DART Probe

[ysabetwordsmith]

NASA has finally gotten around to a concrete step toward the Umbrella: launching a satellite to crash into an asteroid with the intent of changing its orbit.  This is a great way to deflect Earth-threatening objects, if applied at long distance.  \o/

Comments

[siliconshaman]

There is no good way to deflect a N.E.O at close range, the laws of physics won't allow it. So yeah, that's a start.

Well ...

[ysabetwordsmith]

Basically, a little nudge far away is plenty, but the closer it gets, the more power is required to move it far enough to miss. But too much force will break it instead of move it. So there's a limit to how close an object can be and have deflection still work. The farther away, the better.

Of course, the farther it is, the harder it is to reach and to calculate exactly how to nudge it.

So there's an optimum range just inside the limit of where we can detect, measure, and reach things.

Re: Well ...

[siliconshaman]

The inverse square law also applies to the amount of energy you have to apply to deflect an object... so as you say, the nearer the deflection point is, the amount of energy increases as the square. At some point the required energy exceeds the objects structural integrity, at which point it's basically cosmic buckshot.

Hm.. why do I get the feeling that band between where we can't deflect it, and where we can't calculate how to deflect it, is a lot more narrow than anyone realises...

Re: Well ...

[ysabetwordsmith]

>> The inverse square law also applies to the amount of energy you have to apply to deflect an object... so as you say, the nearer the deflection point is, the amount of energy increases as the square. At some point the required energy exceeds the objects structural integrity, at which point it's basically cosmic buckshot.<<

That makes sense. And breaking it up like that is only desirable in the sense of changing a planet-wrecking cannonball into a hail of smaller city-wrecking chunks.

>> Hm.. why do I get the feeling that band between where we can't deflect it, and where we can't calculate how to deflect it, is a lot more narrow than anyone realises... <<

That's probably true. I mean, in theory, the band is "from fracture threshold outward" but the effective range is limited by our current technology. We can spot things quite far away, but that's not necessarily the same as "can calculate the force required for deflection, build and launch a ship with it, make contact and complete the blast successfully."

Re: Well ...

[siliconshaman]

Planet wrecking is still planet wrecking... the amount of potential energy that will be liberated upon impact doesn't change whether it's one big chunk or a cloud of gravel... what varies is if it's released all in one place or spread out over half a hemisphere.

Either way, it's a bad day for the whole planet, you just get to die in a massive blast as the shockwave circles the globe.. or die in a planet-wide firestorm as the atmosphere is superheated by all the individual impacts.

Ironically... the former might be more survivable than the latter. If you're far enough away and in a deep enough bunker, the shockwave from a single blast might be dissipated enough to be survivable. The shot-gun scenario leaves you with an planetary atmosphere mostly devoid of oxygen and heated to a couple of hundred degrees celsius or more. It might not directly kill you at first depending upon construction of your bunker and reserves of 02 ... but you won't be leaving anytime soon.

Re: Well ...

[ysabetwordsmith]

Hrm. Some people have said that an object could be broken down small enough to do no damage. This is difficult, but possible. The theory is that the pieces just need to be small enough to burn up in entry, rather than landing like bombs.

Your argument seems to imply that this would simply overheat the atmosphere into a firestorm. If so, that renders one option completely nonviable -- and there are plenty of people who think that "bomb it to gravel" is viable.

Re: Well ...

[siliconshaman]

NASA did the maths. If you bomb it to gravel, you end up setting the sky on fire basically.

A bomb at short range option only works if you can make a substantial proportion of the resulting gravel miss the planet... which is kind of the whole point anyway... or if you use a big enough nuke to vaporise a substantial percentage of the mass, which then dissipates into space due to thermal effects. (hot gas expands, imparting delta V in random directions etc.)

Although...what debris is left on a reentry trajectory is now very radioactive...

Re: Well ...

[ysabetwordsmith]

That is disturbing given how many people seem to consider fragmentation and/or nuclear explosion to be viable options.

It looks like deflection is the only good one, and that has to be done far away. We may not have that much warning. 0_o

Re: Well ...

[siliconshaman]

Thankfully, NASA has already figured all this out, and that why DART was launched. John Q public and the various congress-critters are still catching up, and Hollywood has a lot to answer for, but the people actually defending the planet are on the ball.

Which is one of the reasons why Arecibo II will end up being built... it was the only deep space radio telescope that could also act as a deep space radar, and gave us a much wider window of detection.

Re: Well ...

[ysabetwordsmith]

>> Thankfully, NASA has already figured all this out, and that why DART was launched. John Q public and the various congress-critters are still catching up, and Hollywood has a lot to answer for, but the people actually defending the planet are on the ball.<<

That would be more reassuring if NASA had more money and decision-making power. Politicians tend to be stupid, and they're the ones setting agendas and budgets.

>> Which is one of the reasons why Arecibo II will end up being built... it was the only deep space radio telescope that could also act as a deep space radar, and gave us a much wider window of detection.<<

I hope so. We urgently need that.