The rods from God's idea is insane and won't work.
We had this back when the Russians announced they were going to drop conventional ordinance from space, and everyone pointed out that they would be lucky to hit the right continent, let alone Ukraine. In order to make this actually work, you would have to have an active aiming system. Which you know, is a missile.
The launch platform can aim it and use math to account for gravity, the atmosphere and all that jazz to hit the target at least close enough. Just like we already do to safely crash/burn up space debris.
No, they can't. The atmosphere is an unknown state, different temperatures, different densities, different wind directions, none of which can be known ahead of time.
That's why weather forecasting is always approximate. You get a percentage chance that it'll rain. You don't get a definite time stamp with 100% accuracy.
We cannot predict atmospheric disturbances to the level necessary to make this a practical system. When they burn up space debris they do it "somewhere over the middle bit of the Atlantic" That's about the level of definition you get. It's not accurate at all.
Someone (veritasium?) Already did an episode on this and concluded even at like 500 feet up from ground, without an active guidance system, it's up to luck to hit within a reasonable distance, IIRC.
From a purely physical point of view, is that realistic?
If all of its energy is kinetic, it means that the energy must result from it's potential energy+any fuel it is propelled with. Ignoring air-friction and terminal velocity for free falling objects, that means that still the energy of a nuclear weapon is required to bring this thing up into space, or stored as fuel for its propulsion.
So unless the projectile is assembled in space, any rocket bringing it into space will contain at least the energy of a nuclear warhead. Gotta be a very nervous launch, knowing that any failure will result in a fire with the energy of a nuke.
The Hypervelocity Rod Bundles project proposed 6,1x0,3 m tungsten rods, weighing about 8200 kg, impacting at about 3000 m/s, meaning about 42 GJ of energy per projectile [wikipedia].
The weakest recorded nuke, the Davy Crocket Tactical Nuclear Weapon, is estimated at about twice that (84 GJ), and the largest, Tsar Bomba, at about 3 000 000x the yield (210 PJ).
That’s their point, how do you get such a heavy thing to orbital speed without spending all that energy? You can’t unless you build it from materials harvested in space.
So a little bit of looking around, and some "Close enough, fuck it" math suggests that the Saturn V over the duration of it's launch emitted about the same amount of energy (190 Gigawatts over 2.5 minutes = 2.85x10e+13 joules, close to 7000 tons of TNT at 2.93E+13 joules) as 1/3 the yield of the Fat Man dropped on Nagasaki (FM = 20,000 tons of TNT = 8.36e+13 joules).
Now I'm not math inclined, so you should take all this with more salt than your doctor recommends, but if the rocket's output is comparable to 1/3 of an actual nuke, then it's not unreasonable to think that converting all of that back into kinetic energy would get you roughly 1/3 of a nuke's output, which could be said to be "the force of a nuclear weapon." It would take a launch of something Saturn V sized or bigger to put one up there, but supposedly Starship would be up to the task if it ever stops exploding itself and/or it's launch pad.
What I'm saying is, it's plausible enough for a blurb on some article.
Gravity is not your friend. Getting stuff into LEO is still expensive af. A kinetic projectile dropped from space might have the same energy as a nuke, but it's still going to be a lot more expensive. Additionally, you don't have options on how that energy is released. It's going into the ground and that's that. A nuke (or any other explosive device for that matter) on the other hand can be detonated at a chosen altitude, or as a bunker buster if that's what you want.
The heavier the object, the more it's going to take to push it out of that orbit. If your weapon system is in LEO, you can realistically only drop a rod on a small envelope along the future trajectory of the weapon system. Polar orbits would have the best coverage, but fly over a target outside of polar regions only twice a day. In order to get a wider range of firing solutions, the projectile needs considerable deltaV for orbital changes. And again, gravity fucks you over here because deep within Earth's gravity well, changing the orbit of a massive tungsten rod takes a lot of fuel. Higher up these deltaV costs wouldn't be as prohibitive and you'd have more options for using the weapon, but that would increase the time from launch to impact into the regieme of hours, way too slow for anything.
The best solution would be to have a huge amount of rods in different orbits (akin to the spacejunk that is Starlink) to maximize the chances of at least one being able to fire on a target at any given place at any given time, but because those rods are still heavy af, such a plan is completely unfeasable.
Rods from gods will never happen, at least not around Earth.
It is simple conservation of energy. All the energy that creates the impact, must come from somewhere. A huge metal rod that lies on the ground is not going to cause any harm, aside from stubbing toes maybe.
Leaving small height differences between the rockets launch site and the final impact site aside, the energy comes either from the rocket that brings it into space, or from propellent that the metal rod uses when launched on its target (it being a missile itself). So you end up at minimum with a rocket to transfer the whole thing into orbit, that is loaded with fuel with the same energy as the energy at the impact site. Given the rocket fuel problem, it is much more fuel, as you also need to carry the fuel for the later stages of the transport rocket up too. Then you also need additional energy for the friciton and to steer the metal rod into its designated target.
Either way you end up either having to assemble the weapon in space, or having a rocket fly into space with enough fuel to release more energy than the weapon could release on impact. So in terms of the claim of force akin to a nuclear weapon, you also need fuel with enough energy like a nuclear weapon.
Gravity does not help at all. You cannot "imbue" an object in an energy field with more energy, than you spend on changing its position gainst the field.
If anyone wants some good sci-fi, I recommend The Expanse, both the books and the show. They make great use of kinetic impactors, especially Nemesis Games.
That would involve building a factory in space. If we're capable of doing that, creating a kinetic OWP with which to bombard the earth would be small ambition.
Gotta mine them in space, but there's still a whole host of other issues with the idea including aiming them, having enough stations to deploy them anywhere on the planet in a reasonable amount of time, and the other non-radioactive problems that result from throwing a fuckton of tungsten at terminal velocity into something.
I remember that this was one of the factors that weirded up the whole cold war. ICBMs are hard to aim, though in the US we were able to find a workable solution. (A Polaris could drop a retarded-descent pizza into my driveway and then conveniently dispose of itself in the nearby unused lot.)
Soviet missiles were not so accurate, so they just build bunches of them hoping to hit their targets through sheer redundancy. (This became dinner talk at Cal-Tech in the eighties since SDI was expected to be able to intercept the entire Soviet nuclear arsenal, including bunches of decoys) So their redundancy was used by General Electric to promote the missile gap, as justification why we needed to buy more GE nukes to close the difference.
This is why, I'm pretty sure, we don't really need to be too afraid of DPRK going madman with their handful of nukes. So far we've seen the Kims lob ICBMs into the pacific, but they haven't shown they could hit a given continent, let alone someplace important, and the US knows from its own experience that ICBM math is hard.
It's well within the character of the US federal government and the armed forces to go forward with an OWP platform program right now, even despite the risks and ethics concerns, sadly.
True, but to hit things within the atmosphere it needs high mass and low drag. The ISS re-entering would have high mass but high drag, and most of it would fall apart when entering and be slowed down by drag so the energy gets spread through a long streak on the atmosphere instead of on the target
Meteorite: As may be concluded from the air pressure, the atmosphere's material is equivalent to about 10 m of water. Since ice has about the same density as water, an ice cube from space travelling at 15 km/s or so must have a length of 10 m to reach the surface of the earth at high speed. A smaller ice cube will be slowed to terminal velocity. A larger ice cube may also be slowed, however, as long as it comes in at a very low angle and thus has to pierce through a lot of atmosphere. An iron meteorite with a length of 1.3 m would punch through the atmosphere; a smaller one would be slowed by the air and fall at terminal velocity to the ground.
talking about tungsten we're looking at minimum 50cm long darts, however this ignores atmospheric erosion
Pop scientists routinely mis-represent facts to make warfare seem unappealing and lame, this is due their 'sense of morality' (read: crying baby noises).
For example, Carl Sagan warned that operation desert storm would cause a (non)nuclear winter and mass famine in Asia.
Why in the hell would anyone bother though? First you got to launch all that mass into a stable orbit. Then you got to assemble the delivery system with the mass as it's most definitely too heavy for a single launch. Then you need fuel to deorbit the mass when you launch because things in stable orbits tend to want to stay there. Then you wait for the mass to deorbit because we couldn't afford to send enough fuel for a rapid deorbit. Also wait to launch till optimal trajectory for your target is achieved and hope that it's not too far side to side from your orbital path because that means even more fuel to deorbit. Also anyone with a halfway decent telescope sees your weapon just sitting there in orbit not to mention being assembled so now it's got a massive target painted on it at all times and is an easy casualty of first strike.
Or we could use the icbm's that are a proven tech, easier to hide though that's not foolproof, can be made mobile, much much more numerous, easier to protect from attack, much cheaper than launching tons of solid metal into orbit, and can strike anywhere on the globe within an hour.
I mean, launch costs are going down over time.
It might make much more sense to put many warheads up with a reusable system like falcon (~3000$/kg) than it does to maintain a fleet of necessarily single-use systems like minuiteman (7,000,000$/~300kg = 23,300$/kg). You might well be able to put four warheads (with an equal mass of de-orbiting propellent into orbit - ~1.7 km/s given solid fuel) for the same cost as one ICBM.
I remember how in the book people show up to the announced site to watch it like tourists, and of course they get atomized. Same idea appears in Independence Day. I always thought “that would never happen, people aren’t that stupid”, but the pandemic changed my mind on that front.
A system described in the 2003 United States Air Force report called Hypervelocity Rod Bundles[10] was that of 20-foot-long (6.1 m), 1-foot-diameter (0.30 m) tungsten rods that are satellite-controlled and have global strike capability, with impact speeds of Mach 10.[11][12][13]
The bomb would naturally contain large kinetic energy because it moves at orbital velocities, around 8 kilometres per second (26,000 ft/s; 8,000 m/s; Mach 24) in orbit and 3 kilometres per second (9,800 ft/s; 3,000 m/s; Mach 8.8) at impact. As the rod reenters Earth's atmosphere it would lose most of its velocity, but the remaining energy would cause considerable damage. Some systems are quoted as having the yield of a small tactical nuclear bomb.[13] These designs are envisioned as a bunker buster.[12][14] As the name suggests, the 'bunker buster' is powerful enough to destroy a nuclear bunker. With 6–8 satellites on a given orbit, a target could be hit within 12–15 minutes from any given time, less than half the time taken by an ICBM and without the launch warning. Such a system could also be equipped with sensors to detect incoming anti-ballistic missile-type threats and relatively light protective measures to use against them (e.g. Hit-To-Kill Missiles or megawatt-class chemical laser). The time between deorbit and impact would only be a few minutes, and depending on the orbits and positions in the orbits, the system would have a worldwide range. There would be no need to deploy missiles, aircraft, or other vehicles.
In the case of the system mentioned in the 2003 Air Force report above, a 6.1 by 0.3 metres (20 ft × 1 ft) tungsten cylinder impacting at Mach 10 (11,200 ft/s; 3,400 m/s) has kinetic energy equivalent to approximately 11.5 tons of TNT (48 GJ).[15] The mass of such a cylinder is itself greater than 9 short tons (8.2 t), so the practical applications of such a system are limited to those situations where its other characteristics provide a clear and decisive advantage—a conventional bomb/warhead of similar weight to the tungsten rod, delivered by conventional means, provides similar destructive capability and is far more practical and cost-effective.[16][17][18]
The highly elongated shape and high mass of the projectiles are intended to enhance sectional density (and therefore minimize kinetic energy loss due to air friction) and maximize penetration of hard or buried targets. The larger device is expected to be quite effective at penetrating deeply buried bunkers and other command and control targets.[19]
The weapon would be very hard to defend against. It has a very high closing velocity and a small radar cross-section. The launch is difficult to detect. Any infrared launch signature occurs in orbit, at no fixed position. The infrared launch signature also has a much smaller magnitude compared to a ballistic missile launch. The system would also have to cope with atmospheric heating from re-entry, which could melt non-tungsten components of the weapon.[20]
The phrase "rods from God" is also used to describe the same concept.[21] An Air Force report called them "hypervelocity rod bundles".[2]