sevenperforce

Agree. Nothing wrong with wind and solar — they are important — but nuclear is arguably “greener” than both. And incredibly vital.

That might have been the case during the Cold War but surely that’s not true anymore. You can’t tell me that all nuclear-capable countries don’t have satellites with 100% coverage that can instantly identify a launch and determine its trajectory. Israel has an established Samson Doctrine. They have a significant thermonuclear arsenal but they will not introduce nuclear weapons into the Middle East unless they are facing an imminent, valid, existential threat. But is a nuclear exchange in the upper half of the northern hemisphere a good reason to start launching? Surely not.

Yeah, the low strikes don’t make much sense. Even with strategic (as opposed to tactical) strikes, it doesn’t make sense to target anything non-military. Obviously Russia is currently hitting non-military targets in Ukraine but Ukraine cannot exactly hit back. And the USA won’t target non-military installations regardless. Even in a worst-case-scenario, I don’t see any reason why any countries other than NATO and Russia would get involved. I mean absolutely yes all of this. I can’t see any reason why any sitting US president would launch a pre-emptive strike on China. Remember that in the United States, the president has 100% control over nuclear launches. Even though the United States officially reserves the right of First Use, that was in the context of tactical weapons, not strategic ones. No presidents we’ve ever had, not even THAT one, would have authorized a pre-emptive strike on a non-combatant state.

The bombing of Hiroshima and Nagasaki wasn’t a nuclear exchange; it was a hostage situation. Why? I don’t see how any other country would want to get involved. Israel certainly won’t. North Korea doesn’t gain anything by launching nukes if Russia is already shooting them at the USA, and China doesn’t want to get involved in nuclear war either.

Tungsten or DU, yeah. Well I imagine that might cause problems on re-entry. A single kinetic kill vehicle is one thing, but if you are launching several thousand pellets into the path of the missile then you're talking about a LOT of bullets raining out of the sky, and tungsten won't melt on re-entry. DU will, but then you've just got a bunch of smaller DU pellets raining out of the sky. Aluminum (or iron at the most) would ensure you're not accidentally pelting an entire city with the equivalent of a few dozen A-10 strafing runs. The real trick here is orbital mechanics -- trying to figure out how to get an intercept-at-launch tangency path for any probable trajectory using the smallest number of orbital platforms and the lowest dV per interceptor. It's not just about entering a path-crossing trajectory, but a path-tangent trajectory, because then the missile has to fly through the entire stream of debris you've put in its path. Obviously wouldn't work for SLBMs so you'd need point defense for that.

That's what I wondered, too. I don't see any nuclear exchange lasting longer than 5-6 hours at most.

Yes, that was my assumption.

Yes, that's my understanding as well. And that actually offers some interesting advantages, because plane changes are cheaper at higher apogees, and higher apogees have longer loiter times.

Say what you will for Elon, but he never shies away from a fight.

I have to think that smaller shots would do enough damage to cause problems on re-entry, at least. The goal is to get your debris cloud/stream on a trajectory which not only intercepts the trajectory of the ICBM, but is actually tangent to it. That tangency means that the ICBM is traveling through your entire debris stream. This also maximizes the impact velocity, since the velocity vectors are exactly opposite at the point of tangency. If you can do this early enough, using an orbital platform with a ton of dV, then you can conceivably take out an entire group of MIRVs before they have a chance to significantly separate. If you’re using a ground-based point-defense interceptor, you’re only going to get a single warhead but it takes much less dV to pull off.

I think it’s obvious the dome approach won’t have sufficient coverage. I’m thinking more in terms of a Brilliant Pebbles replacement. Or in this case a Brilliant Shotgun Shell.

Update: During the Brilliant Pebbles era, Lowell Wood calculated that an impactor of 1 gram or less is sufficient to destroy unarmored objects and an impactor of ~2 kg is sufficient to destroy even the most heavily shielded warheads. How many 2 kg plates would it take to assure a kill? That gets into mean free path analysis....

It was reading about Brilliant Pebbles which got me thinking about this, actually. We have much better targeting capability now than we had in 1991, as well as much better mass-to-orbit capabilities. That increased mass-to-orbit capability could allow each "round" of "ammunition" to produce a big cloud of potential impactors rather than requiring perfect target acquisition. If you can make your transient debris field large and dense and long enough, decoys and MIRVs no longer matter because everything along the LV's trajectory is going to be shredded. But it does require that your orbital platforms either start out in the same plane as the missile (meaning you need many many such platforms) or carry enough dV for a hefty plane change. The sats would be set to activate on launch. If a Great Power state started targeting the shield sats with nuclear anti-sat missiles it would just needlessly signal their intentions and invite a strategic retaliatory strike.

Oh yeahhhhhhhhh Hearkens back.... Now if only they had some engines to reuse

Yeah, that seems like the biggest problem. Yeah, the whole concept was about avoiding the need for target acquisition. With the real Kessler syndrome, all the objects are in orbit and so the odds of a collision go up exponentially over time, whereas you don't have that advantage here. But the idea of a long, thin band of debris tangent to the missile's trajectory seems promising. ICBMs do tend to have a very high apogee which makes a ground-based approach seem more promising than an orbital platform approach. Another possibility would be placing your orbital platforms in a heliosynchronous or semi-heliosynchronous orbit. This way you would need fewer platform clusters to always have Arctic Circle coverage in the same plane as any potential launch.

I wouldn't be so sure. I mean, this is what a single paint fleck did to the windscreen of the Shuttle: That's the $64,000 question... and I'm of the opinion that 'not likely'. Big sky, little bullet. Yeah, I'm inclined to think similarly. Even if the debris cloud was very large, it's hard to know whether it would be dense enough to actually score a hit. Of course if the cloud was large enough then you have to think about a mean free path analysis -- it's not just about finding a single gap, but finding a path through the whole cloud. But even if the "Kessler Dome" approach wouldn't quite work, there might be some ways to use that concept as a better way to kill MIRVs during the coast phase. Like, instead of trying to score a direct hit with an desk-sized exoatmospheric kill vehicle, your payload is designed to release a long streak of debris as close as possible to the ICBM's path, using an ascent profile essentially identical to a fast rendezvous (something we've all done in KSP when your Mun lander has way more delta-V than it needs to reach the command module and so you can just correct your bad ascent with a massive velocity-matching burn). That could have the same effect as a Spartan ABM missile but without requiring a heavy and expensive anti-missile warhead, and it could allow you to target all the MIRVs in a single launch. What's unclear would be how to achieve that effect. The brute-force way would be to put your debris dispenser on top of something like the Spartan ABM and position your launcher near any potential targets, and just try to match the ballistic trajectory of the ICBM but in reverse. There might also be a way to do it using an orbital platform with a solid-fueled deorbit motor.

Oh, the satellites wouldn't blow their payloads just on a whim. They would only blow their payloads if an actual launch had been detected. If we're at the point where one ICBM has been launched, it's a pretty safe bet that whatever happens subsequently is going to happen pretty fast. It's not like the world powers are going to lob one missile at each other every few days or something. For the same reason, a direct attack on the satellites doesn't work; once an attack has launched, there would be an immediate response and so the satellites would blow on their own before getting hit. I may have confused the issue by proposing that they would drop down to 100 km in a high-threat situation. Dropping down to a lower altitude "primes" them, but they would have enough stationkeeping propellant to stay there for a while. Obviously, keeping them "primed" for long periods of time reduces the available mission time. That's what I'm curious about. Would such a debris cloud actually pose a threat to ICBMs with MIRVs?

Super sooty. 11 flights. Wow.

Without any discussion of the current very tragic and very political events happening in Europe... There have been a lot of proposals for different strategies to intercept a ballistic missile. As a refresher, an intercontinental ballistic missile has four flight phases: the boost phase (while the rocket motor is firing), the coast phase (while the payload is coasting through space), the re-entry phase (where the payload or MIRV punches back through the atmosphere), and the terminal phase (from plasma sheath termination to impact). A hypersonic glide vehicle, like the Avangard design, is able to maneuver in a non-ballistic fashion during the terminal phase, but is otherwise the same as an ordinary ICBM. The desire to defend against inbound ICBMs lead to the development of many different anti-ballistic missile systems and designs. Typically, each different type of ABM system targets the ICBM in a different phase: Boost phase. During boost phase, the missile is still moving fairly slowly and its carrier rocket is vulnerable to attack. The YAL-1 airborne chemical laser system was designed for this phase, and we have also tested high-acceleration air-to-air missiles, which could be fired from fighter aircraft. The disadvantage of both of those is that you already need the aircraft to be airborne and in the vicinity when the missile launches. The Super-Excalibur nuclear-pumped x-ray laser system also would have targeted the carrier rocket during the boost phase, but it had its own host of problems. Coast phase. As a rule, ICBMs do not maneuver during their coast phase outside of the atmosphere, making them fairly easy to target. They are, however, very small targets. Plus, if the missile is carrying multiple independent payloads (which is now usually the case), that separation event will happen almost immediately, meaning that you now have multiple targets. The original Excalibur, if it had been built, would have targeted the ICBM at the very beginning of the coast phase. The Spartan ABM missile, launched defensively, would have used a five-megaton physics package to intercept and destroy incoming payloads without requiring a perfect lock on the target. The primary US ABM system, the Ground-Based Midcourse Defense system, uses a maneuvering exoatmospheric kill vehicle to achieve reasonably high probability (>50%) of a direct impact with an oncoming missile while it is still outside of the atmosphere. Re-entry phase. Although the THAAD system is designed primarily for intermediate-range missiles, it is believed to be capable of intercepting ICBMs with a hit-to-kill approach during this phase, although it requires proximity and upgraded guidance. Terminal phase. An ICBM-launched payload spends less than a minute in the terminal phase, making it extraordinarily difficult to intercept. The only successful system was the Nike Sprint missile, which accelerated at approximately 100 g and carried its own physics package for a proximity interception. It was extraordinarily expensive and difficult. It is a thorny problem. But it got me thinking -- what if there was a way to target not ONE missile during the coast phase, but ALL missiles during the coast phase? We all know about the Kessler syndrome, where the breakup of one LEO satellite could create a debris field that threatens other satellites, leading to a chain reaction that makes space inaccessible. What if that basic principle (with modifications) was applied to a coast-phase intercept? Of course, we don't want to actually trigger Kessler syndrome, no matter how dire the situation may be. So the debris field would need to be at a very low altitude, such that all the debris would burn up and re-enter in a matter of days. Imagine a spacecraft carrying its very own ready-made debris field: a few thousand pounds of lightweight aluminum plates. Put a few dozen of these into 300x300 km polar orbits with a range of different ascending-node longitudes, but phased such that several are crossing over the Arctic Circle at any given time. The spacecraft would need to carry enough fuel to lower its orbit into a 100x100 km circular orbit and then raise it back up to 300x300 km, several times. At 300x300 km the stationkeeping cost is reasonably low. In a high-alert situation where the threat of an ICBM seemed likely, all of the spacecraft would lower their orbits down to 100x100 km, where stationkeeping costs are higher. If the threat passed, they would return to 300x300 km. In the event of a launch, the satellites closest to the North Pole would blow their payloads, releasing clouds of orbital debris. These debris clouds in turn would impact each other, creating an massive dome of debris across the Arctic Circle. That cloud would only be concentrated over the Arctic Circle for a few minutes every other hour, of course, but with enough satellites in place, you could create a dynamic, persistent debris cloud that would last for several days. The question, I suppose, becomes whether such a cloud would actually have a chance of damaging or impeding an ICBM passing through that region of space. Or would there be any other way to use a debris cloud approach rather than a "hit-to-kill" approach?

I’m still skeptical about their catching plans. But the smaller payload bay does present an issue. And I’m also sure that they aren’t exactly upset about having the extra control authority. If something goes amiss on descent, that extra wiggle room (no pun intended) could mean the difference between an RUD and a picture-perfect landing. In this case it is less about the suitability of the vehicle and more about the suitability of the payload. Hubble can’t fold its solar panels up and slide back into Starship any more than it could have with the Shuttle. Similarly, the ISS modules originally lofted by the Shuttle are (largely) now permanently fixed to the rest of the ISS; it’s not straightforward to move them.

The context of the “random showerthought” in the OP was how much cooling something could undergo in nature. You cannot reach a negative-temperature system population inversion by “natural” cooling.

The Orbital Defense Platforms in the Halo universe have massive rocket thrusters which rotate the entire space station to allow them to aim the main gun.

Aye. A system with a statistically "negative" temperature is actually hotter than an infinitely hot system because it fills high-energy states before it fills low-energy states.

To the example raised by @Shpaget, the expansion of highly-pressurized gas into a vacuum is an EXCELLENT source of active cooling.

Have you ever read anything from the Halo canon? You would enjoy it. They do all of this.