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View Full Version : Coping with Gravity on the Moon



Andromeda321
2004-Oct-14, 08:10 PM
Ok, this is a random thought I've found myself on lately. In a lot of scifi stories there's detail about people having to excersise etc when out in space so they can return to Earth. I understand that well enough because the astronauts nowadays all excersise so they don't lose too much muscle.
Another aspect of scifi in this regard is what happens to a baby when it's born into space. There are varying degrees of explanations, some say the kid would never be able to come to Earth the others say s/he could but it would be rather uncomfortable.
So I was wondering: what would really happen if a child developed and was born on the moon? Would the gravity of Earth really be so strong it would be prohibitive for that child to ever visit? Thanks. :)

Evan
2004-Oct-14, 08:46 PM
No one knows for sure. All we have is poorly informed guesses.

ToSeek
2004-Oct-14, 09:36 PM
The assumption is that a child raised in lunar gravity wouldn't develop the muscles or the bone mass to be able to cope with Earth gravity, though, as Evan notes, this is just an assumption, though supported to some extent by the experiences of astronauts on long-term flights, who indeed lose muscle and bone mass even if they exercise.

Evan
2004-Oct-14, 09:59 PM
The problem is that we don't know if our zero gee experience applies to low gee. We have exactly zero experience with anything resembling long term exposure to low gee. Some in the medical community think that even low gee would be enough to ensure adequate musculoskeletal development, others think not. It's all guesswork. One of the more likely problems would be with the cardiovascular system. The heart would likely be underdeveloped and when a person raised on the moon was exposed to one gee environment they might well suffer from persistent orthostatic hypotension. That is the dizzy passing out feeling you get when standing up quickly, especially when you are young. It's caused by the vascular system not reacting quickly enough to changes in posture. As a medical condition it can have many underlying causes but it is a common problem with returning astronauts. Unfortunately, we do not have any way to determine what the effects of low gee will be except for living in low gee.

It may be that it only takes some gravity to switch on the bone formation and muscular development, or not. One thing I do know is that I sure would like a vacation on the moon in a suitably equipped hotel. Just think, no more arm going to sleep because someone is lying on it... :D

01101001
2004-Oct-14, 11:28 PM
The problem is that we don't know if our zero gee experience applies to low gee.
How hard could it be to raise a few generations of mice on the ISS in a little 1/6 g cetrifuge?

Hmm, they are doing this 2006 Biosatellite experiment (http://www1.nasa.gov/lb/vision/earth/livingthings/20jan_marsmice.html). Bah. No babies.

Silent Knight
2004-Oct-15, 04:27 AM
They will spin the satellite 34 times per minute to create .38g so couldn't they spin something 89 times per minute to create artificial Earth gravity?

kenneth rodman
2004-Oct-15, 07:13 AM
well yes they gould but then it wouldnt be a low g experiement would it

eburacum45
2004-Oct-15, 07:54 AM
By the time we have a permanent Lunar colony, many decades from now, I expect we will have some kind of genetic manipulation available; it is a good idea to remember that biological science is making remarkable progress in the field of the human genome.
I think it is very likely that the people that eventually colonise space will almost all have genetic modifications of some sort, inheritable or otherwise.

Kaptain K
2004-Oct-15, 12:02 PM
They will spin the satellite 34 times per minute to create .38g so couldn't they spin something 89 times per minute to create artificial Earth gravity?
Yeah, but the Coriolis effects would be dizzying - to say the least!

Evan
2004-Oct-15, 03:13 PM
Here is a program I wrote in 1967 to calculate a table of rotation rates vs radius to provide centrifugal force. It's in FORTRAN.




RUN,S.
LGO.
g
PROGRAM ALPHA (INPUT,OUTPUT)
REAL LIM2 ,LIMIT ,MASS
READ 5, SPEED, MASS, RADIUS, PI, CONST, I,J,LIMIT,LIM2
5 FORMAT(9F8,3)
15 FORMAT(1H6,15X,*FORCE MASS RADIUS SPEED*///)
PRINT 15
25 FORCE=((PI**2)*(SPEED**2)*mass*RADIUS)/CONST
PRINT 20, FORCE, MASS, RADIUS, SPEED
20 FORMAT(1H0,4F20,5)
SPEED=SPEED+I
J=J+I
IF(J,GT,LIM2) STOP
IF(SPEED,GT,LIMIT)MASS=MASS+I
IF (SPEED,GT,LIMIT)SPEED=I
IF(MASS,GT,LIMIT)RADIUS=RADIUS+I
IF(MASS,GT,LIMIT)MASS=I
GO TO 25
END



I still have the card deck for it from UC Berkeley.:D

Silent Knight, the rpms needed to generate a particular "gee" depend on the radius.

Andromeda321
2004-Oct-16, 04:30 AM
Interesting... :-k
So what you guys are saying is if I'd want to write a sci-fi story on the subject I'd better do it soon while the jury's still out. :wink:

Invader Spleen
2004-Oct-16, 05:21 AM
the way i see it, the body will adapt so that it is in the most effiecient form possible, that is to say a child born in zero g will not develope the bone mass or muscle mass to be able to operate in 1g because its not needed for the body to function, therefore it would be wasteful for the body to develope said mass, however if the child was required to go into a 1g environment the by gradulay incresing the gravity at a slow rate, the body will adapt and increse bone density and muscle mass (assuming the increse in gravity isnt too quick)

Evan
2004-Oct-16, 06:14 AM
Invader,

Chances are excellent that a child born and raised in zero gee would be pathologically ill. Zero gee is not in our program and any adaptation to it is almost certain to be very negative, possibly fatal. The last time our ancestors were exposed to zero gee was before they crawled out of the oceans.

eburacum45
2004-Oct-16, 08:04 AM
Dolphins seem to do okay in a bouyant environment;
a little mix and match between chimps, humans and dolphins could produce a space adapted human...

Evan
2004-Oct-16, 04:14 PM
On topic is a book by Lois McMaster Bujold titled "FALLING FREE".

CTM VT 2K
2004-Oct-16, 06:31 PM
Invader,

Chances are excellent that a child born and raised in zero gee would be pathologically ill. Zero gee is not in our program and any adaptation to it is almost certain to be very negative, possibly fatal. The last time our ancestors were exposed to zero gee was before they crawled out of the oceans.

Except that wasn't zero-gee... that was submerged. You can externally simulate zero-gee that way, but the internals still are under 1-gee. Important difference when talking about Internal Medicine.

Evan
2004-Oct-16, 06:50 PM
Yes that is true. It is the closest we come to zero gee but it isn't. That is also why I didn't mention the initial development in utero.