Slashdot Mirror
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."
> (it 'only' weighs 46 million kilograms)
No it doesnâ(TM)t. Kilograms are a unit of mass, not of weight.
Don't worry. Teal'c will take care of Apophis.
Do daemons dream of electric sleep()?
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.
It's basically been confirmed that it's not going to hit the Earth: http://en.wikipedia.org/wiki/99942_Apophis#History_of_impact_estimates, http://en.wikipedia.org/wiki/File:Apophis_pass_zoom.svg, but then this is China we're talking about so they probably don't believe the rest of the world's measurements.
> (it 'only' weighs 46 million kilograms)
No it doesn't. Kilograms are a unit of mass, not of weight.
Yes, this also made me very amused:
Considering it will be falling from a height of several hundred million miles ...
"Apophis pushed through 'keyhole' in space by solar sail. Seven year countdown begins."
I think it's interesting that in most doomsday asteroid scenarios, the US is the one to launch a mission to save the earth. Granted, part of that is because Hollywood wrote those scenarios, but generally the rest of the world doesn't think twice when watching those movies because US is the de facto leader in most things. I think this is a telling inflection point in the history of nations.
I worry that an impact, rather than moving the entire asteroid, could shatter it and make it much more likely that one small (but still potentially dangerous) part would go through the keyhole.
(T>t && O(n)--) == sqrt(666)
So they figured out that generalized multi-body problem, then, I guess? There are so many variables and errors in our best calculations that a mission like that is probably just as likely to doom us as it is to save us. We'd probably end up pushing it right into Los Angeles. (Wait, that could be a good thing...)
You might want to check the numbers again. 2029 + 7 = ?
It appears we have an open definition debate. Let me define it how I see it: When used with a force unit, "weighs" means "has a weight of". When used with a mass unit, it means "has a mass of" despite its etymological link to "weight".
... in gravity assists (which as I pointed out in my submission) could make the mission much cheaper and less risky.
Since they don't have any experience with gravity assists and (no-one) has any real experience with solar sails, I figure they just picked the one that sounded more sexy. If they actually had a long track record of deep space missions (they've only gotten to the moon whereas the U.S. is on its way to PLUTO), they wouldn't go this route. So I think the inflection point is still a ways off.
It's one year early. Our mission to the moon started a 2^32 second timer, counting down to our demise - we were deemed a threat once we began manned space exploration to the moon.
Juno's mass is listed as 3625kg, or almost 8000 pounds, not almost 8 metric tons.
As for the energy obtained from "falling several hundred million miles": that would be exactly the same energy it took to get that far "up" in the first place (not saying that there's no energy to steal from Jupiter, but it's a pretty hair-brained plan, imho, not in the least because such a trajectory would probably take the better part of a decade to complete).
I know Unix fans are a bit on the Zealous side, but diverting an Asteroid to destroy civilisation so as to prevent this coding flaw from coming about is a bit too far.
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.
We can't let mankind's job of destroying itself be outsourced to illegal alien asteroids that can be payed practically nothing.