Kidneys dying in space.

[GuessingEveryDay]

https://www.nature.com/articles/s41467-024-49212-1

TL;DR: Scientists observing many problems with astronauts kidneys after returning from space, and blasting mice with radiation.

Well, this is an interesting twist, kidneys are a lot more sensitive to radiation and break down differently. This means the radiation shielding will need  to be different to help the kidneys last longer. However, the damage appears to be permanent.

[darthgently]

Given the complexity of physiology I've figured that the simplest approach is to have centrifugal pseudo-gravity from day one on a long trip.  It also really annoys me that no serious attempt has been made to incorporate at least a smallish human centrifuge on the ISS where astronauts could spend a few hours a day at least as we've known about the bone loss for some time.  Cosmic rays are an entirely different issue though.   Would lead girdles help?  Only half kidding

[Kerwood Floyd]

I seem to remember reading somewhere that the vibrations from a centrifuge on ISS would mess up all of the experiments that are relying on the micro-gravity environment. Apparently you can have one or the other.

[darthgently]

1 hour ago, Kerwood Floyd said:

I seem to remember reading somewhere that the vibrations from a centrifuge on ISS would mess up all of the experiments that are relying on the micro-gravity environment. Apparently you can have one or the other.

That clarifies a lot, thanks.  Even if the entire set up rotated (non-ISS obviously) microgravity would be restricted to the hub and how that hub area was isolated from any rotational eccentricities would still be a problem.  Maybe extended microgravity will end up being the realm of Teslabots and genetically modified humans with normals making briefer visits.  A rotational hab without the strict microgravity constraints holding station with the microgravity lab/factory ahead or behind in same orbit a safe distance away maybe.

[boriz]

Simulated gravity on a SpaceX trip to mars: Send two starships. Once on a mars trajectory, have them line up nose to nose with a 100m cable linking them together, then give them each a gentle opposite sideways motion, causing them to both swing around the center of the cable, giving the crew say, 0.5G for the majority of the trip.

If there are any psychological crew issues, a crew exchange could be performed. Or perhaps one could carry crew, the other supplies/waste, and maybe once a month a 'mass exchange' is performed.

Either way, the crew will arrive in good condition and fully acclimatised to the lower G on mars.

[jake_taylor]

That's a fascinating and concerning finding.

[Minmus Taster]

Is it possible we could shield astronauts during, for example, a mars transit in Starship by keeping crew quarters away and shielded from the sun? Could we also set up a centrifuge system inside the payload area of the ship in exchange for fewer crew?

[AckSed]

In short, yes, and yes. It'd take a lot of mass and expense, so the question becomes "would we?"

Opinion: only if reusable/semi-reusable cheap heavy lift becomes a thing. That gets you space stations on the cheap, more and cheaper research opportunities, the beginnings of spin-gravity stations, experiments with lightweight shielding, surrounding the astronauts with a wall of water, and so on.

[Exoscientist]

This added onto the known dangers of zero-gravity and cosmic ray damage after long deep space exposure is why I favor fast flights to Mars:

http://exoscientist.blogspot.com/2015/08/propellant-depots-for-interplanetary.html

With propellant depots in place we can do flights to Mars in about a month with just standard chemical propulsion. No ion drive, or nuclear propulsion, or advanced propulsion methods required. It can even be done with a Falcon 9 first stage at approx. 400 ton propellant load.

It can also be done with the Starship, and SpaceX wants propellant depots anyway. BUT to get the fast trip, SpaceX would have to go back to the ca. 40 tons dry mass of the expendable Starship:

Bob Clark

 

  

[darthgently]

1 hour ago, Exoscientist said:

This added onto the known dangers of zero-gravity and cosmic ray damage after long deep space exposure is why I favor fast flights to Mars:

http://exoscientist.blogspot.com/2015/08/propellant-depots-for-interplanetary.html

With propellant depots in place we can do flights to Mars in about a month with just standard chemical propulsion. No ion drive, or nuclear propulsion, or advanced propulsion methods required. It can even be done with a Falcon 9 first stage at approx. 400 ton propellant load.

It can also be done with the Starship, and SpaceX wants propellant depots anyway. BUT to get the fast trip, SpaceX would have to go back to the ca. 40 tons dry mass of the expendable Starship:

Bob Clark

 

  

The problem with depots is long term storage of cryogenics.  I wondered aloud in a post here awhile ago if water and a carbon source could be kept in depots instead and converted into fuel on demand with a big solar array or fission 

Edited June 17 by darthgently

[K^2]

6 hours ago, Minmus Taster said:

Is it possible we could shield astronauts during, for example, a mars transit in Starship by keeping crew quarters away and shielded from the sun? Could we also set up a centrifuge system inside the payload area of the ship in exchange for fewer crew?

It's rough. For the most part, shielding's about either diverting or stopping the particles. The latter scales roughly with how much matter you can put in the way. Earth's atmosphere is density-equivalent to 10m deep pool of water and blocks about as much radiation, and that's after the Earth's magnetic field has a go. Carrying 10 tons of shielding for every square meter you want protected is... well, not entirely unfeasible, but it's problematic.

We're going to need more research on what's the threshold going to be. We clearly can't get everything, but neither does Earth's protection. Somewhere between ISS and Earth there's a "safe enough" threshold. And we might be able to help by blocking more of the radiation that's easy to block. Hard UV, for example, is blocked by a sheet of foil better than by all of Earth's atmosphere. On the other hand, UV isn't the thing that was going to damage someone's kidneys. Next on the list are going to be charged particles. Earth's magnetic field is kind of wimpy. It acts in volume. We have superconductors. Flying with a tiny Jupiter on your ship will create all sorts of engineering challenges, but it should be safe to the crew.

The protons and other nuclei that are both abundant in the solar wind and dangerous to the crew are going to be in the 1MeV/amu range. Taking worst case scenario on charge (e.g. alpha particles) of 0.5q/amu, this gives cyclotron radius of about 30cm at 1 Tesla. So magnetic shielding isn't out of the question on basic principles, but that still leaves engineering the system, flying tests, etc. Worst part is that it's a system that's hard to both build and test at small scale, and it needs to be flown beyond Earth's bow shock before we can be properly sure that it's not going to collapse on an interplanetary voyage. Normally, I'd say we're two decades if we start working now. The growing evidence that we need it for a flight to Mars might cause people to hurry it up, but we have to start gearing up for tests now.

Finally, if we're trying to combine shielding with centrifuge, the complexity skyrockets. (And it was bad already.) Here we have a modicum of good news. Recent research strongly suggests that while untrained individuals do poorly in AG environments above 2rpm, almost anybody can be acclimated to up to 20rpm. This brings the centrifuge radius requirement from 250m radius (half a kilometer in diameter!) which is viable only in a tethered configuration, which sucks for both magnetic and bulk shielding options, down to merely 2.5m, which means an entire centrifuge could fit inside a Skylab workshop. (And in fact, it sort of has...)

Spoiler

Timestamped to the relevant section.

 

This is, as far as I'm aware, the only real test of humans acting in artificial gravity on an orbital station. Obviously, the applicability of said test is very limited for a long list of reasons. And yet, let nobody say it's never been done!

Or, I guess, more relevant to the future missions, Starship's 9m hull can easily fit a small centrifuge inside its cargo compartment. Given all the other equipment that has to be brought, space is going to be at a premium, but if, say, a 3m section of it can be dedicated to the living quarters, with floor diameter probably ending up closer to 4m from center, you can have sleeping cots at floor level, where you'd probably have full 1g, and standing up, your head would be down to about 0.5g. That might not be enough to fully remove negative effects of low g on your eyes, but it's not catastrophic even at 0g for a year, so hopefully good enough? And you can have slightly better conditions sitting down to do any computer work. This would bring centrifuge speed to 15rpm, or a quarter of a revolution per second. Not terribly fast, slow enough to go to the center transfer ring by ladder, and for the crew to use hand grabs to cancel/start their rotation. The transfer tubes to enter the nose or aft storage would have to be pretty narrow to reduce air drag, but they can still easily be similar in size to ISS connectors, making them easy enough to navigate and bring equipment through. The nose section can have the jump-seats for the takeoff and landing portions of the flight, research equipment for use in flight, as well any lighter cargo.

With this sort of the configuration, you can have the engines, a significant amount of fuel on the outbound leg, and most of your heavier cargo/equipment serving as part of the bulk shielding from the solar radiation. Slightly thicker foil on outer wall, and floor of the centrifuge would have to be enough for most of the rest. Toroidal magnetic shield a few meters outside the centrifuge would help reduce effects from radiation coming from the sides reducing the work the ship's walls and centrifuge wall have to do. This won't be enough to bring the background to Earth levels, but it'd be way better than what the ISS is averaging. Hopefully, that's enough, but a lot of test and engineering needs to go into it.

Obviously, a mission like what I'm describing is not even close to what Elon's pitching. It will require a better built Spaceship with a lot of very expensive interior and exterior hardware, as well as several pieces of equipment that have to be engineered and proven to work. But also, I haven't been very optimistic about the promises for cheap flights to Mars both on general principles and based on previous promises from the same people. Nonetheless, I do suspect that Starship and Super Heavy will have to converge on something functional due to being critical to Artemis in its current plan, so the ship and the rocket will likely be available, with the rest to be filled in at the later time. If some of the relevant research is fast-tracked, 2040's is still a realistic goal. Whether any of this actually materializes remains to be seen.

[darthgently]

3 hours ago, K^2 said:

It's rough. For the most part, shielding's about either diverting or stopping the particles. The latter scales roughly with how much matter you can put in the way. Earth's atmosphere is density-equivalent to 10m deep pool of water and blocks about as much radiation, and that's after the Earth's magnetic field has a go. Carrying 10 tons of shielding for every square meter you want protected is... well, not entirely unfeasible, but it's problematic.

We're going to need more research on what's the threshold going to be. We clearly can't get everything, but neither does Earth's protection. Somewhere between ISS and Earth there's a "safe enough" threshold. And we might be able to help by blocking more of the radiation that's easy to block. Hard UV, for example, is blocked by a sheet of foil better than by all of Earth's atmosphere. On the other hand, UV isn't the thing that was going to damage someone's kidneys. Next on the list are going to be charged particles. Earth's magnetic field is kind of wimpy. It acts in volume. We have superconductors. Flying with a tiny Jupiter on your ship will create all sorts of engineering challenges, but it should be safe to the crew.

The protons and other nuclei that are both abundant in the solar wind and dangerous to the crew are going to be in the 1MeV/amu range. Taking worst case scenario on charge (e.g. alpha particles) of 0.5q/amu, this gives cyclotron radius of about 30cm at 1 Tesla. So magnetic shielding isn't out of the question on basic principles, but that still leaves engineering the system, flying tests, etc. Worst part is that it's a system that's hard to both build and test at small scale, and it needs to be flown beyond Earth's bow shock before we can be properly sure that it's not going to collapse on an interplanetary voyage. Normally, I'd say we're two decades if we start working now. The growing evidence that we need it for a flight to Mars might cause people to hurry it up, but we have to start gearing up for tests now.

Finally, if we're trying to combine shielding with centrifuge, the complexity skyrockets. (And it was bad already.) Here we have a modicum of good news. Recent research strongly suggests that while untrained individuals do poorly in AG environments above 2rpm, almost anybody can be acclimated to up to 20rpm. This brings the centrifuge radius requirement from 250m radius (half a kilometer in diameter!) which is viable only in a tethered configuration, which sucks for both magnetic and bulk shielding options, down to merely 2.5m, which means an entire centrifuge could fit inside a Skylab workshop. (And in fact, it sort of has...)

  Reveal hidden contents

Timestamped to the relevant section.

 

This is, as far as I'm aware, the only real test of humans acting in artificial gravity on an orbital station. Obviously, the applicability of said test is very limited for a long list of reasons. And yet, let nobody say it's never been done!

Or, I guess, more relevant to the future missions, Starship's 9m hull can easily fit a small centrifuge inside its cargo compartment. Given all the other equipment that has to be brought, space is going to be at a premium, but if, say, a 3m section of it can be dedicated to the living quarters, with floor diameter probably ending up closer to 4m from center, you can have sleeping cots at floor level, where you'd probably have full 1g, and standing up, your head would be down to about 0.5g. That might not be enough to fully remove negative effects of low g on your eyes, but it's not catastrophic even at 0g for a year, so hopefully good enough? And you can have slightly better conditions sitting down to do any computer work. This would bring centrifuge speed to 15rpm, or a quarter of a revolution per second. Not terribly fast, slow enough to go to the center transfer ring by ladder, and for the crew to use hand grabs to cancel/start their rotation. The transfer tubes to enter the nose or aft storage would have to be pretty narrow to reduce air drag, but they can still easily be similar in size to ISS connectors, making them easy enough to navigate and bring equipment through. The nose section can have the jump-seats for the takeoff and landing portions of the flight, research equipment for use in flight, as well any lighter cargo.

With this sort of the configuration, you can have the engines, a significant amount of fuel on the outbound leg, and most of your heavier cargo/equipment serving as part of the bulk shielding from the solar radiation. Slightly thicker foil on outer wall, and floor of the centrifuge would have to be enough for most of the rest. Toroidal magnetic shield a few meters outside the centrifuge would help reduce effects from radiation coming from the sides reducing the work the ship's walls and centrifuge wall have to do. This won't be enough to bring the background to Earth levels, but it'd be way better than what the ISS is averaging. Hopefully, that's enough, but a lot of test and engineering needs to go into it.

Obviously, a mission like what I'm describing is not even close to what Elon's pitching. It will require a better built Spaceship with a lot of very expensive interior and exterior hardware, as well as several pieces of equipment that have to be engineered and proven to work. But also, I haven't been very optimistic about the promises for cheap flights to Mars both on general principles and based on previous promises from the same people. Nonetheless, I do suspect that Starship and Super Heavy will have to converge on something functional due to being critical to Artemis in its current plan, so the ship and the rocket will likely be available, with the rest to be filled in at the later time. If some of the relevant research is fast-tracked, 2040's is still a realistic goal. Whether any of this actually materializes remains to be seen.

If the 9m diameter SS becomes the new normal, then the rumored 12m and 18m diameter SS Super heavy designs could become the the next designs under test.  This would reportedly be 300t and 1000t payloads respectively and with those diameters a centrifuge along the lines you describe become even more viable and less physiologically sketchy.  Thanks for the deeper dive into the ballpark specifics

Also, consider that spinning the entire craft along its main axis is not out of the question and would provide less complexity.  Or even a combo where the entire craft spinning provides a lunar to Mars gravity with the internal centrifuge adding just enough to get earth level gravity might be something to consider.

[darthgently]

Spinning the entire craft longitudinally could cause wingnut / tennis racket issues though.  Also all that liquid in the fuel tanks could be another problem

 

[AckSed]

This is a chance to mention a recent favourite finding in space medicine involving a bungee cord to simulate Lunar-gravity, and a 10m-wide, 5m-tall Wall of Death, to make a circular vertical track that would allow the runner to experience Earth-normal G-forces when running: https://royalsocietypublishing.org/doi/10.1098/rsos.231906

Essentially, the high dynamic loading of the footstrike when a Lunar wall-runner makes contact reconditions the muscles and bones. They compare volunteers who, when confined to bed for 60 days, underwent 48 sessions of jump training over that time and managed to avoid most of the negative consequences.

The preliminary conclusion is that 8-9 laps of the track per day, split into two sessions, should be enough.

I like the sound of this for two reasons. One, all it needs is a large circular hab, which you could fill with an exercise bike in the centre, or things of that nature. No rotating components, no power needed.

Two, this also suggests that in lunar gravity, you could run up and around the inside of a loop-de-loop. This will definitely be part of my Lunar recreation centre, alongside the Lunar pool and the human-powered flying dome.

[darthgently]

7 minutes ago, AckSed said:

This is a chance to mention a recent favourite finding in space medicine involving a bungee cord to simulate Lunar-gravity, and a 10m-wide, 5m-tall Wall of Death, to make a circular vertical track that would allow the runner to experience Earth-normal G-forces when running: https://royalsocietypublishing.org/doi/10.1098/rsos.231906

Essentially, the high dynamic loading of the footstrike when a Lunar wall-runner makes contact reconditions the muscles and bones. They compare volunteers who, when confined to bed for 60 days, underwent 48 sessions of jump training over that time and managed to avoid most of the negative consequences.

The preliminary conclusion is that 8-9 laps of the track per day, split into two sessions, should be enough.

I like the sound of this for two reasons. One, all it needs is a large circular hab, which you could fill with an exercise bike in the centre, or things of that nature. No rotating components, no power needed.

Two, this also suggests that in lunar gravity, you could run up and around the inside of a loop-de-loop. This will definitely be part of my Lunar recreation centre, alongside the Lunar pool and the human-powered flying dome.

This kind of health enhancing running seems doable on the inner radial surface of something like SS.  But it would impart spin to the ship over time.  Would have to alternate chirality of running direction to cancel over time.  Unless spinning up the ship is desired I suppose

[AckSed]

1 minute ago, darthgently said:

This kind of health enhancing running seems doable on the inner radial surface of something like SS.  But it would impart spin to the ship over time.  Would have to alternate chirality of running direction to cancel over time.  Unless spinning up the ship is desired I suppose.

Always bring your anti-spin running buddy.

[darthgently]

1 minute ago, AckSed said:

Always bring your anti-spin running buddy.

I thought about that, but then you have the problem of creating a wobble as the points where you pass each other, with your combined mass, alternate from one side of the craft to the other. 

A new science emergences: crew athletic craft attitude control theory

[K^2]

3 hours ago, darthgently said:

Spinning the entire craft longitudinally could cause wingnut / tennis racket issues though.

The tumbling is due to intermediate axis. Longitudinal axis is usually the minor axis, which can be stabilized. It is, actually, stable for a perfectly rigid body, but anything with fluids, moving cargo, or people inside would result in destabilization, requiring active correction. It's not hard, though.

That said, there is no reason to spin the entire craft. That would cause all sorts of additional complications. A "cage" for crew quarters would be relatively easy to integrate, which is what I was basing my analysis on. There would be a bit of an air drag, but you just need a tiny amount of motor torque to compensate.

[darthgently]

3 hours ago, K^2 said:

The tumbling is due to intermediate axis. Longitudinal axis is usually the minor axis, which can be stabilized

Not if moving internal fluids are involved.

[K^2]

31 minutes ago, darthgently said:

Not if moving internal fluids are involved.

Yes, if fluids are involved. You just need active compensation to keep the axis alogned.

[darthgently]

59 minutes ago, K^2 said:

Yes, if fluids are involved. You just need active compensation to keep the axis alogned.

Not disagreeing,  I just consider "active compensation" at cross purposes to spin stabilization.  And for a manned craft the size of Starship a requirement for active compensation seems to leave the door open for some energetic failure modes.  I'm thinking that rather than active  compensation maybe something static, like baffles in the tanks or some other way to prevent movement above whatever threshold.  Maybe more like a race car fuel cell than a fuel tank.  Idk. 

I like the internal centrifuge idea. On a 12m or 18m version it would be really something

[Exoscientist]

 The most comprehensive review  of the health effects of long term life in deep space is in the two book series by Dennis Chamberland, a former NASA life sciences engineer:

Departing Earth Forever: Book One - Warning and Promise: The Manual for Today's Colonists Preparing to Launch to Mars and our Moon.
https://www.amazon.com/Departing-Earth-Forever-Colonists-Preparing-ebook/dp/B0B5NH4Z61/

And:

Departing Earth Forever: Book Two - Alien Worlds: The Manual for Today's Colonists Preparing to Launch to Mars and Our Moon.
https://www.amazon.com/Departing-Earth-Forever-Colonists-Preparing-ebook/dp/B0B72HX8MX/

 Though he was formerly with NASA Chamberland has a dim view view of NASA’s approach to safety for such long space flights in deep space.

 

    Bob Clark

[K^2]

5 hours ago, darthgently said:

Not disagreeing,  I just consider "active compensation" at cross purposes to spin stabilization.  And for a manned craft the size of Starship a requirement for active compensation seems to leave the door open for some energetic failure modes.

I'm not saying it's a good strategy. Just that it's technically available. The failure mode's not so bad, though. Unlike a rigid body spinning near its intermediate axis, you're not going to have it flipping back and forward violently. Fluid would facilitate the migration of axis from longitudinal to transverse over a number of revolutions*, with the moment inertia now being along the major axis, drastically reducing angular velocity due to momentum conservation. You'd go from 15RPM and 1G to a few RPM and around ~0.1G. It's unlikely to cause serious injury if all large cargo is secured, and it'd be easy enough to reach some sort of controls to kill the rotation all together.

A centrifuge internal to the cargo bay is still the best option for the starship, though. There's just absolutely no reason to spin the whole thing.

 

* Edit: Solving equations of motion for both completely rigid and "fluid core" bodies is kind of interesting and illuminating. If you can handle very simple differential equations and some tensor algebra, I encourage you to run through them. The relevant equations of motion are Euler's Equations. (Yes, same name as the fluid dynamics ones, but the rigid body ones aren't nearly as scary. Euler sure has a lot of things named after him.)

Edited June 18 by K^2

[kerbiloid]

On 6/17/2024 at 12:07 AM, GuessingEveryDay said:

This means the radiation shielding will need  to be different to help the kidneys last longer.

They wear it for reasons.

Spoiler

 

 

On 6/17/2024 at 2:06 AM, darthgently said:

It also really annoys me that no serious attempt has been made to incorporate at least a smallish human centrifuge on the ISS

Nauka has tried once.

They started crying: "Stop doing! Stop doing!"

 

On 6/17/2024 at 9:08 AM, boriz said:

Once on a mars trajectory, have them line up nose to nose with a 100m cable linking them together, then give them each a gentle opposite sideways motion, causing them to both swing around the center of the cable

And get a slap from the whip wave.
Even more funny then to stop it. There is an angular momentum except just momentum.

***

A 2 m wide pipe circled around the ship, with water flow making them float around the ship.

[darthgently]

1 hour ago, kerbiloid said:

 

On 6/16/2024 at 7:06 PM, darthgently said:

It also really annoys me that no serious attempt has been made to incorporate at least a smallish human centrifuge on the ISS

Nauka has tried once.

They started crying: "Stop doing! Stop doing!"

The cable idea comes up now and then.  The failure of the cable presents some seriously interesting modifications to the trajectory of both craft.  Not to mention the sudden onset of freefall for the crew