Asteroid defense ideas

[MigL]

On 5/2/2024 at 6:31 PM, 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?

The question does not make sense.
Is the asteroid frozen water/methane, or a pebbly rock, or metallic ?
All would require different methods.

As the question stands, my solution ( also non-sensical ) is to move the Earth out of the way.

[TheVat]

1 hour ago, MigL said:

 

As the question stands, my solution ( also non-sensical ) is to move the Earth out of the way.

That is, essentially, what any method that slightly slows the asteroid does.  Hit it frontally with a kinetic weapon, it slows a tiny bit, thus arriving at the impact point a tiny bit later...and Earth has moved slightly farther along in its orbital path.  You "moved Earth out of the way."  😀

 

[Mordred]

3 hours ago, MigL said:

 

As the question stands, my solution ( also non-sensical ) is to move the Earth out of the way.

Lol now that reminds me of a research plan to move the entire solar system by moving the sun.

[Halc]

On 5/10/2024 at 1:00 PM, TheVat said:

That is, essentially, what any method that slightly slows the asteroid does.  Hit it frontally with a kinetic weapon, it slows a tiny bit, thus arriving at the impact point a tiny bit later...and Earth has moved slightly farther along in its orbital path.  You "moved Earth out of the way."  😀

The velocity (both speed and direction) of an object like an asteroid is very frame dependent. So you seem to envision the frame of the sun say, where the asteroid is on a path not towards Earth, but one that will cross Earth's orbit exactly when Earth gets there. You hit it straight on in a direction opposite its motion in that frame. It slows, and the mostly unaltered paths still cross, but the objects are at that point in a different times.

Now do that from Earth frame (the frame from which the rocket was launched).  In that frame, Earth is stationary and the the asteroid is heading straight for us. If we hit it straight on in that frame, it will slow, but still get here a little bit later.  Point is, a straight bullet shot fired from Earth isn't going to divert it. In that frame, to get it to miss, you need to apply lateral momentum to it. This involves sending the rocket on a curved path, wasting fuel compared to the straight path. And only the fuel expended for the lateral motion will effect the asteroid in a deflecting way. So you need a lot of fuel. One batch to get there (all unusable for deflection) and a whole separate batch to apply laterally to the thing.

All this kind of presumes flat inertial motion of both Earth and asteroid, which is accurate if the thing is pretty close, but the idea is to get it when it isn't so close since it takes less effort to divert something far away. A smaller deflection is needed to effect a miss. So maybe our computers predict this collision on some prior orbit and we can manage to hit the thing slightly on some prior pass. Idea is to not hit it when it crosses Earth orbit since no defection there will prevent it from returning to Earth orbit repeatedly.

[Ken Fabian]

MigL (and not only MigL) makes a good point - the objects will be very different in composition as well as size and make very different challenges.

Likewise for Earth orbit crossing asteroids with knowable orbits, (lots of lead time and potential to rendezvous on it's way outwards between perihelion before aphelion with much lower delta-v than the other way) and incoming comets or asteroids out of deep space that give much less warning. Different too between one expected to hit on it's inbound approach or hit outbound after perihelion and passage around the sun. Potential for solar electric propulsion. Rendezvous with an object from far out on the inward approach before Earth's orbit needs a lot more delta-v to match course further out in the solar system and solar electric propulsion would not help.

If collision is predicted for after passing around the Sun then rendezvous between Earth and Sun and nudging it as it passes closest to the sun may give some potential gravity slingshot gain - if that is possible. But any approach that requires a rendezvous uses a lot of energy moving a spacecraft into matching trajectory, energy that could be delivered DART style more directly.

Still not convinced much is gained by gravity tractors over direct thrust, with a broad pad, mat or mesh to spread the load. Maybe. But I am actually more doubtful that any kind of slow thrust will be preferred, however "mounted", as compared to other approaches. 

If it is not huge and is loose rubble (looser will tend to go with smaller) and there is enough time to use Gravity Tractors then I expect explosive scattering would still do the job quicker and more reliably. Nothing delivers more energy or makes more energetic explosions than thermonuclear detonations - and much more energy can be delivered that way for similar payloads. It isn't just the mass of propellant for GT snigging (Aust/NZ term for dragging logs by chain or cable) but the propellant to get there.

DART style kinetic energy transfer  seems to have a lot going for it. On a first consideration it seems like a kinetic impact would simply transfer momentum directly opposite to the impact but (if I understand it) a high speed impact sheds a lot of energy explosively and that is outward from the object's surface in meteorite style - so a tangential impact should blow material sideways to the direction of the impact and direction of the object. Whether the changes are better tangentially or by reducing (or speeding up) the object by a front-on or rear-on blast isn't clear to me; it could be effectively equivalent. Mention was made of penetrating munitions; loose rubble piles would be especially susceptible. Any kind of solid metallic ones, maybe not so successful.

 

On 5/12/2024 at 11:50 PM, Halc said:

Idea is to not hit it when it crosses Earth orbit since no defection there will prevent it from returning to Earth orbit repeatedly.

Sorry, this makes no sense. Likewise there are no straight trajectories - every time it will be a moving object aiming to meet a moving object where their gravity-curved trajectories cross.

Edited May 14 by Ken Fabian

[Halc]

17 minutes ago, Ken Fabian said:

On 5/12/2024 at 9:50 AM, Halc said:

Idea is to not hit it when it crosses Earth orbit since no defection there will prevent it from returning to Earth orbit repeatedly.

Sorry, this makes no sense. Likewise there are no straight trajectories - every time it will be a moving object aiming to meet a moving object where their gravity-curved trajectories cross.

That comment had nothing to do with straight trajectories. It has to do with preventative action against an object whose orbit crosses the orbit of Earth. Of course orbits are curved. Such an object will intersect Earth given enough time. It is officially dangerous.

Point is, if you deflect the object while the object is at Earth's orbit, it will return to that location regardless of the new trajectory you send it (unless you impart escape velocity from the sun to it).  Orbits are regular visitations to the same locations over and over.  So the idea is to deflect the dangerous object when it is well away from Earth order, deflecting into a new orbit that does not intersect Earth's orbit.

My comment above stated that doing it at the wrong time accomplishes nothing.

[Ken Fabian]

On 5/14/2024 at 3:02 PM, Halc said:

Point is, if you deflect the object while the object is at Earth's orbit, it will return to that location regardless of the new trajectory you send it

No it won't. Deflection at any point in it's orbit will make a new orbit and new trajectory and it will be less likely any Earth crossing orbit object will ever cross Earth's orbit again.

[Airbrush]

On 5/10/2024 at 8:03 AM, MigL said:

The question does not make sense.
Is the asteroid frozen water/methane, or a pebbly rock, or metallic ?
All would require different methods.

As the question stands, my solution ( also non-sensical ) is to move the Earth out of the way.

Can a 10 km wide asteroid be a "rubble pile"?  However, composition shouldn't make any difference.  A series of nuclear explosions in the path of ANY 10 km wide asteroid will do two things:  it would fuse together any loose rocks facing the explosion, and cause outgassing with each explosion.  ENOUGH of these explosions, at the correct distance, can change its' course enough to miss earth.  Why not?  Remember, it won't get here for 100 years.

 

Edited May 18 by Airbrush

[zapatos]

On 5/13/2024 at 11:39 PM, Ken Fabian said:

Still not convinced much is gained by gravity tractors over direct thrust, with a broad pad, mat or mesh to spread the load.

What information would convince you?

[Ken Fabian]

Well if you read on I did add 'maybe'. The first link I looked at was to estimates of what a 1 ton spacecraft could do, without including any estimates of how much fuel or reaction mass or the time and fuel to get it into place; I think those will be significant. A thruster on a broad pad would allow higher thrusts, to the limits of the asteroid's integrity and I suspect it doesn't matter which way the orbit gets altered, that if it is changed in almost any way (except maybe intentionally in particular directions) it won't be a future collision hazard, so thrusters could be placed at one of the poles to allow continuous push.

But, again, I am doubtful rockets pushing it or pulling it would be a preferred approach and the time and rocketry constraints will favor other means.

Maybe even a different approach, like an up-scaled version of this to toss rocks at faster than escape velocity, plus a robot to load them into it -

Edited May 20 by Ken Fabian

[Ken Fabian]

On 5/12/2024 at 11:50 PM, Halc said:

Idea is to not hit it when it crosses Earth orbit since no defection there will prevent it from returning to Earth orbit repeatedly.

I can see why you might think that - a course that 'begins' where it crosses Earth's orbit ought to be an orbit that crosses that orbit again. But orbits aren't really that precisely repeating, with precession etc. Any deflection that reduces or increases it's velocity along its trajectory for example will result in orbits that probably won't ever come close again.

On 5/19/2024 at 3:22 AM, Airbrush said:

A series of nuclear explosions in the path of ANY 10 km wide asteroid will do two things:  it would fuse together any loose rocks facing the explosion, and cause outgassing with each explosion. 

This seems like an experiment that would be worthwhile running. I'd still look at penetrating munitions too, to see if we can blow material out directionally.

[Airbrush]

A gravity tractor requires sending a substantial mass to intercept the path of a small asteroid, but it also has to change direction by 180 degrees so it can fly alongside the asteroid.  That takes a LOT of fuel to slow down, stop, and accelerate to match the speed of the asteroid.  More efficient to directly smack it with something either massive or a series of nuclear explosions.  We already have thousands of nuclear bombs.

Edited May 22 by Airbrush

[zapatos]

32 minutes ago, Airbrush said:

More efficient to directly smack it with something either massive or a series of nuclear explosions.

Citation please?

[Airbrush]

10 minutes ago, zapatos said:

Citation please?

Just reasoning that a gravity tractor takes a lot more engineering and time than a direct attack.

I asked ChatGPT and here is what I got:

"In summary, gravity tractors are effective for deflecting asteroids up to about 300 meters in diameter. Larger asteroids might still be influenced, but the effectiveness diminishes, necessitating longer mission durations and potentially additional deflection methods."

Edited May 22 by Airbrush

[zapatos]

28 minutes ago, Airbrush said:

In summary, gravity tractors are effective for deflecting asteroids up to about 300 meters in diameter.

You realize this contradicts your previous assertion, right?

[Mordred]

30 minutes ago, Airbrush said:

Just reasoning that a gravity tractor takes a lot more engineering and time than a direct attack.

I asked ChatGPT and here is what I got:

"In summary, gravity tractors are effective for deflecting asteroids up to about 300 meters in diameter. Larger asteroids might still be influenced, but the effectiveness diminishes, necessitating longer mission durations and potentially additional deflection methods."

You can also use multiple gravity tractors without risk of nuclear fallout.

[Moontanman]

1 hour ago, Mordred said:

You can also use multiple gravity tractors without risk of nuclear fallout.

How are nuclear explosions in space a risk for fallout? 

[swansont]

27 minutes ago, Moontanman said:

How are nuclear explosions in space a risk for fallout? 

The material from the explosion might eventually enter the atmosphere

[Moontanman]

4 minutes ago, swansont said:

The material from the explosion might eventually enter the atmosphere

ok, wouldn't the explosion have to be quite close to the earth for that to matter? I mean worrying about radiation from a nuke in space would be a bit like worrying the ocean will be polluted by salt by adding a bucket of water from the dead sea to the ocean?  

[Mordred]

Mainly depends on several factors though such as the solar wind poynting vectors, distance and asteroid composition.

The hard truth though is no single method works for every possible scenario. Your best off having a range of possible solutions.

[swansont]

1 hour ago, Moontanman said:

ok, wouldn't the explosion have to be quite close to the earth for that to matter? I mean worrying about radiation from a nuke in space would be a bit like worrying the ocean will be polluted by salt by adding a bucket of water from the dead sea to the ocean?  

Fallout isn’t the radiation from the explosion, it’s contamination - the radioactive material leftover or activated in the explosion i.e. the radioactive fission products and anything that becomes radioactive from absorbing neutrons. These things can be radioactive for years 

[ALine]

What if you create magnetic little beads and the shoot them in the general trajectory of a metal debris fields which also can be electrically charged and uncharged. That way when ever there is a clumping of debris caused by the magnet beads + captured debris you can somehow shoot a beam of energy to control the momentum of the particles to slow them down enough to burn up in the atmosphere.

[swansont]

8 minutes ago, ALine said:

What if you create magnetic little beads and the shoot them in the general trajectory of a metal debris fields which also can be electrically charged and uncharged. That way when ever there is a clumping of debris caused by the magnet beads + captured debris you can somehow shoot a beam of energy to control the momentum of the particles to slow them down enough to burn up in the atmosphere.

Beam of energy?

Slowing particles with photons (the closest thing here) is inefficient; photon momentum is E/c. The force you can exert with photon absorption is P/c (P is power) so 300 Megawatts gets you a whopping 1N of force. Single atoms subject to visible light only change speed by a few mm to a few cm per second (depending on the mass) by scattering a photon.

[Airbrush]

On 5/22/2024 at 12:39 PM, Moontanman said:

How are nuclear explosions in space a risk for fallout? 

Because you need to intercept the asteroid when it is still very far away from earth, so a tiny push will add up to a major course change.  Very far away from earth is a safe place to explode nukes.  Gravity tractors are not effective against very large objects, because you need a lot more time to speed head-on at the asteroid, then decelerate to zero and accelerate to match the speed of the asteroid, which is moving about 10 miles per second.  How much fuel will that take?  After you are done with these fuel-expensive maneuvers, you still need a big mass to be effective.

[dimreepr]

1 hour ago, Airbrush said:

Because you need to intercept the asteroid when it is still very far away from earth, so a tiny push will add up to a major course change.  Very far away from earth is a safe place to explode nukes.  Gravity tractors are not effective against very large objects, because you need a lot more time to speed head-on at the asteroid, then decelerate to zero and accelerate to match the speed of the asteroid, which is moving about 10 miles per second.  How much fuel will that take?  After you are done with these fuel-expensive maneuvers, you still need a big mass to be effective.

ICBM's aren't designed to explode in space, let alone escape from the gravity well.

It's not as simple as nukes are the ultimate destructive power, therefore I'm protected if I unleash them.

It's like saying "rat poison, will save humanity"...