I think sending a person across the ocean, under an atmosphere, protected from radiation, with gravity isn't "the exact same" thing as through space. Much less 1000. Pretending that it is...charitably...is silly.

True, but this works in reverse too.

Much harder to get the initial, small scale version of a cycler-based transit system established. But then, because you don't have an atmosphere or ocean or particularly noticeable gravity, scaling it up it probably much, much easier than doing so for ocean-going vessels and the like.

Maybe? My point is if you are going to do it, start with a mental model that fits the task, not one that both isn't remotely the same engineering challenge and ignores the actual hard problems.

Well, we're a good part of the way towards being able to move people from the earth's surface into orbit. Somewhere between, say, 20% and 80%. If that claim is true, then it seems reasonable to be thinking about what comes next, and building a small cycler seems like a potentially reasonable choice.

If we can indeed build a small cycler, then getting to a big one may be much easier than going from a small yacht to a transoceanic liner.

> If we can indeed build a small cycler, then getting to a big one may be much easier than going from a small yacht to a transoceanic liner.

It still falls apart a bit due to the rocket equation. [0] When you're in a safe harbor on earth, it's somewhat simple to increase the size of your boat, most of the rules stay the same.

But as you build bigger cyclers, one will either need bigger rockets or more rockets and then possibly assembly/docking in space, so it's definitely more complicated than making a larger displacement in the water.

[0] https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation

I thought that the whole point of a cycler was to reduce the need for rocket propulsion to a vanishingly small part of the system.

That is true. My comment was more about the initial setup of a larger cycler. Larger cyclers will cost exponentially more rocket mass/fuel/complexity than a smaller cycler. But once in orbit, yes, the design reduces overall fuel costs.

Rocket equation makes faster exponentially difficult; merely heavier scales linearly.

The equation is about mass, not velocity.

The mass a rocket can lift into space is inversely proportional to the mass of the propellant. To increase the payload (a larger cycler like the previous poster mentioned), you need to increase the initial total mass of the rocket, which includes the mass of the propellant.

So it's not linear, it's exponential, the "tyranny" of the rocket equation.

Δv = I_sp * g_0 * ln(m_0/m_f)

Or are you talking about a completely different equation?

This one, which is the only one I know of to get this moniker, is about mass fraction, not absolute mass. You can perfectly compensate for making m_f bigger by making m_0 bigger by exactly the same ratio, hence for fixed Δv, m_0 increases linearly with m_f.

Two rockets joined horizontally has twice the mass of one rocket alone, and accelerates twice as much payload to the same relative velocity as a single rocket.

Two rockets joined end-to-end, with the second rocket being the payload for the first, makes the ultimate payload of the second stage go faster than if it had only been propelled by the second stage with no boost from the first, but significantly less than twice as much faster.

You can also see this example by asking the inverse: if it was exponential with regards to absolute payload rather than the payload as a mass fraction, that would mean that dividing any given payload into two or more parts, launching them separately to the same ultimate velocity, and having them join together in space, would save fuel — it doesn't, QED.

(There are other reasons to build in space, like "our rockets aren't big enough and nobody wants us to build bigger ones", but that's a political equation, not rocket science).

No idea how you think that rebuts my objection.

Eventually yes, but it seems we're putting the cart before the horse.

I really hope it goes well and we end up accelerating things with another space race, this is the best outcome and maybe this is why we're shooting for manned Mars missions... but it's risky. A crew of dead astronauts on Mars could have the opposite effect. Imagine if Nixon really had to deliver that failure message about the moon landing, space exploration could be even worse off than it is now.