Science fiction and ballistics


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Chuck Dye
May 6, 2007, 12:54 AM
A novel currently serialized in ANALOG magazine posits a character wounded by a bullet fired from a range of over a thousand miles in the micro gravity environment of a space going balloon several thousand miles in diameter. The gun is described as breech loading, bullet plus loose powder (yah, improbable.) Assuming any bullet mass, B.C., and muzzle velocity from our own modern ammunition inventory, and the earth standard atmospheric conditions (roughly 59F, 14.504psi, 78% humidity, 0.075lb/ft density) used by ballistics programs but eliminating gravity, at what range would the bullet become just one more piece of debris drifting like plankton? Propose your own atmospheric conditions if you wish.

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Mercury Ballistic
May 6, 2007, 01:46 AM
How will the powder burn with no oxygen?

hso
May 6, 2007, 02:04 AM
The powder has it's own oxygen. How else do you think it burns in a sealed airtight case?

Zak Smith
May 6, 2007, 02:20 AM
According to the JBM calculator, after 6000 yards, a 0.40 BC launched at 2700fps will be going 456 fps. It doesn't accept initial velocities lower than 500fps, so I couldn't repeat it another iteration.

In the first 2000 yards, it lost 71%.
In the second 2000 yards, it lost 35%
In the third 2000 yards, it lost 10%.

-z

Mercury Ballistic
May 6, 2007, 02:21 AM
Oh, learn something new everyday.

Jim Watson
May 6, 2007, 10:21 AM
Good catch, Huck.
There are a lot of things about that system that are sufficiently unconvincing to interfere with the plot.

Chuck Dye
May 6, 2007, 01:37 PM
Ah, but it made me think, Jim, even if only about an unwillingness to suspend that much disbelief.

Mal H
May 6, 2007, 01:52 PM
... a character wounded ...Did they describe the wound? Was it a bump in the eye? Intuitively, that would be about the only painful 'wound" possible after a conventional bullet of any variety traveled 1000 miles in an atmosphere resembling the earth's atmosphere. The bullet may not have come to a complete stop and it might still be travelling in a straight line (highly unlikely), but I'll wager it isn't doing 3 inches per second after that trip.

Oh, and I'm not doing the math required, again it is an intuitive swag.

Jim Watson
May 6, 2007, 02:35 PM
Shallow penetrating wound in the jaw to leave a scar and nerve damage to cause migraines. Riiight.

HiroProX
May 6, 2007, 02:39 PM
There's plenty of physics "uh oh"s in sci-fi. For example, the grav guns from John Ringo's Posleen War books. Nice idea, but unless the projectiles have nearly zero mass the recoil of firing a relativistic velocity heavy metal dart would rip someone's shoulder off.

Chuck Dye
May 6, 2007, 02:41 PM
Described as a penetrating wound to the jaw resulting in permanent, intermittent, debilitating pain.

As Mr. Watson observed, much of the hard science in the tale is unsatisfying.

When I ran multiple iterations of my ballistic program, the PMC .50BMG round slowed to about 415fps, then began accelerating due to gravity. I suspect a program failure as a Myth Busters test found terminal velocities in the 150-200fps range, if memory serves (which is rare these days :))

Mal H
May 6, 2007, 03:51 PM
Most ballistic programs can't even handle 1000 miles (1,760,000 yards). 10 to 1 your program performed some invalid iterations to arrive at the 415 fps.

A similar thing happened in the early days of the technology surrounding the cold war - and we almost went to war due to it. The BMEWS radar in Thule Greenland detected a missle launch from somewhere in the USSR. The red alert call went pretty far up the CoC until someone wise enough took a look at the data, and most importantly, the horizon. The moon was rising in the exact location of the missle launch. The extremely powerful radar signal was bouncing off the moon and since the distance was obviously impossible, the program divided until a reasonable distance was extrapolated. That "glitch" that almost started a war was quickly fixed.

jkingrph
May 6, 2007, 04:03 PM
For a bullet to travel "a thousand miles" earth standard conditions could not apply. You must first have zero or little gravity, atmosperic pressures, humidity, ect must be non existent, ie, you would have to be in the vaccum of space. A bullet could then travel "forever" assuming it did not strike another space object or come close enough to be pulled in by the gravity of another object. Think how effective a large shotgun load like one of the behive rounds would be on say a satilite at long range.

Zak Smith
May 6, 2007, 04:05 PM
jkingrph,

I think the situation was: "a thousand miles in the micro gravity environment of a space going balloon several thousand miles in diameter" which contained air of similar density to standard sea level conditions.

Chuck Dye
May 6, 2007, 09:09 PM
Thanks, Zak.

I proposed modern terrestrial sea level atmospheric conditions only for the convenience of existing ballistics programs and their underlying algorithms. Were I to try to apply rigor to the author's habitat, Virga, I would probably find a considerable range of atmospheric densities would work, an unnecessary complication to the ballistics question.

jkingrph,

In zero G vacuum, if you fail to fire that shotgun so that the recoil impulse it directed precisely through your center of mass, you will have very unpleasant angular momentum as a result. Even without creating spin, you will need to compensate for your recoil. :D

heron
May 6, 2007, 11:01 PM
CANNOT COMPUTE . . . INSUFFICIENT DATA . . .

I could see that shot being made in space, but not in any atmosphere, with or without gravity. Air resistance would stop the thing long before it could go that far.
I'm disappointed with Analog Magazine in any case; I used to have a lot of respect for their editorial standards. I guess everything is going to hell . . .

MattC
May 7, 2007, 12:28 AM
Soft SF vs. Hard SF

Two significantly different sub-genres. Soft SF asks you to ignore the scientifically impossible to advance the story or provide a setting for the story. Some of the stories in this sub-genre are nearly indistinguishable from Fantasy. Hard SF requires of the author to have provable or at least probable scientific basis for basically every claim made in the text.

The story you read was the soft variant. It's not probable and is nothing more than a tacky part of an exotic space adventure. There are fans of both genres. It appears that we (Huck and I) both prefer Hard SF.

Mal H
May 7, 2007, 12:37 AM
I guess I would be in the Carbide SF group then. :)

That's one reason why Arthur C. Clarke was always my favorite SF author almost from childhood on, or rather Childhood's End on.

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