4 ms·

A bullet travels at a relative speed of about 250 to 1250m/s. A ~10g projectile moving that fast has an energy of 600-16000 joules. Everything in low Earth or

by mapt 17d ago

A bullet travels at a relative speed of about 250 to 1250m/s. A ~10g projectile moving that fast has an energy of 600-16000 joules. Everything in low Earth orbit is moving at 7600m/s. A ~10g projectile moving that fast has an energy of 580,000 joules. Getting hit by something moving that fast is roughly equivalent to getting hit by a whole ammo case of bullets at the same speed. There is no armor that can protect you; Even the most solid objects behave like fluids at this relative velocity, potentially incurring more damage from the explosion / shockwave splatter than a thinner object that would allow you to overpenetrate. A cardboard box of ball bearings with a handgrenade in it in LEO being triggered could wipe out nearly everything up there, and depending on the exact altitude it could effectively mine LEO and prevent humanity from using it for a long time, with a selectable duration between months or millennia depending on altitude. "Space warfare" in LEO is a matter of everybody walking around with a personal nuclear weapon strapped to their back that can be activated on a hair trigger. We may well wipe everything out by accident, if it gets too crowded or because somebody stubbed their toe. Regardless, there is no selectivity, and any actor with space launch capability can blot out our access at will in ways that will outlive them. Basically our only hope of continued use is things that persuade us to refrain from attempting to incorporate space into a theatre of war. That box of ball bearings should have higher stakes on the escalation ladder than a tactical nuclear strike. And it probably shouldn't be there in the first place.

lr1970 17d ago
> Everything in low Earth orbit is moving at 7600m/s. A ~10g projectile moving that fast has an energy of 580,000 joules. What matters is the relative velocity of the projectile towards the target. I practice it will be smaller or larger (if the bullet is incoming). But steering an incoming projectile is way harder.
- onion2k 17d ago
  What matters is the relative velocity of the projectile towards the target. True. If you really want to mess space up forever you need to launch a rocket full of sand, slingshot around the moon, and gently sprinkle it in an retrograde orbit. That would be fast enough for something as small as a grain of sand to create pinhole-sized punctures in anything put in orbit, and after a few years the sand would be spread out enough to make any launch essentially impossible. I might have thought about this too much.
  - Fwirt 17d ago
    Space is really, really big. I think it's hard for us to comprehend just how much space is in space, especially in 3-dimensional terms. It would take a lot of sand to mine all of the useful orbital space, and that's just LEO. There's tons of room in higher orbits. It would measurably increase the risk of passing through LEO on the way to other destinations and make some orbital planes unusable for e.g. Starlink or human habitation, but when you're just passing through, the odds of getting punctured are probably still reasonable, at least for unmanned spacecraft. Keep in mind that the ISS maneuvers out of the way when there are several miles to a potential impactor, just in case. We have all our eggs in one basket right now, so everybody is really careful with that one basket.
    - onion2k 17d ago
      It would take a lot of sand to mine all of the useful orbital space, and that's just LEO. Nope. You just need to make it a high enough probability of your spaceship being damaged that people won't take the risk. For humans that's very low. For anything moderately expensive it's quite low. There's tons of room in higher orbits. You have to go through the lower orbits to get there.
      - JumpCrisscross 17d ago
        > You have to go through the lower orbits to get there Math doesn't math. The closest solution I've seen is putting 10^6 to 10^9 kg fragmented debris in the 700 to 1,000 km band to create a 5% failure rate at fastest transit, which is economically devastating. But that assumes away grain-grain collisions. I think when I last ran the math, you'd need to sustain 5 to 10 Starship loads of fragmented debris to that orbit a week to create a proper barrier–near 100% hazard. At which point the solution becomes shooting down those launch vehicles. In a couple years (3 to 10, depending on the solar cycle), the skies would clear to about 1% hazard. That hazard, however, would persist for some time–how long is anybody's guess.
    - LargoLasskhyfv 16d ago
      Then why are they making so much fuss about (tracked) small things drifting by, violating the "safety box" around a satellite or station?
- toast0 17d ago
  > But steering an incoming projectile is way harder. It's usually much easier to steer an outgoing projectile. :P
waste_monk 17d ago
>A cardboard box of ball bearings with a handgrenade in it in LEO being triggered could wipe out nearly everything up there, and depending on the exact altitude it could effectively mine LEO and prevent humanity from using it for a long time Eh, you can do a lot better than that: https://www.linkedin.com/posts/conksat_introducing-fragsat-for-years-spaceflight-activity-7178820296823427073-fkmu https://www.linkedin.com/posts/conksat_introducing-fragsat-f... :)
wat10000 17d ago
It's not quite as bad as that. Space is big and hitting stuff is really hard. Your hand grenade scenario has effectively been done a few times and it (obviously) didn't make LEO unusable. For example: https://en.wikipedia.org/wiki/2009_satellite_collision https://en.wikipedia.org/wiki/2009_satellite_collision There are thousands of pieces of debris in LEO large enough to be tracked, and a lot more that's too small to track but big enough to do serious damage. This isn't good but it's not wiping everything out. Adding a few thousand more pieces of debris would not be even remotely as bad as using a tactical nuclear weapon in war would be.
- mschuster91 17d ago
  > Adding a few thousand more pieces of debris would not be even remotely as bad as using a tactical nuclear weapon in war would be. The worst effect would be a nuclear weapon in space. The resulting EMP would probably fry more than enough electric and electronic devices to throw back whatever country is hit by it by decades.
  - wongarsu 17d ago
    The US famously did that in the 60s (detonating nukes at roughly the height of today's ISS)[1]. Also some less famous ones, including a Soviet test that resulted in the EMP destroying a power plant [2]. Properly aimed at a populated area it would be devastating. And you can detonate bombs far from your enemy's country, then let earth's magnetic field lines transfer the EMP pulse to their territory. Good luck defending against that That said, it'd take far more than one bomb to take down a country, unless we are talking city states 1 https://en.wikipedia.org/wiki/Starfish_Prime https://en.wikipedia.org/wiki/Starfish_Prime 2 https://en.wikipedia.org/wiki/High-altitude_nuclear_explosion https://en.wikipedia.org/wiki/High-altitude_nuclear_explosio...
    - mschuster91 17d ago
      > That said, it'd take far more than one bomb to take down a country, unless we are talking city states Hit the ten biggest metropolitan areas [1] with one nuke each and you'd hit about 88 million people and probably an even bigger share of all industry that isn't farming. The biggest problem is power transformers, there isn't much capacity in manufacturing them, it's already a bottleneck thanks to regular replacement and renewable energy / datacenter buildouts with 24+ months of lead time [2] - now imagine a significant war related impact, the lead time would probably skyrocket to at least a decade. At least one source claims that the radius from a single device could be much, much larger [3], so with proper design to maximize an EMP (which even Starfish Prime wasn't intended to do), it is conceivable that dropping just two of these things over the East and West Coast respectively would cause immense damage. A Fallout-style nuclear war, I think, would be easier to recover from than even a small exchange of EMPs. [1] https://en.wikipedia.org/wiki/List_of_North_American_metropolitan_areas_by_population https://en.wikipedia.org/wiki/List_of_North_American_metropo... [2] https://berlin.cwiemeevents.com/articles/new-normal-component-suppliers https://berlin.cwiemeevents.com/articles/new-normal-componen... [3] https://atomicarchive.com/resources/documents/effects/glasstone-dolan/chapter11.html https://atomicarchive.com/resources/documents/effects/glasst...
gorgoiler 17d ago
While armor is indeed much harder in space, it is not impossible: https://en.wikipedia.org/wiki/Whipple_shield https://en.wikipedia.org/wiki/Whipple_shield Whipple shields use spaced plates to disperse the impact of a projectile on the first plate over a larger area on the second plate, and so on and so forth over four or five plates such that the final plate is not penetrated. My father worked on high velocity impact ballistics and has some very nice multiple exposure results. The light gas guns used to propel the test cubes are just as interesting as the shields themselves.
- notahacker 17d ago
  Whipple Shields are a very important part of protecting things like the ISS, but are optimized more for chance high velocity impacts with tiny bits of debris than an adversary's targeted projectile or their robotic arm grappler, or indeed non-kinetic weapons like directed energy or EMPs which is probably the capability the US intends to imply here.
- freebsd_lovefes 17d ago
  You know nothing about space armor until you manage to shoot down Amarr's dreadnought in Eve Online, tyvm.
- LargoLasskhyfv 16d ago
  New development in sight: https://phys.org/news/2026-09-eggshells-aluminum-material-significant-space.html https://phys.org/news/2026-09-eggshells-aluminum-material-si...
- mapt 15d ago
  They're great for a 20mm x 5mm x 0.3mm fleck of paint or vacuum insulation weighing 30mg, not so much for a 10mm hex nut weighing 11g. Armor can protect you against the smallest debris which post the least risk and decay the fastest. Everything else, not so much. A question for you though - does that insulation vaporizing itself inside a whipple shield generate secondary debris comprised of the whipple shield and condensed aluminum droplets??
trhway 17d ago
You fire a radar guided powerful laser pulse at the incoming object causing small surface ablation , intentionally a bit to the side, which will serve as a small reaction mass eject altering the trajectory of that incoming object.
- mapt 12d ago
  This is not what people think it is. It isn't a delta V or a distance solution - we simply aren't that precise unfortunately. The relative velocities are enormous, the inverse square law distances (lasers are not perfectly collimated, just highly collimated) and opportunity for reflections unacceptable. You do this after you've pulled alongside the object via SEP and ion thrusters, and you sit there ablating the surface with your lightweight pulsed laser from a few hundred meters away in formation, for weeks/months. That saves you chemical propellant proportional to the task, and it saves you enormous mass and complexity in grappling, derotating, and otherwise securing an uncooperative rotating body.
kragen 17d ago
This is not correct, and the experiment has been done a number of times with no real effect, most memorably in 01961, when Project West Ford put 480 million copper needles in 3500-km-high medium Earth orbit (MEO); but it's a little bit challenging to understand why. The first reason is that outer space is just inconceivably big, even just the space in low Earth orbit (LEO). LEO has very nearly the same surface area as the Earth, which is to say, about 40% more surface area than the ocean. But the ocean averages 3.7 km thick, and LEO is 2000 km thick. So, roughly speaking, LEO is 50 times the volume of the ocean. That's a lot of space to miss. There's about 15000 active satellites up there, mostly Starlink. Imagine there are 15000 ÷ 50 = 300 divers swimming at random places in the world's oceans, you have a gun that shoots magic bullets that go 7700m/s and never stop until they hit a diver, and you fire one into the ocean at random. How long is it going to take that bullet to hit someone? It traverses, say, 7700 cubic meters per second, but there are 1.32 × 10¹⁸ m³ (1.32 quintillion m³) of ocean it could traverse, and on average it has to traverse 4.4 quadrillion m³ before it hits someone. It turns out that your poor bullet will bounce around the ocean for about 18000 years, which is the same thing that will happen to one of your ball bearings if it manages to stay in orbit. The second reason is, perhaps surprisingly, air resistance. The atmosphere thins out exponentially but never quite stops. Most satellites are at a height where the orbits of even macroscopic multi-kilogram objects decay within a few years from air resistance unless you boost them; smaller objects like your ball bearings or the West Ford needles decay more rapidly. Indeed, all of the individual West Ford needles have already deorbited, despite being in MEO at four times the height of typical LEO satellites, though 44 needle clumps remain. The third reason is the narrow nature of orbital dynamics. The reason you have to go 7600m/s is that you're in free fall, and you have to miss the Earth when you come down, by having moved far enough horizontally that the Earth isn't there any more. If your hand grenade sends the ball bearings flying backward along the orbit and/or downwards fast enough, they'll re-enter the atmosphere immediately. What's less obvious is that the ball bearings that it sends upwards will re-enter the atmosphere after half an orbit. Depending on how forceful your explosion is, only a narrow circle that stay in almost exactly the same orbit may survive. None of the ball bearings will be lofted to a higher stable orbit. If they couldn't hit the Earth (perhaps because we replaced it with a very, very small black hole) and none of them reached escape velocity, they would all orbit back through the point where the hand grenade went off, once they'd finished an orbit. So (restoring the Earth to our scenario) even after 18000 years, your hand grenade will have only hit satellites at the same height where it went off in the first place, or slightly higher or lower. The Kessler syndrome is a real, serious problem for space access, but it hinges crucially on the number of satellites up there to participate in the fragmentation cascade.

by mapt 17d ago

lr1970 17d ago

> Everything in low Earth orbit is moving at 7600m/s. A ~10g projectile moving that fast has an energy of 580,000 joules. What matters is the relative velocity of the projectile towards the target. I practice it will be smaller or larger (if the bullet is incoming). But steering an incoming projectile is way harder.

onion2k 17d ago
What matters is the relative velocity of the projectile towards the target. True. If you really want to mess space up forever you need to launch a rocket full of sand, slingshot around the moon, and gently sprinkle it in an retrograde orbit. That would be fast enough for something as small as a grain of sand to create pinhole-sized punctures in anything put in orbit, and after a few years the sand would be spread out enough to make any launch essentially impossible. I might have thought about this too much.
- Fwirt 17d ago
  Space is really, really big. I think it's hard for us to comprehend just how much space is in space, especially in 3-dimensional terms. It would take a lot of sand to mine all of the useful orbital space, and that's just LEO. There's tons of room in higher orbits. It would measurably increase the risk of passing through LEO on the way to other destinations and make some orbital planes unusable for e.g. Starlink or human habitation, but when you're just passing through, the odds of getting punctured are probably still reasonable, at least for unmanned spacecraft. Keep in mind that the ISS maneuvers out of the way when there are several miles to a potential impactor, just in case. We have all our eggs in one basket right now, so everybody is really careful with that one basket.
  - onion2k 17d ago
    It would take a lot of sand to mine all of the useful orbital space, and that's just LEO. Nope. You just need to make it a high enough probability of your spaceship being damaged that people won't take the risk. For humans that's very low. For anything moderately expensive it's quite low. There's tons of room in higher orbits. You have to go through the lower orbits to get there.
    - JumpCrisscross 17d ago
      > You have to go through the lower orbits to get there Math doesn't math. The closest solution I've seen is putting 10^6 to 10^9 kg fragmented debris in the 700 to 1,000 km band to create a 5% failure rate at fastest transit, which is economically devastating. But that assumes away grain-grain collisions. I think when I last ran the math, you'd need to sustain 5 to 10 Starship loads of fragmented debris to that orbit a week to create a proper barrier–near 100% hazard. At which point the solution becomes shooting down those launch vehicles. In a couple years (3 to 10, depending on the solar cycle), the skies would clear to about 1% hazard. That hazard, however, would persist for some time–how long is anybody's guess.
  - LargoLasskhyfv 16d ago
    Then why are they making so much fuss about (tracked) small things drifting by, violating the "safety box" around a satellite or station?
toast0 17d ago
> But steering an incoming projectile is way harder. It's usually much easier to steer an outgoing projectile. :P

waste_monk 17d ago

>A cardboard box of ball bearings with a handgrenade in it in LEO being triggered could wipe out nearly everything up there, and depending on the exact altitude it could effectively mine LEO and prevent humanity from using it for a long time Eh, you can do a lot better than that: https://www.linkedin.com/posts/conksat_introducing-fragsat-for-years-spaceflight-activity-7178820296823427073-fkmu https://www.linkedin.com/posts/conksat_introducing-fragsat-f... :)

wat10000 17d ago

It's not quite as bad as that. Space is big and hitting stuff is really hard. Your hand grenade scenario has effectively been done a few times and it (obviously) didn't make LEO unusable. For example: https://en.wikipedia.org/wiki/2009_satellite_collision https://en.wikipedia.org/wiki/2009_satellite_collision There are thousands of pieces of debris in LEO large enough to be tracked, and a lot more that's too small to track but big enough to do serious damage. This isn't good but it's not wiping everything out. Adding a few thousand more pieces of debris would not be even remotely as bad as using a tactical nuclear weapon in war would be.

mschuster91 17d ago
> Adding a few thousand more pieces of debris would not be even remotely as bad as using a tactical nuclear weapon in war would be. The worst effect would be a nuclear weapon in space. The resulting EMP would probably fry more than enough electric and electronic devices to throw back whatever country is hit by it by decades.
- wongarsu 17d ago
  The US famously did that in the 60s (detonating nukes at roughly the height of today's ISS)[1]. Also some less famous ones, including a Soviet test that resulted in the EMP destroying a power plant [2]. Properly aimed at a populated area it would be devastating. And you can detonate bombs far from your enemy's country, then let earth's magnetic field lines transfer the EMP pulse to their territory. Good luck defending against that That said, it'd take far more than one bomb to take down a country, unless we are talking city states 1 https://en.wikipedia.org/wiki/Starfish_Prime https://en.wikipedia.org/wiki/Starfish_Prime 2 https://en.wikipedia.org/wiki/High-altitude_nuclear_explosion https://en.wikipedia.org/wiki/High-altitude_nuclear_explosio...
  - mschuster91 17d ago
    > That said, it'd take far more than one bomb to take down a country, unless we are talking city states Hit the ten biggest metropolitan areas [1] with one nuke each and you'd hit about 88 million people and probably an even bigger share of all industry that isn't farming. The biggest problem is power transformers, there isn't much capacity in manufacturing them, it's already a bottleneck thanks to regular replacement and renewable energy / datacenter buildouts with 24+ months of lead time [2] - now imagine a significant war related impact, the lead time would probably skyrocket to at least a decade. At least one source claims that the radius from a single device could be much, much larger [3], so with proper design to maximize an EMP (which even Starfish Prime wasn't intended to do), it is conceivable that dropping just two of these things over the East and West Coast respectively would cause immense damage. A Fallout-style nuclear war, I think, would be easier to recover from than even a small exchange of EMPs. [1] https://en.wikipedia.org/wiki/List_of_North_American_metropolitan_areas_by_population https://en.wikipedia.org/wiki/List_of_North_American_metropo... [2] https://berlin.cwiemeevents.com/articles/new-normal-component-suppliers https://berlin.cwiemeevents.com/articles/new-normal-componen... [3] https://atomicarchive.com/resources/documents/effects/glasstone-dolan/chapter11.html https://atomicarchive.com/resources/documents/effects/glasst...

gorgoiler 17d ago

While armor is indeed much harder in space, it is not impossible: https://en.wikipedia.org/wiki/Whipple_shield https://en.wikipedia.org/wiki/Whipple_shield Whipple shields use spaced plates to disperse the impact of a projectile on the first plate over a larger area on the second plate, and so on and so forth over four or five plates such that the final plate is not penetrated. My father worked on high velocity impact ballistics and has some very nice multiple exposure results. The light gas guns used to propel the test cubes are just as interesting as the shields themselves.

notahacker 17d ago
Whipple Shields are a very important part of protecting things like the ISS, but are optimized more for chance high velocity impacts with tiny bits of debris than an adversary's targeted projectile or their robotic arm grappler, or indeed non-kinetic weapons like directed energy or EMPs which is probably the capability the US intends to imply here.
freebsd_lovefes 17d ago
You know nothing about space armor until you manage to shoot down Amarr's dreadnought in Eve Online, tyvm.
LargoLasskhyfv 16d ago
New development in sight: https://phys.org/news/2026-09-eggshells-aluminum-material-significant-space.html https://phys.org/news/2026-09-eggshells-aluminum-material-si...
mapt 15d ago
They're great for a 20mm x 5mm x 0.3mm fleck of paint or vacuum insulation weighing 30mg, not so much for a 10mm hex nut weighing 11g. Armor can protect you against the smallest debris which post the least risk and decay the fastest. Everything else, not so much. A question for you though - does that insulation vaporizing itself inside a whipple shield generate secondary debris comprised of the whipple shield and condensed aluminum droplets??

trhway 17d ago

You fire a radar guided powerful laser pulse at the incoming object causing small surface ablation , intentionally a bit to the side, which will serve as a small reaction mass eject altering the trajectory of that incoming object.

mapt 12d ago
This is not what people think it is. It isn't a delta V or a distance solution - we simply aren't that precise unfortunately. The relative velocities are enormous, the inverse square law distances (lasers are not perfectly collimated, just highly collimated) and opportunity for reflections unacceptable. You do this after you've pulled alongside the object via SEP and ion thrusters, and you sit there ablating the surface with your lightweight pulsed laser from a few hundred meters away in formation, for weeks/months. That saves you chemical propellant proportional to the task, and it saves you enormous mass and complexity in grappling, derotating, and otherwise securing an uncooperative rotating body.

kragen 17d ago

This is not correct, and the experiment has been done a number of times with no real effect, most memorably in 01961, when Project West Ford put 480 million copper needles in 3500-km-high medium Earth orbit (MEO); but it's a little bit challenging to understand why. The first reason is that outer space is just inconceivably big, even just the space in low Earth orbit (LEO). LEO has very nearly the same surface area as the Earth, which is to say, about 40% more surface area than the ocean. But the ocean averages 3.7 km thick, and LEO is 2000 km thick. So, roughly speaking, LEO is 50 times the volume of the ocean. That's a lot of space to miss. There's about 15000 active satellites up there, mostly Starlink. Imagine there are 15000 ÷ 50 = 300 divers swimming at random places in the world's oceans, you have a gun that shoots magic bullets that go 7700m/s and never stop until they hit a diver, and you fire one into the ocean at random. How long is it going to take that bullet to hit someone? It traverses, say, 7700 cubic meters per second, but there are 1.32 × 10¹⁸ m³ (1.32 quintillion m³) of ocean it could traverse, and on average it has to traverse 4.4 quadrillion m³ before it hits someone. It turns out that your poor bullet will bounce around the ocean for about 18000 years, which is the same thing that will happen to one of your ball bearings if it manages to stay in orbit. The second reason is, perhaps surprisingly, air resistance. The atmosphere thins out exponentially but never quite stops. Most satellites are at a height where the orbits of even macroscopic multi-kilogram objects decay within a few years from air resistance unless you boost them; smaller objects like your ball bearings or the West Ford needles decay more rapidly. Indeed, all of the individual West Ford needles have already deorbited, despite being in MEO at four times the height of typical LEO satellites, though 44 needle clumps remain. The third reason is the narrow nature of orbital dynamics. The reason you have to go 7600m/s is that you're in free fall, and you have to miss the Earth when you come down, by having moved far enough horizontally that the Earth isn't there any more. If your hand grenade sends the ball bearings flying backward along the orbit and/or downwards fast enough, they'll re-enter the atmosphere immediately. What's less obvious is that the ball bearings that it sends upwards will re-enter the atmosphere after half an orbit. Depending on how forceful your explosion is, only a narrow circle that stay in almost exactly the same orbit may survive. None of the ball bearings will be lofted to a higher stable orbit. If they couldn't hit the Earth (perhaps because we replaced it with a very, very small black hole) and none of them reached escape velocity, they would all orbit back through the point where the hand grenade went off, once they'd finished an orbit. So (restoring the Earth to our scenario) even after 18000 years, your hand grenade will have only hit satellites at the same height where it went off in the first place, or slightly higher or lower. The Kessler syndrome is a real, serious problem for space access, but it hinges crucially on the number of satellites up there to participate in the fragmentation cascade.