Author Topic: Nose tethered BFS Spaceships for artificial gravity during the coastal phase.  (Read 15250 times)

Offline Peter.Colin

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Would it be beneficial and practical to create artificial gravity during the coastal phase? It could be done by connecting the two noses of two ships with a long cable, and use the side thrusters to begin spinning to the desired centrifugal force.
How would this effect the radiation shielding of the ship.
How fast would the ships need to spin?, and could this make looking trough a window still pleasant?

Offline Semmel

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Obvious advantages: less medical problems from zero gravity, easier life on board like eating, toilet, washing, etc. Less problems to find zero g solutions for trivial everyday stuff like washing clothes, pumping liquids, probably easier design of the life support system.

Obvious disadvantages: more difficult solar power generation, communication with Earth and Mars, additional mass for the nose connection system, difficult or near impossible to do course corrections, spin up and spin down difficult to Orchestra without introducing oscillations. Oscillations due to mass (people) moving around in both ships.

Indifferent: I don't think radiation shielding is a thing in general, can't get much worse than it is already. Maybe a total mass gain, despite extra mass of the cable system. Would require extensive engineering and tradeoff.

Online KelvinZero

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Had a fairly over the top thought, certainly not for initial missions

Elon Musk talks about getting to a point of sending many ships in a single launch window. What if these all docked with a lightweight central hub for the flight? The central hub would probably be some sort of cycler. This cylindrical arrangement of ships with engines on the outer side would also provide a fair bit of shielding, should that prove to be an issue.


Offline Peter.Colin

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Had a fairly over the top thought, certainly not for initial missions

Elon Musk talks about getting to a point of sending many ships in a single launch window. What if these all docked with a lightweight central hub for the flight? The central hub would probably be some sort of cycler. This cylindrical arrangement of ships with engines on the outer side would also provide a fair bit of shielding, should that prove to be an issue.

I think that's a very good idea!  :)

Would you point the rotational axis of the central hub towards the sun, for easier solar power generation?

Would the central hub make steering corrections or the connected ships?
« Last Edit: 08/06/2017 06:55 AM by Peter.Colin »

Offline Peter.Colin

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Obvious advantages: less medical problems from zero gravity, easier life on board like eating, toilet, washing, etc. Less problems to find zero g solutions for trivial everyday stuff like washing clothes, pumping liquids, probably easier design of the life support system.

Obvious disadvantages: more difficult solar power generation, communication with Earth and Mars, additional mass for the nose connection system, difficult or near impossible to do course corrections, spin up and spin down difficult to Orchestra without introducing oscillations. Oscillations due to mass (people) moving around in both ships.

Indifferent: I don't think radiation shielding is a thing in general, can't get much worse than it is already. Maybe a total mass gain, despite extra mass of the cable system. Would require extensive engineering and tradeoff.

In the ITS animation, the tanker is put on the BFR with a crane and a cable on the nose (or at multiples sides), probably the ship has a similar nose cable system already.
« Last Edit: 08/06/2017 08:16 AM by Peter.Colin »

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Had a fairly over the top thought, certainly not for initial missions

Elon Musk talks about getting to a point of sending many ships in a single launch window. What if these all docked with a lightweight central hub for the flight? The central hub would probably be some sort of cycler. This cylindrical arrangement of ships with engines on the outer side would also provide a fair bit of shielding, should that prove to be an issue.

I think that's a very good idea!  :)

Would you point the rotational axis of the central hub towards the sun, for easier solar power generation?

Would the central hub make steering corrections or the connected ships?

Keep it simple.  Keep all the intelligence is in the ships themselves - probably much more efficient at first for ships to detach to do course corrections, since burns of a several 100m/s is huge compared to the 20-40m/s of rotation.  What is needed (and I hope Bigelow or similar does this) is a cable-reinforced, inflatable tube module that can take some load.  You cannot just use cables because of the oscillation problem (remember a bridge has both compressive and tensile elements and we're effectively building a suspension bridge in space)

The aim is to get the largest radius of rotation, because this means the rpm can be lower for a given centrifugal acceleration - its the spin which induces vertigo in most people once you get above 4rpm or so.  If you have less than 6 ships/nodes, then you connect directly, or to a dumb central node, but if you have 6 or more ships/nodes in a ring, then the angle between them decreases to 60 degrees or less, and it is a better use of tubes to dispense with the hub and attach the tubes ship to ship, so you get a larger effective radius.

Even for two ITSy ships connected nose to nose, the length of an inflatable tube connector that would fit into an ITSy payload bay could allow on the order of 20m between them, giving an effective radius of at least 30m.  That means that at 4rpm you'd be getting perhaps 0.5 G at the edges, and at least Mars G for much of the crewed area. 

Online KelvinZero

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Just saw some issues with the cycler idea. With 3 month earth-mars times it probably needs 4 synods to return home. Maybe it can't be a true cycler in which case how does it brake into mars orbit, or maybe this thing passes mars and visits the asteroid belt, and you have 4 of them. Not as simple as it first sounded.

Two ships with cables has a lot less question marks, especially if the ship is already designed to be lifted from the nose under 1g like in the animations.

(Off topic, another of my hobby horses is good VR for space travellers. Spin gravity creates a lot of design constraints and you will still be in a cramped spaceship. Good VR, a treadmill and elastic bands could let you jog though expansive fantasy worlds for hours every day.)

Offline Peter.Colin

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Just saw some issues with the cycler idea. With 3 month earth-mars times it probably needs 4 synods to return home. Maybe it can't be a true cycler in which case how does it brake into mars orbit, or maybe this thing passes mars and visits the asteroid belt, and you have 4 of them. Not as simple as it first sounded.

Two ships with cables has a lot less question marks, especially if the ship is already designed to be lifted from the nose under 1g like in the animations.

(Off topic, another of my hobby horses is good VR for space travellers. Spin gravity creates a lot of design constraints and you will still be in a cramped spaceship. Good VR, a treadmill and elastic bands could let you jog though expansive fantasy worlds for hours every day.)

Assuming a cycler central hub takes to long.
I think this central rotating hub structure should brake the same way as it's accelerates, with a few Raptor engines.
I know this consumes a lot of fuel, but this amount of fuel/engines could be minimized by pumping from Earth tankers only the required fuel for accelerating.
And for braking at mars pumping fuel from the connected Spaceships.
The central rotating hub structure can also double as a Mars fluids depot in orbit for mars tankers when they're full at the surface. It makes more sense to store the bulk of the liquids in mars orbit, than on the surface.

Spin gravity begins to feel like normal gravity the longer the cable is, so VR would feel similar to VR on earth.

Of topic:
Does anyone have an idea about how much fuel would be left in a fully loaded Mars tanker when it reaches Mars orbit?



Offline Humuku

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How fast would the ships need to spin?, and could this make looking trough a window still pleasant?

Period of tethered movement is proportional to the square root of the radius of the tether.

Offline livingjw

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Just saw some issues with the cycler idea. With 3 month earth-mars times it probably needs 4 synods to return home. Maybe it can't be a true cycler in which case how does it brake into mars orbit, or maybe this thing passes mars and visits the asteroid belt, and you have 4 of them. Not as simple as it first sounded.

Two ships with cables has a lot less question marks, especially if the ship is already designed to be lifted from the nose under 1g like in the animations.

(Off topic, another of my hobby horses is good VR for space travellers. Spin gravity creates a lot of design constraints and you will still be in a cramped spaceship. Good VR, a treadmill and elastic bands could let you jog though expansive fantasy worlds for hours every day.)

Assuming a cycler central hub takes to long.
I think this central rotating hub structure should brake the same way as it's accelerates, with a few Raptor engines.
I know this consumes a lot of fuel, but this amount of fuel/engines could be minimized by pumping from Earth tankers only the required fuel for accelerating.
And for braking at mars pumping fuel from the connected Spaceships.
The central rotating hub structure can also double as a Mars fluids depot in orbit for mars tankers when they're full at the surface. It makes more sense to store the bulk of the liquids in mars orbit, than on the surface.

Spin gravity begins to feel like normal gravity the longer the cable is, so VR would feel similar to VR on earth.

Of topic:
Does anyone have an idea about how much fuel would be left in a fully loaded Mars tanker when it reaches Mars orbit?

Just enough to land after aerobraking.

Offline guckyfan

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Of topic:
Does anyone have an idea about how much fuel would be left in a fully loaded Mars tanker when it reaches Mars orbit?

A cargo ITS would lift 300t to LEO and can land 450t on Mars when loaded with extra cargo in LEO and going on a slow trajectory. A tanker should be able to land at least those 450t in propellant on Mars. If that would make sense. Maybe as a rescue mission for the first crew if sabatier fuel ISRU fails. Enough methane but LOX would still need to be produced from atmospheric CO2. An unlikely string of events.

Offline Peter.Colin

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Of topic:
Does anyone have an idea about how much fuel would be left in a fully loaded Mars tanker when it reaches Mars orbit?

A cargo ITS would lift 300t to LEO and can land 450t on Mars when loaded with extra cargo in LEO and going on a slow trajectory. A tanker should be able to land at least those 450t in propellant on Mars. If that would make sense. Maybe as a rescue mission for the first crew if sabatier fuel ISRU fails. Enough methane but LOX would still need to be produced from atmospheric CO2. An unlikely string of events.

Let me clarify my off topic question:
A tanker holds 2500t propelant. But when when this tanker leaves Earth and reaches LEO it only contains 380t of propelant, the rest has been spent to reach orbit. The BFR was also needed to get this propelant into LEO and that contained 6700t of propellant.
So only 4.3% of the original propelant reaches Earth orbit, not much...
I was wondering what part of propelant produced on mars surface reaches mars orbit?

Storing most propellant in mars orbit minimizes the amount of storage volume needed, this could be done in the central rotating hub.
« Last Edit: 08/06/2017 10:32 PM by Peter.Colin »

Offline darkenfast

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If the ship can reach Mars in under six months, why in the world would you spend so much mass and added complexity to provide artificial gravity?  We know that crews can be walking on Earth within a day or two of return from the ISS (with some restrictions), and in an emergency can get themselves out of a Soyuz unaided after a bad landing.  The gravity on Mars is one fourth of ours.  They don't have to leap out of their couches and start heavy lifting immediately after touchdown. 

Spending years going to Saturn?  Then maybe we need something.  But not for Mars. 

Online KelvinZero

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If the ship can reach Mars in under six months, why in the world would you spend so much mass and added complexity to provide artificial gravity?  We know that crews can be walking on Earth within a day or two of return from the ISS (with some restrictions), and in an emergency can get themselves out of a Soyuz unaided after a bad landing.  The gravity on Mars is one fourth of ours.  They don't have to leap out of their couches and start heavy lifting immediately after touchdown. 

Spending years going to Saturn?  Then maybe we need something.  But not for Mars.
The nose-tethered option is not that extravagant.

The other options only make sense with much greater scale but they don't add much mass,  proportionally. They even have the possibility of saving mass if you are preaccelerating fuel ahead of time, or packing more people into your ITS like sardines because they will have more volume during the trip. The argument against them is definitely about complexity. This could grow to be a whole new vehicle that (if not a true cycler) also needs to aerobrake.

A nose tethered option for a mission to Saturn is also an interesting suggestion IMO. Maybe we should be using that as our primary justification for a discussion of two nose tethered ITS.

Offline Peter.Colin

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If the ship can reach Mars in under six months, why in the world would you spend so much mass and added complexity to provide artificial gravity?  We know that crews can be walking on Earth within a day or two of return from the ISS (with some restrictions), and in an emergency can get themselves out of a Soyuz unaided after a bad landing.  The gravity on Mars is one fourth of ours.  They don't have to leap out of their couches and start heavy lifting immediately after touchdown. 

Spending years going to Saturn?  Then maybe we need something.  But not for Mars.


Because it would start to smell, washing clothes washing yourself, going to the toilet is not easy without gravity.

And I wouldn't want to drink my glass of champagne out of a bag, that can explode because of the bubbles...  ;)

If a tether can prevent these and more inconveniences, and if the ship (the tanker we know) is allready lifted on the BFR by a nose tether. Why not do it like this.


« Last Edit: 08/07/2017 04:01 PM by Peter.Colin »

Offline docmordrid

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>
Because it would start to smell, washing clothes

Supercritical CO2 laundry. Dry, isolated, works & COTS.

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washing yourself, going to the toilet is not easy without gravity.

There was a shower on Skylab, and space potties are obviously on ISS.
DM

Offline intrepidpursuit

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The ship would have to spend at least several days in microgravity before such a contraption could be assembled, so there still have to be zero g facilities for everything (I think three months of laundry is still easier to carry than something that can clean the laundry in space). Three months isn't long enough to cause major damage to the passengers. They are heading to a reduced gravity environment so they won't need as long to acclimate anyway.

Artificial gravity for mars is WAY more trouble than it is worth.

I hope one day there will be a ship with centripetal gravity, but early mars settlement ships don't need that development burden.

Online KelvinZero

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I hope one day there will be a ship with centripetal gravity, but early mars settlement ships don't need that development burden.
This is why I suggested maybe moving the goalposts to the saturn mission. (Actually someone else suggested it)

What I mean is, I think it is better to just discuss it as a technical problem. It is after you have sorted out how difficult it is that you have the basis to argue where it could be useful and where it is not worth the bother.

A lot of things we will not know for sure until we have moved a lot of people. We only have a small sample set at the moment. Same with radiation. Im convinced we have enough info on both to not be afraid to just begin, but I don't think anyone can be confident of what we will decide is optimal by the time we are shipping hundreds of thousands of people of all ages to Mars.. so just treat it as a technical problem.

Offline guckyfan

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I hope one day there will be a ship with centripetal gravity, but early mars settlement ships don't need that development burden.
This is why I suggested maybe moving the goalposts to the saturn mission. (Actually someone else suggested it)

I did. Not claiming I was the only one.

What I mean is, I think it is better to just discuss it as a technical problem. It is after you have sorted out how difficult it is that you have the basis to argue where it could be useful and where it is not worth the bother.

As such it is an interesting argument.

Offline Paul451

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If the ship can reach Mars in under six months, why in the world would you spend so much mass and added complexity to provide artificial gravity?

What "mass and added complexity"? At Mars gravity and 4-6 RPM, AG is almost free. The only reason not to do it would be out of spite.

We know that crews can be walking on Earth within a day or two of return from the ISS

We also know that that is a meaningless measure of their actual health, and that astronauts experience random orthostatic hypotension episodes for weeks after their return due to a suppressed baroreceptor reflex. According to flight surgeons and works published by long-duration astronauts, typical recovery is 1 day on the ground for 1 day in orbit.

Offline douglas100

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What "mass and added complexity"? At Mars gravity and 4-6 RPM, AG is almost free. The only reason not to do it would be out of spite.

There must be added mass and complexity to do this. How much is up for discussion.

As for a another reason not to do it, what about "it's unnecessary?" Spite has nothing to do with it.
Douglas Clark

Offline Paul451

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There must be added mass and complexity to do this.

Sounds like a religious tenet.

Offline RonM

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There must be added mass and complexity to do this.

Sounds like a religious tenet.

If you look at the ITS design from the original presentation you'll see that there is no provision for docking. Two ITS spacecraft can't dock, let alone spin together for AG. Providing that capability would add extra mass.

Are you talking about spinning an ITS around its long axis? That would require a redesign of the deck layout to function properly in flight and when landed.

Offline alexterrell

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Obvious disadvantages: ....., communication with Earth and Mars, ....
Have a small satellite in "wifi range" - perhaps 2km away, with a big dish pointed at Earth. The "satellite" could also have a telescope on the BFR to check the outside.

Offline blasphemer

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I made a mock up picture of two ITS ships connected by a 200m long cable. Enough for 1g gravity at comfortable 2 RPM.


Offline Peter.Colin

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Very nice!

Now let's hope the cable is not to heavy or complex ..... lol
« Last Edit: 09/04/2017 06:33 PM by Peter.Colin »

Online AncientU

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I made a mock up picture of two ITS ships connected by a 200m long cable. Enough for 1g gravity at comfortable 2 RPM.



I believe the 200-ish meters is a radius, not a 'length' -- the exact number is closer to 225m radius or 450m 'length'
"If we shared everything [we are working on] people would think we are insane!"
-- SpaceX friend of mlindner

Offline Paul451

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If you look at the ITS design from the original presentation you'll see that there is no provision for docking. Two ITS spacecraft can't dock, let alone spin together for AG. Providing that capability would add extra mass.

The refuellers attach side-by-side to the main ships, and on Earth the ships are lifted by the nose to be re-mounted on the booster. They have attachments up the wazzoo, and clearly the necessary prox-ops systems.

However, my objection to the original statement is that it solely assumes costs, but ignores any possibility of benefits or savings. That's pre-defining the issue to failure.

I made a mock up picture of two ITS ships connected by a 200m long cable. Enough for 1g gravity at comfortable 2 RPM.

A cable is a bad idea. Picture a 200m (or 400m, for 1g/2RPM) cable hanging in still air, with an ITS-like platform hanging off the bottom, with dozens to a hundred people moving around. It will twist and oscillate like crazy. In free-space it's actually worse, the oscillations dampen very slowly (bouncing back and forth along the cable). There's a similar problem with compressive structures like trusses. The suggested alternative is a tensegrity structure, a combination of tensile and compressive structures; eg, a truss held under compression by cables. A design suggested for long tethers is to have an inflated tube (or four) providing the compressive-resistive structure, which is held in compression by the tensile cables. In simulations, that apparently dampens all axes of oscillation, including twist, better than just cables, or just trusses.

IMO, 2RPM is ridiculously low. And 1g is too high, if you expect people to permanently colonise Mars. (If 0.38g isn't sufficient, we aren't colonising Mars, so the point is moot.) 4RPM and 0.38g gives you 40m total length. Including the length of the ITS cabins, it's barely worth the cable.

It would be nice to know for sure; since radius/diameter scales with the square of RPM, so doubling the RPM quarters the length. And linearly with g-load, so double the RPM at 38% gravity gives you a ten-fold reduction in length.

Offline Coastal Ron

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A cable is a bad idea. Picture a 200m (or 400m, for 1g/2RPM) cable hanging in still air, with an ITS-like platform hanging off the bottom, with dozens to a hundred people moving around. It will twist and oscillate like crazy.

I'm not sure what you envision all those people are doing, but I can't imagine anything they could be doing that would make an ITS twist and oscillate. And with the tension between the two ITS being so high, random movement of people on both ITS are likely to be very muted vibration-wise. At most all you'd need is a hydraulic damper located somewhere on the cable to smooth out minor vibrations.

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In free-space it's actually worse, the oscillations dampen very slowly (bouncing back and forth along the cable).

However because of the weight of the two ITS, and the rotation keeping the cable under tremendous compression tension* forces, it's going to be hard to get a cable vibrating in the first place, and the natural tendency would be to mute the vibrations out of the cable.

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The suggested alternative is a tensegrity structure, a combination of tensile and compressive structures; eg, a truss held under compression by cables.

Just stringing a cable between two ITS and getting them rotating without free body issues will be tricky by itself, but having to inflate things in between is going to be even harder.

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IMO, 2RPM is ridiculously low.

Low RPM's are much better than higher ones, not only for people but also for safety reasons.

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And 1g is too high, if you expect people to permanently colonise Mars. (If 0.38g isn't sufficient, we aren't colonising Mars, so the point is moot.)

I agree. Even if the ITS flotilla is returning to Earth it should be good enough to have Mars gravity for the trip.

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4RPM and 0.38g gives you 40m total length. Including the length of the ITS cabins, it's barely worth the cable.

It would be nice to know for sure; since radius/diameter scales with the square of RPM, so doubling the RPM quarters the length. And linearly with g-load, so double the RPM at 38% gravity gives you a ten-fold reduction in length.

Are you familiar with the website SpinCalc? It's where I do all of my "what if" simulations for spinning space station designing. Unfortunately though we lack enough real experience, so the variables and results in the calculator are only estimates based on research done here on Earth.

So if a 200m cable is used, and the required gravity is Mars normal (i.e. .38 Earth), then the RPM would be 1.8. According to SpinCalc that should provide artificial gravity with no known spin-related issues.

As for the cabling, there are Ultra-high-molecular-weight polyethylene (UHMWPE, UHMW) cables that could be used that are both very strong and lightweight.

* Corrected "compression" to "tension" as noted by Paul451 (thanks Paul451!)
« Last Edit: 09/04/2017 11:07 PM by Coastal Ron »
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline Paul451

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I'm not sure what you envision all those people are doing, but I can't imagine anything they could be doing that would make an ITS twist and oscillate.

You've obviously never seen a large mass on the end of a long cable.

and the rotation keeping the cable under tremendous compression forces

Que?

Just stringing a cable between two ITS and getting them rotating without free body issues will be tricky by itself, but having to inflate things in between is going to be even harder.

Quite the contrary, it makes everything easier, that's why it's suggested.

Are you familiar with the website SpinCalc?

Of course. (Although I use my own spreadsheet for quick'n'dirty RPM/radius/g-load calcs.) Ted is extremely conservative in his red/yellow/green warnings, which he has acknowledged in other presentations. He does link to the more recent Lackner and DiZio paper, which is part of modern AG research (including ultra-high RPM research like the "Space Cycle" exercise platform), but doesn't actually use it in the calc.

The old Apollo-era research just doesn't hold up. Even at the time, the result were wildly variable between experiments, which should tip you off that they stumbled onto a confounding factor rather than a real effect. Based on recent research, it looks like that uncontrolled variable was the amount of movement test subjects were allowed or encouraged to make, or actively discouraged from making, during the spin-up phase. The less movement, the worse the results. It's not surprising they did that; even today, you still get people saying "High RPMs might be possible if people limit their movements". The instinct is the opposite to how we actually need to adapt.

But it's funny when people say, "We can only go by Earth research," but then very pointedly ignore everything done in the last 35 years.

[IIRC, Space Cycle runs at around 40 RPM and up to 7g.]

Online KelvinZero

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If you look at the ITS design from the original presentation you'll see that there is no provision for docking. Two ITS spacecraft can't dock, let alone spin together for AG. Providing that capability would add extra mass.
There is a spacex animation showing an ITS being picked up by a cable to it's nose in order to place it on top of the 1st stage. That is probably what inspired all this.

My personal feeling is that we will find a way to avoid this, eg vr treadmills with elastic bands for gravity, but it is still fun to think about.

Despite that nose cable art, I would favour something wider, eg multiple widely spaced cables with cross connections specifically designed to damp any oscillation. Someone must have studied this extensively somewhere.

https://www.youtube.com/watch?v=0qo78R_yYFA?t=120

(for some reason, the t=120 did not work.. go to the 2:00 minute mark to see the ITS lifted by cable)
« Last Edit: 09/04/2017 11:07 PM by KelvinZero »

Offline Coastal Ron

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and the rotation keeping the cable under tremendous compression forces

Que?

Mea culpa. Should have said "tension" forces. Glad you pointed that out.

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Quite the contrary, it makes everything easier, that's why it's suggested.

If you say so. This obviously points to the need for actually DOING rotational gravity research in space instead of theorizing about it. Better to have facts than opinions.

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Of course. (Although I use my own spreadsheet for quick'n'dirty RPM/radius/g-load calcs.) Ted is extremely conservative in his red/yellow/green warnings, which he has acknowledged in other presentations. He does link to the more recent Lackner and DiZio paper, which is part of modern AG research (including ultra-high RPM research like the "Space Cycle" exercise platform), but doesn't actually use it in the calc.

OK good. For myself I'm OK with "worst case", which I'm hoping SpinCalc will be, because if I can come up with solutions that work out OK with "worst case", then I should be OK with "reality".
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline Paul451

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For myself I'm OK with "worst case", [...] because if I can come up with solutions that work out OK with "worst case", then I should be OK with "reality".

No. This is why I keep harping on about people insisting on low RPM. It's pre-establishing that the trade will fail.

Radius increases with the inverse square of RPM. It's a huge effect. If you insist on 1g and 1 or 2RPM, then you've virtually ruled out AG in advance, because of course others are going to say "It adds too much mass/complexity", and any consideration of the idea dies. As I said, the difference between 1g/2RPM and 0.38g/4RPM is a tenfold difference in scale.

Picture any other type of engineering where you just hand-waved an order of magnitude difference in the properties or scale.

It would be like designing rockets by insisting that any rocket technology must be capable of SSTO or you won't even look at it, because "if you can solve the worst case then you should be able to solve any other configuration". That's not reasonable, and it's not honest.

Online KelvinZero

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It just occurred to me, maybe a single cable can work.

I was imagining the ship twisting back and forward, with no way to damp the oscillation, sort of like a weight on the end of a string would tend to spin frictionlessly. But the cable would be able to turn it it's socket so there is no 'winding up', also each ship would have a flywheel that would keep each one rigidly oriented. I don't think there is any possibility of the flywheels becoming saturated since it is still a closed system.

That just leaves normal non-twisting oscillation. Even if it is tight like a violin string I think that sort of oscillation can be damped nicely at the endpoints.

Offline Paul451

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It just occurred to me, maybe a single cable can work. [etc]

This is where you make a system ridiculously complicated so you can keep the original idea, because the original idea was "simple".

Offline blasphemer

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If you insist on 1g and 1 or 2RPM, then you've virtually ruled out AG in advance, because of course others are going to say "It adds too much mass/complexity", and any consideration of the idea dies.

It may add mass, but complexity? I dont see why. In fact higher RPMs mean astronauts are more likely to be sick, experience Coriolis forces and any oscillations/instabilities are going to be higher frequency so if anything I would say that high RPM adds complexity. Unless you plan to make your connection rigid, you have to deal with oscillations no matter what.

As for mass, how much does a 100m of cables weight? Lets say it must be sufficiently strong to not break under the weight of two partially fueled ITS spaceships at 0.38g.
« Last Edit: 09/05/2017 12:25 PM by blasphemer »

Offline Paul451

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Offline blasphemer

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Fully fueled 12m ITS weights 2400 tons, unfueled ITS weights 450 tons. Artificial gravity makes sense during coasting so the strength of the cables depends also on how much fuel will remain in reserve after Mars transfer burn. As a lower bound, assuming there is no fuel left and we want 0.38g then cable(s) will have to be strong enough to support at least 450*2*0.38= 342 tons of weight. Anyone know how much kg per length this roughly could be?
« Last Edit: 09/05/2017 12:37 PM by blasphemer »

Offline blasphemer

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I have changed my concept pic by reversing the spaceships so that radius is increased by length of the engine section. Note that this is opposite hanging direction as in ITS video so this may not be an improvement.


Offline blasphemer

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https://www.reddit.com/r/spacex/comments/3ogkfa/artifical_gravity/cvxe4yu/?st=j77ls2q8&sh=1fabfcd4

I found an older reddit thread discussing this idea. Some relevant info:

Quote
We end up with a radius of only about 3500 meters.

Assume MCT weighs 200 tonnes during cruise, and you want to simulate Mars gravity. Using three redundant Dyneema fibers, 50% engineering margin (NASA standard), 50% live load allowance, and 100% overhead for space environment protective coatings, I get a mass of 7.5 tonnes (or 3.8 tonnes per MCT). So it's totally doable.

The other thing is spin/despin fuel. That's another 8 tonnes per MCT.

These are some weird assumptions (3500m radius? 200 tons only?) but in the end cable mass is 7.5 tons and is actually less than half of spin/despin fuel mass. So maybe any AG solution will be dominated by fuel mass instead of mass of the mechanism itself?
« Last Edit: 09/05/2017 01:11 PM by blasphemer »

Offline Paul451

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https://www.reddit.com/r/spacex/comments/3ogkfa/artifical_gravity/cvxe4yu/?st=j77ls2q8&sh=1fabfcd4
Quote
We end up with a radius of only about 3500 meters.
and you want to simulate Mars gravity.

Less than one third of 1 RPM.

{sigh}

Why does talking about AG seem to turn people's brains to chicken soup?

Offline RonM

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I have changed my concept pic by reversing the spaceships so that radius is increased by length of the engine section. Note that this is opposite hanging direction as in ITS video so this may not be an improvement.

This won't work because AG direction will be 180 degrees from the landed configuration. The crew will be walking on the ceilings.

Offline GORDAP

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Fully fueled 12m ITS weights 2400 tons, unfueled ITS weights 450 tons. Artificial gravity makes sense during coasting so the strength of the cables depends also on how much fuel will remain in reserve after Mars transfer burn. As a lower bound, assuming there is no fuel left and we want 0.38g then cable(s) will have to be strong enough to support at least 450*2*0.38= 342 tons of weight. Anyone know how much kg per length this roughly could be?

I'm pretty sure this is off by a factor of 2.  I think the cable only has to be strong enough to hold up a single BFS (with appropriate safety factor, of course).

Offline envy887

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As for mass, how much does a 100m of cables weight? Lets say it must be sufficiently strong to not break under the weight of two partially fueled ITS spaceships at 0.38g.

Let's assume it is Zylon, density 1540 kg/m^3 and tensile strength 5.8 GPa. An ITS craft will mass up to 720 tonnes in cruise configuration, based on the fueled mass and delta-v given in the 2016 IAC presentation. At 0.38 g that is 2.68 million N of force on the cable.

Assuming a factor of safety of a very conservative 3x, that's 8.05 MN required strength, which Zylon can provide with only 13.9 cm^2 area of cable, which masses only 2.15 kg per meter. So a 100 m cable is only 215 kg.

But with a 100 m cable, the delta-v to spin up and down is 5250 kg per ship. The mass of the cable is pretty trivial compared to the mass of spin up/down propellant. Both propellant and cable mass increase with a longer cable, so the shortest possible cable is mass-optimal.

There doesn't appear to be any reason to spin at less than 3 RPM, which can be done with a 50 m cable and 2 ITS ships nose to nose, yielding .38 g on the lowest deck of the passenger cabin, and .27 g on the highest deck.

Offline Coastal Ron

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But with a 100 m cable, the delta-v to spin up and down is 5250 kg per ship. The mass of the cable is pretty trivial compared to the mass of spin up/down propellant. Both propellant and cable mass increase with a longer cable, so the shortest possible cable is mass-optimal.

Sure, the shortest possible cable is mass-optimal, but it may not provide the optimal conditions for humans.

Quote
There doesn't appear to be any reason to spin at less than 3 RPM, which can be done with a 50 m cable and 2 ITS ships nose to nose, yielding .38 g on the lowest deck of the passenger cabin, and .27 g on the highest deck.

If the weight of the cable is minimal, and if human comfort can be increased by increasing the radius of the rotation, then it only costs a small amount of cable weight to provide better human comfort. I'm assuming the amount of fuel required to spin up/down does not change given the radius as long as the resulting gravity is the same.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline Coastal Ron

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For myself I'm OK with "worst case", [...] because if I can come up with solutions that work out OK with "worst case", then I should be OK with "reality".

No. This is why I keep harping on about people insisting on low RPM. It's pre-establishing that the trade will fail.

Radius increases with the inverse square of RPM. It's a huge effect. If you insist on 1g and 1 or 2RPM, then you've virtually ruled out AG in advance, because of course others are going to say "It adds too much mass/complexity", and any consideration of the idea dies. As I said, the difference between 1g/2RPM and 0.38g/4RPM is a tenfold difference in scale.

I understand your concern. Previously I didn't, but now I do, so thanks for explaining it. However there are some situations where your concerns should not be a problem, such as:

A. The example of two ITS joined by cable nose-to-nose, where the weight of the cable is negligible, so the radius of rotation can be lengthened without the inverse square problem.

B. If having a large vehicle/station is a benefit. A rotating space station design I'm looking at requires a large amount of habitable area to be useful, so having a longer radius with lower RPM can provide that.

Quote
It would be like designing rockets by insisting that any rocket technology must be capable of SSTO or you won't even look at it, because "if you can solve the worst case then you should be able to solve any other configuration". That's not reasonable, and it's not honest.

Again, I understand your point, but I would ask you to consider how SpaceX was able to create reusable rockets when everyone else assumed it could not be done. Sometimes you just need to ignore "the rules" to see if there are alternative solutions that still result in the desired outcome.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Online KelvinZero

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It just occurred to me, maybe a single cable can work. [etc]

This is where you make a system ridiculously complicated so you can keep the original idea, because the original idea was "simple".
No I don't think so, because the ships will (Im guessing) already have these flywheels and the software to deal with small corrections in orientation.

What was naive was the idea of the spaceship freely exchanging rotational energy with the cable, like a weight tied to the end of a rope, winding up, then spinning the other way.

Offline Paul451

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I'm assuming the amount of fuel required to spin up/down does not change given the radius as long as the resulting gravity is the same.

Not even close. Angular momentum (and hence fuel requirement) increases with radius and velocity, both of which increase with reduced RPM for the same g-load.

Eg, at the same 0.38g, angular momentum per kg of ship mass at 4, 3, 2, 1 RPM is, approx. 190, 450, 1500 and 12,000 m≤/s respectively. Hence, halve the RPM and you increase the angular momentum approximately 8-fold. Cubic increase.

Sometimes you just need to ignore "the rules" to see if there are alternative solutions that still result in the desired outcome.

I find it funny that you're saying this when you are the one fixating on SpinCalc's red/yellow/green indicators as if they are the word-of-god, and I'm trying to say "No, there's been 35 years of research that says otherwise. The old assumptions are wildly out of date."
« Last Edit: 09/05/2017 10:23 PM by Paul451 »

Offline Coastal Ron

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I'm assuming the amount of fuel required to spin up/down does not change given the radius as long as the resulting gravity is the same.

Not even close. Angular momentum (and hence fuel requirement) increases with radius and velocity, both of which increase with reduced RPM for the same g-load.

Eg, at the same 0.38g, angular momentum per kg of ship mass at 4, 3, 2, 1 RPM is, approx. 190, 450, 1500 and 12,000 m≤/s respectively. Hence, halve the RPM and you increase the angular momentum approximately 8-fold. Cubic increase.

OK, it's good we're having this conversation, as I had the wrong assumption about the ice skater spinning with arms open and arms closed.

Quote
Sometimes you just need to ignore "the rules" to see if there are alternative solutions that still result in the desired outcome.

I find it funny that you're saying this when you are the one fixating on SpinCalc's red/yellow/green indicators as if they are the word-of-god, and I'm trying to say "No, there's been 35 years of research that says otherwise. The old assumptions are wildly out of date."

Well, 35 years of research here on Earth. What we need is a long-duration testing platform in space to validate everyone's assumptions - which I think I may have a valid concept for. Not ready to share yet, but it was inspired by a suggestion on a different topic thread. Specifically it would provide .38G at 3 RPM, while simultaneously providing levels of occupation that would be closer to the center of rotation, meaning less simulated gravity but more angular and tangential velocities (which may be detrimental at some upper limit, which needs to be determined thru actual testing).
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline envy887

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But with a 100 m cable, the delta-v to spin up and down is 5250 kg per ship. The mass of the cable is pretty trivial compared to the mass of spin up/down propellant. Both propellant and cable mass increase with a longer cable, so the shortest possible cable is mass-optimal.

Sure, the shortest possible cable is mass-optimal, but it may not provide the optimal conditions for humans.

Quote
There doesn't appear to be any reason to spin at less than 3 RPM, which can be done with a 50 m cable and 2 ITS ships nose to nose, yielding .38 g on the lowest deck of the passenger cabin, and .27 g on the highest deck.

If the weight of the cable is minimal, and if human comfort can be increased by increasing the radius of the rotation, then it only costs a small amount of cable weight to provide better human comfort. I'm assuming the amount of fuel required to spin up/down does not change given the radius as long as the resulting gravity is the same.

Propellant requirements are roughly proportional to tangential velocity, which increases with the square root of radius.

However, the difference between 2 and 3 RPM is only 6 m/s delta-v per ship, and 44 m (less than 100 kg) of cable. If the difference is worthwhile (which I doubt), then adding that capability is hardly difficult.

Offline biosehnsucht

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There doesn't appear to be any reason to spin at less than 3 RPM, which can be done with a 50 m cable and 2 ITS ships nose to nose, yielding .38 g on the lowest deck of the passenger cabin, and .27 g on the highest deck.

Are you so sure about no reason to go less than 3 RPM? Perhaps a lower gravity target will help, but does 4 RPM for 0.38g come out to less Coriolis effect than 2 RPM at 1g?

Quote
The Coriolis effect gives an apparent force that acts on objects that move relative to a rotating reference frame. This apparent force acts at right angles to the motion and the rotation axis and tends to curve the motion in the opposite sense to the habitat's spin. If an astronaut inside a rotating artificial gravity environment moves towards or away from the axis of rotation, he or she will feel a force pushing him or her towards or away from the direction of spin. These forces act on the inner ear and can cause dizziness, nausea and disorientation. Lengthening the period of rotation (slower spin rate) reduces the Coriolis force and its effects. It is generally believed that at 2 rpm or less, no adverse effects from the Coriolis forces will occur, although humans have been shown to adapt to rates as high as 23 rpm.

Offline the_other_Doug

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I'd ask y'all to recall that the only experiments that I know of that have ever been done with spinning up two vehicles around a tether happened 51 years ago, on Geminis XI and XII.  They found that, on the mass scales and speed of movement they were testing, the recoil force from the tether itself caused the tether to have completely unacceptable dynamics, and even slight movements by the crew would take what appeared to be a stable tether dynamic and push it quickly into a series of disastrous loops.

The problem seems to be that you need the tether to be at full stress before you spin up, in order for it to act as if it is a solid, unbending link between the two end-point masses.  If you at any point stop thrusting the two masses away from each other, along the tether vector, the tether will recoil, start pulling the two masses back together, and start looping like crazy.  The spin-up maneuver, involving as it would need to the continuous thrust to apply pressure along the tether, but decreasing as the spin replaces the thrust to apply tension to the tether, is of such complexity that it would need to be demonstrated several times before you could consider using it operationally.

So -- those who believe that there needs to be an awful lot more real-world testing, in space, of the dynamics of such tethered systems before such a thing is designed into the cruise architecture of a Mars mission are the winners of this discussion at present, IMHO... :)
-Doug  (With my shield, not yet upon it)

Online KelvinZero

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I'd ask y'all to recall that the only experiments that I know of that have ever been done with spinning up two vehicles around a tether happened 51 years ago, on Geminis XI and XII.  They found that, on the mass scales and speed of movement they were testing, the recoil force from the tether itself caused the tether to have completely unacceptable dynamics, and even slight movements by the crew would take what appeared to be a stable tether dynamic and push it quickly into a series of disastrous loops.

But since then we have things like the Colbert and the hoverslam, ie damping oscillations and control of laggy systems has advanced to an incredible art that is used for both trivial and extreme purposes.

I had assumed some sort of intelligent damping. Everything seems to have it now. Even the fact they actually physically did this experiment back then shows how much things have moved on. We are comparing biplanes to harriers

Offline the_other_Doug

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I'd ask y'all to recall that the only experiments that I know of that have ever been done with spinning up two vehicles around a tether happened 51 years ago, on Geminis XI and XII.  They found that, on the mass scales and speed of movement they were testing, the recoil force from the tether itself caused the tether to have completely unacceptable dynamics, and even slight movements by the crew would take what appeared to be a stable tether dynamic and push it quickly into a series of disastrous loops.

But since then we have things like the Colbert and the hoverslam, ie damping oscillations and control of laggy systems has advanced to an incredible art that is used for both trivial and extreme purposes.

I had assumed some sort of intelligent damping. Everything seems to have it now. Even the fact they actually physically did this experiment back then shows how much things have moved on. We are comparing biplanes to harriers

Invalid comparison.  Ever since Kitty Hawk, people have been working on VTOL systems.  The Harrier is not even the most sophisticated example -- but decades and decades of trial-and-error went into it, trying every damnfool thing you can think of, and others besides.  With the results that many different types of VTOL systems exist now - most of them some form of helicopter.

On the other hand, ISS does damping, when running microgravity experiments, by the expedient of telling the crew they can't exercise, and BTW, try not to bounce off any walls for the next couple of hours, OK?

Skylab's second and third crews were told not to run around the water tanks like Pete's crew did, because it was stuff like that that caused the CMGs to wear out way faster than anticipated.  And CMG technology is really no more advanced today than it was 45 years ago, I don't believe.  Especially enormous CMGs.

"Intelligent" damping can only accommodate so much moving and bumping around, and you can't keep a shipload of people still enough to bring the excursions down to anywhere close to the kinds of damping algorithms that are used in satellites and such.  And there has been no -- zero -- systems designed to keep two masses, with movements going on constantly within them, stable spinning around a flexible tether.  Because, unlike VTOL systems, there has never been a demand to develop such a thing.

So, once again -- as far as spinning two spacecraft around on a tether, we are still flying biplanes.  And will continue to do so until and unless someone actually addresses the extremely complex damping needed for such a dynamic and essentially chaotic system.  (How is your intelligent damping system gonna handle it when, out of pure chance, all of the people on the port side of one ship decide to flush their toilets within 15 seconds of each other?  That's gotta be a ton or more of flush-water moving around...)

I truly believe that this will end up being a lot harder than even the people who already think it will be hard really apprehend...
-Doug  (With my shield, not yet upon it)

Online KelvinZero

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On the other hand, ISS does damping, when running microgravity experiments, by the expedient of telling the crew they can't exercise, and BTW, try not to bounce off any walls for the next couple of hours, OK?
The reason I brought up the COLBERT was this:
https://en.wikipedia.org/wiki/Treadmill_with_Vibration_Isolation_Stabilization

The rest is above my pay grade. Might make a great cubesat project, though I think that today you would basically know from simulations. I have seen simulations of how badly undamped cables can behave somewhere, probably on this site.

(edit)
Hey, has anyone mentioned that although this may prove unnecessary for mars, it could be a useful experiment in LEO? I don't think ITS is going to go haring off to mars as soon as it is built. I see all sorts of shakedown runs and other work, and maybe this could include a test with people and ECLSS for some months in mars gravity.

If mars gravity is not good enough for health, there are pretty good reasons to want to know this early.
« Last Edit: 09/12/2017 02:24 AM by KelvinZero »

Offline the_other_Doug

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On the other hand, ISS does damping, when running microgravity experiments, by the expedient of telling the crew they can't exercise, and BTW, try not to bounce off any walls for the next couple of hours, OK?
The reason I brought up the COLBERT was this:
https://en.wikipedia.org/wiki/Treadmill_with_Vibration_Isolation_Stabilization

The rest is above my pay grade. Might make a great cubesat project, though I think that today you would basically know from simulations. I have seen simulations of how badly undamped cables can behave somewhere, probably on this site.

(edit)
Hey, has anyone mentioned that although this may prove unnecessary for mars, it could be a useful experiment in LEO? I don't think ITS is going to go haring off to mars as soon as it is built. I see all sorts of shakedown runs and other work, and maybe this could include a test with people and ECLSS for some months in mars gravity.

If mars gravity is not good enough for health, there are pretty good reasons to want to know this early.

I hear you -- and even COLBERT has had some issues; it's a great improvement, but even its use is not allowed during some experiment runs.

And I agree wholeheartedly with your idea of running a significant series of tests of such systems nearer Earth than in truly deep space.  I wonder if it would be better to run them outside of LEO, though, maybe at a LaGrange point.  In LEO, you get such relatively strong gravity gradients that tethers much longer than 20 feet start curling, based on one end of the tether being in a different orbit than the other.  Spinning the pair just means this dynamic would change as the assembly moved around the center point; I'd be a bit concerned that this would inject a lot of variability and instability into the system that you wouldn't see in deep space.  No need to over-engineer the system to handle problems it won't see en route to Mars, after all.

Also, tethers run through Earth's magnetic field can build up a tremendous electrical charge -- witness the demise of the Shuttle's tethered satellite experiment.  I'm pretty certain that the Sun's magnetic field strength, at least between Earth and Mars, is quite a bit weaker than Earth's is while in LEO.  So, again, that would be a complicating factor you could dispense with by testing at a LaGrange point.

In all, testing stability and damping systems for such a rotation system during a nice, long test flight of your first two Mars-sized ITS'es at L2 or L4 might be the best plan.  Heck, sell seats for the tests at cut-rate prices, for a realistic test of the ECLSS and the damping systems, seeing as how they'll need to deal with lots of people moving around and doing, well, all the things that people do... :)

If the price is right, I'd sure buy a seat.  I'll be retiring in the next few years, and I can't think of anything better to do with my "golden years" than to act as a guinea pig for Elon.  :D
-Doug  (With my shield, not yet upon it)

Offline Aussie_Space_Nut

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I'd ask y'all to recall that the only experiments that I know of that have ever been done with spinning up two vehicles around a tether happened 51 years ago, on Geminis XI and XII.  They found that, on the mass scales and speed of movement they were testing, the recoil force from the tether itself caused the tether to have completely unacceptable dynamics, and even slight movements by the crew would take what appeared to be a stable tether dynamic and push it quickly into a series of disastrous loops.

The problem seems to be that you need the tether to be at full stress before you spin up, in order for it to act as if it is a solid, unbending link between the two end-point masses.  If you at any point stop thrusting the two masses away from each other, along the tether vector, the tether will recoil, start pulling the two masses back together, and start looping like crazy.  The spin-up maneuver, involving as it would need to the continuous thrust to apply pressure along the tether, but decreasing as the spin replaces the thrust to apply tension to the tether, is of such complexity that it would need to be demonstrated several times before you could consider using it operationally.

So -- those who believe that there needs to be an awful lot more real-world testing, in space, of the dynamics of such tethered systems before such a thing is designed into the cruise architecture of a Mars mission are the winners of this discussion at present, IMHO... :)

Please help me get my head around this.

1) Based on the Gemini Tether Experiment (GTE) it would appear that tethers don't work in the context of them being inherently stable.

2) So I went off to do some more reasearch and looked into it a bit more. According to wikipedia the GTE only got up to 0.00015g
https://en.wikipedia.org/wiki/Gemini_11#Scientific_experiments
"The passive stabilization experiment proved to be a bit troublesome. Conrad and Gordon separated the craft in a nose-down (i.e., Agena-down) position, but found that the tether would not be kept taut simply by the Earth's gravity gradient, as expected. However, they were able to generate a small amount of artificial gravity, about 0.00015 g, by firing their side thrusters to slowly rotate the combined craft like a slow-motion pair of bolas.[4]"

3) However even at this very low AG effect the NASA spiel states the following,
https://nssdc.gsfc.nasa.gov/nmc/masterCatalog.do?sc=1966-081A
"The hatch was closed at 9:57a.m. and shortly afterwards the spacecraft were undocked and Gemini 11
moved to the end of the 30 meter tether attaching the two spacecraft. At 11:55 a.m. Conrad initiated a slow rotation of the Gemini capsule about the GATV which kept the tether taut and the spacecraft a constant distance apart at the ends of the tether. Oscillations occurred initially, but damped out after about 20 minutes. The rotation rate was then increased, oscillations again occurred but damped out and the combination stabilized. The circular motion at the end of the tether imparted a slight artificial "gravitational acceleration" within Gemini 11, the first time such artificial gravity was demonstrated in space. After about three hours the tether was released and the spacecraft moved apart."

Saying that the GTE is therefore proof that tethers are unstable, given the extremely low AG effect attained, I think is unfair. (I admit this is my gut feel and is completely unsubstantiated.)

Is it wrong to say, that the greater the tension in the cable, the more stable the system will become?

Offline Eric Hedman

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Is it wrong to say, that the greater the tension in the cable, the more stable the system will become?
It would at this point be unsubstantiated to say this.  It might be true, but at this point tests with larger spacecraft at greater tension and faster rotation need to be done before that assertion can be made.  In larger craft the mass of the human body will be moving around potentially inducing oscillations.  Determining the natural frequency of such a system would be an interesting problem.  It might become necessary to put some kind of dampening system in place.  Of course we won't know unless we try.  The first thing to do is to try to create a computer simulation.

Offline Aussie_Space_Nut

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I wonder if having a rigid pole attached to the nose of the spacecraft, with the tether attached to the end of the pole would help keep things stable?

Offline Peter.Colin

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I wonder if the use of the crane to lift the nose tethered BFS, onto the BFR.
And the oscillations caused by that action are indicative for what would happen in space?
 
« Last Edit: 09/17/2017 10:50 AM by Peter.Colin »

Offline Aussie_Space_Nut

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Offline corneliussulla

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I think Elon stated that the nose would be pointing towards the Sun during flight. I expect for a couple of reasons 1 so solar array could get most energy 2) to limit the effects of solar energy on fuel required for landing. Also if you spin up the ships would mean the solar arrays would then need to withstand partial G forces. Great idea but probably not realistic

Offline Paul451

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Also if you spin up the ships would mean the solar arrays would then need to withstand partial G forces.

It could make deployment easier, since the (presumably thin-film arrays) wouldn't need a stabilising structure to deploy them, they'd just unroll and "hang", then be rolled back up before despin and landing.

Offline Negan

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Also if you spin up the ships would mean the solar arrays would then need to withstand partial G forces.

I don't see how the arrays could be so flimsy as to not be able to handle this. The arrays will have to be deployed and retracted hundreds of times during the ship's lifetime.
« Last Edit: 10/16/2017 10:05 PM by Negan »

Offline Coastal Ron

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I think Elon stated that the nose would be pointing towards the Sun during flight. I expect for a couple of reasons 1 so solar array could get most energy 2) to limit the effects of solar energy on fuel required for landing.

During his recent AMA on Reddit Musk said it was to keep the propellant from boiling, since the tanks are not pressurized.

Quote
Also if you spin up the ships would mean the solar arrays would then need to withstand partial G forces. Great idea but probably not realistic

As currently designed the solar panels would not operate properly if two BFS were connected via their noses and spun.

Also, I'm not sure anyone knows if there are structural attachments at the nose - which if there isn't then there isn't much to discuss...  :o
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline envy887

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I think Elon stated that the nose would be pointing towards the Sun during flight. I expect for a couple of reasons 1 so solar array could get most energy 2) to limit the effects of solar energy on fuel required for landing.

During his recent AMA on Reddit Musk said it was to keep the propellant from boiling, since the tanks are not pressurized.

Quote
Also if you spin up the ships would mean the solar arrays would then need to withstand partial G forces. Great idea but probably not realistic

As currently designed the solar panels would not operate properly if two BFS were connected via their noses and spun.

Also, I'm not sure anyone knows if there are structural attachments at the nose - which if there isn't then there isn't much to discuss...  :o

It's a convenient place to lift for vertical integration at the pad, which is required if the booster lands on and stays on the pad.

Offline intrepidpursuit

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Apollo astronauts reported that the capsule was barely livable in long duration tests on the ground, but much more spacious in freefall. Anyone landing on mars will be in space 3-6 months and then on mars for 18+ months. Gravity during the flight will cause more harm than good imo.

Online mikelepage

Interesting article in part on the effects of living in a low g environment log term.

https://www.brisbanetimes.com.au/world/north-america/astronaut-scott-kelly-on-the-devastating-effects-of-a-year-in-space-20170922-gyn9iw.html

Apollo astronauts reported that the capsule was barely livable in long duration tests on the ground, but much more spacious in freefall. Anyone landing on mars will be in space 3-6 months and then on mars for 18+ months. Gravity during the flight will cause more harm than good imo.

Worth reading the Scott Kelly article above if you haven't already.  He describes the return to Earth after 340 days as being okay for the first 24-48 hours followed by systemic pain, bloating and rashes that were "much, much worse" than after his 6-month stint.  Then "A few months after arriving back on Earth, though, I feel distinctly better."

So what I take from that is that adjusting back to life at 1xg after a year at zero gravity is a very severe ordeal.  It takes at least twice as long as adjusting to zero gravity in the first place, and unless Mars gravity is sufficient to reverse all the effects of zero/partial gravity, there's a good chance the astronaut will die upon return to Earth. 

At the very least, it would be worth having some facility/tethered-BFS's in LEO where returning astronauts can be gradually acclimatised back to 1xg rather than returned to the surface immediately.

Offline intrepidpursuit

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Interesting article in part on the effects of living in a low g environment log term.

https://www.brisbanetimes.com.au/world/north-america/astronaut-scott-kelly-on-the-devastating-effects-of-a-year-in-space-20170922-gyn9iw.html

Apollo astronauts reported that the capsule was barely livable in long duration tests on the ground, but much more spacious in freefall. Anyone landing on mars will be in space 3-6 months and then on mars for 18+ months. Gravity during the flight will cause more harm than good imo.

Worth reading the Scott Kelly article above if you haven't already.  He describes the return to Earth after 340 days as being okay for the first 24-48 hours followed by systemic pain, bloating and rashes that were "much, much worse" than after his 6-month stint.  Then "A few months after arriving back on Earth, though, I feel distinctly better."

So what I take from that is that adjusting back to life at 1xg after a year at zero gravity is a very severe ordeal.  It takes at least twice as long as adjusting to zero gravity in the first place, and unless Mars gravity is sufficient to reverse all the effects of zero/partial gravity, there's a good chance the astronaut will die upon return to Earth. 

At the very least, it would be worth having some facility/tethered-BFS's in LEO where returning astronauts can be gradually acclimatised back to 1xg rather than returned to the surface immediately.

By that logic having gravity on BFS is even worse because colonists will be going through this painful adjustment period and possible death while in transit. Much better to deal with that on earth.

Offline whitelancer64

*snip* there's a good chance the astronaut will die upon return to Earth.  *snip*

[Citation Needed]
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Offline Peter.Colin

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Interesting article in part on the effects of living in a low g environment log term.

https://www.brisbanetimes.com.au/world/north-america/astronaut-scott-kelly-on-the-devastating-effects-of-a-year-in-space-20170922-gyn9iw.html

Apollo astronauts reported that the capsule was barely livable in long duration tests on the ground, but much more spacious in freefall. Anyone landing on mars will be in space 3-6 months and then on mars for 18+ months. Gravity during the flight will cause more harm than good imo.

Worth reading the Scott Kelly article above if you haven't already.  He describes the return to Earth after 340 days as being okay for the first 24-48 hours followed by systemic pain, bloating and rashes that were "much, much worse" than after his 6-month stint.  Then "A few months after arriving back on Earth, though, I feel distinctly better."

So what I take from that is that adjusting back to life at 1xg after a year at zero gravity is a very severe ordeal.  It takes at least twice as long as adjusting to zero gravity in the first place, and unless Mars gravity is sufficient to reverse all the effects of zero/partial gravity, there's a good chance the astronaut will die upon return to Earth. 

At the very least, it would be worth having some facility/tethered-BFS's in LEO where returning astronauts can be gradually acclimatised back to 1xg rather than returned to the surface immediately.

By that logic having gravity on BFS is even worse because colonists will be going through this painful adjustment period and possible death while in transit. Much better to deal with that on earth.

Logic states itís always better from a health perspective to have 0,39 G on the BSF than zero G.

The optimal gravity for health during the different stages of the trips is most likely higher than 0,39 G, and will be dependent on what the effect of Mars gravity has on the human body. That effect is unknown. It could even be that for instance prolonged exposure (years) to 0,8G is more optimal for your health than prolonged exposure to 1G. We just donít know.
« Last Edit: 10/25/2017 05:40 PM by Peter.Colin »

Offline Paul451

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So what I take from that is that adjusting back to life at 1xg after a year at zero gravity is a very severe ordeal.  It takes at least twice as long as adjusting to zero gravity in the first place, and unless Mars gravity is sufficient to reverse all the effects of zero/partial gravity, there's a good chance the astronaut will die upon return to Earth.

I don't think the cumulative damage could ever be enough to kill them. Assuming Musk's preferred 100-and-a-bit day transit time, say 4 months worst case, you have 8 months cumulative zero-g. Bad, but demonstrably not fatal, unless you already had a medical issue (thin heart muscle, etc) which would presumably disqualify you from Mars anyway.

So the only issue is whether Mars gravity provides a restorative effect. And IMO, if it's insufficient to restore health after 4-months zero-g, then it's also likely to result in long term damage to permanent settlers even if they landed healthy. That means no colonies on Mars until there's a SF-level revolution in pharma and/or genetic engineering. (Or any base where you weren't on continuous ISS-like health monitoring and exercise/medication regimes.) Which makes the issue of partial-g during transit redundant anyway. Either time on Mars (plus exercise) can undo the damage of 4mths zero-g, or we aren't going to Mars. I can't see a middle-case.

That doesn't mean that expecting to go straight from 4 months zero-g to active work on Mars isn't an issue, and that even partial-g during transit wouldn't be useful, but there's a big jump from "it's an issue" to "it's fatal". [Aside from accidents. Passing out during an EVA (from combined orthostatic hypotension, hypovolemia, and the loss of Vasovagal response) is not going to make you happy.]



Aside: Out of curiosity, what's the shortest time before an astronaut has reflown after, say, more than a month of micro-g? (Ie, more than Apollo/Gemini/STS/etc.) Have NASA or the Russians ever tried the experiment of flying an astronaut for a standard tour on Mir/ISS (say, 3 or 6 months), then bring them home for a short recovery period, then send them back for another tour of the same length, to look at whether damage is worse on the second tour, even though nominal health at launch was the same in each case.

Interesting to think about the BFS crew (not colonists) who are flying a regular schedule back and forth. How often can they fly. How many trips before cumulative damage (from micro-g and/or radiation) ends their career?

Offline envy887

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Paul, what makes you think that crew will make many or even multiple trips?

Offline Paul451

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Paul, what makes you think that crew will make many or even multiple trips?

Passengers will generally make one trip (with some returns.) But crew is crew. It's their job.

If you can only send them once (ie, two trips, out and return), then you have to hire/train entirely new crew for every synod. If Musk can achieve the colonist numbers he imagines, there's going to be a bunch of ships every trip, that's a lot of crew to replace each time, and a lot of experience wasted. Therefore it seems reasonable to assume the crew will fly as many times as medical standards allow.

Has something been said by Musk to suggest one-time only crews?

Offline guckyfan

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Has something been said by Musk to suggest one-time only crews?

Nothing has been said to suggest crew at all. Some people on board will need some training to run life support and kitchen facilities. But many of the passengers being highly qualified there is no reason there would be no one of them qualified. The ship and its flight functions will not need any crew as most flights will be unmanned.

Online mikelepage

*snip* there's a good chance the astronaut will die upon return to Earth.  *snip*

[Citation Needed]

That was in response to intrepidpursuit's timeline of 3-6 month transit + 18 month Mars stay + 3-6 month transit.

I was at the microgravity research symposium at IAC2017, with plenty of NASA, European and Russian medical researchers present.  While everyone thought a flags-and-footprints (~<12 months?) mission to Mars and back was plausible and within the envelope of human endurance, spin-gravity was mentioned multiple times as the only solution anyone can think of for going longer without even more severe symptoms.  The cumulative effects of extended microgravity do not appear to stabilise after any time point so far documented in humans or rodents.

One of the NASA researchers was particularly pessimistic regarding anything less than 1xG - she was the one demonstrating up to 50% reduction in bone mass of rodents spending only 37 days on the ISS.  Her suspicion was that even those astronauts who are retaining bone mass and density due to exercise regimes - would still have considerable bone remodelling similar to the rats in the experiments.  This means more osteoarthritic symptoms, and specifically, a huge increase in the amount of the dense, brittle "cortical" bone that normally makes up the surface of bone, and a massive reduction in the mesh-like "tribecular" bone that normally fills the main body of the bone.  This means you can maintain the same average bone density even as large voids open up in the main structure, and results in a bone that is far more brittle than before.   Obviously time will tell as the current generation of astronauts grows older, but I think it's a bit crazy not to be seriously exploring solutions now. 

I don't think the cumulative damage could ever be enough to kill them. 
Obviously I do  :P  Some astronauts who had been off world for years could end up in an interesting conundrum if they develop a condition that means they need to come back to Earth surface for treatment, but the gravity makes it an impossibility.  Spin gravity could be the only current-technology solution.


Offline philw1776

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Has something been said by Musk to suggest one-time only crews?

Nothing has been said to suggest crew at all. Some people on board will need some training to run life support and kitchen facilities. But many of the passengers being highly qualified there is no reason there would be no one of them qualified. The ship and its flight functions will not need any crew as most flights will be unmanned.

Precisely.  At least for the first crewed synods a significant portion of the passengers will be technically adept.  Some number of them will have specific training to maintain environmental systems, etc.  Sadly including toilet maintenance.  I see no need for pilots, navigators, etc. on a BFS.  Automation in the 2020s or 2030s is only going to be better than today where all SpaceX flights are successfully automated.
ďWhen it looks more like an alien dreadnought, thatís when you know youíve won.Ē

Offline WindyCity

So what I take from that is that adjusting back to life at 1xg after a year at zero gravity is a very severe ordeal.  It takes at least twice as long as adjusting to zero gravity in the first place, and unless Mars gravity is sufficient to reverse all the effects of zero/partial gravity, there's a good chance the astronaut will die upon return to Earth.
So the only issue is whether Mars gravity provides a restorative effect. And IMO, if it's insufficient to restore health after 4-months zero-g, then it's also likely to result in long term damage to permanent settlers even if they landed healthy. That means no colonies on Mars until there's a SF-level revolution in pharma and/or genetic engineering. (Or any base where you weren't on continuous ISS-like health monitoring and exercise/medication regimes.) Which makes the issue of partial-g during transit redundant anyway. Either time on Mars (plus exercise) can undo the damage of 4mths zero-g, or we aren't going to Mars. I can't see a middle-case.

How about centrifuging on Mars? Regular exposure to 1 G in a centrifuge might provide a sufficient prophylactic against the ill effects of long-term low-G exposure.
« Last Edit: 10/26/2017 10:56 PM by WindyCity »

Offline Lars-J

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How about centrifuging on Mars? Regular exposure to 1 G in a centrifuge might provide a sufficient prophylactic against the ill effects of long-term low-G exposure.

If there are ill effects of Mars gravity, something like that could be done. But we just don't know yet. Long term ill effects in the entire span between 0 G and 1 G is an unknown. But we'll only know by trying.

Offline Aussie_Space_Nut

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Interesting article in part on the effects of living in a low g environment log term.

https://www.brisbanetimes.com.au/world/north-america/astronaut-scott-kelly-on-the-devastating-effects-of-a-year-in-space-20170922-gyn9iw.html

Apollo astronauts reported that the capsule was barely livable in long duration tests on the ground, but much more spacious in freefall. Anyone landing on mars will be in space 3-6 months and then on mars for 18+ months. Gravity during the flight will cause more harm than good imo.

Worth reading the Scott Kelly article above if you haven't already.  He describes the return to Earth after 340 days as being okay for the first 24-48 hours followed by systemic pain, bloating and rashes that were "much, much worse" than after his 6-month stint.  Then "A few months after arriving back on Earth, though, I feel distinctly better."

So what I take from that is that adjusting back to life at 1xg after a year at zero gravity is a very severe ordeal.  It takes at least twice as long as adjusting to zero gravity in the first place, and unless Mars gravity is sufficient to reverse all the effects of zero/partial gravity, there's a good chance the astronaut will die upon return to Earth. 

At the very least, it would be worth having some facility/tethered-BFS's in LEO where returning astronauts can be gradually acclimatised back to 1xg rather than returned to the surface immediately.

By that logic having gravity on BFS is even worse because colonists will be going through this painful adjustment period and possible death while in transit. Much better to deal with that on earth.

Logic states itís always better from a health perspective to have 0,39 G on the BSF than zero G.

The optimal gravity for health during the different stages of the trips is most likely higher than 0,39 G, and will be dependent on what the effect of Mars gravity has on the human body. That effect is unknown. It could even be that for instance prolonged exposure (years) to 0,8G is more optimal for your health than prolonged exposure to 1G. We just donít know.

My simple thought is we need an AG staion in LEO to test all this before we go too far.

However if people insist on just going for it I think the easiest on the human body idea would be as follows.

2 Spaceships tetherd together at Earth spin up to 1g.

On the way to Mars they slowly spin down to 0.38g for their arrival at Mars.

On the way back do the reverse. This would give the body time to adjust.

Will this work? I have no idea!  :)

That is why we need an AG station in LEO to test this stuff out.

Offline HMXHMX

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Interesting article in part on the effects of living in a low g environment log term.

https://www.brisbanetimes.com.au/world/north-america/astronaut-scott-kelly-on-the-devastating-effects-of-a-year-in-space-20170922-gyn9iw.html

Apollo astronauts reported that the capsule was barely livable in long duration tests on the ground, but much more spacious in freefall. Anyone landing on mars will be in space 3-6 months and then on mars for 18+ months. Gravity during the flight will cause more harm than good imo.

Worth reading the Scott Kelly article above if you haven't already.  He describes the return to Earth after 340 days as being okay for the first 24-48 hours followed by systemic pain, bloating and rashes that were "much, much worse" than after his 6-month stint.  Then "A few months after arriving back on Earth, though, I feel distinctly better."

So what I take from that is that adjusting back to life at 1xg after a year at zero gravity is a very severe ordeal.  It takes at least twice as long as adjusting to zero gravity in the first place, and unless Mars gravity is sufficient to reverse all the effects of zero/partial gravity, there's a good chance the astronaut will die upon return to Earth. 

At the very least, it would be worth having some facility/tethered-BFS's in LEO where returning astronauts can be gradually acclimatised back to 1xg rather than returned to the surface immediately.

By that logic having gravity on BFS is even worse because colonists will be going through this painful adjustment period and possible death while in transit. Much better to deal with that on earth.

Logic states itís always better from a health perspective to have 0,39 G on the BSF than zero G.

The optimal gravity for health during the different stages of the trips is most likely higher than 0,39 G, and will be dependent on what the effect of Mars gravity has on the human body. That effect is unknown. It could even be that for instance prolonged exposure (years) to 0,8G is more optimal for your health than prolonged exposure to 1G. We just donít know.

My simple thought is we need an AG staion in LEO to test all this before we go too far.

However if people insist on just going for it I think the easiest on the human body idea would be as follows.

2 Spaceships tetherd together at Earth spin up to 1g.

On the way to Mars they slowly spin down to 0.38g for their arrival at Mars.

On the way back do the reverse. This would give the body time to adjust.

Will this work? I have no idea!  :)

That is why we need an AG station in LEO to test this stuff out.

Good idea!  http://ssi.org/wp-content/uploads/2017/10/201710_ssi_agsr_glab.pdf

Offline Paul451

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How about centrifuging on Mars? Regular exposure to 1 G in a centrifuge might provide a sufficient prophylactic against the ill effects of long-term low-G exposure.

Okay, but for a permanent colony? Imagine the 16th century American colonies had a restriction where everyone of European descent had to spend, say, an hour a day inside a machine like an iron lung (just as an example), and worse, pregnant Euro-descended women had to spend the bulk of their pregnancy in such a chamber in order for the baby to develop properly.

For a short stay scientific base (say a maximum of one synod stay for crew), an ISS-like regime of exercise, monitoring, plus whatever drugs are coming on line for bone-loss would probably be sufficient. I doubt for even a worst case scenario, Mars gravity could be as bad as zero-g. But what's acceptable for a scientific base isn't necessarily acceptable for a colony.

But this is swinging off-topic. My point was that if Mars gravity is sufficient for the health of permanent colonists, then it should be sufficient to heal damage from zero-g exposure. Therefore I think it's safe to assume that any time spent on Mars will reduce the damage from the trip out. Hence it won't be, say, 4 months of zero-g, then no improvement on Mars, then an extra 4-months of zero-g for the return. It'll be 4mths out, then a recovery period on Mars before the second exposure. So the damage during the trip won't be as bad as, say, an 8+ mths on ISS.

[Hence my question about what's the shortest length of time between an astronaut or cosmonaut doing two tours on a space station (either Mir or ISS)? And was the damage from the second tour worse than the first? Has any agency explicitly done that experiment?]
« Last Edit: 10/28/2017 06:48 AM by Paul451 »

Offline Paul451

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2 Spaceships tetherd together at Earth spin up to 1g.

If Mars gravity is sufficient for a colony, it's certainly sufficient for the few months voyage out.

otoh...

On the way to Mars they slowly spin down to 0.38g for their arrival at Mars.

There's no reason to have more than a couple of days to adapt to low gravity. There's very little that the body needs to do (fluid shifting leading to excessive urination seems to be the only thing), it's just a matter of adjusting your coordination and balance, which probably only takes a few hours. One or two days should be plenty enough to ensure you aren't clumsy on the surface in case you need to hit the ground running.

That is why we need an AG station in LEO to test this stuff out.

It doesn't have to be a full "station", in the sense of something on the scale of ISS. A variable gravity animal facility of sufficient size would allow a huge improvement in understanding the shape of the damage-curve between zero and 1g. That allows you to develop a small human test facility near the most critical transition value, to check if the same curve applies to human. Focusing on that region gives you the most bang for buck, so doing the animal experiment first ultimately saves money and time. With three data points for humans, plus dozens for animals, you would have high confidence that you know the shape of the curve.

For example, if the animal facility produces a curve shaped like below, you might design a human facility around lunar gravity to verify the data around that level. The lower the g, the easier to build, the cheaper the experiment. A module and its own upper-stage, spinning end-over-end for three months without resupply. Only if you get a wild divergence between humans and animal results would you spend money on a variable-gravity station on a human scale.

That gives you enough data to know a) that humans should be able to colonise Mars, and b) the lowest (therefore easiest to design) spin-g able to protect against zero-g damage.

[edit: Picture ended up on the wrong message. That's a weird bug. If you have two drafts open, the file will attach to whichever is the first posted.]
« Last Edit: 10/28/2017 06:51 AM by Paul451 »

Offline HMXHMX

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2 Spaceships tetherd together at Earth spin up to 1g.

If Mars gravity is sufficient for a colony, it's certainly sufficient for the few months voyage out.

otoh...

On the way to Mars they slowly spin down to 0.38g for their arrival at Mars.

There's no reason to have more than a couple of days to adapt to low gravity. There's very little that the body needs to do (fluid shifting leading to excessive urination seems to be the only thing), it's just a matter of adjusting your coordination and balance, which probably only takes a few hours. One or two days should be plenty enough to ensure you aren't clumsy on the surface in case you need to hit the ground running.

That is why we need an AG station in LEO to test this stuff out.

It doesn't have to be a full "station", in the sense of something on the scale of ISS. A variable gravity animal facility of sufficient size would allow a huge improvement in understanding the shape of the damage-curve between zero and 1g. That allows you to develop a small human test facility near the most critical transition value, to check if the same curve applies to human. Focusing on that region gives you the most bang for buck, so doing the animal experiment first ultimately saves money and time. With three data points for humans, plus dozens for animals, you would have high confidence that you know the shape of the curve.

For example, if the animal facility produces a curve shaped like below, you might design a human facility around lunar gravity to verify the data around that level. The lower the g, the easier to build, the cheaper the experiment. A module and its own upper-stage, spinning end-over-end for three months without resupply. Only if you get a wild divergence between humans and animal results would you spend money on a variable-gravity station on a human scale.

That gives you enough data to know a) that humans should be able to colonise Mars, and b) the lowest (therefore easiest to design) spin-g able to protect against zero-g damage.

[edit: Picture ended up on the wrong message. That's a weird bug. If you have two drafts open, the file will attach to whichever is the first posted.]

It might look like this, too.  ;(

(Edit, corrected figure)
« Last Edit: 10/30/2017 01:28 AM by HMXHMX »

Online KelvinZero

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That would be quite a cool result in one sense. Unless it looks like a step function above 1.0, it implies gravity a bit higher than earth would have massive health benefits. :)

Offline Dalhousie

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Aside: Out of curiosity, what's the shortest time before an astronaut has reflown after, say, more than a month of micro-g? (Ie, more than Apollo/Gemini/STS/etc.) Have NASA or the Russians ever tried the experiment of flying an astronaut for a standard tour on Mir/ISS (say, 3 or 6 months), then bring them home for a short recovery period, then send them back for another tour of the same length, to look at whether damage is worse on the second tour, even though nominal health at launch was the same in each case.

Valeri Ryumin flew 175 days in space (launched Soyuz 32, returned Soyuz 34) on Salyut 6 flight EO-3, spent 235 days on the ground then launched on Soyuz 35 for another 185 days as part of EO-4.

Fifty four people people have flown two or more flights of four months or more, four have flown five such flights.  Hyperventilation about "damage" appears unwarranted.
"There is nobody who is a bigger fan of sending robots to Mars than me... But I believe firmly that the best, the most comprehensive, the most successful exploration will be done by humans" Steve Squyres

Offline Paul451

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That would be quite a cool result in one sense. Unless it looks like a step function above 1.0, it implies gravity a bit higher than earth would have massive health benefits.

Should someone post the "Great Mambo Chicken" story again?



Fifty four people people have flown two or more flights of four months or more, four have flown five such flights. Hyperventilation about "damage" appears unwarranted.

We're going by reports from flight surgeons and from astronauts about their recovery. Those people are where that information comes from.

Hyperventilation

And no need to be a dick.
« Last Edit: 10/30/2017 04:31 AM by Paul451 »

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That would be quite a cool result in one sense. Unless it looks like a step function above 1.0, it implies gravity a bit higher than earth would have massive health benefits. :)

Hulk agrees  :) humour aside though, if it's like most other biological relationships, it will be sigmoid. In my mind the family of possible curves looks like this:

Offline Paul451

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It might look like this, too. [bad curve]

In that case, you'd do the human experiment somewhere above half a g. If you confirm the results are similar to that on ISS, hence similar to the animal results, you have a reasonable confidence the human damage curve matches the animal one. Sucks for colonisation, but it still saves you time and money compared to a variable gravity human facility capable of testing a full range of gravity values for a minimum 4 months per g-level, across enough humans to eliminate the noise of individual response.



if it's like most other biological relationships, it will be sigmoid. In my mind the family of possible curves looks like this:

Agreed. Moreso, it's likely that each type of damage (muscle loss, fluid weirdness, bone loss, etc) will have its own curve, so the final results will be like your example, with multiple curves, where each corresponds to a different effect. For eg, the red curve might be skeletal muscle (smoothly responding to gravity), the violet curve might be fluid distribution and orthostatic reflex (fairly sharp switch on once you hit the right g-load). The green, blue and cyan curves might be cardiac muscle and types of bone mass, each with their own quirks.

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Valeri Ryumin flew 175 days in space (launched Soyuz 32, returned Soyuz 34) on Salyut 6 flight EO-3, spent 235 days on the ground then launched on Soyuz 35 for another 185 days as part of EO-4.

Fifty four people people have flown two or more flights of four months or more, four have flown five such flights.  Hyperventilation about "damage" appears unwarranted.

So clearly, returning to 1G for upwards of 6 months, in between 4-6 month flights, is sufficient to return astronauts to their baseline health or sufficiently close to it. The "hyperventilation" as you put it, is about something else entirely (comparing multiple stays to long duration flights is apples and oranges).

*If* Mars G is insufficient to produce the "baselining" recuperative effect, then even a flags and footprints mission will be close to 12 months in detrimental conditions and we'll see Scott Kelly level systems. If someone stays on Mars for a full synod under those conditions and then comes back, that's where the risk of fatal consequences upon return is real. It's on the way back I could see spinning two BFS's, starting at Mars G, ramping up to 1G over 4-6 months.

Offline DrRobin

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It might look like this, too. [bad curve]

In that case, you'd do the human experiment somewhere above half a g. If you confirm the results are similar to that on ISS, hence similar to the animal results, you have a reasonable confidence the human damage curve matches the animal one. Sucks for colonisation, but it still saves you time and money compared to a variable gravity human facility capable of testing a full range of gravity values for a minimum 4 months per g-level, across enough humans to eliminate the noise of individual response.



if it's like most other biological relationships, it will be sigmoid. In my mind the family of possible curves looks like this:

Agreed. Moreso, it's likely that each type of damage (muscle loss, fluid weirdness, bone loss, etc) will have its own curve, so the final results will be like your example, with multiple curves, where each corresponds to a different effect. For eg, the red curve might be skeletal muscle (smoothly responding to gravity), the violet curve might be fluid distribution and orthostatic reflex (fairly sharp switch on once you hit the right g-load). The green, blue and cyan curves might be cardiac muscle and types of bone mass, each with their own quirks.

It's a good point that health is not a single scalar variable. I think it's also helpful to restate the obvious point that although we have a good deal of data on microgravity, we have essentially no data on low-gravity beyond what can be tested on vomit-comet-style hops. There is an unspoken assumption here that 1 Earth gravity is optimal for human health, as opposed to evolution just doing the best it can with the gravity it has. As a physician, I will go out on a limb and guess that it will take only a small amount of gravity to get the circulatory system benefits but a near Earth level to get the bone strength benefits, for example. In the case of Lunar gravity, it could be that it has a net harm to tweens going through puberty but a net benefit to seniors struggling with osteoarthritis. It is probably more likely than not that there will be surprises along the way, like the effects of microgravity on visual acuity. Relevant to this group is the question of whether it is worth the resources to try to get data with artificial gravity in LEO before embarking on these missions. It looks like SpaceX is putting their money on "no".

Offline intrepidpursuit

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Based on what we know, it seems possible but unlikely that 1g > 0g > .376g > 0g > 1g will have any catastrophic impact. Especially as we talk about longer term stays on Mars, the Moon or other bodies, more research is needed into the effects of low gravity. Those experiments should absolutely be done in LEO though.

Once we know more, we will learn if the incredible effort and discomfort required to spin transport craft might be helpful for returns from long stays in low gravity or other situations.

Offline Paul451

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the incredible effort and discomfort required to spin transport craft

Que?

Offline intrepidpursuit

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the incredible effort and discomfort required to spin transport craft

Que?

Just read upthread. There is no clear attachment point on the BFS. The crane lift appears to use a spanner bar at least so reach down to points on the sides of the ship. There would have to be a method of stowing and deploying the tether after both craft have carefully synchronously boosted to TMI. Successful removal of the tether would become a new critical step to avoid LOC. The ships won't be able to effectively use solar panels without a major redesign. The current cooling/heating method of pointing toward the sun becomes void. I could go on.

Once spinning the craft will now be much smaller since all the space becomes two dimensional. Transportation between decks becomes laborious and dangerous (picture a 5+ story fall cage ladder).

You can talk about how possible it is all you want, but it would most certainly require a major redesign of major portions of the craft and would reduce the effective interior space. It has a cost which would have to be outweighed by the reward in order to be considered.

Offline Negan

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Transportation between decks becomes laborious and dangerous (picture a 5+ story fall cage ladder).

Duh! Transportation between decks has to happen on Earth and Mars.  Stop trying so hard. ::)
« Last Edit: 10/31/2017 07:56 PM by Negan »

Offline intrepidpursuit

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Transportation between decks becomes laborious and dangerous (picture a 5+ story fall cage ladder).

Duh! Transportation between decks has to happen on Earth and Mars.  Stop trying so hard. ::)

It has to happen once on earth. On mars it will be much easier than on earth due to the lower gravity, though there is no consensus what the gravity would be on the commute, and living in the ship on mars is not the long term plan.

I made lots of other points. Perhaps you should try harder?

Offline Paul451

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the incredible effort and discomfort required to spin transport craft
Que?
[...] without a major redesign. [...] but it would most certainly require a major redesign

What "design"? They radically changed the design within 12 months of announcing it. It will undergo significant redesign over and over as early components mature and they can put more effort into designing second tier systems. The PPT was a crude artists' impression, many of the systems shown are flawed (for eg, the RCS won't work in the places it was occasionally shown, the thermals of the solar-panels/radiators/tanks might not work in LEO, etc etc.) Hell, they'll probably still be making major changes after they start commercial flights. (As with F9's 1.0 to 1.1 tank stretch. Or the changes to the solar panels of cargo-Dragon's trunk vs Dragon V2's.)

But there's no need to panic over it, because Musk doesn't lock designs down before bending metal. There's a reason NSF folk refer to the two presented variants as "0.1" and "0.2" instead of v1 and v2. They are not mature designs. If SpaceX wanted to build BFS with the capability of being spun for gravity, they'd build it. To argue against that, you have to show that these problems are somehow unsolveable; that you somehow can't put hard-points in the nose, that you can't design solar arrays that deploy under gravity, etc etc. To justify your comment, you would need to show that spin-g itself is innately difficult (and uncomfortable).

In reality, Musk (like Zubrin and many Mars enthusiasts here) doesn't really believe that there are issues with the time spent in zero-g, and obviously doesn't believe there can be any issues from Mars gravity. So he is therefore designing around zero-g transit. That is the thread-killer. But hypothetically, for the purpose of the OP's discussion, "it would most require a major redesign" is a silly comment. Everything about the ship requires a "major redesign".

Online KelvinZero

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You could almost get enough length just spinning end over end. For mars gravity in the nose I get something like 4 rpm.. Moon gravity at about 2.5 rpm. That was assuming a radius of 25m. I guess you could get better radius if you fill the bottommost tank and have little cargo.

That seems a good start for basic experiments that could confirm that mars gravity or even moon gravity is sufficient for health.

Offline envy887

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You could almost get enough length just spinning end over end. For mars gravity in the nose I get something like 4 rpm.. Moon gravity at about 2.5 rpm. That was assuming a radius of 25m. I guess you could get better radius if you fill the bottommost tank and have little cargo.

That seems a good start for basic experiments that could confirm that mars gravity or even moon gravity is sufficient for health.

Two ships docked base to base would have a radius in the nose of ~50 meters, only requiring ~2.6 RPM to get Mars gravity. Cargo would only be limited by the tensioned structural strength of the docking mechanisms.

The solar panels would have to be capable of taking the rotation, and would have to be oriented about 90 degrees from the deployment shown (in the same plane as the long axis of the vehicle)

For a LEO test, I think this is a feasible configuration.

Offline Paul451

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The solar panels would have to be capable of taking the rotation, and would have to be oriented about 90 degrees from the deployment shown (in the same plane as the long axis of the vehicle)

"Hanging", in other words. Logically you'd let thin-film panels hang down the sides of the ships (which in this case is towards the nose) and use them as sun-shields. Deploy radiators from the other side, in permanent shadow. (The axis of rotation is pointed at the sun.)

The downside of tail-to-tail is that it would be harder to move between ships. I think being able to move easily between ships would be an advantage of docking ships together when you're flying multiple passenger ships per mission. It means you can reduce the number of specialists (medical staff, technicians, etc), or having specialists able to work together (instead of being scattered across multiple ships, in order to be available on every ship), or being able to empty one ship while doing major ECLSS repairs, or just for socialising. I could see, in the nose-to-nose configuration, you might have a 4-way docking node (launched and retrieved as cargo by one ship) allowing four BFS's to dock in a pin-wheel formation.
« Last Edit: 11/01/2017 03:36 PM by Paul451 »

Offline CuddlyRocket

Especially as we talk about longer term stays on Mars, the Moon or other bodies, more research is needed into the effects of low gravity. Those experiments should absolutely be done in LEO though.

Whether such experiments should be done in LEO or not, I think that there's little chance that they will be! Missions to the Moon and Mars will be the experiments. They'll rely on volunteers and waivers etc. Nobody wants to spend either the money*, or especially the time, needed to conduct such experiments.

(* Particularly if it's their own money!)
« Last Edit: 11/01/2017 10:28 PM by CuddlyRocket »

Offline intrepidpursuit

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Especially as we talk about longer term stays on Mars, the Moon or other bodies, more research is needed into the effects of low gravity. Those experiments should absolutely be done in LEO though.

Whether such experiments should be done in LEO or not, I think that there's little chance that they will be! Missions to the Moon and Mars will be the experiments. They'll rely on volunteers and waivers etc. Nobody wants to spend either the money*, or especially the time, needed to conduct such experiments.

(* Particularly if it's their own money!)

No one will spend their time and money to find out if this is even helpful, but they will spend the time, money, and danger to do it in route, even though it's unclear that it will have any benefits? I am not following your logic.

Online KelvinZero

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Mainly I am wondering if we could dismiss a bunch of dragons all at once. Maybe even moon gravity is enough. Maybe we can adapt 4rpm at mars gravity after all.

As for joining two.. maybe the other one would be all cargo but still a crew BFS.

The crane system could be adapted to allow some moderately convenient access to the cargo side. It could also be a complete backup incase the inhabited vehicle develops faults.

Keeping the propellant cool is an issue. Im guessing we don't need to solve it for a LEO experiment. Success of the experiment actually means less need to worry about the actual OP.



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Two ships docked base to base would have a radius in the nose of ~50 meters, only requiring ~2.6 RPM to get Mars gravity. Cargo would only be limited by the tensioned structural strength of the docking mechanisms.

The solar panels would have to be capable of taking the rotation, and would have to be oriented about 90 degrees from the deployment shown (in the same plane as the long axis of the vehicle)

For a LEO test, I think this is a feasible configuration.

Thank you! I haven't wanted to start a new thread talking about the same thing but base-to-base, but I haven't heard any good reasons why base-to-base docking isn't a much more secure configuration to perform spin-G. 

I mean, the presentation actually *showed* two BFS's docking base to base using secure connections, and low-G acceleration was cited as a way to transfer propellents.  You don't need to invent a new attachment point - one already exists, and gives you all the advantages of a much larger spin radius, so lower angular velocity/Coriolis.

Consider: if you attach nose to nose, what would you do with the (mission critical) acceleration couches for crew during the spin-G cruise phase? (risky to pack them away and reinstall before landing, but they'll be in the way otherwise).  If instead, you go base to base, you leave the acceleration couches hard-attached to the "ceiling" and use the same vertical elevators to change between levels - though at Mars G it will be quite possible to jump up or down single floors without hurting yourself.

The downside of tail-to-tail is that it would be harder to move between ships. I think being able to move easily between ships would be an advantage of docking ships together when you're flying multiple passenger ships per mission. It means you can reduce the number of specialists (medical staff, technicians, etc), or having specialists able to work together (instead of being scattered across multiple ships, in order to be available on every ship), or being able to empty one ship while doing major ECLSS repairs, or just for socialising. I could see, in the nose-to-nose configuration, you might have a 4-way docking node (launched and retrieved as cargo by one ship) allowing four BFS's to dock in a pin-wheel formation.

Not necessarily.  Don't forget that there will be at least the same number of cargo craft as crewed craft.  So in the 2 crew + 2 cargo craft scenario, you could have each crewed BFS docked base-to-base to a cargo BFS to form a spin-able unit.  You could then have those two units to form a single assembly if they aligned their dorsal surfaces - and docked using dorsal ports that will be used to access the ground. 

So the 4 ships would do their trans Mars injection burns separately, then 2x docking base-to-base, then 2x sets dorsal ports dock (crew-to-crew BFSs, cargo-to-cargo BFSs), then start to spin at Mars G.

Interesting to think how much before EDL you would separate the ships.  4 ships would probably need to be coming in within half an hour of each other if they are to land anywhere near each other, or alternatively you might detach the cargo ships and let them arrive a day earlier. 





Online KelvinZero

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You might get a bit better than 50m radius with two joined BFS if you can arrange for more mass to be in the nose of the other (cargo carrying) Mars BFS, along with a bit more landing propellant I suppose.

Offline Paul451

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I haven't wanted to start a new thread talking about the same thing but base-to-base, but I haven't heard any good reasons why base-to-base docking isn't a much more secure configuration to perform spin-G.

The main argument is that you have to design around 3 gravity regimes: Earth/Mars down-is-down, zero-g there-is-no-down, and tail-to-tail up-is-down. I don't think it's unviable, but it might make things more awkward to design. (Testing isn't that hard, though, compared to designing for zero-g. You just flip the test-rig.Ļ)

By contrast, nose-to-nose has the same orientation as on Earth/Mars. So your ECLSS and other plumbing only needs to work on Earth and in orbit.

Ļ Aside: This is another reason for spin-g testing before you go to Mars. It's likely that systems that work at Earth-g will work in Mars-g, and probably Luna-g, but it would be nice to spot the inevitable exceptions to the rule before a critical system fails on Mars. And then, once you've got spin-g, why not use it.

I mean, the presentation actually *showed* two BFS's docking base to base using secure connections, and low-G acceleration was cited as a way to transfer propellents. You don't need to invent a new attachment point - one already exists

During tail-to-tail refuelling, the attachments are under compression. During tail-to-tail spin, they are under quite significant tension.

Again, not impossible to design around, and I suspect the thrust frame will be more than capable of handling the loads, it's just not "it already exists".

though at Mars G it will be quite possible to jump up or down single floors without hurting yourself.

Maybe... just use the ladder?

you could have each crewed BFS docked base-to-base to a cargo BFS to form a spin-able unit.  You could then have those two units to form a single assembly if they aligned their dorsal surfaces - and docked using dorsal ports that will be used to access the ground. 
[...] then 2x sets dorsal ports dock (crew-to-crew BFSs, cargo-to-cargo BFSs), then start to spin at Mars G.

Clever idea. But that configuration isn't stable in rotation.

Interesting to think how much before EDL you would separate the ships.  4 ships would probably need to be coming in within half an hour of each other if they are to land anywhere near each other, or alternatively you might detach the cargo ships and let them arrive a day earlier.

During a day, Mars moves a bit over 2 million km in its orbit. If the crew/cargo is on the same trajectory for most of the trip, you might not be able to change the trajectory enough to have a day's difference in arrival. For eg, if you separate the ships a week from Mars, it means the crew ships need about an 8į change in their trajectory, around 3-4km/s burn.

Offline CuddlyRocket

Especially as we talk about longer term stays on Mars, the Moon or other bodies, more research is needed into the effects of low gravity. Those experiments should absolutely be done in LEO though.

Whether such experiments should be done in LEO or not, I think that there's little chance that they will be! Missions to the Moon and Mars will be the experiments. They'll rely on volunteers and waivers etc. Nobody wants to spend either the money*, or especially the time, needed to conduct such experiments.

(* Particularly if it's their own money!)

No one will spend their time and money to find out if this is even helpful, but they will spend the time, money, and danger to do it in route, even though it's unclear that it will have any benefits? I am not following your logic.

People (with the money) want to go to the Moon and/or Mars. They don't want to spend time and money conducting low gravity experiments in LEO. They'll just go to the Moon and Mars and see what effect this has. Which is basically what they've always done. No-one has gone to LEO to conduct low gravity experiments. Astronauts have been put in LEO for other reasons and they've seen what effect their being in LEO has.

Online KelvinZero

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I haven't wanted to start a new thread talking about the same thing but base-to-base, but I haven't heard any good reasons why base-to-base docking isn't a much more secure configuration to perform spin-G.
The main argument is that you have to design around 3 gravity regimes: Earth/Mars down-is-down, zero-g there-is-no-down, and tail-to-tail up-is-down. I don't think it's unviable, but it might make things more awkward to design.
This is another reason to just start with my original one-BFS suggestion. All the rocket plumbing end would experience gravity in the same direction as on the pad. Only passenger area would be inverted.

I suspect the weight of the BFS is mainly around the tail, and this imbalance could be increased by filling the tanks. This would increase the radius of the spin of the passenger portion.

This experiment could give some critical answers that determine if you need to go further.

----
Idea 2:
A stretched variant of the BFS that weighs ~150t and has no tanks or engines. This is launched as the 150 payload on top of a BFR+BFS cargo, and it stays in space. It is pushed on it's way by a tanker BFS on a trajectory that skims the origin planet, allowing the tanker to aerobrake into low orbit and be reused within days. The passenger portion aerobrakes into orbit at the destination.

The real goal of the above was that only the passenger portion could not be reused frequently. The advantage for spin gravity is that this thing could be at least twice the length of a normal BFS. By putting as much mass as possible at the tail end, including LS, cargo, consumables and storm shelter, you could get significantly higher radius at the passenger end.

This is a thought for the fairly far future of course. It implies you have BFS tankers being serviced at mars and never returning to earth.

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I mean, the presentation actually *showed* two BFS's docking base to base using secure connections, and low-G acceleration was cited as a way to transfer propellents. You don't need to invent a new attachment point - one already exists

During tail-to-tail refuelling, the attachments are under compression. During tail-to-tail spin, they are under quite significant tension.

Again, not impossible to design around, and I suspect the thrust frame will be more than capable of handling the loads, it's just not "it already exists".

Dry mass of BFS listed as 85 ton, most of which will be very close to the centre of rotation and as light as possible if tail-to-tail, or it will be the furthest from centre of rotation and as heavy as possible if nose-to-nose.  However robust the join has to be for tail-to-tail, it has to be more robust for nose to nose... 

Rough guessing at numbers: If spinning tail-to-tail at Mars G, (two crew BFS) the weight on the join will come from the 150 ton payload in each ship + ~30 ton for the frame of each BFS body that's away from the centre of rotation + ~50 ton from each BFS's lot of landing prop x 0.4g? So what, call it 200 ton in tension...

You've got an attachment joint designed to hold a 1300+ ton ship securely to the booster while being accelerated at 3+ G.  That's a weight of 4000+ tons in compression, whilst dealing with all the aerodynamic stresses of launch, including going through max Q.  I can't believe that attachment joint can't take ~200 ton in tension. 

Quote
I haven't wanted to start a new thread talking about the same thing but base-to-base, but I haven't heard any good reasons why base-to-base docking isn't a much more secure configuration to perform spin-G.

The main argument is that you have to design around 3 gravity regimes: Earth/Mars down-is-down, zero-g there-is-no-down, and tail-to-tail up-is-down. I don't think it's unviable, but it might make things more awkward to design. (Testing isn't that hard, though, compared to designing for zero-g. You just flip the test-rig.Ļ)

By contrast, nose-to-nose has the same orientation as on Earth/Mars. So your ECLSS and other plumbing only needs to work on Earth and in orbit.

Fair point, but designing how everything is oriented is going to be an interesting/complex problem anyway.  It looks like they are designing the BFS crewed area around modular "crew cabin" boxes which are wedge-shaped prisms and can be installed circumferentially around the core.  Problem I see is that the orientations of the cabins will all be different, yet everyone has to be oriented the same way head up for the belly-down portion of EDL. 

Attached: I had a bit of fun with imagining a "swivel door" to each cabin which has the acceleration couches installed and could close to allow for privacy.  That way you could just mass-produce the cabin units and install them in place.

Taking it one step further, the "back wall" of each cabin could have another rotational joint (perpendicular to the swivel door, axis pointing towards the centre of the craft), which could be flipped for use either on the ground or in tail-to-tail spin G.  On it would be a "fluids management unit" which could hold each cabin's water supply (for radiation shielding), plus a sink and toilet/bathing facilities.   Fluids could be pumped for reclamation/filtering, but solids would most likely still have to be disposed of separately.

Offline Aussie_Space_Nut

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What about a 4 ship configuration.

2 Cargo ships docked tail to tail.

Then dock a crewed ship nose to nose with each of the cargo ships.

Then when spun up orientation of liveable areas need only be designed for 1g to 0g.

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