NYTimes.com: NASA Launches New Mission: Crash Into Asteroid, Defend Planet Earth

[John Clark]

Some may say it's silly for NASA to spend money to protect people from as remote a danger as an asteroid strike but I don't think so. Impact by an asteroid larger than 10 km would kill nearly every human on the planet but one that big only comes along about once every hundred million years, so if you figure a lifetime of 70 years that means there's about one chance in 1.5 million of one of those behemoths killing you. A much smaller asteroid might only kill 1/1000  as many people but it would be about 1000 times more common, so one of those little guys would have about an equal chance of ending your lifetime early. One chance in 700,000 or so may still seem too low to worry about but it's slightly higher than your chances of being killed by a terrorist, and we've already spent many trillions of dollars trying to reduce that figure, so it doesn't seem terribly extravagant to me if NASA spends a few hundred million dollars to try to reduce the asteroid danger.

John K Clark

==

From The New York Times:

NASA Launches New Mission: Crash Into Asteroid, Defend Planet Earth

The Double Asteroid Redirection Test spacecraft, launched on Wednesday, could be the first to alter an asteroid’s path, a technique that may be used to defend the planet in the future.

https://www.nytimes.com/2021/11/24/science/nasa-dart-mission-asteroid.html?smid=em-share

[spudb...@aol.com]

Russia 2013 had a very close encounter, and in Russia 1910, we suffered from the Tunguska event where a asteroid blew up in the atmosphere over Russian Siberia. 

https://www.space.com/33623-chelyabinsk-meteor-wake-up-call-for-earth.html

20 times the money spent. is well worth the cost. 

Other worries?

Yeah Climate.

Yeah, Super volcanoes.

Finally, Yeah Nuclear. 1st by China, Secondly from Putin piling on.

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[Lawrence Crowell]

I think this is not a practical way of nudging an asteroid. As an experiment on a delta-vee or increment in velocity or momentum it makes sense.

I think a better way to do this is to send a 100 metric ton mass tethered to an ion drive. This large mass is lowered to the asteroid and then a force equal to the mutual gravitation of the mass with the asteroid imparted by the ion drive. Over a time period this asteroid could have a change in momentum.

Let us do some calculations. Suppose we have a 50m diameter asteroid. The volume is V = 4πr^3/3 = 523,000m^3. Let us assume the density of an asteroid is comparable to the Earth on average ρ = 5.0g/cm^3 = 5×10^3kg/m^3 and thus has mass 2.62×10^9kg or 2.62 million tons. The 100 ton (1.0×10^5kg) mass is then tethered just above the surface with a gravitational force

F = -GMm/r^2 = (6.7×10^{-11}N-m^2/kg^2)(2.62×10^9kg)(1.0×10^5kg)/(2.5×10^3m^2)

= 7N

and the acceleration from F = ma or a = F/m is then 7×10^{-5}m/sec^2.

That may not sound like a lot, but the change in velocity is Δv = at, and for this applied over an entire year 3.15×10^7sec this is a change in velocity Δv = 2.2×10^3m/sec. That is over 2km.sec! The displacement of the asteroid by the elementary d = ½at^2 is 3×10^9m, or around 3 million km! Thus, we could tug-boat an asteroid out of harm’s way if we find it soon enough and have enough time to apply a system of this sort.

LC

[spudb...@aol.com]

Sounds similar to Gerard O'Neil's mass driver's save that that this was actual lunar regolith slinging to push asteroids around. Thumbs up for any achievable fix, be they, ion drives, photon sails, laser ablative reaction, etc. 

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[John Clark]

On Fri, Nov 26, 2021 at 8:41 PM spudboy100 via Everything List <everyth...@googlegroups.com> wrote:

> Sounds similar to Gerard O'Neil's mass driver's save that that this was actual lunar regolith slinging to push asteroids around. Thumbs up for any achievable fix, be they, ion drives, photon sails, laser ablative reaction, etc.

But remember a mass driver an ion drive or a laser is useless unless you have some way to power it, and the further from the sun an asteroid is the less effective a photon sail would be. It would take a ridiculous amount of energy to move an asteroid enough to miss the earth if it had a mass of many billions or many trillions of tons unless you can apply that energy long before it was due to impact the earth. That's why we need a much bigger program to detect asteroids and comets that have orbits that intersect earth's orbit, that way we can deal with them early and only need a modest amount of energy to do so.

John K Clark    See what's on my new list at  Extropolis

 

 

-----Original Message-----
From: Lawrence Crowell <goldenfield...@gmail.com>
To: Everything List <everyth...@googlegroups.com>
Sent: Wed, Nov 24, 2021 7:27 pm
Subject: Re: NYTimes.com: NASA Launches New Mission: Crash Into Asteroid, Defend Planet Earth

I think this is not a practical way of nudging an asteroid. As an experiment on a delta-vee or increment in velocity or momentum it makes sense.

I think a better way to do this is to send a 100 metric ton mass tethered to an ion drive. This large mass is lowered to the asteroid and then a force equal to the mutual gravitation of the mass with the asteroid imparted by the ion drive. Over a time period this asteroid could have a change in momentum.

Let us do some calculations. Suppose we have a 50m diameter asteroid. The volume is V = 4πr^3/3 = 523,000m^3. Let us assume the density of an asteroid is comparable to the Earth on average ρ = 5.0g/cm^3 = 5×10^3kg/m^3 and thus has mass 2.62×10^9kg or 2.62 million tons. The 100 ton (1.0×10^5kg) mass is then tethered just above the surface with a gravitational force

F = -GMm/r^2 = (6.7×10^{-11}N-m^2/kg^2)(2.62×10^9kg)(1.0×10^5kg)/(2.5×10^3m^2)

= 7N

and the acceleration from F = ma or a = F/m is then 7×10^{-5}m/sec^2.

That may not sound like a lot, but the change in velocity is Δv = at, and for this applied over an entire year 3.15×10^7sec this is a change in velocity Δv = 2.2×10^3m/sec. That is over 2km.sec! The displacement of the asteroid by the elementary d = ½at^2 is 3×10^9m, or around 3 million km! Thus, we could tug-boat an asteroid out of harm’s way if we find it soon enough and have enough time to apply a system of this sort.

LC

On Wednesday, November 24, 2021 at 6:44:45 AM UTC-6 johnk...@gmail.com wrote:

Some may say it's silly for NASA to spend money to protect people from as remote a danger as an asteroid strike but I don't think so. Impact by an asteroid larger than 10 km would kill nearly every human on the planet but one that big only comes along about once every hundred million years, so if you figure a lifetime of 70 years that means there's about one chance in 1.5 million of one of those behemoths killing you. A much smaller asteroid might only kill 1/1000  as many people but it would be about 1000 times more common, so one of those little guys would have about an equal chance of ending your lifetime early. One chance in 700,000 or so may still seem too low to worry about but it's slightly higher than your chances of being killed by a terrorist, and we've already spent many trillions of dollars trying to reduce that figure, so it doesn't seem terribly extravagant to me if NASA spends a few hundred million dollars to try to reduce the asteroid danger.

John K Clark

==

From The New York Times:

NASA Launches New Mission: Crash Into Asteroid, Defend Planet Earth

The Double Asteroid Redirection Test spacecraft, launched on Wednesday, could be the first to alter an asteroid’s path, a technique that may be used to defend the planet in the future.

https://www.nytimes.com/2021/11/24/science/nasa-dart-mission-asteroid.html?smid=em-share

--.

[Lawrence Crowell]

Of course my idea extends to asteroids in the million ton range. A titan of an asteroid would be much more difficult.

LC