Starship Hull design

Discuss the Traveller RPG and its many settings
h1ro
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Re: Starship Hull design

Postby h1ro » Thu May 25, 2017 6:56 pm

OT: Nobby, can I draw your attention to a question about contra grav (or whatever you want to call it) and ships in orbit I posed over in this thread please?

Re the thread, given that we're talking about a game set centuries in the future with tech that is, well, magical, it's kinda hard to make comparisons with current tech, it's even more difficult to talk about the economical side of things as to the best of my knowledge, it's never been fully developed to the point where you could cost out things like this. I'm kinda happy with that, I take a pass on "Accountants in Space".
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Re: Starship Hull design

Postby phavoc » Thu May 25, 2017 9:14 pm

Nobby-W wrote:
Thu May 25, 2017 6:24 pm
You're back to the straw man argument. I'm not talking about using rockets for anything. I was originally discussing shipping the parts from a third-party shipyard and assembling them at the destination.
Well, not intentionally. I think we are in agreement here.
Nobby-W wrote:
Thu May 25, 2017 6:24 pm
It feels like you are arguing semantics. You talk about a lighter. I talk about a heavy lift shuttle or a freighter to ship to the destination.
Not trying to argue semantics here. The idea of a cargo lighter is one that I haven't seen in any of the books. Lots of ships and enclosed vessels, but nothing that resembles a flying flat bed. One has to assume they exist as special-use engineering vehicles, but I've yet to see any canon materials mention them.
Nobby-W wrote:
Thu May 25, 2017 6:24 pm
Apart from my view that the best place to build the parts for a space station would be an established shipyard that employed engineers familiar with the process, I don't see how this is materially different from what I discussed above.
Perhaps it isn't. I think we can move on from this one.
Nobby-W wrote:
Thu May 25, 2017 6:24 pm
That's not how this works. That's not how any of this works. Orbital velocity on Earth is around 7000m/sec. You don't just float up to 200km and park there - you need a substantial horizontal velocity for the station to remain in orbit. Go play a bit of KSP and learn something about orbital mechanics. It's quite cheap - about £30 - but if you have the patience to wear the learning curve it's a very rewarding game. I'd be happy to bet Cr50 that you will have an aha! moment if you do that.
I'm not going to claim to be a master at orbital mechanics, but I think you are missing something in my argument. Your argument is based upon standard orbital mechanics - that is you need to expend energy, sometimes a great deal, to change your orbit. A rocket needs to enter into a transfer orbit to 'rise' in a gravity well. If you don't have to worry about gravity, which a contragravity vehicle does not, then you would indeed simply go straight up to your desired orbital plane and deposit your cargo. Since we are just talking in generalities here, let's assume the station in question is in geostationary orbit. That makes it easier to deal with. If we were in geosynchonous orbit the argument would be potentially more complex.

Using contragravity to get to your desired orbital plane is no different than using a beanstalk. The counterweight at the orbital end of the beanstalk will have a lot of energy available to transfer to any item or vehicle based on planetary rotation, but it's also relative to the station itself. Orbital mechanics are pretty complicated, but everything we do with them today is because we are mass and energy limited in our space vehicles. With no need to create transfer orbits (Hohmann Transfer orbits), or worry about equatorial effects, using polar orbits, etc, getting where you want to go is much easier. KSP utilizes existing physics, not the special magical physics of the world of contragravity. It's not cheating gravity, it's just ignoring it (and all the other stuff you have to deal with when you can't ignore it).
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Re: Starship Hull design

Postby h1ro » Thu May 25, 2017 9:34 pm

phavoc wrote:
Thu May 25, 2017 9:14 pm
Using contragravity to get to your desired orbital plane is no different than using a beanstalk. The counterweight at the orbital end of the beanstalk will have a lot of energy available to transfer to any item or vehicle based on planetary rotation, but it's also relative to the station itself. Orbital mechanics are pretty complicated, but everything we do with them today is because we are mass and energy limited in our space vehicles. With no need to create transfer orbits (Hohmann Transfer orbits), or worry about equatorial effects, using polar orbits, etc, getting where you want to go is much easier. KSP utilizes existing physics, not the special magical physics of the world of contragravity. It's not cheating gravity, it's just ignoring it (and all the other stuff you have to deal with when you can't ignore it).
OK, this is where we're crossing over with the thread I referenced above.

The confusion comes from the idea that maintaining an orbit relies on orbital speed. I get the space elevator/beanstalk thing but you're crossing from one to the other and that requires the craft to accelerate. Now, OK, the contra grav thing is gonna change things but if you're then transitioning to an orbit as we know satellites do now, you need orbital velocity to do that.
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Re: Starship Hull design

Postby phavoc » Thu May 25, 2017 10:36 pm

h1ro wrote:
Thu May 25, 2017 9:34 pm
phavoc wrote:
Thu May 25, 2017 9:14 pm
Using contragravity to get to your desired orbital plane is no different than using a beanstalk. The counterweight at the orbital end of the beanstalk will have a lot of energy available to transfer to any item or vehicle based on planetary rotation, but it's also relative to the station itself. Orbital mechanics are pretty complicated, but everything we do with them today is because we are mass and energy limited in our space vehicles. With no need to create transfer orbits (Hohmann Transfer orbits), or worry about equatorial effects, using polar orbits, etc, getting where you want to go is much easier. KSP utilizes existing physics, not the special magical physics of the world of contragravity. It's not cheating gravity, it's just ignoring it (and all the other stuff you have to deal with when you can't ignore it).
OK, this is where we're crossing over with the thread I referenced above.

The confusion comes from the idea that maintaining an orbit relies on orbital speed. I get the space elevator/beanstalk thing but you're crossing from one to the other and that requires the craft to accelerate. Now, OK, the contra grav thing is gonna change things but if you're then transitioning to an orbit as we know satellites do now, you need orbital velocity to do that.
Currently maintaining an orbit does require speed because we are subject to the laws of orbital mechanics. And changing orbits using velocity is required because you are still subject to gravity, thus you must expend energy to change your orbit. But if you can cheat gravity by using contragravity then many other things become possible. Getting to orbit becomes easy. Now do keep in mind that the type of orbit you want to do might affect the discussion (this is why I don't claim to be an orbital mechanic expert). An object in geosynch orbit is travelling about 7k mph or so, which is the equivalent speed of the patch of ground beneath it. Another example to get to orbit going (relatively) straight up is a balloon. The balloon's make it up to about 20 miles, but at that height the gas (usually helium) weighs the same as the surrounding atmosphere. Plus expansion and the balloons pop... But you are going up like you would with contragravity. However contragravity would continue to work up to the edge of the your local planetary gravity well.
h1ro
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Re: Starship Hull design

Postby h1ro » Thu May 25, 2017 11:52 pm

Hmm...

Here's my poorly educated take on it.

Everything is orbiting something. The moon orbits the Earth, the Earth orbits the Sun, the Sun orbits the galactic centre. Everything is moving, quickly. Orbiting is all about gravity. If you take away the effect of gravity will you simply fly off into space? Well, no as you have movement/velocity that's been shared with you by the planet or thing that you are on.

At some point tho, if you choose to not obey the rules of gravity/orbiting, you're gonna get left behind in space, because, everything is moving and you're choosing to not move with it.

If, when floating up away from the surface of a planet, you choose not to attain a velocity which will allow you to orbit the planet, you're gonna just float off into space.

Agree?
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Re: Starship Hull design

Postby Nobby-W » Fri May 26, 2017 12:54 am

phavoc wrote:
Thu May 25, 2017 9:14 pm
I'm not going to claim to be a master at orbital mechanics, but I think you are missing something in my argument. Your argument is based upon standard orbital mechanics - that is you need to expend energy, sometimes a great deal, to change your orbit. A rocket needs to enter into a transfer orbit to 'rise' in a gravity well. If you don't have to worry about gravity, which a contragravity vehicle does not, then you would indeed simply go straight up to your desired orbital plane and deposit your cargo. Since we are just talking in generalities here, let's assume the station in question is in geostationary orbit. That makes it easier to deal with. If we were in geosynchonous orbit the argument would be potentially more complex.
The orbital velocity of a geostationary orbit is considerably faster than ground speed at the equator. If you do what you say, then the station will fall back to ground the minute you turn the CG off. Beanstalks work by having a counterweight sitting outside GEO to provide centrifugal force that keeps the beanstalk held up.

I'll leave it to the late James Doohan to sum this up: https://www.youtube.com/watch?v=nfZ12UGiisM&t=22
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Re: Starship Hull design

Postby Condottiere » Fri May 26, 2017 1:41 am

What's the advantage of a beanstalk in a universe full of anti gravity vehicles?

Satellites will get replaced by anti gravity drones loitering in low earth orbit.

While some people may believe that setting up their own space station or taking over an abandoned one gives them a Sealand style sovereignty, they will be sadly mistaken.

Because of space traffic, such facilities are likely to be limited and restricted; legacy stations are likely sent to the breakers, and a new one established.
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Re: Starship Hull design

Postby phavoc » Fri May 26, 2017 1:46 am

h1ro wrote:
Thu May 25, 2017 11:52 pm
Hmm...

Here's my poorly educated take on it.

Everything is orbiting something. The moon orbits the Earth, the Earth orbits the Sun, the Sun orbits the galactic centre. Everything is moving, quickly. Orbiting is all about gravity. If you take away the effect of gravity will you simply fly off into space? Well, no as you have movement/velocity that's been shared with you by the planet or thing that you are on.

At some point tho, if you choose to not obey the rules of gravity/orbiting, you're gonna get left behind in space, because, everything is moving and you're choosing to not move with it.

If, when floating up away from the surface of a planet, you choose not to attain a velocity which will allow you to orbit the planet, you're gonna just float off into space.

Agree?
I wouldn't say that is the case at all. If it where, when you engaged your contragravity at the surface the planet would rotate underneath you, and the entire mechanism around contragravity would be quite complicated and using contragravity anything would be a huge pain in the ass with all the added complexity of having to ensure your anti-gravity field remains constant in relative terms. While it's just fictional it makes it a lot easier to just neutralize the local pull of the gravity well, thus you go 'up' and 'down' relative to the field. For vehicles that utilize contragravity for movement you'd need two fields - one to counteract and allow for horizontal movement, and one to counteract and allow for vertical movement. If you take it from that approach vehicles work, things don't fly off and it's a simplified model that works well for gaming purposes.
Nobby-W wrote:
Fri May 26, 2017 12:54 am
The orbital velocity of a geostationary orbit is considerably faster than ground speed at the equator. If you do what you say, then the station will fall back to ground the minute you turn the CG off.

https://www.youtube.com/watch?v=nfZ12UGiisM&t=22
Ah, Mr. Scott, may he rest in peace. So I did some digging and you are correct Nobby. Orbital speed at the surface of Earth at the Equator is about 1,700kph, and at geosynch orbit is about 11,000kph. The greater speed is required to maintain the same orbital radius as the ground beneath. So I suppose the question then would be how to boost your angular velocity as you went vertical. Your angular velocity to be less than the planet, but would the contragravity field allow you to cheat that and stay in relative position, thus essentially taking on the same angular velocity at any point in your trajectory? Then if you turned off the field you'd still be in the same location relative to where you ascended from.
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Re: Starship Hull design

Postby phavoc » Fri May 26, 2017 1:49 am

Condottiere wrote:
Fri May 26, 2017 1:41 am
What's the advantage of a beanstalk in a universe full of anti gravity vehicles?

Satellites will get replaced by anti gravity drones loitering in low earth orbit.

While some people may believe that setting up their own space station or taking over an abandoned one gives them a Sealand style sovereignty, they will be sadly mistaken.

Because of space traffic, such facilities are likely to be limited and restricted; legacy stations are likely sent to the breakers, and a new one established.
Using anti-gravity to ascend the beanstalk faster means you have orbital access without ships. For bulk freight (say the planet is a farming paradise - that means you could export grain with little cost to get to orbit). For passengers or anything time sensitive it's not as effecient as a ship, but for bulk you can't beat the price (aside from the cost of the beanstalk in the first place).
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Re: Starship Hull design

Postby h1ro » Fri May 26, 2017 1:49 am

Condottiere wrote:
Fri May 26, 2017 1:41 am
What's the advantage of a beanstalk in a universe full of anti gravity vehicles?
In Traveller? None.

Circumstances where they may have an advantage?

Where the cost of anti grav tech is greater than the cost of the materials and construction of the bean stalk. Or where the AG tech is reliant on a resource or such that is rare.

Where anti grav tech is described as having a reduced effect in micro gravity so that anti grav will only get you to X altitude.
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Re: Starship Hull design

Postby Condottiere » Fri May 26, 2017 1:52 am

You still have to transport the goods to the base of the beanstalk.

I assume the beanstalk would be a massive capital outlay, whereas anti gravity vehicles would be the equivalent of semi trailer trucks.
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Re: Starship Hull design

Postby h1ro » Fri May 26, 2017 1:59 am

Condottiere wrote:
Fri May 26, 2017 1:52 am
You still have to transport the goods to the base of the beanstalk.
That's true of most things, it's true that if you can lift to orbit from anywhere on the surface of a planet with a ship then there's a greater chance of a highly distributed network of space ports, if you needed them at all. I could tho see heavy restrictions on space craft operations in atmospheres. Things being what they are, there will be accidents and with larger ships then damage or casualties could be high. Of course, Google might have perfected remotely piloted vehicles by then with an impeccable safety record but as we're talking about Traveller, we can ignore that kind of thing!
Condottiere wrote:
Fri May 26, 2017 1:52 am
I assume the beanstalk would be a massive capital outlay, whereas anti gravity vehicles would be the equivalent of semi trailer trucks.
In Traveller terms it's true to say that AG tech has been around for a very long time and so the original investment to develop the tech has been long since forgotten but that could be the same for bean stalks.
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Re: Starship Hull design

Postby phavoc » Fri May 26, 2017 2:01 am

The cost of a beanstalk is an interesting question. Assuming you could build one out of carbon nano tubes, and you could build them cheap enough, it might be hundreds of millions of credits. But it's a fixed capital cost, so depending on your costs per ton (and your overall tonnage) to lift cargo to orbit it could pay for itself after some period. Like any capital outlay you can spread it's cost over a period, thus the unaffordable become affordable. But without any numbers to work with anyone's guess is just as good as another.
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Re: Starship Hull design

Postby h1ro » Fri May 26, 2017 2:13 am

phavoc wrote:
Fri May 26, 2017 1:46 am
I wouldn't say that is the case at all. If it where, when you engaged your contragravity at the surface the planet would rotate underneath you,
Remember I said that that wouldn't happen as your craft shares the velocity of the planet whose surface it's just left. At some point tho, your craft and the planet below will be going on a separate enough course to be noticed.
phavoc wrote:
Fri May 26, 2017 1:46 am
and the entire mechanism around contragravity would be quite complicated and using contragravity anything would be a huge pain in the ass with all the added complexity of having to ensure your anti-gravity field remains constant in relative terms. While it's just fictional it makes it a lot easier to just neutralize the local pull of the gravity well, thus you go 'up' and 'down' relative to the field.
Yeah, it is complicated and open to many interpretations which is why I think Mongoose don't go into detail (at all). That's fine, I like to add the detail in, especially cos I think travelling to and from and then thru space should be riskier or at least, not taken for granted!
phavoc wrote:
Fri May 26, 2017 1:46 am
For vehicles that utilize contragravity for movement you'd need two fields - one to counteract and allow for horizontal movement, and one to counteract and allow for vertical movement. If you take it from that approach vehicles work, things don't fly off and it's a simplified model that works well for gaming purposes.
I like the idea that AG tech only negates mass and that movement needs conventional thrust or reactionless M drives.
phavoc wrote:
Fri May 26, 2017 1:46 am
So I did some digging and you are correct Nobby. Orbital speed at the surface of Earth at the Equator is about 1,700kph, and at geosynch orbit is about 11,000kph. The greater speed is required to maintain the same orbital radius as the ground beneath. So I suppose the question then would be how to boost your angular velocity as you went vertical. Your angular velocity to be less than the planet, but would the contragravity field allow you to cheat that and stay in relative position, thus essentially taking on the same angular velocity at any point in your trajectory? Then if you turned off the field you'd still be in the same location relative to where you ascended from.
Did you read the aerofins thread?
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Re: Starship Hull design

Postby Condottiere » Fri May 26, 2017 2:19 am

For anti gravity, you either fall forward constantly, or you reject gravity.

For the beanstalk, the game would have to tell us the cost, and we can figure out an economic model to figure out if it's worthwhile.

The beanstalk would be unlikely to serve a region greater than a continent; once you have fusion, energy costs are negligible, but let's assume that the goods and passengers would have a monorail network anchored by the beanstalk.

Anything further away would fly, and if you fly, why not straight up?
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Re: Starship Hull design

Postby h1ro » Fri May 26, 2017 2:23 am

Condottiere wrote:
Fri May 26, 2017 2:19 am
and we can figure out an economic model to figure out if it's worthwhile
I say we go post scarcity and ignore money altogether ;) :mrgreen:
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Re: Starship Hull design

Postby Nobby-W » Fri May 26, 2017 5:38 am

phavoc wrote:
Fri May 26, 2017 1:46 am
Ah, Mr. Scott, may he rest in peace. So I did some digging and you are correct Nobby. Orbital speed at the surface of Earth at the Equator is about 1,700kph, and at geosynch orbit is about 11,000kph. The greater speed is required to maintain the same orbital radius as the ground beneath. So I suppose the question then would be how to boost your angular velocity as you went vertical. Your angular velocity to be less than the planet, but would the contragravity field allow you to cheat that and stay in relative position, thus essentially taking on the same angular velocity at any point in your trajectory? Then if you turned off the field you'd still be in the same location relative to where you ascended from.
The question I would ask is 'why bother?' If you boost the station into orbit (assembled or otherwise) then you don't need CG at all - which is safer, as your station won't crash if your power or CG fails. All editions of Traveller offer the ability to design heavy lift shuttles capable of lugging space station parts into orbit - at whatever size takes your fancy. I'll just re-iterate what I originally suggested about space stations.
  • IMHO and IMTU you would normally buy a space station from a shipyard, just like any other spacecraft. The aerospace outfit will already know how to build space stations.
  • Because the space station is not mobile it must be transported to its destination.
  • The space station would typically be composed of modules that could be manufactured at the shipyard - either on the ground or in orbit. This also makes it much easier to ship.
  • The modules are (broadly speaking) hub modules or service modules. Hub modules form the structure of the station; service modules carry facilities such as accommodation, power, or docking arms.
  • Shipping the modules to the destination is likely to be far cheaper than trying to set up some sort of local manufacturing facility. Unless you were building a lot of space stations locally (which might be the case but probably isn't) then the captial investment of local fabrication is going to be disproportionately expensive if you have to amortise it over just one or two space stations.
  • The shipyard can furnish a team of trained engineers who already know how to assemble the space station.
  • Being modular, the parts can be assembled in a variety of configurations to meet individual requirements.
  • Also, being modular, the space station can be expanded (up to a point) to meet changing requirements.
Some yards would be able to manufacture larger components for use in building large stations such as mid-high capacity high ports. These would need larger freighters to ship, which might be difficult to support in remote regions.

Whether shuttles used to lift parts off-world use AG or manoeuvre drives is a matter of semantics. For moving parts to another system - which you're up for doing unless you have a local class A or B starport anyway - you're going to need a jump-capable freighter big enough to carry the parts. This could be a jump shuttle that carries the parts externally but it doesn't necessarily have to be.

Now, if you're (for example) Trin or some other wealthy high tech world, you will probably have local shipyard and orbital construction facilities capable of building a space station. However, the same principle still applies. Somebody will build parts for the station - either on the ground or in orbit - and a team of engineers will take the parts and assemble the station. Maybe (as somebody suggested) some fraction of the parts could be fabricated in a large 3D printing device. Even Trin will find that the requirements for space stations will expand over time, and will need to add on to them.
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Re: Starship Hull design

Postby Nobby-W » Fri May 26, 2017 5:57 am

Condottiere wrote:
Fri May 26, 2017 1:41 am
Satellites will get replaced by anti gravity drones loitering in low earth orbit.
[ . . . ]
Why would you bother to do this? It makes the satellites more expensive and they need frequent re-fuelling (Per Striker or FFS, CG uses quite a lot of power). If the CG fails or they run out of fuel then your drone falls out of orbit, which makes them a safety hazard. If they're moving at orbital velocity then you don't need the CG so they're cheaper and need far less maintenance.

A pinnace worth about Cr30 million could deposit satellites in orbit, at orbital velocity, and replace and retrieve them for maintenance as needed. If (as per today's tech) the satellites could last for years in orbit then one pinnace could service an entire fleet of satellites.
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Re: Starship Hull design

Postby Condottiere » Fri May 26, 2017 8:12 pm

Electronics tend to be the big ticket item, and you can easily redirect the drone back for maintenance, or refueling.

As for endurance, one percent volume will power the drone for four weeks, and you can have constant coverage.
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Re: Starship Hull design

Postby Nobby-W » Fri May 26, 2017 8:39 pm

Condottiere wrote:
Fri May 26, 2017 8:12 pm
Electronics tend to be the big ticket item, and you can easily redirect the drone back for maintenance, or refueling.

As for endurance, one percent volume will power the drone for four weeks, and you can have constant coverage.
Pick your rule set. I could pull out material considered to be OTU canon that would imply rather lower endurance (maybe 66 hrs) on 1% of the mass. Real technology available now allows a satellite to be put up and operate for 5-10 years unattended. If you had a re-usable launch vehicle like a pinnace then a small fleet of such craft (maybe just 1-2) could service a fleet of 1,000 or so satellites at the rate of one mission every two or three days - without having to install anything more than a set of RCS thrusters and maybe a reaction wheel system on each of your birds. Feel free to have AG drones in your 'verse - it's not my place to dictate such matters - but I don't see your solution being the more economical.

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