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Guru
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NASA Crossbow!

12/16/2011 4:15 AM

Yup Nasa are making a big crossbow to shoot a sampling probe into an asteroid.
It ain't rocket science, but it amused me.
Del

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#1

Re: NASA Crossbow!

12/16/2011 5:27 AM

"The predator" at $700 is purported to be the most powerful crossbow on the market, and capable of 375fps arrow velocity with a 175 lb draw weight, the NASA model has 1000 lb draw weight and 1/2" steel cable but a much larger projectile...awesome

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#2

Re: NASA Crossbow!

12/16/2011 7:04 AM

What kind of wood are they using?

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#3
In reply to #2

Re: NASA Crossbow!

12/16/2011 7:21 AM

I don't think NASA know what wood is.
I did wonder why they aren't using a carbon fibre coposite, but my guess is that steel is more relaiable in the rigours of space, also in the event of failure composites may be liable to spread more debris?
They could save a huge amount of tip mass and thus recoil by removing all the hardware and using a proper modern string material rather than steel cable.
Del

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#17
In reply to #3

Re: NASA Crossbow!

12/17/2011 11:05 AM

NASA is most likely using automotive leaf springs and steel cables due to budgetary constraints. I suspect the steel leaf springs may have been salvaged from a local junk yard. The steel cable is probably came from an elevator somewhere- elevator cables, by law, have to be replaced long before their useful life has been reached. Obviously, a premature failure of a worn steel cable is not going to be a show-stopper at this stage of the game.

Next up- mounting said crossbow to an armored vehicle to replace the cannon (Department of Defense is facing similar budgetary constraints)...

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#4

Re: NASA Crossbow!

12/16/2011 7:44 AM

I just wonder how they are going to correct the opposing forces it will have on the platform which it's fired from. All I can see is the platform spinning in space in the opposite direction. Tethered to the projectile which they intended to retrieve their sample.

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#5
In reply to #4

Re: NASA Crossbow!

12/16/2011 7:47 AM

Indeed, that's why I was surprised they didn't use a lighter weight bow and string. They could easilly get the same power from much less mass and draw weight, they must be wasting a lot of the energy in accelerating the ironmongery rather than getting it all into the projectile.
It's been made by engineers rather than bowyers.
Del

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#13
In reply to #5

Re: NASA Crossbow!

12/17/2011 12:07 AM

It might be that their planning on the added opposing moment of inertia from the recoiling ironmongery (I love that word) mass to help stabilize the launch platform. No offence my furry friend, but this cross bow will not have the luxury of a twelve to thirteen stone marksman holding the crossbow as the 420 grain bolt gets launched.

What I wonder about in this mission is what will happen after the tethered bolt impacts the mysterious comet core? What contingency scenarios have they planned for when comet and probe are not exactly moving in parallel? How do they retract a core sample out of the comet and not a probe into the comet?

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#14
In reply to #13

Re: NASA Crossbow!

12/17/2011 12:18 AM

Silly me.

The crossbow is for terrestrial testing indoors of the harpoon tip. So all of my initial comments are just my foolish fantasy. In space it will be a rocket with no recoil launching the harpoon. At least my questions are still pertinent.

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#15
In reply to #14

Re: NASA Crossbow!

12/17/2011 12:45 AM

Talking to yourself again?

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#7
In reply to #4

Re: NASA Crossbow!

12/16/2011 12:32 PM

Opposing forces. Fire one "up" and fire one down" at the same time.

Arrows are cheap.

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#11
In reply to #4

Re: NASA Crossbow!

12/16/2011 9:06 PM

I wondered the same thing. They're very candid about the recoil in the article, but haven't bothered to explain the consequences of that in space.

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#12
In reply to #11

Re: NASA Crossbow!

12/16/2011 11:02 PM

Possibly as rockets are mentioned in one of the articles I read, the crossbow is just for developing the sampler tip.

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#6

Re: NASA Crossbow!

12/16/2011 11:17 AM

WTF, what is NASA thinking? "Spear" the asteroid with a giant crossbow projectile, it gets stuck/no retract in the chunk of rock/iron or what have you, and the asteroid proceeds to whip around and strike the Earth????? ACKKKK!!!

Thanks Del!

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#8

Re: NASA Crossbow!

12/16/2011 2:32 PM

What they are trying to do is collect samples right. They say it's traveling 150,000 miles per hour spewing chucks of ice, rocks and dust as it goes by. Why not just scoop some of that up isn't that what it's made of.

Would make more sense if they were trying to hitch a ride. Trying to save fuel and the addition pay load it takes to get it up there.

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#18
In reply to #8

Re: NASA Crossbow!

12/17/2011 11:10 AM

Worth noting, I think: scooping up the debris being spewed out means getting material which has already been affected by sunlight to the extent of breaking whatever bonds it had with neighboring particles; penetrating gets "virgin" material from deeper down, not yet heated and thus modified in unknown ways ("unknown way" modification agents will include but not be limited to temperature, cosmic rays, particulates from the sun, and exposure to light itself). When trying to obtain material left over from solar system raw materials, in order to learn as much as possible about what it was like billions of years ago, the less recent change, the better.

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#9

Re: NASA Crossbow!

12/16/2011 3:37 PM

I wonder what the NASA and JPL scientists & engineers are smoking these days?

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#10
In reply to #9

Re: NASA Crossbow!

12/16/2011 3:52 PM

Probably the same stuff they smoked 30 years ago when I worked with them.

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#16

Re: NASA Crossbow!

12/17/2011 9:49 AM

In the video says the crossbow will be used just to measure the needed energy to penetrate for safety reasons but they will shoot the harpoon by explosives.-

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#19

Re: NASA Crossbow!

12/19/2011 4:58 AM

They did say that the crossbow was strictly for testing purposes. A cannon is planned for the actual mission. They considered the cannon too dangerous for testing.

Maybe they'd let Del have the crossbow when they are done doing their test.

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#20

Re: NASA Crossbow!

12/21/2011 3:43 AM

Happy to hear that!

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