# Effectiveness of firing a projectile from orbit to hit a human target

Say if there was a country with bottomless funding for the military developed a weapon where they would fire a projectile/a really big metal stake From a orbiting satellite to hit targets accurately.Actually a real thing someone came up with.

Is it feasible to guide a Kinetic energy penetrator for example to hit a moving human from orbit? Could it be used to hit a person on the ground with a guaranteed 100% chance?

It would seem to me that if the person was moving about in a vehicle or just walking about, he would be able to avoid it without much effort if the metal stake came in one or two minutes later. The average human walking speed would be around 3.1 miles(5km) per hour, which would mean about 544ft(166meters) in 2 minutes. To kill the person(I'm assuming the person has to be in the blast radius), the projectile would have to do more damage than a MOAB which has a 500ft(150meters) blast radius. Is this possible?

• Very much related: What weapon would be most effective for orbital bombardment?
– user
Commented Sep 10, 2016 at 7:49
• Of course, the literal answer to the question in the title is nothing much at all because by "dropping" the projectile while in orbit, the projectile will simply continue in its original orbit. To deorbit the projectile you must actively change its orbit (unless you are relying on low-altitude air drag to do so, which comes with its own set of problems like, it takes a really long time and the war may very well be over by then, and is highly unpredictable so you might end up hitting your own capitol, or perhaps even more likely the ocean).
– user
Commented Sep 10, 2016 at 7:50
• Sorry, just read about that. That was a fail in a certain movie as well, I meant fired.
– Skye
Commented Sep 10, 2016 at 7:52
• Over on Space Exploration, I wrote what turned into somewhat of a newcomer's primer on orbital mechanics (though that wasn't its original intended focus). You may be interested in that. See my answer to Why does the SpaceX Falcon 9 rocket do a 180 flip for reentry?.
– user
Commented Sep 10, 2016 at 7:55
• In your case hitting a tank is not a problem however if you then decided to spare the adjacent one that's pretty hard. It's effectiveness magnify exponentially the more countries you wish to destroy given sufficient funds. Commented Sep 10, 2016 at 8:02

This concept is sometimes known as "rod from god". The rod would have to actively steer through the atmosphere no matter if the target is moving or not. (Essentially it needs to be a robotic glider.)

The way this works is an orbiting satellite (probably orbiting west to east) fires the projectile so that the projectile's orbit intersects the atmosphere. Once the projectile hits the atmosphere, it uses its aerodynamic surfaces to curve its motion (which starts out with a west to east orbit that is very similar to its satellite) downward, toward the target. Without aerodynamic surfaces to cause a sharp turn, the projectile would just careen horizontally through the atmosphere until it had lost most of its orbital velocity. You want to preserve as much of that orbital velocity as possible and change the direction to be aimed at your target.

If your target is moving, the projectile needs to track that movement. One really big hurdle for this particular projectile is that it's moving very quickly, and you want it to hit a very small target. How does the projectile know where that target is located? It is presumably radioed the coordinates of the target before it launches, but how does it keep track of target movements once it launches?

Optical tracking would require a very powerful telescope. If you want to see human sized targets, that requires adaptive optics and a telescope the size of the Hubble space telescope. Your telescope needs to be in the nose of a hypersonic missile, which is an extremely harsh environment for anything, let alone extremely precise optical sensors and transparent windows. Also, there is cloud cover to deal with, and your hypersonic passage through the atmosphere will produce some amount of incandescent plasma in front of your camera.

It probably makes more sense to guide the projectile externally, and just radio coordinate changes up to the projectile. The satellite could presumably do this, unless it's night time or the target is obscured by cloud cover or trees or buildings. Another problem is that the time it takes for the satellite to talk to the projectile gets longer and longer the closer the projectile gets to its target. The one way delay is more than a millisecond, which might be uncomfortably long.

I think the ideal situation would be for the projectile to get multiple streams of data, one stream from the satellite, one stream from its own internal gyroscopes and camera, and at least one more stream from a spotter within a few miles of the target who can actually see it.

That spotter could be a person aiming a device at the target, or it could be a flying our ground-based drone. Regardless the spotter would likely be shooting a low power laser at the target in order to determine its precise distance from the spotter. Subtracting that distance from the spotter's GPS coordinates derives coordinates for the target. The spotter's scope would continuously radio these coordinates up to the projectile so it could alter its course. The projectile would also have its camera attuned to the exact wavelength used by the spotting laser, and it would steer directly for it as soon as it was detectable. The laser would not be visible to human eyes because it would be infrared.

A really good spotter system would also have a camera watching the sky for the glare of the incoming projectile. It would measure the angle between the spotter and the projectile in order to give the projectile more precise information about its current location.

Hopefully you're getting the sense that this is all extremely difficult. While I think it's possible to do at our current technology levels, I haven't heard of anyone doing so. I don't think a 100% hit ratio is ever possible with something like this (at least until some new, unforeseen technological breakthroughs occur). When describing this system, you should emphasize the extreme difficulty of its task, and all of the complexity of the data processing that needs to happen for the projectile to hit its target.

You should also emphasize the extreme physical conditions involved. The G forces would be extreme. The tungsten aerodynamic surfaces would be glowing white hot. The camera window would need to be actively cooled to delay melting and maintain transparency.

Regarding how much damage you could cause with this kind of projectile, it all depends on the mass of the projectile and how much orbital velocity it is able to maintain during its passage through the atmosphere. The wikipedia article you linked to suggests a mach 10 terminal velocity and a kinetic energy roughly equal to the projectile's mass in dynamite. (i.e. a 10 ton projectile results in roughly the same degree of damage that would be produced by 10 tons of dynamite.) In general though, I think it's easy to say that the projectile would produce much more focused and directional damage, whereas the dynamite explosion would produce equal damage in every direction.

One other clever trick would be to have the projectile break into zillions of tiny pieces right before it impacts (unless your target is a bunker 100 feet underground). This would increase the size of the affected ground and keep the damage focused on the surface, rather than spread out under the soil.

• There is even no need for zillions of tiny pieces (which may cause unnecessary civilian casualties). Just make the rod shoot a self-propelled bullet when it gets close enough to the target, and have a spotter direct it with laser (that's already an existing technology bbc.com/news/technology-16810107 ). Commented Sep 12, 2016 at 15:38
• @Alice Wont people still die from the rod coming in at Mach 10? And then you just added a few zillion dollars to make that.
– Skye
Commented Sep 12, 2016 at 15:51
• @Alice I don't know... hitting a moving target with a single bullet while flying at mach 10 sounds awfully difficult. Or am I misunderstanding? Commented Sep 17, 2016 at 1:38

The first thing to get across is that when it comes to Kinetic bombardment you can't simply drop rods from orbit. Instead you need some mechanism to deorbit them.

Now there would be two options:

• Fire the projectile from some sort of platform in space. If this platform can hold only one charge, then it is useless after fired, so you could leave it to be junk. Alternatively you could build a platform for multiple shots, this one would be an easier target, and it may require additional correction maneuvers after firing.

• Have the projectiles be auto-propelled. This have the advantage of facilitating course corrections, which is probably what you want if you want to target moving objects. So you would mount a guidance computer on the rod, and rockets for the initial deorbit and for course correction.

The targeting system would have to be guided from an advantage point that can transmit the coordinates of the target to the projectile. If the target is moving then a stream of data is required. Listening for such stream of data would also serve as warning.

Taking the 11.5 ton figure from Wikipedia.org (which refers to a 6.1 m × 0.3 m tungsten cylinder impacting at Mach 10) the blast radius would cause total destruction in a radius of approx. 48.2m (~ 158.4 feet). Although up to 177m it will still cause moderate damage - at this distance people may get injured by glass and debris. But you need to be in the approx. radius of 32.18m to guarantee death. That means that a guiding system is required to ensure 100% chance of death of a walking/running person.

Refrerences:

# Carpet bombing

Might be an effective way to guarantee a kill over a wide area. If you predict the targets movement a bit and fire off an army of projectiles to cover a wide area. This also removes the nifty problem of aiming a Mach 10 projectile. I doubt the target would survive a few dozen metal stakes coming in at Mach 10. This is of course if you don't really care about the collateral damage. You could probably level an entire city block with it.

• A dozen 10 ton stakes coming in at Mach 10? You could level a lot more than a city block. Commented Sep 12, 2016 at 15:12

You are thinking of a "God Rod" - which I suppose from an Ordnance sense would be considered an EKV - Exoatmospheric Kill Vehicle - fancy way of saying a non-payload bearing device, from outside the atmosphere, that destroys things.

As others have linked this was an idea at one point and in theory can be effective. GEOINT, advanced telemetry in the forms of the rotation of the Earth, weather patterns and the orbit pattern could all be crunched to give you relative accuracy of something of this design.

Even modern military GPS with modern digital waveforms there will not be 100% accuracy, by the time you send the message to the satellite, feed it a 10-digit MGRS (or similar) coordinate, and give authorization, all of that plus the time to decrypt the messages may be extremely negligible but not when you are trying to hit a (relatively) small target from space with a "dumb" munition.

I have personally been with SOTACs overseas who have called in JDAMs, which is about as modern as you can get - and they still weren't pinpoint accurate, usually drifting by 10-100m, and those were launched from 35KM and lower - you are suggesting using an unguided object from 500KM+ - your margin of error just got a lot bigger even with modern technology.

Now, the other things to take into consideration, is if you are using this on a moving target it will not happen. You can have a very large rod that through kinetic energy striking the ground may be able to injure them, but an propelled rod is moving slow compared to a rocket-propelled/rocket-assisted projectile, even the advanced telemetry I mentioned wouldn't be able to predict that - especially given an unknown and erratic variable that is a human being.

The only conceivable way you could have something like this done is making the warhead/payload similar to the PATRIOT EKV - an active guiding vehicle, launched from a satellite platform. The guidance package would be like the PATRIOT in that it has small rocket motors (much like a RAP) to make small corrections, and once within a certain range where the margin of error is mitigate (aka, you are right over the poor SOB) the payload (or rod in this case) ejects/the vehicle detaches/accelerates and slams your target.

A lot of sophisticated (and expensive) technology just to destroy one building, or kill one person. Not to mention all of the implications this system would have, NORAD and any other developed nation with similar technology would be able to identify this and destroy it. There is the matter of airspace, weaponized satellite technology and how you plan on executing the C4ISR element of it come into play as well.