Microgravity effect within spacecraft

[Sword7]

Hello folks,

I researched for zero gravity through Internet and learned something about microgravity effect within spacecraft. Interesting statement explained that objects will slowly "fall" toward denest part of spacecraft like wall, etc. When it hit, it will have own weight itself. It called microgravity.

For IIS or space shuttle, when you put a paper on the denest part like solid metal, it acts like weak magnet or so. Right? If so, does anyone have any information about experiments that astronauts tried and discovered?

Thanks!
Tim

 

[Eagle]

In the space shuttle things fall towards the air conditioner.

 

[Andy44]

I believe that gravity gradient would be stonger by far than the attraction from spacecraft body parts.

Ignoring the air conditioner's effects (which are strong enough to make all of this academic), an object not floating at the spacecraft's center of mass is technically in a slightly different orbit than the vehicle it is riding inside, so it will follow a differnet path until it bumps into one of the bulkheads or some other object in the cabin.

But Eagle is right, of course, the ventilation system creates an air current which outweighs the effects of gravity gradient and causes things to drift toward air intake vents. You'd have to have a pretty long and cavernous vehicle to feel gravitational effects.

 

[tblaxland]

I agree with Andy44. The gravity gradient effect would be stronger than any effect related to the spacecraft's mass. Another important effect is atmospheric drag - this would tend to make free objects inside the spacecraft drift towards the front. Obviously, the higher the orbit, the less both of these effects matter.

In addition to the above, another important effect for any equipment that is attached to the structure is the microgravity environment due to vibrations in the structure itself. These vibrations can come from a multitude of sources: compressors in the aforementioned air conditioners, other pumps, thermal expansion/contraction, rotating solar arrays, astronaut movements & exercise, attitude control, experiments and so on. There is some good info on the STS microgravity environment in this document:
http://gltrs.grc.nasa.gov/reports/1996/TM-107032.pdf

 

[Sword7]

Ok, Thanks for additional info about other effects than microgravity effect like atomsphere drag, etc. For more information about microgravity that I explained earlier, check en.wikipedia.org/wiki/Weightlessness.

Andy44 mentioned that "You'd have to have a pretty long and cavernous vehicle to feel gravitational effects." Oh, that remind me something about the giant spacecraft (the ball) in Star Wars. That might have possible gravitational effects. Did anyone try that in orbit simulator or so?

Thanks again,
Tim

 

[tblaxland]

Andy44 mentioned that "You'd have to have a pretty long and cavernous vehicle to feel gravitational effects." Oh, that remind me something about the giant spacecraft (the ball) in Star Wars. That might have possible gravitational effects. Did anyone try that in orbit simulator or so?

There is a [ame="http://www.orbithangar.com/searchid.php?ID=3743"]Death Star addon[/ame] but Orbiter doesn't simulate the gravitational effects of other vessels in its state propagation, so AFAIK nobody has tried it. Such an effect could be coded into a specific vessel like the Death Star. The thing is that space vessels, even the Death Star, are pretty low density so their Hill sphere tends to be much smaller than the vessel size. Read about Hill spheres.

 

[Andy44]

The Death Star was supposed to be the size of a small moon, and it's mostly hollow, don't forget, whereas a real moon/planet/asteroid is made of solid rock.

Of course, the Death Star was pure handwavium, having artificial gravity and many decks which appeared to be parallel to the equatorial plane while others were aligned with local horizontal, so who knows how any of that is supposed to work in LucasWorld.

 

[Sword7]

Hill sphere

Hello folks,

Ok, thanks for some replies. I read some info about hill sphere. I have another question for you about that. When space shuttle is going away from the planet earth, hill sphere is becoming bigger. Right?

I noticed another interesting something that you mentioned about hill sphere in wikipedia. Also, that mercury-crossor asteroid have its so tiny moon. That asteroid is so tiny like a few km diameter. It only have 22km radius hill sphere. Hmmm.

Oh, I now remember something. NASA tried to land its setallite on so tiny asteroid (perhaps one km diameter) and it has very weak gravity. Setallite acts like feather when landing on surface.

According to space.com news some time ago, NASA is planning to launch setallite with very dense load to pull small asteroid out of collision course aganist our planet earth by using gravitational tractor. I think that it does not work in orbiter software because that had been not implemented for vessels for gravitational effects.

Thanks again,
Tim

 

[tblaxland]

Ok, thanks for some replies. I read some info about hill sphere. I have another question for you about that. When space shuttle is going away from the planet earth, hill sphere is becoming bigger. Right?

Correct. Just note that the space shuttle can't get very far from Earth, so it is always going to have a small Hill sphere.

According to space.com news some time ago, NASA is planning to launch setallite with very dense load to pull small asteroid out of collision course aganist our planet earth by using gravitational tractor. I think that it does not work in orbiter software because that had been not implemented for vessels for gravitational effects.

That is correct.

 

[Sword7]

Tblaxland,

For just curious, what happened to objects when you place them within 120cm hill sphere inside the space shuttle?

Tim

 

[tblaxland]

Technically speaking, if a Hill sphere is smaller than the object itself then it doesn't really exist, ie, there does not exist a stable orbital path around that object. Putting it another way, the Hill sphere calculation assumes that the entire mass distribution is concentrated at a point (the centre of mass). This a reasonable approximation for large distances (ie, distance much greater than the size of the object itself) or for very symmetrical mass distributions (ie, not the Shuttle). Once you get closer to the object, the non-symmetrical nature of it starts to become important.

If we consider the example of the Space Shuttle, once you get close to it, you would have greater gravitational attraction to the denser parts and the assumptions associated with the Hill sphere breakdown. Earth provides a great example of this - orbits precess in their longitude of ascending node due to the earth being oblate (fat at the waist) rather than spherical. The lower the orbit, the greater this effect is. The way to calculate the gravity field once you get close to complex object is to use Gauss' law for gravity (http://en.wikipedia.org/wiki/Gauss%27s_law_for_gravity) but it is no mean feat for such a complex object as the space shuttle and the answer is so small that it can be ignored anyway.

Things start to get interesting when you move inside the object. Take a test mass and put it inside the shuttle. Objects all around act on it and the gravity field has a tends to cancel out. For the limiting case of a sphere, the gravity inside cancels out to zero (see here: http://en.wikipedia.org/wiki/Shell_theorem#Inside_a_shell).

EDIT: This image from the GOCE website (http://www.esa.int/images/C4_2_geoid_B.jpg) gives you a good idea of just how misshapen Earth's gravity field is. (Image not embedded so as to not clag up the thread).

 

[Sword7]

Thanks for some interesting articles that I need for my future programming. I was looking for some info some time ago when go deep below surface like mine, etc. At center of mass, there is zero gravity (all directions from graviational effects). From surface to the center, gravity is gradually less and less. For example, there is hole from surface to surface and drop a ball into the hole. What happened? It would stop at the center.

I reviewed the interesting results from gravity gradiometry and learned something. For LEO orbit, big mountains have slightly more gravitational effect than less dense (ocean) area. Right?

How is about odd-shaped bodies like asteroids, rod, etc.. because gravity formula is designed for spherical bodies?

How measure G force when launching spacecraft into orbit by using gravity, thrust, centrifugal, etc? For example, it is 1.0 G force at ground, it would be 3.0 to 5.0 G force during launch; it would reach 0 G force at orbit, etc... At LEO orbit, is gravity force and centrifugal force equal or so?

Tim

 

[Eagle]

How is about odd-shaped bodies like asteroids, rod, etc.. because gravity formula is designed for spherical bodies?

How measure G force when launching spacecraft into orbit by using gravity, thrust, centrifugal, etc? For example, it is 1.0 G force at ground, it would be 3.0 to 5.0 G force during launch; it would reach 0 G force at orbit, etc... At LEO orbit, is gravity force and centrifugal force equal or so?

Tim

For non-spherical bodies you use calculus to sum the gravitational attraction vectors toward each part of the ship. However if you get far enough away spherical approximations work fine.

The gravitational attraction to an object decreases with the square of the distance. So if you move twice as far from the Earth the attraction is only 1/4 of the original.

The centrifugal force doesn't exist so its best to dismiss it from your understanding. A spacecraft in orbit has enough horizontal velocity so the round Earth falls away underneath it just as fast as the Earth pulls the spacecraft down. No other force needs to exist on the spacecraft.

 

[Hielor]

The centrifugal force doesn't exist so its best to dismiss it from your understanding. A spacecraft in orbit has enough horizontal velocity so the round Earth falls away underneath it just as fast as the Earth pulls the spacecraft down. No other force needs to exist on the spacecraft.

The "centrifugal force" does indeed not exist, but it can be useful when thinking from a rotating frame of reference (which a vehicle "stationary" in orbit is in). Since the rotating frame of reference is accelerated, you end up with the "false" forces appearing to balance things out.

 

[tblaxland]

Thanks for some interesting articles that I need for my future programming. I was looking for some info some time ago when go deep below surface like mine, etc. At center of mass, there is zero gravity (all directions from graviational effects). From surface to the center, gravity is gradually less and less. For example, there is hole from surface to surface and drop a ball into the hole. What happened? It would stop at the center.

No. Things don't stop when there is no gravity, things stop when you apply a force to stop them. What force is there at the centre of mass that stops the ball? None. The ball will go straight through the centre without stopping (it would oscillate from one surface to the other, it is really just like a pendulum).

I reviewed the interesting results from gravity gradiometry and learned something. For LEO orbit, big mountains have slightly more gravitational effect than less dense (ocean) area. Right?

Yep.

How is about odd-shaped bodies like asteroids, rod, etc.. because gravity formula is designed for spherical bodies?

How measure G force when launching spacecraft into orbit by using gravity, thrust, centrifugal, etc? For example, it is 1.0 G force at ground, it would be 3.0 to 5.0 G force during launch; it would reach 0 G force at orbit, etc... At LEO orbit, is gravity force and centrifugal force equal or so?

I think the others have covered centrifugal force pretty well.

 

[Hielor]

No. Things don't stop when there is no gravity, things stop when you apply a force to stop them. What force is there at the centre of mass that stops the ball? None. The ball will go straight through the centre without stopping (it would oscillate from one surface to the other, it is really just like a pendulum).

42 minutes. http://www.mathreference.com/ca-vec,tunnel.html