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?

[dimreepr]

8 hours ago, Airbrush said:

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?

I imagine the timing would be an issue, given the relative approach speed.

[Airbrush]

6 hours ago, dimreepr said:

I imagine the timing would be an issue, given the relative approach speed.

Yes, and I was wondering if a nuclear explosion at the perfect distance from the object to cause outgassing, nudging it, and not break apart a rubble pile?  Maybe the intense heat from the explosion, at the perfect distance, would fuse the rocks together while also giving them a push.  Then continue with as many explosions as it takes to cause enough of a course correction to miss earth.

[Mordred]

27 minutes ago, Airbrush said:

Yes, and I was wondering if a nuclear explosion at the perfect distance from the object to cause outgassing, nudging it, and not break apart a rubble pile?  Maybe the intense heat from the explosion, at the perfect distance, would fuse the rocks together while also giving them a push.  Then continue with as many explosions as it takes to cause enough of a course correction to miss earth.

Theoretically viable it would depend on distance, asteroid size and composition.

[Airbrush]

On 5/1/2024 at 11:12 AM, Mordred said:

Theoretically viable it would depend on distance, asteroid size and composition.

Suppose we discovered a 10 km wide asteroid that will definitely impact Earth in 100 years, what method of asteroid deflection would humanity use?

[Mordred]

At  that range you wouldn't really need much deflection something as miniscule as a 1 degree defection would likely be sufficient if even that.  Likely some form of craft that has sufficient mass to gravitationally causes a change in angle by using its thrusters to simply stay near the asteroid . One could also feasibly save fuel using solar sails to get there. At the mass of the asteroid tethering wouldn't be practical.

Though the  outgassing method is also viable. Those are the two methods I see as most viable out of the ones I'm aware of.

[Ken Fabian]

On 5/3/2024 at 8:31 AM, Airbrush said:

Suppose we discovered a 10 km wide asteroid that will definitely impact Earth in 100 years, what method of asteroid deflection would humanity use?

All the Earth orbit crossing asteroids in the solar system of that size are known and tracked but if one were lined up for possible collision in one century's time lt seems enough time to dismantle that asteroid and scatter the bits into not-intersecting-with-Earth orbits. Would not be easy - a massive project that probably requires more cooperation than humanity is capable of? And maybe it can be exploded into a cloud of debris too wide and diffuse to be dangerous. If that were to use up the world's stockpiles of nuclear weapons - using them for good whilst getting rid of them for good would be good. Too good I expect.

Something unknown, ie from far out, won't give that much time - a few years of warning (maybe) to do things that will... take a few years to do. If I understand right if the debris isn't scattered wide enough it can be as bad as hitting as one mass. A different kind of won't be easy, with a lot more urgency I suppose.

 

Edited May 6 by Ken Fabian

[DanMP]

On 5/6/2024 at 1:43 PM, Ken Fabian said:

If I understand right if the debris isn't scattered wide enough it can be as bad as hitting as one mass.

I think that we can use rotation/spin in order to deflect the debris/parts away from a collision course. If the axis of rotation of the asteroid is more or less parallel with its path, an explosion should split the asteroid in parts going away from the axis/collision path. If the rotation is too weak, we can increase it, with well placed thrusters, prior to the carefully planned explosion. 

If there is no spin, or the axis is perpendicular to the asteroid path, we may use thrusters to deflect the entire asteroid. We can use as thrusters craters/wells on a side (at a pole, if it spins), where we initiate some chemical reactions or we simply heat them using large arrays of space mirrors (ultrathin reflecting sheets). The arrays of mirrors should be deployed in advance, in all directions, and used as solar power plants, before being converted into solar guns. 

 

Edited May 8 by DanMP

[dimreepr]

5 hours ago, DanMP said:

The arrays of mirrors should be deployed in advance, in all directions, and used as solar power plants, before being converted into solar guns. 

The bullet's are less effective, with the square of the distance... 

[Ken Fabian]

On 5/3/2024 at 9:03 AM, Mordred said:

Likely some form of craft that has sufficient mass to gravitationally causes a change in angle by using its thrusters to simply stay near the asteroid

I can't see how this can work, let alone more effectively than mounting thrusters on the object . The thrust is very low, no more than what it takes to hover the rocket over a very low g object, even leaving aside having a rocket exhaust aimed at the object. Sure, it won't break a loose rubble pile apart but it won't move it much. Thrusters mounted on the asteroid, used to the limit the object can take will do more. But I don't think thrusters will work either.

I don't see how boosting a very large mass a vast distance and into a specific course in a whole different direction and (critically) giving it all that delta-v to get there could be better than boosting the object itself (which doesn't seem viable). Given that mass of rockets + payloads are far exceeded by mass of fuel (or reaction mass) that gets used and discarded along the way you better make the payload something more useful than the gravitational attraction of it's mass.

14 hours ago, DanMP said:

I think that we can use rotation/spin in order to deflect the debris/parts away from a collision course.

That still takes energy, a lot of it to spin a large mass (and a big asteroid is a huge mass) even before achieving enough spin to fling anything. All wasted; any capability to give sideways thrust on the object's surface could be better used to launch material away directly, as deconstructing or as a kind of reaction rocket. Or just used directly to shift the course of the object.

If enough time and distance I expect nukes could blow them into a debris cloud wide enough to be low risk - or we could use less than object shattering detonations for blowing asteroid material out directionally as a means of shifting it's course. Aside from that I am struggling to see what would work.

 

It seems clear that to have any chance there has to be both early warning and the means to do something waiting in readiness.

[Mordred]

Well if you care to research the merits and disadvantages the technique is called gravity tractor.

https://en.m.wikipedia.org/wiki/Gravity_tractor#:~:text=The gravitational force of a,the vehicle nor its expelled

Like every potential solution there is advantages and disadvantages. So really the choice of method depends on several factors. Asteroid mass, composition. Amount of correction needed and time to provie the correction is some of those factors.

Here is a research article on the technique.

https://arxiv.org/pdf/physics/0608157

This method doesn't require the asteroid composition, rotation and surface properties. It really only requires trajectory, and mass terms along with sufficient time and obviously communication with said craft for course corrections etc.

Those are the main advantages  the disadvantage is the communication requirement , sufficient fuel and a slow process that requires a large amount of time so early warning is a priority for the method to have sufficient time.

However the method works with asteroids with rotation which negates numerous other methods. (Or complicates).

Edited May 9 by Mordred

[Mordred]

However I should add one can always use multiple gravity tractors.

As per this NASA article suggestion.

https://ntrs.nasa.gov/api/citations/20120013195/downloads/20120013195.pdf

This article gives good details on craft, fuel consumption, mass difference to distance ratios etc. In a pretty easy to relate to,  format.

 

Edited May 9 by Mordred

[DanMP]

11 hours ago, Ken Fabian said:

That still takes energy, a lot of it to spin a large mass (and a big asteroid is a huge mass)

Larger the mass, longer the time from detection to impact, hence more time for the intervention ... And the spin may be pre-existing, needing just some increase. The risk is that the splitting explosion may not work as expected ...

11 hours ago, Ken Fabian said:

any capability to give sideways thrust on the object's surface could be better used to launch material away directly, as deconstructing or as a kind of reaction rocket. Or just used directly to shift the course of the object.

I also proposed something like that:

On 5/8/2024 at 1:56 PM, DanMP said:

we may use thrusters to deflect the entire asteroid. We can use as thrusters craters/wells on a side (at a pole, if it spins), where we initiate some chemical reactions or we simply heat them using large arrays of space mirrors (ultrathin reflecting sheets)

The chemical reactions I mentioned should be violent/powerful enough in order to eject gases and some materials, providing thrust. Heating may also do the job in some instances. 

 

21 hours ago, dimreepr said:

The bullet's are less effective, with the square of the distance... 

Space solar power plants would be spread around the Earth, some of them far enough, so we may have at least one close enough to the incoming asteroid. Also lasers would be used to convey the energy where is needed ...

 

Another idea would be to deflect small asteroids from the belt in order to smash them into the incoming asteroid and deflect it.

[DanMP]

On 5/9/2024 at 5:01 AM, Mordred said:

... the technique is called gravity tractor.

...

However the method works with asteroids with rotation which negates numerous other methods. (Or complicates).

Yes, if we want to use thrusters directly on the asteroid surface in order to push the asteroid off the collision course, a rotation of the asteroid around an axis parallel to its path would complicate things, because the thrusters would rotate and need to be switched on and off. Therefore, in such cases, the gravity tractor technique may be a better choice.

But gravity is a weak "force". If I electrically charge a piece of paper, the electrostatic force overcomes the whole Earth gravitational pull, lifting the piece of paper off the table. So I wonder: if there is, or we create, a net electrical charge on the asteroid and an opposite charge on the ship/ships, it would increase significantly the pull, making easier the effort to change the asteroid trajectory?

The energy may be provided by the space solar power plants I proposed earlier/above and the charging through ionization and ejection of ions or electrons.

If the electrostatic force is bigger than the gravitational pull, and also bigger than the force provided by the ship's thrusters, we can charge the asteroid and the ship with the same charge (negative, by ejecting ions) and push, instead of pull. It would be better for the ship's thrusters to be oriented directly opposite from the asteroid. 

 

When the asteroid is not very big and can be split, using explosives or nukes, the rotation and the axis orientation is actually helpful, as I wrote earlier/above, because the parts would be driven away from the original, dangerous, path, by the centrifugal forces.