I'm going to have to agree with subman that NASA is a waste. Recent ventures by private firms into spacecraft manufacture prove that NASA is incompetent and inefficient. Yes, we have gotten some great things from them in terms of scientific discoveries but I firmly believe a private organization could have gotten them cheaper and faster.

To this day I do not understand why NASA insists on using rockets to propel spacecraft into orbit. Why not simply fly into the upper atmosphere with conventional jet propulsion and THEN use rockets to escape earth's gravity?

As far as the nuking an asteroid thing goes, the prospects of success would be quite dubious. Firstly, the asteroid would have to be identified in time to develop and produce a suitable detonation mechanism. This is compounded by the fact that the intercept would have to take place tens if not hundreds of thousands of miles away to prevent Earth's gravity from sucking it back onto a collision course. A course change of only a very few degrees or even fractions of a degree would be possible. I'm no physicist but when you consider an object weighing hundreds of millions or even billions of tons is hurtling forward at tens or hundreds of thousands of miles per hour, that is quite a bit of inertia to overcome. The idea that even a 500-megaton explosive force could significantly alter its' course in all but the most favourable of circumstances is hard to believe.
As if that weren't enough the energy potential of a nuclear blast is reduced to its' minimum possible area of effect in space as there is no significant medium to transmit force through. Yes, the blast wave itself will be unimpeded, but consider the analogy of sound in air versus water. It travels much farther and even faster in water due to displacement of a significant medium.
It is possible that a string of nuclear detonations in succession could alter the course of an asteroid significantly, provided it has relatively little mass, but we still face the problem of detection and timely interception by appropriate weapons.

Our best defense, for the time being, against world-killing chunks of space rock is the impossibly slim chance they have of hitting Earth before cheap and effective countermeasures can be readily produced.

That's an uneducated jarhead's perspective.:D

edit_ I am pleased to see that in the time it took me to write this subman has posted a.........thing..... that I don't understand but which probably supports my hypotheses.

Hahahaha! Actually it doesn't support it... Its pure data.

The best method right now is a simply solar mirror. Park a spacecraft off to the side of the rock and on the same course and simply channel sunlight into a specific area of the rock. Done long enough, the heat will simply push the rock off its present course and onto a new one. Its a simple and effective concept.

NASA though needs some serious restructuring.

-S

Doesn't support or detract from it one way or the other from what i can tell...

Let me put it into laymens terms then. This is a military board, so we will use a 'bullet' as the analogy.

Go to the range, and you shoot up a solid metal block 1x1' (This represents the asteroid made of pure iron) sitting on a wooden stick (which represents its energy/mass/speed). The full energy of the bullet is transfered into that block and it will probably break the stick it is sitting on since no penetration occured. Course for our asteroid is now changed.

Move on the the range with the paper target (which represents the dirt clod style asteroid - which apparently is a very common form unlike what was previously though). The paper even sits straight up and down by its own weight in this case. Here the bullet has so much kenetic energy, it simply passes through the paper hardly doing anything to the paper at all. This same thing will happen with a nuke on the dirt clod - you won't change its course, but you will punch holes in it and break it up. Now it is many times more deadly as it hits the Earth. The point being, the energy did not pass into the paper to change its course, just like the nuke energy does not pass into the dirt clod asteroid to change its course.

Does that make sense?

-S

That's kind of the problem. We already know about all sorts of asteroids that come near Earth. And we know that pretty much all of them wont hit us any time soon. It's the ones that we don't know about that would kill us.

To successfully "move" an asteroid out of the way, you would need many tens of years of warning; and in many tens of years, that rock has moved many tens of orbits (or in the case of a comet, probably only none since its discovery). You would need the time for mission preparation, technology design (as I'll exlpain later, nukes simply aren't powerful enough), resource pooling, develop an "international plan" between the countries of the world, compile everything together, launch the rocket, wait the many years for it to acutally reach the target, and hope to high hell that it does something.


Only if the asteroid/comet is sufficiently far enough away (very far). And if it's of any decent size (more than a few kilometers across), you can forget about any hope of moving it in time.



Nope, nothing would happen (except a nice light show) unless the rock was inside the nuke's fireball at the time of detonation. Outside of the fireball, only radiation pressure is emitted. There would be no overpressure wave ("shock wave," which would only happen if the detonation happened in a medium [substance]. Space is a vaccum, and there is nothing to carry all that force beyond the fireball).


As I've explained to August, an "air-burst" (misnomer in space) over an asteroid would have almost no effect outside of the fireball. Those tests were conduced in the atmosphere, where the blast created an overpressure wave in the air.


True, however, nukes simply aren't powerful enough. Besides the fact that we don't have any over the size of 10-20 Megatons (the biggest ever being the Russian Tsar Bomba, a 50Mt weapon), even a surface blast would not impart much energy into the asteroid (say, 3km across, a nice lower-than-average size for an asteroid). At most, it would create quite a nice crater. The asteroid would have a substantial amount of mass removed, but it would not destroy the rock.

Also, if a surface blast is conducted, the majority of the energy would be released into space as thermal energy. The overpressure wave in the rock itself would also not do much, except mabye a little physical deformation on the opposite side of the rock.


The only effective way to "move" the asteroid out of the way soon enough is with an engine (literally strapping a rocket engine to the asteroid). However, we do not have anywhere near the means to get such an engine in space, let alone to an asteroid. The sheer mass needed for it would dwarf anything currently built.


It's a sad proposition, but people must understand that should an asteroid be discovered on a terminal orbit with Earth, there is not much hope, if any.

You aren't looking to destroy the rock. Just to barely move it. The nuke could accomplish this. Even a minor one if enough advanced warning is given. However, this would only work on an extremely dense rock. That is what I've been getting at.

In the end, a long warning time and a solar mirror can do the job.

-S

http://en.wikipedia.org/wiki/Without...281994_film%29

?

Cool software everyone should have!

Blast Software!

No abandonware

-S

:D What I've been trying to get at is that it can't simply be moved by a nuke. No nuke in existance has enough power to push it (3km rock) out of the way. The energy needed to move it even say, 15m/s, is extraordinarally high. And, for example, a 15Mt nuke detonated on the surface would not impart 15Mt worth of energy to the rock. Most of it gets lost as thermal energy in the vaccum of space.

Also, if anything, you'd want the rock to be less dense (which would imply less mass). The lower the mass of the object you are trying to push, the easier it will be. To be honest, though, I doubt a realistic nuke (surface blast) could even shatter an averaged sized comet, which is made of ice and dust.

A very, very, very, very long warning time.

Nice find. Installing now...:up:

You're missing the point. The change in direction can only be so tiny, its nearly immeasurable. All that takes is some energy / force however small acting in an opposite direction. E=MC2. You aren't ever going to change its direction, you are only looking to slightly alter its current and future course by a tiny tiny fraction. In the emptyness of space, this becomes huge over time.

You are only making it miss its target. Much like the wind can make a bullet miss its target given enough range in the shot. This is what the nuke, and even the solar mirror represents. In no way are you ever going to seriously alter the course of a massive rock. Even simply changing it a tiny fraction to one side, or slowing it down or speeding it up by a tiny fraction will do the job.

-S

Let's be realistic here. This "tiny, immeasureable bit" of force would have to be imparted well in advance (well over 100 years away). The only problem is that our capeability for detecting relatively small objects is very small (we can only see those objects out to about 2AU, or 2 Earth-Sun distances). In the case of an asteroid, that may leave a few years. In the case of a super elliptical comet, that may leave as little as a half a year.

Say we were to discover an asteroid in the Main Asteroid Belt that would threaten earth in many years. Time would still be needed to further refine the observed orbital elements (orbital period, high point, low point, ect.). Why? Because our predictions and observations are not perfect. There are countless factors, some unpredictable, that affect the orbit of any body in the solar system.

That's the whole problem behind moving the asteroid/comet. Chances are, we are not going to have a long enough warning of an impending impact to be able to make a difference.

Take the supposed Mars-impacting asteroid from last winter. Astronomers had to wait until the rock was very close (within a month before 'impact') before making their final prediction on where the rock would pass (or hit) Mars. Even then they were not sure exactly where it would end up.

The models don't show it like that. 100 years? Where did you get that? Try a year is good enough even for the solar device. In space, nothing is reacting with your rock except gravity. You as a man could eventually get a giant space rock to move with your bare hands given enough time and no counteracting force.

-S

You said to move it only a "tiny, inmeasureable bit." And you would need to do that many years (ok, mabye 100 is a bit much) in advance to have a significant, safe change in its orbit by the time it comes near Earth. That's what I meant. Radiation pressure dosen't impart much energy on an object.

And you still have to add the fact that these "solar mirrors" that are capeable of focusing that kind of energy aren't even developed yet.

True, but only given that you are standing on something (to get it to move away from you), otherwise you both move. And then, it would be a lot of pushing... :)

What are you talking about? The solar mirrors have been developed. It is called thin foil....

With a small amount of weight you can make an area the size of a football field.