3 ms·

> 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 apa

> 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 https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation

PaulDavisThe1st 3y ago
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.
- accrual 3y ago
  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.
ben_w 3y ago
Rocket equation makes faster exponentially difficult; merely heavier scales linearly.
- accrual 3y ago
  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.
  - ben_w 3y ago
    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).

PaulDavisThe1st 3y ago

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.

accrual 3y ago
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.

ben_w 3y ago

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

accrual 3y ago
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.
- ben_w 3y ago
  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).