You seem see their only purpose as being support for deep space missions.

But someone who needs to do other kinds of microgravity and/or large vacuum research, has no reason to go any farther than LEO.

The ‘don’t look back’ attitude of those who are ‘tired of going round and round’ in LEO, never ceases to annoy me…

And without affordable launchers, nobody can hope to get anything done very much, if at all.

No question. I agree completely. But that’s not what the OP said. The issue was whether it was indeed doubtful that a station could not be crewed continuously. It may be doubtful that a LEO space station would deserve support if it were not occupied, given that the lion share of important work being done on it is human factors in microgravity. But one could probably operate it for a long time without people on board.

“Considering how early on the Chinese are with their space program, how risk adverse they are, and how little we really know about their intentions, I’d say there is not enough information to make that statement.”

My statement was intended to mean that the Chinese understand they don’t need to keep Tiangong occupied. But that’s correct that they may or may not understand that not keeping it occupied will keep costs down for them.

“The idea that you need such a station to be continually crewed is nonsense, and in no way, in this day and age, would that keep costs down.”

The reason for having human tended space stations is to learn how to live and work in space WITH HUMANS. I agree that we can do a lot of stuff already telerobotically, and could do more. But that does not address the science that is being done on humans in space related to mitigating the effects of zero G and all the other “bad” things in space with humans. The only way to do that is with humans as test subjects in space, and LEO is the closest place to accomplish that.

“The Chinese understand that with Tiangong.”

Considering how early on the Chinese are with their space program, how risk adverse they are, and how little we really know about their intentions, I’d say there is not enough information to make that statement.

What we do know is that the Chinese are slowing improving their capabilities, and that there record so far puts them about where we were with the Skylab.

But the Chinese have also stated that their eventual goal is to move further out into space, and they are as interested as the rest of us in how to keep their people alive and healthy. So far the length of missions they have done have not been a concern, but as we know when you start doing missions numbering in months, it becomes a much more serious concern.

Overall the only reason for doing anything in space with humans is because there is some form of agreement that we want to do things in space with humans. What they ultimate goals are for that are undefined (and vastly uncoordinated), but the general goal is enough that is sustains continued funding for the ISS and other programs.

Let’s not forget that although the propulsion needed to get from Earth to a cis-lunar station is larger than that needed to get to LEO, the propulsion needed to get from that cis-lunar station to Mars or the Moon is a lot less than that required to get to the Moon or Mars from LEO. So although a cis-lunar development station is logistically somewhat harder than one in LEO, what you build there has a big advantage.

In the long run, to the extent such deep space vehicles can make economical use of lunar ISRU, a LEO development station makes less sense. Yes, that’s a VERY long run.

The idea that you need such a station to be continually crewed is nonsense, and in no way, in this day and age, would that keep costs down. The Chinese understand that with Tiangong. Keeping crew in space keeps costs down? What planet are you living on? In fact, even at a cis-lunar development station, many development tasks (e.g. linking modules for building a deep space vehicle), could be done telerobotically from the Earth. Given the potential for telerobotic operation, fewer, rather than more, humans on the station are probably best. “10-20″ is a wholly artificial WAG number.

“It would also help to have some women.”

Ah, in addition to “people”? Nice call. Again, what planet are you living on?

I agree that stations in LEO have many uses, but let’s not inflate the rationale blindly.

LEO has one huge advantage when it comes to human spaceflight. Lower costs for manning and resupply. Any rocket that can lift about 10-25MT to LEO can lift both people, cargo or build an LEO station. Rockets of that size also have demand outside of manned spaceflight in terms of lifting communications satellites to GEO, GPS, or for spying and this makes them both cheap and relatively available. For stations further out the cost of manning and logistics increases.

A good example is say the Falcon 9. The F9 can lift about 13MT to LEO, but only 4.8MT to GEO(and to lift to L2 would cost about the same, maybe a little less). At 4.8MT, resupply would be impossible with the Dragon capsule. You need a bigger more expensive rocket like FH, Atlas, or Delta or you need to use low delta V trajectories (which can take a few months and also cut into cargo) or SEP.

To send crew likewise would require larger more expensive rockets but crew cannot take slow trajectories and so you again either need a bigger rocket or on-orbit assembly or a propellant depot to get out that far. Basically there is nothing to be gained by going further out but a bigger bill unless there is some objective that cannot be done in LEO.

For a station at L2, I rather doubt that it would be possible to even keep it crewed constantly as most projects I have seen for them tend to call for stations that are man tended to keep costs down. FH might be cheap enough to do it, SLS won’t be cheap or have a flight rate high enough to even attempt a permanently manned station further out.

Also the breakdowns on the ISS life-support have caused them to turn to back ups. It isn’t a problem solved with more back up. If you want to get data on long term spaceflight it is best done from LEO. As for number of people more is better but probably about 10-20 to start drawing conclusions. It would also help to have some women.

http://www.moviemistakes.com/film8

LEO is useful, but not for building deep space habs. Re the movie 2001, I guess it used to be, before LEO was so seriously polluted. Orbital debris is one important reason why space telescopes are not put in LEO anymore. Because of more rapid orbital decay, LEO is somewhat less polluted than higher altitudes, but the problem is still serious. ISS is outfitted with Whipple shields over key sections. Putting such shielding on a deep space vehicle to protect it in LEO would be a waste of mass.

Only 4 people have stayed in space longer than 12 months. All were men. Too small a sample size to get much meaningful data on health effects and yes there are possible health effects.
Too small sample rate for statistics, but enougth to expand duration of expeditions. AFAIK Roscosmos & NASA re going to send few 1-year crews to ISS since 2015. How many people do you want to get representative sample? 100 or 200?

The problem with ISS life-support is that it takes too much crew time to maintain and is a bit unreliable. Honestly, it needs to be upgraded with something a tad more reliable.

“Medical aspects? We already know people can live in space 12-18 months.”

Only 4 people have stayed in space longer than 12 months. All were men. Too small a sample size to get much meaningful data on health effects and yes there are possible health effects. Shorter stays have revealed issues with bone-loss, muscle loss, vision changes(in men),low blood pressure and so forth.

“Also, close biosystems would be useful in a long journeys as a source of oxygen and food, but at first it should be created on Earth. There are no reasons to pull it on the orbit before we build stable system here.”

Ah if you mean closed loop life support, yeah you do want that in an space station to reduce supplies. If you mean growing food in space, yeah you do want that because the seeds and chemicals needed to grow the food could take up less space than the space needed to store food . You don’t need an biosphere for an source of oxygen as both ISS and Bigloew stations would get their oxygen from breaking water molecules.