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#76 2017-01-01 22:23:53

RobertDyck
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Re: What we need to go to Mars - short term projects

Antius wrote:

It would be useful to test human adaptation to the effects of short rotation, high spin rate artificial gravity.

It's been done. At various institutes. Here's the work of a German institute for ESA.
sahc_liege_frontal_595x288.jpg short-arm-human-centrifuge-dlr-lg.jpg

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#77 2017-01-02 08:30:15

Antius
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Re: What we need to go to Mars - short term projects

Thanks Robert.  I believe I have one of their research papers:

http://adsabs.harvard.edu/full/2002ESASP.501..151H

It would be even better if they could test human adaptation in a realistic environment, though it would be more money I suppose.

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#78 2017-01-02 10:21:56

GW Johnson
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Re: What we need to go to Mars - short term projects

I think the more realistic environment would reveal a fainting problem for astronauts standing on their feet,  somewhere around 12-15 rpm.  It's due to an excessive blood pressure gradient head-to-toe.  That gradient is directly proportional to rotation speed. 

For seated astronauts,  the number is higher,  which may explain the 20-something rpm upper limits reported. But what good is a centrifuge in your spacecraft if you have to stay seated instead of exercising?

I think you really want to stay away from those gradient problems.  And I think you really want to make acclimatization and training easier,  too. That's why I was recommending something closer to 4 at most 8 rpm. 

GW

Last edited by GW Johnson (2017-01-02 10:23:25)


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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#79 2017-01-02 10:37:34

Antius
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Re: What we need to go to Mars - short term projects

GW Johnson wrote:

I think the more realistic environment would reveal a fainting problem for astronauts standing on their feet,  somewhere around 12-15 rpm.  It's due to an excessive blood pressure gradient head-to-toe.  That gradient is directly proportional to rotation speed. 

For seated astronauts,  the number is higher,  which may explain the 20-something rpm upper limits reported. But what good is a centrifuge in your spacecraft if you have to stay seated instead of exercising?

I think you really want to stay away from those gradient problems.  And I think you really want to make acclimatization and training easier,  too. That's why I was recommending something closer to 4 at most 8 rpm. 

GW

Thanks Gary.  I do not doubt that there are limits, but at present they seem rather speculative.  There is an impressive lack of hard data on what humans can realistically adapt to.  And the difference between 4 and 8rpm could be measured in billions of dollars.  Maybe at 8rpm the rotating hab can fit within the payload faring of the Falcon heavy, whilst 4rpm requires a more complex geometry with interconnected sections.  I am speculating of course.  But the design implications are hardly likely to be trivial.  Mission concepts that require on-orbit assembly of big rotating sections and multiple launches will inevitably be more expensive.

Last edited by Antius (2017-01-02 10:38:45)

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#80 2017-01-02 10:56:48

GW Johnson
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Re: What we need to go to Mars - short term projects

It's just a centrifugal force calculation.  For one full gee at radius tip,  a 56 m radius spins at 4 rpm,  and a 14 m radius spins at 8 rpm.  If you go to 12 rpm,  your radius is a skosh over 6 m.  Double those for diameter. 

I don't see how things that large can fit within payload fairings as centrifuges to be put inside something.  Nor do I advocate building craft by orbital assembly with diameters that large.

But if you build baton shapes, you can easily get spin radii that large from docked modules launchable by today's rockets.  You just spin the docked stack end-over-end. 

If you adopt the baton shape and docked assembly approach,  there is no need to spend billions to get full artificial gravity at spin rates even untrained civilians can easily tolerate (4 rpm),  as demonstrated every day in amusement parks all over the world. 

Doing this sort of semi-rigid structure completely avoids the development of cable-connected things,  too.  And development there is to do,  because we have never yet flown such a thing.  That's more billions saved. 

Just don't add radius with trusses.  They add inert weight and destroy mass ratio.  Use the propellant and supply modules you already have to have anyway. 

GW


GW Johnson
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#81 2017-01-02 12:07:38

Terraformer
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Re: What we need to go to Mars - short term projects

Do people have to be standing in order to do exercise? Perhaps a centrifuge just for exercise could fit inside an existing fairing, and have a main centrifuge at 0.1-0.2g for daily living.


"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony

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#82 2017-02-08 14:49:29

RobertDyck
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Re: What we need to go to Mars - short term projects

Oldfart1939: NASA just issued a "Request for Information"
NASA Request for Information (RFI) on Human Health Countermeasures and Space Radiobiology Topics
Solicitation: NNJ16ZSA003L
Release: today
Close: Feb 22

You can get the document from that link. Pulling a relevant data from one table. Table columns don't really format here...

Topic 1
Biological, Physiological, and Behavioral Functions of Mice during Partial (0 – 1) G-Exposures Provided by Centrifugation on the International Space Station

Primary Risk or Research Area | Relevant Gap
------
Artificial Gravity | N/A
------
Risk of Early Onset Osteoporosis Due to Spaceflight | Osteo 4: We don't know the contribution of each risk factor on bone loss and recovery of bone strength, and which factors are the best targets for countermeasure application.
Osteo 7: We need to identify options for mitigating early onset osteoporosis before, during and after spaceflight

I'm disappointed they labelled artificial gravity as "N/A". I suppose it contradicts what they're doing with centrifuge research on ISS. After all, artificial gravity *IS* a centrifuge.

But the stuff about Osteoporosis should be relevant to your work.

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#83 2017-02-08 15:46:02

Oldfart1939
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Re: What we need to go to Mars - short term projects

That's very interesting! I'm going to contact my colleague about this development.

The hormone Calcitonin is implicit in Calcium uptake, and there are several other pituitary hormones which I will not mention here that have been identified in the Osteoblast/Osteoclast system.

Maybe I can again become professionally active and keep my brain from turning into a useless pile of mush.

Thanks for the Heads Up!

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#84 2017-02-08 20:46:04

SpaceNut
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Re: What we need to go to Mars - short term projects

The twin study does go even further as to how distructive it really is.....

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#85 2017-02-09 10:52:45

GW Johnson
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Re: What we need to go to Mars - short term projects

NASA has been looking for a couple of decades now for ways to tolerate microgravity disease.  That's so they don't have to include artificial spin gravity in their designs.  They have known for a long time that would be difficult and expensive to do by most of the proposed schemes,  which rules out trying to scale up Apollo hardware for going to Mars or anywhere else beyond the moon. 

The lesson of those 2 decades trying to tolerate microgravity is so very simply and clearly that you can't.  That has been clear for some time now,  and the twin study just adds another nail to the coffin.  As it turns out,  the old guys in the 1940's and 1950's with their spinning wheel designs really were right.  Von Braun,  Ernst Stuhlinger,  that crowd.  NASA should have listed more closely to them. 

The twin study just added another microgravity-induced health problem to the long list so far:  brain damage from swelling here and shrinking there.  It's a fluid imbalance pressure thing.  I suspect the gravity could be fairly low to avoid most of it,  but there's no data to support that.  So add brain damage to bone decalcification,  cardiovascular disease,  vision degradation,  and immune system degradation already identified.

The lesson to be learned is SO SIMPLE:  we evolved at one gee,  so supply as close to that as you can. 

It's all in HOW you do it. 

To raise chances of success while reducing development costs,  do semi-rigid structures,  not cable-connected things that we have never before done.  There are simply fewer failure modes with the hard structure,  and it's something already very well-understood.  Simple as that.

Now,  once you make that decision,  you need to resist the space truss guys looking for a market for their product.  Inert weight growth in a space station is just extra mass to launch.  Inert weight growth in a propulsive vehicle is a sharp reduction in delta-vee capability.  Don't go that way,  you're already short of delta-vee capability anyway. 

That leaves you with two choices:  spin about the longitudinal axis like a rifle bullet,  or spin end-over-end on a long shape.  Physics says to spin like a rifle bullet,  your vehicle's radius must be 56 m at 4 rpm for 1 full gee.  That's building "battlestar galactica",  which is ridiculous (excepting only nuclear pulse propulsion colonization transports,  something inappropriate for small exploration expeditions). 

So your only practical choice is the baton shape,  spun end over end.  Use the gross dimensions of a Bigelow B330 just for something to run numbers on.  330 m^3 inside for each module,  is volume for at most 3 persons,  at 100+ m^3 per person.  Figure two plus a similar-sized module with docking ports,  airlock,  and spin-up flywheels.  Crew could easily be 4 to 6.  These things are about 6 m dia inflated,  and about 15-20 m long. 

Assume for the sake of argument you also have perhaps a dozen propellant tank modules that same length but likely slimmer,  and maybe 2 or 3 supply/storage modules that same size as the B330.  Dock your 2 hab modules in line with the flywheel module,  and the two supply modules,  putting the engines on the end of the last supply module.  Cluster the propellant modules alongside this core on all sides,  so you can use tank structure and propellant contents for radiation shielding. 

That's a string of 5 modules each 15-20 m long,  with a lateral dimension on the order of 10 m (tank-core-tank other side).  The overall length is somewhere in the vicinity of 75-100 m for a radius from cg in the vicinity of 37 to 50 m.  It's more-or-less a "slender" rigid baton.  Spin it up to the max tolerable 4 rpm,  to get somewhere in the vicinity of 0.66 to 0.89 gee in the end of the hab cluster.  Put your daily work stations in that end. 

Put your recreational/off-duty stuff further toward the cg at lower spin gee,  and put your sleeping quarters closest to the zero-gee cg location.  There's no benefit from gravity while prone sleeping,  or the bed rest studies would not be as good a simulator of microgravity as they are. 

If the core module string is 6 units long,  you are in the 90-120 m overall length range,  and you get closer to 1 gee at the tip.  Once you are long enough to reach 1 gee,  you can start decreasing the spin rate.  Simple as that. 

Ride the 6-8.5 months to Mars with a daily work shift near 1 gee and recreation/off-duty time at significant partial gee,  and stay very nearly fully earth-fit healthwise.  Then you can tackle whatever physical challenges await you at journey's end,  be that "out there" or "upon return home".  Simple as that!

The stock B330's are 20 metric tons,  launchable with Atlas-5,  and in pairs with Falcon-Heavy.  A water tank 2 m dia x say 18 m long would weigh around 56 tons,  and that's heavier than any of our propellants.  Such tanks could be sent up on Falcon-Heavies,  already loaded with propellant.  Or two at a time (or bigger diameter) on SLS Block 2.  But I'd use Falcon-Heavy,  because you'd pay a lot less to launch the necessary propellant mass. 

That's how you build a manned orbit-to-orbit transport that could take you anywhere in the inner solar system.  Build it once,  use it again and again.  The biggest cost is launch propellants for each mission,  until somewhere down the line you create propellant manufacture infrastructure in space.  There’s nothing here that cannot be done with the rockets we already have. 

It's just plain common sense and some minimal physics,  plus an awareness of what engineering technologies are currently available and what they can really do. 

GW

Last edited by GW Johnson (2017-02-09 10:58:30)


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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#86 2017-02-09 12:53:05

Oldfart1939
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Re: What we need to go to Mars - short term projects

GW-

It seems that Ridley Scott too, understood the gravity issues when he directed "The Martian?" The Andy Weir book was great, but the concept of incorporating the wheel design into the Shuttler-Type spaceship was frosting on the cake! They combined Buzz Aldrin and Elon Musk to arrive at a reasonable solution. One way of addressing this problem is gaining a better understanding of the underlying hormonal changes induced by zero G or microgravity. That's probably MY field where I can make the greatest contribution. This is another area where the deep space research will ultimately have an Earthly payoff by gaining a better understanding of post menopausal osteoporosis. One of the current treatments for Osteoporosis utilizes a pituitary hormone, Calcitonin; this is a regulator of calcium uptake, and it's been shown to be quite effective. Patients get periodic injections of very small quantities of this hormone which speeds up incorporation of Calcium into bone tissue. The real issue is a bit deeper, and that involves the stem cells involved, known as Osteoblasts (bone replacement cells) and Osteoclasts (bone erosive cells). Both are produced, but in osteoporosis, the Osteoclasts seem to have the upper hand and bone tissue is degraded faster than the cells are being replaced. What's needed is identification of which growth factors accelerate Osteoblast formation, and attenuate Osteoclast production.

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#87 2017-02-10 05:18:29

louis
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Re: What we need to go to Mars - short term projects

The immune system seems to degrade in zero G.  I don't think we understand whether that's because 1G is vital to the immune system or because people in space are essentially not having their immune systems triggered all the time, unlike people on Earth, who mix with lots of people, animals and plants etc. My hunch is the latter.

One useful experiment might be for astronauts (sounds like an old fashioned word now!) to actually self infect with a range of (fairly mild) viruses etc during an extended space flight and see whether that stops the immuno suppression.

Or has that already been tried?


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#88 2017-02-10 06:01:07

elderflower
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Re: What we need to go to Mars - short term projects

I think immune systems are much like most other body functions. If you don't exercise them, they wither. This goes for bones, muscles, brain, heart, lungs etc.

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#89 2017-02-10 10:57:23

GW Johnson
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Re: What we need to go to Mars - short term projects

The bone density loss thing is certainly a use-it-or-lose-it thing.  Exercise helps,  that's been demonstrated.  But unless you are severely exercising for much of the day,  it only slows down the loss.  That's where at least partial gravity should help,  by "exercising" you all around the clock for that portion not prone sleeping,  just like here at home.  How much gravity provides what benefit is unknown and probably nonlinearly related. 

The cardiovascular degradation thing is probably just the same sort of use-it-or-lose-it thing as bone density loss.  Same comments apply. 

The vision loss thing seems (as near as we can tell) to be a fluid pressure maldistribution thing inside the body.  We evolved to have a distribution of pressures that respond to one gee standing or sitting for about 2/3 of a day/night cycle.  Take that away,  and the pressure distribution goes out of balance,  which changes the shape of the eye,  thus degrading visual acuity.  Returning to one gee should restore a proper balance and thus restore visual acuity,  but I have seen nothing about that in print.  I would also think that partial gravity should partly restore fluid pressure balance,  so that the visual acuity degradation is less,  and also that the beneficial effect is non-linearly related to partial gee level.  Problem is,  nobody knows because those experiments have never been done. 

The new brain damage thing identified by the twin study (swelling here,  shrinking there) is also thought to be a fluid pressure imbalance thing from lack of gee.  Same comments apply. 

The immune system thing works by no mechanism yet understood,  as near as I can tell.  But the correlation seems to be,  poorer function if isolated in space with no gravity. 

There also seems to be some sort of change in the DNA associated with being isolated in space without gravity.  That is another new outcome identified by the twin study.  Nobody has a clue yet how that works.  But the list of effects just keeps growing. 

The common thread here is presence or absence of gravity.  Having it improves health.  Period. 

Is that not enough to determine that we need to supply it on long manned missions into deep space? 

GW

Last edited by GW Johnson (2017-02-10 11:02:05)


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

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#90 2017-02-10 11:12:34

Oldfart1939
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Re: What we need to go to Mars - short term projects

GW-

I am in total agreement that the solution to all the observed signs of degenerative disease are alleviated by artificial (centripetal force manufactured) gravity, and would appear to be a requirement for deep space journeys. Other than Robert Zubrin, who else has addressed the issue in such a straightforward manner? Certainly not NASA, not Elon Musk. The Hermes spaceship in The Martian did---much to my appreciative surprise. I'm sure that after the biochemists address the problem, various pharmaceuticals will be able to somewhat attenuate the bone decalcification problem through hormonal manipulation, but that is symptomology. Treating the symptoms and not the underlying problem which is best addressed by provision of some artificial gravity.

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#91 2017-02-10 11:36:59

louis
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Re: What we need to go to Mars - short term projects

But what sort of artificial gravity? If on Mars we add to the 1/3 gravity with lead boots, belts and shoulder pads and cap, so we replicated 1G , would that be enough to stimulate the hormonal system? 

Oldfart1939 wrote:

GW-

I am in total agreement that the solution to all the observed signs of degenerative disease are alleviated by artificial (centripetal force manufactured) gravity, and would appear to be a requirement for deep space journeys. Other than Robert Zubrin, who else has addressed the issue in such a straightforward manner? Certainly not NASA, not Elon Musk. The Hermes spaceship in The Martian did---much to my appreciative surprise. I'm sure that after the biochemists address the problem, various pharmaceuticals will be able to somewhat attenuate the bone decalcification problem through hormonal manipulation, but that is symptomology. Treating the symptoms and not the underlying problem which is best addressed by provision of some artificial gravity.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#92 2017-02-10 11:55:48

Oldfart1939
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Re: What we need to go to Mars - short term projects

Gravity on Mars is ~ 40% of that here on Earth, which should keep the hormonal control system functioning pretty well. In hindsight, the ISS should have been built to the von Braun "bicycle wheel" model wherein the numbers of gees could be varied for experimental purposes. Why NASA overlooked that possibility astounds me.

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#93 2017-02-10 16:17:28

GW Johnson
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Re: What we need to go to Mars - short term projects

Louis: 

Go for near 1 gee at least 8 hours out of 24,  with another 8 hours at some partial gee.  Do that during the space crossings to and from whatever destination.  Whatever partial gee there is at the destination should help,  and if you maintain 1 gee for 8/24 hr during the transit home,  you should be pretty near Earth-normal fit on arrival.  Opinion,  not proven fact.

Mars has 0.384 gee at its surface.  That's a fair enough fraction of a gee not to worry over much for something like a year or two's exposure.  Especially if you are re-acclimatizing with 1 gee 8/24 hr during the journey home.

The problem is the emergency bailout scenario upon arrival:  something like 12-15 gees during an emergency free-return entry. 

GW

Last edited by GW Johnson (2017-02-10 16:18:50)


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

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#94 2017-02-10 17:04:52

RobertDyck
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Re: What we need to go to Mars - short term projects

I'm worried that zero-G causes more than just loss of use. Fluids within cells convect, but without gravity there is no convection. That could impede certain functions. One experiment in Skylab was to burn a candle. (Or was it an early Shuttle flight?) The flame did not form the typical tear-drop shape, instead formed a ball of unburnt products. The flame appeared to stop burning, but when an astronaut gently blew on it, the flame re-appeared. Researchers thought they might be able to harvest some partially combusted products by using a straw. But this demonstrates significant effects of zero-G. Could lack of gravity cause some intra-cellular functions to stop? Bone loss appears to be more rapid than just lack of use. The same thing that inhibits the immune system appears to inhibit bone formation. With bone decalcification continuing but bone formation not, that imbalance causes bone loss.

This is why I suspect partial gravity such as Mars or Lunar gravity will reduce zero-gravity effects to merely loss of use. That will be abated by regular EVAs wearing a 106 pound mass MCP suit. (Estimating exactly half the mass of Apollo A7L-B suit.)

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#95 2017-02-10 17:10:09

RobertDyck
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Re: What we need to go to Mars - short term projects

GW Johnson wrote:

Mars has 0.384 gee at its surface.

Where did you get that number? I noticed in an interview, Elon Musk claimed it has 37% gravity. The website Solar Views gives equatorial surface gravity in m/sec^2. Mars = 3.72, Earth = 9.78. Dividing = 0.380368098%. Round off for significant figures gives 38.0%.

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#96 2017-02-10 17:53:55

louis
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Re: What we need to go to Mars - short term projects

I'm not really a fan of AG in transit. I don't want another 20 years' delay sorting out in-transit AG systems. We know well motivated astronauts survive well in over one year of zero G.  We are only looking to survive 6-8 months in zero G for a Mars transit. The issue is - can you then quickly recover in a 0.38 (plus 0.62 weighted clothing) G-regime?  If you can, it's Mars Mission on! smile My guess is, this is doable.

GW Johnson wrote:

Louis: 

Go for near 1 gee at least 8 hours out of 24,  with another 8 hours at some partial gee.  Do that during the space crossings to and from whatever destination.  Whatever partial gee there is at the destination should help,  and if you maintain 1 gee for 8/24 hr during the transit home,  you should be pretty near Earth-normal fit on arrival.  Opinion,  not proven fact.

Mars has 0.384 gee at its surface.  That's a fair enough fraction of a gee not to worry over much for something like a year or two's exposure.  Especially if you are re-acclimatizing with 1 gee 8/24 hr during the journey home.

The problem is the emergency bailout scenario upon arrival:  something like 12-15 gees during an emergency free-return entry. 

GW


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#97 2017-02-10 17:55:33

GW Johnson
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Re: What we need to go to Mars - short term projects

RobertDyck: 

0.384 gee is uncorrected for the centrifugal force of planet spin.  It is based on G,  R,  and M.  It is what you use in orbital mechanics.  You are concerned about 0.004 gees worth of the effective surface gravity answer?  When I got that close? 

Louis: 

There's no need to spend 20 years "proving" spin gravity in transit works.  What you want to avoid is giant-radius spacecraft designs,  truss structure additions to inert weight (that cripple mass ratio fatally),  and undeveloped spin-up/spin-down/failure modes with cable-connected ideas. 

I have already posted multiple times about the spinning-baton shapes that we already know how to do right now.  For someone to propose 20 year's development of spin gravity is a lie at best.  At worst,  well,  that's not fit language for polite company. 

As to whether weighted clothing worn on Mars would help,  that is entirely unproven.  But in fact I do suspect it would help with the bone density and cardio vascular issues.  I do NOT think it would help with visual acuity or brain damage issues,  those being gradient pressure-distribution issues instead of simple physical resistance issues.  Whether it would help with the immune-degradation issue is entirely unknown.

GWJ

Last edited by GW Johnson (2017-02-10 18:12:02)


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

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#98 2017-02-10 18:38:05

louis
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Re: What we need to go to Mars - short term projects

And yet, and yet it does not move...I mean your "spinning-baton" shapes. If it was that easy I would expect someone would have tried it in the last getting on for 60 years of space travel.

Straight to Mars, no diversions please! smile

However, I think your assessment of the effect of weighted boots and suits on Mars is probably spot on. smile


GW Johnson wrote:

Louis: 

There's no need to spend 20 years "proving" spin gravity in transit works.  What you want to avoid is giant-radius spacecraft designs,  truss structure additions to inert weight (that cripple mass ratio fatally),  and undeveloped spin-up/spin-down/failure modes with cable-connected ideas. 

I have already posted multiple times about the spinning-baton shapes that we already know how to do right now.  For someone to propose 20 year's development of spin gravity is a lie at best.  At worst,  well,  that's not fit language for polite company. 

As to whether weighted clothing worn on Mars would help,  that is entirely unproven.  But in fact I do suspect it would help with the bone density and cardio vascular issues.  I do NOT think it would help with visual acuity or brain damage issues,  those being gradient pressure-distribution issues instead of simple physical resistance issues.  Whether it would help with the immune-degradation issue is entirely unknown.

GWJ


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#99 2017-02-10 19:53:58

Oldfart1939
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Re: What we need to go to Mars - short term projects

The only conceptual problem I can see in the Zubrin "tether" system is it's increasingly awkward the larger the system becomes--that is--the larger spacecraft will become in the future. The effects  seem to be cumulative under prolonged absence of gravity, and returnees from the ISS after only 3-4 months seem to be minimally affected. I'm all for having a brainstorm session; however the Ridley Scott Mars spaceship Hermes looked pretty interesting. Just how well it would function under strong acceleration--that's a big structural question. Probably NOT very good. The Martian combined the "cycler" concept of Buzz Aldrin with much of the Mars Semi Direct scenario of Zubrin. Before I became affiliated with this group, I was thinking of something along the lines of a semi-rigid structure between two sections of the Mars vessel, sort of the GW Johnson model. If NASA gets too deeply involved in the biochemistry and hormonal regulation area where I've spent a large part of my professional career, it may be another 50 years before they are ready to "venture forth where no man has gone before."

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#100 2017-02-11 11:12:59

GW Johnson
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Re: What we need to go to Mars - short term projects

Louis:

The dynamics of rigid spinning bodies has been well understood for well over a century now.  We're really good at it.  Balancing tires on cars is one application of it.  Balancing gigantic steam turbines in power plants is another.  And don't forget about propellers and windmill blades. 

The more flexible the structure,  the harder it is to deal with,  though.  Very much harder.  Which is why I like rigid structures for spin gravity so much better than cable-connected stuff.  Leave the cables on stuff that doesn't move much,  like suspension bridges. 

It hasn't been done for 60 years of space travel for two reasons (1) we haven't had the experience building large structures of docked items until recently (that's how we built ISS),  and (2) it was accidentally tried on Neil Armstrong's Gemini flight when his Gemini-Agena docked structure spun out of control due to a stuck thruster. 

We should have started doing this as soon as we built ISS.  We didn't.  But here of late,  we now have some components to do it with:  from Bigelow.  It would not take much at all to adapt Bigelow's zero-gee B330 into something we cold dock together and spin for gravity.  It already has a strong core. 

Louis and Oldfart1939:

I don't think NASA really wants to take on the Mars mission precisely because it is dangerous,  and they have become extreme risk-averse.  They have a Bigelow BEAM module on the station now,  but are spending over a year just to open the door and go inside.  Ridiculous!

It's also why spin gravity has been largely ignored by NASA management:  microgravity disease is an excuse not to go.  Just like galactic cosmic radiation exposure is brought up again and again as an excuse not to go.  Solar flare radiation will be brought up as a reason not to go if the other two are knocked down.  They will finally use confinement/insanity as the reason not to go:  the crew needs space,  which requires a big vehicle,  and that is expensive (based on SLS costs and availability,  not commercial launchers). 

Oops,  Cassandra has made another prediction.  Like always,  nobody will like it,  and blame the messenger.

What concerns me if they do adopt spinning-baton spin gravity is the gas seal for a spin/no-spin joint.  That part is not developed,  and thus provides another reason not to go.  You avoid it by spinning the entire vehicle,  no joint.  If you need to dock or undock something, just de-spin.  The way to do that economically is an electrically-powered set of flywheels.  That completely avoids the stuck thruster problem and the problem of spin-up propellant quantity,  that they saw on that Gemini-Agena. 

It is actually fairly easy to think your way around these problems and devise a practical Mars or asteroid in-situ mission with a high degree of safety and health designed-in from the get-go.  Not doing this is prima facie evidence that NASA does not want to go anywhere beyond the moon. 

GW

Last edited by GW Johnson (2017-02-11 11:22:37)


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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