Sure, less mass constraints can allow lower cost, but remember what the question is: are space assets in with cheap logistics less mass constrained than terrestrial vehicles on a per platform basis? An AIM-120 costs roughly a $1 million dollars for a 160 kg missile. If we ballooned that to a 300 kg missile for a similar mission, would we get a $500k missile through lower mass constraints? Or are the drivers of what makes the platform (in this case a single missile) expensive relatively insensitive to the total size of the missile? doubling the mass could easily have a lower cost per kg: a 300 kg missile might only cost $1.2 million rather than $2 million, but that's because most of the cost (sensors/guidance system) is relatively insensitive to scale, putting a large fixed cost to the missile, while more fuel and explosive is cheap.
Yes, there would be some savings. Guidance and sensors, with the right design, can be very sensitive to scale, because they are electronics.
Of course "per kg" pricing of missiles is completely random and is going to vary greatly with the missile and its sensors due to the latter dominating the pricing. Unguided rockets cost hundreds to few thousands dollars each, but suddenly jump to few tens of thousands if you put laser guidance on them.
So yeah, if used properly, the lesser constraints would allow building guided munitions out of cheaper components, by compensating for a lot of the EM interference shielding and other factors that make them normally expensive by just slapping shielding material on it.
The main trick with sudden popularity of drones is that by use of commercial components, they can be used to homebrew something of similar effect to a guided munition, at a small fraction of the price.
Maybe at the margin you could just squeeze out a lower cost for a higher mass: If the $1 million initial cost is, say 50% sensor, adding 150 kg of explosive and fuel for higher speed/larger blast area at $20,000 might be able to shave $100,000 off the missile cost while preserving effectiveness, So net you get to a $920k missile. But, that would also be only a 8% cost saving for a 100% increase in mass. That might be hard to justify throughout the rest of the supply chain.
Remember your initial argument was over cheaper logistics allowing you to afford more systems through cheaper unit prices: that each individual missile is cheaper, so you can afford more units. Not Each missile costs the same, but is 3x as heavy for a 50% per unit improvement. That I don't see as particularly likely, with how this tech generally works and were the cost bottlenecks generally seem to be.
For purpose of military calculatuions, in the end it adds up either way. If you have more effective missiles, by all chance you will need less of them, money saved!
Also we were talking about satellites, not aerial missiles, designs of which are far less affected by attempts to spend large amounts of money on miniaturization to dodge few kilograms of launch cost, and then radiation proofing the thing for space, also with the above in mind.
I'm especially dubious space assets can reasonably achieve lower per unit costs than terrestrial equivalents: space fighters/missiles likely cost at least roughly similar to terrestial equivalent, and likely more. The space AIM-120 weighing 300 kg and costing less than the planetary AIM-120 doesn't seem plausible. At best I would expect you to reach rough parity in capital costs per platform.
In most cases, yes, in some, funny effects can happen. Say, ICBM vs SRBM. On Earth, SRBMs are much cheaper. But let's say you have a planetary invasion supporting missile cruiser, and
someone thinking like me guessed that the ground pounders may want long range nuclear weapons for support, and it would be pointlessly silly to ship truck TELs down to make that happen. When he considers what missiles to put on the cruiser, he notices that the terrestial rules for sizes and costs of ballistic missiles go out of the window, because the whole missile is already in space to begin with, and a SRBM, potentially even with further downscaled fuel load and engine, is going to be able to do the job of a ICBM.
In space, any reentry capable tactical missile is more or less a ICBM.
How are you figuring 15k? Transport cost is $5k, everything else $5k for $10k total seems perfectly reasonable. It doesn't matter to my general point, but I don't understand the concern. Fuel if anything might be a lighter burden than capital, at least on the interstellar leg of things, because it can likely be secured in system, likely for fairly low costs. Water for example probably has extraction costs in the dollars to maybe $100s per ton. Even hydrogen at current energy prices would be in the range of $2-3k per ton (specifically hydrolox, so 1-6 ratio hydrogen/oxygen: pure hydrogen would be closer to $15k per ton, but pure hydrogen engines would also be getting better delta v per ton too).
Again, we have established that logistical costs are very much non zero. Any idea how much all the chemical plants to make hydrolox out of materials gathered from local moons and asteroids and then refined into chemical grade would take in tons? We're talking tens to hundreds of thousands of tons here.
And again, the low tech assumptions here are probably not applicable. If you are invading another star system, it's almost certain your state of art (and your peer's) is something better than hydrolox or pure hydrogen, that's XX century tech.
I'm not sure of the rest of the criticism: part of the point of consuming fuel is to give a better sortie rate than "immobile" platforms, though a mixture of redeployment ability, so fewer planforms are needed, and increased survivability: even at 5 sorties, going from expending a $10 million dollar system per sortie to a $10 million system per 5 sorties plus $50,000 of fuel is a huge cost saving per sortie, from $10 million to $2.05 million per sortie.
If "stationary" platforms require 300 platforms to fulfill your mission, while mobile ones only need 200 but your burning 4,000 tons of fuel per day, at $10k per fuel the 300 platforms are not the more economic option until day 25 of the campaign, assuming both are zero casualty strategies.
You don't get it. At larger numbers, beyond few dozens, statistically there is no need for any platforms to move except for dodging. In which case fuel use becomes proportional to enemy attempts to take down the platform, rather than a regular cost.
And then comes planning with cheaper, more expendable platforms - immobile means no need for engines after all, little more than a space box with a comm system and a bunch of missiles or something on it. Something is firing at it? Make it dump its missiles that should be most of its value at whatever shot at it, who cares if it gets destroyed afterwards.
If there are casualties, and expending fuel lowers them, the favorability of more mobile systems increases, and the benefits of flexibility grows too: regular shifting makes setting up "ambushes" harder, keeps the enemy more on their toes, allows responses to enemy action like massing forces or to plug gaps created by those casualties.
Note though that mobility, especially high end kind of it, comes with significant needs in engines and fuel storage, and the related complexity reflected in costs too, yet still in no way guarantees survival - especially with laser equipped enemies.
And no, at sufficient scale response will inherently be always available, you don't get the value of a full coverage sat network. Amassing forces? There is no need to move sats when every minute there are at least a few different sats coming into range.
By that line of thinking, if the ground defenses are not suppressed enough to allow more or less immobile sats to have decent survivability, you may stick to your missile cruisers until then, with their already high investment in engines to rely on for dodging, and leave the sats for a later stage of campaign once the defenses are suppressed more.
Admittedly some orbits are less of a problem: ISS for example gets a launch window over any particular point effectively once every 24 hours for roughly 10 minutes.
Maintaining such a completely predictable orbit makes targeting the platform much easier, leaving it much more venerable. More polar orbits, or narrower effective ranges might give less than 1 a day. Or maybe not. Still doing some more research.
Another site I found did seem to suggest a shuttle to the ISS actually had closer to 2 launch windows every 24 hours, which does make some sense.
So, mobility advantage for increasing the number of attacks per time period may be incorrect (though over a planetary scale being able to reposition into more favorable orbits for particular targets on a regular basis may still be valuable) but the survivability advantage seems quite reasonable.
Launch windows like that are built on the assumption of optimal fuel use for the vehicle, launching from Earth rather than to Earth, and probably many other factors too.
ISS orbital period is roughly 90 minutes. A "train" of platforms deployed at equidistant points of that orbit, amounting to, say, 90 sats, will mean that at any point in time, ground forces anywhere on the planet will be able to call on at least several sats to blast something near them, possibly more depending on the weapon system on them, up few dozens.
