If we didn’t study human health in microgravity, then we wouldn’t know the health effects of microgravity or that a spinning Mars-transit vehicle is preferred.

Making a spacecraft spun up on the end of a tether may be the way that we go, but we do not yet have much experience with tethers, much less spinning with them. It is likely that we will need a large craft so that the astronauts going to Mars can move about and do research, to alleviate boredom, on their voyage, so the tether would have to be strong enough to hold the entire weight of the large transit vehicle.

The gravity level that is needed for such a transit is also not known, and we do not yet have a spinning space station that would allow us to try different levels. Spinning the ISS is not an option. It is not designed for the stresses, and the solar arrays need to continue pointing to the sun. Spinning it would negate virtually every experiment that is planned to be performed on the ISS. So far, studying zero G is within our grasp, so to not do it would be wasteful.

1G may be far more than enough, and to construct a 1G craft would be very expensive — perhaps more so than studying the effects of zero G.

Various concepts are being proposed, some are serious (e.g. Aldrin Cycler https://en.wikipedia.org/wiki/Mars_cycler ), but none have been funded for development.

I eagerly await next month, when SpaceX will describe their immediate plans for Mars. Their discussion may include funding levels for studying methods of transporting people to Mars (e.g. tether, cycler, Bigelow Habitat, etc.).

pzatchok asked: “Is dragon cargo slated to be discontinued when the passenger Dragon is finally in service?”

So far there are no customers for it, after the NASA contract, but if Bigelow puts up some of their Space Habitats — and we all expect them to — then a non-NASA customer base will quickly form to bring/return supplies and experiments. SpaceX would be competing with Sierra Nevada and Orbital ATK.

Both Dragons complement each other in their abilities.

Rotational gravity would be nicer, but not necessary and not a priority to begin with. In the long run I think that rotating space crafts to asteroids will be bigger than surface bases on the Moon and Mars. But in the short run neither is the way to go.

If not couldn’t the cargo craft be reconfigured as an emergency life craft?
12 hours of life support(think Apollo 13), inflatable crash couches and use the cargo tie down points to attach simple harnesses They already have radios on them. just fit it for vocal use.

land it anyplace close to friendly a navel vessel for a pick up. You have a few hours or so to arrange it.

Localfluff: In my interviews with Russian astronauts who spent a year or more in space, they made it very clear that there were problems when returning to Earth after six months in space. Granted if they had to they could manage somewhat on their own, but to dismiss these issues would be a big mistake. The bone loss issue especially cannot be ignored.

I think you are taking these issues too lightly.

And it is certainly easier to deal with transitioning from microgravity to Mars’ .38g. To be careful they’d wait with the first EVA on Mars’ surface for a week or two. The time it takes for them to be fully readapted to gravity on Earth. Simulated gravity is not a stumbling block we need on the way to Mars. Only way to find out if there’s a hidden problem. is to go to Mars and find out. If it weren’t for the major mechanical risks for explosion or launch/landing failure, microgravity would be somewhat of a worry. But it is insignificant compared to the unavoidable real risks and certainly not worth a specially constructed space station to investigate. Martian gravity should be explored on Mars.

I do think that a slow rotation of even the ISS as it is, could be pleasant. It would make dust move more efficiently towards the walls and the ventilation, instead of flying in everyone’s faces. And give the body a sense of orientation, making it possible to for example sit down and to sleep without being tied down. But astronauts love weightlessness.

Heck, people choose to get pregnant, how dangerous isn’t that!? If astronauts are a bit weak and brittle, they’ll deal with it. Not worse than catching a cold, which will happen on Mars too.

Localfluff wrote: “6 to 9 months in microgravity is not a problem, the ISS and MIR have proven for hundreds of people.”

Actually, what has been learned from these long term space station flights is exactly the opposite, that microgravity is a problem if you want to go to Mars. At the end of each of these missions the astronauts were weak and badly in need of assistance. The recovery crews have to help them from the capsule, and they need help getting to chairs where they must sit for a period of time so as to not overstress their very confused and weakened cardiovascular, balance, and muscular systems.

If you go to Mars and arrive on the planet’s surface in the same state, you will have serious problems. There will be no one to help you, and you will not be able to function adequately in the 1/3 Earth gravity. Moreover, these problems only refer to the loss of balance and physical weakness. The loss of bone density in the weight bearing bones remains unsolved. The hip bones of astronauts might not break upon arrival at Mars, but the visit will not do much to restrengthen those bones, and during the return voyage they will continue to lose density. By the time they get back to Earth, a good percentage (probably more than half) of all astronauts will have bones that will not be able to withstand Earth’s gravity.

What we do not know is how much gravity does a human need to prevent these problems. It might be that a gravity of 1/10th Earth’s would be enough to prevent bone density and muscular loss. Or not. We don’t know. To find out we need to do tests, beginning with a centrifuge in orbit. Unfortunately, only once has a centrifuge been placed on a space station (Mir) and only for a very short time. During its very small handful of tests of plants, there were strong indications that it won’t take much gravity to solve these issues. If this is found to be true, it will reduce significantly the engineering challenges for making a spinning interplanetary.

The low mass of a tether and the rigidity of a truss, could maybe be combined by using an airbeam, a pressurized hose. Being a boy, I kind of appreciate that concept intuitively :-)

Several companies are working on truss systems. It might be more beneficial to go that route in the long term, or even the short term.

Would it all depend on duration? The longer the duration of the experiment, the larger the volume needed. No one can stay in a little itty bitty capsule for any extended period of time. This brings up another issue where existing habitats, even Bigelow’s, are designed without floors.

None of these are big deals but once someone decides to do something, what they decide to do dictates the other requirements.