You are not logged in.
In the sprit of further exploring space elevators I propose what I call the atmosphere scoop. Generally space elevators are placed in GEO, the moon uses the Lagrange points. Venus has no practical GEO. Even the earth rotates very slowly. For most of the way to GEO gravity is quite a bit larger then centripetal acceleration. GEO is 36 000 km above the surface of the earth. http://www.spaceflight.esa.int/users/fi … lt]However the ISS never gets much past 416 km above the earth. Gravity does not drop by ¼ until around 6000 km from the earth. If the space elevator is moving faster then 1 revolution per 24 hour then it could be placed at a much lower orbit. The question is there a stable aerodynamic shape that can ram significant quantities of air into a tube at orbital speeds. What altitude would such a vehicle operate at? What is the density of the air at that altitude? What is the temperature and pressure of the compressed gas due to the ram? How much fuel would it take to over come the friction forces? The engine should use the fuel that is pumped up to orbit. Weather such a system could be made significantly lighter then the normal space elevator depends on the propulsion method and the power source. The thought is if you can get enough carbon by pumping fuell into space this way you could build a normal space elevator. One big problem I see is at higher altitudes the air is most hydrogen and not nitrogen and carbon dioxide.
Dig into the [url=http://child-civilization.blogspot.com/2006/12/political-grab-bag.html]political grab bag[/url] at [url=http://child-civilization.blogspot.com/]Child Civilization[/url]
Offline
Like button can go here
Since a supply of fuel is continuously being bumped up maybe resisto jets would be appropriate for station keeping. The engine might not have to fire continuously. There could be several engines. One at the scoop, one at LEO and one at the top of the pipe. Maybe you would need a higher ISP to keep the thing up. It depends on the drag and the rate fuel is pumped up.
Resistojets
Resistojets operate by passing gaseous propellant through an electric heater and then expanding it through a conventional nozzle to create thrust. Resistojets are normally operated as enhanced chemical propulsion systems where electric heating is used to further expand and accelerate propellant that has already undergone a chemical reaction.
The most successful application of this technique to date has been the superheating of catalytically decomposed hydrazine, which offers the advantage of fuel commonality with a frequently used monopropellant chemical propulsion system.
The specific impulse that can be achieved with hydrazine resistojets is limited because the molecular mass of the gases used is relatively high and because the maximum heating surface temperature that can be sustained with available materials is limited to around 3000 K. This results in an achievable exhaust velocity of about 3500 m s-1 (Isp = 350 s) some 40% better than without superheating, with an efficiency of up to 80%.
Resistojets were first used experimentally in space during the mid nineteen-sixties. Their first operational use was for north-south station keeping on the Intelsat-V series of geostationary communication satellites in the 1980s. They were also used for orbit insertion
from: http://sci.esa.int/science-e/www/object … 7]Electric Spacecraft Propulsion
Dig into the [url=http://child-civilization.blogspot.com/2006/12/political-grab-bag.html]political grab bag[/url] at [url=http://child-civilization.blogspot.com/]Child Civilization[/url]
Offline
Like button can go here
Hi John!
It's an interesting thought but I suspect atmospheric drag is going to be the show-stopper.
If the scoop is kept high in the atmosphere, to minimise drag, your centre of gravity will be higher, meaning a lower orbital velocity and consequently slower scoop speed, and there's less gas available to scoop.
On the other hand, if the scoop is allowed to operate in lower denser regions of the atmosphere, where intake of gases would be much greater, and your centre of gravity lower and orbital speed higher, the effects of drag on the whole structure would also be much greater.
It seems likely to me you'd either have too little gas flow to make it worth the trouble, or so much drag you'd be using all the gas flow just to feed the station-keeping engines!
Of course, I may be quite wrong about the whole thing and a mathematical evaluation might demonstrate it can be done. But I doubt it because it smacks a little too much of the old classic perpetual-motion-machine concept. Friction is a powerful dissipator of energy and entropy is hard to beat.
:bars:
The word 'aerobics' came about when the gym instructors got together and said: If we're going to charge $10 an hour, we can't call it Jumping Up and Down. - Rita Rudner
Offline
Like button can go here
There was a plan to use long draglines in space to propel packages just by swinging them. What if we use a line through an atmosphere would it work and could it simply syphon through the line. Or would it be dragged down.
Interesting idea this.
Chan eil mi aig a bheil ùidh ann an gleidheadh an status quo; Tha mi airson cur às e.
Offline
Like button can go here
It seems likely to me you'd either have too little gas flow to make it worth the trouble, or so much drag you'd be using all the gas flow just to feed the station-keeping engines!
Of course, I may be quite wrong about the whole thing and a mathematical evaluation might demonstrate it can be done. But I doubt it because it smacks a little too much of the old classic perpetual-motion-machine concept. Friction is a powerful dissipator of energy and entropy is hard to beat.
Well the question is what kind of specific impulse do you need to keep a reasonable fraction of the fuel and how big a power plant would you need to provide the energy. I chose resisto rockets because you would need less energy but maybe there would be enough fuel coming up for those engines to work and you would need a higher ISP engine. Anyway I was thinking if it could be done you could gradually boost the orbit of the upper station and lower the orbit of the scoop. Friction would become less an less lower the rotational speed came. Clearly there is a point where it is practical but it may require such a long cable that you might as well build a normal space elevator or pipeline.
Dig into the [url=http://child-civilization.blogspot.com/2006/12/political-grab-bag.html]political grab bag[/url] at [url=http://child-civilization.blogspot.com/]Child Civilization[/url]
Offline
Like button can go here
NASA had something like this on the drawing table, once.
PROFAC But it was only for H, I think. Got scrapped because ion engines were not mature enough, and they didn't have a nuclear reactor (another option) small enough.
Weve]http://www.newmars.com/forums/viewtopic.php?t=2458]We've been talking about this in another context BTW.
Offline
Like button can go here