Space Elevator Question?

[bdewoody]

OK, assuming one can be built, how long will the ride up to a point where you can detach from the elevator take? I've been watching the Science Channel and in an ad for their upcoming space week they state that the ride will take 3 months. If that's true it seems like it will be a freight elevator only. <div class="Discussion_UserSignature"> <em><font size="2">Bob DeWoody</font></em> </div>

 

[tomnackid]

The only point on a space elevator that is actually in orbit is at geosycnchronous orbit, 26,200 miles above the equator. This would be the only point where you can step off the elevator and be in orbit. Any lower and you would fall to earth. Any higher and you are flung off into the solar system (which is usefull for interplanetary travel). <br /><br />So, do the math! At 60 miles per hour it would take 437 hours to reach geosynchronous orbit. That's about 18 days. None of the "climber" designs tested so far go anywhere near 60 miles per hour so several months for a trip seams reasonable. Of course by the time a space elevator actually gets built the climber technology may be better. Most speculations about human-rated space elevators propose some kind of magnetic levetation system like that used in high speed trains like Germany's Transrapid. The biggest problem is that even at 200 mph it would take almost 6 days to reach geosynchronous orbit. Not too bad, but that means spending a lot of time passing throught the van Allen radiation belts. The Apollo spacecraft (the only crewed vehicle to pass throught the belts) was traveling at 25,000 mph (Earth's escape velocity) and only spent a few minutes in the belts reducing the radiation hazard, but the astronauts still took some radiation damage from the trip. A crewed elevator car would have to be heavily shielded.

 

[thereiwas]

I seem to recall reading that Mars has no magnetic field, as its inner core cooled off much sooner than Earth's and so is not spinning. That would then mean that there is nothing like the van Allen belts around Mars.<br /><br />Perhaps the smaller planets without such belts are better places to use elevator technology.

 

[rocketman5000]

you should be able to step off the elevator at any point where your orbital velocity is great enough to obtain orbit. At altitudes below GEO you will simply move relative to the cable when you let go.

 

[tomnackid]

You are correct. I should have said that geosynchronous alititude is the only place where you can step off and be in a CIRCULAR orbit. Of course a stable orbit is just a fall taht does not intersect the ground. I remember seeing a diagram showing what orbits you would go into if you stepped off before GS. Most will eventually interesect the ground or the atmosphere making them unstable.

 

[bdewoody]

OK, but if you detached from the elevator in a capsule that has small thruster's couldn't you adjust your path to get into a circular orbit at some desired altitude ? Say the orbit of the space station.<br /><br />I can see where it would be much more difficult to re-attach to the elevator and ride it down. But boy wouldn't that be a much safer way to come home? <div class="Discussion_UserSignature"> <em><font size="2">Bob DeWoody</font></em> </div>

 

[larper]

You wouldn't need small thrusters. You would need giant thrusters. And lots of fuel. Say about an ET worth of fuel and shuttle engines to put a shuttle into ISS orbit after detaching from the elevator. What don't you need? The SRBs.<br /><br />All the elevator did for you was get you above the atmosphere, which IS a huge savings. But, it doesn't mean you don't have to match orbital velocity. At ISS altitude, you would still need to apply a delta-v of about 17000mph. <div class="Discussion_UserSignature"> <p><strong><font color="#ff0000">Vote </font><font color="#3366ff">Libertarian</font></strong></p> </div>

 

[nexium]

Most of the preliminary climber specs call for a constant speed of 200 kilometers per hour. Somewhat faster is desirable, but problems grow fast with higher speed. The coreolis forces are thought to be a minor problem, but the rollars heat the ribbon at high speed. If rollars are one meter in diameter, the climber moves upward at 3.14 meters per turn. At 1000 turns per minute, the speed is 3140 meters per minute = 3.14 kilometers per minute = 188 kilometers per hour. 5000 RPM is likely practical for the rollars, but not the ribbon. The ribbon may stay hot for an hour after the climber passes as heat loss in the vacuum of space is by radiation of infrared photons only. Neil

 

[docm]

<font color="yellow">The lowest mile or so of the ribbon will likely find itself a favored path for lightning during a thunderstorm.</font><br /><br />More than that. Thunderheads go up 5-6 miles plus AFAIK no one has satisfactorily addressed how the ribbon would behave in a sprite, elves, blue jet or other such super-discharge. Sprites and elves go as high a 60 miles. <div class="Discussion_UserSignature"> </div>

 

[nexium]

I understand there are a group of tethered balloons that are more or less permanently stationed at 15,000 feet = 4.5 kilometers altitude in the USA south west. I presume there is occasional lightening damage and occasional loss. Since these are to detect drug traffic the lightening data may be difficult to access. Liftport and the Dr. Brad Edwards plan is to locate the first few space elevators in an ocean local near the equator where thunder storms are very rare. None the less rare lightening losses are expected, so the first elevator or two will not be designed for humans.<br />I agree, the effects of sprite, elve, blue jet, or other super discharge are not known, nor is it known how well the ribbon will conduct electricity. My guess is the ribbon will not conduct as well as copper or steel.<br />Could an ion engine maintain long term an altitude of 50 miles, while dangling a mile of #30 copper wire, with soon to be available technology, to study elves, sprites and blue discharge? Neil

 

[MeteorWayne]

The fact that the ribbon would not conduct electricity as well as copper ot steel might not be a plus. It would mean higher resistance= more heat. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[nexium]

I agree, a wet string (Ben Franklin) may be more valnerable to lightning etc. than copper wire the same cross sectional area. If the ribbon has a non-conductive binder, the binder may be distroyed by micro arcs. Carbon melts at about 3550 degrees c, so the CNT may remain stong even if heated white hot. Neil

 

[docm]

<font color="yellow">Carbon melts at about 3550 degrees c, so the CNT may remain strong even if heated white hot.</font><br /><br />First we have to discern what type of lightning were talking about. Lightning comes in two flavors; negative and positive.<br /><br />Negative makes up 95% of lightning. Up to 500 MJoules and temperatures near 28,000 °C (50,000 °F). So much for CNT's 3,550 °C <img src="/images/icons/tongue.gif" /><br /><br />Positive lightning makes up 5%, can last up to 10x longer and deliver up to <b><font color="yellow">300 GJoules</font></b> God knows how hot it would get, but positive lightning has brought down airliners.<br /><br />IMO you'd better build that ribbon out of Unobtainium. <div class="Discussion_UserSignature"> </div>

 

[nexium]

anvel suggested: If we accept the notion that tens of thousands of miles of this ribbon can be manufactured and lowered/raised from GEO, we can accept the notion that the bottom few miles are sacrificial, and can be rebuilt in short order. Perhaps an electrical surge detector could be placed at ten or twenty miles up. If a lightning inspired surge were detected, a lower portion of the ribbon could be uncoupled via explosives or some such thus protecting the majority of the ribbon by sacrificing the lower few dozen miles of it. <br />Me: Disconnecting is not difficult, but how do we compensate for the lost twenty tons of tension plus perhaps a ton of ribbon? We can dump some of the counterweight, but it will take 7 plus hours for that to affect the bottom end of the ribbon. If we have a station at GEO altitude, we can pull the ribbon from the top and push it toward Earth. This will take about 2 hours to affect the Earth end of the ribbon. Perhaps both the station pull and the counter weight reduction are best. Perhaps about an hour before the shortened ribbon is reattached to the anchor ship, the GEO station can reverse = pulling ribbon up and pushing it toward the counterweight. It will not be possible to launch any climbers at the anchor ship until the ribbon is stablized with it's reduced counterweight, but out going climbers can move slowly away from the GEO station toward the counterweight to gradually recover the lost mass at the counter weight. The anchor ship can slowly unreel more ribbon to restore the original length.<br />Fortunately lightning problems will be rare, and so will a ribbon cut by an aircraft collision or terrorist in the ocean location liftport has selected. Neil

 

[nexium]

I was listening with half an ear, so perhaps one of you can supply details. It seems there has been a debate as to weather carbon is a magnetic material or non-magnetic. An experiment confirmed, I don't know which. Mag lev looks more attractive, if carbon can be made highly magnetic.<br />A ten kilometer tower is likely possible with a broad enough base, but it would be extremely costly even if cheap very stong and light material becomes available. We may build a one kilometer tower in the next year or two. Generally it is prudent to increase the height only a little in each subsequent tower, to reduce the number of unpleasent engineering surprises, so it may take a century to work our way up to building ten kilometer towers.<br />Tower is desirable if we build the liftport on land, but we are presently thinking an anchor ship in the ocean where storms and lightening are very rare and the ship can likely dodge the tiny storms that do occur rarely.<br />I think the fountain concept will work, but it requires a large energy input even when there is no pay load to lift. Neil

 

[docm]

<font color="yellow">I don't know which. Mag lev looks more attractive, if carbon can be made highly magnetic. </font><br /><br />Link....<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p><b>Carbon Joins the Magnetic Club</b><br /><br /><b><font color="yellow">The exclusive club of magnetic elements officially has a new member—carbon. Using a proton beam and advanced x-ray techniques, researchers at the Department of Energy's Stanford Linear Accelerator Center (SLAC) in collaboration with colleagues from the University of Leipzig in Germany have finally put to rest doubts about carbon's ability to be made magnetic. The results appeared in the May 4 edition of Physical Review Letters.</font></b><br /><br />Scientists have long suspected that carbon belongs on the short list of materials that can be magnetic at room temperature, but proof of that hypothesis has languished in controversy for nearly a decade. Since antiquity, magnetism has appeared to be a trick performed only by iron, nickel, cobalt and a handful of rare alloys.<br /><br />"In the past, some groups thought they had discovered magnetic carbon," said Hendrik Ohldag, the paper's lead author and staff scientist at the Stanford Synchrotron Radiation Laboratory (SSRL) at SLAC. "Unfortunately, they realized later that they were misled by small amounts of iron, cobalt or nickel in their samples."<br /><br />Carbon's possible magnetic identity first emerged when meteorites were found containing bits of the magnetized element, but those flecks of carbon were packed in close proximity to nickel, leading to the suspicion that the observed magnetism came from the nickel. But until now, attempts to prove that pure carbon can be magnetized have remained unconvincing.<br /><br />"With carbon, we know how to make things very small," said Ohldag. "On the other hand we know a lot about how to process and store information u</p></blockquote> <div class="Discussion_UserSignature"> </div>

 

[marcel_leonard]

I for one don’t see the practicality of a space elevator; if you look at the orbital mechanics of a rotating earth not mention weather dynamics this project seems about as feasible as the super cannon that could shoot satellites into orbit. If anything thing it seems to me that in the long run a space elevator would be a more expensive option for orbital deliveries… <div class="Discussion_UserSignature"> "A mind is a terrible thing to waste..." </div>

 

[tomnackid]

Um, the military HAS shot things into orbit using slightly modified naval guns. As for the orbital mechanics [of space elevators] they have been worked out since Kontantine Tsilokovsky. In fact he first proposed the concept back at the beginning of the 20th century--although as a though experiment, not as a serious engineering concept. The problem lies in the engineering not the physics. Its is a BIG, BIG, BIG project. One we might not be ready for in terms of materials and equipment for a long time.<br /><br />As for the practicality: Using a rocket to put something into orbit is like throwing your paylaod across a canyon. It either makes it or it is destroyed--either way its a violent proposition. A space elevator is like carrying it across on a bridge.

 

[docm]

<font color="yellow">As for the orbital mechanics they have been worked out since Kontantine Tsilokovsky. In fact he first proposed the concept back at the beginning of the 20th century--although as a though experiment</font><br /><br />Actually the gun-as-space-launcher concept started with Jules Verne's 1865 story "From the Earth to the Moon") and its 1870 sequel "Around the Moon".<br /><br />Personally I think the space elevator has numerous complications that while singly problematic could also add up to a "perfect storm" situation. <div class="Discussion_UserSignature"> </div>

 

[tomnackid]

I meant the orbital mechanics of space elevators. Sorry.

 

[bdewoody]

I agree, thats why I started this thread by saying OK assuming you can build one.<br /><br />We will probably find a way to neutralize/repel gravity before we are able to build a space elevator. <div class="Discussion_UserSignature"> <em><font size="2">Bob DeWoody</font></em> </div>

 

[gunsandrockets]

<Um, the military HAS shot things into orbit using slightly modified naval guns.><br /><br />The modified 16" gun for HARP only fired suborbital shots. From what I recall a large amount of high altitude data was aquired for considerably less cost than sounding rockets.<br /><br />There were plans for orbital shots, but they were never conducted. I believe the orbital projectile was called the Martel. It was a gun launced rocket.<br /><br />I think a gun launched rocket has tremendous potential for cheaply delivering durable, bulk payloads such as propellant and life support consumables into LEO.