NASA has stated that between 2 and 3 RPM are the likely limits for humans to be able to function in an artificial gravity environment. I would go conservative and just call it 1RPM as the best place to start.
Using the easy-to-find “SpinCalc” website we get a tether length of 5868 feet to generate 1G rotating at 1RPM. I believe this over-one-mile tether system is what will eventually be used to generate artificial gravity for astronauts. This seems impractical but actually it is space with all the room needed and tether materials like Spectra are light and strong.
Debilitation is the lesser evil though and the more difficult problem is Dosing. That will, for a small crew with a small living area, require well over 1000 tons of water shielding. And this gives us some idea what a “true” Spaceship will look like: a “Bola” over a mile long spinning at 1 RPM with an over-one-thousand-ton-mass at either end. On the plus side the water shield will facilitate closed-loop life support.
The tether system will likely be several tethers with “elevators” used to transport mass and fine tune and dampen out oscillations. Astronauts would ride these elevators a half a mile to the center of the tether to and from a zero gravity “mast” and docking station.
Starting with a basic mass of 2000 tons, which is about 4 times that of the ISS, add the structures which must take the loads associated with spinning and also the tether system. Everything necessary for Space Station, Lunar Cycler, or Spaceship operation may or may not come in under the 1000-ton mass budget opposite the water shield/crew section.
Start with a basic Space Station and then add propulsion systems for Lunar Cyclers and eventually Nuclear Spaceships. The two options for a Spaceship are some new form of Nuclear Electric or Nuclear Pulse. A Nuclear Pulse system would require reeling in the tether system and configuring the Spaceship for propulsion and then, after the necessary number of pulses, “splitting the ship” and going back to artificial gravity cruise mode.
Mars is a “dead end” for colonization for several reasons. Musk has led humankind away from the path envisioned by Gerard K. O’Neill and has done humankind a great disservice. A sci-fi meme and its proximity are the sources of much of the attention, time, and resources directed at Mars. Its gravity well and lack of oceans should cancel this attraction out but does not simply because scientists are not willing to tell the truth. Oceans are where life will be found. Not a radiation blasted desert in a partial vacuum. Icy bodies with oceans have shallow gravity wells and ice resources for conversion into fuel which make them the places to land and send submarines. Mars seems like it can be reached with chemical propulsion but due to the need for radiation shielding this is false and misleading. A deception. Nuclear energy will be required for any Human Space Flight Beyond Earth and Lunar Orbit (HSF-BELO). With some form of nuclear propulsion other than nuclear thermal the just-close-enough Mars reasoning disappears. Ceres should be the first human mission destination. Not Mars.
In 2008 the scientific community had an opportunity to join together in solidarity and promote a path for America and allies to pursue in space. The discovery of ice on the Moon should have completely changed the course of NASA in regard to Human Space Flight and made the pure research community beneficiaries of a new focus on space. A certain entrepreneur and a lack of cooperation within the science community squandered that golden moment. If acted upon fourteen years ago we could have been seeing humans landing on the Moon and occupying a permanent base by now. Sidemount was the Super Heavy Lift Vehicle capable of sending payloads to the Moon. NewSpace and “the flexible path” was the end of the dream.
We now have a second opportunity, but the window is closing again. Space Solar Power by way of lunar resources is the solution to the Climate Change Crisis but, like the ice on the Moon, not a single word is being said about it. Nothing. The trillions of dollars of international funding in a Space Solar Power infrastructure would empower the research community and enable them to accomplish missions they cannot even dream of now. Wake up….Human Space Flight is the path to more science missions, not in competition with them.
Ice on the Moon 