Do not get into this page if you are trying to read a book. This is for after you’ve read it. Likewise follow the custom of putting a subject and then dropping down a number of lines to make it possible for a reader to duck out if they don’t want the information yet.
I will answer questions about pronunciation, etc, all the little questions I’m normally asked. I won’t discuss things that disturb my creative process, like where I’m going or such. You can theorize among yourselves.
Ah! Sorry to bang on, but you know what us techy types are like. So the ship is hauled in so it’s hull is alongside the station torus rather than at right angles to it?
I’m sure that the Pride is described as having a corner in the access tube – this would explain it.
The ship approaches on its directionals only, after braking. At this point the computers have to talk to each other to do a dock. The docking cone extends, mates up, as grapples go on from both sides. The cone apparatus and grapples operate at that point to shift the ship into a snug configuration.
Re stations, Btw: The station, as it builds, grows not by adding to the radius, but by becoming a longer cylinder. It is created as wide as it will ever be. Pell’s original station was physically moved out of its orbit and a new, larger ring constructed. The original station is now dedicated to food production. There is yet another one which is a shipyard…
JCrow, you’re assuming all berths are in one line. Consider:
o…o…o…o…
..o…o…o…o.
o…o…o…o…
etc., where you separate the docking ports (o) by as much space as needed. And computers make the docking trivial. (I’ve often thought the whole tail-standing jet should be tried again now that we have engines putting out more thrust than the weight of the jets, and more importantly, computer controls.
And without looking up GW’s exact numbers, in generalities, the idea is certainly correct. If you did the possibly convenient thing and made a space station big enough to rotate at 1 gee (9.8 m/s/s, of course–my typo) with one rotation every 24 hours so day and night happen “naturally”, the station would rip itself to pieces even with the most optimistic guesses about what could be achieved with carbon nano-tubes. If I did my math right, back when.
Walt, I’m thinking more of clearing adjacent ships while on final approach… The economics of the station suggest that you want to be able to dock a lot of ships at once, right? That’s my assumption, anyway. It comes down to a factor of your closing speed needed to get your ship’s schnozz inside the “swept zone” (volume occupied by the adjacent ship’s stern mere moments ago) just after it gets out of the way.
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Lucy on approach
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[ ]
[ ]
[ ]
[ ]
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Norway
# Dublin [ ]
# [ ] [ ]
# [ ] [ ]
# [ ] [ ]
# [ ] [ ]
# [ ] [ ]
# [ ] [ ]
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#—-O————-O————-O—-station ‘wall’
moving thataway: —>
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You have to go fast enough to get into engagement **after** the adjacent ship rotates out of the way (and before the next one comes along), but not going so fast that you can’t slow enough for a safe engagement once you get there. Of course, it all depends on how big the ships are–but I see these as Really Big Critters (Saber is described as being a kilometer long in Faded Sun).
Your idea works, though, in that you can stagger the docks laterally along the axis of the torus–hard to describe, hopefully the lame-o ASCII above worked out–but if the axis of station rotation is considered north-south, and if the pressurized volume is long in that north-south direction (hundred thousand-plus population, it had better be!), the docks can alternate being closer to the northern and southern edges of the torus.
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—————————– ‘North’ wall
O………….O………….O
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…….O………….O…….
—————————– ‘South’ wall
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That also provides a convenient avenue to bail out of a missed approach. If you hose up your approach, you can kick the directionals hard sideways (station’s north or south as appropriate) and slip out of the plane of rotation (have to clear the next ship), versus having to blast hard back, a vector your ship likely can’t do all that well without turning over anyway.
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Abject apologies for the long post….
Rats….
# one more time…
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#………………..Lucy
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………………….[.]
Dublin…………….[.]..Norway
[.]…………………….[.]
[.]…………………….[.]
[.]…………………….[.]
[.]…………………….[.]
[.]…………………….[.]
[.]…………………….[.]
-O————O————–O—–
The avatars make it hard, don’t they? I’m used to a site that puts them out of the text box in the left column.
Another thing to remember is the coordinated nature of this whole dance. Let’s use GreenWyvern’s formula (so I don’t have to look it up!)
“v = sqrt(ar)
“where v = tangential velocity, a = centripetal acceleration, r = radius”
So for round numbers a=10 m/s/s, r=1000 m (1 km), 10 x 1000 = 10,000, square root = 100 m/s. And you’re rotating in about 63 seconds (compute circumference, 2 pi r, and divide by v).
So, some distance away from the station, you get to 100 m/s headed to rendezvous with your docking port, nose inside the cone. You start rotation and match it with the station and the port. So, when you actually get to the station, everything should match up, and you should end up grappled.
But the big point is that the rest of the docked ships are rotating, too, in sync with the station, and you. So to a great extent, they “stay out of your way”.
Makes for an interesting dynamic, to spiral inwards staying fixed on a radial position wrt the station! (and asks a lot of your directionals to constantly blast sideways, all your mains are doing is pushing you inward, radially, unless you skew your approach to get the lateral accel from the mains) I had viewed this as an intercept problem, i.e. you blast straight in, timing your arrival such that your probe hits the guidance basket (at near-zero closing speed!), which certainly put a hell of a jolt on the structure as it swings into sync with the station.
The basic formulae are, for w (omega, angular velocity) w=SQRT(a/r), where a is centripetal acceleration (desired G) and r is station radius; and rim (tangential) speed v=rw.
For a station radius of 1km, w=.03radians/sec and rim speed is 31.6m/s. 2km is .02rad/sec and 44.7m/s.
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CJ posted:
“work it through about 12 deck levels to figure how large you had to be to avoid big differences in deck 1 versus 12”
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In most/all of your books, CJ, you talk about the overhead of the docks being so high that you have weather taking place–I dunno how high that has to be, but say that was 100m, then thereafter 5m between adjacent decks for plumbing and accessways as well as people, and you have about 160m of ‘thickness’ from outer rim to inner rim. If Pell’s radius was, say, 2km, and you have 1G at the docks, then the apparent G at the ‘top’ of the stack would be .92G, just enough less to be relaxing.
“Makes for an interesting dynamic, to spiral inwards staying fixed on a radial position wrt the station! (and asks a lot of your directionals to constantly blast sideways, all your mains are doing is pushing you inward, radially, unless you skew your approach to get the lateral accel from the mains)…”
You forget that the speed of the station’s rim and rotation are constant. If you enter approach correctly–already spinning and at a correct closing speed matching station rotation–then all you do is keep the mains going until you dock. You don’t need lateral acceleration–it would upset the illusion of gravity, too.
Of course, the advantage of the unpowered tangential approach is virtually nothing can go wrong. At least, something has to actively go wrong, accelerating the ship.
Just back from 5 days in the moutains, away from computers, cellphones, and work!
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Walt, I am having a bad brain-cell day, I guess (got to reboot after 5 days away). Of course the station’s rim speed is constant. But how can I spin my ship around the station’s center of rotation without constant acceleration? For I must do that to stay in constant position relative to a specific point on the station’s rim (the docking cone) as I approach. I must be misunderstanding your meaning of ‘spiraling in’? When I say ‘tangential approach’ I mean to approach as the reverse of your thrown-knife analogy.
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CJ, I guess we need a round-table session on docking mechanics. Got a con handy? 😉
Angular momentum acts just like normal momentum–it’s preserved. If the station is rotating at one rpm and the ship is rotating at one rpm, they’ll stay in sync unless someone accelerates *angularly*. The mains accelerate linearly–a forward acceleration not a rotation (pitch–or yaw or roll).
So, for the non-spiral case, you head for the station so your speed is the same as the speed of rotation at the docking port. Then (to do it one step at a time) you start rotating and sync so your nose will be aligned with the port at the time you rendezvous, and that you are rotating at the same angular rate as the station. Then everything will match up when you rendezvous.
The spiral case is harder (and it’s not exactly a spiral–I forget the technical term), but not if we do the reverse motion thing again–the thrown knife. Imagine the ship undocking from a 1 gee station and immediately applying 0.5g (arbitrary number) thrust. No problem, right? The ship still accelerates away from the rim at the remaining half gee. The ship leaves the station more slowly, but the passengers have some gee. The ship spirals out because it’s still rotating in sync with the station, so the mains change the direction they’re pointing; but since the acceleration is constant, the passengers sense nothing after the drop from 1g to 1/2g at undock. Now reverse the movie for docking.
The deal is, rotation is constant, so we don’t have to worry about that part. The ship is drifting laterally at the speed of the docking port; that’s also constant–no worry. The mains accelerate the ship longitudinally, so they affect neither the lateral speed nor the angular rotation. As long as the ship ends up at the right place at the right time, everything works.
Another way of looking at it (which if you’ve already got it may destroy your understanding 🙂 ) is we know everything is relative. So consider things relative to the ship. The ship is making circles, using the mains to hold in the circle (instead of gravity or a station’s structure). It’s just making circles, keeping its passengers comfy. The circle is drifting toward the station at the speed of the station rim (on which the empty port is making a similar circle). If the circles drift together in sync and the ship and the docking port match up, you’re docked.
Or, imagine one of the ships undocking. It would spin away like a thrown knife. Or, more like a merry-go-round horse leaving the pack–quite safely, without collision–and going off at a tangent. Reverse and mirror that movie, and that’s what docking looks like.
It’s been a long time since I worked with this, but Pell’s ring is pretty big. I recall trying to figure how far up the astronaut you could get stability with what rotation, and then to work it through about 12 deck levels to figure how large you had to be to avoid big differences in deck 1 versus 12.
There’s a little bit in Heavy Time, where there’s a vending machine that was relocated to another deck and the cup always tips over…
It would make sense to stagger the docking positions- you might as well use the whole
breadth of the cylinder. But from the people-walking-along-docks scenes in DBS and the Chanur books that doesn’t seem to be the case; it seems like every ship has its own little slice of the dock. You never have anyone looking across the dock at the guys docked parallel to them.
Actually, IIRC it’s businesses on the far side- bars and sleepovers and things. I always got the impression that you come down your ramp and you’re looking across an expanse of open floor to a wall of shops on the far side.
Maybe that’s an artifact of the cone positions and all the ships are docked dead center on the ring, but if they really are all docking on one edge of the rim, wouldn’t that uneven mass distribution mess with the station’s orbit? That’s an argument against staggering, too, come to think of it.
How wide are the docks anyway?
I think Walt has it. I tried explaining this over on Shejidan (complete with PooPoint diagram) but didn’t get very far. If a ship undocks, it will immediately start moving sideways in a straight line at station rotational velocity. It can’t catch up with the ship in the next dock, or be overtaken by the one behind. So you just wait until you’re clear of the torus, and off you go. Docking is the exact reverse. No spiralling in needed.
Those of us who don’t have the math can play with station diameters/spin and resulting g force at http://www.artificial-gravity.com/sw/SpinCalc/SpinCalc.htm
If the stagger is merely a zig-zag (two rows), the docks would still be in a line, more or less.
Balance is always a problem. Imagine the extreme case where the ship weighs as much as the station, and one ship docks. Now the ship and the station are rotating about the docking grapple! So, the station has to hugely out-mass the ships, or it has to have a balance system to keep it from wobbling, like weights on a tire, except more so since you’re not talking about little manufacturing inconsistencies. And it has to act fast, at the moment of docking. (Though after that moment, you could slowly move ballast in order to reset the fast balance system.) The weights being off-center is a comparatively minor problem.
You don’t need to spiral, but the advantage is keeping the ship under acceleration for the passengers’ sake. The rotating section can do this, but then you go from light gee under rotation, to its rotation plus the station’s rotation (but one at right angles to the other, so a vector addition, something like 0.5g + 1.0g = 1.12g).
The MCAS Tustin blimp hangers (2) have their own weather, and they’re just under 60m: http://en.wikipedia.org/wiki/Marine_Corps_Air_Station_Tustin
Dang it, I forgot to multiply one G by 9.8 to get m/s/s in the above numbers! So at R = 1000m you should get w=0.1 rad/sec or 37.3 RPMs, rim speed of 99 m/s; at 2km, 26.4 RPMs and 140 m/s rim speed. Deck 12 sees 0.89G at 1km radius, 0.95 at 2km, with 60m dock overhead.
JCrow – is Spincalc off or is it you? 1000m radius indeed gives a rim speed of 99m/s, but a rotation rate of .94 rpm.
I fail to see why the physics of Ms. Cherry’s works have to be real or even consistent. While many of the stories are set in space or in the future, the action and the characters are the important things.
Well, it doesn’t have to be, but it’s still interesting to speculate about. And since she herself did some of these calculations long ago, it’s a question that might have a rational answer within the Alliance/Union books.
Nobody is trying to analyze the electromagnetism underlying the Finisterre ambient or worrying about tc’a biochemistry, because those topics were obviously beyond the scope of the science covered in the books. But the spin of Pell Station is potentially calcuable.
Agreed. It’s easy for an author to take the lazy way out and chuck in off-the-shelf stuff like artificial gravity, food synthesisers, tractor beams etc, but much harder to take the time to write a tech that is believable and workable. One of the things that drew me to CJ’s books was this relatively low tech nuts-and-bolts feel. I don’t object to fantastic high-tech (Niven is another of my favourite authors) but CJ has an unusual approach that I find refreshing.
THanks for the kind words. I actually figure when we’re actually colonizing other worlds, a low-tech approach can work pretty darned well, before you have a population base large enough to sustain a lot of more exotic answers. Sort of like going camping: you may take a match (old-ish tech) to start a fire (prehistoric) and use a modern knife or axe (prehistoric in principle, and all highly portable) to sustain life on fish (old tech) and rabbits, etc…If cast out to survive in a tough environment we’d probably be into our Cosmic Boy Scot manual, looking for the old way to refrigerate, heat, shelter, etc. Solar power’s probably a failure to advance in metallurgy meant you were taking your life in your hands until they figured out good boilers and pressure-release valves. It’s all deliciously interconnected. It was cannons that taught us about metal strength and good casting. The early ones were made of wood with brass bindings and the life of cannonneers was short.
I do try to think it through: if they have A, that means they also have A2, A3, A4 and several offshoots. One of the things I enjoyed doing in historical studies was figuring out the sometimes unusual paths technology took. The Anticythera Clock is a good case in point: if only they’d been able to popularize that technology and have it available at a few later points in history…but powering carts wasn’t what they were after. They wanted a good timekeeper. A didn’t meet B for a long, long time to come.
Wow! “…the mechanism is an astronomical analog calculator or orrery…” — http://en.wikipedia.org/wiki/Antikythera_mechanism
I was once asked who I’d like to talk to who was dead. Heron of Alexandria. He invents automata, automatic mechanisms, and puts on plays. Slap him up-side the head! Two thousand years wasted….
“I fail to see why the physics of Ms. Cherry’s works have to be real or even consistent.”
‘i took the pair of eggs and place three in my right back pants pocket and the remaining 2 in my left back shorts pocket, tu keep them safe when i seat.’
The above violates tense, number, continuity, typography, spelling, and physics (at least!) Each violation jars a reader who is aware of the field. Many science fiction readers have a background in science, and would be jarred out of immersion in a novel by science incorrectness or inconsistency.
Also, bad science, such as Star Trek’s, means you don’t have limits, and can solve any problem by deus ex machina, for which the later Star Trek series were notorious.
It’s not precisely “nobody” who worries about t’ca biochemstry, since I just posted a comment about it on the evolution thread, altough I’ll grant you that the difference between “nobody” and “very few” is usually negligible for practical purposes.
I stand corrected. 🙂
(Plants, though? Chemotrophic heterotrophs, surely.)
Methane is the most fully saturated of the hydrocarbon possible. Biologically, there is nothing you can do with it without stripping off the excess hydrogen. Once you’ve done that, it’s a much more conventient source of carbon than carbon dioxide, wich is incredibly hard to reduce to complex organics. But the process still requires energy, which makes it an autotroph, ecologically a producer, and therefore…a plant.
Animals would breathe hydrogen and exhale methane, ammonia, and water. These have a terrestrial equivalent in the methanogenic bacteria, which would very likely be much more successful if free hydrogen were more abundant and they weren’t poisoned by oxygen.
The other possibility that occurs to me is that “methane breather” could be a misnomer, and they would actually be breathing the hydrogen mixed in with a mostly methane atmosphere, in the same way that oxybreathers live off the oxygen in a mostly nitrogen atmosphere.
Animals breathe oxygen (the rest of the air doesn’t matter) and add hydrocarbons (sugars) to make energy, exhaling CO2. The get the sugars from plants which fix hydrocarbons and expel oxygen.
Now suppose the plants fix oxygen and expel hydrocarbons. Now animals eat the fixed oxygen and breathe the hydrocarbon (methane).
Yet another county heard from….
You don’t need to fix oxygen, but I agree with Walt’s general point- they may well be fixing their carbon from the atmosphere, but why are we assuming they don’t obtain the energy needed to do so from food? We haven’t heard about them having any sunlight requirements, and one would need to perform an awful lot of photosynthesis to move around like an animal… Plus the tc’a at least have mouths.
Perhaps “fix” is the wrong term: Chemistry was long ago. Make into a solid, as hydrogen is made into a solid in forming hydrocarbons. Breathe the gas, eat the solid, and combine to generate energy.