Ted Semon, a retired software engineer, chronicles the efforts to develop a space elevator on the Space Elevator Blog, and volunteers for The Spaceward Foundation which administers competitions to develop several of the core technologies that will be needed to build the elevator.
Ted attended and spoke at the 2008 Space Elevator Conference held at the Microsoft Conference Center in Redmond. In this interview he discusses the concept of the space elevator, and the status of current efforts to bring it to life.
In a related interview, Maurice Franklin, the Microsoft employee who brought the conference to Redmond this year, reflects on the conference and on the goals and status of the project.
JU: How did you become interested in the space elevator?
TS: I've always been a science fiction fan, and I read Arthur C. Clarke's Fountains of Paradise many years ago. The idea of the space elevator seemed so obviously the right way to get up out of Earth's gravity well.
When I retired from the software world a few years ago, I decided to learn what was happening with the concept. There were blogs and websites, but nothing coherent, so I decided to pull the information together myself on the space elevator blog.
JU: At this point were we into the modern era of the development of the concept?
TS: Yes, this was in 2006. I'd read the Brad Edwards book, but it was hard to find out what was currently going on, so I started the blog.
JU: The concept as described by Clarke is quite different from the modern one that's emerging, right?
TS: In some ways yes, in some ways no.
JU: Can you spell out the differences?
TS: OK, there are several. He had located his port on the island of Sri Lanka. Current thinking is that it won't be a land port, it'll be an ocean-going port, so you can move the space elevator if you need to, and get it out of the way of satellites and other things in orbit.
JU: I gather that's a "when", not an "if".
TS: Exactly. There's stuff up there, it's going to intersect the elevator, you've got to deal with that.
JU: And the object being moved, just to be clear, is a 100,000 kilometer strand of material.
TS: Right. It's a carbon nanotube tether, or rope, or ribbon, whatever you want to call it. One end is anchored to an earth port, something like an ocean-going oil platform, and the counterweight ands at 100,000 kilometers up.
By moving the ocean-going platform you can induce a wave that travels up the ribbon. You know which objects in space to worry about, at least the big ones, because you track them. And you know what's going on with the ribbon because you have sensors embedded in it, and climbers going up and down that signal their location. So you should be able to always move the ribbon out of the way of a collision.
JU: So one difference from Clarke's original vision is that the platform is mobile and sea-based. What are some other differences?
TS: Cost. He had imagined the cost would be something like the Earth's combined gross national products for a year, or some enormous number like that. The number now that looks more realistic is on the order of 10 billion dollars.
JU: And what accounts for that lower estimate?
TS: More knowledge now about how it's going to be built.
JU: Maurice Franklin and I discussed this, and his take was that the Clarke scenario assumed a huge mass parked in geosynchronous orbit, and that mass would be very expensive to lift. That ties into another evolution of the concept, which is that it's not now anchored with a large mass at 22,000 miles, but extends far beyond that.
TS: Right. Something like 100,000 kilometers. The counterweight in the Edwards plan is about 600 metric tons, quite a bit smaller than the Clarke scenario.
JU: The reason that's possible is?
TS: Because it's farther out in orbit. Well, it's hard to say an object anchored to Earth is in orbit, but it's 100,000 kilometers out.
JU: At its endpoint.
Let's see. He had also talked about the material being a carbon or diamond monofilament. I guess that's similar to carbon nanotube, and we should probably say he was right on that score.
He hadn't talked about powering the climbers, though. They used batteries. In the Edwards concept, the climbers are laser-powered. Lasers will be aimed at photovoltaic cells on the bottom of the climbers.
JU: So the climber is the robot that's attached to the tether, and ascends and descends?
JU: I've got some sense of what a carbon nanotube is. A sheet of carbon atoms folded into a cylinder. But I'm not at all clear now that translates into a 100,000 kilometer cable. What's the architecture of that cable?
TS: It's composed of fibers. When you buy a 50-foot rope at a store, there's no fiber in there 50 feet long. They're all woven together, and that's what'll happen with carbon nanotubes too.
Right now the longest ones I know of, and have actually seen, are 5, 10, 15 millimeters long.
JU: The individual fibers?
TS: Right. So one challenge is to grow a longer fiber. MIT, for example, is working with a company called NanoComp.
JU: There's obviously a limit to how far you can go in that dimension, so then it's a question of how to compose a ribbon out of these strands, probably at several levels of hierarchy. Just like the way the Golden Gate Bridge cables are multistranded at several levels of hierarchy.
TS: Yes. The textile mills are very good at this stuff. If you give them fibers, they will weave you cables. The issue is going to be giving them carbon nanotube fibers of sufficient length and strength. That's where the bottleneck is now.
JU: What kind of diameter of cable are we talking about?
TS: If you're looking at the Edwards scenario, it's going to be a ribbon that's roughly 20 inches wide. And it is a ribbon.
TS: When you're in space, you want as wide a surface as possible. So a micrometeorite strike won't sever the ribbon, it'll only poke a hole in it. And if you have it woven correctly, the strain is taken up by nearby fibers.
However the ribbon can be problematic in the atmosphere, because of wind effects. So it may be a cable in the atmosphere, widening out to a ribbon above.
JU: There needs to be a procedure for maintenance and repair, what's being discussed there?
TS: Some people are talking about making the tether into a big loop that's constantly rotated down to Earth where you do the maintenance. Nice in theory, but you've doubled the length. And what do you do about having a cable in the atmosphere and a ribbon above?
Another scenario is that the tether is made of segments. People worry that if the ribbon were cut, the two ends would fly apart. Not so. They'll sit there for some time, then gradually pull apart, but not like a snapping cable.
JU: Not catastrophic?
TS: No, as long as you get to it in time. So you should be able to disconnect and reconnect segments.
Another possibility: The climbers continuously reweave the ribbon as they go up and down.
JU: The carbon nanotube fiber and laser power beaming technologies seem to be two key ingredients in development. And those are what the space elevator games test, right?
TS: Yes. On the carbon nanotube front, there's a lot of work being done by industry and universities, and not only for the space elevator. Most people don't know or care about that, they just see a market for things much lighter and stronger than steel.
And with carbon nanotubes being measured at 2, 4, 6, maybe even 8 gigapascals -- and these are big jumps over a few years ago -- there's a real sense that we're getting close to being able to make a ribbon strong enough to support an elevator.
JU: How strong is that? What are the forces acting on the ribbon?
TS: The original Edwards scenario called for 130 gigapascals. Since then there's been some rethinking. Some good aerospace engineers think it can be dropped to 60 or even 40 gigapascals. That doesn't mean 130 is outside the realm of possibility, but we'll get from 8 to 40 and 60 a lot sooner.
JU: But the existing results are for radically shorter lengths.
TS: Yes, but you just need to something long enough to be woven.
JU: Ropes stretch, though, and we don't have any examples of 100,000-kilometer ropes or cables.
TS: Well, the total amount of cable in the San Francisco Bay Bridge would exceed the length of the space elevator.
TS: It's different of course because it winds back and forth and around things, but there is some experience there.
JU: In terms of the laser power beaming, is this also a case where development is occurring for all sorts of other reasons?
TS: Exactly. NASA sponsors the space elevator games, but they mainly care about very strong materials, i.e. carbon nanotube tethers, and they care about power beaming, because they see applications for these things.
Boeing has just come out with a solid state laser in the 25 kilowatt range, and they say they can go to the 100 kilowatt range. If you can get 20 of those, that's enough to power your climbers.
JU: What are the current applications of those?
TS: Beaming power to a moon buggy so it doesn't have to carry batteries. Airships that stay up for weeks at a time.
JU: Are any of these concepts real yet?
TS: No, not yet, but the needs exist and they're trying to develop the technology to satisfy those needs.
JU: I gather one potential showstopper is the threat of natural or manmade attack.
TS: Actually the latter wasn't discussed too much at the conference, mostly the former. Micrometeorites, space junk.
That's being addressed in two ways. For small things, make the tethers wide enough, and engineer a replacement lifecycle. For large things, move the elevator out of the way.
JU: That computational grand challenge dovetails with Microsoft's strengths and interests, so that might be one interesting outgrowth of having had Microsoft sponsor and host the conference.
TS: That'd be great!
JU: Give us a sense of who was at the conference, what was discussed, and what emerged.
TS: There are two answers, I guess. First, there were a lot of old pros, people who've been working on this for years, and have come up with the intial concepts and solutions.
Then there are some new people in the last year. Some were invited, some just showed up.
There's an effort to make this into an international campaign. We've adopted the "four pillar" concept. It's something you need for any huge infastructure project. The pillars are: technical capabilities, a business plan, a legal and insurance framework, and public support.
That hadn't come together in the past, but this year we think we've gotten the enthusiasm, and especially the international support, to sustain that four-pillar approach going forward.
JU: We mentioned the Golden Gate Bridge. I recently learned that it wasn't a federal project, it was a municipal project. Likewise, the space elevator would perhaps ideally not be a big federal project.
TS: I don't think it has to be. I gave a talk this year on who I thought would build the first one. Ten billion dollars is a large sum, but not out of the reach of non-governmental entities. Money's an issue, but it's not going to be the showstopper.
I do think you'll need a government involved for defense, and for insurability, because international treaties will have to be written, and I think a government will be able to do that more easily than a business consortium.
I could see a group of US businesses getting together and saying to the US government, we'll take the financial and technical risk, in return please defend our elevator and help us deal with the insurability. If you do, we'll make you a deal: free launches, or discount launches. I'm sure there's a deal that can be made.
JU: In terms of why to do it, obviously everyone close to the concept takes it on faith that it's a good thing to do for all sorts of compelling reasons. To me, the solar satellite concept is maybe the most compelling, is that the application advocates tend to lead with?
TS: Many do. I don't personally. I'm skeptical. We use so much energy, and to put enough stuff into space to create space-based solar power that would make a significant dent, well, the amount of material is huge.
And we're not going to have a space elevator for 20 or 30 years. Meanwhile our problems will keep getting worse. We may have pilot projets, but nothing that'll power your refrigerator...
JU: ...or have any significant effect on greenhouse gases.
TS: Correct. Having said that, the concept is outstanding. And while I'm skeptical, I'm in the minority. Most advocates see it as a huge reason to build the space elevator.
JU: What are the other reasons that come up?
TS: Look at what you get: Enormous capacity, low cost, safer launches, and low environmental impact. Any industry that needs those benefits will want the space elevator.
JU: Such as?
TS: Well, what's making money right now is communications satellites. That's a big and growing industry. It'll be much easier to build satellites that don't have to reach orbit in rockets, and much cheaper to send them up.
Another will be orbital tourism. Being able to go up 100 miles, spend the afternoon, and come down -- we think that'll be a big moneymaker.
Then there are industries that don't exist today, except in labs, that need a space environment. To get them up today, you're talking about thousands of dollars a pound in rockets, and not a whole lot of pounds. With a space elevator it's hundreds of dollars a pound or less, and a lot of capacity.
I think once it's there it'll make a ton of money for somebody, maybe lots of somebodies, because you want more than one space elevator.
JU: Right. The first one is the bootstrap that gets you to others.
TS: Yes, and once you've got two, now you're in business. One of your failsafe scenarios is that you can leverage one to fix the other.
JU: So at the conference, the discussion was more about how to get it done than why to do it. What were the conclusions?
TS: That we're closer than ever. Arthur C. Clarke said that a space elevator would be built 50 years after people quit laughing about it. Well, people quit laughing some time ago. I think his prediction is a bit pessmistic. I think we're looking at 2020 to 2030 to actually be able to put one up. There's a general feeling that this is a real possibility, that it could happen in our lifetimes.
JU: If I were to attend the space elevator games, what would I see?
TS: You'll see a helicopter lifting a steel cable 1 kilometer up, and you'll see teams attaching climbers to the cable, and beaming power to photovoltaic cells on the climbers. We're hoping to have several competitors this year with a real shot at winning the prize.
JU: And the prize is?
TS: There are two. If you can get up the kilometer cable in two meters per second, and you're the only one who does, there's a million dollar prize. If you can do it at five meters per second, and you're the only one who does, there's a two million dollar prize.
JU: Really? So a million bucks for a laser-powered climber to go two meters per second, and nobody's claimed that yet?
TS: That's right. Last year it was 100 meters, and before that 50.
JU: So you've raised the bar?
TS: And the prize money, yes.
JU: And what's the other prize?
TS: For the strongest tether. Also a one million and two million dollar prize. You have to beat that house tether. Yours can be two grams, the house tether can be three, and it's made from commercially available material. So if you bring something new, like a carbon nanotube tether, and it can beat the house tether which is heavier, you can win the prize.
JU: And the lengths are?
TS: Two meters I think.
JU: Oh, OK, so nothing like the kilometer climb.
TS: No, it's a two-meter loop. Yours and the house tether are placed onto a special machine designed for this event, it stresses them equally, whichever breaks first loses.
Nobody's come close to winning that one yet. But last year we had our first carbon nanotube tether. MIT brought it, working with NanoComp. But it had been done so close to the competition that they weren't able to weave it a loop. So they actually tied a knot.
JU: They tied a knot!? [laughs]
TS: Exactly. But this year they'll have more time to prepare, and we know of at least one other team bringing a carbon nanotube tether.
So our ideal scenario for this year is that we have a carbon nanotube tether that blows away the house tether, and a 5-meter-per-second climber.
JU: And it'll happen where?
TS: Not definite yet, but we're hoping for Meteor Crater in Arizona.
JU: It's inspiring to think about this stuff!
TS: It's very inspiring to be on the inside. I got involved just because I was interested, but now I'm a huge fan and I'll do everything I can to help make it happen.
JU: The project seems to be attracting a variety of folks, from all walks of life, who are showing up, and wanting to participate, and finding ways to participate.
Maurice Franklin, for example, a Microsoft employee, has now made a real contribution by organizing this year's conference. But he also talks about some other folks who showed up, uninvited, with relevant engineering credentials, and made real contributions.
TS: That's right. People like Maurice will be the lifeblood of this project. And when you get involved, and start to see that this isn't some science fiction idea that's never going to happen...
JU: ... and that there are serious people, with serious engineering credentials, working the problem in a pragmatic way. It might not happen, but it could. Thanks Ted!
TS: Thank you, Jon.