"Delivering supplies by space" Topic

Just kicking a few ideas about, looking at the amount of shipping you need to support a planetary invasion :-)

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Any sentient space faring race intent on conquering earth would have conducted extensive recon and pre planning before setting out. As much as possible they would have planned to resupply from resources on earth or another neighboring planet or moon.

Of course much would depend on what attracted them to earth in the first place. If the goal was to enslave humanity for use as a labor force offworld, then the expedience of biological or chemical WMDs would be off the table from the jump.

Yes, if the inhabitants are just making a nuisance of themselves, destroy the world.
If you want the minerals then just destroy the inhabitants.

I was looking at the possibilities of how you'd organise 'conquest' and as you say, prepositioning supplies and heavy equipment makes an awful lot of sense

Given the travel time issues (FTL is such a crutch) there might be an ironic possibility of a vast armada come to earth to harvest the dinosaurs for use as Beasts of burden.

Oops…

This is why humanity will never get any further than the moon until we get fission/fusion powered space craft. Right now it takes about 15 pounds of fuel to get one pound of payload into space. Even assuming we get oxygen and water on Mars itself, we have to take literally everything else.

Don't get me started on the economics of an intergalactic empire. Basically you either need magic (Star Wars) or cheap, on demand wormholes.

Seems to me that if you really wanted to capture and hold a place as big as a planet you would want to pre-position your logistical tail as close as possible – robot freighters for example – and plan/hope for a short victorious war – also would be good if you manufacture logistics on site, i.e. have a factory ship that could turn out things from local resources

I suppose we could convince them to love elephants? If they cannot get dinosaurs.
I agree with Extra Crispy, we need 'handwavium' but the problem from a wargames perspective is that handwavium can be applied to solve problems that are actually problems the player should solve.
But certainly we have seen space travel go down two totally different lines to to totally different futures. So in one, it's actually comparatively cheap, so you have 'tramp freighters' and tourists. In the other it's expensive and only the state or fabulously rich can afford it.

And yes, I think Frederick has come up with something a couple of others have suggested. Pre-position, but you're the first to suggest a proper Sci fi solution, the factory ship fabricating stuff from local resources.

I've began to imagine a planetary invasion would look a lot like a bombing run and supply drops from WWII. Ships run like bomber formations with each group to drop whatever in key locations on the planet. With troops on the ground the ships could drop missiles or bombs in more precise locations so as to avoid using nukes, but the invading troops would have to hold landing zones for their supplies.

We actually have nuclear tech that can propel a spaceship to sustained acceleration rates of 1G or higher.
The problem is that, by treaty, this tech can't be used because it involves nuclear explosions— very small, shaped nuclear explosions. But by the Outer Space Treaty and the Test Ban Treaty any such nuclear explosions are forbidden.

Look up Project Orion. We almost built the thing back in the ‘60s. Still could.
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There's also NERVA, which is also viable:
en.wikipedia.org/wiki/NERVA

And Project Timberwind:
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And DRACO:
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As it is, SpaceX has already reduced cost to orbit to $1,200 USD per pound. Starship, when completed, is expected to reduce the cost to under $200 USD per pound. These rates are achieved to a great extent through reusability of the rocket components— it saves a lot of dough when you're not having to build an entirely new rocket every time you want to launch something into space.

But even with that, chemical propulsion will always be the "slow way."

As for interplanetary and even interstellar travel, solar sails might be a viable solution— there's no fuel needed, just the "sail" and the light of the Sun. Constant acceleration to midpoint,* then shift the sail against orbital movement, and decelerate constantly to the destination. For manned interplanetary travel, it's probably not really viable past Jupiter, as the rate of acceleration obviously falls with distance from the Sun. Still, it would be exceedingly cheap, and possible to launch supply "trains" as it were, essentially looping in a constant series of craft which link up with payloads (possibly even manned) in Earth orbit (or nearby), and then "dropped off" at a target destination, such as a Mars colony. The sails never land; they just loop and loop and loop, with the payload being boosted with chemical (or nuclear) rockets to connect with the sail at its Earth end, and if necessary collected by similar rockets in Mars orbit… or just dropped to the planet's surface via aero braking and either local rocket landers or parachutes. And stuff from Mars could be sent back the same way, making interplanetary trade indeed a viable possibility.

*The "midpoint" for such a trip would not actually be halfway; it would be to a point where solar acceleration would be sufficient to slow the craft to a viable orbital insertion point at Mars. As noted, this would be based on the amount of light and thus light pressure the sail would receive as the distance from the Sun decreases (or increases for a return flight.)