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#126 2018-01-26 12:30:41

RobertDyck
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From: Winnipeg, Canada
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Re: Alternate BFR (Big Falcon Rocket)

The Centrifuge Accommodation Module was supposed to test that. It was a module as large as the US science module Discovery. It held a centrifuge the same diameter as a module; not large enough for a person, but plenty large enough for laboratory mice, rats, guinea pigs, etc. When the US decided not to build it, Italy paid for it and Japan built it. It was complete and waiting for launch at KSC. One more Shuttle launch would have carried it. One last Shuttle ET was built, a contractor at JSC told me they tried to convince Obama to launch it, but there wouldn't have been anything left for a rescue mission should something go wrong, so Obama didn't approve it. That module is now an outdoor exhibit in Tokyo.

I've said we could launch it. Not sure if it could be cleaned up, prepared for launch, or if a new one would be required. Could be cutting a hole for a door in the side and exposing it to rain means it can't be launched. For years I suggested launching it with Russia's shuttle called Ptichka. But in 2005 that orbiter was sold to a South African company that dismantled the flight deck, and scratched the heat shield tiles. That company "disappeared", the shuttle is still at the Baikonur cosmodrome, but it's no longer space worthy. But now, we could launch the centrifuge module on Atlas V with a service module from Cygnus to rendezvous with ISS. The station's arm could then berth it. This sort of research is exactly what ISS was built for, so DO IT ALREADY!

That would answer your questions about how much gravity astronauts need.

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#127 2018-01-26 14:35:59

Oldfart1939
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Re: Alternate BFR (Big Falcon Rocket)

Robert-
This is just another example of the misallocated priorities assigned by NASA to any REAL research that would affect man's ability to function on protracted deep space missions. Dealing with long-term microgravity effects is one of the primary detractors from any realistic Mars outpost/settlement/colony plans.

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#128 2018-01-26 18:25:52

SpaceNut
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Re: Alternate BFR (Big Falcon Rocket)

At the time it was transision of funds from what was thought to not be relative to finishing the station and low interest to any other than the workfare program shift. This is really one of the questions that we need more than 2 data points to solve.....

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#129 2018-01-27 09:38:02

Oldfart1939
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Re: Alternate BFR (Big Falcon Rocket)

Could a newly constructed Centrifuge Accommodation Module be carried to the ISS in the unpressurized trunk of a Falcon 9 Dragon? This is definitely a project worth doing!

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#130 2018-01-27 10:25:56

elderflower
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Re: Alternate BFR (Big Falcon Rocket)

For people I would think you would need a much larger diameter than would be practicable on the ISS so that the rotational speed will be kept low. Otherwise Coriolis and Gyroscopic effects would dominate.

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#131 2018-01-27 11:26:21

GW Johnson
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Re: Alternate BFR (Big Falcon Rocket)

4 rpm at 56 m radius = 1 gee at the tip of that radius.  Gee is linearly proportional to radius,  and to the square of the spin rate.  There are very strong but ill-defined limits to spin rate.  4 rpm seems tolerable even to unacclimatized crews,  for long-term exposure.  8 rpm requires considerable training and acclimatization for long-term exposure. 

Higher spin rates can be tolerated by people seated and restrained,  but only for short-term exposure (!!!),  as in a brief centrifuge run.  I calculate potential fainting problems due to blood pressure gradient in standing individuals at about 12 rpm,  based on seated fainting tolerance in aircraft without a gee suit. 

There are two directions that are practical and stable to spin a vehicle in space.  One is what everybody first thinks of,  about the long axis,  like a bullet or an artillery shell.  This is where launch vehicle shroud diameter sets the spin radius very short,  forcing you to very high spin rates.  The other stable direction is "head-over-heels" about the short axis,  like a majorette's spinning baton at a Friday night football game. 

That one (baton mode) gets you very much longer spin radii for far lower spin rates,  since nearly all space vehicle designs are 3-to-10 times longer than wide (diameter).  Folks seem to have a mental block about that spin mode,  though.  They never consider it,  and they should.  It makes spin gravity designs far easier.

Actually,  it's the same mode as all cable-connected-module spin gravity proposals.  But as a rigid baton,  there's far easier and better-developed dynamics to deal with.  By far.  Why make things hard and risky,  when you don't have to?

GW

Last edited by GW Johnson (2018-01-27 11:30:34)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#132 2018-01-27 17:42:50

SpaceNut
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Re: Alternate BFR (Big Falcon Rocket)

Sure tumbling end over end gives you a mean diameter but that would only give you the diameter of the rocket to walk within times 2 for each end but a rocket built to spin around the centerline of the length would give the distance of that section length for a 360 degree around that sections to use for walking and more.

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#133 2018-01-27 22:07:42

Void
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Re: Alternate BFR (Big Falcon Rocket)

While we might prefer a space wheel if we could afford it perhaps it would be good to see how far the Baton Mode might get us.

If I were to suggest another BFR model.  One where the nose section was a detachable cone-farring, and that compartment could bring a cone shaped Bigelow type inflatable structure to orbit.

Then, could we link these together into a linear structure, a set of them modular per O.F.

Use high tensile cables to make sure that spinning it would not cause it to fling apart.  Do we then have some type of a "Baton Mode" option?

A linear stick of "Cones" could give several compartments of different Gee forces, and so be useful to experiment on what is worth the bother.

Once you know what the minimums are that you want for various purposes,  (Human time length exposure health issues), then you might consider investing in a more expensive geometric structure.  Maybe even a wheel of inflatable cones.

Last edited by Void (2018-01-27 22:11:32)


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#134 2018-01-27 23:30:29

Oldfart1939
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Re: Alternate BFR (Big Falcon Rocket)

The Centrifuge Accommodation Module is for RATS! As an experiment to see what the long term effects of various fractional gravities have on physiology. There is nothing special about the bicycle wheel, and in fact the "baton" model would be far easier to build and maintain. I would not try for 1 g on the bicycle wheel or baton; I would suggest 0.4 g as that is roughly the gravitation on Mars.

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#135 2018-01-28 05:44:09

elderflower
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Re: Alternate BFR (Big Falcon Rocket)

I would fit two centrifuges, Run one as Mars gravity and one as earth gravity as a reference point. After a couple of years run, they could be changed to  moon gravity, Ceres gravity or Pallas gravity, or whatever else seems attractive. It doesn't need to be a one shot experiment, so we can spread the costs.
You need the reference unit to ensure that you are looking at gravitational effects rather than Coriolis forces etc.

Last edited by elderflower (2018-01-28 05:49:22)

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#136 2018-01-28 07:00:27

Terraformer
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Re: Alternate BFR (Big Falcon Rocket)

If they're the same size, the earth gravity one will have to spin faster. So you won't be able to compare them anyway.

It makes sense to do the animal experiment first, and let that guide the selection for the human experiment. Start with whatever seems to work in rats.


Use what is abundant and build to last

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#137 2018-01-28 10:06:15

Oldfart1939
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Re: Alternate BFR (Big Falcon Rocket)

Elderflower; regarding experimental design for the gravitation experiments, we need a variety of conditions. We already have earth gravitation HERE. We should start with the essential conditions for Mars (0.4 g), and then Lunar (0.25 g).

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#138 2018-01-28 10:19:29

Terraformer
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Re: Alternate BFR (Big Falcon Rocket)

Lunar is 0.17, not 025.


Use what is abundant and build to last

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#139 2018-01-28 12:30:28

RobertDyck
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Re: Alternate BFR (Big Falcon Rocket)

Actually, lunar equatorial surface gravity is 1.62 m/s². That's 0.1654 g, which is so close to 1/6 that we can say 1/6. I could try to convert high precision data from GRAIL and average that, but for the purpose of this forum I think that's enough.

Mars equatorial surface gravity is 38.0% that of Earth (0.38 g).

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#140 2018-01-28 13:05:00

Oldfart1939
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Re: Alternate BFR (Big Falcon Rocket)

I would plan on several generations of rats being sacrificed to these experiments. If I were the principal investigator, I would retain a control group of litter mates under zero g as a control; then a rat lifetime experiment on a Lunar gravity of ~0.165, then examine both groups and check bone densities and have blood draws for some basic chemistries and then quick-freeze the remains. The analyses can be done on Earth. Second experiment at a midpoint between Mars and Moon, say at 0.25-0.27 g. Same experiment with identical control group. Then a third experiment at 0.38 g simulating Mars. Then we have a 3 data point curve of results for starters. Then maybe another couple lower points on the curve; 0.08 g and 0.04 g. We may see a point at which bone decalcification initiates. Maybe even a 0.5 g data point as well. Based on experimental findings, we could ascertain a minimum g level for deep space missions for health maintenance.

Addendum: If enough litter mates are available, there should also be an Earth based subject for a baseline.

Last edited by Oldfart1939 (2018-01-28 15:41:29)

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#141 2018-02-07 12:40:02

Void
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Re: Alternate BFR (Big Falcon Rocket)

Don't get your underwear in a twist!

Buzz Aldrin's "Cycling Spaceship".  How might something like that fit with BFR?

https://buzzaldrin.com/space-vision/adv … cupy-mars/

To be honest, I have only a vague notions of what this is about.

But I would change it so that the ship parks in Earth and Mars orbit periodically.
The reason is that if companies like SpaceX do achieve near 100% hardware recovery, then propellants for moving up and down will be much cheaper.  Also if the Neumann drive works, then companies like SpaceX can bring metal propellants to orbit.

Later, Moon rockets may be able to bring metals up from the Moon.

And then there is Ballistic capture.  I would think that with all of the above options, ballistic capture would be a very good fit.

......

While BFR, whatever it finally becomes could have several versions, one that hops from Earth point to Earth point and only has seats like a jet liner, and one for deep space with cabins.  I just don't see the value of lifting the cabin mass up and down from orbit, and also long term life support equipment.  Why lift that up and down?

Of course there is going to be a refueling version.

But look at the international space station.  It has functioned for quite a time.  The question is if it were designed as a deep space spaceship, how many trips could it have already made between Earth and Mars?

https://www.nasa.gov/mission_pages/stat … index.html

The deep space spaceship would have a limited lifetime, but probably quite a few re-uses.

And I would suggest that it would be designed to have a minimal synthetic gravity sufficient to keep people separated from the waste materials which are emitted from their bodies.  (Feces, Urine, Mucus, vomit, ect.)

My method would be to have a "Freezer Toilet" the minimum gravity would assure that the disposed items would drop into it like an outhouse.  The freezing would help to make it stay there by sticking, and would also render it biologically inert.  And if somehow there were flies in the ship they would most likely get frozen as well.

And I think the odors could be controlled very well just by that and lids and air fresheners.  But if all else failed a little spray of a freezable fluid, would put a coating on the offending materials.

K.I.S.S.

Last edited by Void (2018-02-07 12:55:16)


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#142 2018-03-04 11:26:23

Void
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Re: Alternate BFR (Big Falcon Rocket)

Oh well, I am back with this.

Remember this is "Alternate BFR".  A knock off of SpaceX BFR.  How I might attempt to alter it for reasons of my own or you might alter it for reasons of your own.

Alternate BFR and synthetic gravity:

Spin Calc: (Again)
http://www.artificial-gravity.com/sw/Sp … inCalc.htm
BFR Rocket Dimensions: (The 2nd stage)
SpaceX_BFR_launch_vehicle.jpg
https://en.wikipedia.org/wiki/BFR_(rocket)


Quote:

Diameter: 9 m (30 ft)

So you could run spin calc on that.  I originally was thinking of spinning it on it's diameter, but then I thought of GW's baton.

So, if you did baton mode:
Length: 48 m (157 ft)

If I did that right, it comes out to 4.322892265817837 RPM for 1 g.

I don't think I want 1 g.  Maybe too much stress on the ship, although to launch from Earth and land on Mars it may be quite rugged.

Gravitations I might like are:
Sanitary Synthetic Gravity:  I arbitrarily assign .05 gee, in the hopes that that could be sufficient.
Here I am intending to be able to get rid of vomit and diarrhea.  And boogers, and other potential obnoxious emissions of the human body.  I imagine being on a BFR with 100 other people and an outbreak occurs.  Does anyone care to be in zero gee with that?

Of course my solution is baggie lined freezer toilets and sufficient sanitary gravity to separate humans from their bodily emissions.
On change out of the "Baggies" perhaps a light vacuum and static charge can cause the replacement to cling to the presumed metal sides of the "Freezer".

I don't know if there would be much physical benefit to sanitary synthetic gravity, but I am sure their would be health and mental health benefits.

The baggies would be of a size appropriate and I suppose size would be based on presumed preferred change out times.

Lunar Simulated Synthetic Gravity:  (~1/6 g)Who really knows yet what is the minimum synthetic gravity to delay deterioration sufficiently for a trip to Mars?  Well, since it looks like people will be on the Moon in a few years, this is a good point to examine.

Mars Simulated Synthetic Gravity: (.38 g)  Honestly, if this does not prove to be enough, then we are going to reconsider the notion of living on Mars full time, or come up with exotic synthetic gravity schemes in orbit of Mars, or on its surface.  So, it is a good thing to know ASAP.

......

Solar Arrays on BFR if you spin it:  (Some problems)

If a solar orbit, then I make a visual map so that we can have a common visual.  In the case of a baton spin, then the spin center can be said to have a "South Pole" and a "North Pole".  I would have the south pole aimed at the sun, and of course the north pole then pointed towards the outer solar system.  Then the solar arrays could placed in a static south/north configuration with the cells of course pointed at the sun.  They will also need pivots and motors so that you can re-orient them when BFR is not spinning.

For Earth orbit or Moon orbit, I have not taken the time yet to visualize this.  I guess the pivoting may be used a lot in that case, or you would not use synthetic gravity in Earth/Moon orbit.

But the very nice thing I see is that as soon as BFR can achieve LEO, you can begin to do synthetic gravity tests.  (If I have not made a critical mistake in understanding).

.......

Radiation problems:
Well, hopefully you can put a storm shelter at one or both ends of the ship, and it could also be a gym, with sanitary facilities, and emergency food and water.

Normally your preferred location of dwelling might be in the interior of the ship as much as possible but during a mild storm, you would sleep on the north side of the ship.  In a severe storm go to the shelter go to the shelter baby, baby.  (Frank Zappa).

In the most dire of situations, I suppose the ship would be de-spinned, and the only safest place would be then then "North" end of the ship.

......

This then I think might have the potential to free BFR from the necessity of Hohmann transfers.  Not that they would be prohibited.

Ballistic capture gives much better options for launch windows, and if you use electric rockets, some possibility of fuel savings.  Although I think fuel savings are a very much secondary consideration under the new circumstances of the possible reduced cost of fuel with the BFR tanker ship.
Ballistic capture takes longer, but allows much better options for launch windows, and may offer the opportunity to enter Mars orbit without aeroburn, and then later if you do aeroburn, it could be more gentile.

Here I am thinking that (For later missions, when a settlement has already been established), a ion tug could even bring the BFR from a ballistic capture orbit down to a LMO (Low Martian Orbit).  Then an aeroburn would be relatively gentile.

.....

I might as well get it over, and describe another option.
BFR with Ion Rocket capabilities:

Well since for a long time solar cells will likely be manufactured on Earth, and carried to Mars by BFR, as I think it likely that insitu manufacture of them will come some considerable time later, consider putting them to use on the trip to Mars.

So, in the cargo hold of BFR on launch have an ion rocket with it's propellant, and the solar panels for Mars.

Launch, open the doors, and if possible hook it to the BFR, using the solar panels for Mars for power.  During this phase it may be difficult to do the synthetic gravity method.  I am not sure.  Maybe a pivot on the south pole of the ship hooking to the ship as it spins.  Something to ponder.

Anyway you use the best portion of the available solar power on the trip.  Just on a guess, if you get to 1.15 AU out, you then pack away all or most of the solar panels, depending on if you intend to send the ion rocket back.  You have options for the ion rocket:
1) Throw it away.
2) Take it with you to Mars as a replacement for ion rocket tugs in Martian orbit.
3) Send it back to Earth in a very slow mode.  You would only give it a very limited number of the solar panels and would take most with you to land on Mars.


When you were done with Ion Rocket propulsion you would then fire up the chemical engines to do a burn to Mars.  With a chosen intention of a Hohmann or Ballistic method of capture.

......

There are quite a few options mentioned in this post.  It is likely that members will not like some of them.  I would ask you to consider other combinations of the options in that case, instead of picking something you don't like and then dismissing everything here.

Thanks, I am done.

Last edited by Void (2018-03-04 12:25:43)


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#143 2018-03-05 12:32:25

Void
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Re: Alternate BFR (Big Falcon Rocket)

Well, I made a mistake.  Imagine that!  The shame!

Here is the real RPM number for 1 g @ 78.5 feet, if I am not mistaken again.

6.113492870997343  RPM

And I think I may be done with this and quite a lot of other things soon.


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#144 2018-03-05 17:49:09

SpaceNut
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Re: Alternate BFR (Big Falcon Rocket)

The gravity would be felt by the feet as they would be perpendicular to the axis of spin and the taller one is the less gravity you will feel at your head while working. It will only be fully felt when sleeping.

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#145 2018-03-05 20:11:55

Void
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Registered: 2011-12-29
Posts: 7,831

Re: Alternate BFR (Big Falcon Rocket)

Spacenut said:
Quote:

The gravity would be felt by the feet as they would be perpendicular to the axis of spin and the taller one is the less gravity you will feel at your head while working. It will only be fully felt when sleeping.

Fair enough this is a rough work.  Trying to puzzle a method from the supposed specs given by SpaceX.

Perhaps I might restate your statement as:
The gravity would be felt more by the feet as they would be perpendicular to the axis of spin and the taller one is the less gravity you will feel at your head while working. It will only be fully felt when sleeping.

And say that for synthetic gravity that is pretty much inevitable.

Remember that more than anything I value sanitation gravitation.  After that, the luxury of 1/6th g and .38 g are also valued.  I don't really care as much for 1 g.

But thanks for the response.

And I confess, I am not as knowing as some would be about what effects spin would have on the inner ear at this specs.  Obviously for more typical common people, which is what would be the case here, what is the limits of their tolerance of this situation before you make them nauseous?   Obviously if you want sanitary gravity making them vomit is not a preference.

If you can avoid this then spin up to the limits to avoid most vomiting.  And I don't know what that is.  I would start with the desire, and seek an answer to this question.

Last edited by Void (2018-03-05 20:17:05)


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#146 2018-03-05 20:40:24

Void
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Re: Alternate BFR (Big Falcon Rocket)

And that leads to a really thrilling question (For me):
Do bones each decide how much they should accumulate mass individually or do they make that decision in collaboration?  This is one way to test the question. The same question will be asked in:
"Index
» Science, Technology, and Astronomy
» Modified gym equipment to partially simulate low gravity."

Last edited by Void (2018-03-05 20:42:06)


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#147 2018-03-05 21:38:53

SpaceNut
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From: New Hampshire
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Posts: 29,433

Re: Alternate BFR (Big Falcon Rocket)

xamusement_park_physics_4.png.pagespeed.ic.gj3gthM4Rg.png

If we are tumbling the construction means the diameter is all that you get to walk on but since we build with that in mind there is all the stuff on that surface making it such that we can not walk. The same problem is on the walls of the section of the walls will have the controls on its surface. Making it such that we will not be able to stand vertically to move about without stumbling, causing damage to ourself or to the ship. So unless the zones are design free and clear to make us of the surfaces to move on we will only be able to partially use the gravity as intended.

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#148 2018-03-05 23:28:53

Oldfart1939
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Registered: 2016-11-26
Posts: 2,452

Re: Alternate BFR (Big Falcon Rocket)

Void-
The biochemistry of bone assembly and deterioration is not very well understood, but the key is it's an endocrinology question which you are asking. This is an area in which I did some work about 7-8 years ago before I fully retired from doing active chemistry and biochemistry.
There are 2 types of stem cells involved in bone architecture: Osteoblasts and Osteoclasts; Osteoclasts (OC), are involved in removal of older bone cells and in the decalcification pathway; Osteoblasts (OB) are responsible for regeneration of bone mass and bone tissue in general. These are essentially 2 competing systems which under normal gravity, work just fine until advancing years slows the production of OB cells and osteoporosis develops. There is a polypeptide hormone which controls and stimulates production of these cells and is frequently used clinically to treat Osteoporosis in post-menopausal females. One approach for controlling bone decalcification in microgravity COULD  be use of Calcitonin in periodic injections to stimulate replacement of weakened bone tissue; unfortunately there is not an approved drug that would inhibit OC production. How the living system determines how much or how many of these various cells are produced is not understood; this is a classic feedback system, but to date we haven't found the transmitter or receiver of the stimulus called "weight." So...this was the last biochemistry problem I was working on when I retired.

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#149 2018-03-06 01:22:12

RobertDyck
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Re: Alternate BFR (Big Falcon Rocket)

I'm hesitating here. Oldfart1939 in an actual expert in this field. Should I chime in?

Void, there are a couple known controlling factors. Bones first evolved as a means to store calcium. That was their first purpose, evolved in a worm with a notochord during the time recorded by fossils in the Burgess Shale. When your body needs calcium, lack of calcium stimulates a sequence of hormones that cause osteoclasts to tunnel through bone, dissolving it to release calcium into blood.

Bones have nerves. If bones are stressed so that your bones ache, that means bone in that spot is not strong enough for whatever you did. This stimulation of nerves triggers a cascade of a sequence of hormones that cause osteoblasts to build bone. So building bone is not even all over your body, it's specific to the areas where you stress bone.

In a healthy person, this process balances. As you exercise, you stress bone. This causes bone to build in the places you stressed. As your body needs calcium, it dissolves bone. Last I read, bone is dissolved evenly all over your body. This process of building and tearing-down results in equilibrium. Since building bone only occurs where nerves are stressed, you tend to have thick bone where you need it, lighter bone where you don't. So your body is constantly tuning your skeleton.

In old age this process fails for a couple reasons. First, your body has to build bone fairly quickly to respond to a stimulus. If it doesn't, that can result in osteoclasts dissolving bone where it's needed. Thin bone can break. Elderly people should exercise regularly to stimulate bone formation, in order to prevent brittle bone. If they sit around doing nothing, scared at their own shadow, they won't stimulate nerves in their bones, which will result in thinning bone.

The other reason is my own hypothesis. This isn't confirmed by any medical practitioner, just my own guess. That is, osteoporosis can be the result of nerve damage. Many researchers have focused on biochemistry, ignoring the overall process. If nerves in elderly bones become damaged, they can't initiate bone formation. But since osteoclasts are triggered by blood chemistry, the need for calcium, they aren't slowed by damaged nerves. This imbalance will cause thinning bone.

In space, you have basically no physical stress. However, bone loss appears to be much greater than can be accounted for by lack of exercise. Bed rest studies have compared results with space. Those confined to bed experienced muscle atrophy and bone loss, but not nearly as rapid as astronauts. Why? On Earth, even in bed you fight against gravity. Your bones hold your body together. Breathing requires lifting the chest, that means at least tissue attached to ribs will place that much stress on those bones. Not much, but in space it's zero stress. Still, it appears space causes more dramatic bone loss than that. One guess that I've posted on this forum before is that cells experience convection within cells. That zero gravity will negate convection, interfering with normal chemical reactions. If this hypothesis is true, then Moon level gravity should be enough to restore those chemical reactions. Difference between Moon and Earth gravity should be just a matter of exercise. Stress on muscles, and stress on bone. The Centrifuge Accommodation Module with it's centrifuge was supposed to test that with laboratory animals. It was never launched. sad

Oldfart1939, I wish one of our past members was still here. I had excellent conversations with Dr. Richard Sylvan about this. He was really passionate about the Centrifuge Accommodation Module. He was an oncologist, but ironically he had cancer himself. Sadly, he passed away in April 2008. That's 10 years now? He told me they had mapped many of the hormones that control bone.

To answer your question directly: bones "decide" how much they should accumulate mass individually.

Last edited by RobertDyck (2018-03-06 02:18:20)

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#150 2018-03-06 01:41:22

RobertDyck
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Re: Alternate BFR (Big Falcon Rocket)

I did a quick Google search, found this...
Physiology in Extreme Conditions: Adaptations and Unexpected Reactions

In reference to bone metabolism, the levels of vitamin D, bALP, osteocalcin, calcitonin, parathyroid hormone (PTH), and Ca++ have been investigated. Results from the Mir18 mission showed a significant decrease in 1,25(OH)2-vitamin D and its precursor 25(OH)-vitamin D. Calcitonin levels were not affected either in space or back on Earth. The observation that PTH values rapidly increase upon return to Earth (Smith et al., 1999) indicates detrimental mass bone restoration, as PTH promotes bone resorption and elevates blood Ca++ levels by activating osteoclasts. However, PTH acts on kidneys too, increase Ca++ and decrease (PO4)3- reabsorption (Lee et al., 2009), suggesting that bone loss in microgravity may be due mainly to impaired kidney function and vitamin D production, rather than to a significant calcitonin and PTH imbalance. Therefore, reduced vitamin D level may decrease Ca++ fixation in bones and reabsorption in kidneys, causing increased Ca++ excretion despite normal levels of calcitonin and PTH (Smith et al., 1999). Vitamin D level increases later on, upon a prolonged re-exposure to gravity, to promote net bone fixation.

I took the liberty of adding parentheses to (PO4)3- because the actual document has "4" as a subscript and "3-" as a superscript immediately above the "4". This forum doesn't support sub/superscripts.

Last edited by RobertDyck (2018-03-06 01:54:32)

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