How hard would it be to “nuke em from orbit”? What’s required?
(Yes, I’m aware of kinetic energy weapons. Rods from God, Flying Crowbars et. al. Let’s stick with a nuke please.)
Nuke who from orbit?
Stranger
Em.
(Extra characters screw you, Discourse.)
Intercontinental ballistic missiles travel at about 24000 kilometres per hour, in a suborbital loop.
Objects in LEO travel a bit faster, at 28000 kilometres per hour.
To successfully nuke something from orbit, your orbital nukes need to compensate for an extra velocity of about 4000 kilometres per hour. I’m sure someone has already made studies of this design problem.
Any spacecraft designed to reenter from orbit has already solved this problem. For Mercury and Gemini, they had dedicated solid propellant reentry motors which reduced the speed to suboribital. For Apollo (from orbit) the Service Module Propulsion System engine was used to reduce speed before it was separated from the command module. (From Lunar return the trajectory of the CSM was aimed for direct reentry without going into Earth orbit.) For the Space Transportation System (“Shuttle”) the Orbital Maneuvering System (OMS) was used to slow the Orbiter Vehicle for reentry.
Although ICBMs generally fly a suborbital (roughly elliptical) ballistic trajectory after boost, they fly to a high altitude well above most suborbital vehicles or Low Earth Orbit. ICBMs can be and are repurposed to deliver spacecraft to orbit (and, with a little help from ‘kick’ motors, even beyond; the Peacekeeper-based Minotaur V vehicle delivered the LADEE spacecraft to Lunar orbit). Large ICBMs can also be used to put a nuclear armed reentry vehicle into a short duration orbit in what is termed a Fractional Orbital Bombardment System; in essence, the payload is put into a section of orbit and then deorbited to hit a designated target. The purpose of this is to delivery an attack from an unexpected direction such that over-the-horizon radar early warning systems don’t detect it or discriminate from a satellite until it is on terminal track. A version of the Soviet/Russian R-36 (NATO: SS-18 ‘Satan’) was designed to do this, and there were studies to perform this with both the LGM-25C ‘Titan II’ and LGM-118 ‘Peacekeeper’ ICBMs (although never tested or deployed).
Stranger
Thanks!
The other problem is logistics; a spacebattleship in LEO would only be able to observe a very limited portion of the surface at any one time, and sending a nuke to a more distant object would require a siginificant boost - maybe sending the missile into a much higher suborbital trajectory. Is there much benefit to launching from orbit if your ship is on the other side of the planet, orbiting at a different latitude?
The angular aspect of the Earth from the ISS at an altitude of around 420 km is ~140°, so from there an astronaut could see about 1/4 of the Earth’s surface at any time. If you are using a nuclear weapon you presumably only need to know the approximate location of the target (unless you are shooting at something mobile such as a carrier group) and the trajectory from orbit is going to be a spiral that is at least some significant fraction of the Earth’s circumference. The bigger problem is a target that is not relatively close to the azimuth of the orbit; anything that is far to one side or another of the orbital trajectory is going to require substantial impulse to change azimuth or waiting until it is sufficiently close to when the trajectory passes close to the target. If you have a fairly low azimuth angle and your target is at a higher latitude, the impulse to reach the target will be significant because it may have to negate most of the momentum it started with in the launching ship’s orbit.
Stranger
I would assume that not having crew on board potentially simplifies some of the re-entry arrangements - acceleration forces don’t have to be tailored to preserve meatbags.
Let’s assume I have a Aliens Colonial Marines battleship in equatorial LEO (staffed with meatbags) that can launch nuke missiles. How capable do the missiles need to be reach any place on the planet?
How quickly? Just wait less than an hour, and your ship will be on the other side of the planet anyway. And if your ship’s orbit is highly inclined (at least, an inclination equal to your highest-latitude potential target), you’ll eventually pass directly over any given point (at least, directly enough for nuking purposes)
Semi related question, how does one foresee a fusion power plant (just 10 yrs away!) Getting damaged in such a way that it causes a thermonuclear detonation yielding 40 megatons?
Well, it certainly alleviates the need to keep accelerations within human tolerances, carry a habitat system, or protect against dynamics that are harmful to people, and you can almost arbitrarily build a reentry vehicle and nuclear package that can survive any plausible acceleration or dynamic environment. The acceleration, however, is going to be limited by the thrust available by your propulsion system, and as a general rule the greater the specific impulse (a measure of the propellant mass efficiency of a propulsion system) the lower thrust your propulsion system is going to have because high thrust systems tend to have higher molecular weight exhaust products. Solid rocket boosters have been developed which exceed 100 g and going supersonic before they leave the launch rail or silo, but the also only fly for a few seconds before being expended.
There is not a simple answer to the that question but something that should be understood is that a reentry vehicle that is released from the spacecraft isn’t just going to fall down onto the planet below; absent of any additional impulse it will just continue in orbit along with the spacecraft. In order to descend and hit a target it has to be slowed, and to hit something that is to the side of its orbital track requires additional impulse to change the azimuth (angular plane) of the trajectory. How much depends on how fast you want to hit the target and the details of the starting orbit relative to the location of the target. You can calculate this roughly from the vis-viva equation for an ‘orbit’ that would intersect the target plus the orbit cranking calculation for the plane change but the details can be quite complicated even before you consider the aerodynamic effects of atmospheric reentry. At a minimum, your missile needs to be capable of reducing the orbital (tangential) speed to less than 7 km/sec or else the missile will continue to fall above the horizon.
It can’t. The difficulty with all viable forms of power-generating nuclear fusion is actually keeping the plasma constrained and at sufficient temperature and pressure conditions to fuse at all. A thermonuclear weapon does this by actually imploding fuel (using a fission reaction to provide sufficient X-ray yield), which does creates this environment for only a few “shakes of a lamb’s tail” (one shake is 10 nanoseconds) after which the system is consumed by the plasma and radiation flux. A magnetic confinement fusion system that lost plasma containment might accidentally release a burst of hot plasma that would destroy the reactor and damage surrounding facility but it wouldn’t produce megatons of TNT equivalent destructive energy, and an inertial confinement system using lasers or light ions would probably just fail to get to fusion conditions at all.
Stranger
Less than an hour is all some farmboy needs to stuff a torpedo down your exhaust port.
So, there must be some reason all nuke-armed silos, submarines, and aircraft are manned by human beings. Is nuclear Armageddon something we want to entrust to a fully automated (and potentially hackable) system?
Werner Von Braun was a strong proponent of the idea of an orbiting nuclear arsenal, so I assume at least some factions in the US military were considering it. Von Braun wrote an article for Life magazine sometime in the late 50s that was nominally about the challenges of manned space flight, but near the end he couldn’t help but wax enthusiastic about nuclear-amed space stations that would, as he saw it, give the US dominion over the entire planet. It was not an uncommon sentiment during the height of the Cold War.
You mean this guy?
von Braun was a proponent of a lot of things that upon reflection don’t represent the best in critical thinking and moral philosophy. An orbiting nuclear arsenal has a number of issues (maintenance and replacement/return/recycle of weapons, defense against attack, the cumulative effect of energetic cosmic rays and solar protons on electronics, et cetera) and the United States and then-Soviet Union didn’t seem to have much of a problem keeping the world under threat of nuclear annihilation without orbital weapons.
Stranger
Hey, I didn’t say I agreed with him! 
In fact, that article reflects the militaristic sentiment of the Cold War era in a rather shocking way, and Von Braun was even more aggressively militaristic than most.
Incidentally, I dug into my archives and found the article. I had misremembered a couple of things – it wasn’t an article by Von Braun, it was an article quoting him, and it wasn’t the late 50s, it was from the issue of August 31, 1953. This is part of the pertinent text:
The satellite station, says Von Braun, looking the U.S. military leaders straight in the eye, will pay off as nothing has done since the time of the Roman legions. If placed in its orbit by the U.S., it will give the U.S. a permanent military control of the entire earth. No nation will challenge the power that looks down upon it from an artificial moon. No nation will attempt to challenge it; the earth will enjoy pax Americana and can beat its radars into television sets.
The satellite station, explains Von Braun, will provide the two essentials of successful war: observation and bombardment. It will swing around the earth once every two hours, and as the earth slowly turns beneath it on its own axis, every part of its surface will come into view.
… Although Von Braun has won an enormous following among lay enthusiasts who dream of hot-rodding off the tedious earth, in more informed circles he is no hero. His proposal gives other guided missile men cold chills … They know that each forward step is difficult and dangerous, and they believe that Von Braun proposed to take one thousand steps as if they were one.
I always have viewed Von Braun as someone who was so enamored of rocketry, that he’d propose just about anything that would let him and his team build rockets to launch it into space.
V2 rockets, Moon landings, orbital nuclear weapons (which the Soviets did do with the Fractional Orbital Bombardment System (FOBS), for what it’s worth), all are examples of things he backed because they would fund and keep him and his crew in business building and launching rockets.
Just for the sake of clarity, FOBS is a ground-based system that delivers the payload to an orbit, and then deorbits later in the trajectory. This is distinct from space-based orbital weapons that are permanently stationed on-orbit.
There is no real advantage to space-based nuclear weapons except that they can be deployed without a boost track that can be spotted by early warning infrared surveillance satellites. The tradeoff for this is vulnerability, lack of easy maintainability, the cost of deployment, and of course instability in the deterrence regime because the only real purpose is to perform a disarming first strike.
Stranger
Yes, several problems -
If someone is going to develop nuclear weapons (dear leader?) what would a world-dominating USA do about it? Start a war by bombing their nuclear plant? That only works for Iraq. Then the facilities are put deep underground.
Obviously, anyone planning nuclear weapons would also need to protect themselves from the USA’s orbiting platform, as well as their own delivery system, and so would also invest in orbital rockets. So now, are you also going to bomb any country working on large rockets?
Pretty soon it starts to look more like a world dictatorship.
The orbiting platform is vulnerable - it does not even have to be a nuclear attack - conventional explosives will take out an orbital platform unless it’s made of a huge amount of armor launched over many rockets, many years. It’s not even necessary to use explosives. “accidental” kinetic collisions could do some interesting things. Once you allow another country to place things in orbit, you are a sitting duck for someothing in a higher orbit.
(What was that old sci-fi story where two sides were firing guns at each other on an asteroid, until the discovered that most of the bullets were in a ground-skimming orbit and it was unsafe to fly to or from the surface. There- we have another use for StarLink)
The orbital trajectory of "nuke from orbit is not really difficult. Pick launch point A from the platform orbit, and impact point B on earth, connect A and B with an orbit, allow a slight deviation for reentry deceleration and then determine how much specific impulse is needed to make the change from orbit to trajectory orbit.