The Ultimate Arch

[rogers_buck]

In the distant future we may have robotic space factories capable of mining asteroids and other bodies. That's the setting for this concept.<br /><br />Imagine that our industrious robots create a giant hoop of high-quality steel alloy. The hoop is so large that it will fit over the planet earth with about 100km clearance. This is no mere coincidence...<br /><br />Fast forward to a few years later when our enormous hoop has intercepted the earth in its orbit and has oscillated in a coaxial resonance to settle around the equator. The atmosphere at 100km up would do a nice job of damping the oscillations without burning up our hoop. Once at rest, the hoop just hangs there in the sky with only enough angular momentum to keep it sationary relative to the ground. Ignoring tidal forces the pull of gravity on the hoop is uniform around its circumference and the venerable old ancient arch of the hoop carries the load by compression.<br /><br />Attached to the hoop at regular intervals are modules bolted down by the robots for shipment. Now that the hoop is safely in place about the equator, the modules come to life and drop cables the 100km to the surface of the earth. The modules are attached to the hoop by strong magnetic fields are both for lifting and electricity.<br /><br />The hoop is now ready for operation. The electric cables are plugged into the grids all over the world. Steadilly the modules apply torque to the hoop to increase its angular momentum. When desired levels are obtained the modules can begin their work. The lifting crane from a given module picks up a payload off the surface of the earth and hoists it to the 100km platform atop the module. Once safely aloft, the payload is launched on a maglev trolly onto the band itself. The payload uses the hoop as a track to accelerate to the desired linear velocity before detaching. The angular momentum stolen from the hoop is then replaced by the modules.<br /><br />This scenario ignores the earth's magetic f

 

[vogon13]

The compression loads in your hoop would be rather severe . . . . <br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[rogers_buck]

When rotating at orbital velocity the compression loads would be zero. What do you calculate them to be at zero velocity?<br /><br />Pick a thickness for the hoop and you can calculate the volume since we stipulated the radius would be earth+100K. Plug in the density of steel and that will be the total loading on the hoop.<br /><br />

 

[Boris_Badenov]

I realize this is being nitpicky, but you mean the circumference, not the radius. <div class="Discussion_UserSignature"> <font color="#993300"><span class="body"><font size="2" color="#3366ff"><div align="center">. </div><div align="center">Never roll in the mud with a pig. You'll both get dirty & the pig likes it.</div></font></span></font> </div>

 

[rogers_buck]

No, the altitude of the hoop is 100K. I should have said R-earth instead of just earth for clarity.<br />

 

[vogon13]

100 km isn't far enough out of the atmosphere for orbital velocity without tremendous drag losses.<br /><br />So I assumed (sorry) the hoop wasn't at orbital velocity.<br /><br />I retract that compressive strength problem forthwith.<br /><br /><br />However, the hoop will not be stable (for complex orbital mechanics reasons). If one side of the hoop should descend ever so slightly (and the other to raise) it will contact the surface in short order. Compression and tension loads during this final phase will be extreme.<br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[rogers_buck]

Your only retracting so you don't have to do the arithmetic. To get a calculation out of a vogon you have to stick your digit, uh, never mind...<br /><br />But your initial point is within the bounds of my scenario. Until someone does the arithmetic we can't be sure that a steel hoop couldn't support its own mass without any rotation at all. A big number, but steel is pretty strong in compression.<br /><br />The ring is anchored all around by the modules and cables. It can't be perturbed unless something goes seriously wrong. By then, there won't be any terrorists because we will have killed them all off. The implants will take care of any of their relatives.<br /><br />

 

[rogers_buck]

Oh, the 100K was arbitrary, but I don't think there would be much in the way of aerodynamic problems in the ionosphere. It might actually be usefull as fuel for an ion ram jet riding on the maglev.<br />

 

[vogelbek]

If you're planning to hook up cables to the surface of the earth, the ring better be rotating at 1 rpm per day. To make a zero-loading condition on the ring, the thing had better be in a geostationary orbit, and that is a big ring!!<br /><br />Im inclined to think that a better use for all that metal would be to build a halo-type space structure, in an independant solar-orbit. You of course would need to have it rotating to have artifical gravity effects, and tall side-walls to keep the atmosphere in (I dont know how quickly the atmosphere would diffuse out the top though).<br /><br />I have a suspicion that unless we can outsmart the rocket equation with unobtainium-balonium alloy space elevators or milion sec isp, high thrust fusion rockets, the long term economics will be two branches of mankind - those who live exclusively in space, floating arround and taking what resources they can, and those who still live on earth, with limited means to actually get into space.

 

[rogers_buck]

>> you're planning to hook up cables to the surface of the earth, the ring better be rotating at 1 rpm per day. To make a zero-loading condition on the ring, the thing had better be in a geostationary orbit, and that is a big ring!! <br /><br />No, the modules are attached to the hoop only by a maglev field. The modules act as motors to exchange energy with the hoop. The hoop can rotate at orbital velocity @100K and the modules will remain stationary. The hoop could conceivably be at rest if it could structurally handle the stress, but it would more likely need to be spinning so it could be flimsy.<br /><br />When one of the module hoists up a payload it robs energy from the angular momentum of the hoop. The hoop will be kept at a constant altitude by the other modules anchor cables. The robbed energy will be replaced by the modules thrusting against the hoop. Once the payload is at the module it is transferred to a maglev trolley and launched onto the hoop. Again, energy is robbed from the angular momentum of the hoop as the payload accelerates to orbital velocity and beyond before detaching. The modules then electrically replace the lost energy by thrusting against the hoop.<br /><br />It is even conceivable that the hoop could be spun beyond the orbital velocity at 100K, right up to the tensile strength limit of the material. This could allow for more massive payloads than the compression strength of the hoop could support.<br /><br />No need for a GEO hoop.<br /><br />As far as the use of metal is concerned, the total length of power cables on the earth could rap the earth several times over. Robots work far cheaper than illegal aliens and this concept assumes the metal comes from asteroids and is pretty much free. The hard part would be getting the finished hoop out in the asteroid belt and safely around the earth. It would need to come in from above the ecliptic and drop down over the earth. It would oscilate around the equator in a strange orbital mode o

 

[nexium]

Turning the same speed as the equator, may be no more difficult than several other aspects of this project. It would allow less than 100 km altitude and about 0.98g inside the hoop.<br />If the hoop turns 17,000 miles per hour with respect to the air at an altitude of 100 km, then we need to think two hundred kilometers altitude to avoid large air friction loss. As the hoop warmed from perhaps 150 degrees k to about 250 degrees k, thermal expansion would increase the circumfrence to provide perhaps 100 km more altitude as the oscillations were damped. Neil

 

[nyarlathotep]

>"Im inclined to think that a better use for all that metal would be to build a halo-type space structure, in an independant solar-orbit. You of course would need to have it rotating to have artifical gravity effects, and tall side-walls to keep the atmosphere in (I dont know how quickly the atmosphere would diffuse out the top though)."<br /><br />With no gravity it would boil off instantly, you'd need to make the structure a toroid.

 

[rogers_buck]

Reentering space ships don't start to heat up much until below 80km. Not much in the way of partial pressure in the high ionosphere. You might want to choose you altitude for a different reason, like to avoid a partiuclar ion species. The delterious effects of the hot ions would be a problem.<br /><br />There are all kinds of interesting problems like thermal expansion. One part of the hoop would be shaded while the other part in the sun. The hoop would be rotating but that would create stress. Anything this big any stress becomes enormous overall. There are also the thermal electric effects that would be in full play, not to mention what happens when you move metal through a magnetic field. Just imagine how much of a jolt you would get during a solar flare... The electro-dynamics of this system are interesting in their own right - could be a show stopper, could be a source of stored electric power with a cosmic recharge...<br /><br />The robots might need to wrap the ring in a pretty white paint job. While they are at it, perhaps they could install lights on the inside edge. It would make for an amazing spectacle at night - the ecliptic a solid arc of light from horizon to horizon.<br /><br /><br />

 

[rogers_buck]

I think I'm going to write the arch into my science fiction story I'm working on.<br />

 

[derekmcd]

What would the effects be on weather patterns over the long term? If it is stationary over the equatorial circumferance of the earth, there would a permanent shadow (it would change in latitude with the seasons, of course). The umbra could be quite large depending on the angular size. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[rogers_buck]

Since the hoop would likely be only a couple of meters thick at most, there would be no noticeable shadow from it at 100K above the earth. The scattered sunlight passing through the troposphere would overwhe such a narrow shadow.<br />

 

[vogon13]

AT 100 KM, air resistance will be cumulative and severe. You will need a power source to maintain speed.<br /><br />If the hoop spins around earth at less than orbital speed appropriate for its' altitude, we are back to enormous compression loads that no known material can resist.<br /><br /><br />Installing the thing over the equator is going to be a real trick, too. As it approaches earth it will attempt to turn itself inside out. (really)<br /><br />It won't be pretty . . . .<br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[rogers_buck]

Steel alloy has really good compression characteristics, we need to run the numbers to see how slow we could go. Seems like there would be a few percentage points either way to play with.<br /><br />It might well be impossible to put the ring around the earth. The robots might need to actually build it there.<br /><br />

 

[owenander]

I'm sure there would be a more cost efficient and more practical method to use that much resources from asteroids.

 

[annodomini2]

Something similar is discussed here:<br /><br />http://uplink.space.com/showflat.php?Cat=&Board=businesstech&Number=530017&page=5&view=collapsed&sb=5&o=0&fpart= <div class="Discussion_UserSignature"> </div>

 

[barrykirk]

Just wondering....<br /><br />What is the maximum height possible for a tower based on the compression strength of steel?<br /><br />If it's over say 200 Km than what about anchoring a conventional space elevator to the top of the tower?<br /><br />That would keep the space elevator out of the atmosphere which is one of the biggest problems for a space elevator. It would also reduce the strength to<br />weight requirements slightly because the cable is slightly shorter.<br /><br />The portion of the space elevator eliminated is the part with the highest g-force, because it's closest to the earth and the part with the lowest centripetal acceleration.<br /><br />anyway just wondering.

 

[vogon13]

Have a docking port at the bottom of the space tether at the altitude Spaceship 2 can reach.<br /><br />Cheap easy access to the solar system . . . <br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[barrykirk]

Sure there is.... Just make the arch out of pure unobtanium... It will work. LOL

 

[Boris_Badenov]

<font color="yellow"> Have a docking port at the bottom of the space tether at the altitude Spaceship 2 can reach. </font><br /><br />SS2 hits about 2500 mph. A space tether in orbit would be traveling at around 18,000 mph. If you tried to transfer from one to the other you would experience g forces in the 500 range.<br /><br /> A Vogon might be able to handle that, but this fat chef sure couldn't<img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <font color="#993300"><span class="body"><font size="2" color="#3366ff"><div align="center">. </div><div align="center">Never roll in the mud with a pig. You'll both get dirty & the pig likes it.</div></font></span></font> </div>

 

[vogon13]

The tether hangs down from geostationary orbit over the equator. SS2 is launched from the equator. Speed relative to the tether at the top of SS2 trajectory is zero.<br /><br />Reach out and grab the damn thing.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>