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Even worse, the best engineering and math grads are being hired by financial institutions, to program computers to game the stock market with millisecond computerized trades.

Any useful results?

I know what a nuclear bomb in the atmosphere does - we've all seen the pictures. It's less obvious how the energy manifests itself if a nuclear bomb is detonated in space.

If it merely makes a thin layer of the asteroid surface very hot - rather than volatilising "meters of surface" - there's not going to be a lot of momentum transferred. Energy is m.v^2, while momentum is only m.v. And if some of the momentum ends up rotating the asteroid - which is what is going to happen if the surface illuminated is not exactly normal to the blast - it's not going to be making a difference to the orbit.

Nowhere near as huge - for the same expenditure of energy - as splitting the asteroid in half and giving each half an equal and opposite velocity increment. Do the math.

Which involves changing the momentum of bits of the asteroid. Momentum is mass times velocity. We probably can't ship enough mass up there to generate enough momentum by ejecting what we've brought up there from the asteroid, though ion drives accelerating a small mass to a very high velocity might be able to do enough over a rather long period. People have run the numbers on that.

This leaves us with the option of dividing up the asteroid and giving each of the fragments momentum in different directions. The fragments as a whole still have the same momentum, but you've used up your energy to give the fragments extra velocity in opposite directions.

Since momentum is proportional to velocity, and energy is proportional to velocity squared, the most efficient way to use the energy we've brought to the asteroid is to split it in half, and give each half an equal - but opposite - velocity change.

The direction matters and the best direction depends on where the asteroid vis-a-vis Earth on its orbit. We'd not want the velocity changes to be at right-angles to the orbital path when the asteroid was precisely on the opposite side of the sun to the earth - the 90 degrees and 270 degree points would be optimal for acceleration at right angles to the orbital path. At the 180 degree point you'd wanted to split the asteroid across the direction of motion and leave the front half going faster (ending up in a higher orbit) and the back half going slower (and ending up in a lower orbit).

It's kind of difficult to work out how to split a lump or rock (or nickel-iron or whatever) from the ground. The speed of light gets to be inconveniently slow over the distances involved.

You haven't thought all that hard about this, have you.

-- Bill Sloman, Nijmegen

Vacuum turns out to be not very interesting. It's not very safe, either.

On the other hand, you are the kind of ass who thinks that using a nuclear bomb to volatilise a thin layer of material on the surface of an asteroid is a more efficient way of using the energy available than sticking the bomb in the middle of the asteroid, and using the same energy to to move a lot more material rather more slowly.

The fact that I'm not doing anything at the moment, and that you are happily occupied, does seem to suggest that our society values presentation skills over the capacity to think about what you are presenting.

And your exaggerated self-belief will let you sell rather more of them than their true merit would justify.

Something having to do with misleading customers. Not intentionally, since we all know that you sincerely believe that your gear is the best thing since sliced bread.

Showmanship might be a more a neutral formulation.

Not that I imagine that even Phineas Taylor Barnum would be able to do much good if stuck in my current situation. Sydney may offer a more receptive audience - I'll get to find out in a couple of weeks.

-- Bill Sloman, Nijmegen

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We probably wouldn't get to hear about the successful results of zero- gravity work. There were some proposals about materials separation processes that might work a whole lot better in the absence of gravity- driven convection. There's a lot of outer space up there, and no prospect of anybody getting a monopoly on that, so secrecy might be a better to protect any advantage that was discovered - if you wanted to orbit a separation factory you would probably tell people that you were just going to use the facility to do asteroid mapping as a preliminary to asteroid mining.

-- Bill Sloman, Nijmegen

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The stratosphere is pretty boring too, and perfectly lethal if you get exposed to it for more than a minute two.

I'm still going to be spending most of a day up there in a bit over a fortnight, and I'll come down again in Australia, having got there rather faster (and more cheaply) than I would have done by sitting on a boat at sea level.

-- Bill Sloman, Nijmegen

Lots of gammas, xrays, fast neutrons. Plenty enough to vaporize meters of surface, from a blast kilometers away.

Meters is easy. Look at the crater even a 20 kiloton bomb makes. A megaton of bomb, depositing a couple of a per cent of its energy into the surface of an asteroid, would ablate a lot of fast-moving stuff.

Energy is m.v^2, while momentum is only

Gosh, really?

And if some of the momentum ends up rotating the asteroid - which

How are you proposing to split it in half? Land, set up drilling rig, drill, implant bomb? Wasn't there some stupid Bruce Willis movie where they did just that? Ablation doesn't require an intersecting, velocity-matched orbit, or a landing, or a drilling rig, just a flyby some kilometers away. We have everything we need to do that already.

Or, better, the whole thing. A year or so in advance, the required velocity change would be small, no need for Hollywood dramatics. The required kick is millimeters per second. Do the math.

Momentum

Why not push the whole thing, a little, in one direction?

You can make it miss in space (not cross Earth's orbit), or miss in time (cross, but when we're not there); either will do. There are people who know how to do orbital calculations. It's not my speciality, and it's not yours.

An automated flyby is well within our current capacity. We do slingshot missions to the moons of Jupiter, with astounding precision. Use radar to time the detonation to within nanoseconds. A megaton of nuke doesn't need to be placed very accurately.

Fathead.

We don't need efficiency. We need to use a megaton bomb to change the velocity of a chunk of rock by some millimeters per second. One would probably want to fire the nuke kilometers away. The math looks fine to me, orders of magnitude to spare.

Society (usually) values productive people over useless ones.

Translation into English?

My customers can return anything that they aren't happy with. It rarely happens. We loaned some people a breadboard laser driver, a hack we did just to test the output circuit. They won't give it back, and insist that we put a price on it and let them buy it. Doncha just hate people like that?

Do you expect them to seek you out and plead for your help?

You probably do.

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Because there isn't any?

If there were, NASA would press release it to every venue on the planet.

How does Obama "invest" in glass? Kimda old tech, no?

Cool! I really liked the first part.

Not familiar with that one (can't look at videos online).

Have you seen 2016?

Splitting it in half just makes two planet killers. Instead of pushing each half out of the way (and hoping both get moved exactly the right amount, why not move the entire thing one direction or the other?

The plot's been used many times. The Willis movie was a pretty bad one.

Exactly. Making two planet killers (or more) doesn't seem to make much sense.

It had to be, since that's all he does.

I rather like most of his stuff. I just watched an early one "Blind Date".

I knew someone must like his bad acting.

Not if neither of them is going to hit the earth. There a loads of potential planet killers out there in earth grazing orbits, and the art is going to be find the ones that are actually going to hit us in the foreseeable future.

why

Conservation of momentum. I'd invite you to think about it if I had a higher opinion of your intellectual powers, but the physics involved - though perfectly elementary - is clearly beyond you.

The physics happens to be correct. That doesn't necessarily guarantee a good movie.

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And the mass of the asteroid is?

Icarus is the first asteroid on the list of the earth-crossing minor planets

It's 1.4km in diameter and weighs 2.9x10^12 kg. Changing it's velocity by 1mm/sec over a year requires 3.2x10^-11 metre/sec^2 of acceleration, or a forces of about 100 Newton.

There are some experimental ion thrusters around that could almost manage that but they draw about 5kW, and haven't yet run continuously, let alone continuously for a year.

One hundred NSTAR thrusters could do the job, and have run for 3.5 years at full power, but each one draws 2.3kW, 230kW for one hundred of them.

It's feasible, just.

It's been done - for an ion engine mounted on a tolerably small asteroid, as I mentioned.

sense.

It would, if you had any quantitative idea of the numbers involved. It takes a lot more energy to generate a given amount of momentum change by accelerating ions to 5km/sec than it does to generate the same amount of momentum change by accelerating 1.45x10^12 kgm to 1mm/sec.

Both halves of the asteroid will miss the earth by the same margin, and you've invested 1.45x10^6 joules to do it. The ion beam has used up 5x10^6 more energy doing the same job.

-- Bill Sloman, Nijmegen

ote:

That was part of cash-for-caulkers. Change to gov't approved windows, and the taxpayers picked up 1/3rd of the tab.

Yes. Clinical, I thought.

-- Cheers, James Arthur

The physics is pretty simple. The math to get into the ballpark is easy. I'd be shocked if you couldn't do it in a few minutes.

Once you have a workable set of numbers, the easy knob to turn is the distance from the asteroid to the nuke. That tunes the energy deposition over orders of magnitude.

Building and powering a drilling rig, way out there, would be nasty. Do you know how labor intensive drilling a deep hole is? How heavy all that drill pipe would be, given a hole big enough for an h-bomb? What will you use for drilling fluid? How would you anchor the rig to the surface, in zero or negative g, with unknown surface shape and composition and texture? What if it turns out to be rubble? What if the whole thing is iron; would you drill through that?

And how can you predict how a complex object of unknown internal composition will break up when nuked from a drill hole?

Since you haven't a clue how much of the asteroid surface would be volatilised, you can't do the math in any convincing way.

How was the energy from a nuclear bomb going to get deep enough into the surface to volatilise metres of the surface?

Pop stars and film stars are highly valued. Do you want to call them productive?

Pull the other leg. Even Jamie could understand that. You may not want to understand it, but that's another problem.

JVC versus BetaMax. Something doesn't have to be all that good to be good enough.

A few years ago I talked to a guy in Sydney who acted as an agent between people who need short term electronic consulting and potential consultants. I was going to be there for a couple of months from when I talked to him, which would have been enough to complete some of the jobs his customers wanted done, but I would have been back in Europe when things might have started to go wrong, and the people who wanted the work done wanted their consultants to be within reach when the gear started being used.

I'll have to find him - or somebody like him - after I arrive (and after all the bureaucratic rubbish has been dealt with) and find out what the situation is like now.

You might even believe that, but you are probably just being unpleasant.

-- Bill Sloman, Nijmegen