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Sending humans to Mars actually feasible?

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#51 WaterMaster

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Posted 25 July 2013 - 03:14 PM

... is the gravity of a heavy body (e.g. the earth) the same as the gravity of the large spinning space station?


In a spinning space station, the inhabitants are not experiencing gravity, but rather centrifugal force.

#52 Jarad

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Posted 25 July 2013 - 03:36 PM

It's not exactly the same. The gravity we feel on earth is because the earth's mass is curving local space/time. This is another area where Danny is probably a better person to ask than me if you want to get into real detail.

In the case of a spinning space station, space/time is not being curved. You are moving, and the floor of the space station is pushing up against your feet changing your direction of motion from a straight line to a curve.

Mechanically, both result in force pushing down your body, putting stress on your bones and muscles. That's good enough for the purpose we want here.

At the more detailed level, the force on your body on earth is proportional to r^2, where R is the distance to the center of the earth. Since we are pretty far from the center of the earth, the difference between your head and feet is pretty miniscule.

On a spinning space station, it will be proportional to R, where R is the distance to the center of rotation. Since that is likely to be a lot smaller than the earth, the difference between your head and feet is likely to be noticeable. Also, the direction of "down" will change pretty quickly as you move around the station. So it will probably take some getting used to. Learning how to play "catch" with a ball on a rotating station would be rather challenging - it won't travel the same line it would here on earth, and the line will be different if you throw into the spin, against the spin, or across the spin. The force also depends on the square of the rotation rate, so you will "weigh" more if you run spinward, and "weigh" less if you run anti-spinward.

Jarad

#53 Otto Piechowski

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Posted 25 July 2013 - 03:39 PM

Thanks Jarad.

Danny! (Other hard core physicist types). If gravitons are real, whatever they are, are they present, just as present, of the same type in the gravity well of a planet and the "gravity" of the space station both effecting the same gravitational effect/feeling on the human body?

Otto

#54 Ira

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Posted 25 July 2013 - 05:19 PM

Imperial College London has a plan. Behold, nothing up my right sleeve...nothing up my left...

http://news.cnet.com...from-mars-a-...

/Ira

#55 derangedhermit

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Posted 25 July 2013 - 05:44 PM

Seems to me that it would make sense to design the next LEO space station to rotate and generate artificial gravity as a test bed.

Jarad


The one up there now is modular, is it not? Just send up a long cable on the next Russian launch, split it in two and start the pieces spinning; might as well get some useful science out of the thing.

The only good reason that I could see to do that one was to keep Russian missile builders off the black jobs market.

Why would we think about building another? Or am I wrong, and we've gotten significant science out of it? More Teflon, or was it Tang?

Unless NASA is hiring me to work on it; in that case I'm all for it. A friend of mine got fired for incompetence while managing a Chik-Fil-A store in Houston, and got a job at NASA as a procurement officer; he's bought billions of dollars of stuff, says it's lots of fun, says the fast-food job was too hard.

#56 ColoHank

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Posted 25 July 2013 - 06:46 PM

Mechanically, both result in force pushing down your body, putting stress on your bones and muscles. That's good enough for the purpose we want here.



I wonder... is that conjecture or fact? I should think we won't know for sure until we test it over a long term in an otherwise weightless environment.

#57 llanitedave

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Posted 25 July 2013 - 10:08 PM

Relativity considers the force due to gravitational acceleration and the force due to velocity acceleration to be exactly equivalent. Centrifugal force,as Jarad states, will create slightly different affects due to the "tidal" qualities of the limited rotational radius, but at any instantaneous time and location, it will still be exactly the same as gravity. You might be able to tell whether your feet are slightly heavier than your head, but then you can always lie down until the feeling goes away!

Biologically, it should be far superior to weightlessness.

As for attaching a tether to the ISS and swinging it around, I doubt that it will be a good idea. The ISS wasn't designed to withstand any significant torques. You'd need a vessel built with the capability in mind.

#58 Rick Woods

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Posted 27 July 2013 - 11:39 AM

Seems to me that it would make sense to design the next LEO space station to rotate and generate artificial gravity as a test bed.

Jarad


The one up there now is modular, is it not? Just send up a long cable on the next Russian launch, split it in two and start the pieces spinning; might as well get some useful science out of the thing.


Ahh, why start now?

The only good reason that I could see to do that one was to keep Russian missile builders off the black jobs market.

Why would we think about building another? Or am I wrong, and we've gotten significant science out of it? More Teflon, or was it Tang?

Unless NASA is hiring me to work on it; in that case I'm all for it. A friend of mine got fired for incompetence while managing a Chik-Fil-A store in Houston, and got a job at NASA as a procurement officer; he's bought billions of dollars of stuff, says it's lots of fun, says the fast-food job was too hard.


Wow! Now that's interesting! You could take that in a couple of completely different ways...

#59 Rick Woods

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Posted 27 July 2013 - 11:46 AM

How about this one; let's assume the Red Planet (movie) thesis is true, that we are killing the earth and will make it effectively uninhabitable in a few generations; is it realistically possible to terraform Mars? And, is it possible to terraform Mars in a time span of benefit to us who are, hypothetically speaking, killing the earth?



No and no. There's nowhere near enough gravity on Mars to sustain an atmosphere capable of supporting human life. Mars also has a weak and incoherent magnetic field, so what little atmosphere it has is vulnerable to further stripping by the solar wind, and its surface is bombarded by cosmic radiation. Not a very friendly place.


Theoretically, Mars could be terraformed, but: It would take a thousand years or more; it would require a lot of new technology that hasn't been developed yet (but could be); and the real kicker, the final product would only be temporary for the reasons Hank gave.

Anyone who thinks that, when we've finished trashing Earth, we can terraform Mars and go live there, is seriously deluded. Dangerously deluded, if they happen to be in a position of power where such fantasies could affect decision making.

#60 FirstSight

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Posted 03 August 2013 - 07:45 PM

While it would be fun to go, I am unable to articulate a compelling business case that would convince a nation that the science value of this mission would be worth the cost.


A manned trip to the moon made no more "compelling business case" back in the 1960s than a manned trip to Mars does in the 2010s or 2020s, beyond the competitive national pride and prestige in the potential accomplishment. Yes, we got some moon rocks back for analysis from the Apollo missions, but now that we've advanced remote robotic capabilities in the 40 years since the manned lunar missions, that original advantage is vastly less compelling for any similar goal of returning some Martian samples to Earth. Better yet, we've advanced remote analysis capabilities to the point where even that is less compelling, though still useful (since the variety of testing possible on Earth is broader and more flexible than the limits of what we're able to send along with the spacecraft).

There's really no compelling "business case" for ANY manned mission to ANY of the planets, beyond that which existed for the original quest to land a man on the moon. The quest is more like mountain climbing in its fundamental goal: because it's there.

#61 llanitedave

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Posted 04 August 2013 - 04:31 PM

To paraphrase Franklin and Faraday, what is the compelling business case for a newborn baby?

#62 Rick Woods

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Posted 05 August 2013 - 08:53 PM

That case was made 9 months earlier...

#63 llanitedave

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Posted 05 August 2013 - 09:12 PM

Similarly, in this case the launch is its own reward!

#64 Rick Woods

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Posted 06 August 2013 - 09:54 PM

:lol:






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