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 Post subject: Re: Hard Space
PostPosted: Wed Jun 15, 2016 1:15 pm 
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Golan2072 wrote:
A question about constant acceleration - what do you do when in orbit? Can you stay in orbit and still keep constantly accelerating?
It's dynamically possible -- think about swinging a bucket of water on a rope, with acceleration taking the place of the force on the rope. Your orbital period will be shorter, as if the world's gravity were actually gravity+acceleration. It might be a useful tactic for (e.g.) getting more frequent passes by orbital fire support over a battlefield.


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 Post subject: Re: Hard Space
PostPosted: Wed Jun 15, 2016 7:23 pm 
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thrash wrote:
Golan2072 wrote:
A question about constant acceleration - what do you do when in orbit? Can you stay in orbit and still keep constantly accelerating?
It's dynamically possible -- think about swinging a bucket of water on a rope, with acceleration taking the place of the force on the rope. Your orbital period will be shorter, as if the world's gravity were actually gravity+acceleration. It might be a useful tactic for (e.g.) getting more frequent passes by orbital fire support over a battlefield.

Very interesting... I was also thinking about tethering the ship to a weight launched to a certain distance from it and rotating it, as I recall reading about it somewhere. Would this work?

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 Post subject: Re: Hard Space
PostPosted: Wed Jun 15, 2016 7:31 pm 
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Golan2072 wrote:
A question about constant acceleration - what do you do when in orbit? Can you stay in orbit and still keep constantly accelerating? Otherwise instead of constant acceleration, you will need spin habitats which will greatly complicate the deckplans.


Technically, you're always accelerating while in orbit. Acceleration is change in velocity, and velocity is always changing while in orbit because it's a vector and the direction of motion is changing.

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 Post subject: Re: Hard Space
PostPosted: Wed Jun 15, 2016 7:34 pm 
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My thought about worlds - in this kind of setting, Governments and even Law Levels are less important than in "standard" Traveller, especially in the official colonies - as typical corporate outposts and colonies with Earth governments' "Flags of Convenience" tend to have similar regimes, which rarely have sweeping powers (if at all) outside the small settled area, while inside the settled area they tend to be relatively restrictive. Unofficial colonies outside of the main frontier tend to be more chaotic, but rarely have the variance in government seen in "standard" Traveller universes. What is more important, socially speaking, is what Generation the colony is -i.e. established 1st Generation world, intermediate 2nd Generation colony or a new, barely-settled, barely-explored 3rd Generation colony; and whether or not it is an Outpost - a tiny base on an otherwise uninteresting and/or uninhabitable world used for transit and possibly exploration - or a fully-fledged colony. The presence of Visitation Zones and Research Stations is also highly important...

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 Post subject: Re: Hard Space
PostPosted: Wed Jun 15, 2016 9:22 pm 
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Golan2072 wrote:
Very interesting... I was also thinking about tethering the ship to a weight launched to a certain distance from it and rotating it, as I recall reading about it somewhere. Would this work?
That's essentially the same as having a rotating hull section, only the entire ship+tether+weight is the rotating section. Just remember that the assembly rotates around its center of mass, so you either need a weight comparable to the mass of the ship or a very long tether to get a reasonably long rotation arm and correspondingly low rate of rotation at the ship. Details of deployment -- reeling out the tether and spin-up/spin-down -- are usually complicated, and may argue against using this for short (<~weeks) durations.


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 Post subject: Re: Hard Space
PostPosted: Thu Jun 16, 2016 2:27 pm 
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Golan2072 wrote:
Heavy freighters usually travel from high port to high port - as loading an unloading with shuttles could be unwieldy - and thus rarely appear on the frontier.


Depending on how common starships are in your universe, large freighters might be pretty common nevertheless.

In my 2300-style hard sci-fi universe, a supply freighter would have its cargo containers on the outside, attached to a central spine (like the Mammoth-class from 2300AD ... very vaguely like kernels on an ear of maize). Adapting my concept for a Jump universe, the freighter would jump in, make for orbit ... then simply drop the containers in a geostationary orbit around the planet, then burn for 100D and jump out. Reaction mass is precious in my universe, so the freighter actually "slingshots" using a combination of local bodies and solar sails to correct its velocity from the previous system it was in to the new one. It times its closest point carefully so it is practically right over the colony to drop off containers. The containers have thrusters and enough reaction mass (or possibly solar sails, we're in the life zone after all) to put them into the orbit if the freighter drops them off at the right point. The freighter never stops - it uses its velocity and course to gravity whip itself out of the gravity of the world in an outbound corse where it'd where it'd jump out once it hit 100D again. Meanwhile the orbit the containers are in would be stable enough for a few months. The natives can send up their to-orbit craft to grab the containers as local resources allow.

This works pretty well in a universe where ships aren't all that common - there's no perceived danger of "looters" simply showing up and absconding with the containers before the colonists can retrieve them (of course, economic realities might also make it pointless abscond with containers anyway). The colonists, if they have exports, would use a catapult system to shoot items into space (assuming colonists basically only have bulk goods like grain or beef or refined metals) which again would be in geostationary orbit over a set pickup point for the freighter to pick up even as it drops off the containers.

In a universe where there's sufficient numbers of ships for there to be ships in private hands with less-than-reputable types who might lurk around in a system waiting for cargo containers. They don't have to hide. They can obnoxiously sit up there in orbit in plain sight "camping" the planet like it was an MMORPG - the pirates could shoot likely shoot down any armed shuttles or whatever the colonists send up (and colonists are unlikely to have defensive satellites or anything). However, the pirates know attacking the colony itself would be suicide - maybe literally or figuratively. For the same reason attacking the freighter itself would be counter-productive - they just want to skim a bit off the top, not kill frontier trade or actually kill people which would probably make the navy (or navies) do something about it. Provided they just obnoxiously wait around for the freighter to unload, then wait until the freighter is on its way to scoot in and take a few containers, then leave the rest to the colonists, then jump out themselves. Everyone but the pirates will be really angry, but the naval response might be pretty lukewarm since nobody is directly killed or kidnapped.

However, in such a universe, it's more likely the cargo containers would actually be a kind of one-way dead glider. It'd wait in orbit until the landing pad on the surface transmits the proper challenge/reply then it'd let itself be programmed from ground control for a proper re-entry path (this lets the onboard computers be very basic, as well as the avionics on the glider could be cheap and basic). The container-shuttle would have enough reaction fuel to push it into a proper re-entry path, then it'd glide in the rest of the way like a dead glider. The glider would be made just capable enough to land the supplies (it'd be likely the landed glider could then be broken down for basic construction materials or disassembled, boxed up and sent up again by catapult to be picked up by the next freighter to be reused - but chances are they'd just be broken down on the surface to be recycled, so they'd probably be made of metals that can be melted down and reused instead of plastics or other synthetic materials that cannot be recycled easily). More exotic methods might be used involving steerable parachutes or even a lighter-than-air system that would slowly lower the containers to the surface as well. Inclement weather on the landing area might make landing hazardous so again, the containers could wait in orbit until ground control signals them to come in.


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 Post subject: Re: Hard Space
PostPosted: Thu Jun 16, 2016 5:06 pm 
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If reaction mass it so precious and depending on how to do residual velocity with Jump, there could be a Transfer Station located at the 100D limit, so the big boys don't even have to move into orbit. Then the Transfer Station puts the Modules/Pods into orbits as desired by the world.

On a very busy world, there could be a LOT of modules floating around and ships would be limited to specific entry/exit paths to avoid those floaters.

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 Post subject: Re: Hard Space
PostPosted: Thu Jun 16, 2016 8:40 pm 
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Epicenter and Cyborg IM1 - I love these ideas! Will definitely include them in this setting...

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 Post subject: Re: Hard Space
PostPosted: Fri Jun 17, 2016 2:18 am 
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Cyborg IM1 wrote:
If reaction mass it so precious and depending on how to do residual velocity with Jump, there could be a Transfer Station located at the 100D limit, so the big boys don't even have to move into orbit. Then the Transfer Station puts the Modules/Pods into orbits as desired by the world.

On a very busy world, there could be a LOT of modules floating around and ships would be limited to specific entry/exit paths to avoid those floaters.


The idea is that solar systems have different angular velocity to each other. I think the moment you get rid of reactionless thrusters, reaction mass will be precious and the 500-pound gorilla lurking in the room of space travel. A high mass ship like a megafreighter probably wants to maintain a certain velocity at all times. They'd run "circuits" of systems (maybe three or more systems), chosen for their distance (a factor in Jump) and their relative angular velocities to each other (a factor in accelerating).

The moment freighter jumps in, it's already moving with an eye towards matching its velocity to the delivery planet but this is a compromise - it also has to be planning for the angular velocity of the next system it is going to visit. All will is pretty much bent towards having the cargo ship spend as little time in the system as possible since time is money and easing its trip to the next system down, utilizing things like gravity slinging and solar sails to reduce reaction mass usage. I don't see the big freighters ever "stopping" at a transfer station; all transfers of cargo and even personnel are done while the freighter is hurtling through the system by lighters that match the velocity (with some "slowing" by the freighter). Since the frieghters are ramjet designs (again, they're not ramscoops - they don't use the stuff they scoop for fusion reactions and thrust to approach some % of lightspeed or whatever) - refilling reaction mass would actually be done by droneships releasing a "cloud" of the relevant gas in the path that the freighter will take, then the freighter activating its scoop when it flies through the cloud; because not every system would have the infrastructure to do this, it can only be done in more advanced systems, they'd have reserves of reaction mass for systems without it so they could visit systems without such services.

Since a system like this is going to have a certain slack, the cargo containers would be capable of their own course corrections and velocity matching to the target planet. The more capable the cargo containers are of course corrections and adjusting their own velocity, the less space they have for cargo and the more expensive the containers are, so there's a trade-off there as well - they'd probably use a combination of "thrusters" and solar sails to match velocity. Of course, as you said, instead of matching the planet, more advanced systems might have a transfer station whose job is to "catch" the cargo containers, greatly increasing the profitability of cargo hauling since those systems could use very basic cargo containers, likely thrown in the direction of a gigantic dispersed magnetic accelerators which would "catch" the containers and slowly match their velocity to the accelerator, at which point lighters could pick up the containers and fly them to their destination or whatever.

Setting up flight paths like this would be complex and painstaking, involving precise measurements of angular velocities and orbits of multiple bodies in multiple star systems. Then the freighters themselves would be very tightly run ships. The crews of such ships dealing with endless problems that'd crop would be the subject of countless documentaries about "marvels of our modern age" on vids ("However, because the pods for New Jerusalem have leaked their reaction mass due and Captain Sanchez can't spare them from the Lumiere's tanks to refill them, the crew have a discussion about what they can do about it. The last resort, of course, is for the pods to be jettisoned, but she is well aware that inside the pods of tons of goods, correspondence, the lifeline between worlds, so she's reluctant to do this. Master Chief Wu has a suggestion - by angling the ship's solar sails, they can make the entire freighter spin on its axis. By using the unloading arms extended out to their full 100 meter length, they could "pitch" the pods like a baseball pitcher to the awaiting station. Wu's preliminary numbers look good...")


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 Post subject: Re: Hard Space
PostPosted: Fri Jun 17, 2016 1:19 pm 
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Quite true.

If you are using a 2-D Traveller style map, then perhaps a simplification of the relative velocity equation would be to roll 1D for the hex face that the system is travelling towards and another 1D for relative velocity. This is a gross simplification and ignores the fact that most systems are generally moving together around the galactic core and large groups of systems tend to travel together, but it might be interesting. Each die point of velocity represents 1 G-day of acceleration (making this up at the top of my head)

You could have what appears to be a well situated system that is almost never visited because it is travelling the opposite direction (and very fast) compared to other nearby systems (I'm looking at you Barnard's Star!).

If that is too random for you, use a 2D table with the 6-8 values all being the same hex direction (a more rational approach).

Systems that are moving in the same direction at almost the same velocity will naturally attract additional trade.

It gets complicated, but the Hex-Velocity value becomes just another entry on the UWP line (along with trade codes etc.).

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