From: vince@offshore.ai (Vincent Cate) Newsgroups: sci.space.policy Subject: Re: More Space Elevator news References: <744cc401.0406291219.7cc926@posting.google.com> <40E23F2D.2EEC057D@earthlink.net> <889ef2b7.0406300404.5d67cb3d@posting.google.com> NNTP-Posting-Host: 207.42.133.252 Message-ID: <9186edb5.0406302316.683c5c65@posting.google.com> henry@spsystems.net (Henry Spencer) wrote in message news:... > However, I would beg to differ about the real issue. The real issue is, > can beanstalks be *economically competitive*? Nanotube-based structural > materials will greatly improve the performance of conventional reusable > rockets well before they are good enough for beanstalks. And the more > optimistic economic analyses for beanstalks typically require assumptions > which would also do wonders for rocket economics. > > Merely beating today's rockets is not good enough; a new technology must > beat new rockets built using similar assumptions. That's much harder. Not only new rockets but it would also have to beat other new technologies, like rotating space tethers, as well. A rotating tether can recycle the energy from one tourist returning to Earth and give it to a new tourist going up. A rotating tether can be much shorter than a beanstalk and so cheaper. You can gradually transition from getting 40% of your delta-V from a tether to getting 95% from a tether as your rope material gets better, so you can start business far sooner. By the time a beanstalk becomes technically possible there should be a long established rotating tether business, so it would be harder to get people to invest in the beanstalk. A rotating tether can be below the Van Allen belts and toss cargo quickly through them so that radiation is not such a problem to either the tether or the cargo. A rotating tether can lift a cargo in less than an hour while a beanstalk takes much longer, so amortizing the capital costs over the cargo works better for the rotating tether. Etc. The rotating tether would always need some other method to get the cargo up to something like 100 km, but this could be a very reusable suborbital rocket. The design might be like the "pop-up booster" like John Carmack is working on, like SpaceShipOne, or something else. I think that suborbital tourism will drive this tech so that in 10 or 15 years it is very cheap to get to 100 km, even without nanotube-materials. A 200 lb person for $2,000 in 15 years, or $10/lb to get to 100 km, seems easy. -- Vince ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Vincent Cate Space Tether Enthusiast vince@offshore.ai http://spacetethers.com/ Anguilla, East Caribbean http://offshore.ai/vince ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You have to take life as it happens, but you should try to make it happen the way you want to take it. - German Proverb