APOD: Rotating Asteroid Bennu from OSIRIS-REx (2018 Nov 13)

Comments and questions about the APOD on the main view screen.
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neufer
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Re: APOD: Rotating Asteroid Bennu from OSIRIS-REx (2018 Nov 13)

Post by neufer » Sat Nov 17, 2018 7:18 pm

Chris Peterson wrote:
Sat Nov 17, 2018 3:29 pm
BDanielMayfield wrote:
Fri Nov 16, 2018 4:53 pm
neufer wrote:
Fri Nov 16, 2018 1:26 pm

Given two asteroids of equal mass and Earth impacting trajectory, one of which is a loose rubble pile and
one is a solid body, which poses the greater threat, and which threat would be easier to ward off?
It depends on the mass. Above a certain point, the composition won't make much difference in terms of impact damage. At smaller sizes (maybe a few hundred meters or less) the lower porosity object may break up higher, with less mass reaching the ground at a hypersonic velocity. An airburst can cause a lot of local damage, but a large impact affects the entire planet.

Which one is easier to deal with while still in space probably depends upon the method used. Using some kind of thrusters seems likely to be best for a solid body. Fragmenting it with a bomb might be best for a rubble pile. Methods like painting one side or parking a big mass in orbit around it should work about the same for either.
The (nuclear) bomb solution is no doubt the simplest option for a rubble pile.

However, an interesting alternative (non-bomb) solution in a case
like Bennu might be to slowly spin it up until it tears itself apart:
.................................................................................
Experimental ion thrusters have now achieved 5N.

A solar powered pair of such thrusters over 4 decades could produce
a total impulse of ~12,600,000,000 Ns (using just ~200 tonnes of propellant).

Connecting such a pair of thrusters by a 550 m equatorial shaft through the center of Bennu
could be used to decrease its rotational period from 4.288 h down to just ~39 minutes.

And Bennu would be torn apart long before its rotational period got down to 39 minutes.
.................................................................................
11 km high carbon fiber towers connected to the 550 m equatorial shaft
would reduce the necessary thrust & fuel by a factor of 40 !

This permits all sorts of interesting possibilities...
... includes having a single (tacking) solar sail do the job.
Art Neuendorffer

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Re: APOD: Rotating Asteroid Bennu from OSIRIS-REx (2018 Nov 13)

Post by skyy_strukk » Wed Nov 21, 2018 2:48 pm

Asteroid Bennu would make a fine conversation piece in any meteorite collection.

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Re: APOD: Rotating Asteroid Bennu from OSIRIS-REx (2018 Nov 13)

Post by MarkBour » Thu Nov 22, 2018 2:06 am

neufer wrote:
Sat Nov 17, 2018 7:18 pm
However, an interesting alternative (non-bomb) solution in a case
like Bennu might be to slowly spin it up until it tears itself apart:
... Bennu would be torn apart long before its rotational period got down to 39 minutes.
(In spite of the appearance in the post id=287393, I think this is neufer, I am quoting here.)

I'd be reluctant to put my life on the line with a solution of this nature. After a couple of years, might we not find the situation that we have a spinning saw blade, doing almost nothing, but rotating in between two relatively unaffected, slightly-separated piles of rubble?
Mark Goldfain

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Ann
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Re: APOD: Rotating Asteroid Bennu from OSIRIS-REx (2018 Nov 13)

Post by Ann » Thu Nov 22, 2018 2:52 am

MarkBour wrote:
Thu Nov 22, 2018 2:06 am
neufer wrote:
Sat Nov 17, 2018 7:18 pm
However, an interesting alternative (non-bomb) solution in a case
like Bennu might be to slowly spin it up until it tears itself apart:
... Bennu would be torn apart long before its rotational period got down to 39 minutes.
(In spite of the appearance in the post id=287393, I think this is neufer, I am quoting here.)

I'd be reluctant to put my life on the line with a solution of this nature. After a couple of years, might we not find the situation that we have a spinning saw blade, doing almost nothing, but rotating in between two relatively unaffected, slightly-separated piles of rubble?
I think the Earth would be worse off if two piles of rubble came careening our way than if a single asteroid came for a visit.

Ann
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neufer
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Re: APOD: Rotating Asteroid Bennu from OSIRIS-REx (2018 Nov 13)

Post by neufer » Thu Nov 22, 2018 3:33 am

Click to play embedded YouTube video.
Ann wrote:
Thu Nov 22, 2018 2:52 am
MarkBour wrote:
Thu Nov 22, 2018 2:06 am
neufer wrote:
Sat Nov 17, 2018 7:18 pm

an interesting alternative (non-bomb) solution in a case like
Bennu might be to slowly spin it up until it tears itself apart.
I'd be reluctant to put my life on the line with a solution of this nature. After a couple of years, might we not find the situation that we have a spinning saw blade, doing almost nothing, but rotating in between two relatively unaffected, slightly-separated piles of rubble?
I think the Earth would be worse off if two piles of rubble came careening our way than if a single asteroid came for a visit.
Art Neuendorffer

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Re: APOD: Rotating Asteroid Bennu from OSIRIS-REx (2018 Nov 13)

Post by MarkBour » Thu Nov 22, 2018 5:26 am

Ann wrote:
Thu Nov 22, 2018 2:52 am
I think the Earth would be worse off if two piles of rubble came careening our way than if a single asteroid came for a visit.
Ann
Hmmm ... I suppose if that all happened and we still had a little time and fuel, we could stop the saw, then move it and try again.
How would you feel if it was broken into 4 equal pieces? 10?

I think Tom Lehrer would vote for it ... more pieces ought to make a prettier fireworks show at the end.
Mark Goldfain

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Re: APOD: Rotating Asteroid Bennu from OSIRIS-REx (2018 Nov 13)

Post by Ann » Thu Nov 22, 2018 5:52 am

MarkBour wrote:
Thu Nov 22, 2018 5:26 am
Ann wrote:
Thu Nov 22, 2018 2:52 am
I think the Earth would be worse off if two piles of rubble came careening our way than if a single asteroid came for a visit.
Ann
Hmmm ... I suppose if that all happened and we still had a little time and fuel, we could stop the saw, then move it and try again.
How would you feel if it was broken into 4 equal pieces? 10?

I think Tom Lehrer would vote for it ... more pieces ought to make a prettier fireworks show at the end.
Well, I just fear that any attempts to split asteroid Bennu might result in a hailstorm to end all hailstorms on the Earth!

Ann
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Re: APOD: Rotating Asteroid Bennu from OSIRIS-REx (2018 Nov 13)

Post by neufer » Thu Nov 22, 2018 12:35 pm

Ann wrote:
Thu Nov 22, 2018 5:52 am
MarkBour wrote:
Thu Nov 22, 2018 5:26 am
Ann wrote:
Thu Nov 22, 2018 2:52 am

I think the Earth would be worse off if two piles of rubble came careening our way than if a single asteroid came for a visit.
Hmmm ... I suppose if that all happened and we still had a little time and fuel, we could stop the saw, then move it and try again.
How would you feel if it was broken into 4 equal pieces? 10?

I think Tom Lehrer would vote for it ... more pieces ought to make a prettier fireworks show at the end.
Well, I just fear that any attempts to split asteroid Bennu might result in a hailstorm to end all hailstorms on the Earth!
A lot of Chelyabinsk superbolide windows broken but, at least, everyone will be prepared this time.
Art Neuendorffer

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Re: APOD: Rotating Asteroid Bennu from OSIRIS-REx (2018 Nov 13)

Post by Chris Peterson » Thu Nov 22, 2018 2:07 pm

Ann wrote:
Thu Nov 22, 2018 5:52 am
MarkBour wrote:
Thu Nov 22, 2018 5:26 am
Ann wrote:
Thu Nov 22, 2018 2:52 am
I think the Earth would be worse off if two piles of rubble came careening our way than if a single asteroid came for a visit.
Ann
Hmmm ... I suppose if that all happened and we still had a little time and fuel, we could stop the saw, then move it and try again.
How would you feel if it was broken into 4 equal pieces? 10?

I think Tom Lehrer would vote for it ... more pieces ought to make a prettier fireworks show at the end.
Well, I just fear that any attempts to split asteroid Bennu might result in a hailstorm to end all hailstorms on the Earth!

Ann
Bennu isn't big enough even as a single impactor to do more than create a big hole in the ground and make a mess of a few hundred square miles. Like a really bad wildfire. Break it up into even a few pieces, and they wouldn't even be large enough to produce craters.

This discussion is more relevant to kilometer scale asteroids.
Chris

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Re: APOD: Rotating Asteroid Bennu from OSIRIS-REx (2018 Nov 13)

Post by neufer » Thu Nov 22, 2018 3:58 pm

Chris Peterson wrote:
Thu Nov 22, 2018 2:07 pm
Ann wrote:
Thu Nov 22, 2018 5:52 am
MarkBour wrote:
Thu Nov 22, 2018 5:26 am

Hmmm ... I suppose if that all happened and we still had a little time and fuel, we could stop the saw, then move it and try again.
How would you feel if it was broken into 4 equal pieces? 10?

I think Tom Lehrer would vote for it ... more pieces ought to make a prettier fireworks show at the end.
Well, I just fear that any attempts to split asteroid Bennu might result in a hailstorm to end all hailstorms on the Earth!
Bennu isn't big enough even as a single impactor to do more than create a big hole in the ground and make a mess of a few hundred square miles. Like a really bad wildfire. Break it up into even a few pieces, and they wouldn't even be large enough to produce craters.

This discussion is more relevant to kilometer scale asteroids.
The ion rocket torque machine on long poles should work just fine on Ryugu, IMO.

162173 Ryugu is a near-Earth object and a potentially hazardous asteroid of the Apollo group.
It measures approximately 1 kilometer in diameter.


Give me the place to stand, and I shall move the earth.
- Said to be Archimedes's assertion in demonstrating the principle of the lever; as quoted by Pappus of Alexandria, Synagoge, Book VIII, c. AD 340
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Up close & personal

Post by neufer » Mon Dec 03, 2018 7:59 pm

Click to play embedded YouTube video.
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