4 ms·

Depends on the situation, though usually because of the force. Spinning a spaceship around a point with a long cable, you obviously produce a (fictitious if yo

Depends on the situation, though usually because of the force. Spinning a spaceship around a point with a long cable, you obviously produce a (fictitious if you're pedantic) outward force, that's kind of the point. For that fictitious force to exist though, that very force acting on the spaceship must be counteracted by an equal and opposite reaction force provided by your cable, creating the action-reaction pair required for tension. This much is obvious. The problem arises when you think about how large that force is. To generate an apparent artificial apparent gravitational acceleration of 1 G for the occupants, the entire ship must experience the same spin and thus the same acceleration. That's the source of the problem, the force you're counteracting is the same as the weight of the ship on Earth. What is being asked here is to hang a loaded spaceship from a building with cables. That might work for smaller spacecraft, whose mass is measured in metric tonnes, but it won't work for anything larger. You can get incredibly strong and light cables out there, but one capable of functioning in the space environment, light enough to launch, and strong enough to counter the tens of meganewtons of force required from it is going to be more difficult to find. Not only that, but you need to consider the counterweight as well. Because of the cable, the tension force total is also dependent on the acceleration of the counterweight. Since launching a heavier counterweight than an entire habitable ship is probably out of the question, you'll probably need twice as long a cable and experience roughly twice the force required just to lift the ship on earth. Needless to say, that's getting a bit out of the realm of current space capability. Not to mention the immense size you'd need to make a ship like this for the situation to not cause immense discomfort.

throwaway0a5e 5y ago
>That's the source of the problem, the force you're counteracting is the same as the weight of the ship on Earth. What is being asked here is to hang a loaded spaceship from a building with cables. We're talking about 10,000-100,000lb (i.e. just the crew module) depending on mission profile and the craft in question. You can handle that and more with commodity wire rope and hardware. Whoever we're sending to Mars will probably appreciate having a useful tow rope on Mars anyway so it's probably wise to just use a boring old steel cable rather than something that weighs 3lb but isn't up to the rigors of surface use. Remember, we're using "needs to go into space" margins here, not "overhead lifting on earth in a jurisdiction where OSHA matters" or "what makes Redditors sleep at night" margins here so you're not going to need a behemoth of a cable. Furthermore, you don't even need to generate 1g, just enough to not cause health problems and greatly simplify craft design.
- kamray23 5y ago
  Yeah something that small is going to be fine. But the ISS will not be. It's 440 metric tons, generating 4.4 MN of force on a cable. That's not going to spin. And you're sending something to Mars here. In the ideal case we'll be sending six worth of supplies at the same time per person per ship. The amount of people permitted by NASA's guidelines on long-term habitation on a ship based purely on volume range from 1 for smaller ships to 30 for something the size of Starship. Hauling everything they need is not going to be below 50 metric tonnes by any means. We can probably spin as much as we like here, near the Earth, but anything further away is going to have ropes the breaking strength of which is again measured in meganewtons and the width of which is going to be around half a meter. Making that out of steel for the kind of cable you'd need for comfortable spinning (~1 rpm, 1.6 km of cable) is not going to space any time soon. At the very least 6 months of food is required for the crew module, or some complex procedure of periodic de-spin & rendezvous with a cargo vessel. The kinds of missions NASA has been planning are 30 months in overall length if everything goes well, though 24 of that is not required to be accessible during transit. Spinning again in ĺow martian orbit is going to be quite feasible, once you jettison all of your life support and such and instead do very frequent cargo stops.
iso1631 5y ago
Even 0.1G would do wonders with things like stopping blood pooling and moving co2 Two starships at 200t each linked by 10 cables would need 40kN each, a 5cm diameter cable, at 2.5kg/m a 1km cable, you'd need need 25 tons of cable, about 10% of the cargo capacity. You'd be well under 1rpm https://www.engineeringtoolbox.com/wire-rope-strength-d_1518.html https://www.engineeringtoolbox.com/wire-rope-strength-d_1518...
- kamray23 5y ago
  Starships when full weight some 1300 tons, which is what you'd want them to be at while waiting in LEO or in martian orbit. They'll be a little lighter in transit, but not empty, since they have a lot of other tasks and getting back to worry about. Working at 0.1 G certainly would be probably fairly possible. If you go with Kevlar, it's actually just 2.5 tonnes, very well within your cargo needs. The required cables for something that small could very well be produced on Earth and launched up. It's still probably cheaper to just go with sleeping bags, and replicating Mars gravity is going to go on the "very difficult" side again, but yeah 0.1 G and other such very low gravity situations are certainly possible.

throwaway0a5e 5y ago

>That's the source of the problem, the force you're counteracting is the same as the weight of the ship on Earth. What is being asked here is to hang a loaded spaceship from a building with cables. We're talking about 10,000-100,000lb (i.e. just the crew module) depending on mission profile and the craft in question. You can handle that and more with commodity wire rope and hardware. Whoever we're sending to Mars will probably appreciate having a useful tow rope on Mars anyway so it's probably wise to just use a boring old steel cable rather than something that weighs 3lb but isn't up to the rigors of surface use. Remember, we're using "needs to go into space" margins here, not "overhead lifting on earth in a jurisdiction where OSHA matters" or "what makes Redditors sleep at night" margins here so you're not going to need a behemoth of a cable. Furthermore, you don't even need to generate 1g, just enough to not cause health problems and greatly simplify craft design.

kamray23 5y ago
Yeah something that small is going to be fine. But the ISS will not be. It's 440 metric tons, generating 4.4 MN of force on a cable. That's not going to spin. And you're sending something to Mars here. In the ideal case we'll be sending six worth of supplies at the same time per person per ship. The amount of people permitted by NASA's guidelines on long-term habitation on a ship based purely on volume range from 1 for smaller ships to 30 for something the size of Starship. Hauling everything they need is not going to be below 50 metric tonnes by any means. We can probably spin as much as we like here, near the Earth, but anything further away is going to have ropes the breaking strength of which is again measured in meganewtons and the width of which is going to be around half a meter. Making that out of steel for the kind of cable you'd need for comfortable spinning (~1 rpm, 1.6 km of cable) is not going to space any time soon. At the very least 6 months of food is required for the crew module, or some complex procedure of periodic de-spin & rendezvous with a cargo vessel. The kinds of missions NASA has been planning are 30 months in overall length if everything goes well, though 24 of that is not required to be accessible during transit. Spinning again in ĺow martian orbit is going to be quite feasible, once you jettison all of your life support and such and instead do very frequent cargo stops.

iso1631 5y ago

Even 0.1G would do wonders with things like stopping blood pooling and moving co2 Two starships at 200t each linked by 10 cables would need 40kN each, a 5cm diameter cable, at 2.5kg/m a 1km cable, you'd need need 25 tons of cable, about 10% of the cargo capacity. You'd be well under 1rpm https://www.engineeringtoolbox.com/wire-rope-strength-d_1518.html https://www.engineeringtoolbox.com/wire-rope-strength-d_1518...

kamray23 5y ago
Starships when full weight some 1300 tons, which is what you'd want them to be at while waiting in LEO or in martian orbit. They'll be a little lighter in transit, but not empty, since they have a lot of other tasks and getting back to worry about. Working at 0.1 G certainly would be probably fairly possible. If you go with Kevlar, it's actually just 2.5 tonnes, very well within your cargo needs. The required cables for something that small could very well be produced on Earth and launched up. It's still probably cheaper to just go with sleeping bags, and replicating Mars gravity is going to go on the "very difficult" side again, but yeah 0.1 G and other such very low gravity situations are certainly possible.