Chinese Researchers Propose Asteroid Deflection Mission

wisebabo writes "Researchers in China have proposed sending a solar sail-driven probe to hit the asteroid Apophis to make sure it has no chance of going through a 'keyhole' near earth in 2029. If it goes through the keyhole, then it will hit the earth seven years later. The reason why they need to use a solar sail is because they want the very small probe (~10kg) to hit the asteroid in the opposite direction, a retrograde orbit which would otherwise require an insane amount of fuel (after being put on an escape trajectory, it would need to first cancel out the earth's orbital momentum and then basically speed up to a likewise high velocity in the opposite direction). They are doing this to hit the asteroid at a very high impact speed. While Apophis may not literally be capable of wiping us out (it 'only' weighs 46 million kilograms), it might be able to wreck our civilization." Read on for the rest of wisebabo's thoughts.

wisebabo continues, "Rather than putting the fate of our species into the hands of an untried technology (no solar sail has yet imparted substantial delta-V to its spacecraft) may I suggest an alternative? By using Jupiter as a gravity assist, we could send a much heavier probe to hit it at comparable speeds. For example, the Juno spacecraft, recently launched to the gas giant weighs almost 8000kgs. Jupiter could sling a spacecraft around so as to completely cancel its orbital momentum (with no fuel expenditure!). Then it will fall directly towards the sun and, if guided correctly, could hit Apophis broadside. Considering it will be falling from a height of several hundred million miles, it would pack quite a wallop. Admittedly, the impact will be on the side rather than head-on, but that should be okay since all we have to do is assure that Apophis doesn't pass through the keyhole, which is only 600m wide. Don't get me wrong, I hope solar sails become widely used for the (slow, cheap) transport of cargoes in the solar system. It's just that I wouldn't base the defense of earth on them."

Comment removed

[account_deleted]

Comment removed based on user account deletion

Pretzels

[Anonymous Coward]

Well I hear lots of organizations and governments have made plans to deflect an asteroid with a missile should one threaten to hit Earth. I think it wouldn't be a bad think to practice a little on asteroids that are passing close but not threatening us. I think we'd want to be ready for when a real danger shows up.

Re:Chinese

[Nidi62]

It's probably because, at least until recently, the US would be the country that would be best able to absorb the brunt of the costs associated with a mission such as this. Also, US-affiliated technology would have to play some sort of role regardless. But really, should a scenario like this actually occur, I would expect that most countries would contribute in some way.

Re:Might make it worse?

[Nyeerrmm]

The problem is that the only way to be 100% sure (or even 10% sure) of an impact risk is to send something out there to track it with proper radio science measurements.

Generally the approach any mission should take is not to prevent an impact, which implies that you will have something approaching good knowledge of whether or not it would pass through a keyhole, but rather to reduce the probability of impact. Because the center of the distribution from your knowledge (largely gaussian) is going to be offset from the keyhole, you need to nudge the asteroid further in that same direction to move it out past a 5-sigma or 6-sigma or 7-sigma ellipse, whatever your desired goal is.

The annoying truth about dealing with anything in deep space is that its all probabilistic. You never really know where anything is, and you always have to quote your certainty values.

Re:Idiotic and Dangerous

[cdrguru]

The biggest problem with an impactor might be fragmentation. If you had a nice solid rock that was certainly going to hit the Earth one of the very, very last things you would want to do is break it into lots of little pieces. Two or three (calving) wouldn't be that bad and might even be better than one big rock, but lots of little pieces would be extremely bad.

Why? Because of a little thing called atmospheric heating. Drop a rock into the Earth's atmosphere and if it is small enough it will burn up (ablative heating) in the atmosphere. The heat released into the atmosphere is negligable. However, if you drop 10,000 little rocks into the atmosphere things could get a bit uncomfortable because the heating would no longer be negligable. Drop a million fragments of a shattered comet or asteroid into the atmosphere and while there won't be an impact crater, ejecta or big tsunami but everything on Earth dies from the heat and potentially fires.

This is why all the cheering at the end of the movie Deep Impact was the cheering of uninformed people and was rather disappointing. By following the script of that movie everything on Earth would have died, probably more horribly than if there had been an impact.

So, let us emphasize this a little bit. Big rocks are bad. Fragmenting big rocks is very, very bad. Potentially fragmenting something is to be avoided at all costs.