Nuclear detonations in outer space

In article ,
Mike Rhino wrote:
If a decent sized asteroid was on track to hit Earth in 2 months, nukes
wouldn't be powerful enough to make it miss...

Two months is actually a long time. A quick (and fairly naive)
calculation suggests that 1.5m/s of deflection, applied in the right
direction, suffices to turn a dead-center hit into a full miss with that
much advance notice. Of course, that assumes the bomb *arrives* at the
asteroid two months ahead of impact...

MIT's 1967 "Project Icarus" estimated a 71% chance of deflecting Icarus
successfully with four 100MT bombs, the first launched 73 days before
impact and arriving 13 days before impact. (Two more bombs would be
emergency reserve, reaching Icarus less than a day before impact and
attempting to destroy it [or major fragments of it, if previous bombs had
broken it up] rather than deflect it.) With some fairly conservative
assumptions, they estimated an 8m/s deflection from a 100MT bomb.

Mind you, they had the advantage of being able to assume about a year's
advance notice (Icarus's close approach was in June 1968) for developing
their hardware, *and* the ability to commandeer the Saturn V development
effort to provide launchers for large bombs. Neither 100MT bombs nor
launchers capable of carrying them are off-the-shelf items nowadays.

...If we had 5 or 10 years lead time, it would be easier to
change its course, because the deflection needed is less. Ideally, you
wouldn't detonate these nukes near Earth.

With years of lead time, bombs might not be needed at all -- there are
non-nuclear deflection schemes that are feasible if you have plenty of
advance notice. On short notice, though, you just need too much energy
to get it any other way.

Do we have a good way to deliver nukes to an asteroid that is 10 million
kilometers away?

We have the technology -- indeed, noting Project Icarus, we pretty much
had it forty years ago -- but what we don't have is suitable off-the-shelf
hardware embodying it. We'd need big bombs, some sort of long-lived
maneuvering stages to carry them (Project Icarus assumed a variant of the
Apollo SM), and launchers capable of lifting them. The maneuvering stage
we could probably splice together from existing hardware fairly quickly --
although we'd want to test it before relying on it -- but the bomb and the
launcher are bigger problems.

The trend in nuclear weapons in the last 40 years has been to smaller
bombs, as missile accuracies improved, multi-warhead missiles became
available, and the inefficiencies of large nuclear bombs became clearer.
(As weapons, big bombs waste a lot of their energy re-re-re-pulverizing
the already-smashed area near ground zero.) Bombs of more than one or
two megatons have become rare, and hundred-megaton bombs were never stock
items even in the old days(*). So getting a bomb big enough to deflect an
asteroid, on short notice, could be problematic.

(* The Soviet "Tsar Bomba" -- nominally 100MT although never tested at
full yield -- was theoretically an operational weapon briefly, but was
so clumsy that it was never taken seriously even by the Soviets. )

And we have nothing anywhere close to the Saturn V in load-lifting
ability. It had 4-5x the payload to a high-energy trajectory of the
current champion, Delta IV Heavy.

Delta IV Heavy's launch capability is actually a moderately good match to
the sort of bomb that could probably be put together on short notice. My
guess would be that we could throw together a 20-25MT bomb as a variant of
past weapons (the largest the US admits to was the 9MT bomb that armed the
B-52 and Titan II, although one of the more obscure later B-52 payloads
was allegedly a three-stage bomb capable of 25MT), although again we'd
probably want to test it before trusting it. And assuming linear scaling
of mass with yield, a D-IVH could probably put that into the sort of
trajectory Project Icarus specified. Kinda marginal but it might be
enough, given a year's warning.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

In sci.space.policy Michael Turner wrote:

Ian Stirling wrote:
Nuclear detonation should only be used when less drastic methods
fail. Because it will spray bits and pieces in *every*
direction, including the original path.

It's the only real practical way to move very large asteroids.

"Very large"? I doubt you could even measure how much Ceres would be
deflected.

Actually, I have done the numbers for ceres, you can actually get a
decent delta-v, considering that you have 30000 or so nuclear weapons
available to throw it at, each pushing tens of thousands of tons off the
surface at 5Km/s.


Most *very* large asteroids are not on an Earth-crossing path anyway.
You need to talk about NEOs of a size that we should be concerned
about.

Of course, I was meaning 'very large' in terms of damage.


You don't explode it and try to blow up the thing.
You set it off when the asteroid fills a decent fraction of the sky as
seen by the bomb.

This then flash heats the top few centimeters or millimeters, and causes
it to rapidly boil off and blow away in the direction of the bomb,
causing a thrust away from the bomb.

Depending on how long it boils, the net thrust might be perilously
close to zero. Most asteroids rotate. If you're lucky, the needed

It's heated to 3-5000K, explode is probably closer to the fact than
'boil'.

delta V is roughly aligned with the axis of rotation. Or the asteroid
has a lot of volatiles on the surface (probably not, for an NEO.) You
can't count on being lucky.

Rock is quite meltable enough.


And would it be enough anyway? Most of the effects of nuclear
explosions on Earth are caused by shock waves. If there are no
shockwaves (or only bomb detritus waves), you're wasting virtually all
of the energy. The designers of Orion knew this, and assumed a sheet

The shockwaves are there - the shockwaves on earth happen because the
bomb heats the surrounding atmosphere, as it absorbs X-rays.

The shockwaves in htis case would simply be remote from the bomb.

of reaction mass between the explosive and the pusher plate, composed
so as to absorb a lot of the radiation passing through it. We won't

Often sprayed on.

have the choice of composition for whatever's on the surface of an
Earth-crossing asteroid, unless of course we apply the material
ourselves, and that's a whole different ball game.

Certainly.

I read once of an experiment at Eniwetok (?) where they suspended some
hollow metal spheres quite close (maybe a few hundred meters?) from an
H-bomb test. The spheres were left intact (OK, scorched a little).
Being spheres, they distributed the forces from the shock wave quite
evenly. Being metal, they reflected a fair portion of the radiation.

IIRC they were graphite coated metal.

This will cause a net thrust on the asteroid, even if it's a pile of
gravel.
You then wait till it coalesces back together mostly, and repeat until
it misses earth.

Could work, but how many times do you repeat? How many times *can* you
repeat. Since this is proposed for asteroids expected to hit fairly
soon, coalescescence would probably take an unacceptably long time,
considering the low gravities involved. You might get only one shot,
and not enough to make much difference at all.

Last I checked, using nukes to deflect/decompose asteroids had been
shown to have so many problems that they stopped thinking about it
seriously, except at major Hollywood movie studios.


I suspect that a better use of the same lift capacity would be to send
kinetic payloads in a roughly retrograde orbit toward the asteroid,
giving you a lot more relative kinetic energy with respect to the
asteroid's inertial frame. Explosions might play a role in
distributing the payload to cover a lot of the surface, in the instant
before impact, so that you don't have a projectile just plowing through
rubble and out the other side. But the explosions would likely be very
low energy compared to a nuke -- conventional explosive would, if
anything, be preferable.

As I understand it, it's the only way to go for large asteroids, or
small times.
Kinetic payloads are horribly, horribly limited in energy.

For long lead times, more options open up.
All the way up to Orion for launching a few tens of thousands of bombs
at once.

http://en.wikipedia.org/wiki/Project..._propulsion%29

In article .com,
Michael Turner wrote:
This then flash heats the top few centimeters or millimeters, and causes
it to rapidly boil off and blow away in the direction of the bomb,
causing a thrust away from the bomb.

Depending on how long it boils, the net thrust might be perilously
close to zero. Most asteroids rotate...

Not really relevant -- the time scale for this is seconds at most, and
more probably a fraction of a second.

And would it be enough anyway? Most of the effects of nuclear
explosions on Earth are caused by shock waves.

Much of the energy is initially emitted as soft X-rays -- exactly what's
wanted for this particular technique. It's the later interaction with
surrounding matter, notably the atmosphere, that converts most of it to
blast, heat, etc. (The bomb fireball is incandescent air, heated by the
X-ray flash.)

...The designers of Orion knew this, and assumed a sheet
of reaction mass between the explosive and the pusher plate, composed
so as to absorb a lot of the radiation passing through it...

The physics of this is very similar to what's wanted with the asteroid
surface; the greater distance between bomb and reaction mass doesn't
change the situation much. (Said physics unfortunately is quite close
to what happens inside an H-bomb, so most of what's known about it is
highly classified.)

We won't
have the choice of composition for whatever's on the surface of an
Earth-crossing asteroid...

Correct. On the other hand, we also don't care very much about getting
maximum effect for minimum mass, since the mass is supplied by the
asteroid. The energy efficiency probably won't be as good as if we
got to choose the material, but we've got lots of energy available...

This will cause a net thrust on the asteroid, even if it's a pile of
gravel...

Could work, but how many times do you repeat? How many times *can* you
repeat...

Quite possibly only once, for a rubble-pile asteroid (note: only some
asteroids are rubble piles), but once is enough if you do it right and
have adequate lead time.

Last I checked, using nukes to deflect/decompose asteroids had been
shown to have so many problems that they stopped thinking about it
seriously, except at major Hollywood movie studios.

Uh, no, while there has been a lot of attention to non-nuclear methods,
the nuclear approach remains credible -- just politically unpalatable in
some quarters. There are unanswered questions about it, but that's true
of most of the alternatives as well. And it has some chance of working
with quite short warning, which very few of the alternatives do.

It *would* be nice to know a whole lot more about the physical structures
of asteroids before we had to try something like this.

I suspect that a better use of the same lift capacity would be to send
kinetic payloads in a roughly retrograde orbit toward the asteroid,
giving you a lot more relative kinetic energy with respect to the
asteroid's inertial frame...

Nope, sorry, doesn't work. We can't launch *anything* into retrograde
solar orbits -- our launchers are nowhere near being able to do that. The
energy of a sizable nuclear bomb utterly dwarfs anything today's launchers
can impart.

...The same ICBMs used to loft CubeSats
and Bigelow's test modules (retrofitted SS-18s, of which there are a
few dozen remaining I think) can send a small payload to Mars,
according to the current (Russian) launch services vendor. It would be
interesting to calculate what could be done using *all* current ICBMs
for kinetic deflection of an NEO...

Not very much. Most current ICBMs are *much smaller* than the SS-18;
nuclear warheads and their delivery systems have gotten smaller, not
larger, in the last half-century. And deflection with kinetic-energy
systems tends to need a lot more kinetic energy than what current launch
systems can impart, unless you have many years of advance notice.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

Henry Spencer wrote:

Uh, no, while there has been a lot of attention to non-nuclear methods,
the nuclear approach remains credible -- just politically unpalatable in
some quarters. There are unanswered questions about it, but that's true
of most of the alternatives as well. And it has some chance of working
with quite short warning, which very few of the alternatives do.

This Apophis 2029/2036 bombshell was dropped on us a bit suddenly, in
my view. Are there other similar, *known* threats looming in the next
50-100 yr window that nobody is yet ready to admit to - lol...?

How much potential NEO threat tracking by asteroids of known orbits is
currently being performed, I wonder. Is there a resource limitation in
doing long range orbit tracking of *every* single NEO, currently
topping some 20,000+ identified objects in total?

It *would* be nice to know a whole lot more about the physical structures
of asteroids before we had to try something like this.

Asteroid reconnaisance missions surely ought to rank pretty high in
priority, compared to looking at the plumes on Enceladus...
The latter couldn't hit you even if it tried!

AA
http://www.myspace.com/aa_spaceagent

In sci.space.policy message 45aab23d$0$8730$ed2619ec@ptn-nntp-
reader02.plus.net, Sun, 14 Jan 2007 22:44:13, Ian Stirling
posted:

You don't explode it and try to blow up the thing.
You set it off when the asteroid fills a decent fraction of the sky as
seen by the bomb.

This then flash heats the top few centimeters or millimeters, and causes
it to rapidly boil off and blow away in the direction of the bomb,
causing a thrust away from the bomb.

IIRC, from a BIS article, not quite.

From a bomb /in vacuo/, much/most of the energy is in fast particles.
Most of that is dumped a short distance below the surface, causing that
to boil and push the upper material out. That means that although the
same energy departs outwards, it does so slower and hence with more
momentum. Alternatively, think of the top layer as a tamper which
contains the pressure so that it acts on the main body for a longer
time.

The BIS article was, however, over ten years ago now; the journal may
have been JBIS or BIS's more popular monthly. Perhaps someone with
access will search back numbers ...

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Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

Henry Spencer wrote:
(Two more bombs would be emergency reserve, reaching Icarus less
than a day before impact and attempting to destroy it [or major
fragments of it, if previous bombs had broken it up] rather than
deflect it.)

What's the point in breaking up an asteroid that's about to impact?
That would only make the imact worse. Like the difference between
a single thousand-megaton bomb that detonates in one place and a
thousand one-megaton bombs that detonate all over one hemisphere.
Most of the energy of the thousand-megaton bomb will be wasted
killing the dead even deader, while leaving those more than a
hundred miles away unscathed.
--
Keith F. Lynch - http://keithlynch.net/
Please see http://keithlynch.net/email.html before emailing me.

Dear Keith F. Lynch:

"Keith F. Lynch" wrote in message
...
Henry Spencer wrote:
(Two more bombs would be emergency reserve,
reaching Icarus less than a day before impact
and attempting to destroy it [or major fragments
of it, if previous bombs had broken it up] rather
than deflect it.)

What's the point in breaking up an asteroid that's
about to impact? That would only make the imact
worse.

*Might* only make it worse. Might spread the destruction out
over hundreds of years (as we re-encounter the remainders).
Might shatter into bits the atmosphere alone will take care of.
Might at least prevent opening up the core of the planet and
inverting one or more plates.

Like the difference between a single thousand-
megaton bomb that detonates in one place and a
thousand one-megaton bombs that detonate all
over one hemisphere. Most of the energy of the
thousand-megaton bomb will be wasted killing the
dead even deader, while leaving those more than a
hundred miles away unscathed.

Unscathed, except for the earthquakes, ash cloud, nuclear winter,
etc. Isn't a 50-50 chance better than none?

David A. Smith

Henry Spencer wrote:
[Quite a lot of credible-sounding stuff]

Well, coming from you, Henry, I guess I'll just declare most of my
objections unfounded. How refreshing to get into a battle of wits with
an opponent who is actually armed. ;-)

Actually, I'd like it very much if diverting asteroids with nuclear
explosives could be shown to work, and maybe that wouldn't be hard to
demonstrate if you could get a one-time exception to deploying nuclear
weapons in space. It could help make the case that, in some future
where nuclear deterrence is obsolete [deep breath, not held], the best
place to sequester nuclear warheads would be on the Moon, where, with
enough observation capacity, threats could be discerned more quickly,
and, with enough launch infrastructure, rapid response would be
facilitated. After all, who could object to Orion-style propulsion
from the Moon to a threatening asteroid?

I also also like it because any such Earth defense complex would
facilitate asteroid *exploitation*, not mere *deflection*. And
wouldn't it? After all, if the threat is only very sporadic, you might
as well start using some of the defenses for useful purposes, just as
building and maintaining dikes against floods and storm surges
sometimes has the nice side-effect of freeing up more farmland and
residential land.

Call it the Dutch Strategy for public/private optimization of public
good. Too bad that it seems to require an entire Earth as peaceful,
integrated, wealthy and goal-aligned as Holland. But maybe we'll get
there in my lifetime. Or to some acceptable approximation thereof.

-michael turner
www.transcendentalbloviation.blogspot.com

In article ,
Keith F. Lynch wrote:
(Two more bombs would be emergency reserve, reaching Icarus less
than a day before impact and attempting to destroy it [or major
fragments of it, if previous bombs had broken it up] rather than
deflect it.)

What's the point in breaking up an asteroid that's about to impact?

The "if previous bombs had broken it up" referred to *inadvertent*
breakup: the previous bombs were meant to deflect it, not break it up.

Even breaking up an asteroid that's still a day away may make large parts
of it, perhaps even all major pieces, miss Earth.

Breaking up an asteroid that's *about* to impact may, as you note, be a
bad idea, because having it hit one location is better than having it hit
several or many.

However, note that I say "may", because if you can break it up finely
enough that the pieces will explode in the atmosphere before reaching the
surface... that *might* be desirable, depending on where it's going to
hit. It'll still be really hard on whatever's underneath (as witness
Tunguska), and the affected area will be rather larger. On the other
hand, if it's going to hit ocean -- not unlikely, given how much water
there is on Earth -- it might do less damage to populated areas and to the
biosphere if it didn't reach the surface. (An ocean surface hit is much
worse than land, because the water redistributes the energy quite well.)
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

In article .com,
wrote:
...the nuclear approach remains credible... And it has some chance of
working with quite short warning, which very few of the alternatives do.

This Apophis 2029/2036 bombshell was dropped on us a bit suddenly, in
my view. Are there other similar, *known* threats looming in the next
50-100 yr window that nobody is yet ready to admit to - lol...?

Nothing known. The one or two other cases people have worried a bit about
have all turned out to be definitely false alarms when more data became
available. Apophis probably is too, but what happens in 2036 is so
sensitive to the exact path it follows in 2029 that our current knowledge
of its orbit is not good enough to positively say so.

How much potential NEO threat tracking by asteroids of known orbits is
currently being performed, I wonder. Is there a resource limitation in
doing long range orbit tracking of *every* single NEO, currently
topping some 20,000+ identified objects in total?

Yes and no. As I understand it, the main problems are (a) we haven't
found them all yet, and (b) often we don't have enough data to have
particularly good orbits determined for them. Item (a) is actually being
addressed reasonably well, with the exception of some problematic cases
like asteroids whose orbits lie almost entirely inside Earth's (and which
are therefore quite difficult to see). Item (b) would benefit from
greater observing resources for prompt followup observations after
discovery; many of these objects are very difficult to spot unless they're
quite close, so there's a premium on fast action.

Once we've got the orbit nailed down reasonably well, assessing the threat
(if any) and keeping it updated now and then is not a big problem.

It *would* be nice to know a whole lot more about the physical structures
of asteroids before we had to try something like this.

Asteroid reconnaisance missions surely ought to rank pretty high in
priority, compared to looking at the plumes on Enceladus...
The latter couldn't hit you even if it tried!

The solar system's small bodies have long had trouble getting the
attention they deserve, sigh...
--
spsystems.net is temporarily off the air; | Henry Spencer
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