h a l f b a k e r yCogito, ergo sumthin'
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UPDATE: I've proven that the idea described below is impossible even with todays strongest materials. See annotations.
Currently launching things into space uses is extremely polluting and uses vasts amounts of fuel.
If we can build a gigantic trebuchet with modern materials (carbon fiber) that
can fling things into space we could have a clean space program. It could even be wind powered.
I would like the giant trebuchet to be built in an underground chamber that is under vacuum. That way there will be no air resistance until the projectile leaves a small trap door on top of the chamber.
A trebuchet is superior to a cannon because the acceleration occurs over a longer period of time and is thus more gentle.
Sling
http://www.skidmore...Slingshot.nomad.jpg
The kind of sling I meant. [jmvw, Nov 02 2006]
Trebuchet range calculator for Apple and Windows
http://www.algobeautytreb.com/
[jmvw, Nov 02 2006]
And the mathematics behind the range calculator...
http://www.algobeau....com/trebmath35.pdf
Discusses the mechanics behind a number of Treb variations. [zen_tom, Nov 02 2006]
Space shuttle emissions
http://www.madsci.o...973014746.Es.r.html
Page seems to downplay pollution of space shuttle. [jmvw, Nov 03 2006]
Spreadsheet of simple sling model
http://spreadsheets...Lotn6obSNEs-IGLWwIg
You'll need to set up a google account for this. [jmvw, Nov 03 2006]
momentum exchange tethers
http://www.tethers.com/MXTethers2.html
ok, so it's not underground but who cares [fenn, Mar 22 2008]
more formulas
http://yarchive.net...sling_launcher.html
some more discussion of ground-based slings [fenn, Mar 22 2008]
rotovator to orbit without rockets
http://www.tethers....HASTOLAIAAPaper.pdf
fly fast enough and an orbiting skyhook can grab you. [fenn, Mar 22 2008]
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“Give me a place to stand and a lever long enough and I will move the world”
Archimedes, 220 BC
I would be interested to know just how long the lever would need to be.
The mass of the weight would also be a a not insignificant consideration.
The irony is that the HB tagline that fell on this idea was "Faster than a Stationary Bullet"
Oh how I miss Bristolz!. I can imagine the picture but have no way of rendering it. |
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careful, here be [carbon fiber magic] dragons. |
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Magic? Maybe.. it'd be fun to do some calculations on this one. If not a trebuchet, a giant sling? |
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(edited; PollyNo9, sorry, I meant a sling or shepherds sling, not a catapult) |
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It would be fun to do some calculations? You mean you haven't? |
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Alternatively, mount the trebuchet on a solar powered electromagnetic railgun, duct tape some buttered toast to the underside, and run the calculations for immersion in custard, then when the projectile hit fresh air the drop in viscosity combined with maximum velocity would cause it to accelerate beyond the atmosphere. |
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I don't know how to tackle the trebuchet, but in case of the sling.. if we'd have a line that is 1 km long, we'd have to hurl this around until it turns 16 times in 9 seconds. |
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I have not been able to find rope that is light and strong enough to do this. With a weightless rope, the force on the rope that whips a 1000kg satellite around would be 12.5 MN, but the weight of rope strong enough to do that is considerable (about 15000 kg for the rope I found) and for that we'd need a stronger rope, that is heaver and so on. With a 100 m rope, the centripetal force would be 125 MN and with a 10 km rope it would be 1.25 MN |
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egberts method may work better. |
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//Give me a place to stand and a lever long enough and I will move the world”
Archimedes, 220 BC// far be it for me to disagree with old Archimedes but where exactly was he figuring on standing when he was gonna shift the world? |
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He leaves that to you when he asks for a place to stand. What he fails to ask for is a suitable fulcrum point about which he can develop a moment. |
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Hang on, let me develop a moment. |
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I just take mine to Boots. |
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//far be it for me to disagree with old Archimedes but where exactly was he figuring on standing when he was gonna shift the world?//
On a turtle. The earth was supported by a giant turtle in those days, so he’d have to find two more turtles--one for himself and another for his pivot point. |
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Meaning that should anyone have wanted to move the Earth back in those days, rather than faffing about with levers and pivots, all they actually needed was a big enough piece of lettuce. |
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//Currently launching things into space uses is extremely polluting// Really? In what way exactly? Which materials are released into the environment and in what quantities? |
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It's not extremely polluting. |
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Perhaps. I found a page that claimed it isn't, see link, but that page also talks about water and CO2 as the only combustion products of kerosene, which doesn't seem entirely accurate. Either way, the amount of fuel consumed is humungous. The CO2 production is huge and today this is a considerable pollutant. |
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I doubt emissions of space launches have been researched as well as automotive emissions or if emissions were ever measused. |
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Having to lift all of the fuel required for launch accounts for a large percentage of, well, the fuel required for launch. However, even eliminating this, you're still trying to get out of a rather large gravity well. A trebuchet would be a big improvement, but still fairly profligate in terms of energy usage. |
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Phlish, my intuition tells me you're right, but I am unable to verify this. I did verify it for the sling and there seems to be no rope that even comes close to having a sufficiently high strength/mass ratio. |
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... and since a trebutchet is, in fact simply an enlarged version of the staff sling, the materials needed would be quite similar. |
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I'm guessing that if you put this in a vacuum, that would be a big vacuum area, and opening the door for the projectile to fly out might cause a draft strong enough to stop the projectile. Even if not, creating such a vacuum is likely to cause more problems than it solves. |
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A better solution might be to build the trebutchet on a very tall platform... or figure out some way to loft it by blimps... to an altitude where the wind resistance is significantly less. |
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An even better solution might be to reserve trebutchet space programs for smaller airless worlds, such as the moon... or oen of the moons of Mars anyway. |
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I would point out that since the trebutchets are gravity powered via counterweight, there is a very real question as to whether or not the gravity used to pull one object down can be used to leverage another object beyond orbit at all. |
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I did some additional calculations and was able to prove that this idea actually is impossible, even with carbon fiber. |
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I used a simple model that assumes a long round stick with a point mass satellite at the end that is whipped around and flings the satellite away. I found out that even carbon fiber does not have sufficient tensile strength to do this. The mass of the boom itself is always sufficient to tear it apart. |
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Considering that this is impossible, a trebuchet, which arm will not have less weight or more tensile strength is also impossible. |
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For those interested, I made my spreadsheet available in Google spreadsheets. See the link. |
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ye_river_xiv, my model is what you called a staff sling. |
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//I would point out that since the trebutchets are gravity powered via counterweight, there is a very real question as to whether or not the gravity used to pull one object down can be used to leverage another object beyond orbit at all.// |
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I don't see why not (given less gravity). Just use a long enough boom and enough weight. Our restriction on earth is in material strength. |
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I think I'll let a next idea "very tall tower" pass for now. |
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ATTENTION: Would the next person to make it into orbit please toss us down a line? Thanks! |
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I was thinking one could do this in
stages, with a very (very) large treb
hurling up a smaller one, which in turn
hurled a smaller one, and they told two
friends, and so on and so on. But I do
not think that a flying trebuchet will
fling anything - all parts are moving
together, and so there is no difference
to harness. |
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Not only is this not impossible, it's quite feasible. Much more feasible than the silly space elevator, to the point of being possible to construct and launch with today's materials. The general idea is known as a momentum exchange tether. See tethers.com link |
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Not wind powered, but solar powered.
There's even a neat animation on that page showing the tether picking up a payload mass and flinging it into a higher orbit. |
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With some modest improvements in material strength to weight ratio, the tether could pick up items from the Earth's surface. |
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Yeah! and that vacuum is gonna seal itself. |
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//extremely polluting and uses vasts amounts of fuel// Couldn't we just fit the Space Shuttle with a catalytic converter? Hybrid space shuttles maybe? |
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// But I do not think that a flying trebuchet will fling anything - all parts are moving together, and so there is no difference to harness. // — [bungston] |
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Consider the idealised trebuchet mentioned above, where the payload is a point mass. That point attains a maximum velocity (limited by materials) of v1. |
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Now, make that point the pivot center of a smaller trebuchet, T2, itself the "payload" of T1. |
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Just prior to attaining v1, the smaller trebuchet (T2) is activated. Prior to activation, all parts of T2 are, as you correctly point out, moving at ~v1. But upon activation, the counterweight of T2 experiences an acceleration towards the ground, falls down (relative to the pivot center), and accelerates the far end of T2 (relative to the pivot center) in the ordinary manner. |
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The only part of T2 which experiences no delta-V is the pivot center. The counterweight and the payload both experience delta-V - both relative to the pivot center *and* relative to the earth. |
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The release of T2 should be timed such that its payload end attains maximum velocity (v2) at the same moment as v1. |
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v2 is *relative* to the pivot point of the second trebuchet, which is itself travelling at v1. So the velocity of the second-stage payload relative to the earth is v1 + v2. |
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One can continue this procession of smaller and smaller trebuchets to the point of diminishing returns, which is likely to be (wild guess) somewhere between three and five stages. As long as all the mechanisms are timed to attain maximum relative velocity simultaneously, the effective velocity is (v1 + v2 + ... +v{n}) |
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This is no less feasible than staged rocketry, which is in entirely the same manner a solution to the limits of known materials and fuels. A single stage to orbit rocket, in the time of Konstantin Tsiolkovsky, was shown to be an impossibility with known materials, so the staged rocket was proposed as a solution, later proven in practice. |
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Sub-note: should materials for a single arm trebuchet / single rope sling prove insufficient, consider constructing wheels instead, on the principle of bicycle wheels, where the forces are distributed as a combination of tension and compression amongst different members. |
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/Just prior to attaining v1/.../But upon activation, the counterweight of T2 experiences an acceleration towards the ground, falls down / |
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I am glad to read an anno from you, Bunsen. Imagine I myself am T1, flying thru the air and approaching speed v1, and a rutabega in my hand is T2. I release T2 as I fly thru the air. I do not think it will fall away from me or experience any new acceleration. Rather it will continue in the air alongside me, just as it was when it was in my hand. |
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Yes, the second stage trebuchet is in free-fall
after launch so it has effectively zero gravity and
won't work. |
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A catapult or crossbow that stores energy using
tension is better for later stages anyway since
they store more energy per unit mass than a
trebuchet [citation needed]. The advantage of a
trebuchet as a siege weapon is that it can be
transported without the counterweight, making it
more portable than the equivalent catapult. The
counterweight can be assembled or filled using
materials gathered near the destination. (Or was
the majority of the trebuchet normally assembled
using locally harvested timber?) I'm really just
making this up you know... |
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Does that make said tre' a sustainable locovore kind of weapon? |
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" anyone have wanted to move the Earth back in those days, rather than faffing about with levers and pivots, all they actually needed was a big enough piece of lettuce" |
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//(Or was the majority of the trebuchet normally
assembled using locally harvested timber?) I'm really
just making this up you know...// |
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According to Michael Pancreas's excellent history of
Roman (and other) siege weapons, trebuchets were
normally transported in kit form, having been
manufactured at the nearest secure location with
access to the necessary materials (ie, trees). |
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There are also records of very large trebuchets being
designed, Transformer-stylee, to interconvert
between being a horse-drawn wagon and a
trebuchet. In this respect, they were a bit like those
fairground rides that fold up to become an HGV
trailer. |
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The counterweights were sometimes sourced at the
point of use, but often not. The ideal counterweight
is a single solid mass, and some care was needed in
selecting or making one. |
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I think a railgun up the side of Everest would prove more
effective than a trebuchet at sea level, allowing the vehicle
to exit the accelerator at 1/3 atmospheric pressure, no
pumps or gates needed. |
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Accelerate over 50km, and ignite chemical engines during
the last few km. Engines would probably not be at
maximum at that point since it's pretty close to where
rockets encounter maximum dynamic stresses due to air
friction. |
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Perhaps a system like this on Mars could actually launch
something directly into orbit. On the Moon, for sure. |
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Then again, a trebuchet is the Rube Goldberg machine of
projectile launchers, so wins on coolness alone. |
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Now I want a handgun trebuchet, and a fishing rod
trebuchet, and a bionic baseball-pitching trebuchet arm.
There's just something so alluring about the click-drop-
rotate-fling that mesmerizes me. |
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