NASA to bomb a comet for July 4th

[Flatlander]

ARTICLE

Los Angeles — Not all dazzling fireworks displays will be on Earth this Independence Day. NASA hopes to shoot off its own celestial sparks in an audacious mission that will blast a stadium-sized hole in a comet half the size of Manhattan. It would give astronomers their first peek at the inside of one of these heavenly bodies.

 

[MA-Caver]

ARTICLE

And NASA will be responsible for altering the course of the comet to send it hurling towards earth on a collision course... way to go guys!

 

[Rich Parsons]

And NASA will be responsible for altering the course of the comet to send it hurling towards earth on a collision course... way to go guys!

Hmmm, This is what I read in the article:

But not to worry. NASA guarantees that its experiment will not significantly change the comet's orbit nor will the smash-up put the comet or any remnants of it on a collision course with Earth.

One wonders if you were serious, sarcastic or being funny, with the lack of emoticons. :idunno:

 

[Tgace]

Perhaps there is a little piece of "target practice" going on here for future collision issues as well???

 

[Shaolinwind]

Oops double post, sorry.

 

[Shaolinwind]

Hmmm, This is what I read in the article:



One wonders if you were serious, sarcastic or being funny, with the lack of emoticons. :idunno:

Sounds like a joke to me, in fact he beat me to it.

 

[arnisador]

I think this is a good chance to get a look inside a comet. Sounds cool!

 

[Rich Parsons]

I think this is a good chance to get a look inside a comet. Sounds cool!

I agree also, it should generate lots of data for review and research.

 

[MA-Caver]

Rich (and anyone else... ) c'mon... you took me seriously with that post?? hee hee

 

[Rich Parsons]

Rich (and anyone else... ) c'mon... you took me seriously with that post?? hee hee

Not me but those who do not know you

 

[Bester]

Which WMD will they be using?
Sadamns, Dubyas, or the complete Hulk Hogan Film Library? That last one's a really big bomb!

 

[Sapper6]

Which WMD will they be using?
Sadamns, Dubyas, or the complete Hulk Hogan Film Library? That last one's a really big bomb!

who knows. regardless of what is used, it won't look like it does in the movies.

This is one of those things that Hollywood will almost always get wrong, because they want them to look like the audience expects them to look, and have absolutely no interest in teaching physics!

There is not too much data available (in public, anyhow) on what explosions in space really look like, so I will have to limit myself to what I think they should look like. (At least I do have an interest in teaching physics.)

Details about the amount of energy and matter involved in the explosion affect the appearance. A universal generality, true in space as on Earth, is that, other things being equal, a larger explosion (inevitably seen from a larger distance by any witnesses who survive to describe it) appears to happen more slowly than a smaller explosion seen from closer at hand. However, bear in mind that the actual energy release event of any actual explosion happens very quickly.

On Earth, the interaction with the surrounding matter, be it air, water, or whatever, means that the initial energy is very quickly, in a few milliseconds, spread out over a fairly large amount of matter, no matter what the nature of the explosive. This material, typically air, forms a luminous fireball that expands at the speed of sound in the air that has been heated by the explosion, which is faster than the speed of sound in ordinary cool air. The result is a shock wave at the surface of the fireball. As the fireball expands it compresses and heats the surrounding air, while losing energy by radiation and also because of the work it is doing on the outside air, all of which causes it to cool. Eventually it cools to the point where it is no longer luminous, the shock wave moves out ahead and makes the BANG! that we hear and that may knock down buildings, and a cloud of swirling debris, smoke, and maybe brownish nitrogen oxides are left behind.

In space, the first few milliseconds proceed as they would in air (say), but then the transfer of energy to the surrounding air never takes place. As a result the initial small, intensely hot fireball simply keeps expanding at very high speed, and the expanding gases and any fragments fly off in straight lines. The fireball cools by radiation at first, but as its density drops it becomes so transparent that radiation is suppressed. For a chemical high explosive, the expansion speed would be a few thousand feet per second. So for a moderate size explosive -- say 1 meter across -- the products will expand to 100 meters in probably less than 0.1 sec, meaning the density will have decreased by a factor of a million, and the visible explosion will effectively be over. Visually the effect would be of a very brief, brilliant flash in a region only a little bigger than the actual extent of the explosive material. Of course there would be no billowing swirling smoke, and any fragments would almost certainly be moving too fast to be visible. The effect would probably be something like that of a big flashbulb.

For a nuclear explosion, the fireball would radiate mainly in the x-ray and ultraviolet, which are not visible to the eye, although the visible part of the radiation would produce a blue-white flash. The expansion speed would be many hundreds or thousands of times faster than for a chemical explosion, so that the time scale would be less than a millisecond. All the material near the source would be vaporized, so there would be no fragments. If the explosion was truly in space, and not in a tenuous atmosphere, then viewed from a survivable distance the effect would probably be similar to, but even less spectacular than, a chemical explosion.

There is one account of a nuclear explosion in the public literature that I know, that of the 1 Megaton "Starfish" explosion in 1962 over Johnston Is. in the South Pacific. Because it was not really in space, but in the upper atmosphere a few hundred km high, it created a ghostly fireball hundreds of km in extent, much less brilliant than in air, but still "a fearsome sight" (according to Bernard J. O'Keefe, "Nuclear Hostages", 1983).

Regarding visual fireworks, I would expect none in vacuum, but as the Starfish example shows, even a small amount of matter could have a spectacular effect. For a nuclear explosion especially, spectacular fluorescence effects could occur due to the excitation of the upper atmosphere by ultraviolet and X rays. Also, the burst of high-energy charged particles from a nuclear explosion near the Earth can be caught in the Earth's magnetic field, and then channeled into the upper atmosphere, producing auroras that may be spectacular over large parts of the globe.

The effect of gravity should depend on the velocity of the ejecta compared to the escape velocity of the body in question. For a nuclear explosion near an airless body like the Moon (in the absence of a strong magnetic field), the material ejected would be moving so much faster than escape velocity that it would simply stream off in straight lines, with essentially no effect. For a chemical explosion, the velocity of the ejecta on the Moon would be comparable to but mostly less than lunar escape velocity, so that the fragments would typically follow elliptical ballistic trajectories that would bring them raining down all over the Moon, hundreds or thousands of km from the original explosion, for many minutes or even hours. If the explosion was well above the surface, some fragments might go into lunar orbit. A few might strike the Earth.

 

[Sapper6]

and it won't be nuclear charged either...

On April 11, 2002, the Washington Post wrote an article suggesting that the Defense Science Board may study using nuclear-tipped interceptors for the U.S. national missile defense system.

The House Armed Services Committee formally endorsed the idea in its report on the Fiscal 2003 Defense Authorization bill:

The committee understands that the Department may investigate other options for ballistic missile defense * nuclear-armed interceptors, blast fragmentation warheads, and directed energy technologies * as alternatives to current approaches based predominantly on hit-to-kill technology. The committee would consider such an examination of alternatives to be a prudent step, consistent with the commitment to evaluate all available technological options for this critical mission.

The one national missile defense ever deployed by the United States -- the Sentinel system completed in 1974 -- used nuclear warheads. Those warheads would probably have exploded over the heads of Canadians citizens or American citizens in North Dakota. That system was abandoned shortly after it was made operational because the system was determined to be ineffective.

There are serious problems with moving forward with nuclear tipped interceptors:

1. Nuclear explosions in outer space could produce significant collateral damage to U.S. and foreign satellites and the Earth's electromagnetic fields. Past nuclear tests in space--prior to the 1963 Limited Test Ban Treaty, which bans nuclear testing in the atmosphere, in outer space, and under water--crippled U.S. civilian and military satellites and knocked out some U.S. communications on Earth. The U.S. and other countries are highly dependent on commercial communications satellites, weather prediction satellites and spy satellites. Nuclear-tipped interceptors could seriously disrupt the global economy, travel and military intelligence.

2. The Defense Department has conducted studies showing that a nuclear detonation in space, whatever the source, would be a shock our entire planet cannot healthily absorb. An April 2001 study by the Defense Threat Reduction Agency entitled "High Altitude Nuclear Detonation against Low Earth Orbit Satellites" concluded that a single low-yield nuclear burst in space could disable every commercial and government satellite in low earth orbit in a matter of weeks. Replacement of damaged satellites at current launch rates would be extraordinarily difficult, expensive, and time-consuming, while higher background radiation levels would continue to degrade any new systems put in orbit for months afterward.

3. Nuclear-tipped kill vehicles could cause of serious risk of Americans being exposed to high levels of dangerous radiation. The missile intercepts are most likely to occur in low earth orbit. At this height, it is possible for radiation produced by a nuclear detonation to fall back to earth. It is partially for this reason that Sen. Ted Stevens heard complaints from his constituents when the idea first surfaced, leading him to vigorously oppose nuclear-tipped interceptors.

4. Exploring nuclear-tipped interceptors is a tacit admission that the current hit-to-kill warhead technology will never work. There is no evidence that the current technology, chosen by the Pentagon many years ago, will ever be able to deal with the decoy and countermeasure problem. Furthermore, there is no evidence that even the currently-planned layered missile defense system will be able to defend the United States consistently and reliably under all conditions.

5. To deploy a nuclear warhead on an interceptor, the Administration would have to undertake nuclear tests. Any testing would violate the Comprehensive Test Ban Treaty and deal yet another blow to the nuclear non-proliferation regime.

Two quotes from Arms Control Association press release, April 17, 2002

"Arming missile defense interceptors with nuclear warheads will almost certainly create more problems than it will solve," said Steve Fetter, a physicist at the University of Maryland who served as special assistant to the assistant secretary of defense for international security policy during the first Clinton administration. One problem Fetter noted is that employing nuclear-armed interceptors would actually impair the U.S. ability to defend against missile attacks. "High-altitude nuclear explosions would blind the radars and infrared sensors that track incoming warheads," he stated.

Wolfgang K. H. Panofsky, a physicist and director emeritus at the Stanford Linear Accelerator Center, observed that nuclear explosions in space would "blackout communications on Earth within line of sight and produce long-lasting lethal effects on

satellites." Prior to entry into force of the 1963 Limited Test Ban Treaty, which prohibits nuclear testing in the atmosphere, in outer space, and under water, U.S. nuclear testing in space disrupted U.S. civilian radio and television signals and crippled some U.S. reconnaissance and communications satellites. Panofsky pointed out that a late 1950s series of small nuclear test explosions in space "generated interference with radio astronomy for a decade."

John Rhinelander, who served as the legal adviser on the U.S. SALT I delegation,

The Pentagon's exploration of nuclear-armed interceptors is also "an implicit admission by the Pentagon that it's concerned about whether current U.S. missile defense programs based on hit-to-kill technology can work effectively, particularly against incoming warheads with decoys and countermeasures.

 

[Rich Parsons]

and it won't be nuclear charged either...

Nuclear would be too destructive and make the data worthless, by changing the contents, the reconstruction would not be exact. Better to just find some extra Trinitrotoluene particles mixed in with the other chemicals.

 

[arnisador]

And NASA will be responsible for altering the course of the comet to send it hurling towards earth on a collision course... way to go guys!

Look at it this way...they're making extraterrestial caves for you to explore!

I expect the data will just be percentages of the stuff that's in the 'dirty ice' theory. But, confirming that a comet has H2O would back up the theory that comets brought much of our water to this planet.

 

[arnisador]

Nuclear would be too destructive and make the data worthless

I would think so. Better to use just straight impact, given the speeds involved, I'd think. The 'kinetic kill' approach as they say.

 

[MA-Caver]

Look at it this way...they're making extraterrestial caves for you to explore!

I expect the data will just be percentages of the stuff that's in the 'dirty ice' theory. But, confirming that a comet has H2O would back up the theory that comets brought much of our water to this planet.

Aye, on another discussion board (for cavers) there was talk about possible caves on Mars and what wonders/mysteries they would hold. Sadly, not in my life-time however, but one day perhaps.