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#1 2022-09-03 05:32:50

Mars_B4_Moon
Member
Registered: 2006-03-23
Posts: 8,892

Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

In 1957 a Soviet 'space dog' was launched, in 1969 the USA Won the SpaceRace by Landing Men on the Moon. In all this time do we still not know how much Fake Gravity it takes to stay in Good Health? How much would it  need to make plant and tree and grass grow health, to transport bee, fish, bird, dog, cat, pig, rabbit, human or other animal and avoid Urinary tract infections, space motion sickness in human, a Strong health system to fight autoimmune diseases, how much Gravity to Avoid significant Muscle Loss, visual impairment or intracranial pressure, Bone loss, Orthostatic Intolerance?

I tried checking for the answer on a NASA site but it was a waste of time, maybe nobody knows.

Other new mars discussions

Artificial gravity station?
https://newmars.com/forums/viewtopic.php?id=7246
1 gee artificial Gravity on Moon and Mars surface
https://newmars.com/forums/viewtopic.php?id=10295
Artificial 1g Gravity on Mars vs in Space
https://newmars.com/forums/viewtopic.php?id=7655
50 years after...
https://newmars.com/forums/viewtopic.php?id=6180
Artificial Gravity
https://newmars.com/forums/viewtopic.php?id=7136

Last edited by Mars_B4_Moon (2022-09-03 05:42:47)

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#2 2022-09-03 05:41:50

Mars_B4_Moon
Member
Registered: 2006-03-23
Posts: 8,892

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

Mars Gravity Biosatellite was a proposed mission meant to study the effect of artificial gravity on mammals, wheel space station, also known as a von Braun wheel also proposed by Konstantin Tsiolkovsky and Herman Potocnik, the ISS Centrifuge Demo a 2011 NASA proposal,  Voyager Station is a proposed rotating wheel space station, Lunar Orbital Station a Russian design and Nautilus-X modules are based on the technology used by the inflatable living quarters proposed by Bigelow Aerospace http://www.physorg.com/news/2011-02-nas … craft.html .

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#3 2022-09-03 06:13:17

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 16,754

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

For Mars_B4_Moon re new topic...

Best wishes for success with this new topic ....

Your post #2 appears to include proposals by others, but for some reason your list does not include 2+ years of work by RobertDyck.

If you have time, you may discover work by RobertDyck and others that explore this topic.

RobertDyck is making the bet that Mars Gravity ** is ** sufficient to provide for good health of living creatures, but (as you point out) no one appears to have done actual experiments to find out.

(th)

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#4 2022-09-03 07:05:44

Void
Member
Registered: 2011-12-29
Posts: 6,976

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

This is a wonderful topic.  Very soon after Starship becomes capable of LEO, it will be possible to test it.

Dr. Johnson has proposed in the past, as I recall that to tumble the Starship end over end a .5 g force could be generated.

If this proves practical, then g forces of 0 to .5 could be tested in LEO.

These missions would not need refilling and might be performed on test subjects after deploying Starlink Satellites.

I recall Terraformer wondering if 1/10th g might allow for functional plumbing.  That could be tested as well.

Of course, human rated life support will not come until later, but these things might be tested on other animals that are used in medical research already.

A big question I have is what is the response curve for simulated gravity?  In other words, will 1/10th gravity reduce deterioration by what time interval?  Zero g seems to be limited by about 6 months to a year, if I recall.  Would 1/2 g simulation double that?

I am guessing that it is not a straight line.  You would not be likely to test it, but what might you need to keep a human healthy for 5 years?

Obvious values to test would be 1/6th and ~1/3 g.

I have recently witnessed conversation indicating that 3D printing in orbit would be more possible if even a small amount of spin gravity were provided.

Here is an interesting article about perception of up and down in g fields: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4153541/

I am having trouble understanding it so far, but it seems to indicate the Mars gravity at least will be enough for that.

Quote:

Estimates of this threshold vary considerably depending on the methods employed [19] but there is a general agreement that accelerations along the long axis of the body above about 0.15 m.s−2 (0.02 g) are reliably detectable.

I have a feeling that to some degree at lower g forces the human mind will eventually adjust to less than .15 g.  But of course that is not yet tested.

Done.

Last edited by Void (2022-09-03 07:28:54)


Done.

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#5 2022-09-03 07:58:26

Mars_B4_Moon
Member
Registered: 2006-03-23
Posts: 8,892

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

Yes I should have credited the other ideas explored by RobertDyck, I am also of the idea of what exercise workout method keeps people healthy for a few weeks on the ISS might apply to Mars and what keeps plant, animal and people healthy to Mars might also be adapted to keep them healthy on longer trips to Titan, Callisto, Mercury, Europa, Ganymede, Miranda, Enceladus.

and on the subject of checking the websites for info, one person told me a long time ago they don't always have all the answers so if you ask the independent agency of the US federal government government with tens upon tens of thousands of educated experienced employees you might expect a reply but instead you will get Never-A-Straight-Answer

Winnipeg
http://canada.marssociety.org/winnipeg

Other ideas discussed in old new mars topics


Getting to Mars with REAL technology, & what's currently missing.
https://newmars.com/forums/viewtopic.php?id=8327
Hybernation using today's medical technology
https://newmars.com/forums/viewtopic.php?id=9556
Good Health in Transit to and From Mars
https://newmars.com/forums/viewtopic.php?id=9672
Powered Spacesuits
https://newmars.com/forums/viewtopic.php?id=6968
Rejuvenation - reversing aging
https://newmars.com/forums/viewtopic.php?id=10058
Animals on a terraformed Mars - what should we populate Mars with?
https://newmars.com/forums/viewtopic.php?id=352
Habitat air
https://newmars.com/forums/viewtopic.php?id=7157

Last edited by Mars_B4_Moon (2022-09-03 08:01:20)

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#6 2022-09-03 10:52:42

tahanson43206
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Registered: 2018-04-27
Posts: 16,754

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

For Mars_B4_Moon re #5

This post is NOT intended as a criticism, or even a correction....

It is instead an acknowledgment of a shortcoming of a fellow NewMars member....

You said:

Yes I should have credited the other ideas explored by RobertDyck,

In those few words, I believe you have (accurately) summed up two years of work that were (I believe) ** intended ** to lead to Real Universe results.

The efforts over two years have ended up rated as "ideas explored"

RobertDyck (and friends) ventured into an effort to transform all that work into a Real Universe result ....

The result might be thought of as one of Void's ballistic delivery packages arriving on Mars.

The debris is widely scattered.

The attempt to begin with such a simple step as applying metal skin to the outside of the rotating habitat led to realization that far more work is needed to build up the ability to try that again.

I am attempting to lay the ground work for another attempt.

Dropbox folders have been created to hold work that I am hoping will be carried out by NewMars members in a collaborative spirit, using software tools and native intelligence to create models of the rotating habitat.

For your readers (who I'm confident far exceed those of other members) there are three designs for a Large Ship in various stages of development.

By agreement, all three use the same habitat specifications as defined in the Large Ship topic (Check Post #1 - I'm fairly sure RobertDyck has posted the specifications there, or in a nearby subsequent post).

The differences in the three designs are clear, and (hopefully) interesting ...

1) The original Large Ship looks like a forging hammer with a circular head ... it has unitary rotation
2) The kbd512 "practical" Large Ship has counter rotating habitats that share a common axis of rotation
3) The design of tahanson43206 is based upon work of a Spanish professor, and has two counter rotating habitats with parallel axis of rotation.

All three would be able to operate at the rate of rotation specified by RobertDyck for Large Ship ... 20 seconds per turn

All three could operate at other rates of rotation, but for planning, the rate specified by RobertDyck is taken as the common measure of performance.

That rate yields Mars gravity.

Thus, the experiences of passengers and  crew would NOT be the .5 G of the topic you have created, but instead .4 G.

(th)

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#7 2022-09-03 15:16:37

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,423
Website

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

Myself,  until we know better from actual experiment,  I advocate staying near 1 gee,  because that is what we evolved in.  We are "fit" for it by design,  if you will. 

56 m radius at 4 rpm is pretty close to 1 full gee.  56 m radius is a "battlestar galactica" that you must build,  if you use the rifle bullet spin mode most folks think of. 

However,  there is another spin mode we already know to be stable from "Friday night lights" at the football fields for many decades now:  end-over-end like a baton.  You do not have to build a "battlestar galactica" to achieve that,  but it does limit the space inside where near 1 gee prevails.  However,  you do get spaces all along that radial distance on both sides of the cg to explore the effects of reduced gravity. At half radius,  half a gee,  etc.

I use 4 rpm as a sort of empirical value for max spin rate an unacclimatized inner ear can tolerate for long times.  Some others say 3 rpm.  Others advocate for higher values.  But 4 rpm is the best estimate I could find.

For scaling to other radii and spin rates:  gee ~ radius * spin rate squared.

GW

Last edited by GW Johnson (2022-09-03 15:16:56)


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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#8 2022-09-03 17:24:13

Void
Member
Registered: 2011-12-29
Posts: 6,976

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

I like your baton spin method, and suggest again, that if a Starship brought cargo to LEO, then after that it might be used for testing that method in LEO, while perhaps not requiring much in the way of more hardware or propellants.

For instance, in the support of space stations, the spin testing might be sort of a freebee.  Perhaps it would only have test animals on board.  That would possibly reduce the needed life support.  They could be observed live and also perhaps be brought down for further study.  This could be an easy way to get clues about what Martian gravity will do.  Of course, the Moon itself would not need to be tested in this way, as this could be done on the Moon.

I would think that an ideal level to get to would be to be able to keep a human healthy in orbit for a much more extended period.  That then to allow a person to sign up for a space station and do work, maybe even for 5 years, come home with some good pay.

Done.

Last edited by Void (2022-09-03 17:29:17)


Done.

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#9 2022-09-03 20:21:33

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 28,747

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

A baton is a symmetrical designed for central spin configuration as mass is equal from is center to either end of it. An end semi spin into the air settles to a central spin after just 1 complete cycle and continues after that since it is non shifting mass.

A rocket is neither balanced nor centered for spin in the end over end configuration as the tanks will still have some fuel slushing around which will cause a wobble of center.

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#10 2022-09-04 03:23:50

Void
Member
Registered: 2011-12-29
Posts: 6,976

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

Spacenut, it is nice that you gave a reply, but............

Quote:

A baton is a symmetrical designed for central spin configuration as mass is equal from is center to either end of it. An end semi spin into the air settles to a central spin after just 1 complete cycle and continues after that since it is non shifting mass.

A rocket is neither balanced nor centered for spin in the end over end configuration as the tanks will still have some fuel slushing around which will cause a wobble of center.

If the above were a concern, it would apply equally to Dr. Johnson's proposal to do a baton spin for a Starship headed to Mars, where a maximum g of ~.5 would be possible somewhere in the ship.  Probably the nose.

I expect that the main tanks would be purged so as to insulate the header tanks from heat.  The header tanks might slosh when the object was spun up or down, but I don't expect it to slosh much otherwise.

As for center of spin, a Starship might have an elevator on its leeward side, so if you really wanted to get things in and out of it you could center the elevator, for connecting to the ship, and then move the elevator to an airlock.

And that might make me wonder if a baton, not a Starship could be constructed as an initial spin gravity device, instead of twin cylinders, or a wagon wheel type thing.  It is hard to say if that would have sufficient utility to justify the action.

So, I once again suggest that a single starship could be used in LEO, to test spin gravity. 

Important test points would be Lunar, Perception of Up/Down, and Mars simulation.

It is very probable that a cargo ship would do.  After unloading a bulk of hardware, a relatively small portion of the Starship may contain a special cabin(s), either permanent in the structure or a "Capsule" of some size simply put into the Starship.

For a Mars gravity simulation, we then learn something about the reaction of life to that.

Of course, for the Lunar simulation, the same but you can also produce similar data for that on the Moon itself,
Then those two compared, you might discover if there are difference between biology in spin gravity of Lunar magnitude and biology in the Lunar gravitational field of similar magnitude.

Of course, this will keep a Starship out of service for a time in LEO, so a judgement would have to be made on the relative value of using it for these experiments.

But the point is that you would have early data, before actually trying to build an orbital spin gravity space station.

This might pay off as you would have a better notion of how that would be best formulated.

Done.

Last edited by Void (2022-09-04 03:38:30)


Done.

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#11 2022-09-04 06:09:35

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 16,754

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

For Void and SpaceNut ....

This confusion using words has gone on long enough....

Void, please use your skills is making images to show two Starships rotating about a common center point, with a tether (cable or girder unimportant).

The baton image has been used for many years, and there are many discussions and images.

The point that (I think) SpaceNut made is that the two ends of the baton, and in fact the ** entire ** structure must be perfectly balanced, just as is true for a real baton.

Just design your system so it is perfectly balanced, and all objections will (or at least ** should ** ) fade away.

(th)

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#12 2022-09-04 07:28:33

Void
Member
Registered: 2011-12-29
Posts: 6,976

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

Such a drawing would be of a single Starship.

As I recall GW Johnsons proposal was to tumble a Starship, and get up to .5 g.  I would not have adopted the idea so seriously if it had not come from that source.  Where he suggested this for a trip to Mars, I am suggesting it in LEO, for experimental activities to give measurements of reality.

If we were to use a Mars ship, then I presume that you could put 100 people on it and spin it, and they could stay there for 6 months.  But I think that that would be overkill.

If you had a cross between a cargo ship and a passenger ship, you could test fewer people and maybe no people at all.  Perhaps fish, which they already do in the international space station.  Maybe mice, whatever.  The point is that if you paid for the flight with rideshares, after delivery of those to their tasks, the Starship would still be in LEO, and you could spin it and do some testing.

You could also test 3D printing in a low gravity field.

Quote:

The point that (I think) SpaceNut made is that the two ends of the baton, and in fact the ** entire ** structure must be perfectly balanced, just as is true for a real baton.

Just design your system so it is perfectly balanced, and all objections will (or at least ** should ** ) fade away.

(th)

It would be self-adjusting.  It would simply spin on an axis, just like a small asteroid would.

I don't see the need for the elevator in this situation, but it could be present, so that wherever the spin axis was, it could reach it.  Of course, as the elevator changed position the spin axis would change as well by a relatively small measure.  But the elevator and the spin axis could be made to agree or be proximate to each other.

To be useful, the elevator would need to be able to reach the airlock, and I expect that it could, unless bad practices were used.

The bad part of this would be that at least one Starship would be out of service for a significant period of time.
A good part of it would be that the ability of the ship to host living things for significant time periods would be tested.

The good thing is you could test 3D printing, and living creatures, in synthetic low gravity fields, and there might be other things that have not been thought of yet.

Last edited by Void (2022-09-04 07:42:25)


Done.

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#13 2022-09-04 07:39:55

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 16,754

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

For Void ... thanks for continuing the discussion ....

Tumbling a starship is not productive.

Please show a diagram of two starships rotating about a common axis.

This is a very old concept.

It goes back many decades.

There is nothing new about this idea.

Please show a diagram of two starships joined by a tether or a girder rotating about a common axis.

Most renderings of this idea show the tips of the starships joined, so gravity flows toward the base.

(th)

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#14 2022-09-04 07:44:32

Void
Member
Registered: 2011-12-29
Posts: 6,976

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

Are you toying with me?

Quote:

Tumbling a starship is not productive.

Wrong! And please have the decency to allow me to complete a post.

Now, you tell me why it is not productive.

If you want to tumble two Starships, then you portray that and defend it.

Done.

Last edited by Void (2022-09-04 07:45:34)


Done.

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#15 2022-09-04 08:18:58

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 28,747

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

Tumbling 2 starship nose to nose renders no AG for the crew.

Attaching the 2 ship butt to butt would allow for the spin rate generation of AG over the length of the capsule section to have a wide variety of AG. In launch configuration the ceiling is above the crew but once AG is up its now the floor from a design perspective for how equipment is placed.

AG of motion was used to solve refueling flow from one ship to the other by forward constant motion with fuel being moved from the lead ship to the one following.

The header tanks over time will off gas and need to vent into the main tanks as sloshing will produce heat and warming of the fuel. After a period of time all fuel will have vented into the main tanks and no longer slosh as its not liquid any longer.

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#16 2022-09-04 08:47:29

Void
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Registered: 2011-12-29
Posts: 6,976

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

A small apology (th)

Spacenut said:

Tumbling 2 starship nose to nose renders no AG for the crew.

Attaching the 2 ship butt to butt would allow for the spin rate generation of AG over the length of the capsule section to have a wide variety of AG. In launch configuration the ceiling is above the crew but once AG is up its now the floor from a design perspective for how equipment is placed.

AG of motion was used to solve refueling flow from one ship to the other by forward constant motion with fuel being moved from the lead ship to the one following.

The header tanks over time will off gas and need to vent into the main tanks as sloshing will produce heat and warming of the fuel. After a period of time all fuel will have vented into the main tanks and no longer slosh as its not liquid any longer.

OK, you do two starships, and I reserve to one.

We need to address your concerns, and to get test data we need test subjects, we can try this: https://www.smithsonianmag.com/smart-ne … 20research.
Quote:

Life in space is hard on the human body. The lack of gravity's pull can quickly take its toll—bone density declines, muscles deteriorate and more. But compared to a fish, humans have it pretty easy, Michael Byrne reports for Motherboard.

For several years, scientists working with the Japanese Space Agency (JAXA) studied the effects of life aboard the International Space Station for a small school of medaka fish. Also known as Japanese rice fish, medaka are small, freshwater fish native to Japan. And they are invaluable for space research. Not only are they easy to breed, but they are transparent, giving researchers a clear view at their bones and guts as they adjust to life in space, Jessica Nimon writes for NASA’s International Space Station Program Science Office.

So with the 2 ship setup, tests from 0 to 1 g could be done at the same time, I guess.
With one ship, the 0-.5 g  We already have 0 g on the ISS, and I presume 1 g on Earth.

I would like to have enough data for a curve.  This could also include rates of deterioration over time as well I would think.  If the Header tanks boil off then they would have to be resupplied from a depot, which would complicate things.

So, your concerns about sloshing and boil off.

The Starship is intended to be able to have full header tanks all the way to entry to Mars which could be a 6 month duration.  So that trip has a certain environment of heating.  If in LEO, your sunlight is more than as the ship travels to Mars.  But you are sometimes shaded by Earth, perhaps a bit less than 50% of the time?  But the Earth radiates heat as well.  So, apples to apples here is not perfect.

Now, I don't think that the fish are going to slosh the header tanks fluids around much, so I don't see that that is a heating problem.  Humans in a Starship going to Mars might slosh things a lot more.

If you arrange to spin up, yes, a bit of sloshing then, but until you spin down, there should not be much sloshing.

If, however, you do want to cool the tanks, you might do a Blue Origins solution and have a tank of liquid Hydrogen and Oxygen on board, and vent the Hydrogens boil off, to cool the Methane and Oxygen, and then burn Hydrogen and Oxygen for power.  I don't think it is that needed, but there is a solution.

The reason I went with one ship was to reduce complications and costs and to get useful test data.

A number of fish tanks distributed, might give that data.  I will not specify a time duration.  It could be weeks or months.

Done.

Last edited by Void (2022-09-04 09:01:26)


Done.

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#17 2022-09-04 09:44:14

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 16,754

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

For SpaceNut .... any chance you can find an image of a baton ???

That image might help our readers to visualize what might be possible with two starships rotating about a common center of mass.

There may even be images created by others showing the proposed configuration.  I ** know ** the idea of rotating spacecraft with a tether is decades old.

(th)

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#18 2022-09-04 10:09:01

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,423
Website

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

I suggested baton spin as a generic means.  It would have been easy to connect (dock) a number of launchable cylindrical modules into a long stick as a space station,  then spin it end over end to generate artificial gravity.   Something about 100-120 m long,  spun at about 4 rpm,  would have 1 gee near each end,  varying linearly down to zero at the center.  That would have been easy to build in LEO as a lab for investigating partial gee,  as long ago as about 1990.  But we never did.  Rather stupid,  in hindsight.

If you apply this notion to Spacex's Starship,  it takes 2 of them docked.  Nobody knows yet how the design will finalize,  but that concept was tail-to-tail docking for propellant transfer by ullage thrust.  For artificial gravity,  spin the docked pair end-over-end at about 4 rpm.  They're 50 m long each,  so that's 1 gee at the nose tips,  and about 0.9 gee in the pressurized crew spaces.  The downside is that it's upside down,  acting out the noses,  opposite to what obtains sitting on the pad to launch.

For propellant transfer,  spin the docked pair up like a rifle bullet,  for a "spin ullage" solution.  You only need about 1 rpm.  The propellants in the tanks get slung outward to the cylindrical walls of the tanks,  especially if you build some perforated radial baffles inside those tanks. What you need are some extra plumbing along those lateral tank walls as the drains.  Just pump it with ordinary pumps.  It's just an alternate plumbing and radial baffle problem,  with no bladders,  no no pistons,  nothing else.  That's the easiest way to transfer cryogenics with technologies and hardware that we already have. 

GW


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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#19 2022-09-04 10:36:30

Void
Member
Registered: 2011-12-29
Posts: 6,976

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

Here is what I think you want.  It was an early version of LEO refilling method: https://www.bing.com/images/search?view … ajaxserp=0

Of course, Lunar Starship is not expected to have flaps or a heat shield as we know it.  I do wonder if you could get away with just stainless steel, or stainless steel with some kind of cheap cloth like heat shield, if you did not plunge fully into the atmosphere.  That is if you did multiple passes into the upper atmosphere, just a skim, several times.

I hope we can be peaceful like, but I do note that the topic here is "Index» Human missions» Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?"

Kind of rude for me to chastise the moderators smile

I am perfectly fine with expanding the scope to 1 g as well.

Have a good day!

Done.

Last edited by Void (2022-09-04 10:42:32)


Done.

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#20 2022-09-04 11:39:37

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,423
Website

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

Whether or not you need significant heat shielding doing aerobraking depends upon the specific scenario.  If you just need a tiny tad of braking,  then skimming through high up will not generate much heating.  But that cannot work if you are trying to capture in one pass,  for all but the most elongated (and unstable) elliptical capture orbits.  That's for an approach only near escape.  If faster,  all capture dV's are large,  no matter what.  For that,  you must do a large braking dV,  and that means going much deeper into the atmosphere.  The heating will be about as severe as the deceleration is.

The other thing to beware of:  the plasma sheath about the craft is pretty much opaque to re-radiated IR beyond about 10 km/s at entry.  That rules out refractory heat shields or metal surfaces re-radiating.  Your only remaining choice is ablatives.  Which pretty much rules out fabrics of any type,  ceramic or carbon.  Carbon uncooled by re-radiating will get very hot and ablate.  And fabrics are inherently thin.

It is possible to get more than one use out of an ablative heat shield.  But after a few,  you replace it.  The PICA-X on Dragon falls in that category.  So did the carbon-carbon composite nosetip and leading edges on the shuttle.  And the Avcoat on Apollo,  etc.  And X-37B is pretty much identical to shuttle in its heat shielding.  Those ceramic tiles cannot work much above orbital entry speeds,  because they equilibriate by re-radiating IR to space during entry.  At 10 km/s they cannot re-radiate because the plasma sheath is opaque to IR.  They will instead quickly (seconds!) soak out beyond their destruction temperature.

GW

Last edited by GW Johnson (2022-09-04 11:43:55)


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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#21 2022-09-04 11:40:11

tahanson43206
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Registered: 2018-04-27
Posts: 16,754

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

For Void ....

Nice set of images!  Thanks!

For SpaceNut .... can you (if you have time) find some baton images so our readers can see the more commonly accepted understanding of the concept.

Rotating two starships, nose to nose and held by a tether or girder, would permit slow rotation and massive gravity if desired.

To my way of thinking, the suggestion of rotating two starships as shown in the refueling image seems doable but less than ideal.

GW Johnson has already pointed out the upside-down nature of the experience for passengers and crew.

On the ** other ** hand, if the starships are fitted with the clamps to permit end-to-end refueling, then those clamps would be handy for the rotation.

All in all, the images seem (to me at least) quite helpful for developing the topic.

***
Picking up on Void's reminder about the 1/2 G specification in the topic title ....

One thing seems certain.... if the starship venture reaches the point where two vessels are secured end-to-end for refueling, then an experiment with rotation is possible with a very small expenditure of propellant mass.

That would be a useful experiment to perform.

As  a reminder (since it seems not everyone is thinking about this complication) ... the mass of the rotating vessels must (MUST) be precisely matched along every axis and in every location, so that the rotating object is perfectly balanced, as a baton would be.

(th)

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#22 2022-09-04 11:45:40

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,423
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Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

Everywhere-balanced. 

Same is true for a spinning wheel. 

GW


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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#23 2022-09-04 11:54:49

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,423
Website

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

As for half a gee,  or any other fractional gee. 

I suspect without any evidence that Mars gravity may be enough to ward off or at least lessen the negative health impacts of zero gravity.  For all I know,  even lunar gravity might work. 

Point is,  we simply DO NOT KNOW,  because the necessary experiments were never run. 

Second point:  we will NOT know until the necessary experiments actually are run.

The means to have done this have pretty much existed since about 1990.  That's when we assembled the space station by docking-together separately-launched modules. 

The least-massive example of such a spin gravity lab in LEO would be about 6 or 7 cylindrical modules,  each about 15 m long,  into a long stick we can spin up like a baton.  If 100-120 m long,  spun at almost 4 rpm,  that's 1 gee at the ends,  half a gee halfway up each leg toward the center,  and zero gee at the center,  which is where you can put two docking ports parallel to the spin axis (you match spin and dock,  just like in "2001 A Space Odyssey").  This could have been done 3 decades ago,  and we would have already had our answers today for what to do on long missions.

20-20 hindsight:  we've been egregiously stupid about this.  So,  set it right:  put one up there and get on with the damned job!  Others might differ,  but in my opinion,  that's even more important than going back to the moon.

GW

Last edited by GW Johnson (2022-09-04 11:57:30)


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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#24 2022-09-04 19:20:49

Void
Member
Registered: 2011-12-29
Posts: 6,976

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

I think you are right about what should have been done.

But like many things in life a lost chance may require a harder path.  With the world going to hell, in a handbasket as the saying goes, I would look for any progress.

So, I would hope to venture some preliminary testing with a single starship, and then perhaps then two.

Then knowing a bit more of what seems to be real, do as you have said.  This could be good for companies that are having microgravity stations, if there could be some hope of reconditioning a orbital human periodically.

As far as synthetic gravity machines go, the double cylinder gives the most for mass, I think, but it is way overscale of what we should be venturing at this point.

The wheel is interesting, but perhaps it is also overkill at this stage in our development.

I do like your baton, and I trust that it will behave as far as gyroscopic effects are concerned.

I wonder if a "Dumbbell" might also behave?  After you figured out what g force would do the most medically for orbital people with a relatively cheap progression 1) Starship 2) Double Starship 3) Your multi module baton.

Then you may know what g force is the best.

The modules if they were cylinders joined flat surface to flat surface might not have the same diameter.

A gravity that simulates Mars might be big, so that research analog work for Mars could be emphasized, and that at .38 g.  But you might have a smaller diameter for the higher g modules, perhaps all the way to a small gym at 1 g.

Somewhere in there might be a module of less than .38, for testing of manufacturing methods on the Moon, or even less to try to find a minimum gravity for 3D printing and some types of agriculture.

Could that be made to behave well gyroscopically?

Done.

Last edited by Void (2022-09-04 19:29:39)


Done.

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#25 2022-09-04 19:35:05

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 28,747

Re: Is Half Gravity 0.5 G Centrifugal enough to stay Healthy to Mars?

A noser to nose would require a docking ring and collar assembly but it could be done as similar to the dragon with the nose that folds out of the way to dock with the ISS.
YJieMo7ba38kr8ZyTKgab5-1200-80-696x392.jpg


The starship would in the butt to butt alignment needs more that 3 points on the edge to make a secure hold.

here a few styles of a baton, from dance, marching and flame
62957-227.jpg?etag=5184061&type=GenerateThumb&w=600&h=650

62963.jpg?etag=5C93079&type=GenerateThumb&w=940&h=650

OIP.c0ixMMBxf0eI0fW78nrBgwHaCW?pid=ImgDet&rs=1

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