khallow - 19/10/2007 7:46 PMBarry, I don't see a rotovator working from Earth's surface due to a combination of air resistance losses (both in winding up to speed and operating at speed) and just the physical space that the rotovator would operate in. If you were speaking of using this on the Moon, then that would be a different story.
Therefore another trick to achieve lower stresses is that rather than picking up a cargo from the ground at zero velocity, a rotovator could pick up a moving vehicle and sling it into orbit. For example, a rotovator could pick up a Mach-12 aircraft from the upper atmosphere of the Earth and move it into orbit without using rockets, and could likewise catch such a vehicle and lower it into atmospheric flight. It is easier for a rocket to achieve the lower tip speed, so "Single Stage To Tether" has been proposed. One such is called the Hypersonic Airplane Space Tether Orbital Launch (HASTOL).[9] Either air breathing or rocket to tether could save a great deal of fuel per flight, and would permit for both a simpler vehicle and more cargo.
Space elevators are going to be slow, limited to low mass loads and due to their extreme size very costly to build.
Rocket-based space launch systems are inherently limited by the physics of rocket propulsion. More than 90% of the rocket's weight is propellant, and the rest is split between the weight of the fuel tank and the payload. It is very difficult (if not impossible) to make such a vehicle safe or low cost. A target cost of $1000 per kg is proving to be impossible to reach. In comparison, airliners charge us about $1 per pound, and train transportation is in cents per pound
The Space Elevator is the most promising Space Transportation system on the drawing boards today, combining scalability, low cost, qualify of ride, and safety to deliver truly commercial-grade space access - practically comparable to a train ride to space.
The climbers travel at speeds comparable to a fast train, and carry no fuel on board ...
A space elevator will never work. Even if some wonder material were discovered that could actually take the stress (instead of snapping under its own weight), that cable would not survive long. After all, it has to go through LEO, and will inevitably be struck by space debris.
Build an orbital "Sky Bridge" all the way around the planet, despin the structure until it matches speed with the ground, and then lower guide cables to the ground, followed by construction of towers.Should take only a 1000 years of concerted effort or so. Then access to space would be cheap and routine. Maybe.
Quote from: aquanaut99 on 01/08/2011 04:31 pmA space elevator will never work. Even if some wonder material were discovered that could actually take the stress (instead of snapping under its own weight), that cable would not survive long. After all, it has to go through LEO, and will inevitably be struck by space debris.What if you just made a shield or shields for the tether in LEO? (Please see diagram)
QuoteSpace elevators are going to be slow, limited to low mass loads and due to their extreme size very costly to build.That's not what I'm seeing cited by the current SE experts who are in practical development of the SE ( see links here). A dollar value is cited that is much less than comparable construction values for ISS or rockets. I'll dig out the exact refs and citations but here's one ...
Thus, is the space elevator out of order? Our opinion is: at present, yes; but never say never. However, our proposed flaw-tolerant concept could be key for a terrestrial space elevator design far in the future. Moreover, a lunar space elevator, because of the lower gravity, could perhaps be realized with existing materials and an opportune flaw-tolerant structural design. Tethered space systems, pioneered by Grossi and Colombo in 1972, are more intriguing in the new era of nanomaterials.