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How To Deflect an Asteroid With Today's Technology
Matt_dk writes "Apollo 9 astronaut Rusty Schweickart is among an international group of people championing the need for the human race to prepare for what will certainly happen one day: an asteroid threat to Earth. Schweickart said the technology is available today to send a mission to an asteroid in an attempt to move it, or change its orbit so that an asteroid that threatens to hit Earth will pass by harmlessly. But what would such a mission entail?"
What if we only have the ability to divert it a little bit, if and when that comes? Then we only control WHERE it hits, not WHETHER it hits. So how do we choose, I wonder?
The most beneficial thing we could do is build a system to detect such asteroids as early as possible. Once located, it's easy to deflect an asteroid that's far away. A small nudge or impact from a probe or the like would push it out of an intercept course while it's still far away. The closer it gets, the more force is required to push it off at an angle that will keep it out of our way. It may take a few newtons of force to deflect an astroid coming in from as far away as saturn, but much more to deflect an asteroid that's already close to mars.
I guess in simpler terms, if we had a really awesome early detection system, all we need is a small rocket launched from the ISS to impact it, wheras with a crappy system, we need Bruce Willis.
Oddly, we are doing detection totally wrong. We have several scopes out there looking for asteroids. But they will be picking up monster ones. The ones that are far more likely to hit us will not be picked up as easily. So what is needed? A cheap cheap telescope that can be roof mounted, and uses POE to provide data/power. In doing that, it will encourage a number of geeks around the world to install these. Then the scope relays data back to a central server where pics are compared. In particular, if one gets a flash, not a big deal. OTH, if several spread around the world get a flash in the same area (basically sunlight glancing off an asteroid as it slowly turns), then it says that the area should be looked at. This approach will enable us to know WHERE to look for small to medium asteroids.
I prefer the "u" in honour as it seems to be missing these days.
The "impact" method stands the chance of splitting the asteroid into man little pieces, and since that process of splitting absorbs energy less of it is available to deflect the body from its current course. To have enough mass going at a high enough velocity to contain enough energy to nudge it into a different trajectory you need heavy lift rockets with very fast final stage projectiles. The more velocity the more energy, but the more of that energy that will create debris that potentially causes even more problems. The best solution would be a very heavy object moving slowly, but the would be impossible to lift and deploy. Using nukes would allow a smaller projectile, but would very likely cause radioactive debris to renter earth's atmosphere. Not good. Its better to land on it and push it into the sun's gravity well.
The 'Gravity tractor' method requires just as much energy as pushing the asteroid, but you need LOTS of mass to make it work. Again you need heavy lift equipment to make this work, and I seriously doubt you can lift enough mass into space, and move it to where it needs to be, in time to effect the trajectory by much. You are still better off using that same fuel to get there quickly and push it lightly for a while into a new trajectory.
A vehicle placed at Venus's orbit, though, would be able to see those potentially dangerous asteroids quite well.
Do we have evidence that small asteroids can be detected this way? Does a small asteroid's albedo ever get high enough to be picked up by a small telescope?
one way to change an asteroid's trajectory over a long period of time is to take advantage of the Yarkovsky effect.
We don't only find the monster ones.
We commonly track asteroids under 500 feet wide; much smaller than a planet-killer.
It will be comparatively easy to detect a planet-killer sized asteroid and determine its trajectory in plenty of time to launch a deterrent mission.
A surprise impact by anything with major destructive capability is vanishingly unlikely at this point. Improvements in detection shouldn't be prioritized, but should be allowed to continue at a normal pace.
Deciding how to minimize the destruction should be the focus, and we don't really know how to do it with a high degree of confidence, yet. So deflection technology should be prioritized.
You couldn't do it by station-keeping next to the asteroid. You'd have to maintain thrust directed at the asteroid. First, the thrust couldn't last very long, and second, it would just push the asteroid back away from the ship. You could fire it in a conical pattern, but then you decrease the effective thrust you get from your fuel.
All you really do by putting a lightweight object near an asteroid is create a heavier asteroid. If you have enough reaction mass to manage the sort of station-keeping you imagine, then you might as well put the vehicle on the asteroid and point the thrust outward, and push the asteroid into another trajectory.
I would buy one of these in a heartbeat, and SETI already has the software and server resources to start to handle this. The expensive part though, will be the mechanisms for positioning, and reliably tracking in the night sky. Good tracking isn't cheap, as even the slightest vibrations will obfuscate really small objects. Add to that vibrations inherent on the roof of a home, Doors, washing machines, children playing, loud cars, wind etc. You would need a small solid tower separate from the home, as well as a lightning rod etc.
- Dan.
~ People that think they are better than anyone else for any reason are the cause of all the strife in the world.
So please, stop doomsaying, the experts say they are ready to nuke the sucker if that's what needs to be done.
MIT were saying that back in the 60s, so it's not really news.
But there's the slight problem of being able to _get_ a nuke to the asteroid in the first place; the MIT study used an Apollo CSM on top of a Saturn V with a 100MT nuke on board, and there's not much hope of being able to fix up one of the remaining Saturn Vs to fly at short notice and nuke an incoming asteroid today (they also planned to launch 5-6 of them to allow for failures and near misses).
Nukes provide just a very short impulse; transferring it to the whole rubble pile might turn out to be problematic.
Gravity tractors (and few other methods) can work months, years; and force from them works uniformly (or in the case of some other methods - very gently)
One that hath name thou can not otter
Just because your target mass is large, doesn't mean you need a lot of mass to change its course. If you have a spaceship "heavy enough" to move a 1-ton rock, then it's also "heavy enough" to move a 100-ton rock because an object's deflection in a gravitational field is independent of that object's own mass.
This is an extension of an experiment you've probably seen in high school physics. Drop a tennis ball and a bowling ball, and they move just the same under gravity's influence.
But that's not to say that moving a larger mass is "free"; it does require more energy. As your tractor exerts 100x more force on the larger asteroid, it will also suffer 100x more force pulling it back toward the asteroid. Since your tractor isn't your impactor, it will have to spend energy fighting that force.
Now I have no idea what sort of propulsion you would use to maintain the tractor's position relative to the asteroid. If you used a chemical rocket then "more energy" requires "more mass", but that would seem to have a problem anyway in that you'd be throwing your exhaust right at the asteroid, pushing against your own gravitational pull.
In any case, remember that the Earth is a relatively small target, and the courses would have to intersect in 4 dimensions (don't foret time) to cause a collision. Given years of lead time, the "push" required wouldn't be as much as you may think.
Who's going to be responsible for damages in court if they screw up and direct it more towards earth though?