by Chris McMahon
I am probably only scratching the surface here, but I have come across a few things worth summarising.
The first is a pretty old article, but it has a good discussion of the broad array of physical effects of microgravity – specifically on pregnancy.
The biggest problem is radiation – namely cancer and radiation sickness. The radiation will also kill sperm and zygotes, terminating pregnancy at an early stage. But assuming you can fix that with some sort of radiation shielding, here are some of the effects of microgravity:
Osteoporosis: irreversible bone loss, increased calcium excretion, impact on the liver as it tries to process increased calcium and phosphorous excretion.
Fluid & Electrolyte balance: The loss of gravity changes the distribution of pressure. Body fluids redistribute, with around 2 litres adding pressure to the heart and lungs. It also affects hormones, causing a diuretic effect as well as reduction in blood plasma.
Red cell volume decreases, with changes to cell shape. The immune system is also suppressed.
There is a decrease in muscle tone, loss of body mass (although the body lengthens by 5cm due to loss of tone – at last a way to get taller!).
Irreversible changes to the heart.
Other changes to the hormonal system.
It’s interesting to note that the currently proposed Non-Atmospheric space exploration vehicle Nautilus-X, is being designed with a rotating habitable centrifuge ring to simulate partial gravity (here is another link). This is conceived for long duration manned missions to the Moon and Mars, and may even serve as a space-based hospital. The current idea is to have this stationed at Lagrange points L1 or L2 depending on the destination.
The first link above has an interesting table that shows the artificial gravity possible with the 30ft and 40ft diameters at various RPMs. The lowest is 0.08g at 30ft and 4 RPM, the highest 0.69g at 40ft and 10 RPM.
This concept includes some inflatable modules, similar to the Bigelow Aerospace inflatable habitats. Radiation mitigation systems may include tanks of water or liquid hydrogen . Yikes.
Personally, I like the idea of the hollowed out asteroid. Nothing like a few metres of rock to keep the rays out. We need to figure out how to move these medium sized astral bodies around anyway. If we don’t, then what are we going to do if we actually see a large asteroid heading for us? We need to see the thing coming with plenty of time in advance (which means a better observation network) and place a few Nuclear Thermal Rockets on it to shunt it out of the way (which means a lot more space-based capability then we have).
Come across any other good concepts for space vehicles with simulated gravity?
Mad Genius Club 
14 responses to “Microgravity and Space Travel”
Start with a reasonable-sized asteroid parked in a Lagrange point (or in a Earth/Mars cycler orbit). Then carve a circular ring-shaped tunnels in said asteroid. Fit the tunnels with railroad rails. Put Pullman cars on said railroads and set them in motion at whatever speed will provide passengers enough gravity to keep the boys in medical happy. Bring the trains to a stop with each shift change and cycle crews according to schedule from medical.
The trains are likely to impart gyroscopic forces on the asteroid so run them in counter-cyclic pairs. Tweak their relative angular velocities when you need to adjust the asteroid’s attitude.
Why yes, I do feel quite clever. Since there’s nothing new under the sun, I’d be obliged if one of you can tell me who’s already written up something like this.
Have to say, Steve, I\’ve never heard anything like it!
Hi, Steve. I’ve not seen anything that uses railway cars before. Usually its a small thruster of some sort on the exterior surface.
I think getting the spin is not the hard part. I’d imagine mechanical engineers are going to have real fun getting the seals right at the axis – which I would imagine you would still want stationary for thrust and communications (alignment of dishes) etc.
I had this idea for a ‘asteroid ship builder’ essentially a dirty great spaceship, perhaps powered by solar panels that shot a hole right through the centre of the asteroid with a laser. You could have a standard diameter which would take your axis assembly – essentially the heart of the spaceship in terms of thrust etc. Then you could tunnel out from the central core to whatever depth made sense and then make the ring inside the rock.
Nice concept to have these gnarly old prospector types actually inside an asteroid:)
Spinning a habitat on a tether risks catastrophic failure of the tether. But a train of pressurized cars is safer because you’ve got the bulk of the asteroid to keep things contained.
The challenge is digging the tunnel, but we have tunnel boring machines. Leave the asteroid in an un-spinning state with attitude control to simplify docking. Bonus points for a non-stop railway. Train cars can be propelled using linear-induction.
Robots can dig tunnels while the asteroid is in transit from its original orbit. The trains can be used like reaction wheels for attitude control as soon as the first tunnel is complete.
The trains are an interesting idea, but I can’t help but think of all the mechanical linkages and systems required.
A tether should be safe. At least its only one design element – if you get the strain right you should be OK.
I don’t foresee a lot of mechanical linkages–except wheels and suspension, and hitches. Nothing unproven or difficult here.
The systems would all be electrical. You just need armature coils in the floor of each car if you space drive coils periodically along the track to implement a linear induction motor. Linear induction systems are proven technology used in in Cedar Point’s Top Thrill Dragster ride and various maglev train projects.
I’m just not comfortable spinning up a tethered system, spinning it down, or docking with a spinning habitat.
Sorry to be obsessive. But I just did some figuring. The space station in the movie 2001 rotated two times per minute. This wheel in space was roughly 1000 ft in diameter. Unless my arithmetic fails me, that corresponds to 6283.18 ft/min or 104.7196667 ft/sec or 71.39977275 mph. We’ve been running trains at that speed for over a century.
Since centripetal force is mv^2/r, you want to keep r small. Larger r means more tunneling and requires faster train speeds.
I believe this is workable and may use it in a story.
You are just thinking to small. If we build big enough spaceships they will provided their own gravity 😉
But then the people on Earth complain about how you’ve messed with their tides, and the engines just _eat_ fuel. 😉
Hi, I like it! That’s thinking outside the gravity well:)
Some time back in the Pleistocene I read a book that claimed that anything more than IIRC 3RPM is very disorienting. Or it may have been difficult to adjust to, if you keep coming and going. Must track those stone tablets down . . .
Hi, Pam. The same thing was going through my head when I was reading that Nautilus summary. The Aldrin cycler is huge in diameter compared to the Nautilus, with a counterweight at the end of a long cable – probably precisely to avoid this. If you find a link to the effects of RPMs please let me know.
I’m tempted to say George Gamov. And I think my older son, the aerospace engineer may have absconded with it. A quick web search . . .
From Wiki:
“NASA studies with chickens and plants have proven that this is an effective physiological substitute for gravity.[citation needed] Turning one’s head rapidly in such an environment causes a “tilt” to be sensed as one’s inner ears move at different rotational rates. Centrifuge studies show that people get motion-sick in habitats with a rotational radius of less than 100 metres, or with a rotation rate above 3 rotations per minute. However, the same studies and statistical inference indicate that almost all people should be able to live comfortably in habitats with a rotational radius larger than 500 meters and below 1 RPM. Experienced persons were not merely more resistant to motion sickness, but could also use the effect to determine “spinward” and “antispinward” directions in the centrifuges.”
Here’s an interesting one, with references and links.
http://www.permanent.com/zero-gravity-effects-on-humans.html
Another ancient memory, from a Bar discussion. I love that place, so many experts.
My idea was to take nickle-iron asteroids, drill into them and plant explosives. Spread a mylar parabola so as to heat the asteroid. Get it up to where it is _just_ nicely pliable, then fire the bombs. Blow the whole thing up like a balloon, or series there-of.
The expert Bar denizen, whose name I do not recall, pointed out the uncomfortable fact that the Ni-Fe combo found in most asteroids of that type was quite brittle, and the temperature range that would qualify as “malleable” very, very small. It would _not_ be as easy as I had envisioned. But I still liked the idea of forming the asteroid, rather than removing so much mass.
Using the whole thing had the added advantage that you could start with a smaller asteroid, which would be more common, rather than targeting the few very large asteroids and removing mass to gain living space. Not that anything is stopping the intrepid Space Builder from moving the material from the inside and adding it to the outside.