"2001 A Space Odyssey" space station: Rotating or contra-rotating?

[DaveC426913]

It's a bit 'how long is a piece of string?' without some idea of the actual speeds involved. A plane will be landing at 100mph and can't go much slower. A docking space ship can be approaching at less than walking speed and can slow down, reverse or nudge left and right. This is more like the mooring a boat scenario. We use inflated fenders for a 4ton boat coming up against a dockside and they work fine for dealing with a nudge of 1knot. I really can't see any significant problem with this aspect of space navigation.

Sure. As you point out, going slow (for the sake of safety) is a compromise to efficiency (in terms of throughput). You want to go slow because this design is not very fault-tolerant. There are other designs that are more fault-tolerant.

So, generally, in docking bay design, efficiency is a factor. So is safety and fault-tolerance. They must be balanced against priorities. That's the point of this discussion - the pros and cons of various designs.

Your images assume a certain style of engineering...

No. The OP did that.

There are other designs, certainly. My response all along has been specifically to the safety of the 2001-style rotating docking bay that the OP brought to the table.

 

[Ibix]

space fighters make little tactical or economical sense:

The portrayal of space combat in fiction is another topic. I was just noting that using centrifugal force to "drop" small craft had been done in fiction.

 

[Filip Larsen]

No amount of suspension and heavy-duty tires will minimize a broadside collision with a station wall.

I think no one here disagrees that the further away from the spin axis you approach a spinning station the more severe any unintended contact with the station will be, at least until well passed the rim, so the operational assumption must be that there already are a precise and safe enough approach control system that only allows the approaching spacecraft near any "danger zone" when its relative trajectory and rotation is within limits.

You also seem to assume that the spacecraft will float into the bay and then "lower" itself onto the floor (and rest there by weak centripetal acceleration). I instead assume that initial contact takes place with some (automated) arm when the spacecraft is at the right "depth" into the bay. The arm can either present a central passive docking target that the craft actively docks with, or more likely, an active arm (or more) that grabs the almost-passive spacecraft when its holding in a box (i.e. berthing just like its done today, except the berthing box is inertially rotating).

 

[DaveC426913]

I think no one here disagrees that the further away from the spin axis you approach a spinning station the more severe any unintended contact with the station will be, at least until well passed the rim, so the operational assumption must be that there already are a precise and safe enough approach control system that only allows the approaching spacecraft near any "danger zone" when its relative trajectory and rotation is within limits.

Yes. All of which is much simpler and safer in a non-rotating frame.

You also seem to assume that the spacecraft will float into the bay and then "lower" itself onto the floor (and rest there by weak centripetal acceleration). I instead assume

I am not assuming that. No aspect of my scenario concerns itself with how the final contact is made.

I am simply pointing out (once again) that, as long as both objects are rotating, they are in a configuration that, if perturbed at all, can rapidly escalate to a collision, because of the intrinsic relative motion of rotation. This does not occur with a non-rotating configuration.

 

[sbrothy]

The portrayal of space combat in fiction is another topic. I was just noting that using centrifugal force to "drop" small craft had been done in fiction.

I realize that. I just couldn't help myself. :)

 

[Filip Larsen]

This does not occur with a non-rotating configuration.

Your argument, if taken to the extreme means no part of the station can rotate because it would otherwise have failure modes that would allow off-axis contact that could escalate. It doesn't really help you counter-rotate the bay unless the bay itself can maintain its inertial fixed attitude independently of the rotating part of the station in all foreseeable failure modes, and I don't see that is possible unless the rotating and non-rotating part has no contact at all during docking procedures making the design rather complicated and prone to even more failure modes.

I am still going maintain that the simplest overall solution for a spinning station to have docking capability will be to let the docking "volume" co-rotate with the station and use well-known sensors and automation technology to handle a safe approach and docking/berthing.

I guess one way to settle this argument is to just wait and (let our grand kids) see which kind of spinning station with simultaneous docking capability is build first. I guess we could have one already in 50-100 years or so if we are lucky.

 

[DaveC426913]

Your argument, if taken to the extreme means no part of the station can rotate because it would otherwise have failure modes that would allow off-axis contact that could escalate.

That certainly is an extreme; it's a false dichotomy error.

"A ship in a harbour is safe, but that is not what ships are built for."

The goal is not to eliminate any and all safety concerns; the goal is to attenuate them - to recognize that separation in both space and time is a really good way of mitigating safety issues. And that low relative velocities of objects in proximity is desirable.

A moving object that's a hundred yards (and 60 seconds) away is orders of magnitude less hazardous than a one that's ten yards (and 6 seconds) away - in both space and time. Likewise, a hazard at 1m/s is way less dangerous than a hazard at 5m/s. I think this is a pretty basic engineering principle.

A more general way of saying this is that cargo doorways, docking stations and other similar structures are well-known bottlenecks, and are nearly always a high-safety risk - being navigable usually only by trained and authorized crew for good reason.Finally, in an unrelated example that makes the same point of hazard-attenuation, you don't put oncoming highway traffic right next to each other on a highway. A wide, grassy meridian attentuates (in both distance and time) the danger of collision with other vehicles moving at 200km/h relative. But we don't need to do that for co-moving vehicles, because a collision (while unwanted) will usually be at nonlethal speeds.

It doesn't really help you counter-rotate the bay unless the bay itself can maintain its inertial fixed attitude independently of the rotating part of the station in all foreseeable failure modes, and I don't see that is possible unless the rotating and non-rotating part has no contact at all during docking procedures making the design rather complicated and prone to even more failure modes.

I don't know what you're suggesting. Is your scenario realistic?

I am still going maintain that the simplest overall solution for a spinning station to have docking capability will be to let the docking "volume" co-rotate with the station and use well-known sensors and automation technology to handle a safe approach and docking/berthing.

I agree; it's the simplest. I never suggested otherwise.

What I said was:

Cheapest maybe, but not safest.

I guess one way to settle this argument is to just wait and (let our grand kids) see which kind of spinning station with simultaneous docking capability is build first. I guess we could have one already in 50-100 years or so if we are lucky.

It's not a right or wrong. There's no settlement. It's a matter of the specific needs, goals, budget and safety concern of whomever is building and populating a specific station in a specific future world.

For example, In 2001, we can presume that they chose the design they did because (among other reasons):
- the technology might be newish. They don't have the tech to make a hundred-yard-circumference air-tight seal, so they cant make a reliable, cheaply-maintained rotating dock yet.
while at the same time
- the arrival/departure traffic of the clipper(s) means they don't have to worry about throughput - a clipper coming once a day or even once a week - has no reason to hurry through the docking bottleneck.

A different age, a different function, and we have different needs and abilities.

 

[Filip Larsen]

I agree; it's the simplest. I never suggested otherwise.

Fair enough.

So let us address safety. I am interested in hearing how you see a counter rotating docking bay can be designed to be "more safe" than a co-rotating bay when considering the total set of expected operations relevant to docking, that is docking itself of course but also transfer of people and cargo between the rotating parts, likewise transfer of power and fluids, and the needed mechanisms, power and control to maintain relative rotation?

It is difficult (for me) to see that any design that introduces what must be a fair bit more complexity and involving a fair bit more of the station can end up with everything being more safe. In engineering (including aerospace) an often used approach to reduce risk of (full system) failure is modularization to increase redundancy and limit failure modes between separate system (component isolation). But how do you modularize a counter-rotating bay except by keeping it almost fully isolated?

 

[DaveC426913]

Fair enough.

So let us address safety. I am interested in hearing how you see a counter rotating docking bay can be designed to be "more safe" than a co-rotating bay when considering the total set of expected operations relevant to docking, that is docking itself of course but also transfer of people and cargo between the rotating parts, likewise transfer of power and fluids, and the needed mechanisms, power and control to maintain relative rotation?

It is difficult (for me) to see that any design that introduces what must be a fair bit more complexity and involving a fair bit more of the station can end up with everything being more safe. In engineering (including aerospace) an often used approach to reduce risk of (full system) failure is modularization to increase redundancy and limit failure modes between separate system (component isolation). But how do you modularize a counter-rotating bay except by keeping it almost fully isolated?

I don't disagree with you. But there are two very different types of safety.

Safety in engineering is making sure you have the right materials in the design and good inspection/maintenance hygiene. It is essentially routine, by the same people under the same, controlled circumstances. This is ideal.

Safety in operations is a very different ballgame, happening in real time, and under a much wider array of possible circumstances.

You really want to maximize the former, because you want to minimise the latter.Still, you do make a good point about the modularization, and the mitigation of full-system failure. Which is why - I suggest - the station depicted in 2001 was not of nonrotating design. Such a design, - with the futuristic materials it would require - is still years in the story's future.

 

[Filip Larsen]

there are two very different types of safety.

Just for the record, I was addressing the possible level of safety in operations (for crew, material and mission) considered achievable or feasible for a potential docking system based on its design, i.e. very much using safety by design which is a cornerstone principle in crewed aerospace engineering.

So (just to repeat) my objection to a counter-rotating bay is primarily based on that I am not able to see a design that does not have some high consequence failure modes, i.e the failure modes of a co-rotating bay seems far more manageable and isolated to the approach and docking system itself, and thus in my book, far more feasible for a realistic first-time system. However that is just me; it would still be interesting to know if there are any feasible (advanced) designs out there for a spinning station with a counter-rotating hub.

 

[DaveC426913]

So (just to repeat) my objection to a counter-rotating bay is primarily based on that I am not able to see a design that does not have some high consequence failure modes, i.e the failure modes of a co-rotating bay seems far more manageable and isolated to the approach and docking system itself, and thus in my book, far more feasible for a realistic first-time system.

Yeah, I don't disagree. A failure of the sealing ring threatens the entire station.

 

[sophiecentaur]

Yeah, I don't disagree. A failure of the sealing ring threatens the entire station.

If we think the visiting ship couldn’t dock itself then why not have a rotating grab, capable of working off-axis. That could even get the dumbest vehicle on board.
It annoys me a bit that PF, usually so forward thinking is allowing Arthur C ‘s 80 year old ideas to be leading so many of these posts.

 

[Filip Larsen]

It annoys me a bit that PF, usually so forward thinking is allowing Arthur C ‘s 80 year old ideas to be leading so many of these posts.

Are you upset with the course of the discussion in this thread or is it the particular options under discussion that irks you?

 

[sophiecentaur]

Are you upset with the course of the discussion in this thread or is it the particular options under discussion that irks you?

It’s the fact that the contributions seem to be from Arthur C or Hollywood. So little in the way of Engineering or Science. It’s Lego thinking.
Too harsh? Maybe.

 

[DaveC426913]

If we think the visiting ship couldn’t dock itself then why not have a rotating grab, capable of working off-axis. That could even get the dumbest vehicle on board.

Sure, but I think that is a slightly different tactic than this thread was intended to pursue. At the risk of speaking for the OP, it didn't seem to be meant as a free-for-all exercise of the imagination for an unlimited tech level and expense; it had a starting scenario, and asked about the pros and cons of alternatives - presumably for the very near future - i.e. AD1967's take on AD2001, in the childhood of the space age.

That is the implied parameters I have been deliberately living within.

It annoys me a bit that PF, usually so forward thinking is allowing Arthur C ‘s 80 year old ideas to be leading so many of these posts.

Er ... none taken, I guess...? I haven't seen anyone discouraging any forward-thinking ideas. So far, only a couple have been offered. I hope I'm not (somehow) dominating the conversation. (In fact, I hope I'm keeping it alive and fertile.)

Feel free. But again, IMO, it behooves us to meet the OP's post "where it is". i.e. given a tech level, budget and function, what are alternatives, not so much what can we fancifully imagine.I mean if we want to go with imagination, I once sketched out a docking bay that allowed high throughput, while allowing shuttles to land on a runway just like an airplane, except that it was spiral-shaped, allowing the shuttle slowly spin up to rotational speed as it braked, while at the same time, easing occupants into station gravity in a more normal "down is towards my feet" orientation.

I could try to dig up the sketch if all bets are off.(BTW, we still use A.C.Clarke's geostionary orbital satellites, so I wouldn't be too quick to dismiss his ideas as archaic.)

 

[sophiecentaur]

Sure, but I think that is a slightly different tactic than this thread was intended to pursue. At the risk of speaking for the OP, it didn't seem to be meant as a free-for-all exercise of the imagination for an unlimited tech level and expense; it had a starting scenario, and asked about the pros and cons of alternatives - presumably for the very near future - i.e. AD1967's take on AD2001, in the childhood of the space age.

That is the implied parameters I have been deliberately living within.Er ... none taken, I guess...? I haven't seen anyone discouraging any forward-thinking ideas. So far, only a couple have been offered. I hope I'm not (somehow) dominating the conversation. (In fact, I hope I'm keeping it alive and fertile.)

Feel free. But again, IMO, it behooves us to meet the OP's post "where it is". i.e. given a tech level, budget and function, what are alternatives, not so much what can we fancifully imagine.I mean if we want to go with imagination, I once sketched out a docking bay that allowed high throughput, while allowing shuttles to land on a runway just like an airplane, except that it was spiral-shaped, allowing the shuttle slowly spin up to rotational speed as it braked, while at the same time, easing occupants into station gravity in a more normal "down is towards my feet" orientation.

I could try to dig up the sketch if all bets are off.(BTW, we still use A.C.Clarke's geostionary orbital satellites, so I wouldn't be too quick to dismiss his ideas as archaic.)

Designing a docking bay (and I mean design) would involve some idea of traffic levels. Is it reasonable to assume high density? That would assume a lot about energy and materials supply. So advance by several more hundred years.
Why think in terms of aircraft and runways? Runways are only used because of the physics of flying these days. (Just above) Zero approach speed is easiest and safest.

I have to admit that thought designs of retro engineering systems doesn’t appeal to me. It’s a modern extension of model railway layouts in the attic; more model making than future Science.

More estimates of values and system spec would float my boat.

 

[DaveC426913]

Why think in terms of aircraft and runways? Runways are only used because of the physics of flying these days.

Because it was fanciful, and you were looking for more imaginative solutions. I didn't say it was practical.

 

[sbrothy]

Are you upset with the course of the discussion in this thread or is it the particular options under discussion that irks you?

One thing which has always been "grinding my gears" with the story is that at some point in the story Rama uses Sol as a gravity assist. Compared to it's (technomagic) engine power (which isn't much but is described in the story as "sufficient" and there's a wall to make sure the "Cylindrical Sea" in the middle of the craft doesn't overflow when it uses this "magical" propulsion.

Using Sol as a gravity assist it would have to be very precisely aligned and the power obviously couldn't exceed the inbuild propulsion or the sea would overflow. So if the gravity assist can't exceed the inbuild propulsion why use it at all? One would think that using the assist would be because it's free power which would exceed Rama's propulsion drive but all in all I have a hard time for it to make sense.

Do I make sense at all?

PS:

This post wasn't really an answer to your question as such. I just answered the last post. I' don't feel irked at all. Where did you get that impression? Or exactly perhaps I didn't answer specifically the question wasn't aimed at me. If so I apologize.

 

[Filip Larsen]

I' don't feel irked at all. Where did you get that impression? Or exactly perhaps I didn't answer specifically the question wasn't aimed at me. If so I apologize.

No worries. My question was directed to sophicentaur.

 

[Filip Larsen]

It’s the fact that the contributions seem to be from Arthur C or Hollywood.

I can of course only speak for myself, but except for the OP question which was referring to the spinning station from the movie "2001 : A Space Odyssey"(1) I am referring to real-life aerospace engineering principles to the extend that I am aware of them as an engineer that has had a life long interest in aerospace designs and simulation. Also, I feel the discussion I have been involved in here had tried to refer to relevant physical principles. Granted, the discussion has probably been on an amateur level compared to with what a professional team of aerospace engineer would have discussed if tasked with designing such a station (e.g. as a feasibility study for relevant future technologies), but that is just how this forum works.

But isn't the solution easy? You just provide relevant critique to the specific points you think are too amateurish or too much based on movies and we take it from there?

(1) I don't recall the level of detail Clark described the station with in his original story, but granted, he most likely had enough influence on how most things was depicted in the movie to call is "his" designs).

 

[DaveC426913]

Using Sol as a gravity assist it would have to be very precisely aligned and the power obviously couldn't exceed the inbuild propulsion or the sea would overflow. So if the gravity assist can't exceed the inbuild propulsion why use it at all? One would think that using the assist would be because it's free power which would exceed Rama's propulsion drive but all in all I have a hard time for it to make sense.

Do I make sense at all?

Gravity - and thus, gravity assist - works on the entire craft, wall, floor and water. The craft is in freefall, even as it is falling toward or away from the Sun. Occupants will neither see nor feel anything.

So it does not constrain acceleration - but with one caveat: if it gets too close to the Sun, it may experience tidal forces (i.e. different parts of the 50km long cylinder actually experience different degrees of gravity because it's so close).(You'll have to get up earlier than that in the morning if you want to catch A.C. Clarke out on a technical issue. :) )

 

[sbrothy]

Aaaah. That explains it. I've wondered about this since seeing Space Odyssey 2010 where they aerobreak but otherwise seem to be unaffected. In fact I've been afraid to ask this question because I thought the answer would be something along those lines and make me look like a fool :) . So no matter how hard my spacecraft is "assisted" I shouldn't worry about everything and everyone getting squished up against one wall?

How incredibly unintuitive but we've been over that.

Thank you.

 

[Ibix]

So no matter how hard my spacecraft is "assisted" I shouldn't worry about everything and everyone getting squished up against one wall?

You're in free fall the whole time, just like being in orbit (because you are in orbit, just a hyperbolic one). Tidal forces will still affect you and tend to elongate you along the radial direction, but unless you're orbiting close over a neutron star or black hole you'd need specialist equipment to spot it inside a reasonable sized spacecraft.

 

[DaveC426913]

... a reasonable sized spacecraft.

Rama is 50km long.

(Only 20 across, if they wanted to orient it to minimize tidal forces.)

Actually, it shouldn't matter. The Cylindrical Sea rings the waist of the ship - at its CoM - and far from the poles, where the most tidal forces would be felt.

Any water tidal action would only be across the width of the Sea from wall to wall, which is less than 20km. And it would be equal. In other words, it would not slosh toward one wall more than the other; it would simply get a smallish sea swell on each wall, as the water bowed slightly toward the poles.

You'd have to be in a pretty good tidal gradient - acting across less than 20km - to get the Sea to overflow its banks.

 

[Ibix]

Rama is 50km long.

The Earth is 12,800 km across and the lunar tides vary water height by a few meters. You'd have to do the calculations for a relatively close pass of the Sun (the mass is a lot more than the Moon, but you can't get so close as we are to the Moon).

 

[DaveC426913]

The Earth is 12,800 km across and the lunar tides vary water height by a few meters. You'd have to do the calculations for a relatively close pass of the Sun (the mass is a lot more than the Moon, but you can't get so close as we are to the Moon).

The Cylindrical Sea is only 20km across - much smaller than the largest lakes, which do not experience tides to-speak-of. Someone needs to do some calcs (not 'it'!).