This peisode is brought to you by Raycon. To paraphrase Ellen Ripley of Aliens “Sometimes you need to nuke the entire site from orbit. It’s the only way to be sure…” So today we are returning to our Space Warfare and Future Warfare series, looking at Orbital Bombardment, something that might come into play as a regular weapon of war in the next century. And we’ll be looking at that in a few weeks too, with an episode on the Next Century of War. At the time I’m writing this, near the end of 2020, I just had occasion to give a guest lecture and talk at the US Air Force Academy, and unsurprisingly it got me thinking on the future of warfare again, particularly its progression into orbital space. On the personal side, it reminded me that it's been a decade since I left the Army and two decades since my first time working for the military, as a research intern for the Air Force at AFIT back when I was 19 in my senior year as a physics major at KSU.
A few years later I left grad school where I had been working toward a Ph.D. in theoretical physics to enlist in the US Army, where I finished out that decade. At the time there had been a lot of talk of going to the Moon again, and the urgency of replacing our shuttle program, neither of which has since happened, and it reminds of popular expression in the military, “Hurry Up and Wait”, as it so often seems like everything involving the space program seems like both a constant rush of improvement and a constant test of patience.
Another thing I noticed in my time in the Army, besides its fondness for acronyms, was that everything was always the most important thing. Almost every bit of advice I got from my mentors was phrased as “The Most Important Thing to know about being a soldier is…” or “The First Rule of Warfare is…”. Many were contradictory, and nothing was ever the second most important thing or second rule, and there seemed to be hundreds of these little gems of wisdom, and that is the origin of our long-running gag on the show of the First Rule of Warfare, which includes a few dozen first rules at last count. One of my personal favorites, the unofficial motto of my old field artillery unit and of our show nowadays, is that if Brute Force isn’t working, you’re not using enough of it. That is both very descriptive of what is involved in orbital bombardment and its exact opposite, since it allows precise and surgical strikes.
The First Rule of Warfare is always to seize the high ground, you cannot get much higher than orbit, and it is a great place to launch attacks from. Though as we will see today, it has its own weaknesses and vulnerabilities too, an orbital weapons platform is very vulnerable to attack from groundside facilities and anti-satellite or ASAT weapons. We see the use of orbital bombardment a lot in science fiction, and today we’ll consider some popular examples and ask how realistic they are from a science perspective too, as well as a practical military perspective.
It takes immense amounts of energy to get things into orbit, and anything up there has access to that energy. What comes up must come down, unless it is in a stable orbit, which still tends to degenerate with time, and when it comes down it's picking up as much kinetic energy as you used putting it up there. Keep that in mind because we can’t get more energy back from a mechanical impactor than we put into it in the first place.
Exceptions can be made, though, if we’re talking about propelling that object towards Earth, which adds extra energy into the impactor. We will discuss a few different approaches to orbital bombardment today and how it might get used, as well as means of defending or countering it. Now first it is important to understand that things don’t just hang over planets, barring some clark-tech anti-gravity drive, or from some structure like an orbital ring. So what we’re almost always discussing is some spaceship or weapons platform orbiting the target planet, or moon, or asteroid, and firing down on it. Except you’re not actually firing ‘down’.
You, yourself, are whirling around the planet, possibly in a nice simple circular orbit, possibly in something rather elliptical, and what you’re actually doing is kicking your projectile into a different orbital path, one that intersects with the planet below and preferably with a specific part of it. Now this might be something moving far faster than orbital speeds, like a laser beam or simply a slug fired out of a space catapult or mass driver or rail gun at speeds far in excess of orbital craft. In this case so long as you have line of sight you are effectively firing in a straight line, or as close to it as a bullet is. This is the best approach if you have the technology and energy budget for it, because you retain all that orbital velocity (which you have already paid for) and is essentially what we see in science fiction most of the time. There are a couple of problems though.
First, you still have targeting windows since you are orbiting. Second, things moving fast into an atmosphere suffer even more abuse from re-entry and might burn up or get knocked off course easier. It would be very hard to build something designed to enter an atmosphere at thousands of kilometers a second that could have exterior guidance and sensor packages that wouldn’t be wrecked by tearing through all that air at those kinds of speeds, so precision strikes aren’t simply a matter of dropping a rock on your target and very clever cutting-edge engineering and materials would be needed even to attempt something like this. Beam weapons might do better but have the issue of scattering in air, not to mention thermal blooming, which is a big issue with high energy beams. Air distorts beams, air being super-heated by a beam distorts them more and more chaotically. That’s a major issue with trying to shoot down ICBMS with lasers, and it is just as severe from orbit to ground as ground to orbit.
The other thing is if you have weapons able to move that fast and through an atmosphere with any precision, it tends to imply the other side has them too, and a satellite or spaceship in orbit is a heck of a lot more vulnerable than some groundside facility buried under a mountain or some submarine that only surfaces long enough to shoot you. Even more so since spaceships have to worry about moving all their mass around, including their protective armor, so generally can’t afford as much of it as ocean-going vessels, let alone a fixed facility. They are shooting up, and you are shooting down, so everything they send has less energy from clawing its way out of a gravity well and everything you have gains energy in the descent.
And that’s a lot of energy, but when we’re talking about energy beams, it is next to nothing, the speed of light is tens of thousands of times faster than most planet’s escape velocities. As for solid slugs or missiles, if we are talking about ones moving many times orbital speeds, then the energy loss or gain from being groundside or in orbit gets to be fairly minimal and the reality is that while a fleet of kilometer long warships with guns as big and wide as skyscrapers sounds nasty, and certainly is, an entire industrialized planet is going to just tear through that like it was a swarm of gnats if both sides are on the same approximate technological level. The disadvantage of being at the bottom of a gravity well is all your strikes are a bit weaker and all theirs a bit stronger, but the advantage of being at the bottom of a gravity well is that you have a lot more mass to be using as armor and weapons. We looked at this more extreme case in our episode Planetary Invasions, and the short form is that while armadas and orbital bombardment are awesome if your fleet has a big technological edge or is invading and bombarding some lightly populated or low-tech colony world, if you try that on some industrialized planet you are only going to succeed in causing a navigational hazard from the wreckage of your fleet.
Getting into a shooting match with a planet from orbit violates the first rule of warfare, “Don’t Get Shot, that’s the other side’s job”, which is best achieved by doing all your shooting from too far away for them to easily aim at you. Alternatively a planet can’t move around to avoid being hit. In space warfare, especially the high-tech kind involving folks able to move at a decent fraction of light speed, the disadvantage of being at the bottom of a gravity well is that all that mass is hard to move and easy to hit. That does sadly spoil a lot of classic Science Fiction, especially Space Opera, though if you want to occupy a planet you eventually need to get into orbit around it and presumably do some bombardment and we’ll discuss that scenario later, but let’s consider the more near-term and modern-tech approach for now.
When dealing with weapons orbiting and deploying at fairly similar speeds, the usual notion is to have the orbiting weapon be in a stable orbit, be it circular or highly elliptical, low orbit or high orbit, and transfer to an orbital path that now intersects the planet. That is easy enough to do, the tricky part is getting the timing right to hit the place you want to hit and making sure it can arrive at its destination on target and without burning up. Tungsten rods are a popular option for this, Tungsten is fairly cheap as dense and heat-resistant materials go and isn’t fissile so doesn’t raise any nuclear concerns.
Such an object would slam into the ground at about Mach 10 and be very good at penetrating hardened targets. You may have heard of this weapon discussed as Project Thor or a “Rod from God”. It’s not going to match the firepower of a nuke, but is worth more than its weight in chemical explosives. It also doesn’t violate the Outer Space Treaty’s ban on deploying chemical, biological, or nuclear weapons from space. Last I heard the engineers at SpaceX seemed confident they were going to get launch cost to orbit down to under a thousand dollars a kilogram, possibly well under, so the prior cost concerns on such tungsten rods costing hundreds of millions of dollars a piece to get into space are probably on their way out.
If it costs a few million dollars to get a rod into orbit, well that’s competitive with a bunker buster bomb, the various Massive Ordnance Penetrator, or MOP, bunker buster bombs generally cost a few million apiece too. What’s more, that’s the price to get them up from Earth, it’s cheaper to fly one in from the Moon or some tungsten rich asteroid, nor do you have to use tungsten, uranium is a popular suggestion and plenty of other metals, alloys, and ceramics would work. It’s probably a lot easier to set up an off-Earth manufacturing chain for metal rods than sophisticated bombs full of explosives, so these are likely to see a future in warfare. They do not match an atomic bomb, let alone a hydrogen bomb, in destructive potential, but they definitely make a good tool for getting into armored targets. Don’t assume incidentally that you can easily hollow one out and fill it with explosives or guidance packages either, such things don’t handle the kind of stresses and heat a kinetic weapon made of a solid slug of simple metal can. That said if you can get something in there that can act as a decent fuse or detonator, some ten ton rod of metal suddenly shattering into bullet-sized hypersonic fragments, presumably around a million of them, either once inside an armored bunker or high up in the air would be a vicious anti-personnel or even anti-vehicle weapon.
If you had one that could reliably fragment as air bursts then deploying larger ones or several of them would probably let you chew through a city. In an industrialized orbital and cislunar economy, something we will pass through on our way to settle our solar system and the galaxy beyond, there should be a point at which producing and shipping these rods ran to mere thousands of dollars a piece, allowing you to keep arsenals of millions of them on hand, and they do then become a great weapon for both groundside attacks and orbital strikes on things like space stations too. Of course you can counter one by good detection and interception, and nobody with a serious presence in space wants a major conventional war in orbit either as it sets off Kessler Syndrome, a cloud of debris in orbit making it hard to pass through without heavy armor or sweeping it clear with something like a laser broom. Such rods are good for cracking into such armored targets though.
Kessler Syndrome events are something parallel to MAD or Mutually Assured Destruction concepts of the Cold War, in that any major player can set one off, but we also want to keep in mind that thinly armored spaceships and space stations or habitats is not something we should expect to exist indefinitely. Such rods become potent weapons exactly because mining and shipping metals from the Moon or asteroids gets so cheap, so shipping in armor plating gets cheaper too, and while a chunk of metal fragments zipping around a ten kilometers a second sounds horribly dangerous, it isn’t the same as a projectile forged with penetration in mind and shot right at you, and it is quite likely a lot of stuff built in orbit will start to include levels of armor and point defense able to handle that sort of debris, or even those sort of kinetic strikes. On the other hand, some components simply aren’t easy to armor. Solar panels, radiators, sensors, and antennae would likely need to quickly retract inside your armor when RADAR or LIDAR detects incoming debris. Perversely, once you retract your sensors to protect them from debris, you can no longer see incoming debris.
Also your rocket engine bell nozzles better not take a hit while thrusting because they’ll be running at their material limits. Even small impacts would likely destroy a nozzle. Ships in motion, accelerating, decelerating, or maneuvering, are very visible and very vulnerable targets compared to objects simply drifting. Now I mentioned how they aren’t as powerful as a nuke and barring the Outer Space Treaty there is good reason to put your nukes up there. ICBMS have good reach but are limited, compared to an orbiting device, and usually maintaining those rockets fueled-up for short notice launch is far more costly and difficult than building and maintaining the actual nuclear warheads. Incidentally this is not the same as FOBS, or a Fractional Orbital Bombardment System, which is just launching a nuke into orbit briefly on its way back down, as a way of extending its range to anywhere on the planet and concealing the target location, at least in terms of the launch path not revealing it.
Folks sometimes get confused by this because it sounds like something that would go higher than an ICBM but rather it’s the exact opposite, a depressed trajectory to no more than 150 kilometers of altitude, precisely because it is at orbital speed, while alternatively ICBMS go almost ten times higher and fall back down. ICBMS only reach about 6 or 7 kilometers per second, decently slower than orbital speed, so it can be confusing why they go higher, but the key thing to remember is that while things in orbit might only be a couple hundreds kilometers up, all that rocket fuel isn’t to get them that high, it’s to get them going sideways fast enough to fall around the planet perpetually. We only put them high up to get them over the air drag of the atmosphere. Ignoring air drag on the way up, you only need to shoot something at a couple kilometers a second to get it up to those altitudes, so it will fall down to the ground.
That’s just fine for shooting things up there incidentally, since they are moving sideways at several kilometers per second, if you fire some over-powered flak cannon up like a fountain in their way, or a pod that’s more aerodynamic and will explode as flak, all that flak needs in terms of lateral velocity is enough to spread out in a cloud the orbiting satellite, tungsten rod, defense platform, or whatever will pass through and be damaged by the cloud of flak before the flak falls back down. Incidentally this is essentially the same way you counter more distant strikes too, like interplanetary bombardment, asteroid strikes, or relativistic kill missiles sent in from deep space. Those are all going so fast that it only takes them running into something to explode, so you defend by simply putting things in the way that are much smaller and cheaper and need little propulsion either. Orbital bombardment has the advantage that there’s very little time for detection, more so since the planet’s horizon can obscure the weapon as it approaches. Bunker buster rods from god and atomic weapons aren’t the only things orbital bombardment is good for. A popular trope of science fiction is sending down drops pods with troops in them.
So, you might want to be using this for some non-military purpose like sending in emergency rescue personnel or supplies. For that matter, the Rod from God might be a good way of excavating – it's weird to think of using orbital strikes to cut a road through a mountain range or dig a hole for a building’s foundation, but we use explosives for these often enough anyway, and it might be very handy as a tool for terraforming other worlds. Now back on the notion of drop pods for troops, you obviously can’t be dropping someone inside a hollowed out metal rod, even if it’s a robot or cyborg able to handle way more gee force. This is called lithobraking, as opposed to aerobraking, and it's when you slow something down by ramming it into rock or earth instead of by air drag. Needless to say not much is going to survive ramming into the ground at several kilometers per second, though if it did, that’s nothing you want to pick a fight with! Anything that walks out of a crater it made probably is something you should run away from and hope it doesn’t follow you. You can actually make stuff that would survive that impact by applying the same concept as an air bag, though in cases like that your pod might be a very long rod that basically acts like some cross between a rifle barrel and a spring, as its whole job is to try to extend the period the cargo of the pod experiences the braking action as the pod itself rams into something.
But, even if you made one that somehow minimised the g-forces experienced by the troops inside to something survivable, they’re still going to have to dig themselves out of the crater created by the impact, one with molten materials trying to dissolve their boots while they’re at it. That violates the first rule of warfare: don’t create a hellscape for your troops to deal with before they even encounter the enemy. Though I suppose they could use the crater as a defensive dugout.
We also see concepts like that in boarding torpedoes in some science fiction and I think they’d be most realistically viable for attacking spaceships, space stations, or asteroids where those folks in the things are decelerating only at a rate they could survive, from a speed that could be slowed down from in a few hundred meters. Humans can’t handle more than 10-g of deceleration without passing out, but we can handle more without dying and we can build machines, and yes probably cyborgs or genetic superman, able to handle a lot more. At 10-g of deceleration a human can decelerate down from 10 kilometers per second in 100 seconds, so an orbital drop pod decelerating at that rate from that speed has to pour on the gas at an altitude or distance of 500 kilometers. That still makes it a hard target to hit given it’s probably jittering around as it does this and would still be moving as fast as a speeding bullet till that last kilometer or so.
Also that 10 g’s is just to avoid passing out while experiencing protracted acceleration or deceleration. While humans in car crashes often experience over a hundred g’s and live or even walk away, the first rule of warfare is: don’t send your troops into battle feeling like they’ve just walked away from a car crash. So even 10g’s is probably a bit on the high side for a practical troop drop. Still, if the folks, or robots, on board could handle a 1000-g acceleration, and we can build some machines able to handle that, like fuses on artillery rounds for instance, then they only need 1 second to drop speed and can start their braking at 5 kilometers out. How you’re actually slowing down from these speeds is tricky, but my best guess for an ideal method that involved something like a small pod would be a parachute made very large and out of something of very high tensile strength like graphene and carbon nanotubes.
That parachute is an easy but irrelevant target, poking a million tiny holes in a kilometer wide drop pod parachute wouldn’t matter much, and note that this does not require a gentle landing that offers the enemy plenty of chances to shoot you as you descend slowly through the air. You’re potentially undergoing the same horrible g-forces we just talked about, but on an automatic timed basis to slow you to a crawl right before hitting then maybe using mild lithobraking or rockets to finish the drop. This strikes me as much more useful for rapid delivery of supplies to a combat zone or rapid delivery of people to an emergency where no one is shooting at them, or at least no army is shooting at them with high-tech weapons meant for killing paratroopers. Otherwise I’d tend to think dropping bombs, not combat troops, would make more sense in most cases, but then again you always want your troops in-theater quickly, just in case folks start trying to shoot them even if it previously seemed safe, so this might be the method used, it’ll save fuel and a bunch of giant parachutes certainly makes clean radar returns and targeting a nightmare. Of course you might also be fighting your way down in waves.
As we often point out in other episodes on space colonization, it is likely planets will have massive orbital infrastructure, and indeed might have far more people and far more industry up in orbital space than down on the planet. They also might have active support structures like space towers and orbital rings, or even live in a multi-layered matryoshka world, in which case your orbital bombardments and or actions might be happening at much slower speeds and smaller distances. The same would apply to attacking moons or colonized asteroids and those are likely to massively outnumber planets, so presumably be more common targets in conflicts. Dropping from an Orbital Ring a hundred kilometers up is no different than dropping from a plane except you need that initial protection from vacuum and cold, you are falling through very thin air so you can get quite fast, but this isn’t re-entry speeds, and orbital rings can frankly be at any altitude, as can space towers, see those episode for details, but trying to fight your way down a hundred kilometer tall space tower with 30,000 floors strikes me as a nightmare scenario for an infantry regiment, on offense or defense. Frankly, this strikes me more as a generational war than a battle.
We tend to think, from the sheer scale of the weapon powers involved, that planetary invasions would be quick affairs, at least to get groundside, but it really might be the sort of thing that takes generations of travel to get to the orbital space of the planet, decades of fighting to claim the thousands or millions of orbital stations and habitats, and just as long fighting your way down to the ground, relying on the defender not wanting to trash their own ground-to-orbit transport systems like orbital rings and towers as cover for seizing them one slow and brutal footstep at a time. Remember again what we said earlier, as massively powerful as orbital bombardment seems, that planet probably can punch back much harder, so it wouldn’t be that surprising to deploy a strategy that focused on seizing and holding little bits of valuable real estate one bit at a time, discouraging them from deploying their heaviest weapons, possibly to the point that it was more like an invasion by migration. That brings me to the first rule of warfare: Keep your wars short. Don’t plan a war with troops that start off as teens and end up fighting until they’re octogenarians looking for an old folks home.
It is hard to say of course, it might be fast or slow, but our usual assumptions about future warfare are also that it's more automated, faster, and more precise, and that might not turn out to be the case across the board, nor necessarily stay the same over time. Every century sees new innovations in warfare, often turning the prior fundamental strategies, truths, and rules on their heads, and we’ll see what the Next Century of War might hold in our next episode of the series. Whatever happens, though, always remember the first rule of warfare! We’ll get to our schedule and announcements in a moment, but first if you’re looking for a good pair of earbuds with noise isolating features, without dangling wires. and at half the price of other premium earbuds, I’d recommend trying out Raycon’s Everyday E25 Earbuds.
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and Raycon has a 45-day free-return policy. Whether you’re taking up a new hobby—or just want to make your day-to-day a little more comfortable—Raycons are the perfect way to bring premium audio to everything you do, and if you’d like to give them a try, click the link in the description box or go to buyraycon.com/isaacarthur to get 15% off your Raycon purchase. So today we were looking at Orbital Bombardment and we will continue to exam the future of warfare in the coming months, and we will probably end up doing an episode devoted to the Space Force at some point. I mentioned that I had the privilege of guest lecturing at the Air Force Academy some months back and I’ve also had the chance brainstorm with some folks about industry and defense in space, and I wanted to give a quick shout out to my friend Colonel Peter Garreston, author of “Scramble for the Skies: The Great Power Competition to Control the Resources of Outer Space” and editor of “STATE OF THE SPACE INDUSTRIAL BASE 2020”.
I’ll link to those in the video description and the 2020 report is a great outlook at the situation in space development right now, I hope you’ll find Peter’s work as insightful as I do. Again we will be looking more at future warfare in two weeks, in “the Next Century of Warfare”, on March 4, but before then we will be asking if it is possible to colonize solar systems around Red Giants and other short lived massive stars, then we will finish February out with our Livestream Q&A, Sunday, February 28th, at 4pm Eastern Time. If you want alerts when those and other episodes come out, make sure to subscribe to the channel, and if you’d like to help support future episodes, you can donate to us on Patreon, or our website, IsaacArthur.net, which are linked in the episode description below, along with all of our various social media forums where you can get updates and chat with others about the concepts in the episodes and many other futuristic ideas. You can also follow us iTunes, Soundcloud, or Spotify to get our audio-only versions of the show. Until next time, thanks for watching, and have a great week!