the basics of an orbit are litteraly that the object is falling towards earth, but has too much foward momentum to hit, it keeps missing. (very hitchiker, the secret of an orbit really IS to throw yourself at the ground, and miss)
and that small of a height, youd have to have an ENOURMOUS speed. or, something to slow the fall, which would take a lot of energy over time. On 5/15/05, Jones Beene <[EMAIL PROTECTED]> wrote: > Is it possible to position a large unmanned aircraft in > semi-permanent stationary "quasi-orbit" but at only 20-50 km in > altitude? > > This concept would allow such things as a really cheap replacement > space telescope, or an antenna array high enough to broadcast > television and broad-band communications all over a vast > undeveloped area, such as the state of Alaska, say, or > Afghanistan... or many other applications where satellites are too > expensive an option, or don't have enough power. But it could even > be a high "launching pad" for small satellites itself - IOW it > would be like dispensing with the first two stages of launch. > > Maybe it is possible soon. There has been a lot of interest in > space tethers here, and jet-stream windmills. Both just out of > reach with present technology. This concept is a little of both > and I don't think this slant on tethers has ever been considered > even though it is (probably) within the reach of present > technology. It appears to me, having just dreamed this up - that > combining two ideas into a hybrid could get this field 'soaring' > in the near term without the need for a major breakthrough in > structural materials (such as a stronger fiber than > Kevlar/Dnyeema)... > > The problem now is that the best fiber is just not strong enough > for useful tethers which allow stationary earth orbit, of the > geo-synchronous variety - but they are strong enough for several > tens of km, now - as long as you do not have large loads like > dealing with a wind-mill in the jet-stream of several hundred > MPH. And tethers have been made electrically conductive with > little penalty. Last month Robin estimated the longest Kevlar > cord that would sustain it's own weight is 290 km. For Dyneema it > is a bit longer. > > Extrapolating from available information, lets look at some > 'ball-park' figures. Lets say we have an electrically conductive > cable-tether, actually three of them which can carry 1-10 > megawatts of high-voltage three-phase AC power to 20-50 km of > altitude to power the craft in question electrically from the > ground-up. Is that possible? > > You would have to construct the three tethers in such a way that > every 10 meters or so you have a small pulsing strobe light, > visible during the day. This, and an electronic warning signal, > plus robotically controlled "tower operators" radioing-out to > pilots in the neighborhood - would help keep the tether from > being hit by other airplanes. > > We want to get a large drone airplane above the weather and > just slightly above the jet stream, but still at an altitude with > enough air pressure for large efficient propellers to work > against. Unlike the "jet-stream wind-mill" idea, the cable can be > much lighter than the windmill version, even though it is higher > in altitude, but of course it is using-power, not producing it it. > > Let's "bootstrap" another concept in order to put a "stationary" > craft and a succession of small payloads up there cheaply, and > keep the craft there (above the weather) for as long as the > materials and electrical motors, robotics, etc. will hold up with > limited maintenance - maybe 5-10 years. We can lift additional > loads up to it, assuming that the loads can be light and "KD" and > assembled robotically on the craft in question. This would be > beneficial for a high altitude ultra-cheap launch of payload to > even higher altitude. > > BTW, KD is a term used in manufacturing in the USA to > mean "knocked-down" which implies the product is designed so that > small parts can be disassembled and easily reassembled (usually by > the customer, like the cool stuff at Ikea). It is kind of an > anachronistic term nowadays as the parts were usually never > assembled first to make sure that they fit, as was once done. > > OK this is going to get a bit complicated. After all, it is a > hybrid. First - Check out "Flying circles around the helicopter" > in April 30 edition of 2005 "New Scientist" by David Hambling > http://www.newscientist.com/article.ns?id=mg18624971.600 > > To paraphrase: As far back as1956, fixed wing missionary pilots > learned this trick, which few others have heard of, even today, > although there is no good reason why it cannot be scaled up to a > much larger size. > > Basically, in situations where you can't afford a helicopter, a > low speed aircraft which can fly in tight circles over a "bull's > eye" drop point where a tether (rope) is lowered. The tether > naturally begins to take the vortex inverted-cone shape and > eventually can touch earth at a **single stationary location** > Items can be lowered or raised on > this rope. The tight circular flight path combines with the forces > of gravity and drag to hold the rope almost motionless at its > lower extremity, reminiscent of the tornado vortex. > > This "bucket drop" technique has proved invaluable for certain > situations using small planes but it has been largely ignored as > to scale-up - until now. Lately, a team of engineers at the Royal > Melbourne Institute of Technology in Australia are exploring the > same basic principles to devise a more sophisticated air delivery > system. They are working on an automated device that will allow > them to pick up and put down large loads - including people - with > hardly a jolt. If their system is successful, it could be > revolutionary... but they have perhaps missed the best use of all. > > Rather than use a traditional airplane to carry a tether up for a > few hours, just to replace what a helicopter can do - now we are > going to power an electric, very large drone computer controlled > airplane, from the ground-up, via the conductive tether, which is > still strong enough to raise a succession of light KD payloads for > launch form that high altitude - or many other potential uses. > > Manning the craft with humans is unnecessarily risky. The > payloads, perhaps one of them being the next version of Hubble in > KD form, can even manage to self-propel themselves up the > stationary tether using power induced from the tether itself to > drive their own propellers. They will not need to be pulled up. > > Of course, you can just mount items like a lower altitude space > telescope on a specially designed single purpose drone aircraft, > rather than launch one more cheaply, but it would be a problem to > keep it focused on one spot in the cosmos while the plane was > making continuous tight turns. > > That 20-50 km long electrically conductive tether (actually it > would have to be longer to account for the slack in the vortex), > will power a rather large robotically controlled airplane, driven > by electric motors once in place, and designed to automatically > operate at this altitude in continuous tight circles, constantly > adjusting and correcting for the wind speed etc, using a few xbox > computers, of course - and the tether is always plugged into the > same megawatt (could be more or less) power source, which could > itself be railcar mounted. > > Because so much power is available from the stationary source, > there is no need for solar cells on the craft, as they can hardly > carry their own weight anyway. > > Jones > > -- "Monsieur l'abb�, I detest what you write, but I would give my life to make it possible for you to continue to write" Voltaire
