Tilting at Asteroids

JimPooley writes "The European Space Agency are conducting a feasibility study into a future mission to knock an asteroid off course. A Spanish company are planning the 'Don Quixote' mission to launch a pair of spacecraft at an asteroid. One hits the asteroid, while the other monitors it to see what happens."

Comments

Cheaper, easier and

[PhysicsGenius]

more accurate to paint them white and let the sun do the work.

Re:Cheaper, easier and

[Xilman]

More accurate, perhaps, but not as much fun.#

To be serious: I'm not convinced its either cheaper or easier. If the impactor is nothing but a solid lump of metal with some terminal guidance on board that is going to be a lot cheaper and simpler than a robot big enough and smart enough to paint several square kilometers of asteroid surface. Admittedly, the observation probe has to be smarter and so more expensive.

What is not clear to me is why the observer has to hang around for so long and so far away. Why can't it just carry a radio beacon and hard-land on the asteroid after waiting for the impactor's immediate effects to dissipate. Thereafter the asteroid's position and velocity could be determined from earth-based observations with very high accuracy and for decades afterwards. That's pretty much what we're doing with the old Pioneer and Voyager probes.

Paul

Same Thing we do Every Night

[medcalf]

Hidalgo and Sancho? Is anyone else humming "Mouse of La Mancha"?

I see a grey rock and I want it painted white...

[Mad Bad Rabbit]

Xilman writes:

To be serious: I'm not convinced its either cheaper or easier. If the impactor is nothing but a solid lump of metal with some terminal guidance on board that is going to be a lot cheaper and simpler than a robot big enough and smart enough to paint several square kilometers of asteroid surface. Admittedly, the observation probe has to be smarter and so more expensive.

The impactor could be flimsy drums of titanium oxide powder, with some terminal guidance on board and a self-destruct charge. A few hours before the probe hits the asteroid, ground control detonates the probe and turns it into a big cloud of white dust. This keeps going and hits the asteroid, coating the surface with reflective pigment.

>:K

Re:Typical

[Danse]

God can kiss my shiny metal ass if he thinks I'm in favor of just letting some rock smash into the planet and kill everything. Besides, if you believe in God, then it works in your favor either way. If the asteroid hits the earth, then it was God's will. If we destroy the asteroid, then it was just God testing us.

Re:This is worthwhile

[Ethidium]

The danger is there. The indefinite survival of the species requires dealing with it sometime. Yes, climate change, warfare, disease (AIDS, cancer, et al) are all threats to the survival of our species. So is asteroid impact. We don't know how immediate any of them are, so we had better get planning. Just because something doesn't happen often doesn't mean it won't happen soon.

500-Year floods happen about once every 500 years, right? Doesn't mean it didn't happen in 1993. "A few times every hundred million years" could mean tomorrow. Sky surveys are great, but they don't have the whole sky covered, nor will they in the near future. To quote a popular space-opera, "it's a big-ass sky."

Kicking it off course by a few mm takes 1000 years

[geoswan]

...If all goes to plan, the asteroid's orbit will be disturbed in the beginning by a few fractions of a millimetre...

I did some of the math for this, on the back of an envelope, when we were this asteroid story from late July.

That asteroid was thought to have something like one chance in 300,000 of hitting the Earth in 16 years. I chose 10 years as the amount of time it would take to get something out there to divert it. I assumed it was headed straight at the Earth's center. Then I asked myself how much of a nudge we would have to give the asteroid so it would no longer hit the Earth?

If an asteroid were headed right towards the Earth, we would have to give ti a big enough nudge to change its target by d-day by something like 5,000 kilometres. That is 5*10^9 millimetres. So if gave an asteroid that was going to hit Earth a nudge of one millimetre per second at right angles to its current trajectory, wouldn't it take at least 5*10^9 seconds to change a direct hit to a near miss?

There are only 3.1*10^7 seconds in a year.

So a course change of 1 mm per second will protect us if we have something like 150 years lead time. But adding in a safety margin, and considering they only plan to divert the asteroid fractions of a mm, then that sounds like at least 1000 years.

Re:Kicking it off course by a few mm takes 1000 ye

[Mt._Honkey]

This is only a test run. I imagine that if we were to actualy try to save the planet, we would hit it with a MUCH bigger satalite, moving MUCH faster. And paint it white. And maybe hit it with some nukes. Add it all up, and you'll get more than just that

In other news...

[Snafoo]

The European Space Agency has discovered that, when hit with a space ship at a high velocity, the asteroid can slow and be sucked into the gravity well of a nearby planet.

You have three minutes to call your parents one last time. Don't die lonely.

Costs of Asteroid diversion

[geoswan]

Oh yeah, some slashdotters were suggesting that if we were going to go to the trouble of diverting an asteroid, like 2002 NT7, so it didn't hit us, why didn't we go all the way, and divert it enough to capture it in a useful low earth orbit?

The simple answer is that would be a cost a lot more energy. 2002 NT7 would have hit Earth with a velocity of 28 km per second. Earth's escape velocity is 11 km per second. To divert it so it wouldn't hit earth required changing its velocity by something like 28 centimeters per second. Capturing it in LEO would require changing its velocity by close to 28 kilometers per second.

Those velocities differ by a factor of 10^5.

Now maybe my Physics is really rusty, but the formula for kinetic energy is one half mass times the square of the velocity. So, unless my physics is rusty, the energy to capture 2002 NT7 would be 10^10 times greater than just diverting it.

If we really needed a big pile of rock in LEO wouldn't we be better off just quarrying the moon?

Re:Kicking it off course by a few mm takes 1000 ye

[geoswan]

This is only a test run. I imagine that if we were to actualy try to save the planet, we would hit it with a MUCH bigger satalite, moving MUCH faster. And paint it white. And maybe hit it with some nukes. Add it all up, and you'll get more than just that.

Sure, it would make sense to give an Earth striking asteroid every thing we have got. But the goldarn BBC article didn't say which asteroid they were planning to use as a target. 2002 NT7 is 2 kilometres in diameter. There was an earlier asteroid to hit the news a couple of months ago which was something like 200 meters in diameter. Since the volume, and hence the mass would differ by the cube of the difference in radius, diverting the first one would require 1/1000ths as big a nudge as the larger one.

I'd like to know how large the target of this mission is.

Re:Kicking it off course by a few mm takes 1000 ye

[Jerf]

Orbital mechanics are funny. In an ideal system (no light effects, just straight Newtonian gravity and no external effects), if you go up to a satellite in some orbit and give it some sort of instaneous whack with a stick, the effect is to put the satellite into a new orbit. This orbit will intersect with the old orbit in two places, one where you whacked it and one somewhere else.

Point? If you just change the orbit a little, you don't get anything like a multiplication that you do to estimate how different the satellite's location over time will be then it would have been. In fact you get an oscillation, which with a low enough amplitude will still hit the Earth.

You really want to exert some force over time to change the actual course of the asteroid. I think that's how the painting the asteroid idea comes into play; it changes the dynamic of the applied forces on the asteroid and can have a real effect on where it will be in the future.

Maybe...

[flonker]

I had an interesting thought. If an asteroid was to hit the Earth, what would the government do? Tell everyone, and have them all panic? Or launch a secret mission to try to divert it? I'd guess the latter. Anyway, a mission to change the course of an asteroid is extremely hard to hide. So why not just say that it's a "test run"?

Nah, they'd tell you, and loudly

[ynotds]

It's only through spreading panic that governements retain their illusion of relevance. The worst of them manage to panic us sufficiently about drugs, illegal immigrants, sex, terrorists, corruption, hackers, disease and the purported untrustworthiness of our fellow man that enough turn out to vote to maintain some appearance of legitimacy to their exercise of the military, taxation and diplomatic privileges of statehood. What better than an asteroid heading for earth to ensure a star wars candidate gets reelected?

More practically, there is another significant scientific question which might be resolved by giving a nudge to an asteroid. Right now Newton's gravitational constant is only known to an accuracy of 0.15% which is worse than crude compared to other important physical constants. The problem is basically that it's hard to measure precisely between objects on the earth's surface and we only have crude estimates of the weights of planets, etc. However if we were able to impart an accurately measured and large enough impulse to an asteroid which has its own satelite, with precise tracking before and after, it might just enable us to improve that accuracy by some orders of magnitude.

Re:This is worthwhile

[orkysoft]

What I am trying to say is the time and money we devote to a problem should be roughly proportunate to the size of the danger times the probablity of it occuring.

Okay. size_of_danger * probability, you say.

Now, in the case of an asteroid impact which can eliminate many species (all 'big' animals and plants), I'd say size_of_danger approaches infinity. If a big enough rock hits us with enough speed etc., we're all toast. Not just a couple hundred people in some backwater place. All of us. Even if the probability is extremely low, it is not zero. It's happened before, several times.

infinity * really_small_number == infinity

That's why people think it's a priority.

Re:This is worthwhile

[orkysoft]

Why do you think global warming will wipe us all out? I think it'll be bad for global biological diversity, i.e. many species will go extinct, but it won't wipe out most of the life on earth. It'll just make the earth a less interesting place :-/