How Can We Effectively Destroy An Asteroid Headed for Earth?

[DaveC426913]

The proposal I saw was to send a rocket out to the meteor, and let the meteor's own gravity grab the rocket. Then, the rocket could thrust away from the meteor with some force less than the force it would need to escape,

Okay, well this is functionally identical to flying a rocket out and attaching it the asteroid and letting the rocket thrust do the work. The fact that you are attaching the rocket to the asteroid by gravity is a logistical detail.

 

[DaveC426913]

Dave,

That's what I would expect; but he forgot to tag the end with a

Dr. Gregory Greenman
Physicist

And no, he doesn't seem to be joking.

 

[LURCH]

Okay, well this is functionally identical to flying a rocket out and attaching it the asteroid and letting the rocket thrust do the work. The fact that you are attaching the rocket to the asteroid by gravity is a logistical detail.

Exactly. It's just a way of elliminating the problems of attaching a thruster to the asteroid if it's spinning, or if it's composition is a loose conglomorite rather than a solid rock. (Or if these properties are unknown)

BTW, I think it should be stated that this is a rather enginious solution to those problems, but with the limitations mentioned earlier, it just doesn't seem practicle.

 

[DaveC426913]

Exactly. It's just a way of elliminating the problems of attaching a thruster to the asteroid if it's spinning, or if it's composition is a loose conglomorite rather than a solid rock. (Or if these properties are unknown)

BTW, I think it should be stated that this is a rather enginious solution to those problems, but with the limitations mentioned earlier, it just doesn't seem practicle.

Right. OK, this all stemmed from P_V's suggestion of using gravity of a moveable object to deflect the asteroid.

These two solutions have nothing whatever to do with each other.

 

[Chronos]

Chronos,

I'm afraid your are in ERROR.

A nuclear blast in space in the vicinity of the asteroid DOES generate a shock wave in
the asteroid, and it doesn't require an atmosphere. You just don't understand the
mechanism.

When the nuclear device is detonated in the vicinity of the asteroid; it will intensely
radiate the surface of the asteroid. It is the radiative heating and blow-off of asteroid
material that WILL launch as shock wave into the asteroid.

That's how inertial confinement fusion, or laser fusion works also. The intense
radiation by the laser, and the blow-off or ablation of the fusion pellet surface, will
launch a shock wave into the fusion pellet.

Dr. Gregory Greenman
Physicist

Perhaps you missed my point. Nuclear blasts in space do not produce shock waves like they do in air, water, etc, since there is no medium available to propogate a shock wave. So, a nuke would have to be detonated near enough to the surface of the asteroid to vaporize some of its mass in order to impart any momentum. Explosions in a vacuum generate very high energy projectiles. Explosions in a medium generate high energy shock waves, which is a far more effective way to impart kinetic energy to a mass. Detonating a nuke near enough to the surface of an asteroid to be effective risks fragmenting it.

 

[Astronuc]

Nuclear blasts in space do not produce shock waves like they do in air, water, etc, since there is no medium available to propogate a shock wave. So, a nuke would have to be detonated near enough to the surface of the asteroid to vaporize some of its mass in order to impart any momentum. Explosions in a vacuum generate very high energy projectiles. Explosions in a medium generate high energy shock waves, which is a far more effective way to impart kinetic energy to a mass. Detonating a nuke near enough to the surface of an asteroid to be effective risks fragmenting it.

Morbius certainly understands the physics of nuclear explosions in a vacuum.

The point of detonating a nuclear warhead is exactly to use the 'radiation/thermal' energy to vaporize some mass of the asteroid which will 'deflect' it. Most of the nuclear warhead will be vaporized, so high energy projectiles are not a significant problem. A nuclear blast will likely cause some fragmentation of the asteroid, but those fragments would likely be volatized.

The radiation and thermal energy from a nuclear detonation will reach the asteroid surface before any blast wave, so the blast wave will interact with vapor and liquid, rather than solid, so fragmentation should not be a problem. I would imagine that someone is doing simulations to predict the thermo-mechanical response of a nuclear blast on an asteroid.

 

[Morbius]

Perhaps you missed my point. Nuclear blasts in space do not produce shock waves like they do in air, water, etc, since there is no medium available to propogate a shock wave. So, a nuke would have to be detonated near enough to the surface of the asteroid to vaporize some of its mass in order to impart any momentum. Explosions in a vacuum generate very high energy projectiles. Explosions in a medium generate high energy shock waves, which is a far more effective way to impart kinetic energy to a mass. Detonating a nuke near enough to the surface of an asteroid to be effective risks fragmenting it.

Chronos,

How is the nuke going to fragment the asteroid? You're thinking like the nuke was
still in the atmosphere! When you blow up a nuke; you expect it to "fragment" or
blow apart the stuff that's near it - but that is due to the blast wave from the nuke.

However, as you correctly point out - there is no blast wave in the vacuum of space!

Astronuc is quite correct - the material that constituted the nuke will be vaporized -
[actually it's beyond being vaporized - it's a plasma] so you don't have projectiles.

No - the major effect of the detonation of a nuke in space on material nearby is the
radiation. Place the nuke at the proper distance from the asteroid that you wish to
deflect - and the radiation will vaporize some of the material on the surface of the
asteroid, and the resultant blow-off will yield a reaction force that will deflect the
asteroid.

The effect of the radiation heating of the surface of the asteroid DOES PRODUCE
a shock wave IN THE ASTEROID! There'e no conventional nuclear blast wave
because the detonation is in a vacuum. However, the radiation can cause shock
waves to be generated in the material the radiation hits.

What one does is to detonate the nuke at the correct distance from the asteroid, so
that the radiation effects generate the proper deflection force. This was well covered
in the papers at the Planetary Defense Workshop that I cited above.

Dr. Gregory Greenman
Physicist

 

[Morbius]

one only needs to find the asteroid before it gets anywhere close to Earth. within a time frame of about 5-10 years, do you not think that we can divert an asteroid with a satellite that can be trasported near it? It's more plausible than blowing it up with nuclear missles. or transporting a rocket there. A satellite like object near the asteroid can offset it's course by a very small amount, but if done at a large distance away from earth...it can significantly deflect the asteroid's path. use of missles are just plain ridiculous and may be considered if we detect this thing too late...but then again...it's too late.

POSITION_VECTOR,

If we are going to deflect an asteroid, which can be miles in diameter; we are going to
have to deflect it YEARS ahead of time. But even then, you have to apply some
very large forces to the asteroid. The gravitational force from some once Earth-bound
satellite isn't going to do it.

Besides, any deflection forces you get from the gravity of the satellite will have
come from the rockets used to put the satellite there.

Suppose I have a ball of magnetic material sitting on the table. I hold in my hand a
magnet, and I swipe the magnet close to the ball and deflect it. The ball rolls off.
Where did the energy to roll the ball come from? It came from ME. The magnetic
field merely conveyed the energy via the magnetic force. But the energy came
ultimately from me. Using the magnet actually made the process less efficient -
I could have done better by hitting the ball directly with my hand.

The same is true with your satellite. Ultimately, the energy to deflect the asteroid
came from the rockets. By using the gravity of the satellite; you merely made the
process LESS EFFICIENT. It would be better to use the force of the rockets
directly. Deflecting an asteroid is going to take a LOT of force, and we don't have
any to spare; so we really won't be able to accommodate the inefficiencies of using
gravity.

As I stated before, the most efficient way to transport energy to some distant
place is via nuclear energy, hence it will be useful to have some nuclear weapons
on hand for the purpose. Perhaps that factored into President Clinton's decision
on August 11, 1995 to alter US policy to one that will retain nuclear weapons in
the US stockpile, for the indefinite future.

Dr. Gregory Greenman
Physicist

 

[Morbius]

Exactly. It's just a way of elliminating the problems of attaching a thruster to the asteroid if it's spinning, or if it's composition is a loose conglomorite rather than a solid rock. (Or if these properties are unknown)

LURCH,

Using gravity doesn't help you plant the rocket on the asteroid, even if it's spinning or
a loose consistency.

Gravity is a "central force". The force vector will be along the vector from the center
of mass of the asteroid to the center of mass of the rocket. Therefore, since the
force vector and radius vector are co-linear; the gravity can't induce a torque on the
rocket. Therefore, if the asteroid is spinning, the rocket WON'T spin up to match it.
You will still have the problem of a rocket attaching itself to a spinning object in any
case.

No - gravity is pretty useless here. Anything you can do with gravity, can be done
better by doing it directly.

If your asteroid is spinning, or even if it has a surface of loose consistency; if you
accellerate your rocket in space and slam it into the asteroid in a collision; the
asteroid is going to pick up the momentum. Where else would the momentum go?

Dr. Gregory Greenman
Physicist

 

[Morbius]

The radiation and thermal energy from a nuclear detonation will reach the asteroid surface before any blast wave, so the blast wave will interact with vapor and liquid, rather than solid, so fragmentation should not be a problem. I would imagine that someone is doing simulations to predict the thermo-mechanical response of a nuclear blast on an asteroid.

Astronuc,

EXACTLY CORRECT!

Yes - the interactions and responses of materials to the effects of nuclear explosions
indeed have been, and are; being simulated. Those are very complex calculations;
certainly not "back of the envelope" or "hand-waving" types. However, it's the type
of thing that been done for year for other reasons.

Dr. Gregory Greenman
Physicist

 

[LURCH]

LURCH,

Using gravity doesn't help you plant the rocket on the asteroid, even if it's spinning or
a loose consistency.

Gravity is a "central force". The force vector will be along the vector from the center
of mass of the asteroid to the center of mass of the rocket. Therefore, since the
force vector and radius vector are co-linear; the gravity can't induce a torque on the
rocket. Therefore, if the asteroid is spinning, the rocket WON'T spin up to match it.
You will still have the problem of a rocket attaching itself to a spinning object in any
case.

No - gravity is pretty useless here. Anything you can do with gravity, can be done
better by doing it directly.

If your asteroid is spinning, or even if it has a surface of loose consistency; if you
accellerate your rocket in space and slam it into the asteroid in a collision; the
asteroid is going to pick up the momentum. Where else would the momentum go?

Dr. Gregory Greenman
Physicist

You missunderstand the method being proposed. The idea is that the thruster be attached to the object by gravity alone; it never comes into physical, "material" contact with the object. This way, the rocket never has to sit on the surface. I believe the term used was "gravitational tethering".

It is precisely because gravity is a central force that the problems of spinning or loosely conglomerated targets are elliminated. If the object is spinning, the rocket, which is a short distance away, does not spin, and can point its nose (and its thrust) in one constant direction. Because the force and radius vectors are co-linear, no angular momentum is exchanged (well, not enough to mention, anyway). If the object is of loose composition, the tug of gravity will work on the whole group of objects as a single mass. Where a thruster on the surface or an impactor might just blow a hole right through the object, a thruster at a distance would pull on the center of mass for the group.

 

[theCandyman]

For gravity, F = G mM/r^2. [G = 6.7 * 10^-11 N m^2/ kg^2]

Now use this equation and calculate how much force using just gravity will affect the asteroid. Now only that, but if the asteroid is of a threating size, it might be impossible to make a rocket massive enough to affect it.

 

[DaveC426913]

For gravity, F = G mM/r^2. [G = 6.7 * 10^-11 N m^2/ kg^2]

Now use this equation and calculate how much force using just gravity will affect the asteroid. Now only that, but if the asteroid is of a threating size, it might be impossible to make a rocket massive enough to affect it.

The rocket is not supposed to be massive; the rocket acts by applying thrust.

And how much it affects the asteroid is determined only by how much time it has to do so. Even a small rocket will have an effect; it's only question of 'is it enough to do the trick?'

 

[DaveC426913]

You missunderstand the method being proposed. The idea is that the thruster be attached to the object by gravity alone; it never comes into physical, "material" contact with the object. This way, the rocket never has to sit on the surface. I believe the term used was "gravitational tethering".

So, if I understand correctly, the rocket's acceleration is constrained by the escape velocity of the asteroid. No matter how powerful the rocket has the potential to thrust, it must stay below escape velocity or it will break free.

 

[Morbius]

So, if I understand correctly, the rocket's acceleration is constrained by the escape velocity of the asteroid. No matter how powerful the rocket has the potential to thrust, it must stay below escape velocity or it will break free.

Dave,

You are correct. The amount of force the rocket can exert on the asteroid is limited
by the mutual gravitational attraction between the rocket and asteroid, and the
requirement that the rocket stay below escape velocity.

This SEVERELY restrincts the amount of force that can be applied. Even if we
deflect the asteroid YEARS in advance; it is going to take some VERY LARGE forces
to deflect asteroids of a size that would be a threat to the Earth.

Dr. Gregory Greenman
Physicist

 

[LURCH]

Yes, in this method detection would have to be even earlier than the other techniques mentioned. And, as we all were reminded last week,

https://www.physicsforums.com/showthread.php?t=130554

We don't have very adequate early detection.

This SEVERELY restrincts the amount of force that can be applied. Even if we
deflect the asteroid YEARS in advance; it is going to take some VERY LARGE forces
to deflect asteroids of a size that would be a threat to the Earth.

Also very true. But on the plus side, this method would put a direct correlation between the amount of energy available (in practicale terms) and the amount needed. Larger objects would require more thrust, but they would also have a stronger gravitational tether, and be able to handle more thrust. Nevertheless, the amount of thrust needed compared to the amount that could be applied per unite of time is such a huge ratio, we'd have to start with much more advanced warning than we're likely to get.

And we'd have to know the strength of the gravitational field around the object before we could begin thrusting, so we don't just escape. This is notoriusly difficult to calculate for an object traveling through open space. I suppose we could find that out by firing a preliminary projectile near the object (kind-of a shot across its bow), and measure how the path of that projectile is altered by the close encounter. But the margin of error would be pretty big. I think we'd have to send an engine with veriable thrust, so we could dial it back if it started to escape, or crank it up if it started to get closer to the object. Not impossible, but pretty complicated.

And of course, as has been stated, this method reduces the amount of effect we could have on the object. Current scenarios are dependant upon detection years in advance, so that the small effect we could have on the cousre of the object would be sufficient when multiplied by time to impact. Gravitational tethering makes the effect we could have so small that the time to impact would have to be many decades; [probably about a century. This raises two big questions,
1)Can we accurately predict a collision event 100 yrs in advance?
I'm doubtfull, we have a cattelog of a few objects that might hit in the next twenty years, and we can't even speek with much certainty about them. They "probably won't".
2)Projecting the kind of tech we are likely to have 100 yrs from now, why bother?
If we have a hundred years of warning, then we can be pretty sure that we'll have a much more reliable method in place in plenty of time.

I still say the best solution is to blast 'em!

 

[Morbius]

I think we'd have to send an engine with veriable thrust, so we could dial it back if it started to escape, or crank it up if it started to get closer to the object. Not impossible, but pretty complicated.

LURCH,

The main engines on the space shuttle are variable thrust. During the launch of a
space shuttle, the engines throttle back to reduce aerodynamic stress on the vehicle,
and then as the air gets thinnner with altitude, the engines throttle up again.

Dr. Gregory Greenman
Physicist

 

[LURCH]

Ah yes, of course. I was still thinking of ion propulsion. If this method were to be viable at all, I think that the low specific impulse and long duration of Ion Drive would be a necessity.

VASIMR's (ion drives with veriable specific impulse) exist, but last I heard there were only prototypes in testing. Have any been flown? I thought I remembered eharing that the ESU was going to use that propulsion system for its next Lunar orbiter, but I don't know if that's still in the future.

Aslo, here's an interesting article on this very topic;

http://flux.aps.org/meetings/YR04/DPP04/baps/abs/S1905.html

NASA's Prometheus program seeks to develop new generations of spacecraft nuclear-power and ion propulsion systems for applications to future planetary missions...

...Another potential Prometheus mission of high science interest would be an extended tour of primitive bodies in the solar system, including asteroids, Jupiter family comets, Centaurs, and Kuiper Belt Objects (KBO). The final landed phase of this mission might include an active keplerian experiment for detectable (via downlink radio doppler shift) acceleration of a small kilometer-size Centaur or KBO object, likely the satellite of a larger object observable from Earth. This would have obvious application to testing of mitigation techniques for Earth impact hazards.

 

[Astronuc]

VASIMR's (ion drives with veriable specific impulse) exist, but last I heard there were only prototypes in testing. Have any been flown?

VASIMR have yet to be perfected - they are still problematic and have little thrust. None have been flown.

 

[Morbius]

Ah yes, of course. I was still thinking of ion propulsion.

LURCH,

"It beats me. But isn't she a beauty? Interesting design.
I've never seen anything like her. And ion propulsion at that.
They could teach us a thing or two."

--LCDR Montongomery Scott, from the Star Trek episode "Spock's Brain"

Dr. Gregory Greenman
Physicist

 

[Orion1]

I performed a calculation using the Teller equation and information from this thread for subsurface nuclear explosion blast cavity radius and produced the result:

Teller equation:
r(h) = C \frac{Y^{\frac{1}{3}}}{(\rho h)^\frac{1}{4}}}

Y = 1 \cdot 10^6 \; \text{kt} - proposed yield (for complete destruction)
\rho_{Fe} = 7.87 \; \text{g} \cdot \text{cc}^{-1} - Ferrous density

r(h) = 80 \cdot \frac{(1 \cdot 10^6)^{\frac{1}{3}}}{(7.87 h)^{\frac{1}{4}}} = \frac{4.776 \; \text{km}}{h^{\frac{1}{4}}}

r(h) = \frac{4.776 \; \text{km}}{h^{\frac{1}{4}}}

h = penetrator depth, although the constant C is for Granite, the result should be close.
[/Color]

 

[SAZAR]

They say if we needed to destroy and asteroid headed for Earth the fastest easiest way is witha nuclear bomb. If we used it it would destroy it but it would create thousands of pieces falling to Earth which would be much worse.

In a special it was said that it would take a bomb on the order of 1,000 megatons to completely destroy an asteroid. It would not only be the biggest bomb ever built but it would need to be put on the biggest rocket ever built. My soloution could be simple. INstead of building one big bomb build about 10 smaller ones. launch 10 smaller nuclear warheads and attach them all to the asteroid. THen at the precise moment they all go off.

SInce there would be 10 each one would be around 100 megatons. And since it not one concentrated into one place they would have a better chance of destroying all the asteroid. I think 100 megatons is well within our bombmaking capabilitites. If we make them light enough we could put 2 on each rocket only requiring 5 launches. This sounds easy and simple. Why hasn't anybody ever thought of this?

Movie: "Meteor"

http://www.imdb.com/title/tt0079550/
(watch that movie)

PS: pay attention to the year it was made.

 

[SAZAR]

About the theme itself...
...No doubt; some sort of bomb is in order: nuclear or even anti-matter...
...But, it would be interesting to see some more ingenious (but effective!) solutions...

 

[the_force]

About the theme itself...
...No doubt; some sort of bomb is in order: nuclear or even anti-matter...
...But, it would be interesting to see some more ingenious (but effective!) solutions...

What is an Anti-matter bomb? :)

Do we even have a rocket that can take a 1000MT nuke? Maybe use a couple of the Soviets Tsar designs. lol

Only way - Mutate out minds and get smarter. Might need to wait until the next human mutation takes place :)

 

[Astronuc]

What is an Anti-matter bomb? :)

Do we even have a rocket that can take a 1000MT nuke? Maybe use a couple of the Soviets Tsar designs.

An antimatter bomb, as the name implies, is a bomb in which the active material is antimatter - most likely cryogenic anti-hydrogen, since making anti-atoms of Li or heavier atoms (elements) is exceedingly difficult. Even making pico-grams of anti-hydrogen takes a long time and it's not all at once. Storage is another exceedingly difficult problem.

Assuming one could amass a gram scale quantity of anti-matter - how would it work? Likely a reaction would be initiated between matter and antimatter, which would cause a burst of mesons and gamma rays, which would disperse the remaining solid anti-matter, which would interact with whatever matter it encountered, so likely the area would be a large volume of plasma. The energy release rate would be limited by how quickly the matter and anti-matter interact.

A 1000MT (1 GT) nuke would be very large, and that has not been the focus of mainstream reasearch. The main goal of late has been smaller more compact nukes for specific targets rather than large areas like cities.

 

[the_force]

Hey

Yea, we are making more bombs like SRAM-T, insted of the megaton nukes that were created in the cold war. I read a journal that stated the USA still has Nuclear missiles locked onto Russia and vice versa.

Does anyone think we will see a nuclear exchange in our life time?

 

[Morbius]

Yea, we are making more bombs like SRAM-T, insted of the megaton nukes that were created in the cold war. I read a journal that stated the USA still has Nuclear missiles locked onto Russia and vice versa.

the_force,

All that stuff about the USA and Russia having missiles "locked onto"
each other is a bunch of BALONEY!

The missiles have auto-pilots; like an airplane. Right now, all those
auto-pilots are OFF - the missiles are OFF.

When you want to fire the missile; you "spin it up" and boot-up the
auto-pilot. Then you enter the coordinates of the target in the
auto-pilot's computer.

Saying that we have missiles "locked on" Russia is like saying that your
powered-down and off computer is "locked on" your favorite website.

Dr. Gregory Greenman
Physicist

 

[Morbius]

Yea, we are making more bombs like SRAM-T, insted of the megaton nukes that were created in the cold war.

the_force,

Actually the USA hasn't produced a new nuclear weapon in YEARS!

The last nuclear weapon design that entered the stockpile was the
"nuclear bunker buster" the B-61 Mod 11 which entered service in
1997, and was developed at the behest of President Clinton:

http://www.fas.org/faspir/2001/v54n1/weapons.htm

The B-61 Mod 11 was a modification of the B-61 family of gravity bomb,
rather than a "clean sheet of paper" design.

The last totally new designs were the W-87 Peacekeeper ICBM warhead
designed by Livermore, and the W-88 Trident D-5 SLBM warhead designed
by Los Alamos. Both of these were commissioned in the '70s under the
Carter Administration [ the Peacekeeper was originally called "MX"].

The SRAM warheads, W89 for SRAM II, and W91 for SRAM-T never made
it beyond the feasibility study stage. The SRAM program was canceled
over a decade ago.

Dr. Gregory Greenman
Physicist

 

[the_force]

Hey

Thanks Morbius for clearing up the BALONEY :)

Does Russia still make nuclear weapons?

 

[Morbius]

Thanks Morbius for clearing up the BALONEY :)

Does Russia still make nuclear weapons?

the_force,

A while back in 2004, Russian President Vladamir Putin announced that Russia
was working on new nuclear weapons:

http://www.cbc.ca/world/story/2004/11/17/russia-missiles-041117.html

Dr. Gregory Greenman
Physicist