Asteroid defense ideas

[Airbrush]

Does anyone have an idea of the most efficient and expedient way to deflect, redirect, or slow an impending asteroid impact?

Obviously, if it is a solid block of metal or rock, just hitting it with a large mass going at a fast enough speed, may change its' velocity enough.

Here's my idea I haven't heard about yet.  Since asteroids can be a solid block of metal, or rock, or a fragile rubble pile or fluff, or anything in between, catch it with a giant net.  Launch a rocket towards the asteroid, and at the correct moment the rocket turns around and decelerates to zero, then accelerates the opposite direction to match the velocity of the asteroid.  Then the rocket launches 4 separate rockets, each pulling the corner of a giant, square, cable net.  The rockets decelerate the asteroid enough, so it won't hit earth.

Edited April 17 by Airbrush

[TheVat]

Seems like doing it the hard way, and deceleration takes a lot more newtons than deflection.   I would favor a high energy laser that strikes one side to form a jet of vaporized material.  Depending on the mass of the rock and its distance, a few hundred newtons of thrust could steer it off its collision course.  

[MigL]

Not very realistic Airbrush.
A ten kilometer asteroid  would require a rocket two orders of magnitude larger ( at least ) to perform that sort of stunt.

As TheVat explained, the farther away you can influence the asteroid's trajectory, the less force is needed to produce sufficient deflection.
I'd go with small and high speed, coupled with adequate detection time ( pre-impact ).

[Halc]

21 hours ago, Airbrush said:

Launch a rocket towards the asteroid, and at the correct moment the rocket turns around and decelerates to zero, then accelerates the opposite direction to match the velocity of the asteroid.  Then the rocket launches 4 separate rockets, each pulling the corner of a giant, square, cable net.  The rockets decelerate the asteroid enough, so it won't hit earth.

Decelerating the rocket just wastes all the momentum it already had. If you have delta-V left over, accelerate more, not decelerate. This gives maximum momentum transfer to the thing, which is what is needed to deflect it. Of course, it's best to hit it more or less from the side, which is inefficent for something coming more or less straight at you.

 

9 hours ago, MigL said:

the farther away you can influence the asteroid's trajectory, the less force is needed to produce sufficient deflection

Indeed, but also the harder it is to tell if the effort is needed at all, or if the effort will actually make the trajectory worse, due to miscalculation.

Look at all the news about some asteroid that's going to hit Earth, and then it misses it by a mere million km. You can't send a defection mission out to every big rock that might get that close, but by the time we know it will hit, it's too close that a small defection is enough.

 

It's also harder to get something out to an incoming object quickly if its further away. Takes more delta-V to get out there, leaving less to actually impart momentum to the thing.

I don't think nukes are very effective in a vacuum. It will leave a nasty stain and small crater and will defect almost not at all, unless you can get the thing to embed itself a ways in without destroying the mechanism in the process. There is armor-piercing technology that helps with that sort of thing. Look at the bunker-buster bombs they have, designed to penetrate a long way and still explode, sometimes even hours later. But those bombs are heavy and not too fast, hitting at far slower speeds than what would likely occur in a rocket/asteroid interception.

[Mordred]

My favorite method requires early detection take your spacecraft and instead of trying to trap it in a net. Which as mentioned isn't practical. Simply maintain distance from the asteroid and let gravity do its thing. Use the spacecraft plus the gravitational interaction between the two divert the asteroid to a new vector path. The further away you can do this the less change in vector angle that would be required for a miss.

[dimreepr]

I put my faith in 'The Avengers', sorry couldn't resist; essentially it's all about the ETA, so our best defence is keeping our eye's peeled...

23 hours ago, TheVat said:

Seems like doing it the hard way, and deceleration takes a lot more newtons than deflection.   I would favor a high energy laser that strikes one side to form a jet of vaporized material.  Depending on the mass of the rock and its distance, a few hundred newtons of thrust could steer it off its collision course.  

I have to wonder if that would be effective, by the time a focused enough beam to make a difference, had any effect, it seems to me that it would probably be too late to make a real difference.

[Mordred]

7 hours ago, dimreepr said:

I put my faith in 'The Avengers', sorry couldn't resist; essentially it's all about the ETA, so our best defence is keeping our eye's peeled...

I have to wonder if that would be effective, by the time a focused enough beam to make a difference, had any effect, it seems to me that it would probably be too late to make a real difference.

Depends on the asteroid composition. The usefulness of a laser is to generate outgassing. For example an icy asteroid if you shoot a laser at it would more readily generate water vapors which would then provide thrust.

[dimreepr]

12 hours ago, Mordred said:

Depends on the asteroid composition. The usefulness of a laser is to generate outgassing. For example an icy asteroid if you shoot a laser at it would more readily generate water vapors which would then provide thrust.

I'm not questioning the theory, I'm questioning our ability to deliver; I'm minded of 'the big bang theory', the episode where they try to bolw up the moon with a laser, they needed a photon multiplier to see if they hit the target.

Jokes aside, can we confine the beam well enough to a/ hit the correct part of the target and b/ deliver enough energy to initiate the jet, at a great enough distance to effect the necessary change in trajectory; we can put plenty of energy into the beam from earth, but I imagine there would be difficulties in confining the beam through our atmosphere, and a space based laser, I would imagine they'd have difficulty with generating enough initial energy.

[Mordred]

I doubt using a laser from Earth regardless of how powerful would be of much use. Ideally you would want to use the laser on a side perdendicular to its trajectory. If you fire from Earth you would thr asteroid head on and outgassing wouldn't be as useful.

[Airbrush]

On 4/17/2024 at 7:32 AM, TheVat said:

Seems like doing it the hard way, and deceleration takes a lot more newtons than deflection.   I would favor a high energy laser that strikes one side to form a jet of vaporized material.  Depending on the mass of the rock and its distance, a few hundred newtons of thrust could steer it off its collision course.  

What if it is a rubble pile?  The "cable net" idea will work with any kind of smaller asteroids, but don't do the deceleration as someone suggested.  Just open the net wide and crash into the rubble pile or rock with whatever mass is available.

On 4/17/2024 at 8:14 AM, MigL said:

Not very realistic Airbrush.
A ten kilometer asteroid  would require a rocket two orders of magnitude larger ( at least ) to perform that sort of stunt.

As TheVat explained, the farther away you can influence the asteroid's trajectory, the less force is needed to produce sufficient deflection.
I'd go with small and high speed, coupled with adequate detection time ( pre-impact ).

Of course, the "cable net" idea works only for smaller asteroids.  For one 10km wide you better discover it many years before impact.  How do you deflect a 10km asteroid?

[Ken Fabian]

Anything really big is going to present serious problems - but on the other hand they are easiest to detect. Mostly the biggest ones have been identified - and cleared of suspicion.

Getting precise course prediction from as far out as possible will be important - identifying one aimed in the vicinity of Earth will include near misses too until it gets closer and you better not change it's course only to discover later that you've aimed it more closely rather than deflecting it away.

I don't know to what extent changing albedo can be useful - spreading black soot over part of a comet could trigger more outgassing, or white coating to reduce it. For the stony and metallic objects, no. Any "light sail" effect is probably going to be extremely small.

I think any gravity effect from a spacecraft will be extremely small too; if we can move enough mass to the vicinity to change it's course it seems to me we will be better usign that capability directly to move the mass of the object.

Not convinced the net idea is any help - keeping impulses, however made, below the threshold for breaking loose "rubble pile" types apart seems better. Unless they are small enough that breaking them apart is a viable option - larger ones being less likely to be rubble piles in the first place.

[Airbrush]

Will a series of nuclear explosions in the path of a giant asteroid be enough to cause outgassing that will push it slightly, and without breaking apart a rubble pile?