# Couldnt a Magnet be used to throw objects into orbit? **URL:** \ **Category:** Factual Questions\ **Created:** [January 28, 2009, 6:54pm UTC](https://boards.straightdope.com/t/couldnt-a-magnet-be-used-to-throw-objects-into-orbit/483412 "2009-01-28T18:54:21Z")\ **Posts on this page:** 9\ **Page:** 2
**Author:** ![Tenebras](https://avatars.discourse-cdn.com/v4/letter/t/977dab/32.png) [@Tenebras](https://boards.straightdope.com/u/Tenebras)\ **Post date:** [January 28, 2009, 11:48pm UTC](https://boards.straightdope.com/t/couldnt-a-magnet-be-used-to-throw-objects-into-orbit/483412/21 "2009-01-28T23:48:29Z")
> [@Inigo\_Montoya](#): > > And (hijack) whatever happened to the cable-system to heaven wherein cables are anchored to the earth and extend well into space? Centrifugal force keeps the cables rigidly erect (heh) and you get stuff into space via elevator. The problem is that you have to build the cable out of unobtanium. The tensions involved in a space elevator are ridiculously large, and increase as the mass of the cable itself increases. So you need something which is crazy strong and crazy light. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 29, 2009, 12:43am UTC](https://boards.straightdope.com/t/couldnt-a-magnet-be-used-to-throw-objects-into-orbit/483412/22 "2009-01-29T00:43:08Z")
Except that that’s rapidly becoming an obtanium. Carbon nanofibers are strong and light enough; now we just have to figure out how to make them long enough and cheap enough. ---
**Author:** ![runcible\_spoon](https://avatars.discourse-cdn.com/v4/letter/r/9fc29f/32.png) [@runcible\_spoon](https://boards.straightdope.com/u/runcible_spoon)\ **Post date:** [January 29, 2009, 1:51am UTC](https://boards.straightdope.com/t/couldnt-a-magnet-be-used-to-throw-objects-into-orbit/483412/23 "2009-01-29T01:51:45Z")
> [@Tenebras](#): > > The problem is that you have to build the cable out of unobtanium. The tensions involved in a space elevator are ridiculously large, and increase as the mass of the cable itself increases. So you need something which is crazy strong and crazy light. Well, that’s what space fountains are for. ---
**Author:** ![Tenebras](https://avatars.discourse-cdn.com/v4/letter/t/977dab/32.png) [@Tenebras](https://boards.straightdope.com/u/Tenebras)\ **Post date:** [January 29, 2009, 4:20am UTC](https://boards.straightdope.com/t/couldnt-a-magnet-be-used-to-throw-objects-into-orbit/483412/24 "2009-01-29T04:20:54Z")
> [@Chronos](#): > > Except that that’s rapidly becoming an obtanium. Carbon nanofibers are strong and light enough; now we just have to figure out how to make them long enough and cheap enough. It depends on what you think an appropriate safety factor for an undertaking like this is. Here’s a paper I found by googling. [Link (pdf)](http://chaos.swarthmore.edu/courses/PDG07/AJP/AJP000125.pdf). I didn’t check the figures, but he’s doing the right kind of thing. If you look at the end of section 4 he says > [@](#): > > Suppose > we also incorporate a safety factor of 2 into the design, > that is, we ensure that the stress in the cable is only T > =50 GPa everywhere, which is half the maximum stress that > can be borne. Now, I don’t know about you, but if I’m going to build a gigantic ribbon into the sky, I want something more than a safety factor of 2 built into it. Especially since in these calculations we’re ignoring > [@](#): > > Among these threats are vibrations in the cable induced > by geophysical and astronomical sources, lightning > strikes, meteors, space debris, wind, atomic oxygen, radiation, > and erosion of the cable by sulfuric acid droplets in the > upper atmosphere. Perhaps even more alarming is the possibility > that the cable might snap and wrap itself around the > Earth, unleashing all sorts of catastrophes in its wake. We’re also ignoring tidal forces from the moon and the sun, as well as a rather impressive thermal gradiant. We’re assuming that the carbon nanotubes which are acceptable for terrestrial purposes can also be used in space. As in, half-way to the moon. If a mile of this cable costs as much to build and install as a mile of border fence along the Mexico border, we’re talking about around 150 trillion dollars. ---
**Author:** ![Tenebras](https://avatars.discourse-cdn.com/v4/letter/t/977dab/32.png) [@Tenebras](https://boards.straightdope.com/u/Tenebras)\ **Post date:** [January 29, 2009, 4:28am UTC](https://boards.straightdope.com/t/couldnt-a-magnet-be-used-to-throw-objects-into-orbit/483412/25 "2009-01-29T04:28:48Z")
Missed the edit window. There’s a guy called Edwards who thinks he can build one of these for $20 billion dollars\* at some point in the future. Given that the Burj Dubai tower is budgeted at $4.1B dollars, I’m a bit skeptical. - Some sources say $20B, some say $10B. The links I’ve seen to his actual paper have all been dead so I don’t know. ---
**Author:** ![aerodave](https://avatars.discourse-cdn.com/v4/letter/a/f08c70/32.png) [@aerodave](https://boards.straightdope.com/u/aerodave)\ **Post date:** [January 29, 2009, 4:36am UTC](https://boards.straightdope.com/t/couldnt-a-magnet-be-used-to-throw-objects-into-orbit/483412/26 "2009-01-29T04:36:00Z")
Wait…a safety factor of 2 isn’t enough for you? Have you been on an airplane lately? (And by lately, I mean ever). There, you’re dealing with a system which has catastrophic consequences for failure. But the typical factor of safety on all the important bits is 1.5, and for many subsystems, it is only 1.25. That’s just conventional aircraft design wisdom. The reason is not to invite risk, but going any more conservative makes an airplane that’s too heavy to fly. Or at least too heavy to fly anywhere efficiently. ---
**Author:** ![Tenebras](https://avatars.discourse-cdn.com/v4/letter/t/977dab/32.png) [@Tenebras](https://boards.straightdope.com/u/Tenebras)\ **Post date:** [January 29, 2009, 4:59am UTC](https://boards.straightdope.com/t/couldnt-a-magnet-be-used-to-throw-objects-into-orbit/483412/27 "2009-01-29T04:59:46Z")
Conventional aircraft design wisdom is also to test the hell out of everything, which is what allows them to get away with such low margins. They don’t build airplanes by saying “well, if the plane is in level flight on a clear day and none of the passengers weigh more than 130 pounds we’ll need this joint to be able to withstand force x. Let’s call it 2x and move on, shall we?” I’m not an aeronautical engineer, but according to wikipedia the safety factors range from 1.25 to 2, depending on the part you’re talking about. (The 2.0 figure is quoted for the passenger compartment, which I consider to be one of the important bits.) The current state of the art for CNTs seems to be around 65 GPa and all of these papers assume that somebody can make a product with a tensile strength twice that. If you’re building a space elevator without a counterweight you’re talking about a cable 144 000 km long. With a counterweight you can reduce that to only 100 000 km. If anything goes wrong the whole thing falls out of or into the sky and the safety factor of 2 was being applied to the wonderfully static world in which we build this space elevator out of CNTs which are twice as strong as actually exist and we built it on an airless planet which is the only object in the universe. Short version: I think a safety factor of 2 in this context is a wee bit optimistic. ---
**Author:** ![The\_Second\_Stone](https://avatars.discourse-cdn.com/v4/letter/t/bbe5ce/32.png) [@The\_Second\_Stone](https://boards.straightdope.com/u/The_Second_Stone)\ **Post date:** [January 29, 2009, 5:29am UTC](https://boards.straightdope.com/t/couldnt-a-magnet-be-used-to-throw-objects-into-orbit/483412/28 "2009-01-29T05:29:09Z")
IIRC I’ve been on a ride at Disneyland California Adventure that is a roller coaster that starts out as a rail gun, going flat, fast acceleration and then curves upwards. You could do a coil gun that ran for a few hundred miles an hour to build up speed and then slowly curve it upwards. At 3gs acceleration you could launch people this way (assuming they had a steering rockets, etc) and at 10gs or more you could launch just equipment. It would be a helluva lot cheaper than a space elevator. ---
**Author:** ![runcible\_spoon](https://avatars.discourse-cdn.com/v4/letter/r/9fc29f/32.png) [@runcible\_spoon](https://boards.straightdope.com/u/runcible_spoon)\ **Post date:** [January 29, 2009, 6:29am UTC](https://boards.straightdope.com/t/couldnt-a-magnet-be-used-to-throw-objects-into-orbit/483412/29 "2009-01-29T06:29:38Z")
> [@The\_Second\_Stone](#): > > IIRC I’ve been on a ride at Disneyland California Adventure that is a roller coaster that starts out as a rail gun, going flat, fast acceleration and then curves upwards. You could do a coil gun that ran for a few hundred miles an hour to build up speed and then slowly curve it upwards. At 3gs acceleration you could launch people this way (assuming they had a steering rockets, etc) and at 10gs or more you could launch just equipment. It would be a helluva lot cheaper than a space elevator. Except that, as noted, they’re gonna come back down at some point, and it’s gonna hurt. The main issue, though, is that to get up to low earth orbit (let’s assume they take a rocket with them to stabilize the orbit), they have to be going really, really fast to get that high. I calculate that getting to 350 km (which is about where the ISS is) would need an initial upward velocity of 9600 km/hr. In a vacuum. And that’s just the upward velocity - if you don’t want to be run over by the ISS at 27,000 km/hr, you also need a hell of a lot of forward velocity. I’m too tired to run the numbers right now, but suffice it to say, it’s REALLY GODDAMN FAST. And, again, wind resistance is going to make it have to be even faster, and also set you on fire. These are significant downsides. As a side note, the space fountain which I (somewhat facetiously) brought up suffers the same issues, although it generally sidesteps wind resistance by using a vacuum filled tube. The makeup of the miles-long vacuum-tube hanging from space, of course, is left as an exercise for the reader. [Previous page](https://boards.straightdope.com/t/couldnt-a-magnet-be-used-to-throw-objects-into-orbit/483412.md?page=1)