[Spaceships] getting into orbit without superscience?

[Gnaskar]

Originally Posted by Fred Brackin

Not this one. Space elevators mass a _lot_.

The weight scales super-linearly with required length, and linearly with gravity. Length scales to the power of 1.5 with orbital period.

Space elevators on Earth might be extremely heavy, ranging from 17ktons to 1.6Mtons, depending on available tensile strength. On other worlds, they can be significantly lighter. We might be imagining very different things when we say "colony", but for me investing 10 ktons into orbital infrastructure is a sensible thing for a colony to do.

Originally Posted by Fred Brackin

I'm kind of dubious about the seaplanes too. The first stage is not realy a problem but it's less help than soem people think too. The likely problem is that you seem to have the second stage/orbiter being a seaplane as well and I don't really think a hypersonically streamined shape is going to do well with a boat-shaped underside.

I'm not assuming a launch platform first stage, like the ones we have today. I'm talking a full blown rocketplane stage with 10 times the mass of the upper stage and 70-80% propellant. Somewhere in the 3-4km/s delta V range, off the top of my head. And that's assuming methane/lox or hydox. If metallic hydrogen is available, it can do far better. Though even with methane/lox, it would be an SSTO with 10% cargo on a Mars sized world, so it's plenty capable on its own.

The second stage doesn't really need wings, to be honest; a capsule shape with side mounted engines would do. You could even mount the engines behind protective covers if you're worried about salt water. Since it doesn't need to work in atmosphere, my preference would be to give it inflatable propellant tanks. But if your suspension of disbelief can't handle extruding pontoons through a heatshield, it probably isn't going to like inflatable tanks.

Would something like this work on Earth? Probably not. It could in theory, but not with any margin, so it's probably better to reserve this concept for worlds that take about a km/s less to orbit.

Originally Posted by ericbsmith

Both of these still require huge infrastructure. Which means highly populated worlds. Which tends to edge out the tramp freighter for large megahaulers, whether they're corporate owned or government run or even independently run is rather beside the point - it removes the plausibility of a small ship owned/run by PCs from being able to hop from system to system.

I disagree. In a multiworld setting, you don't need to build everything on world. Worlds with smaller colonies can import advanced launch structures from the bigger central worlds. If there aren't at least some highly populated worlds, where are your PCs getting a cheap secondhand ship from? Also, increased automation can make it practical for smaller colonies building bigger bits of brute infrastructure, while also making ships cheaper.

Megahaulers are only useful if they can fill their holds at their target port. So you aren't going to see them visiting ports where the beanstalk can only take 10 tons per hour, since it would take that beanstalk a decade to lift up a million tons. But the 300 ton cargo bay on a tramp is just right for a day spent transferring cargo.

Originally Posted by ericbsmith

Beanstalks or the use of orbital transfer stations also reduces the ability of PCs to have planetside adventures, which is a primary trope of the sci-fi genre.

Roughly half the Traveller plots I've read start with contriving some reason to separate the PCs from their ship and leave them stranded on a planet. If the campaign starting point is that ships can't land and they're always going to have to take a transfer ride to visit the surface, that's a whole lot easier to arrange.

Realistic spaceships are cramped and often don't have gravity. Most crews are going to take shore leave whenever they have the option. Especially on short sleeve worlds.