Red Planet

[doltish]

I hope this hasn't been brought up and I did a search in this topic in the interest of not posting a repeat so here goes.

I was reading the Bad Astronomy review of Red Planet and he mentioned that he was all aflutter when he noticed the space station had two rotating rings each going in opposite directions to keep the station itself from spinning. I included the passage at the bottom of the post.

But anyway, even if there was only one ring would it be possible to put another ring within that single larger ring and have it rotate in the other direction? Wouldn't this have the same effect and consolidate the size of the station/ship? Can I watch space movies where the spacecraft have only one spinning ring and still feel content because I can *assume* they check this website regularly and already thought of the ring-in-a-ring possibility?

Just wondering.

Incidentally, they used spinning wheels on the ship to simulate gravity, which would work. I was amazed to see two wheels, spinning in opposite directions. This is exactly what you want to do! If you have only one wheel spinning, the ship itself will try to spin in the other direction (this is called ``conservation of angular momentum'', for those of you that love jargon). Having a second wheel spinning in the opposite sense counteracts that. Also, a single spinning wheel makes it very difficult to steer the ship, so having a second one again counteracts that. Very well done, and fine attention to detail on the part of the crew of the movie.

[Sever]

welcome to the board!

[Pinemarten]

Welcome to the board.

When they first invented two prop helicopters they tried to rotate them in the same direction. It was a disaster.
If a space station had a wheel within a wheel it would counter rotate to the direction of the largest force. I think the balance would be too difficult to maintain.

[SpaceTrekkie]

But would it beable to maintain balance in the inner-smaller wheel turned faster than the outer one?

[Pinemarten]

The speed wouldn't matter. It would have to do with the angular momentum. Mass, distance, velocity, force, etc.

[Colt]

Yes you could do that but I would not want to.. My main question however is how would you get to the outside ring through the inner ring?

It's assumed that Discovery in 2001 had a weight that counter rotated to keep it from spinning the entire ship which would work better than having two rings. -Colt

[Alex W.]

Mount a (literally) massive metal ring inside the wall of the habitation ring, rotating in the opposite direction, and you should balance the momentum.

[johnwitts]

Yes you could do that but I would not want to.. My main question however is how would you get to the outside ring through the inner ring?

It's assumed that Discovery in 2001 had a weight that counter rotated to keep it from spinning the entire ship which would work better than having two rings. -Colt

The rotating ring in discovery had no such counter rotating ring. This explains why, in 2010, Discovery is spinning when the Floyd and the crew reaches it. To get rid of the spin, they reapply power to the rotaing ring to bring the spacecraft back under control. Actually, this rotating carousel section would be very useful to help maintain attitutude during engine burns...

[DataCable]

Also, a single spinning wheel makes it very difficult to steer the ship, so having a second one again counteracts that.

Something just struck me wrong about this the first time I read that review. He's referring to the tendancy of a gyroscope to resist torque against it's axis of rotation (is that the proper terminology?). Now, I understand how having 2 counter-rotating sections would nullify each other's effect on the non-rotating section, but don't they also compound, rather than cancel, the gyroscopic resistance to torque, regardless of wether they spin in the same or opposite directions?

Or am I just way off base here?

Of course, this reminds me of a story told to me once about my grandfather, whom at some time, set up several battery-powered gyroscopes in his briefcase or luggage, with the axes at right-angles to each other. When an unsuspecting someone was asked to carry it for him, they had no problem lifting or carrying it... until they tried to turn a corner. :-k

[johnwitts]

'Upsetting' a gyroscope can in itself be used to cause something to turn, with a large degree of precision. The front wheels of bicycles and motorcycles are gyroscopes held not quite balanced. To make a turn, the front wheel has to be 'upset' and will recover by turning the bike. On Harleys, the forces needed to upset this balance are massive, and corners have to be booked way in advance. On proper motorcycles, like Yamahas, this force is tiny, hence nimble, if a bit twitchy, handling.

[captain swoop]

'Upsetting' a gyroscope can in itself be used to cause something to turn, with a large degree of precision. The front wheels of bicycles and motorcycles are gyroscopes held not quite balanced. To make a turn, the front wheel has to be 'upset' and will recover by turning the bike. On Harleys, the forces needed to upset this balance are massive, and corners have to be booked way in advance. On proper motorcycles, like Yamahas, this force is tiny, hence nimble, if a bit twitchy, handling.

No not quite the handling of a bike is all to do with the rake of the forks and and the castor angle. Any bike with extended forks a shallower head angle increases the castor angle and the bike will be harder to turn.

Sports bikes have steep forks, very little castor angle and a short wheelbase.

[Ripper]

Though raked out fromt ends are detrimental to turning it has little to do with gyroscopic effect. You have to keep in mind that motorcycles turn by counter-steering. To turn left you steer right. I know this sounds counter intuitive, but it is a fact. Look at it this way. As you steer right the contact patches of the tires are shifted to the right relative to the center of mass of the bike. The bike leans to the left, and you go left. The best way to get out of a turn is to apply a little counter-steering and get on the gas, big time. The incerese in speed causes centrifugal force to pull the bike upright. This means a motorcycle will tend to stabilize as it accelerates. Hence the old saying, "When in doubt, gas it out." I am sure the gyroscopic effect of the wheels helps stabilize the bike, but it is the effects of counter-steering that keeps it up.

[Colt]

Yes you could do that but I would not want to.. My main question however is how would you get to the outside ring through the inner ring?

It's assumed that Discovery in 2001 had a weight that counter rotated to keep it from spinning the entire ship which would work better than having two rings. -Colt

The rotating ring in discovery had no such counter rotating ring. This explains why, in 2010, Discovery is spinning when the Floyd and the crew reaches it. To get rid of the spin, they reapply power to the rotaing ring to bring the spacecraft back under control. Actually, this rotating carousel section would be very useful to help maintain attitutude during engine burns...

Ah but then you must realize that the Discovery is rotating along its long-axis... This is a problem. There is no space in the habitat module of Discovery for a ring that would pass its movement on to the entire ship. *digs around* I think this is it : http://www.planet3earth.freeserve.co...ce_odyssey.htm he figured out where everything is in the habitat module. Discovery should have been spinning around its long-axis, not rotating.

I should rephrase though.. It would make logical sense to have a counterweight. -Colt

[Ripper]

A whole ring is a bit much anyway. You can put a module at the end of an arm. It would be a lot cheaper. I understand that NASA is thinking of just having a small centrifuge inside the ship and having everyone spend an hour or so each day to avoid bone necrosis.

[johnwitts]

Though raked out fromt ends are detrimental to turning it has little to do with gyroscopic effect. You have to keep in mind that motorcycles turn by counter-steering. To turn left you steer right. I know this sounds counter intuitive, but it is a fact. Look at it this way. As you steer right the contact patches of the tires are shifted to the right relative to the center of mass of the bike. The bike leans to the left, and you go left. The best way to get out of a turn is to apply a little counter-steering and get on the gas, big time. The incerese in speed causes centrifugal force to pull the bike upright. This means a motorcycle will tend to stabilize as it accelerates. Hence the old saying, "When in doubt, gas it out." I am sure the gyroscopic effect of the wheels helps stabilize the bike, but it is the effects of counter-steering that keeps it up.

Hmmm.... Try taking the front wheel off a bike and just throwing it down a road really fast. It wants to remain upright and in a straight line...

[johnwitts]

Yes you could do that but I would not want to.. My main question however is how would you get to the outside ring through the inner ring?

It's assumed that Discovery in 2001 had a weight that counter rotated to keep it from spinning the entire ship which would work better than having two rings. -Colt

The rotating ring in discovery had no such counter rotating ring. This explains why, in 2010, Discovery is spinning when the Floyd and the crew reaches it. To get rid of the spin, they reapply power to the rotaing ring to bring the spacecraft back under control. Actually, this rotating carousel section would be very useful to help maintain attitutude during engine burns...

Ah but then you must realize that the Discovery is rotating along its long-axis... This is a problem. There is no space in the habitat module of Discovery for a ring that would pass its movement on to the entire ship. *digs around* I think this is it : http://www.planet3earth.freeserve.co...ce_odyssey.htm he figured out where everything is in the habitat module. Discovery should have been spinning around its long-axis, not rotating.

I should rephrase though.. It would make logical sense to have a counterweight. -Colt

In the book, it describes the carousel as being between the flight deck and the pod bay. Don't know if this fits in with what's in the movie or not, but it makes sense for 2010.

[kucharek]

Ah but then you must realize that the Discovery is rotating along its long-axis... This is a problem. There is no space in the habitat module of Discovery for a ring that would pass its movement on to the entire ship. *digs around* I think this is it : http://www.planet3earth.freeserve.co...ce_odyssey.htm he figured out where everything is in the habitat module. Discovery should have been spinning around its long-axis, not rotating.

Spinning around the long-axis is instable. Sooner or later it turns into a spin around the other main axis. The Apollo spacecraft during ttrans-lunar/earth-costs also did spin around the long axis (PTC). This had t be controlled by firings of the attitude control thrusters, as after some time a wobble built up. The "Apollo 13" movie has some references to this.

[Colt]

I think we all may be getting a bit confused here.. Are we talking about the movies or the books? I don't recall what it says exactly in 2010 but in the movie the ship is tumbling end-over front. For that to happen it would have had to have had the carousal near the middle of the ship (where the fuel tanks are). If the carousal is sandwiched between the flightdeck and podbay than the ship should have been swining around the habitat module. :s :-? All very confusing with the different sources. :-s

I'm not quite sure what you mean Kucharek. -Colt

[johnwitts]

I think we all may be getting a bit confused here.. Are we talking about the movies or the books? I don't recall what it says exactly in 2010 but in the movie the ship is tumbling end-over front. For that to happen it would have had to have had the carousal near the middle of the ship (where the fuel tanks are). If the carousal is sandwiched between the flightdeck and podbay than the ship should have been swining around the habitat module. :s :-? All very confusing with the different sources. :-s

I'm not quite sure what you mean Kucharek. -Colt

No, no, no Colt! No matter what causes the spin, whether external or internal, it will always spin around it's centre of mass.

[daver]

I think we all may be getting a bit confused here.. Are we talking about the movies or the books? I don't recall what it says exactly in 2010 but in the movie the ship is tumbling end-over front. For that to happen it would have had to have had the carousal near the middle of the ship (where the fuel tanks are). If the carousal is sandwiched between the flightdeck and podbay than the ship should have been swining around the habitat module. :s :-? All very confusing with the different sources. :-s

I'm not quite sure what you mean Kucharek. -Colt

No, no, no Colt! No matter what causes the spin, whether external or internal, it will always spin around it's centre of mass.

In the book, friction with the bearings eventually transferred the angular momentum from the carousal to the ship. Discovery would not be stable spinning around the long axis; it would eventually end up spinning end-for-end. Clarke i believe pointed this out in the book.

[Ripper]

Johnwitts, the gyroscopic effect of the spinning tires helps to stabilize the bike, but it is not what holds the bike up. I can ride forward and easily stay upright at less than 5mph. A assure you that the gyrospopic effect at that speed is insufficient to keep up the 600+lbs of the bike and rider. What keeps a bike up is countersteering. If you put an unbalanced load on a gyroscope it will still shift in that direction, just more slowly. Countersteering provides immediate feedback that counters any tendency to lean in one direction.

[johnwitts]

Johnwitts, the gyroscopic effect of the spinning tires helps to stabilize the bike, but it is not what holds the bike up. I can ride forward and easily stay upright at less than 5mph. A assure you that the gyrospopic effect at that speed is insufficient to keep up the 600+lbs of the bike and rider. What keeps a bike up is countersteering. If you put an unbalanced load on a gyroscope it will still shift in that direction, just more slowly. Countersteering provides immediate feedback that counters any tendency to lean in one direction.

Agreed, at very low speeds, a bit like riding a unicycle where it's all balance. But at higher speeds, like over 20mph or so, there's no way that a rider could keep the thing stable without the 'inbuilt' stability of the gyroscopic effect of the wheels. At really high speeds, over 100mph, most bikes become that stable that turning the bars has very little effect, save for bending the forks slightly.

[RichField]

Hmmm.... Try taking the front wheel off a bike and just throwing it down a road really fast. It wants to remain upright and in a straight line...

Slight tangent:
I had the unfortunate opportunity to view this first hand. On Tuesday morning, the pickup driving next to me in the right lane lost its front driver's side wheel and tire. The road I was on was fairly straight and I was amazed how many times I could check the rear view mirror and still see it tagging along just behind me. I eventually lost it on an incline.

The truck did not fare quite as well, but it appeared that the driver was able to maneuver safely to the side of the road and bring it to rest. Unfortunately I was not in a position to safely stop and offer assistance.