4 ms·

> By launching your rocket from the ballon city and returning to orbit. (I'm struggling to see the novel problem.) I think Newton’s third law may cause trouble

by boolit 1y ago

> By launching your rocket from the ballon city and returning to orbit. (I'm struggling to see the novel problem.) I think Newton’s third law may cause trouble-but I’m no physicist.

JumpCrisscross 1y ago
> I think Newton’s third law may cause trouble No more than for a floating platform on the ocean. (Or frankly any sea or airborne firing platform.) If your launch mass is a significant fraction of station mass, and you can't counterweight, you could float it off to the side and then have the baloon detach when its engines fire. But none of this is in even the top thousand problems that come with colonising Venus.
- dr_dshiv 1y ago
  You fly the rocket on the bottom of a plane, then fire it out. Assuming these cloud cities have landing strips, right? Managing ballast might be a challenge…
  - JumpCrisscross 1y ago
    > You fly the rocket on the bottom of a plane, then fire it out This requires engineering the rocket to withstand structural loads in two directions as well as a ~90-degree rotation under thrust. Not trivial. (It's been a major handicap for airlaunch on Earth.) Landing on and taking off from floating platforms is like the one part of Venusian colonisation we've actually solved.
  - vidarh 1y ago
    Or you just drop it off the side.
- dredmorbius 1y ago
  Floating on a liquid surface is markedly different from floating within a fluid (liquid or gaseous). To float on a liquid, one merely needs to maintain a lower average density within the vessel than the surrounding liquid. Assuming a largely hollow vessel (as with a ship or barge), it's possible to add or remove considerable payload without losing stable flotation characteristics as the draft of the vessel automatically compensates for the variation, displacing more or less liquid, and maintaining equilibrium. To float in a fluid, one must maintain precise neutral buoyancy, which is an entirely different animal. As pressure varies with depth or altitude, the tendency is for a vessel to contract as it sinks and expand as it rises, leading to a runaway buoyancy shift (increasingly negative with depth, increasingly positive with height). Many military submarines operate at comparatively shallow depths, often only slightly more than their overall length* (for larger submarines), given both the immense pressures of even modest ocean depths (a few hundred metres), and the compounding nature and risks of runaway buoyancy loss. Plans for cargo airships face corresponding problems in that when offloading cargo or passengers it is necessary to vent or otherwise scavenge lifting gas (the expense and/or challenges of either venting or compressing helium are great), or to onboard a corresponding mass of ballast. Where suitable water is plentiful the latter is fairly viable, but there are many applications proposed for cargo airships which suggest transport of heavy cargos sites with limited capabilities for same (no facilities, deserts, salt- or otherwise-contaminated water which might play poorly with buoyancy-compensation systems aboard the airship). Rocket launch from an inhabited floating atmospheric platform would require accumulation of large stores of fuel (the Tsiolkovsky rocket equation also works against you), as well as presenting various risks associated with enormous barely-contained explosions (should you be lucky). The risks are immense, and hand-waving them away is disingenuous to the extreme.
  - JumpCrisscross 1y ago
    > To float in a fluid, one must maintain precise neutral buoyancy, which is an entirely different animal You're right, I was oversimplifying. An aerial or submerged launch platform, then. > the tendency is for a vessel to contract as it sinks and expand as it rises, leading to a runaway buoyancy shift (increasingly negative with depth, increasingly positive with height) This is inherent to the cloud city design. Rockets would be a subclass of buoyancy risks, eclipsed entirely by atmospherics. > Rocket launch from an inhabited floating atmospheric platform would require accumulation of large stores of fuel (the Tsiolkovsky rocket equation also works against you), as well as presenting various risks associated with enormous barely-contained explosions This is a fair criticism. It's also solved by having offboard propellant storage and launch platforms. > risks are immense, and hand-waving them away is disingenuous to the extreme Didn't mean to suggest it isn't risky. Just that the risks from the rocket launch component are dwarfed by many, many others, and to the extent there are risks here, they are ones we've already solved on Earth in analogous contexts. (Maintaining buoyancy isn't remotely the main problem with launching rockets from high-altitude blimps.)
    - dredmorbius 1y ago
      How do those offboard propellent storage and/or launch platforms keep from plummeting to the planetary surface? What is their buoyancy-management system? You're offloading the problem, not solving it.
      - potato3732842 1y ago
        >What is their buoyancy-management system? Some of y'all have never seen a marina with floating docks and it shows. More of the same. This entire problem is basically ye-olde spaceX barge only with different factors in the equation and running in both directions (instead of just landing). Yes, without a hard cut in buoyancy like you get with something that's way denser than air floating in something way denser than it all the math gets a little wonky but it's all still fundamentally the same. When you load a few million pounds of shit you sink a few thousand feet instead of a few inches like a barge in water would, and when that weight turns out to be a rocket that yeets itself you move around thousands of feet or miles instead of feet like a barge, but when you're floating in the air with nothing to crash into who cares.
teamonkey 1y ago
It’s not even science fiction https://youtube.com/shorts/MqiSQD6HipQ https://youtube.com/shorts/MqiSQD6HipQ

by boolit 1y ago

> By launching your rocket from the ballon city and returning to orbit. (I'm struggling to see the novel problem.) I think Newton’s third law may cause trouble-but I’m no physicist.

JumpCrisscross 1y ago

> I think Newton’s third law may cause trouble No more than for a floating platform on the ocean. (Or frankly any sea or airborne firing platform.) If your launch mass is a significant fraction of station mass, and you can't counterweight, you could float it off to the side and then have the baloon detach when its engines fire. But none of this is in even the top thousand problems that come with colonising Venus.

dr_dshiv 1y ago
You fly the rocket on the bottom of a plane, then fire it out. Assuming these cloud cities have landing strips, right? Managing ballast might be a challenge…
- JumpCrisscross 1y ago
  > You fly the rocket on the bottom of a plane, then fire it out This requires engineering the rocket to withstand structural loads in two directions as well as a ~90-degree rotation under thrust. Not trivial. (It's been a major handicap for airlaunch on Earth.) Landing on and taking off from floating platforms is like the one part of Venusian colonisation we've actually solved.
- vidarh 1y ago
  Or you just drop it off the side.
dredmorbius 1y ago
Floating on a liquid surface is markedly different from floating within a fluid (liquid or gaseous). To float on a liquid, one merely needs to maintain a lower average density within the vessel than the surrounding liquid. Assuming a largely hollow vessel (as with a ship or barge), it's possible to add or remove considerable payload without losing stable flotation characteristics as the draft of the vessel automatically compensates for the variation, displacing more or less liquid, and maintaining equilibrium. To float in a fluid, one must maintain precise neutral buoyancy, which is an entirely different animal. As pressure varies with depth or altitude, the tendency is for a vessel to contract as it sinks and expand as it rises, leading to a runaway buoyancy shift (increasingly negative with depth, increasingly positive with height). Many military submarines operate at comparatively shallow depths, often only slightly more than their overall length* (for larger submarines), given both the immense pressures of even modest ocean depths (a few hundred metres), and the compounding nature and risks of runaway buoyancy loss. Plans for cargo airships face corresponding problems in that when offloading cargo or passengers it is necessary to vent or otherwise scavenge lifting gas (the expense and/or challenges of either venting or compressing helium are great), or to onboard a corresponding mass of ballast. Where suitable water is plentiful the latter is fairly viable, but there are many applications proposed for cargo airships which suggest transport of heavy cargos sites with limited capabilities for same (no facilities, deserts, salt- or otherwise-contaminated water which might play poorly with buoyancy-compensation systems aboard the airship). Rocket launch from an inhabited floating atmospheric platform would require accumulation of large stores of fuel (the Tsiolkovsky rocket equation also works against you), as well as presenting various risks associated with enormous barely-contained explosions (should you be lucky). The risks are immense, and hand-waving them away is disingenuous to the extreme.
- JumpCrisscross 1y ago
  > To float in a fluid, one must maintain precise neutral buoyancy, which is an entirely different animal You're right, I was oversimplifying. An aerial or submerged launch platform, then. > the tendency is for a vessel to contract as it sinks and expand as it rises, leading to a runaway buoyancy shift (increasingly negative with depth, increasingly positive with height) This is inherent to the cloud city design. Rockets would be a subclass of buoyancy risks, eclipsed entirely by atmospherics. > Rocket launch from an inhabited floating atmospheric platform would require accumulation of large stores of fuel (the Tsiolkovsky rocket equation also works against you), as well as presenting various risks associated with enormous barely-contained explosions This is a fair criticism. It's also solved by having offboard propellant storage and launch platforms. > risks are immense, and hand-waving them away is disingenuous to the extreme Didn't mean to suggest it isn't risky. Just that the risks from the rocket launch component are dwarfed by many, many others, and to the extent there are risks here, they are ones we've already solved on Earth in analogous contexts. (Maintaining buoyancy isn't remotely the main problem with launching rockets from high-altitude blimps.)
  - dredmorbius 1y ago
    How do those offboard propellent storage and/or launch platforms keep from plummeting to the planetary surface? What is their buoyancy-management system? You're offloading the problem, not solving it.
    - potato3732842 1y ago
      >What is their buoyancy-management system? Some of y'all have never seen a marina with floating docks and it shows. More of the same. This entire problem is basically ye-olde spaceX barge only with different factors in the equation and running in both directions (instead of just landing). Yes, without a hard cut in buoyancy like you get with something that's way denser than air floating in something way denser than it all the math gets a little wonky but it's all still fundamentally the same. When you load a few million pounds of shit you sink a few thousand feet instead of a few inches like a barge in water would, and when that weight turns out to be a rocket that yeets itself you move around thousands of feet or miles instead of feet like a barge, but when you're floating in the air with nothing to crash into who cares.

teamonkey 1y ago

It’s not even science fiction https://youtube.com/shorts/MqiSQD6HipQ https://youtube.com/shorts/MqiSQD6HipQ