How Can We Effectively Destroy An Asteroid Headed for Earth?

[the_force]

Hey

Thanks for that article, good read!

Geez, I think Putin wants the cold war back in light of recent events

 

[quetzalcoatl9]

what if the device to deflect the asteroid contained disk of polymer "propellant" that would be vaporized by the thermonuclear detonation in the direction of the asteroid, a la Orion? Would this be a more efficient transfer of energy to the asteroid than direct radiation interaction with the asteroid material?

 

[Morbius]

what if the device to deflect the asteroid contained disk of polymer "propellant" that would be vaporized by the thermonuclear detonation in the direction of the asteroid, a la Orion? Would this be a more efficient transfer of energy to the asteroid than direct radiation interaction with the asteroid material?

quetzalcoatl9,

If I get your question; you want a disk of material that sits between the bomb and the
asteroid; which the bomb will vaporize, and the expanding vaporized propellant would
then impact the asteroid and transfer momentum to it.

My question is why put anything between the asteroid and the bomb. If the propellant is
vaporized by the bomb; the hot vaporized material will expand in both directions - toward
the bomb, and away from the bomb. Only the half that is heading toward the bomb will
contribute to deflecting the asteroid.

In essence, only HALF the aborbed energy is then available for deflecting the asteroid.

Why not let all the radiation from the bomb "impact" on the asteroid?

What are you trying to accomplish with this disk of propellant? It isn't needed.

Dr. Gregory Greenman
Physicist

 

[quetzalcoatl9]

Why not let all the radiation from the bomb "impact" on the asteroid?

good point - i guess my thinking was that the polymer disk was proposed for use by the Orion craft to better transfer the energy. However, I also forgot that an Orion objective was for the spacecraft to not be destroyed (i.e. the pusher plate stay intact and get irradiated+ablated as little as possible), a constraint that need not hold with the asteroid :)

 

[Alphabit]

I read from somewhere that there was a way to divert the path of an asteroid by applying gravity to it... I assume they would do it through applying a constant force over a certain period of time.

 

[Morbius]

I read from somewhere that there was a way to divert the path of an asteroid by applying gravity to it... I assume they would do it through applying a constant force over a certain period of time.

Alphabit,

Yes - that's one proposal. However, gravity is a very weak force unless you have huge
amounts of mass. The idea was to put a spacecraft near the asteroid and let the gravity
of the spacecraft deflect the asteroid.

Naturally the gravity of anything of a mass small enough for us to boost into space is going
to be EXTEMELY small. So this scheme works ONLY if you have a few DECADES of
lead time.

For example, suppose we were to discover that one of the asteroids that had an Earth
crossing orbit was going to impact the Earth a few decades from now. This asteroid is
going to orbit the Sun many, many times before impacting Earth. Such an object would
succumb to a gentle push for many years to deflect it. Then you might be able to use gravity
to deflect the asteroid.

However, suppose we discover an asteroid or comet that is coming at us from the region
of space out beyond Pluto. This asteroid isn't going to loop around the Sun for many
decades giving us time to gently deflect it. Suppose this asteroid is on a collision course
with Earth on THIS orbit. This asteroid needs to be given a BIG PUSH and NOW in order
to make it miss Earth.

A gravity type deflection scheme would be ABSOLUTELY USELESS against such
an asteroid. That would be where we would need some way of applying much, much
larger forces.

Dr. Gregory Greenman
Physicist

 

[joema]

...this scheme works ONLY if you have a few DECADES of
lead time...However, suppose we discover an asteroid or comet that is coming at us from the region of space out beyond Pluto...Suppose this asteroid is on a collision course with Earth on THIS orbit...A gravity type deflection scheme would be ABSOLUTELY USELESS against such an asteroid...

A little more on this: the gravity tractor works by making the asteroid miss the "gravitational keyhole", not by deflecting it to miss the Earth's angular diameter. These regions are very small -- I think 400 meters wide for Apophis. Yet to achieve this takes about 1 year, and is generally at least 2 orbital periods out.

Apophis has an orbital period of about 1 year, so maybe the minimum lead time would be about 2 years, not including prep time for launch plus travel time. So figure 3 years as the absolute minimum, and that assumes having mostly off-the shelf capability.

The proposed gravity tractor is not a small, simple vehicle. It's 18 metric tons (40,000 lbs), uses a nuclear reactor and ion engines. The technology is taken from the now-cancelled NASA Prometheus project: http://en.wikipedia.org/wiki/Project_Prometheus.

Even if you knew 3+ years in advance, I don't think there's a currently operational launch vehicle capable of lifting 18 metric tons to Earth escape velocity, plus enough surplus propellant to rendezvous with an asteroid moving at 30 km/sec.

Taking Apophis as an example, if it were initially discovered at the farthest distance from earth, and determined to be on a collision course, you'd have about 6 months. If an asteroid came from the sun's direction (where telescopes can't see) you might have 2 months. In such cases (as already mentioned) a gravity tractor would be useless.

 

[Morbius]

The proposed gravity tractor is not a small, simple vehicle. It's 18 metric tons (40,000 lbs), uses a nuclear reactor and ion engines.

joema,

In the celestial mechanics of natural stellar satellites; 18 metric tons is a PITTANCE!

Dr. Gregory Greenman
Physicist

 

[joema]

joema,

In the celestial mechanics of natural stellar satellites; 18 metric tons is a PITTANCE!...

Yes, agreed. My point was it might require (by the standards of previous deep space probes) a very large and powerful vehicle, using nuclear-electric propulsion. This in turn requires a very large launch vehicle, larger than any currently available.

However there are two high-level scenarios:

(a) Deflect asteroid to miss small gravitation keyhole in space, which if achieved will cause asteroid to miss Earth on a subsequent encounter. This can be done with a very small probe, using solar-electric propulsion and existing launch vehicles. It could be similar the Deep Space 1 probe, already tested: http://en.wikipedia.org/wiki/Deep_Space_1

(b) Deflect asteroid to miss Earth (it's on a direct earth-impact trajectory). Small vehicles like Deep Space 1 could only handle a small asteroid (150-200 m dia), and only if detected pretty far out. The Schweikart paper discussed these: http://arxiv.org/pdf/physics/0608157

If the object is larger or detected later, a much heavier nuclear-electric gravity tractor would be required, probably around 20 metric tons. This was described here: http://space.newscientist.com/article/dn8291--gravity-tractor-to-deflect-earthbound-asteroids.html

The gravity tractor concept is very interesting and elegant, but as you explained it only works in some circumstances. You need years (likely many years) of warning time.

There are various approach trajectories where the object wouldn't be seen in time with current detection technology. In those cases a nuclear deflection, probably using a non-fragmenting stand-off detonation, would seem the only option. The lead time to launch could be very short -- possibly months, conceivably weeks, since existing ICBMs could be used.

 

[Morbius]

The Schweikart paper discussed these: http://arxiv.org/pdf/physics/0608157

A physicist colleague of mine who works in the field of asteroid deflection was telling
me recently about a debate he had with Schweikart. He was not AT ALL impressed
with Schweikart's understanding of the problems and much of the relevant physics.

I would certainly quibble with Scweikart's contention that only the gravity tractor
deflection scheme can be "fully controlled". I would like to see more of the plans
for the "nuclear - electric" propulsion systems. What I have seen of these have
been pretty lacking in design details.

In those cases a nuclear deflection, probably using a non-fragmenting stand-off detonation, would seem the only option. The lead time to launch could be very short -- possibly months, conceivably weeks, since existing ICBMs could be used.

Many of the schemes, like gravity tractors, etc - work only in one end of the threat
spectrum - the asteroids in low eccentricity orbits that will require many orbits before
they impact Earth - hence a long enough lead time for a relatively weak application of
force to deflect the asteroid.

The gravity schemes don't work when you have asteroids or comets in highly eccentric
orbits that are "way out there"; but are heading for impact on their current orbit. These
are the ones that will offer very short lead times from the time we detect the object to
the time it has to be deflected. Those are the ones that are going to need a big push
since we don't have years for the ultimate effect of the push to accrue.

The stand-off nuclear weapon detonation would seem to be our only hope for these. This
technique will also work for the asteroids that would succumb to the gravity tractor. In
other words, the stand-off nuclear weapon detonation covers a much greater fraction of
the threat spectrum. It's even good for "rubble piles" - an object composed of many
discrete objects held together by mutual gravity. You can't push on a rubble pile with
spacecraft . Only a "body force" like a gravity tractor, or the ablation due to a stand-off
nuke will work well on a "rubble pile".

Dr. Gregory Greenman
Physicist

 

[DaveC426913]

joema,

In the celestial mechanics of natural stellar satellites; 18 metric tons is a PITTANCE!

Dr. Gregory Greenman
Physicist

True, but a 400 meter wide keyhole is equally a dust mote.

 

[Astronuc]

NASA Report on Asteroids Suggests Nuclear Option
by Nell Boyce
http://www.npr.org/templates/story/story.php?storyId=7867322

Morning Edition, March 13, 2007 · Scientists have sent Congress a report on ways to prevent an asteroid from hitting Earth. Among the proposals: Use nuclear weapons to nudge a big space rock off a collision course. Some scientists don't think much of that idea.

Scientists Gather at Conference to Stop Asteroids
by Alex Chadwick
http://www.npr.org/templates/story/story.php?storyId=7713661

Day to Day, March 5, 2007 · A Planetary Defense Conference that starts Monday will look into possible methods of preventing asteroids from hitting Earth. William Ailor, a director with The Aerospace Corporation, talks about the threat of a direct hit.

Still a controversial topic.

 

[Morbius]

Still a controversial topic.

Astronuc,

A colleague of mine is active in the asteroid deflection field. He told me he was recently
at a conference that featured a paper by former astronaut Schweikert, who outlined the
parameters of a "gravity tractor" spacecraft .

My colleague did a calculation to show that you get more deflection impulse into the
asteroid if you CRASH the gravity tractor into the asteroid; than if you use it as a gravity
tractor.

Dr. Gregory Greenman
Physicist

 

[Astronuc]

A colleague of mine is active in the asteroid deflection field. He told me he was recently at a conference that featured a paper by former astronaut Schweikert, who outlined the parameters of a "gravity tractor" spacecraft .

My colleague did a calculation to show that you get more deflection impulse into the asteroid if you CRASH the gravity tractor into the asteroid; than if you use it as a gravity tractor.

Well I suppose it will likely be a one way trip, but it sounds like some folks want a 'reusable' space tractor.

I think though an impulsive load makes much more sense - and the further out the deflection, the better.

 

[Morbius]

Well I suppose it will likely be a one way trip, but it sounds like some folks want a 'reusable' space tractor.

I think though an impulsive load makes much more sense - and the further out the deflection, the better.

Astronuc,

Yes - even if a "gravity tractor" is used as intended; it will take a LONG time to deflect the
asteroid.

I also think an impulsive load makes WAY more sense. If you crash the tractor into the
asteroid; you can then measure the new trajectory of the asteroid and determine if the
deflection is enough. If there were any wrong assumptions in the original calculation; e.g.
the asteroid mass; the process can be repeated.

Since the "gravity tractor" is a much more gradual deflection; by the time one finds out
that the deflection rate is too slow with the "gravity tractor"; precious time has been
wasted.

Dr. Gregory Greenman
Physicist

 

[joema]

My colleague did a calculation to show that you get more deflection impulse into the asteroid if you CRASH the gravity tractor into the asteroid;...Since the "gravity tractor" is a much more gradual deflection; by the time one finds out that the deflection rate is too slow with the "gravity tractor"; precious time has been wasted...

The deflection rate is determined by the relative masses of the vehicle and asteroid, plus the hover height. Two of those would be known, the asteroid mass could be estimated. So even before launch the deflection rate could be estimated.

However your point about more deflection from actual impact makes sense. Kinetic energy increases as the square of velocity (KE = 1/2*m*v^2). Just to reach the asteroid, the velocity would be extremely high, and the impact velocity (relative to the asteroid) even higher.

The proposed gravity tractor might be 18 metric tons: http://news.nationalgeographic.com/news/2007/02/070217-asteroid-impact.html

It would probably be boosted to at least 15 km/sec on a direct escape trajectory, something like the New Horizons probe: http://en.wikipedia.org/wiki/New_horizons

The asteroid relative impact speed would probably at least 25 km/sec.

Thus the impact energy would be 5.625E12 joules (1.56E9 watt hours).

That's roughly equivalent to 1.4 million kg (!) of high explosives.

Don't know what the max energy imparted by a gravity tractor, but it must be far less than this.

Also the gravity tractor has an additional burden -- it must decelerate from high speed to rendezvous with the asteroid. Thus all that fuel mass required for rendezvous is subtracted from payload mass. I'd be curious if your colleague took that into account. It's possible the gravity tractor is even worse than first appears.

 

[Morbius]

Thus the impact energy would be 5.625E12 joules (1.56E9 watt hours).

That's roughly equivalent to 1.4 million kg (!) of high explosives.

joema,

In terms of explosive yield; 1 kiloton = 4.186 terajoules = 4.186e+12 joules.

So the impact energy is 1.34 kilontons; which is the same energy as a very small
atomic bomb - the Hiroshima bomb was over 10X as powerful, and the Nagasaki and
Trinity bombs were about 15X as powerful.

It's also many thousands of times less powerful than a thermonuclear device with a
mere fraction of the weight of the impactor.

When it comes to making alterations to the trajectories of asteroids; 1.4 million kg of
high explosive energy is UNIMPRESSIVE.

Dr. Gregory Greenman
Physicist

 

[joema]

...When it comes to making alterations to the trajectories of asteroids; 1.4 million kg of high explosive energy is UNIMPRESSIVE...

Yes, agreed. I only meant the energy and resultant momentum change imparted from a direct kinetic impact is probably much greater than that from a gravity tractor of the same payload mass at liftoff.

The gravity tractor concept is interesting and may be useful in some circumstances, but it seems quite limited in the delta V imparted to the asteroid. Especially considering the additional booster payload requirement to lift enough propellant for deceleration and rendezvous, plus that required for station keeping at the asteroid.

The kinetic impact method could use all the mass during direct impact, which increases the imparted energy.

You're right if you need more than a tiny deflection, it appears nuclear is the only near-term option using currently available technology.

The light weight of a a nuclear warhead would allow extremely high velocity, thus enable short reaction time intercept options unavailable with any other technique. E.g, the Nasa New Horizons probe weighed 478 kg and was boosted to 16.2 km/sec by an off-the-shelf Atlas V. It crossed the moon's orbit 9 hours after launch. An asteroid-deflecting nuclear warhead (plus terminal guidance) could easily fit within the same space/mass.

Typical warhead yield-to-weight is 350 kg per megaton, so an approx. 250-500 kt warhead might fit that booster size, leaving about 300-400 kg payload for packaging, guidance, terminal propulsion, etc.

Years of advance warning is good -- it enables more options. But the common notion that no other workable options exist for a timeframe on the order of months isn't really correct.

 

[Morbius]

You're right if you need more than a tiny deflection, it appears nuclear is the only near-term option using currently available technology.

Years of advance warning is good -- it enables more options. But the common notion that no other workable options exist for a timeframe on the order of months isn't really correct.

joema,

Agreed. The gravity tractor only works if you have extended advanced warning of an
asteroid on collision course. A gravity tractor is useless if a "quick" deflection is needed.

As you point out; a nuclear warhead can be used for a "quick" deflection. The nuclear
option is also available if there is extended advanced warning.

So one "solution", the gravity tractor only works in one limit of the threat spectrum, but
not the other. The nuclear option works in both limits. I wonder why limited resources
should be expended on a "solution" that only works in one limit; when a solution that
works in both limits is available.

Dr. Gregory Greenman
Physicist

 

[Aero Stud]

There's an international student competition about this subject of an asteroid deflection being held now. Except they're limmited to using one specific settelite launcher or something like that. Guys from my AE semester at the Technion started working on it as well. It's actualy a specific asteroid I think, something like 300 meters in diameter with some small chance of hitting us in something like 2027. Don't remember more details.

joema,

Agreed. The gravity tractor only works if you have extended advanced warning of an
asteroid on collision course. A gravity tractor is useless if a "quick" deflection is needed.

As you point out; a nuclear warhead can be used for a "quick" deflection. The nuclear
option is also available if there is extended advanced warning.

So one "solution", the gravity tractor only works in one limit of the threat spectrum, but
not the other. The nuclear option works in both limits. I wonder why limited resources
should be expended on a "solution" that only works in one limit; when a solution that
works in both limits is available.

Dr. Gregory Greenman
Physicist

The problem with the nuclear option is that if the asteroid is big anough you are likely to end up with several smaller parts, with pretty much the same trajectory and still way too big to burn in the atmosphere. It might even be worse than before in terms of expected damage.

Gravitational deflection may be a good solution when we know years ahead of the impact and the asteroid is not too big.

Personally, the best current option I can think of is nuclear, also. Except that instead of sending one missile we should use a battery of missiles that will hit the asteroid and its parts one at a time in a controlled manner - so we could take it apart to small anough pieces systematicly and/or deflect it and its parts. Also, depending on the asteroid's composition we could make rockets that could penetrate some distance inside by coming in at relatively high speed, if it promises better results.

One of the biggest problems is the amount of info we have about an asteroid. It could be made of many different materials, with different densities and moments of inertia or even be comprised of multiple parts moving together caught by their mutual gravity. Without collecting this information about the asteroid first, predicting the results of a nuclear bombardment is very difficult.

 

[Morbius]

The problem with the nuclear option is that if the asteroid is big anough you are likely to end up with several smaller parts, with pretty much the same trajectory and still way too big to burn in the atmosphere. It might even be worse than before in terms of expected damage.

Aero Stud,

WRONG WRONG WRONG!

Unfortunately, you fallen for the naive unscientific "clap trap" that you usually see in the
media about the nuclear option - that the intent is to blow up the asteroid.

NOBODY in the field of nuclear deflection is proposing that!

The object of using a nuclear device is NOT to blow up the asteroid but to DEFLECT it.

You deflect the asteroid by blowing up the bomb NEAR the asteroid but NOT on the
asteroid.

The radiation from the bomb will ablate the surface of the asteroid and result in a
impulse which DEFLECTS the asteroid. A nuclear warhead used in this manner will
result in a deflection impulse MANY times greater than what is available from ANY
type of rocket propelled by chemical propellant.

Dr. Gregory Greenman
Physicist

 

[Aero Stud]

I think that maybe you didn't quite read into what I wrote at the end. Which is basically the main problem. We don't know what those things are made of. There's a huge variety of objects out there. And even looking at them a lot from down here and up in orbit and even going near them, the uncertainty factors are still relatively high. So they're not just golf balls floating around. Besides, we never blew up a nuclear warhead in space before. Not to mention, that unless you promise the political guys high chances of success they, with all the public pressure in addition, won't allow any nuclear weapons to be launched into space.

 

[Morbius]

I think that maybe you didn't quite read into what I wrote at the end. Which is basically the main problem. We don't know what those things are made of. There's a huge variety of objects out there. And even looking at them a lot from down here and up in orbit and even going near them, the uncertainty factors are still relatively high. Besides, we never blew up a nuclear warhead in space before. Not to mention, that unless you promise the political guys high chances of success they, with all the public pressure in addition, won't allow any nuclear weapons to be launched into space.

Aero Stud,

WRONG! WRONG! WRONG!

You need to do some RESEARCH before you post!

We certainly HAVE blown up nuclear warheads in space!

It is now against Treaty to do so - but in the early days of atmospheric nuclear testing
we certainly DID put nuclear warheads on missiles and detonate them in space. In fact,
that's how the phenomenon of ElectroMagnetic Pulse or EMP was discovered.

Actually we DO know a fair amount about the composition of asteroids, and there have
been probes sent to rendevous with asteroids, and even land on them; from which we
have found out a lot.

Even so - the lack of knowledge composition of the asteroid is NOT an unsurmountable
obstacle to deflecting it. The nuclear warhead will vaporize ANYTHING!

As far as the political problem - for Heaven's sake THINK about it. If we suddenly find
that an asteroid is heading for Earth somewhere from beyond the Ort Cloud and it's
going to impact on THIS orbit - the only thing powerful enough to deflect it will be a
nuclear weapon.

Do you REALLY think the politicians and the environmentalists are going to say,
"Oh NO - don't use a nuclear weapon - I'd rather have the Earth destroyed by an
asteroid than to use a nuclear weapon!"

If it's a question of SURVIVAL of the Earth - launching a nuke will be ZERO problem.

Dr. Gregory Greenman
Physicist

 

[Aero Stud]

You need to do some RESEARCH before you post!

We certainly HAVE blown up nuclear warheads in space!

Really, in space ? Never heard of it. Sorry.

Actually we DO know a fair amount about the composition of asteroids, and there have
been probes sent to rendevous with asteroids, and even land on them; from which we
have found out a lot.

Even so - the lack of knowledge composition of the asteroid is NOT an unsurmountable
obstacle to deflecting it. The nuclear warhead will vaporize ANYTHING!

I know about the asteroid (don't remember more to add an "s" ), but they can be a lot different. I agree nothing is unsurmountable here, but it is a problem - and if you're considering different alternatives then things like this have their weight I think.

About the nuclear missile vaporising anything again everything it's relative, if it's several miles wide and made mostly of iron - there's a lot of blowing up needed there so who knows. I agree with the nuclear missiles, just saying that to be sure it's better to use several than hope just one big missile will do it and not forget to at least try to develop other options, can't hurt I think.

As far as the political problem - for Heaven's sake THINK about it. If we suddenly find
that an asteroid is heading for Earth somewhere from beyond the Ort Cloud and it's
going to impact on THIS orbit - the only thing powerful enough to deflect it will be a
nuclear weapon.

Do you REALLY think the politicians and the environmentalists are going to say,
"Oh NO - don't use a nuclear weapon - I'd rather have the Earth destroyed by an
asteroid than to use a nuclear weapon!"

If it's a question of SURVIVAL of the Earth - launching a nuke will be ZERO problem.

Dr. Gregory Greenman
Physicist

I think that when there are other solutions to compete with and/or the impact is not certain then people may prefer to wait until it is certain and the solution chosen is the best one, which doesn't leave that much time. But it's not really an argument, more of a sidenote to the nuclear option which like I said I generally argue for too. I see that maybe you're a bit emotional about the discussion.

The chemical rocket in case of a gravitational diflection just delivers the mass. Even a 1 ton mass can do a lot to say phousands of tons if the trajectory change is many years prior to impact. I don't see though how they can do it for now if they can't even calculate whether there will be an impact or not - and that's a pretty wide range at the end.

 

[joema]

...we never blew up a nuclear warhead in space before...

There have been numerous nuclear detonations in space (note the typical definition of "space" is 100 km altitude):

http://www.johnstonsarchive.net/nuclear/hane.html

 

[Aero Stud]

There have been numerous nuclear detonations in space (note the typical definition of "space" is 100 km altitude):

http://www.johnstonsarchive.net/nuclear/hane.html

Interesting. Did they also measure how the explosion changed the trajectories of those sattelite's that are mentioned ? Considering that's the primary objective here.

 

[joema]

Interesting. Did they also measure how the explosion changed the trajectories of those sattelite's that are mentioned ? Considering that's the primary objective here.

Don't understand your point. Those explosions weren't intended to change the trajectory of anything.

The point is numerous nuclear detonations in space have already happened, so doing it again in deep space to deflect an asteroid wouldn't be new. It would be much farther out in space, likely not visible from earth.

The fuzing and guidance technology for doing a precision stand-off detonation is well developed. It's essentially off-the-shelf technology.

Given years of advance warning, there are various options for asteroid deflection -- kinetic impact, gravity tractor, nuclear, etc. Given less than a year, the nuclear option is probably the only one available.

Given the stakes, it seems you'd probably want diverse redundant methods. That way if one fails, you'd try others.

 

[Aero Stud]

Don't understand your point. Those explosions weren't intended to change the trajectory of anything.

What I'm saying is that if we haven't measured in any way the effects of the explosion in terms of deflecting objects in space, for example by means of tracking those sattelite's, if any, that were destroyed directly by the impact and not due to EMP short-circuiting them, then are we currently able to predict accuratly anough the effects of such deflection explosions (assumng we know all we need to know about the asteroid itself). Or in simpler words, can you calculate accurately anough the momentum you'll impart by an explosion X feet away on a surface of Y dimensions at Z angle ?

The fuzing and guidance technology for doing a precision stand-off detonation is well developed. It's essentially off-the-shelf technology.

Given years of advance warning, there are various options for asteroid deflection -- kinetic impact, gravity tractor, nuclear, etc. Given less than a year, the nuclear option is probably the only one available.

Given the stakes, it seems you'd probably want diverse redundant methods. That way if one fails, you'd try others.

Yup, developing other options shouldn't be neglected.

 

[Morbius]

Or in simpler words, can you calculate accurately anough the momentum you'll impart by an explosion X feet away on a surface of Y dimensions at Z angle ?.

Aero Stud,

YES - that's essentially how inertial confinement fusion works; both the laser driven
and the pulse power driven - on a small scale.

The same thing happens on a large scale; but I'm not going to talk about that.
But the physics is the same.

http://www.space.com/businesstechnology/technology/nudging_not_nuking_000211.html

http://www.llnl.gov/planetary/

http://www.aero.org/conferences/planetarydefense/documents/Barbee_et_al_NASA_NEO_Workshop_Paper_June_2006.pdf

http://pdf.aiaa.org/preview/CDReadyMPDC04_865/PV2004_1481.pdf

Dr. Gregory Greenman
Physicist

 

[joema]

What I'm saying is that if we haven't measured in any way the effects of the explosion in terms of deflecting objects in space, for example by means of tracking those sattelite's, if any, that were destroyed directly by the impact...

I was simply responding to your statement that nuclear devices have never been detonated in space, which they have. I wasn't saying they were used to deflect or destroy satellites; to my knowledge they haven't been.

However it's not necessary that nuclear explosions in space be tested against actual asteroids before attempting a deflection. Nor is it necessary to know it would work. It would be nice additional information, as more quality data is generally better. However nuclear explosions have been tested thousands of times on earth. The effects on materials are well understood. In some tests a vacuum chamber was positioned adjacent to the device to measure effects against materials in a vacuum.

The ablative impulse from X and neutron radiation vaporizing a thin layer of material can be calculated. The magnitude and type of energy release based on warhead type is known, and the asteroid deflection can be calculated.

Here is a research paper where this was done (1.1MB .pdf): http://www.llnl.gov/planetary/pdfs/Interdiction/04-Solem.pdf

In any asteroid deflection technique (nuclear or non-nuclear), you wouldn't rely on a single attempt. There would be simply too much at stake. You'd have multiple redundant methods. E.g, four gravity tractor missions, anyone of which could achieve necessary deflection, launched sequentially. They'd likely be backed up by several nuclear methods if all of those failed.

If reaction time didn't permit non-nuclear methods, you'd likely have several nuclear deflections used conservatively in a repeating shoot-look-shoot sequence. That way the actual achieved deflection of the first detonation could be measured and used to fine tune the stand off distance of the subsequent ones.