I was going back through Space Stations and after some thinking, I started scratching my head in regards to the implementation of docking arms. After further review I think it's not a logical construct.
For those that have not seen Supplement 14, here's the primary description of what docking arms are, and what they do:
Docking Arms
External arms which connect to the vital feeds on a starship, docking arms do not allow for the transfer of cargo or passengers without the use of shuttle craft. They do allow for a ship to refuel and for atmosphere to be exchanged. Each ton of docking arms allows 20 tons of starship to dock.
For example, a ship with 200 tons of docking space could only dock a 100 ton starship. However it would only take 5 tons worth of docking arms to dock the same vessel.
Conceptually I have no issue with it or them. It's a space-equivalent of a cowboy tying up his horse to the rail outside a saloon that also has a water trough. Your horse (ship) isn't going anywhere and while it's just standing there it can get a drink (fuel and atmosphere). But it's still limiting, as you have to take your horse back to the livery stable to get fed. The space equivalent means you need a shuttle to get to the station (unless you plan on floating across in your ship).
So here are my specific issues:
(1) The tonnage scaling makes no real sense. One ton of docking arm allows for 20 tons of ship. The designer part of me is a big fan of percentages and scaling. So a scoutship can 'dock' at a 5ton addition and get fuel. A 5,000 ton freighter can 'dock' at a 250ton addition. But after a certain point it stops making sense. One could argue that the larger docking arms are necessary because of the added mass of a ship, and the increased need for larger pipes to pump larger quantities of hydrogen, except that doesn't quite work out. As long as the ship is stationary smaller docking arms should be more than adequate to keep the ship attached in in place. We can make cables today that can hold massive amounts of weight that also have to deal with stresses that aren't present in space. As for the size of the fuel pipe, that, too, gets to be ridiculous because fluid engineers will tell you that you don't build pipes that large to pump more fuel. You increase the pressure/flow to pump faster. Not to mention that if you had a huge diameter pipe on the station your flow is going to be limited by your internal piping - which will always be smaller due to the need to squeeze every cubic centimeter of useful space out of a spacecraft. The only logical reasoning I can find to make them so big is to physically extend the arm away from the station.
(2) The operation of a docking arm doesn't make a lot of sense either. Today, at airports we have planes that will park away from a jetway (assuming there is one). Buses with passengers will come to the aircraft. Fuel trucks will drive out to refuel, and cargo too will be loaded externally on the aircraft. So a ship, once it arrives and is on-station, could also be serviced in such a manner. And it would have to if any cargo or passengers needed to be exchanged. It would be just as easy to have the transfer lighter/shuttle that delivers or picks up people and goods to bring fuel too.
(3) The book gives a chart of docking fees. Technically a ship docked externally via a docking arm is assumed to be docked, just the same as a ship that is inside a hangar. The problem here is that the fee for docking is the same, whether you are internal or external. External docking is far and away a much less useful state to be in. Yet the pricing for docking doesn't reflect this. It would probably be cheaper to just take up station a few kilometers away and use a small craft to access the station. This would save you the docking fee and it's what you would need to do anyway if you wanted to board the station.
(4) Docking arms take up their full tonnage as part of a stations overall tonnnage. That, too, doesn't make sense really. They are protrusions away from the station and have no access points other than fuel/atmosphere connections. There is no corridor, and even if we were to assign SOME tonnage to anchoring them to the hull and providing pumps and piping, the scalar model breaks very quickly. To hold a 5,000 ton freighter in place should really take no more space than to hold say a 500 ton ship. The tensile strength of the hull materials is more than sufficient, as would be a relatively small set of pumps to transfer hydrogen. So while you could rate a docking arm for larger tonnages, there should be no need to add actual tonnage once you reach a certain plateau. Each plateau could be rated for ships UP TO a certain size, and then you'd use the next size up.
When I first heard about the concept behind docking arms I thought we were talking about space jetways, which would be extended from the station, perhaps along arms or corridors, that would allow people to leave via the ships airlock and walk onboard the station. Instead of a large hangar (with the 30% overage in required displacement) you could make a space station to operate much more like an airport, with the long arms of docking areas radiating out from a central area. Ships without large amounts of cargo would be able to dock and the crew/passengers board the station. This would still allow a station to service a larger number of vessels AND allow easy egress to/from the ship. You could even have 'passenger' and 'freight' designated arms, such that the 'freight' arm is large enough to allow the loading/unloading of bulk cargo and containers in a sealed atmosphere environment. Hangars would still be needed, but routine docking and servicing could be accomplished via this concept.
It would be simple enough conceptually to also add in fueling (and even atmosphere) connections to the jetway so that the ship would be able to load and unload while taking on fuel at the same time. As they are listed, docking arms are really nothing more than fueling stations. And if they were listed as such (with the appropriately smaller charge) then they would make perfect sense.
Does anyone else see things this way? How would you treat them? Do you think that docking arms missed the conceptual boat?
For those that have not seen Supplement 14, here's the primary description of what docking arms are, and what they do:
Docking Arms
External arms which connect to the vital feeds on a starship, docking arms do not allow for the transfer of cargo or passengers without the use of shuttle craft. They do allow for a ship to refuel and for atmosphere to be exchanged. Each ton of docking arms allows 20 tons of starship to dock.
For example, a ship with 200 tons of docking space could only dock a 100 ton starship. However it would only take 5 tons worth of docking arms to dock the same vessel.
Conceptually I have no issue with it or them. It's a space-equivalent of a cowboy tying up his horse to the rail outside a saloon that also has a water trough. Your horse (ship) isn't going anywhere and while it's just standing there it can get a drink (fuel and atmosphere). But it's still limiting, as you have to take your horse back to the livery stable to get fed. The space equivalent means you need a shuttle to get to the station (unless you plan on floating across in your ship).
So here are my specific issues:
(1) The tonnage scaling makes no real sense. One ton of docking arm allows for 20 tons of ship. The designer part of me is a big fan of percentages and scaling. So a scoutship can 'dock' at a 5ton addition and get fuel. A 5,000 ton freighter can 'dock' at a 250ton addition. But after a certain point it stops making sense. One could argue that the larger docking arms are necessary because of the added mass of a ship, and the increased need for larger pipes to pump larger quantities of hydrogen, except that doesn't quite work out. As long as the ship is stationary smaller docking arms should be more than adequate to keep the ship attached in in place. We can make cables today that can hold massive amounts of weight that also have to deal with stresses that aren't present in space. As for the size of the fuel pipe, that, too, gets to be ridiculous because fluid engineers will tell you that you don't build pipes that large to pump more fuel. You increase the pressure/flow to pump faster. Not to mention that if you had a huge diameter pipe on the station your flow is going to be limited by your internal piping - which will always be smaller due to the need to squeeze every cubic centimeter of useful space out of a spacecraft. The only logical reasoning I can find to make them so big is to physically extend the arm away from the station.
(2) The operation of a docking arm doesn't make a lot of sense either. Today, at airports we have planes that will park away from a jetway (assuming there is one). Buses with passengers will come to the aircraft. Fuel trucks will drive out to refuel, and cargo too will be loaded externally on the aircraft. So a ship, once it arrives and is on-station, could also be serviced in such a manner. And it would have to if any cargo or passengers needed to be exchanged. It would be just as easy to have the transfer lighter/shuttle that delivers or picks up people and goods to bring fuel too.
(3) The book gives a chart of docking fees. Technically a ship docked externally via a docking arm is assumed to be docked, just the same as a ship that is inside a hangar. The problem here is that the fee for docking is the same, whether you are internal or external. External docking is far and away a much less useful state to be in. Yet the pricing for docking doesn't reflect this. It would probably be cheaper to just take up station a few kilometers away and use a small craft to access the station. This would save you the docking fee and it's what you would need to do anyway if you wanted to board the station.
(4) Docking arms take up their full tonnage as part of a stations overall tonnnage. That, too, doesn't make sense really. They are protrusions away from the station and have no access points other than fuel/atmosphere connections. There is no corridor, and even if we were to assign SOME tonnage to anchoring them to the hull and providing pumps and piping, the scalar model breaks very quickly. To hold a 5,000 ton freighter in place should really take no more space than to hold say a 500 ton ship. The tensile strength of the hull materials is more than sufficient, as would be a relatively small set of pumps to transfer hydrogen. So while you could rate a docking arm for larger tonnages, there should be no need to add actual tonnage once you reach a certain plateau. Each plateau could be rated for ships UP TO a certain size, and then you'd use the next size up.
When I first heard about the concept behind docking arms I thought we were talking about space jetways, which would be extended from the station, perhaps along arms or corridors, that would allow people to leave via the ships airlock and walk onboard the station. Instead of a large hangar (with the 30% overage in required displacement) you could make a space station to operate much more like an airport, with the long arms of docking areas radiating out from a central area. Ships without large amounts of cargo would be able to dock and the crew/passengers board the station. This would still allow a station to service a larger number of vessels AND allow easy egress to/from the ship. You could even have 'passenger' and 'freight' designated arms, such that the 'freight' arm is large enough to allow the loading/unloading of bulk cargo and containers in a sealed atmosphere environment. Hangars would still be needed, but routine docking and servicing could be accomplished via this concept.
It would be simple enough conceptually to also add in fueling (and even atmosphere) connections to the jetway so that the ship would be able to load and unload while taking on fuel at the same time. As they are listed, docking arms are really nothing more than fueling stations. And if they were listed as such (with the appropriately smaller charge) then they would make perfect sense.
Does anyone else see things this way? How would you treat them? Do you think that docking arms missed the conceptual boat?
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