How Can Human Bodies Do Reaction Control Movement In Space Without RCS?

[Spacescifi]

Like if an astronaut is floating in a suit in outer space, he can spin on his own, flip on his own, etc without relying on his RCS from his suit.

I guess we have biological reaction wheels or an equivalent.

Maybe we can imitate whatever humans use and adapt it to spacecraft one day.

[Nuke]

i think of it more as swimming in air. astronauts seem to have some techniques for controlling their orientation in the station.  in vacuum you need thrusters or gyros like any other spacecraft. however i think they make do with whatever handholds and footholds exist on the outside since nobody really uses an mmu anymore.

[AckSed]

Well yes, but also no.

The force of an arm or leg moving in free space is insignificant compared to the power and precision of a gyroscope/reaction wheel.

Granted, our primate ancestry makes us OK at brachiating from one handhold to the next in microgravity, or using footholds to anchor a weightless body.

The real trick would be adding a cybernetic prehensile tail, for three points of contact and leaving hands free.

A brachiating service robot is an appealing idea.

Edited November 24 by AckSed

[Nuke]

i think a big problem with magboots is that the materials they stick to tend to be heavy and not suitable for spacecraft construction. magnets can stick to aluminum if they are spinning though, but that requires a more complicated and power hungry boot.

[Vanamonde]

[Nevermind. I have been persuaded that I was wrong.]

Edited 16 hours ago by Vanamonde

[darthgently]

2 hours ago, AckSed said:

Well yes, but also no.

The force of an arm or leg moving in free space is insignificant compared to the power and precision of a gyroscope/reaction wheel.

Granted, our primate ancestry makes us OK at brachiating from one handhold to the next in microgravity, or using footholds to anchor a weightless body.

The real trick would be adding a cybernetic prehensile tail, for three points of contact and leaving hands free.

A brachiating service robot is an appealing idea.

Or go for 4 points of contact and add a cyber prehensile elephant-inspired trunk to the front of the helmet along with the cybertail.  Wot.

[Lisias]

2 hours ago, Vanamonde said:

Humans can't rotate in space without expelling or touching something. Those are Newton's laws. 

Perhaps not.

Take 4 weights (didn't even tried to calculate how much mass you need on each), tie them in your wrists and ankles. Then:

• Close your legs and spread your arms. Twist your body below the waist to the right;
• Spread your legs and close your arms. Now twist your body above the waist to the right;
• Rinse, repeat.

I doubt the physical efforts will worth the stunt (not to mention managing to rotate only on the desired axis), but just for the sake of the bragging rights, yes, you can rotate in space without expelling or touching something without Newton deciding it's time to update his résumé.

Someone knows someone that can talk to someone on ISS? This may be something fun to try if they have enough space somewhere there.

Additionally, since space is curved, if you are orbiting something you can tie some weight on a long rope and tie it your feet and then throw the weight away slowly so the rope elasticity don't bring it back when the rope stretchs. The Gravity Gradient will, eventually, put you in a radial out or radial in position and you will stay there, slowly rotating to keep your attitude.

You can even "swim" on a curved space.

https://www.science20.com/hammock_physicist/swimming_through_empty_space

[Mr. Kerbin]

I mean, if you have a spacesuit, you have to move your body to move the suit, therefore touching it. Also, there is air.

Even then, your body parts move around inside you and “touch” each other.  Your bones, muscles, etc.

[AckSed]

33 minutes ago, Lisias said:

Someone knows someone that can talk to someone on ISS? This may be something fun to try if they have enough space somewhere there.

Don Pettit is 1) known for performing interesting little science experiments every single time he's gone to space 2) on the ISS right now (as the oldest current NASA astronaut!) 3) is on reddit and X (https://x.com/astro_Pettit). He'd definitely be up for it.

 

[kerbiloid]

It's enough to sit and rotate a finger. The spaceship will be rotating in the opposite direction.

[farmerben]

A human would have a hard time turning around.  A cat can do it.  Basically touch your toes with your fingers then roll around to a full backbend.  Dunno a human that can do it, almost though.

[Pthigrivi]

On 11/24/2024 at 8:19 PM, Lisias said:

Perhaps not.

Take 4 weights (didn't even tried to calculate how much mass you need on each), tie them in your wrists and ankles. Then:

This gives me an idea though... couldn't you take a dumbell in one hand, pass it to your other hand behind your back, swing it around and pass it to yourself in front and so on passing the weight in a circle around your torso? Wouldn't your body rotate opposite?

… and if so, could you tuck your knees with dumbells in both hands and just windmill your arms for pitch-control?

Edited November 26 by Pthigrivi

[kerbiloid]

Even more, you can even fly to the stars without rockets, just by having two masses (say, the dumbells) and sequentionally bringing them together and extending them sideways.

That was the idea of a gravitational engine from the Tekhika-Molodyozhi / Tech For Youth  magazine from 1970s.

You are a material point at some R distance from the reference body (say, Earth).
You have two weights masses of M mass. (For simplicity, you don't have a mass yourself).

When the masses are put together, the gravity force = 2 * PlanetMass * M / R².

When the masses are extended sideways by B distance from you (i.e. their CoM position stays same, but each mass is now at B distance, perpendicularly to the radius vector), the gravitational forces changes, as each mass position relative to the planet center is changed, and is equal to sqrt(R² + B²).

So, in the extended position the gravity force = 2 * PlanetMass * M / (R² + B²).

As the total mass of the ship stays same = 2 M, so the radial gravity acceleration is:
retracted = 2 * PlanetMass * M / (2 * M * R²) = PlanetMass / R².
extended = 2 * PlanetMass * M / (2 * M * (R² + B²)) = PlanetMass / (R² + B²).

So, by extending/retracting the masses perpendicularly to the reference radius by any engine (electric, Stirling, muscle, or any other) sinchronously to the passing the apocenter and pericenter, you can make your orbit evolve from round to highly-eccentric, and then hyperbolic.

Of course, there are no hyperbolic orbits in the Universe, only elliptic ones, as any hyperbola means just changing of the reference body of your current elliptic orbit. Moon - Earth - Sun - Galaxy - something-bigger-than-galaxy - ad infinitum.

This lets you move either around the Earth, or between the galaxies, depending on your patience and amount of fuel for the engine (food for your arms if you are using the dumbells), as the resulting acceleration is of course very low, unless you are orbiting a neutron star or a black hole.

On the other hand, if you have a quantum teleporting device to produce a quantum oscillation of two masses, maybe you can use some quantum effects to save the energy.

[RedAl1en1]

maybe the vestibular system?

[Codraroll]

On 11/24/2024 at 9:35 PM, Spacescifi said:

Like if an astronaut is floating in a suit in outer space, he can spin on his own, flip on his own, etc without relying on his RCS from his suit.

No, he cannot. That premise is flawed from the start. With the amount of scientific discussions you've had over the years, it honestly surprises me to see such a basic misunderstanding of very elementary physics.

But if you want to have astronauts maneuvering without RCS in a zero-G environment, create a massive magnetic field in that limited area you're working in, then do shenanigans with electromagnets. If will probably be a lot more hassle than spraying compressed gas around, though, and have side effects out the wazoo and back. Like requiring a silly amount of power to maintain the field, and having it casually frying any nearby electronics.

Maybe it's cheaper just to feed the astronauts a lot of pea soup.

[Superfluous J]

On 11/24/2024 at 3:35 PM, Spacescifi said:

Like if an astronaut is floating in a suit in outer space, he can spin on his own, flip on his own, etc without relying on his RCS from his suit.

2 hours ago, Codraroll said:

No, he cannot. That premise is flawed from the start. With the amount of scientific discussions you've had over the years, it honestly surprises me to see such a basic misunderstanding of very elementary physics.

It's not a misunderstanding of physics. It's a misunderstanding between two people communicating.

No, you cannot add angular momentum to yourself if you're floating in space.

Yes, you can (if you're basically sitting still) change your orientation to any way you want. It's not easy (especially in a bulky space suit) but it is absolutely possible.

[Pthigrivi]

44 minutes ago, Superfluous J said:

Yes, you can (if you're basically sitting still) change your orientation to any way you want. It's not easy (especially in a bulky space suit) but it is absolutely possible.

Exactly. Thats the premise of a reaction wheel. A person sitting in an office chair can rotate themselves about by rotating their waist slow then fast but I think this is only because they’re abusing the coefficients of static and kinetic friction where the shaft meets the sleeve at the base of the chair. In space everything would cancel out. You need to rotate a mass fully around your center of gravity to rotate. Im confident passing a dumbbell around your waist is mechanically similar to an electric reaction wheel. The total rotation on the system remains static but the mass fraction that is your body can be manipulated by rotating the dumbbell opposite. Im less certain about doing somersaults by windmilling your arms. Do the forces on your shoulder joint cancel out? Or does the rotation of the mass fraction of your arms create an opposite rotation in the rest of your body?

Edited November 27 by Pthigrivi

[kerbiloid]

When you are rotating a finger, your whole body is rotating in the opposite direction, together with the attached spacecraft.

It's basics from the school 6th grade.

[Superfluous J]

I think the best way to think about it is to think about moving your arms up and down, as if you're just doing the arm movements of jumping jacks. If you did that in space, it wouldn't rotate you at all it'd just move your body up and down to keep your center of mass the same. We'll call this "jumping jack style"

Then imagine having your arms at your waist, and rotating them forward in front of you so they went from pointing down to pointing up, like you were signaling a touchdown in American Football. This would rotate your body to compensate, and also move it down to conserve center of mass. Well call this "football style"

Now imagine doing half of each of those things. Start with your arms at your sides, raise them in front of you "football style" until they're above your head, and lower them "jumping jack" style back to your sides. This would slowly rotate your body in space without ever moving you laterally or introducing spin.

Doing similar things could orient you any way you wanted.

Edited November 27 by Superfluous J

[AckSed]

We're approaching "reverse sprinkler" in the intersection of intuitive/counterintuitive.

[kerbiloid]

No need in intuition when you have a physics schoolbook.

Btw, the gyroscopic stabilization works exactly this way. You are rotating a small mass fastly to counterrotate the big mass slowly.

[AckSed]

We need to define the experimental setup.

We have:

One (1) human in a spacesuit;
Floating in microgravity (Lagrange point for preference);
At rest with zero movement;
In full vacuum.

We assume:

Absent any external force, with no air to push against, the astronaut can, by moving their arms, torso and/or legs in some combination, impart a rotational movement and thus change their orientation.

The question we're asking is: is this true?

[AckSed]

To further pin it down, we're assuming that this works by shifting their centre of mass, and rotation can be cancelled out by moving back again in exactly the same way.

[Kerwood Floyd]

8 hours ago, Superfluous J said:

This would slowly rotate your body in space without ever moving you laterally or introducing spin.

Can you explain to me the difference between rotation and spin?

[AckSed]

In this context rotation is moving along about an axis with a start point and desired end point, while spin is uncontrolled, continuous rotation.

Edited November 27 by AckSed
Correction