The photo above is from the European Space Agency.


This image shows the results of a lab test impact between a small sphere of aluminum travelling at approximately 6.8 km/second and a block of aluminum 18 cm thick. This test simulates what can happen when a small space debris object hits a spacecraft.

Al sphere diameter: 1.2cm
Al sphere mass: about 1.7 g
Impact crater diameter: 9.0 cm
Impact crater depth: 5.3 cm

In such an impact, the pressure and temperature can exceed those found at the centre of the Earth, e.g. greater than 365 GPa and more than 6000 K.


The aluminum ball projectile is about .47 caliber 26.23 gr travelling at 22,000 fps.

The cross section of the aluminum block is interesting. The impact crater looks like a parabola. I am curious about the crack below the crater. I wonder if that has something to do with the grain boundaries of the aluminum and the metal sort of delaminated.


  • RogUinta

    You missed a zero. 6.8 km/s is over 22 THOUSAND feet per second.

  • Zach

    6800 m/s is 22,000 FPS, not 2,200

  • Kyle

    I see the math error is already covered.

  • Phillip Cooper

    Better try that math again, sport. 6.8km/sec is 6.8 KILOMETERS PER SECOND.

    Not 2200fps.

    That’s, you know, what “kilometers, Per second”, means.
    (also, see Zach below for the fps translation) πŸ˜‰

  • nova3930

    We don’t do the maths around here boy!

  • nova3930

    BTW, that’s what’s known as a hypervelocity impact and some of the effects are insane. Metals basically act like fluids under the impact conditions. That delamination on the back probably relates to those fluid-like conditions.

    One of my college professors at the time was doing research for NASA concerning impact shielding for the ISS. We actually got to play with the light gas gun a little bit. Turns out, just about the most weight efficient way to shield from those impacts is to stack up layers of paper thin metal with gaps between them.

    • JumpIf NotZero

      Anyone using the term “delamination” is really really really confused though.

      • nova3930

        Yeah, it’s not the correct term for what you’re seeing up there but I was trying to maintain consistency with the discussion at hand. Delamination doesn’t apply outside of materials with multiple layers ie layered composites and similar. The limits of my “expertise” in impact mechanics boils down to having that professor and playing with the light gas gun so :p

      • Aerindel Prime

        Yep. What is really happening is spalling.

        • Major Tom

          The initial phases of it anyways.

    • noob

      Light gas guns are badass. If only there was a way to make a semi auto one without a barrel length round of ammo with burst disks on both ends.

  • Pseudo

    I get that simple unit conversion errors can happen, but you really think your buddy’s rifle could do that to an aluminum plate? Actually, have roughly 11 times the energy of the pictured impact? Sheesh, this calls for common sense much more than basic math skills.

    • Nicholas C

      I just realized my mistake. It’s not 2200 but 22,000 fps. Lol

      • noob

        Don’t feel bad. in 1999 the $125m Mars Climate Orbiter burned up in the Martian atmosphere because NASA’s engineers failed to convert units from Imperial to metric.

        • Ben Warren

          In 1492, Columbus discovered the West because he failed to convert from Persian miles to Roman miles in his calculations.

        • RocketScientist

          Gross mis-statement of fact. NASA spec’d requirements that the software for a piece of ground support equipment output specific impulse values in SI units of Newton-seconds in the SIS (software interface specification). The contractor (Lockheed Martin) that supplied the software instead had it output specific impulse values in pound-force-seconds.

        • Sulaco5

          I don’t know, I think the taxpayers could have a good cry…

  • TheNotoriousIUD

    Seems like aluminum on aluminum would just splatter at that speed.

    • Form Factor

      Would love to see it with an tungstencarbide APDSFS ….

      • Major Tom

        Depleted uranium or go home!

    • Marc


  • Hoplopfheil


  • MrDakka

    The spalling is caused by shear stresses of the impact. Since most ductile materials including metals fail in shear, spalling is what occurs.

  • Sunshine_Shooter

    Article: “In space, small debris can impact vehicles with mind-blowing results.”

  • John

    I get very similar performance from my 10mm.

    • KidCorporate

      I knew it was in here somewhere.

  • JumpIf NotZero

    I wonder if that has something to do with the grain boundaries of the aluminum and the metal sort of delaminated.

    wow. Um…. no.

    • Edeco

      Snrk, it’s not the phrase I’d have used, but I’m wondering if that piece of metal isn’t cast and if the part that buckled is a skin.

  • Sianmink

    I wanna know how they’re getting a .47 cal aluminum ball up to 22,000 fps.

    • Sledgecrowbar

      I clever and proprietary combination of nitrous and nitromethane.

      • Goody

        He’s probably got a hundred grand under the hood of that pellet!

  • Form Factor

    So about 39309 Joule …. dang, but out of tungstencarbide would been cooler.

  • JSmath

    The effect occurring on the back end is spalling. The HESH or HEP tank rounds were designed to take advantage of this, only to include turning the “delaminated” (I agree with Jump, that is quite possibly one of the least accurate terms to use in reference to this) portion into lethal chunks of flying metal fragments.

    From Wikipedia on Spall: “One of the simplest forms of mechanical spalling is plate impact, in which two waves of compression are reflected on the free-surfaces of the plates and then interact to generate a region of high tensile stress inside one of the plates.”

    The grain boundaries actually likely had a lot to do with the characteristics of the separation, but probably far less than changing the dimensions and constrainted portions of the target would.

    • Robrecht

      If we want to use accurate terms… It’s not actually spalling until bits have broken off into fragments and gone flying around. This is actually a cavitation.

  • Jim Page

    Wow. Must be .47 +P+

  • Bill

    So it doesn’t meet FBI standards?

    • Major Tom

      If it does that to metal, imagine what that will do to your flesh…

      • noob

        I wonder what happens if somebody was dressed in an honest to god apollo moon suit and got into a firefight. Would they just shrug off 9mm?

        • Scott Wagner

          They would die. Those suits were not designed to withstand projectile weapons.

          • Tuulos

            They are designed to withstand micrometeoroids which are tiny objects moving at very high speeds so depends.

          • Frederick Murre

            Space suits generally rely on whipple-effect to stop micrometeoroids, lots of layers of semi-tough material, that decelerate the itty bitty hyper velocity bit of rock into vaporizing, then catching the spray with the next layers.

            The old suits did this with metal-film covered nylon and glass fiber canvas, some of the modern ones use at least a few layers of kevlar. – still they weren’t anticipating heavy strikes from multi-gram bullets. Probably a toss-up.

          • Pastor Dan

            Yeah, those guys probably wore Depends while they were in their suits. πŸ˜‰ The multi-thousand-dollar toilets were in the spacecraft. No Porta-Johns left on the Sea of Tranquility.

      • LGonDISQUS

        Right through, like red hot bb”s through snow.

        • Frederick Murre

          At those speeds, unfortunately I think you could look forward to traumatic amputation, and at least softball sized permanent holes, as the water in your body tissue is flash-heated to steam from the energy and explodes outwards.

          If it hits bone, you’ll get several hundred fps bone fragments.

  • MrBrassporkchop

    Garbage ammo. Doesn’t pass Interstellar FBI aluminum block ballistics test. You’re a damn fool if you were to trust your space cruiser with this anemic round.

  • Brent Wilkerson

    Tough crowd today…..

  • Somebody needs to put a pair of googly eyes on that.

  • nonobaddog

    It is funny it didn’t deform the aluminum ball at all. πŸ˜‰

    • Kivaari

      That’s not the ball, it vaporized.

      • noob


      • nonobaddog

        Does that mean they had two balls? πŸ˜‰

  • J-

    The hole on the far side is caused by spallation. As the force of impact is transferred through the plate it creates reagions of intersecting compression waves. Like sound waves in air, in between the regions of high pressure, there are regions of vacuum. In a solid, those regions create internal tensile stresses that exceed the tensile strength of the material and tears itself open from the inside. Grain boundaries have nothing to do with it. Ductile failure in aluminum is transgranular.

  • Jeff Heeszel

    I wonder how they got the pellet going 15,000 mph?

    • No one

      Light gas gun.

      They’re pretty commonly used for testing high speed impact scenarios in the Aerospace industry.

    • Edeco

      You should get access to a light gas gun and shoot a feral watermelon and a gummy bear with it πŸ™‚

  • El Duderino

    28,000+ ft-lbs of energy. Maybe even the 10mm guys will show some respect?

  • Aaron

    Happy to see that space agencies still take space impacts seriously.

    • Pastor Dan

      I thought Sandra Bullock had disproven most of this.

  • Edeco

    Neat. Even before choosing The Way of The Gun I’ve been interested in trans-4,500 (or so) fps ballistics. I know a light gas gun is a near-completely different animal, and have some idea of the technical hurdles but I’d love to see practical small-arm velocity increased, somehow.

    • Physic

      ? over 3700fps aerdynamic problems occur anyways

      • Edeco

        What problems?

        • Form Factor

          It increases drag too much.

          • Physic

            Boat tail underpressure cant go beyond a certain point, but nose overpressure does rise further and further with increased velocity, and way too much if you go over 3700.

          • Edeco

            I know drag is related to vel^2, maybe there’s some other velocity factor after 3700. But yanno, meh – paradigms affecting practical velocity have changed before.

          • Edeco

            Too much for what? It’s not just “too much” because 22-250 is a thing. I mean, thanks for your thoughts, but like I said I know there are technical hurdles.

  • thedarkknightreturns

    Conventional firearms would heat up like crazy in space, a method to cool firearms other than the typical air cooling will be needed if we are to deal with the martian problem.

    • Goody

      No bullet drop and highly vulnerable targets (spacesuits & spacecraft) means that smaller, cooler rounds would be more viable. 22 mag, 9mm, etc. The low level of heat would be dissipated by thermal radiation.

      A higher tech solution would be sabots – using a lower friction sleeve to get higher velocity with less heat. Then there’s magnetically driven projectiles, gyrojets, etc…

      • thedarkknightreturns

        Honestly for big stuff in space I see railguns being useful. Most conflicts will eventually be fought in an atmosphere so conventional weapons are still useful. Zero G space requires some different toys though. It’s fun to think about.

  • roo

    I love it when someone says….the metal “crystallized” and broke…..yea, you were all thinking it…you non-engineers

  • MR_Mr_Deplorable_Hapla

    Is that the original projectile, or just used for illustration? I would have thought aluminum would have deformed,,if not vaporized???