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Robert Tulip
2010-Jun-27, 11:12 PM
Attached is a drawing of an imaginary space trebuchet.


At what points would the physics of this model prove unviable?
How big is the gap between the maximum physical size and power of a trebuchet and the velocity needed to send material to orbit?
How big would it need to be to send a payload of 100 grams to geostationary orbital height?
How would the arm of the trebuchet snap at the scale needed for the required velocity?
When and where would be the first points of breakage after release of counterweight?
Could the arm snap at the arrow points on release of payload, leaving the beam to spin around the fulcrum?
What material properties would prove most problematic (cost, rigidity, torque, etc)?


Many thanks for any information on these questions.

korjik
2010-Jun-27, 11:31 PM
You would need to be able to accelerate a mass to 11kps in around 100 meters. That would be accelerations in the tens of thousands of gs.

Do we need to go on?

Robert Tulip
2010-Jun-28, 04:20 AM
You would need to be able to accelerate a mass to 11kps in around 100 meters. That would be accelerations in the tens of thousands of gs.

Do we need to go on?

Thanks korjik.

So okay, revising the approach slightly, if you dropped ten tons of water from a tower two kilometres high onto one end of a beam to spin the beam around a fulcrum, how high could you sling a ten gram ball?

Forgive my ignorance, I’m just wondering about the physics of how much energy can be transferred from a falling object in this way. For example, if the weight is falling at 110 meters per second, it has to shift that momentum into upward motion one hundred times as fast, 11 kilometers per second, to send a ball to the 36,000 km geosynchronous height. In the example here the downward force, ten tons at 110 metres per second, is 100,000 times the mass of the ten gram ball, and has to transfer 100 times its own speed to the upward speed of the ball, by spinning the beam to crack the rope of the trebuchet like a whip. Is this conceptually possible with super-hard materials? Could any materials withstand this acceleration?

Jeff Root
2010-Jun-28, 04:55 AM
When I read the topic title, I assumed that you meant a trebuchet
in Space, or possibly on the surface of the Moon. A trebuchet on an
asteroid would actually be the only sensible location.

The limiting factor for getting something into Space with a trebuchet
on Earth's surface would likely be aerodynamic and frictional heating,
which would melt or burn through any material used as a "rope".
Although the rope might snap before it could reach speeds where
heating became the dominant factor.

-- Jeff, in Minneapolis

Robert Tulip
2010-Jun-28, 05:36 AM
When I read the topic title, I assumed that you meant a trebuchet in Space, or possibly on the surface of the Moon. A trebuchet on an asteroid would actually be the only sensible location. The limiting factor for getting something into Space with a trebuchet
on Earth's surface would likely be aerodynamic and frictional heating, which would melt or burn through any material used as a "rope". Although the rope might snap before it could reach speeds where heating became the dominant factor. -- Jeff, in Minneapolis

Thanks Jeff, does that mean a small trebuchet on an asteroid could send material to the earth? Would it be possible to send a self-assembling robot trebuchet to an asteroid?

On the acceleration, what is the formula to calculate how long getting from 0 to 11 kps in 200 metres would take? (more or less than 0.05 seconds?)

Could the barriers that the rope goes over and under to accelerate it be magnetised so the rope passes through a magnetic field, without friction except from the air?

If the rope is some sort of fine ceramic metallic chain, will it definitely burn through and break well before reaching 11 kps?

Apologies if this is frivolous, I am just wondering how far this concept is from practicality. Seems impossible!

whimsyfree
2010-Jun-28, 08:12 AM
You would need to be able to accelerate a mass to 11kps in around 100 meters. That would be accelerations in the tens of thousands of gs.


The OP idea is a non-starter, but a launcher with that sort of acceleration is possible: the space-gun.

Jeff Root
2010-Jun-28, 08:13 AM
A small trebuchet on a near-Earth asteroid might be able to send
material to Earth, or into the L4 and L5 Lagrange orbits. In the main
asteroid belt, a small trebuchet might be used to send material from
one asteroid to another, or to an orbiting facility in the main belt.

To calculate the time required to reach a given speed over a given
distance, assuming constant acceleration (which may or may not be
a good assumption for a trebuchet), and assuming I've thought it out
correctly, just divide the distance by the speed difference!

200 m / 11,000 m/s = 0.018 s

I'm looking at photos in a book, of a stainless steel model aircraft being
subjected to simulated conditions of flight at about Mach 6. The nose
and wings were completely melted. 11 km/s at sea level is Mach 32.

I don't know how long the model was subjected to those conditions.
It takes time for anything to heat through. Very little heat would be
conducted in just 0.018 second, but at 11 km/s, the entire thickness
of the material might erode away even in such a short time.

You can probably find the limits of what magnetic fields can do to
help in this situation by looking up "magnetic rail gun", "mass driver",
and "Gerard K. O'Neill".

-- Jeff, in Minneapolis

Robert Tulip
2010-Jun-28, 03:38 PM
A further iteration. Changing to a space catapult as attached, I imagine even by imparting much of the power by spinning the axle no materials would be strong enough to accelerate at this pace.
Thanks

Robert Tulip
2010-Jun-29, 03:51 AM
Could such a catapult (http://www.bautforum.com/attachment.php?attachmentid=13357&d=1277739415), on maximum feasible scale, provide a platform to launch a powered rocket?

Jens
2010-Jun-29, 03:58 AM
If you drop a 50-ton block from a kilometer up, aren't you simply going to smash the catapult at the bottom? I wonder whether you could make a contraption that could withstand that kind of a shock.

Robert Tulip
2010-Jun-29, 05:37 AM
Probably that scale is too big.

The catapult will break apart immediately on launching the cargo. The beam and the impact weight would fall around it leaving the catapult axle still standing and spinning fast.
The release of power is close to instantaneous at a few hundredths of a second, so the beam delivers the acceleration on impact and then breaks away.
If the axle also spins by motor at the launch speed, the falling weight will combine energy with the axle to deliver two simultaneous power sources.
Partly why I think of it happening in the ocean is so the beam falls to sea for safe recovery and re-use.

Could it be a way to launch mirrors into space for solar energy supply?

If you got the maximum feasible size catapult for a 10 kg rocket, could this boost assistance be anywhere near enough to get to geostationary height of 36,000 km?

Does the lack of rigidity of materials at this stress level make the whole topic unfeasible?

mugaliens
2010-Jun-29, 06:29 AM
Robert, the materials required to make such a thing possible for an Earth-based space trebuchet simply do not exist, not even by several orders of magnitude. If the materials did exist, however, the best solution would be to build it on land. There are many water sources near the equator, including the Amazon river, which would supply the water mass for the weight.

Jeff, the asteroid approach is not feasible, either, as the asteroid does not have the requisite gravity to power the device. At best, you'd be able to achieve escape velocity from the asteroid, but that would not involve enough delta-V to appreciably change the projectile's orbit.

Jeff Root
2010-Jun-29, 07:09 AM
I wasn't considering how the trebuchet would be powered when I
suggested that the only places where they might be useful would be
on asteroids. I was commenting on slingshot-type devices in general,
not necessarily on Robert's specific gravity-driven mechanism.

-- Jeff, in Minneapolis

astromark
2010-Jun-29, 07:26 AM
The energy to convert into velocity does exist. The strength of materials required to harness such does not.

A smoking pile of twisted metal is not the best way to lift objects into space.

After looking at the numbers Jeff provided I have a cunning plan...

Let us assemble a 'rocket.' :)...

Van Rijn
2010-Jun-29, 08:14 AM
A further iteration. Changing to a space catapult as attached, I imagine even by imparting much of the power by spinning the axle no materials would be strong enough to accelerate at this pace.

Thanks

Google:

momentum exchange tether

tether propulsion

space rotovator

for concepts using strong cables (like carbon fiber cables) in space. They aren't exactly trebuchets but the concept is fairly similar. In all cases you don't want the tethers moving rapidly through the dense parts of the Earth's atmosphere, but that could still be very useful: For instance, imagine Rutan's suborbital rocket hopping up 60 miles to catch the end of a tether, and going from there to orbital velocity.

WayneFrancis
2010-Jun-29, 02:41 PM
The OP idea is a non-starter, but a launcher with that sort of acceleration is possible: the space-gun.

Yes but it is only good if you are only interested in sending a solid metal object into space. Anything electronic is bound to be destroyed by the g-forces involved.

WayneFrancis
2010-Jun-29, 02:43 PM
The energy to convert into velocity does exist. The strength of materials required to harness such does not.

A smoking pile of twisted metal is not the best way to lift objects into space.

After looking at the numbers Jeff provided I have a cunning plan...

Let us assemble a 'rocket.' :)...

I like that plan.

IsaacKuo
2010-Jun-29, 03:00 PM
Yes but it is only good if you are only interested in sending a solid metal object into space. Anything electronic is bound to be destroyed by the g-forces involved.
Back in WWII, millions of electronic radar proximity fuses were produced for artillery shells.

Robert Tulip
2010-Jun-29, 11:21 PM
The energy to convert into velocity does exist. The strength of materials required to harness such does not.
A smoking pile of twisted metal is not the best way to lift objects into space.
After looking at the numbers Jeff provided I have a cunning plan...
Let us assemble a 'rocket.' :)...
The question, then, is how big a model could be built so parts would be re-usable, after activating and disassembling on impact of falling mass and release of payload?

The idea is to use the power of gravity to lever mass towards space. The catapult would be designed so the power of the falling mass would be converted into energy to bounce a small object high in the air, with all residual energy from the impact removed by the breaking off of the beam from the axle.

Operating at sea would mean the platform would have some give, holding up the fulcrum bar after the impact and release, with the idea that all parts are reusable, and energy operating cost is low compared to a rocket.

If a similar method could send a solid payload up through the lower atmosphere, could it be caught by a tether or other elevator to lift through the upper atmosphere?

Van Rijn
2010-Jun-30, 12:06 AM
The question, then, is how big a model could be built so parts would be re-usable, after activating and disassembling on impact of falling mass and release of payload?

The idea is to use the power of gravity to lever mass towards space. The catapult would be designed so the power of the falling mass would be converted into energy to bounce a small object high in the air, with all residual energy from the impact removed by the breaking off of the beam from the axle.


This makes no sense on Earth. On the moon, or on some other airless worlds, you could slowly extend a balanced cable while spinning it up, and eventually (assuming high tensile strength materials) get one spun up enough for significant tip velocities.

On Earth, use rockets to hop out of the atmosphere and do your tether tricks in space. It doesn't take that much energy to hop up 60 miles anyway.

mugaliens
2010-Jun-30, 06:25 AM
For instance, imagine Rutan's suborbital rocket hopping up 60 miles to catch the end of a tether, and going from there to orbital velocity.

Yee-ha! Sounds like quite a ride to me! When do we board?

Robert Tulip
2010-Jun-30, 11:00 AM
I've done a much simplified third version attached. The idea is that a high tensile beam could be held at tension like a bow, with a weight on one end and secured to the ground at the other end. When the weight hits there is the added energy of the release of the weight below, with the release of tension making the beam flick like a whip. The entire beam would follow the weight down into the ocean below the fulcrum. I wonder how high a ten metre model would send a tiny payload?

If the launch height needed is 60 miles, to reach a space tether, is a catapult out of the question?

Van Rijn
2010-Jun-30, 10:49 PM
If the launch height needed is 60 miles, to reach a space tether, is a catapult out of the question?

I think so. It would be extremely impractical.

The velocity requirement isn't quite as great if you're only trying to "hop" to that altitude. Still, it requires extreme acceleration in the launch hardware, and launch hardware that can deal with the stresses and air resistance. Then the launched capsule also needs to deal with air resistance and it somehow has to reach a small target also moving at high velocity.

Compare that to a small rocket that can be easily launched, can accelerate at something people can handle, and can flexibly adjust its trajectory to meet a space tether.

Developing a practical space tether system is tricky enough itself. This idea would be far more difficult.

Robert Tulip
2010-Jul-03, 03:01 AM
I think so. It would be extremely impractical. The velocity requirement isn't quite as great if you're only trying to "hop" to that altitude. Still, it requires extreme acceleration in the launch hardware, and launch hardware that can deal with the stresses and air resistance. Then the launched capsule also needs to deal with air resistance and it somehow has to reach a small target also moving at high velocity. Compare that to a small rocket that can be easily launched, can accelerate at something people can handle, and can flexibly adjust its trajectory to meet a space tether. Developing a practical space tether system is tricky enough itself. This idea would be far more difficult.

Thanks. A physicist friend calculated for me that a 60 km hop would require speed of 4000 kph in a vacuum. A projectile would hit the air like a brick wall. It would need a vacuum tube stretching kilometres high to get through the heaviest part of the atmosphere.

If it somehow were possible that a projectile fired from earth could reach a height of 60km, would it be moving relative to the launch point when it reached the end of the line (the turning point of the parabola)?

The idea of a space tether is interesting. I will raise that as a new thread.

grapes
2010-Jul-03, 07:59 AM
To calculate the time required to reach a given speed over a given
distance, assuming constant acceleration (which may or may not be
a good assumption for a trebuchet), and assuming I've thought it out
correctly, just divide the distance by the speed difference!

200 m / 11,000 m/s = 0.018 s
Assuming constant acceleration, use average speed, not final speed. The instant it spent going 11km/s is matched by the instant is spent going 0km/s, and 10km/s by 1km/s, etc.

So, 200 m/ (11,000 m/s /2) would be 0.036 s if you've done your math correctly :)

But that would be an acceleration of 11,000 m/s in .036 s, or 11,000/.036 m/s/s, or 305556 m/s/s, about 30,000 g's

Jeff Root
2010-Jul-03, 09:23 AM
I was expecting (and in a way, hoping) that if I made a mistake like
that, it would be caught immediately. Five days?

The way I figured it, for constant acceleration, the average speed is

vave = d / 2 t

vave t = d / 2

t = d / 2 vave

t = d / ∆v

t = 200 m / 11,000 m/s

So the factor of 2 cancels out. If that is wrong, I would appreciate
your showing me where I goofed, and I won't be surprised. And for
exactly the same reason, I won't be too surprised if you goofed,
because I was very surprised when I did this five days ago and saw
that the factor of two cancels out. Hence the exclamation mark.

-- Jeff, in Minneapolis

astromark
2010-Jul-03, 09:23 AM
Thats funny if its correct...and I am sorry for this but...

"Did they paint the back wall pink ? No. That was the crew... Oh. " So at 30,000 g's its not really a practical idea is it.

The whole idea of using the leverage of a catterpult is past its use by date... Line up the solid boosters and lite em up.

astromark
2010-Jul-03, 10:19 AM
As little as there is on this... I have looked into it and found some information.
This 'Trebuchet' and the 'Tether' idea are both stuck with the insufficient strengths of materials available issue...
which is a shame because they both have some merits. What seems like a low input of energy could yield a lift to orbit.,
But as is always the way with these things... If it sounds to simple. It is.
This sort of fits the same criteria as those internet sweepstakes that you never enter, but win anyway... which is also a shame...
If it sounds to good to be true... It is.
Through history several good examples of this sort of thing have swung into view before.
The 'Harrier Jump Jet' worked but...
The reusable space vehicle worked but...
A slingshot into space, but...
We should always stop and take stock of these things however because it is just this sort of thing that could be stumbled across.
Something for nothing or next to it would be great...
Not everything invented was being built for the intended purpose... There is a long list.

IsaacKuo
2010-Jul-03, 11:46 AM
The way I figured it, for constant acceleration, the average speed is

vave = d / 2 t
Got it wrong with step one. By definition, the average velocity is d/t, not d/2t.

If that is wrong, I would appreciate your showing me where I goofed, and I won't be surprised.
It goes wrong with step one, and the rest of the steps are meaningless given the error in step one.

Hornblower
2010-Jul-03, 10:13 PM
Thanks. A physicist friend calculated for me that a 60 km hop would require speed of 4000 kph in a vacuum. A projectile would hit the air like a brick wall. It would need a vacuum tube stretching kilometres high to get through the heaviest part of the atmosphere.

If it somehow were possible that a projectile fired from earth could reach a height of 60km, would it be moving relative to the launch point when it reached the end of the line (the turning point of the parabola)?

The idea of a space tether is interesting. I will raise that as a new thread.

My bold for reference. That depends on the angle at which it is fired. If vertical at the release point, it will be nearly stationary relative to the ground when its vertical motion coasts to a stop.

Jeff Root
2010-Jul-04, 04:33 PM
The way I figured it, for constant acceleration, the average speed is

vave = d / 2 t

vave t = d / 2

t = d / 2 vave

t = d / ∆v

t = 200 m / 11,000 m/s

So the factor of 2 cancels out.


Got it wrong with step one. By definition, the average velocity
is d/t, not d/2t.

It goes wrong with step one, and the rest of the steps are
meaningless given the error in step one.
I agree that I got it wrong.

I think I agree that I got it wrong in step one.

I disagree that the average velocity is d/t.

We are given the distance d = 200 m and the final speed,
11,000 m/s. For a constant speed of v = 11,000 m/s, the
equation v = d/t gives that speed. For constant acceleration
from zero to 11,000 m/s, the formula vave = d/2t
gives the average speed of 5,500 m/s. But that may not be
the best equation to use. It confused me and led me astray.
What equation should I have started with to keep final speed
and average speed clearly distinguished from each other?

-- Jeff, in Minneapolis

IsaacKuo
2010-Jul-04, 11:03 PM
I disagree that the average velocity is d/t.
You will continue to confuse yourself as long as you disagree about this. This is the very definition of average velocity.

What equation should I have started with to keep final speed
and average speed clearly distinguished from each other?
You could theoretically start with the definition of average velocity, which is that vave=d/t.

However, this does not help you because you don't know t.

Instead you need to start with another way to determine average velocity. You could guess that average velocity is equal to half of the final velocity, which in this case turns out to be true.

Robert Tulip
2010-Jul-05, 01:53 AM
you need to start with another way to determine average velocity. You could guess that average velocity is equal to half of the final velocity, which in this case turns out to be true.

In the example of the space catapult, why would the acceleration be constant?

Over the 0.02 seconds required to travel 200 meters, would the catapult shift virtually instantly from zero to top speed?

It is like if you drop a ton of bricks out of an upper window on to one end of a see-saw. The beam reaches maximum velocity at moment of impact, determined by the speed and mass of the falling weight.

Jens
2010-Jul-05, 03:15 AM
In the example of the space catapult, why would the acceleration be constant?

Over the 0.02 seconds required to travel 200 meters, would the catapult shift virtually instantly from zero to top speed?

It is like if you drop a ton of bricks out of an upper window on to one end of a see-saw. The beam reaches maximum velocity at moment of impact, determined by the speed and mass of the falling weight.

I doubt that is true. It probably appears that way, but in fact it is taking time to accelerate, and I suspect that the beam is bending violently as it tries to keep up, but to our eyes it's just too fast and it appears to have accelerated instantly.

Jeff Root
2010-Jul-05, 04:12 AM
Constant acceleration is just a first approximation. With some
details about the construction of the catapult, a more detailed
profile of the acceleration can be figured, if the difference is
enough to be warranted. Which it likely is.

My apologies for my foolish error. It was foolish, although I still
don't see how to avoid it, and I sure expected someone would
have caught an error like that sooner. At least it was caught.

-- Jeff, in Minneapolis

Robert Tulip
2011-Nov-26, 01:37 PM
Talking today with someone about the idea of a space trebuchet (http://www.bautforum.com/showthread.php/105379-Space-Trebuchet?p=1752367#post1752367), we discussed some hypothetical modifications. I doubt this would work, but am interested to know why not.

I apologise if there are basic flaws of magnitude or materials in this idea. I am just wondering how far it is from feasible.

1. Raise launch device on platform ten miles or more above earth for launch of load into space by whip. Use arrays of skyhook balloons (http://en.wikipedia.org/wiki/Skyhook_balloon) tied to the four corners of the platform to lift it to launch height, to reach an altitude where launch constraints are less - less atmospheric resistance and lower escape velocity. Idea is to launch at the equator in the Pacific Ocean, to send a payload straight up to geostationary orbit.

2. Use a whip on an axle as launch device. The idea is to raise the platform structure from earth to launch height , and drop a heavy weight to spin a rigid beam around an axle mounted on a platform raised by balloon array. The axle through the beam is set spinning fast in neutral by a motor. The beam is tied at one to a rope with a payload at the end. The weight falls on the beam to set the beam spinning around the axle and crack the whip. At the moment of downward impact of the weight on the beam, the beam goes into gear with the axle. to spin the beam as fast as possible and convert as much as possible of the energy to spin rather than downward motion of the platform. The aim is that the skyhook balloons and the beam and platform should survive the launch to be used again.

3. When the weight hits the beam, it starts the beam spinning about the axis to crack the whip and launch the load straight up. Moment of load release is calculated for maximum upward velocity, as the whip reaches full vertical extension. Meanwhile, the weight falls to earth after hitting the beam, which spins fast around its axle so the platform remains at stable height. The balloons are slowly deflated to land the platform for re-use.

4. The idea is that a space station at geostationary orbit would receive new materials by this method, which aims to be emission free. It would require sufficient accuracy to get the load near enough to the station for retrieval. If feasible, small loads of air, food, water, metal, etc could be launched to the space station. The aim is for all launch materials to be fully reusable.

Questions

What is the difference in escape velocity and atmospheric resistance for a launch 10 or 20 miles up compared to surface launch?

Is this model conceptually feasible? Could it approach satellite launch velocity for a small payload?

What size of balloons are needed to lift a heavy load to that height?

If a 1 kilogram weight was launched by this method with fast enough speed to reach geostationary orbit (http://en.wikipedia.org/wiki/Geostationary_orbit), 22,000 miles above sea level, would it burn on launch if the launch height was well above the planetary surface?

Could the axle be strong enough to keep the platform and the balloons intact through launch?

Could a balloon platform raise such a device to sufficient height for space launch?

Could a beam spin fast enough to send a load more than 20,000 miles straight up?

Thanks

PraedSt
2011-Nov-26, 02:15 PM
What is the difference in escape velocity and atmospheric resistance for a launch 10 or 20 miles up compared to surface launch?Escape velocity- minimal difference, air resistance- appreciable difference.

What size of balloons are needed to lift a heavy load to that height?Depends heavily on mass of the load. If you give me a figure I could try and work it out.

The rest of your questions need a knowledge of materials.

ETA: Have you heard of the Slingatron? It's another mechanical launch device.
http://www.slingatron.com/spacelaunch.htm

antoniseb
2011-Nov-26, 02:16 PM
... "Did. they paint the back wall pink ? No. That was the crew... Oh. " So at 30,000 g's its not really a practical idea is it. ...

That's right Astromark!. Any mechanism we create to accelerate something to high speed over a short distance will create absurdly high g's. Taking as an example something where you have constant g's over a fixed length (such as a rail gun, or a well designed trebuchet) the final velocity is the square root of the acceleration times the square root of the distance over which the acceleration occurs. This is pretty limiting. Just imagining something on a grand scale, suppose you built a 100,000 km long rail gun, going from the back side of the Moon out through the EM-L2 point, and you could accelerate a spacecraft at 9 g's for the whole length of the gun... your exit velocity would only be 93 km/second. This is enough to escape the Sun, but it would still take thousands of years to get to the nearest star.

PraedSt
2011-Nov-26, 02:18 PM
By the way, you know you can't get to GEO by launching "straight up", right? You still need a fair amount transverse velocity.

Senor Molinero
2011-Nov-30, 01:02 AM
FYI the largest projectile gun was the Paris Gun of WWI which could launch a shell 120km distant passing through max altitude of 40km. Muzzle velocity = 1600m/s.

whimsyfree
2011-Nov-30, 11:25 PM
A further iteration. Changing to a space catapult as attached, I imagine even by imparting much of the power by spinning the axle no materials would be strong enough to accelerate at this pace.
Thanks

That's not a trebuchet. Nothing works that way because it is impossible. If the falling weight compressed a gas you could make a sort of light gas gun. What the point to that over using explosives to compress the gas would be I don't know.

antoniseb
2011-Nov-30, 11:54 PM
That's not a trebuchet. Nothing works that way because it is impossible. If the falling weight compressed a gas you could make a sort of light gas gun. What the point to that over using explosives to compress the gas would be I don't know.
As a small-scale mockup, you could look at the Punkin-Chunkin videos. This is also useful for helping to understand the difference between Trebuchet, Catapult, and Air-Cannon.

PraedSt
2011-Dec-01, 08:50 PM
That's not a trebuchet. Nothing works that way because it is impossible. If the falling weight compressed a gas you could make a sort of light gas gun. What the point to that over using explosives to compress the gas would be I don't know.Well, I like what he's doing here. He's trying to find a mechanical solution to the launch problem. The approach sometimes works- the space elevator is part mechanical for example.

publiusr
2011-Dec-04, 09:19 PM
I can't help but wonder if an asteroid bola is the way to go. Use cables to cut a rotating asteroid into two pieces, which are held by cables, tethers, etc. At a certain point, release one. The rotational energy is then released instantly into translational velocity of an asteroid released into a certain direction at certain times.

Robert Tulip
2011-Dec-05, 11:25 AM
Why don't they use balloons to carry space rockets up high in the atmosphere before switching on the engine?

Ufonaut99
2011-Dec-05, 12:34 PM
I also read a book once that suggested that, since MagLev trains can get pretty fast nowadays, why not have a really long, really fast train powered all the way up to take off. Of course, you'd need a handy mountain pretty near the equator for a take off point - rather like this one (http://en.wikipedia.org/wiki/Mount_Kilimanjaro).

neilzero
2011-Dec-05, 03:35 PM
Yes a 6 kilometer mountain helps, but it's still 20 times farther to LEO = low Earth orbit. Huge, but fragile balloons can get to about 30 kilometers, but with pay loads perhaps 1% of the balloons' mass. Worse, following launch, the balloons are beyond economical repair, and a cubic kilometer of hydrogen is released in the upper atmosphere = The world stock pile of helium is a few cubic kilometers, so the price of helium would rise rapidly, as there is no practical way to get a new cubic kilometer of helium per year.
As the others posted we are not even close with present technology, for any variations on a Trebuchet. We are closer for a Brad Edwards type space elevator, space based solar power, flying cars and hundreds of other ideas we likely will never do. Materials likely to be available in this century are not strong enough and payback looks improbable even if we could build it with trash. Neil

IsaacKuo
2011-Dec-05, 04:32 PM
I can't help but wonder if an asteroid bola is the way to go. Use cables to cut a rotating asteroid into two pieces, which are held by cables, tethers, etc. At a certain point, release one. The rotational energy is then released instantly into translational velocity of an asteroid released into a certain direction at certain times.

It isn't. You are limited to low tip velocities due to the strength of the tether. You can get better performance from expanding gas (i.e. a rocket or an explosive). Generally, gas pressure offers superior performance to mechanical gizmos. This general principle is visible in Pumpkin chunkin contests, where compressed gas launchers outperform mechanical launchers by a wide margin.

PraedSt
2011-Dec-06, 10:20 AM
Why don't they use balloons to carry space rockets up high in the atmosphere before switching on the engine?You need very big balloons and they're also hard to control.
Some plans: http://en.wikipedia.org/wiki/ARCASPACE http://en.wikipedia.org/wiki/JP_Aerospace

whimsyfree
2011-Dec-08, 08:20 PM
It isn't. You are limited to low tip velocities due to the strength of the tether. You can get better performance from expanding gas (i.e. a rocket or an explosive). Generally, gas pressure offers superior performance to mechanical gizmos. This general principle is visible in Pumpkin chunkin contests, where compressed gas launchers outperform mechanical launchers by a wide margin.

I've never heard of Pumpkin chunkin contests but it became obvious to our ancestors that compressed gas launchers (cannon) outperformed mechanical launchers (trebuchets) by a wide margin a long time ago.