Could a bullet be made of something that could go from orbit to Earth's surface?

"Scott T. Jensen" wrote:
I'm up on the Space Station and I go out for a nice little space walk.
I take along my specially designed hunting rifle and fire a bullet
down at the planet. What would the bullet need to be made of for it
to make it all the way to the surface and not burn up on entry to our
atmosphere? Is there anything the bullet could be made of that would
be able it to make the trip? And would the speed of the bullet affect
its chances? Would also the bullet go weird like how bullets do when
you shoot them into a pool of water?

The muzzle velocity of an M16 is ~ 950 m/sec (obviously not a hunting rifle
- unless you include humans in your hunting list). Firing straight down is
not be nearly as effective as you would think - much more effective is
firing "backward" against the direction of orbit. And counterintuitively
(unless one is familiar with orbital mechanics) the best place to fire
"backwards" is at the highest point in the orbit (the apogee). The worst
place to fire is at the lowest point in the orbit (the perigee). Obviously
in a nearly circular orbit it doesn't matter much when you fire.

The muzzle velocity of an M16 should be more than sufficient to drop a
bullet's perigee into the earth's atmosphere (for most low earth orbits of
interest) such that the orbit decays into the surface.

The speed of the bullet will probably be on the order of ~7000 m/sec as it
enters the atmosphere. A lead bullet probably wouldn't survive - but I
suspect a carbon-phenolic or silicon-dioxide (i.e. rock) bullet probably
should make it - or at least mostly.

Sander Vesik wrote in message ...
In sci.space.tech Scott T. Jensen wrote:
I'm up on the Space Station and I go out for a nice little space walk. I
take along my specially designed hunting rifle and fire a bullet down at the
planet. What would the bullet need to be made of for it to make it all the
way to the surface and not burn up on entry to our atmosphere? Is there
anything the bullet could be made of that would be able it to make the trip?
And would the speed of the bullet affect its chances? Would also the bullet
go weird like how bullets do when you shoot them into a pool of water?

If the bullet reaces surfaces then changes are good you left Earth
Orbit...


How's that? A rifle has a muzzle velocity of 1 km/s, but I mass three
to four orders of magnitude more than bullet, so my delta-v is less
than 1 m/s. My SAFER should be able to make up for that:
http://quest.arc.nasa.gov/space/teachers/suited/6work.html says that
they are good for 3 m/s delta-v.


You couldn't
achieve it with a chemical gun, for example.


If I fire the bullet against orbital velocity and decrease the
velocity of the bullets' orbit by 1 km/s, it *is* certainly going to
de-orbit. The delta-v used to deorbit spacecraft is typically much,
much less than that. I think the Space Shuttle de-orbit burn results
in a delta-v of the order of 100 m/s.

You do not need to kill all the bullet's orbital velocity to enable it
to survive re-entry. There are now ceramics that can probably permit
an object as small as a bullet to survive re-entry heating:
http://asm.arc.nasa.gov/projects/sharp/press_release.shtml. This
vehicle had a sharp nose with a 5 mm radius of curvature and survived
re-entry.
--
Andrew J. Higgins Mechanical Engineering Dept.
Assistant Professor McGill University
Shock Wave Physics Group Montreal, Quebec CANADA
http://www.mcgill.ca/mecheng/staff/academic/higgins/

Sander Vesik wrote in message ...
In sci.space.tech Scott T. Jensen wrote:
I'm up on the Space Station and I go out for a nice little space walk. I
take along my specially designed hunting rifle and fire a bullet down at the
planet. What would the bullet need to be made of for it to make it all the
way to the surface and not burn up on entry to our atmosphere? Is there
anything the bullet could be made of that would be able it to make the trip?
And would the speed of the bullet affect its chances? Would also the bullet
go weird like how bullets do when you shoot them into a pool of water?

If the bullet reaces surfaces then changes are good you left Earth
Orbit... The major effort is not making the bullet reach surface but
maiking a gun that could impart it with enough velocity. You couldn't
achieve it with a chemical gun, for example.


Idly curious,
Scott Jensen

I tried to post this earlier, but I haven't seen it appear yet, so
I'll repost it.

All the posts I've seen so far are wrong.

If you are in the space station, then you are traveling at 18,000 mph.
Firing a bullet from orbit gives a velocity (let's say 1500ft/s or
1000mph) to the bullet IN ADDITION to the velocity it already had
(like throwing a ball out of a moving car).

If you want a bullet to hit the earth's surface, then the best way to
do it is to fire it directly opposite your direction of travel (thus
slowing it to 17,000mph) and causing it to "dip down" into the
atmosphere, similar to when the shuttle does a deorbit burn.

A typical bullet wouldn't make it through the atmosphere. It would
look like a slowly moving shooting star for a few seconds before it
completely vaporized. You'd need a material that could comfortably
stand 3500F (i.e. not steel), as well as being somewhat resistant to
corrosive enviroments. Tungsten has a chance of making it.
Molybdenum and Nobium might make it too. A chunk of graphite might,
if it survived the firing intact.

Dave

Scott T. Jensen wrote:

I'm up on the Space Station and I go out for a nice little space walk. I
take along my specially designed hunting rifle and fire a bullet down at the
planet. What would the bullet need to be made of for it to make it all the
way to the surface and not burn up on entry to our atmosphere? Is there
anything the bullet could be made of that would be able it to make the trip?
And would the speed of the bullet affect its chances? Would also the bullet
go weird like how bullets do when you shoot them into a pool of water?

Idly curious,
Scott Jensen

Since you are 'on the Space Station', your velocity relative to the
Earth is high (someone said 18000 mph). Rifle velocities are much
less, roughly 1000 - 1500 mph. This means that you can't
change the bullets velocity all that much compared to the ISS.

I'm not an expert on orbital mechanics, but I suspect that if you
fired in the proper direction (which may not be obvious), the
slug would eventually hit the atmosphere. It would still have
most of its orbital velocity, and come in at over 16000 mph.

A lead slug would almost certainly burn up. Some armor penetrating
rounds have steel or tungsten inserts. The tungsten ones would
have a much better chance of making it.

Whether it would skip off the atmosphere at first approach I can't
say. A lot depends on the angle of approach.

I'm not sure why you'd need a 'specially designed' rifle.
The vacuum is not an issue. Temperature and lubrication
might be. For these reasons a bolt action is probably
preferred.

Peter Trei

Peter Trei wrote in message
I'm not sure why you'd need a 'specially designed' rifle.
The vacuum is not an issue. Temperature and lubrication
might be. For these reasons a bolt action is probably
preferred.

Peter Trei

Somewhere, someone knows the answer to that. The soviets are reported
to have launched and test fired a 23 or 30mm aircraft cannon on salyut
3:
http://www.astronautix.com/craft/almazops.htm

"On 24 January 1975 trials of a special system aboard Salyut-3 were
carried out with positive results at ranges from 3000 m to 500 m.
These were undoubtedly the reported tests of the on-board 23 mm
Nudelmann aircraft cannon (other sources say it was a Nudelmann NR-30
30 mm gun). Cosmonauts have confirmed that a target satellite was
destroyed in the test."

Based on this page
http://www.geocities.com/Pentagon/Base/1852/index2.html
both have a muzzle velocity of about 700 m/s, which would be plenty
lower the projectiles perigee well into the atmosphere, if fired in a
counter-orbital direction. (I seem to recall a typical soyuz deorbit
burn being only about 100 m/s)

In article ,
hop wrote:
The vacuum is not an issue. Temperature and lubrication
might be...

Somewhere, someone knows the answer to that. The soviets are reported
to have launched and test fired a 23 or 30mm aircraft cannon on salyut 3...

The way you deal with temperature is to control it -- wrap the thing in
thermal blankets and supply electric heat to keep it warm. (If you're
planning to fire it intensively, *then* you have to think about cooling,
mind you...)

Lubrication simply requires a change of lubricants. There *are*
vacuum-compatible lubricants.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

In sci.space.tech hop wrote:
Peter Trei wrote in message
I'm not sure why you'd need a 'specially designed' rifle.
The vacuum is not an issue. Temperature and lubrication
might be. For these reasons a bolt action is probably
preferred.

Peter Trei

Somewhere, someone knows the answer to that. The soviets are reported
to have launched and test fired a 23 or 30mm aircraft cannon on salyut
3:
http://www.astronautix.com/craft/almazops.htm

This would be a really, really cool display.

All you need is a way of accurately pointing the gun, and timing each
shot, and you have letters of glowing fire.

If you are talking about shooting a payload to orbit Gerald Bull worked on
the HARP project in the 1960's to research the possibility to launching a
payload via a ground based cannon

see: http://www-istp.gsfc.nasa.gov/stargaze/Smartlet.htm

"Ian Stirling" wrote in message
...
In sci.space.tech hop wrote:
Peter Trei wrote in message
I'm not sure why you'd need a 'specially designed' rifle.
The vacuum is not an issue. Temperature and lubrication
might be. For these reasons a bolt action is probably
preferred.

Peter Trei

Somewhere, someone knows the answer to that. The soviets are reported
to have launched and test fired a 23 or 30mm aircraft cannon on salyut
3:
http://www.astronautix.com/craft/almazops.htm

This would be a really, really cool display.

All you need is a way of accurately pointing the gun, and timing each
shot, and you have letters of glowing fire.