and alignment is key to making threads of macro-strength. I do agree that we’re getting closer, but I don’t think we’re all that close yet. Spinning CNTs into threads is a whole different kettle of fish than spinning normal animal or plant fibers into threads.
And finally, let’s talk about my “favorite” subject, space-based solar power (SBSP). I’m already on record as being very skeptical (to say the least) about SBSP being able to provide power except under unique, niche circumstances. Dr. Edwards talked about the Obayashi project to build a space elevator and provide SBSP for Japan. Let’s run the numbers for “just” Japan. The most current electric generating capacity I could find for Japan was for 287,000,000 kW (for 2013). Energy available at earth’s orbit is 1.3kW/m2. What efficiency number should we use? Let’s say 40%. I think that’s generous. Yes, I know there are cells out there which are slightly more efficient, but they are expensive and, when you see how much we’re going to need, I think that cost economy will play a role here. So, to generate 287,000,000 kW will require about 440,000,000 m2 of solar cells (or 440 km2). This is roughly equivalent to the land area of the Seychelles or of New Orleans. How much mass? If you figure 5 kW / kg (see the Space Elevator Feasibility Condition for details), you come up with 57,400,000 kg (or 57,400 metric tons). Now that’s just for the cells themselves. There will also need to be a massive structure holding them together, an enormous amount of cables, antennas to beam the power to earth and also some sort of propulsion / steering system (along with the propulsion mass) so that you can keep the collection array pointed at the sun and the transmission array pointed at Japan. The best I can do here is a guesstimate – 50% more for the ancillary mass? I think that’s probably ballpark. So, a total mass of about 86,000 metric tons. If you have an elevator that lifts 100 tons to GEO every week, then it’s going to take you 860 weeks (16&1/2 years) to just lift the mass up there. Then you have to either lift personnel to put it together and maintain it or else robots to perform the same. You’ll need to periodically replace the panels due to space debris and other space-related hazards and you’ll need to replace the propellant too. And that’s assuming everything goes right. Things always go wrong, so you’ll need to deal with that too.
Add that all up and you can see why I’m skeptical about this. Now, if you wanted to replace “just” the nuclear generating capacity of Japan with SBSP… Nuclear plants provide about 18% (roughly 1/5th) of Japan’s electric power – at least they did when they were all online. So if you wanted replace just the nuclear power generating ability with SBSP, well, then, maybe… Maybe that is a possibility, with an engineering project dwarfing anything else created by human beings.
Color me skeptical, very very skeptical…
One final note; Dr. Edwards talks about his company – I’m assuming he’s referring to this.