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Fraser
2005-Dec-29, 07:29 PM
SUMMARY: Forget about nuclear weapons, if you need to move a dangerous asteroid, you should use a tractor beam. Think that's just Star Trek science? Think again. A team of NASA astronauts have recently published a paper in the Journal Nature. They're proposing an interesting strategy that would use the gravity of an ion-powered spacecraft parked beside an asteroid to slowly shift it out of a hazardous orbit. Dr. Stanley G. Love is member of the team and speaks to me from his office in Houston.

View full article (http://www.universetoday.com/am/publish/podcast_gravity_tractor_beam.html)
What do you think about this story? post your comments below.

Mayonaze
2005-Dec-29, 07:56 PM
I know the science and technology discussed here is very young, but the talk of "nudging" asteroids away from harmful orbits seems a little short sighted, sort of like my teenager "cleaning up" his room by stuffing his junk under his bed. In time, wouldn't it be better to mine them for what they are worth and then just fly them into the sun? Is there any way that having these loose bodies around could be a neccessary part of the solar ecosystem?

zrice03
2005-Dec-29, 10:26 PM
It's not really short sighted. Earth is a very tiny target compared to the size of the inner solar system. Moving an asteroid out of the way a little would probably remove a potential impact completely, or at least to many millenia in the future. Also, it is extremely unnecessary and energy intensive to "just fly them into the sun". Its very hard to get a normal space probe close to the sun, never mind a multi-billion ton asteroid.

SolusLupus
2005-Dec-30, 12:28 AM
I'm still all for mining asteroids, personally :)

But yeah, it's not very "short-sighted".

Cohen the Barbarian
2005-Dec-30, 03:07 PM
I am puzzled. Putting a spacecraft close to an asteriod will surely produce a two-body system. They will attract each other by gravity, but the only way to move the pair would be with the ion or plasma drive of the spacecraft.
In what way is this better than using the spacecraft as a pusher?

GBendt
2005-Dec-30, 05:38 PM
Hi,

I think the idea is rubbish.
The gravitational force between the two bodies is just a few N.
This force will pull the spacecraft much faster towards the asteroid, instead the asteroid to the spacecraft. The asteroid has a mass of millions of tons, while the mass of the spacecraft will be much less.

The acceleration of the spacecraft by this force will be much higher than that of the asteroid. Thus, the spacecraft will move much faster towards the asteroid than the asteroid moves towards the spacecraft, and the spacecraft will come into contact with the asteroid. At this point, the gravitational force between the two cannot affect the orbit of the asteroid any more.

Therefore it is necessary to keep a constant distance between the two. You need a rocket engine on the spacecraft which has to fire permanently at a thrust which exactly compensates the acceleration of the spacecraft that is caused by the gravitational force.

If you placed this rocket engine onto the asteroid and fired it there, you can have the same accelerating effect than you have by the gravitational force, without the need for a heavy spacecraft.

An ion engine is a machine which provides a constant, but very low thrust. I wonder how a multi-ton spacecraft is thought to be accelerated by a low-thrust engine such that it can reach any asteroid and adjust its own vector speed to that of the asteroid within a year (!!!) ?

Regards,

Günther

GOURDHEAD
2005-Dec-30, 06:06 PM
An ion engine is a machine which provides a constant, but very low thrust. I wonder how a multi-ton spacecraft is thought to be accelerated by a low-thrust engine such that it can reach any asteroid and adjust its own vector speed to that of the asteroid within a year (!!!) ?
The operational concept described at http://home.comcast.net/~mbmcneill7/ includes ion emgines of immense power as well as a power beam that can be directly applied to the surface of a potentially colliding object to nudge it out of Earth's path. This system is especially useful for objects discovered only a few days prior to what would otherwise be an Earth collision or to massive (moon or greater) objects that had been in an independent MW orbit and only recently wandered into the solar system or large comets (e.g., Sedna-sized) recently deflected into the inner solar system from the Oort cloud or Kuiper belt. We may wish to deploy PBG relay stations in orbits inside but near that of Jupiter that are continuously fed from the near solar PBGs so the speed of light lapse (~40 minutes) does not prove significantly detrimental to our intended purpose of asteroid/comet deflection/destruction when the larger bodies are encountered.

Survival requires both eternal vigilance and continuous preparedness.

Fraser
2005-Dec-30, 06:54 PM
Hi,

I think the idea is rubbish.

Did you listen to the interview or read the transcript? Dr. Love dealt with all of the issues you're talking about.


This force will pull the spacecraft much faster towards the asteroid, instead the asteroid to the spacecraft. The asteroid has a mass of millions of tons, while the mass of the spacecraft will be much less.

Yes the asteroid weighs way more than the spacecraft, but if you keep them side by side for a year, you can make a tiny change in the asteroid's orbit.


You need a rocket engine on the spacecraft which has to fire permanently at a thrust which exactly compensates the acceleration of the spacecraft that is caused by the gravitational force.

The spacecraft will be firing its rocket continuously to offset being pulled towards the asteroid. The asteroid has no rocket to stop it from being pulled in.


If you placed this rocket engine onto the asteroid and fired it there, you can have the same accelerating effect than you have by the gravitational force, without the need for a heavy spacecraft.

Landing a spacecraft on an asteroid is hard. If the asteroid is rotating, you can only fire your rocket for certain periods.


An ion engine is a machine which provides a constant, but very low thrust. I wonder how a multi-ton spacecraft is thought to be accelerated by a low-thrust engine such that it can reach any asteroid and adjust its own vector speed to that of the asteroid within a year

You launch it from a traditional conventional rocket, as powerful as you like. This will put it into roughly the right orbit that you want. The ion engine they're considering will have a tremendously higher thrust.

Read the original Nature paper, if you don't like the concept, and feel free to find a mistake in their math.

GBendt
2005-Dec-30, 09:15 PM
Hi Fraser,

I read the transcription.

I think that asteroids pose a threat to earth and that it is important to check what can be done if we find that there is an asteroid on its way to crash into our home planet. The solution that we take should be an effective and feasible one. I do not think that the solution proposed by Dr. Love is an effective and feasable one. I´ll ecplain why:

If you try to use a 20-ton spacecraft to move a 1 million ton asteroid by means of the gravity which acts between both, that spacecraft will move 50000 times faster towards the asteroid, than the asteroid does towards the spacecraft.
The gravity force between the two is weak. If e.g. the 1 million-ton asteroid has a diameter of 200 m and you have your spacecraft just above the surface, its distance from the asteroid´s center of gravity is 100 m. The resulting gravity force between the two thus is 0,132 N. The resulting acceleration of the asteroid by this force is 0,132e-9 m/s².
To keep this acceleration steady, you must keep the distance of your spacecraft steady just above the surface of the asteroid.
After a day, the asteroid will have moved by 48 cm. If the activity is mantained for a full year, the asteroid will have moved by 56 km. The "side speed" of the asteroid will be 4 mm/s after that year. At this speed, the asteroid will move 130 km/year.
If it is meant to miss the earth in a situation where without human interaction that asteroid would hit the earth centrally, you must terminate your shifting mission 52 years before the day of impact to avoid this impact to happen. In these 52 years, the asteroid will have moved by the radius of the earth, and will thus miss it.
Dr. Love talks of a lead time of a couple of decades. This might be a bit short for the greatness of the effect that can be achieved by the proposed method.

See: asteroids are not ball-shaped bodies, instead they look much more like oversized potatoes. And these asteroids are rotating. If you try to hold a precise constant distance to a surface which is uneven and is moving up and down, you will have a hard task to control that. You have to move your craft permanently. This makes the task to keep a constant distance to the asteroid difficult, as any collision of the craft with the asteroid must strictly be avoided.

Dr. Love says that he thinks that he can travel to a dangerous asteroid within a year. This sounds like setting of from earth, hurtling towards that asteroid, approaching it and parking the spacecraft next to the asteroid, and start activities.
The problem is that you must find a route of your spacecraft through space which brings you to a spot of an orbit around the sun where your location, speed and direction is exactly that of the asteroid which is there. It took and takes contemporary missions many years to achieve that. Remember the NEAR mission to Eros.

A spacecraft setting out into space to shift an asteroid by the proposed method will have to be out in space for many years. As we can´t know the masses of asteroids before we are very close to them, the crew may find that it will not be able to solve the task if the asteroid turns out to have more mass than the craft can move to an extend which is required to save the earth: Such a situation would be a desaster.

We are far from having such a spacecraft. It will take decades to develop it and to make it a reliable craft. This may take more time than we have when we need it. And if we have it, it may turn out to be only able to handle small asteroids in a situation when a gigaton body has selected us for his destination...

Therefore, I think we should look at alternatives.

Regards,

Günther

agingjb
2005-Dec-30, 10:49 PM
It's clear that maintaining a mass somewhere near an asteroid would have a cumulative, if slow, effect. Would a light sail enable the maintenance of a suitable mass in place without the need for a continuous and permanent thrust?

GBendt
2005-Dec-31, 12:13 AM
Hi agingjb,

I read some proposals which assume that solar radiation might be caught in a sail which is applied to an asteroid. The pressure by the light is intended to push the asteroid then very gradually out of its orbit. But I never read figures which indicate if, and how much, force can be realised by this measure.

This design has at least a technical problem, as the asteroid will very much likely be in some rotation. If you try to attach a large light sail to a rotating asteroid, you need a firm handle on the asteroid, and this is not easily established.
The effect of gravity on such an asteroid is so low that you can jump into space easily right from its surface. If your landing on it is too hard, you craft will bounce off back into space. And if you push a drill into the asteroid to establish a fixed point, the pressure that you apply on the asteroid by this may push you from the surface.

There are other proposals which recommend to add white color to the surface of an asteroid to enhance its light reflecting properties. This is meant to convert the entire asteroid into something like a light sail. When you preoceed this way you do not need to land on the asteroid and the whole affair of painting the asteroid might be completed in a short time.

I only found guesses on the force of the light that is obtainable by such a design. The fact is: This is still a fiction and its effectiveness has neither been proven nor tested.

Perhaps anyone has more information on that?

Regards,

Günther

galacsi
2005-Dec-31, 12:55 AM
Hi Fraser,

We are far from having such a spacecraft. It will take decades to develop it and to make it a reliable craft. This may take more time than we have when we need it. And if we have it, it may turn out to be only able to handle small asteroids in a situation when a gigaton body has selected us for his destination...

And this ion engine as perfect as it is still needs fuel , a lot of fuel if firing for years ..... And fuel consomption decrease the mass of the spacecraft ....


Therefore, I think we should look at alternatives.

Regards,

Günther

GBendt
2005-Dec-31, 01:17 AM
Hi Gourdhead,

I like the idea of ion engines of immense power. But how immense can the power of such an engine be? And how lasting?
The Saturn V carried 2800 tons of fuel, and the engines of its first stage, I was told, had a power of 400 million horsepower. After a few minutes, the fuel was spent and the huge powerful engines became useless waste.

If you have an ion engine, this needs a fuel, too, but the energy to accelerate the fuel through the nozzle is not provided by chemical oxidation, as is the case in conventional rockets, but by electric fields by which high-mass ions are accelerated. As soon as you have spent that fuel, there is nothing left for the electric fields to accelerate.

If you increase the voltage across the electric field in the ion engine, this improves its thrust. But you cannot raise the voltage across electrodes beyond all measures. If that voltage becomes too high, this will cause a discharging flash instead of more thrust, no matter how many gigawatts of electric power you invest. If you want more thrust then, you have to invest more fuel.

In nuclear powered submarines, the nuclear reactors provide gigawatts of electric power for many years, making these vessel independent from any energy supply from outside. If you use such a nuclear reactor in a spacecraft, this may offer gigawatts of electric energy for years, too. But this does not give you the fuel for your engine to propell your craft through the space.

If you stop the engines of a ship, the ship slows down and finally stops. If you stop the engines of a spacecraft, this will move on and follow its path which is defined by its impulse and by the gravity forces that are acting from sun and the planets. If you want to stop the spacecraft, you need plenty of fuel. to bring the spacecraft´s impulse to a lower value. If your fuel is spent, you are trapped and lost forever.

Therefore it is essential to design a route for a spacecraft that requires as less fuel as possible to reach a certain destination.
Even ion engines of immense power are useless when their fuel is spent. These mighty machines may make some things a bit easier, but only a bit easier. When flying in the interplanetary space, your fuel will be the most precious good on board.

Regards,

Günther

TropicalCoder
2005-Dec-31, 02:59 AM
Hi Fraser,

I just listened to your interview with Stanley G. Love tractor beam. Of course I loved it, as I love your site, but that’s not the point of my comment. The point is, your guest failed to make the case of why it is better to use gravity rather than simply mount the same thrusters his hypothetical spacecraft will have onto the surface of the asteroid. Now, in his defense he did say, “… those ideas have been suggested, but they have some difficulties”. However, as I was listening to the interview, my immediate worry was the hot gas coming out of the thrusters would strike the asteroid, and I expected you would interject at some point and ask him about that. Apparently, you had more faith in him than I did, and towards the end, your faith seemed justified as he did clear up that little dangling loose end by saying “Of course you need to tip your thrusters out away so the plume of hot gas coming out of them doesn't hit the asteroid.”

Now remember, we want the space ship as close to the rock as possible, or at least the bulk of it’s mass as close as possible, because the gravity weakens with the square of the distance. The hypothetical asteroid is a couple of hundred meters wide. How high up away from the surface can you get those thrusters? Well, just imagine a football stadium, like he says. Imagine a long, spindly rocket hovering over the center of the stadium, with the bulk of it close to the surface, and way up high on the craft, a pair of thruster nozzles. Now if we don’t want their exhaust to hit the stadium, we steer them so the exhaust is at an angle to the surface. Let pick an arbitrary angle, of, say 22.5 degrees and see how high up our thrusters have to be, such that angled at 22.5 degrees, the exhaust won’t hit the surface.

Simple high school trigonometry tells us that the nozzles have to be at least a hundred meters above the surface. Now, let’s accept that – reluctantly - as reasonable - a hundred meter long space ship. (It’s after midnight here where I am and I am exhausted and can’t do the math! – but I don’t need to, because simple intuition tells me I am right that just to get it down to a 22.5 degree deviation from the vertical will require a very tall ship!)

Then I immediately thought – ok – imagine one thruster deviating by – say - 22.5 degrees from the vertical, to one side, while the other thrusters deviates from vertical to the opposite side by the same amount, and we accept a very tall ship. OK – now it works – except – you now have thrust at a vector such that you waste 30% of the fuel in comparison with an engine mounted on the surface of the asteroid. (Another great leap of intuition!) Meanwhile, that ship is getting lighter by the day so has less gravity pull on the rock as time goes by.

Damn – I was going to give you a dazzling display of my primitive math skills, but I couldn’t pull it off – I’m just way too tired and I can’t think, but you get my drift. It doesn’t seem the most efficient way to do things, or at least, your guest didn’t give us sufficient justification for using his approach, and you failed to call him on that. Please fill in the blanks in my math and stick to him next chance you get. But being a science fiction fan since I was a kid, it was fun imagining a “real” tractor beam there for a couple of minutes!

TropicalCoder
2005-Dec-31, 03:30 AM
...and another thing. I don't think we know for certain much about what kind of electrical charge to expect an asteroid to have. If it's negative, it's going to attract those positive ions from the thuster right to it. Then imagine all these highly accerlerated ions striking the asteroid - exactly what we wanted to avoid!

Or perhaps if it's neutral, after time it's bound to accumulate a positive charge. Is that going to enhance the thrust, adding a repulsive force between the rocket and the asteroid? ...or will it just throw off all our carefull calculations? Do we know much about operating an such an engine so close to an asteroid?

phunk
2005-Dec-31, 03:37 AM
The problem with mounting the engine on the asteroid is that many asteroids are suspected to be very lose rubble piles. If you try to push you may push into it. Also, irregular shapes and rotation mean you have to very carefully time the thrust to push it in the right direction. While the gravity tugboat may be less efficient than pushing, it will be much easier, doesn't need to land, doesn't need to turn its thrusters on and off while it rotates, etc.

Also, you can send more than one of these tugs to work in parallel. 2 of them will cut the time required in half.

Gerald Lukaniuk
2005-Dec-31, 07:13 AM
Clearly this is a crackpot idea coming from some ivory tower academics. It is scare that the solution to the asteroid threat might come from them rather then some of the above repling members who show a better grasp of physic and a greater sense of the urgency of using a proven correct and reliable. Imagine that after putting all our eggs in one basket and waiting a year we fingd the theory doesn't work or there is a new unknown factor like say dark matter or electrostatics or invisible companions, or the bad math that crippled hubble. Perhaps the tidal action asteroid ont the ship might pull it apart or have these clowns forgotten newton's laws of action reaction, Given too much time pork barrel politics is guarantied to complicate the project until it is useless and unreliable. A simple fast no brainer solution would be in order. Dropping down a few nukes spew out vapourized rock in the direction opposite to where we want go would work just as good as a slow release of the same amount of energy slowly through an ion engine. If these guys are to sqeamish for the big gun approach dropping down some white hot near critical reactors into a crater could become a poor man's rock vapor rocket engine or we could use very loud rock bands.
Detection is where we should put our money. Obital radar or lidar or some type of long range magnetic electostatic or gravitational sensing would all be more senseable that the above gradeten science project.

agingjb
2005-Dec-31, 09:35 AM
The rotation of the asteroid, as has been remarked, makes attaching a thruster, or a light sail, difficult. A separate mass, if it could be held in position (actually the position required would probably change) would provide some deflection over time.

I suggested a light sail (not attached to the asteroid) if for no other reason than to save fuel; I ask, again, whether a light sail could provide sufficient thrust to sustain a useful mass in stasis against the gravity of the asteroid.

Gerald Lukaniuk
2005-Dec-31, 08:41 PM
While rotation adds to the sillieness of a tractor beam sidekick it wouldn't be a problem for using on rock thrusters or sails. Either they could be installed at the axis of rotation ie the North or South poles of the thing assuming they are not pointed at earth and thus yield a predictable trajectory. If not centered the boogie would loop and spiral around it trajectory unpredictably like a balloon that didn't get tied but with our luck and against huge odds it might still end up whacking us in the butt. I still thinks sails or thusters are the best idea. Another wacky conceptwould be to use electrostatic attraction to our advantage. For instance if the moon were given a huge electrostatic charge relative to the earth using ion engine a neutrally or oppositely charged object might preferenciably be attracted to the moon when it starts feeling our inverse square. Perhaps this sort of thing is already happening and might explain our little runt sidekick's terminal acne.

phunk
2006-Jan-01, 09:05 PM
Imagine the mess that would make... If you could put enough charge on the moon to actually attract an asteroid, it would all bleed off into space, probably taking most of the dust off the surface of the moon in the process.

GBendt
2006-Jan-02, 01:06 AM
Hi,

Asteroid are bodies of unknown mass, unknown shape, unknown composition and unknown rigidity, and each is rotating in its own sense and its own rate. They travel through space at high speed, e. g. 25 km/s, and they have a high mass compared to what we can move at that spped through space. If the asteroid has a diameter of 100 m, its mass may be about 1 million tons.

If you take that megaton asteroid crashing into our earth at 25 km/s, the kinetic energy of this asteroid is converted into heat within a few milliseconds. This energy is 312,5e15 joule, and this is roughly equivalent to that of 70 million 20 kiloton atomic bombs. We should take measures to prevent such an impact to happen on our planet.

If we apply a low force on that megaton asteroid, the acceleration by this force will be very low, and thus this force must act for a long time, to give the asteroid an additional speed which alters the orbit of the asteriod such that it will no longer cut the orbit of our planet.

If we can be sure that a low force is able to do the job, we need a place on the asteroid where we apply this force. It will be necessary to land on this asteroid, which is very difficult because its gravity is so low that you would bounce back into space even at a landing speed of 1m/min. You can´t walk on it, as just stepping on its surface might push you up into space. Your body weight on that little 1 megaton asteroid would be a few milligrams. The mere vibrations from your bobbing heart might lift you from the surface.

It might be useful to apply something like a lasso, to catch the asteroid by this, and thus getting a firm hold to this celestial body. This hold gives you a safe basis to fix the thruster and its controls, energy and fuel supply firmly to the asteroid.
A light sail must be extremely large and its postion must be controlled such that it is permanently, and fully, lit by the sun. Even then we don´t know how to achieve this permanently on an asteroid that is rotating. The rotation might reduce the efficiency of the design considerably.

If we apply a 20 megaton fusion bomb and fix this one to the asteroid´s surface, and ignite it from a safe distance, the explosion will generate a heat of a hundred million centigrades within nanoseconds. Several thousand tons of the asteroids material will be vapourozed at the instant, and the resulting pressure will blast a deep crater into the asteroid, casting a huge mass of hot vapour, dust und gravel at a high speed into space. The reacting force will accelerate the asteroid, and this will change its orbit. To what extend, we do not know.
But we can guess.
When the Deep Impact craft crashed into comet Temple 1, this impact set an energy of 4,5 tons of TNT free. This impact blew 1000 tons of comet matter out into space. If we apply a 20 megaton fusion bomb on an asteroid, this has an effect of 20 million tons of TNT. The bomb should thus have an effect which is 400 thousand times greater. It should really be able to change the orbit of the asteroid. Let us hope, early enough.

Regards,

Günther

phunk
2006-Jan-02, 01:15 AM
But if an asteroid is a loosely bound rubble pile, the 'lasso' could just cut right through it, and the nuke could be absorbed without much impact on the orbit. A nuke could also just break it into smaller pieces, hitting the earth with a buckshot instead of a slug. Still very bad. There are too many unknowns trying to blow it out of the way with a nuke. The nice thing about the gravity tug, is that it has no dependance on the shape or composition or rotation of the asteroid, all that matters is the mass and how close you can get to the center of mass.

saski
2006-Jan-02, 09:13 AM
Lu and Love's proposal has the advantage of avoiding anchorage with the asteroid, but let me suggest a variation which involves heavy anchorage but would be more powerful.

They have a preprint on arXiv, by the way:

A Gravitational Tractor for Towing Asteroids
Edward T. Lu, Stanley G. Love
http://arxiv.org/abs/astro-ph/0509595

Generally we can assume the asteroid spins. Anchor a revolving tether at any point, extending past synchronous orbit; and let it support a conveyor belt taking dust and gravel from the surface to somewhere past the synchronous radius. Far enough past, and the belt will be powered by the centrifugal force of the load; basically, from the asteroid's rotational kinetic energy. Run a crusher and sieve on the surface to keep the belt fed.

The released dust will be in orbit near escape, or actually liberated; escape velocity will probably be under 1.0 m/s (Deimos 7.8 m/s, Phobos 4.5 m/s). Solar light pressure will push fine dust away in a plume, and the dust will transfer momentum to heavier particles. Near Earth orbit we get about 5 Newton per million square meters normal to the Sun. So the plume is effectively a lightsail applying gravitational force to the asteroid. Of course the force falls off as inverse square; but a few N/km^2 gives a long acceleration time, so our conveyor belt can surely keep the plume replenished. For each kilogram per second delivered, about 30,000 tonnes per year is added to the plume.

The devil is in the details; but these are the same details applying to the robotic component of any asteroid mining plan (for which slow-falling kicked up dust will probably be a big headache). It could be worth handing this scheme and some R&D money to some of the private space mining groups who already have their eyes on the Near-Earth Asteroids.

galacsi
2006-Jan-02, 10:07 AM
But if an asteroid is a loosely bound rubble pile, the 'lasso' could just cut right through it, and the nuke could be absorbed without much impact on the orbit. A nuke could also just break it into smaller pieces, hitting the earth with a buckshot instead of a slug. Still very bad. There are too many unknowns trying to blow it out of the way with a nuke. The nice thing about the gravity tug, is that it has no dependance on the shape or composition or rotation of the asteroid, all that matters is the mass and how close you can get to the center of mass.

I think this discussion has convinced me. It is a very bright idea. And the bigger the asteroid , the bigger is the gravity and the more the spacecraft can pull it.

Irregular shape is not a show-stopper ,it just decrease the efficiency of the traction , fuel consumption is not a problem because if earth future is in balance there will be no shortage of fuel.

As somebody said before you can put several space tractor in line. So if one fail or need repair other can manage.

GBendt
2006-Jan-02, 06:02 PM
Hi Phunk,

If the asteroid is a pile of rubble which is kept together by weak gravity, a rope, if pulled tight, might cut into this pile. It depends on the tightness with which you pull, and the size and shape of the pieces of that pile of rubble how deep it will cut.
The gravity between the pieces may be low, but each piece has its mass, and such each piece has its inertia. If the rope is going to cut into the asteroid, it will have to move million of tons, one by one, if it to cut its way through. This will take a long time, and it is most likely that it will get stuck somewhere inside the asteroid.

But this idea of yours is wrong:

the nuke could be absorbed without much impact on the orbit. A nuke could also just break it into smaller pieces, hitting the earth with a buckshot instead of a slug. Still very bad.

A nuclear explosion creates a temperature and a pressure which is equivalent to that which exist inside a giant star: 100 million centigrades, 10e16 pascal pressure. This is a pressure of 10e16 N/m². What fosters your idea that matter which is hit by a force of 10e16 newtons on each square meter of its surface exposed to this pressure will feel nothing of it? This is a trillion tons per m²!!

An exploding nuclear fusion bomb is equivalent to millions of tons of dynamite, exploding all together on one spot within 10 nanoseconds. The resulting fireball is so bright, eyewitnesses said that compared to its brightness, the disk of the bright sun looked like a piece of grey cardboard.

The shock wave caused by the explosion will desintegrate the pile and blast a vast expanding cloud of debris out into space. Not a single piece of the pile will move after the blast just as it has moved before the blast. No piece of the pile will be able to follow the orbit it followed before, as the momentum of every single component is changed. This is simple physics.
If you change the momentum of a body that moves through space, then you change its orbit.

It is most unlikely that any piece of the asteroid will hit the earth after the blast. Especially when this blast occurs hundreds of millions of kilometers away from us, out in space.

Regards,


Günther

phunk
2006-Jan-02, 06:33 PM
Well, here's a simple question. When a nuke goes off in a vacuum, what medium is that pressure in? What does the 'shock wave' travel through?

GBendt
2006-Jan-02, 06:49 PM
Hi Saski,

This is a nice idea: take the asteroid piece by piece and use the asteroid´s rotation energy to throw piece by piece out into space.

But your idea with the conveyor belt does not work. There is no force available to keep the dust and gravel on the conveyor belt. You are applying a situation which is possible on earth into an environment where these conditions do not apply.
Where do you get the energy from to lift pieces of the asteroid from its surface? I still don´t see how this can work.


Curious Regards,

Günther

phunk
2006-Jan-02, 07:40 PM
Hi Saski,

This is a nice idea: take the asteroid piece by piece and use the asteroid´s rotation energy to throw piece by piece out into space.

But your idea with the conveyor belt does not work. There is no force available to keep the dust and gravel on the conveyor belt. You are applying a situation which is possible on earth into an environment where these conditions do not apply.
Where do you get the energy from to lift pieces of the asteroid from its surface? I still don´t see how this can work.


Curious Regards,

Günther

You pick strange reasons to say it won't work.

The conveyor belt doesn't have to be literally a belt. It could be buckets with lids, 2 belts back to back with the material sandwiched between, or any number of other configurations. The energy to lift material could come from solar cells or nuclear generators. An electric motor turning a conveyor doesn't have the problem of needing to carry fuel like a rocket would, it can be solar powered and operate nearly indefinitely.

Van Rijn
2006-Jan-02, 11:23 PM
Well, here's a simple question. When a nuke goes off in a vacuum, what medium is that pressure in? What does the 'shock wave' travel through?

Yep. GBendt, you might want to research the differences between a nuke exploding in a vacuum and one exploding when surounded by matter. In vacuum there are minimal blast effects. Also, the force required to disrupt an asteroid is much more than the force required to slightly shift its trajectory. Further, breaking up an asteroid is just about the last thing you want to do, as it would be even harder to deal with the fragments. If nukes are used to move asteroids, they would have to be on the surface or under it, the explosions carefully timed to act as a type of Orion drive. Depending on the composition and rotation of the asteroid that may be very difficult to do.

saski
2006-Jan-03, 12:50 AM
How the conveyor belt powers itself:

Imagine ourselves in cylindrical (r, theta, z) coordinates centered on the asteroid's axis and rotating with it. At any location, gravitational acceleration is inward, varying between r^-(1 + something) at the anchor point and r^(-2) at large distance. At the same location, centrifugal acceleration is r * omega^2 outward, where omega is angular rotation speed. With increasing distance along my tether, gravity force decreases and centrifugal force increases. The synchronous orbit radius is the distance r where they balance.

Imagine the lifting side of the conveyor belt as a taut rope. Mass attached within the synchronous radius pulls the rope inward; mass attached beyond synchronous radius pulls it outward. The rope will accelerate inward or outward depending on whether the sum of the forces is a net inward or otward force.

So if there is sufficiently more mass beyond synch radius, it will raise the belt and all masses on it from the surface up. To keep the belt rising steadily, release mass from the outward end at the same rate we add it at the surface. To keep the forces balanced, release must be at the radius where the sum of gravity and centrifugal force is the negative of that at the surface. Total outward acceleration of the released mass therefore has the same magnitude as the total inward acceleration at the surface.

It is rather like a siphon in operation. The falling liquid in the output arm is pulling up the rising liquid in the input arm, courtesy of surface tension.

It is not perpetual motion: as mass is released, the reaction on the belt marginally slows the asteroid's rotation.

How the conveyor belt is constructed:

I'm vague on this, because it depends on the composition of the material being raised. I confess that I first thought of charging dust by friction, so that it clings to the belt as in a van der Graaf generator. (Then a brush discharges it at the release point.) But really a chain of lidded boxes may be more robust. If the asteroid were made of Lunar dust, powdered basalt, then charging might be appropriate. For carbonaceous chrondrite material, well maybe, but the boxes are sure to work.

Anyone mining engineer will see a dozen problems with the whole idea, but will also think of solutions for half of them. In absence of a complete sound solution, the Lu-Love gravity tug is still practical. I think in future, when some asteroid mining projects are in operation, this centrifugal mass release scheme will seem to be a natural extension.

Gerald Lukaniuk
2006-Jan-04, 04:10 AM
It would be such a rare opportunity that a big lump of possibly useful metal would find it's way bang on earth why not turn a tragedy into a windfall by trying to divert the thing into a usefull earth orbit. The acquistion of usefull minerals in space near by and a platform for a space city would be pay back for the billions spent trying to send it away and it would probably take less energy than if we sent it away. If it were of a fragile nature we could spread it into a nice Saturn like ring around our equator. Again I will repeat that in the vacuum of space it's been well demonstrated the electrostatic traction would do a lot more thas making hair stand on end and nuclear furnaces, solar energy columnators or starwars laser cannons would create jets of vaporized asteroid matter gentle enough to move the asteriod around without breaking it up.

SolusLupus
2006-Jan-04, 04:26 AM
Create an orbit around the earth? That's just way too risky.

What if you mess up? One wrong calculation, and boom. You've just created armageddon (no, not the movie, the concept). This is even assuming you have the tools to make it work.

syed_maroof
2006-Jan-04, 09:02 AM
pardon my ignorance, but cant we, instead of using gravitational pull which requires about a year to change the path of asteroid, actually pull it by means of attaching a space ship to the asteroid and using its thrusters to change the path? It shouldnt be too difficult in zero gravity environment. It will also give greater control of the entire situation. I think a 20 ton nuclear powered space ship will have sufficient fuel to burn to bring about a meaningful change in the path of an asteroid. Such an action will also require less reaction time.

SolusLupus
2006-Jan-04, 05:46 PM
pardon my ignorance, but cant we, instead of using gravitational pull which requires about a year to change the path of asteroid, actually pull it by means of attaching a space ship to the asteroid and using its thrusters to change the path?

Can you imagine docking with a ship or space station that has a very significant spin? Hint: It's not easy, and is extremely likely to damage the docker and the dockee.

phunk
2006-Jan-04, 05:57 PM
pardon my ignorance, but cant we, instead of using gravitational pull which requires about a year to change the path of asteroid, actually pull it by means of attaching a space ship to the asteroid and using its thrusters to change the path? It shouldnt be too difficult in zero gravity environment. It will also give greater control of the entire situation. I think a 20 ton nuclear powered space ship will have sufficient fuel to burn to bring about a meaningful change in the path of an asteroid. Such an action will also require less reaction time.

That's one method, but the spin of the asteroid can make docking tricky and steering it even trickier. The gravity tug idea was offered as an alternative to docking and pushing the asteroid.

GBendt
2006-Jan-05, 11:27 AM
Hi van Rijn,

The explosion creates radiation which heats up matter. The heated matter is vaporised and this builds up pressure. This mechanism works fine even in spece, as long as the explosion takes place close to that matter.
I assumed that the fusion bomb is placed on the surface of the asteroid.

Regards,

Günther

Gerald Lukaniuk
2006-Jan-07, 12:32 AM
Create an orbit around the earth? That's just way too risky.

What if you mess up? One wrong calculation, and boom. You've just created armageddon (no, not the movie, the concept). This is even assuming you have the tools to make it work.
Its all in tne math. We've gotten pretty good calculating energy requirements to obit our probes around planets and drop down robots. If time and energy are insufficient to deflect it away from us we may have no choice but figure out how tho put it in orbit. At least we know where it is. If we deflect it who knows if and when it or parts of it will come back.

SolusLupus
2006-Jan-07, 12:35 AM
Its all in tne math. We've gotten pretty good calculating energy requirements to obit our probes around planets and drop down robots. If time and energy are insufficient to deflect it away from us we may have no choice but figure out how tho put it in orbit. At least we know where it is. If we deflect it who knows if and when it or parts of it will come back.

It would only be good as a last resort. We do have pretty good calculations, but hardly enough for me to trust the mathematicians to end up with an asteroid orbiting us. There's just too many factors involved, and if you mess up, LOTS of damage. Too much relying on too much.

Ideally, we'd have plenty of time to divert an asteroid. Non-ideally, maybe this idea could end up being the only one available to us.

in which case, I can only say, good luck, and may the Flying Spaghetti Monster be with us.

Gerald Lukaniuk
2006-Jan-07, 12:42 AM
If the earth is threaten by a doomsday asteroid its no time to think about being neat. If a bolt of electrostatically charged dust were to leap out from the moon and hit the time the momentum of said dust would alter its trajectory. An electrostatically induced dust wall has possibly been observed on the border between light and dark proving the moon can be charged up possibly enough to give an asteroid a tug.

phunk
2006-Jan-07, 02:10 PM
By the time an asteroid was on its way past the moon, it would be way too close to deflect. Besides, what are the odds of it passing close to the moon on the way in?

GBendt
2006-Jan-08, 11:50 PM
Hi Saski,

the law of the conservation of the angular momentum is the law of the conservation of the angular momentum, not the law of the conservation of angular speed of a rotating system.
If you lift matter from the surface of the rotating asteroid, this matter will maintain its momentum, which is the product of mass and speed. This momentum will not rise with the distance you put between the lifted matter and the asteroid.
Such, the centrifugal force the increase of which you want to use to run your system will not show up.

Regards,

Günther

Gerald Lukaniuk
2006-Jan-09, 12:30 AM
Bombarding the asteriod with projectiles of moon rock fired from chemical or nuclear powered cannons installed on the moon could be used to knock the asteroid of course.

Omicron Persei 8
2006-Jan-13, 10:51 PM
Bombarding the asteriod with projectiles of moon rock fired from chemical or nuclear powered cannons installed on the moon could be used to knock the asteroid of course.


Well now you risk breaking it apart again. And, remember this now, you have to deal with all of that momentum it already still has. Breaking into pieces just means all those pieces hit earth now. It's not like those piece will just drift into space on different trajectories.

RenderingSanity
2006-Jul-10, 03:02 PM
Why not somehow hook the astroid physically and use regular high powered thrusters to accelerate the astroid? It wouldn't be that hard, even with short notice to speed it up so it just passes earth early or use it's momentum to tow it into a slightly different path.