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$2 Million NASA Power Beaming Challenge Heating Up
carstene writes "Qualification rounds for the NASA Centennial Challenge Power beaming contest are underway at the Dryden Flight Research Center. The contest uses a scale model of a space elevator as a race track. Entrants must build a robot to climb a cable, suspended by helicopter, 1 km into the sky without any on board energy storage. The teams are using high power laser beams to transmit power from ground stations to photovoltaic arrays on the robots. If a team can accomplish this at 5 meters per second average speed then they could win up to 2 million dollars. One day this technology could be used to power rovers in shadowed areas of the moon or to recharge electric UAV's in-flight or even a space elevator in the far future. A blog of the event can be found here. Full disclosure: I'm a member of the LaserMotive team that you can follow on twitter, or or via blog."
what really sucks is when you're stuck between floors
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That's why I like the idea of a Launch Loop better (not that it doesn't have its issues too). It uses kinetic energy to maintain the structure rather than tension so it could in theory be built with modern materials. It also launches in minutes rather than the days, weeks, or even months that some space elevator designs call for. It would have a much higher launch capacity and is built on the ground rather than having to boost a cable into orbit. It doesn't require an anchor weight in high orbit and since the energy for launch is also transfered mechanically you don't have to worry about beaming power anywhere. Finally, it would act as a huge and efficient energy store, meaning we could, in theory, use 100% solar/wind power and use a launch loop as the worlds biggest battery for night time and cloudy days.
http://en.wikipedia.org/wiki/Launch_loop
NASA: "We'd like you to hover for a few hours dangling a cable."
Pilot: "Boring!"
NASA: "Oh, and several teams will be shooting lasers in your direction."
Pilot: "Now you're talking!"
what brave soul wants to pilot the test helicopter anchoring the top of the beanstalk, while engineers of varying degrees of competence are aiming powerful directed energy beams at an object suspended a short distance below them.
"Do not glance outside of cockpit with remaining eye."
Welcome to the Panopticon. Used to be a prison, now it's your home.
Last I heard there were bigger problems with space elevators than the energy required to get up there.
A circular geosynchronous orbit in the plane of the Earth's equator has a radius of approximately 42,164 km (from the center of the Earth). A satellite in such an orbit is at an altitude of approximately 35,786 km above mean sea level.
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Well, you know, in a way, the huge distance by itself isn't that big a problem.
The big problem is the material science, creating macro-scale nanotubes long enough to be woven into a cable or ribbon, and strong enough to support the ribbon itself plus whatever we want to lift. Last I heard (and I'm admittedly not following it closely at all) they could manufacture single nanotubes a meter long, and had nanotubes less than an order of magnitude from the desired tensile strength. But not at the same time. Still, it's promising, but there's a long way to go.
Once you've solved the material science problem, and hopefully made large-scale manufacturing feasible if not cheap, then it's mostly a matter of motivation. Laying down and occasionally carving paths through the mountains for 75,000km of interstate probably sounded daunting, but it got done because there was a perceived need. Between the military uses and commercial uses, I think it would exist for the space elevator too. But it would probably be the DoD who would have the money to do it. With low cost to orbit, Project Thor would be an economical reality. That's my pitch. I'm sure we could add more. Of course we have time, though, because for now, large-scale manufacturing of carbon nanotube cables is still a dream, and thus so is the elevator. :)
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Most of strength isn't needed for the payload but for the weight of the cable, so you gain very little by making a smaller payload elevator.
The point wasn't to reduce the tensile strength required; that material science problem still needs to be solved.
The point was that once you have accomplished that and it's a matter of manufacturing and will, you can make use of smaller cables in stages while waiting for the full construction to finish, much like you could use portions of the interstate system before it was done. But instead of making roads that are full width, but not the full length needed, you're making ribbons that are full length but not full width.
At least one substantial elevator proposal uses this approach.
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While the efficiency of a heat engine is great, the power to weight ratio is awful. So much in fact that it is really hard to build one that can lift itself.
A laser that is matched to the bad gap of a pv cell can be over 50% efficient. So it is not too bad on that front and a lot less weight then a heat engine.
By the way, a Sterling Engine is an engine made of silver, a Stirling Engine is a heat engine.
When you get caught in between the Moon and New York City... I know it's crazy, but it's true.
"Don't let fools fool you. They are the clever ones."
Turns out that divergence is set by the wavelength, larger the wavelength the bigger the minimal divergence. Check out http://en.wikipedia.org/wiki/Diffraction-limited_system . Our lasers wavelength is 808 nanometers. Compare that to say 1 centimeter for microwave and you can see that microwaves will always require a much bigger "lens/mirror" to focus them.