Starship Hull design

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

Postby phavoc » Sat May 27, 2017 2:25 am

Nobby-W wrote:
Fri May 26, 2017 5:38 am
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.
It wouldn't crash at all. There is no lift in space. At a minimum it would have the angular velocity of wherever on the planet it left. The issue would be if you wanted the station to be in a specific orbit. If you didn't care where the station was then it's orbit would still be stable. The station's thrusters should be more than sufficient to keep the station in place.
Nobby-W wrote:
Fri May 26, 2017 5:38 am
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.
No, not really. It's like saying how a balloon and a plane get to 1,000 feet off the ground is the same. Arriving at the same destination is one thing, but how you get to that place is still different.
Nobby-W wrote:
Fri May 26, 2017 5:38 am
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.
I agree that many stations will end up being built with parts imported from other places, especially with smaller population, poor or low tech worlds. Those stations will be of minimal size to handle their orbital traffic, with the downports most likely being far busier than any high port station.

Exceptions to that rule would be those system with low populations or tech level that still have a Class A/B Imperial starport. Depending on distance and such it may be cheaper to build the necessary infrastructure in a system to build the starport, or at least you would bring in manufacturing ships to make the basic materials locally from asteroids or local mineral deposits and then ship in your electronics and other specialized parts that would be better suited for assembly elsewhere. There are many variations on this same theme that are reasonable and possible.
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Re: Starship Hull design

Postby phavoc » Sat May 27, 2017 2:37 am

h1ro wrote:
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.
The advantages of a beanstalk are the same sort of advantages that barges or railroads have over planes and trucks - a reduction of cost in transporting goods. In the US railroads move 300 containers at a time with only two crew and much less fuel than it would take 300 trucks to do the same. Water transport of bulk goods is the cheapest way to move something. But water doesn't go everywhere, and rails don't either.

In any of the cases listed above you have to look at the goods being transported and the overall cost of boosting 1Dton of goods to orbit. Yes, 100 modular cutters could move the same amount of cargo to orbit much faster than it would take to move the same cargo TO the beanstalk, and then UP the beanstalk. Grain doesn't care how fast it is moved, or ore or whatever. So you move it as cheap as possible.

There is also the question of people. It takes a minimum of 100 pilots for those cutters. It might only take you a dozen or so technicians (who would be far cheaper than a pilot) to oversee cargo transloading on to the beanstalk. Those ships will have definite speed advantages over a beanstalk. Never underestimate cost advantages when it comes to making choices.
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Re: Starship Hull design

Postby Nobby-W » Sat May 27, 2017 5:29 am

phavoc wrote:
Sat May 27, 2017 2:25 am
Nobby-W wrote:
Fri May 26, 2017 5:38 am
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.
It wouldn't crash at all. There is no lift in space. At a minimum it would have the angular velocity of wherever on the planet it left. The issue would be if you wanted the station to be in a specific orbit. If you didn't care where the station was then it's orbit would still be stable. The station's thrusters should be more than sufficient to keep the station in place.
Nobby-W wrote:
Fri May 26, 2017 5:38 am
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.
No, not really. It's like saying how a balloon and a plane get to 1,000 feet off the ground is the same. Arriving at the same destination is one thing, but how you get to that place is still different.
This makes no sense at all. It looks like you didn't understand what I said but I really can't either tell what you are talking about or gain any insight into either your reasoning or the point you're trying to make.
Last edited by Nobby-W on Sun May 28, 2017 6:36 pm, edited 3 times in total.
Condottiere
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Re: Starship Hull design

Postby Condottiere » Sat May 27, 2017 9:20 pm

1. Once you get power from fusion plants in Traveller, I doubt that the cost of energy is really an issue.

2. Going by current politics influenced economic policy, foreign governments/corporations will likely try to sell their space station components indigenous regimes, whereas indigenous regimes would prefer to keep the money within their own economic ecosystem and build the components themselves.

3. A beanstalk could probably be part of a continental wide automated transport delivery system, but it also provides a single point of failure.

4. Without actually knowing a game generated cost of building one, you can only guess if a beanstalk is viable.
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Re: Starship Hull design

Postby Sinanju » Sat May 27, 2017 10:44 pm

I can't really see any practical reason for building a beanstalk in an environment where antigrav and M-Drives are available, even if they have to be imported from offworld.

A lot of nations in Africa are leapfrogging over the cost and effort of stringing thousands or millions of miles of telephone line by jumping directly to cell phones. Landlines were invaluable in the development of telephone systems, but now that something better is available, why bother? It's cheaper and easier to set up cell phone repeater towers and service those than to try to maintain a network of phone lines and string lines to every home that wants a phone. It's *doable* if you really want to go to all that time and expense. But why?

Ditto for a beanstalk. If the tech exists (even if imported), you *can* build one, but why? Why not build a starport (or a series of spaceports) and use spacecraft to boost your payloads to orbit? As mentioned earlier, a beanstalk--among other potential problems--is a single source of failure. If it gets destroyed, you lose all your space travel capability. If a ship crashes, there are still plenty of others.
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Re: Starship Hull design

Postby phavoc » Sun May 28, 2017 6:29 pm

Sinanju wrote:
Sat May 27, 2017 10:44 pm
I can't really see any practical reason for building a beanstalk in an environment where antigrav and M-Drives are available, even if they have to be imported from offworld.

A lot of nations in Africa are leapfrogging over the cost and effort of stringing thousands or millions of miles of telephone line by jumping directly to cell phones. Landlines were invaluable in the development of telephone systems, but now that something better is available, why bother? It's cheaper and easier to set up cell phone repeater towers and service those than to try to maintain a network of phone lines and string lines to every home that wants a phone. It's *doable* if you really want to go to all that time and expense. But why?

Ditto for a beanstalk. If the tech exists (even if imported), you *can* build one, but why? Why not build a starport (or a series of spaceports) and use spacecraft to boost your payloads to orbit? As mentioned earlier, a beanstalk--among other potential problems--is a single source of failure. If it gets destroyed, you lose all your space travel capability. If a ship crashes, there are still plenty of others.
For your primary access to orbit a beanstalk (when you have contragravity, fusion power and M-drive) is a bad idea.

But for the same reasons we have barges and trains today a beanstalk can be an economical and practical device - cost. Moving large amounts of bulk cargo cheaply is the goal of any supply chain.
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Re: Starship Hull design

Postby h1ro » Sun May 28, 2017 6:46 pm

As a tourist thing I'd ride a beanstalk any day of the week!

I'd happily hitch a ride on a rocket or grav ship too, just saying is all!
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Re: Starship Hull design

Postby paltrysum » Mon May 29, 2017 5:16 am

Sinanju wrote:
Sat May 27, 2017 10:44 pm
Ditto for a beanstalk. If the tech exists (even if imported), you *can* build one, but why? Why not build a starport (or a series of spaceports) and use spacecraft to boost your payloads to orbit? As mentioned earlier, a beanstalk--among other potential problems--is a single source of failure. If it gets destroyed, you lose all your space travel capability. If a ship crashes, there are still plenty of others.
Just playing devil's advocate: While it's true that it makes little sense using phone lines (beanstalks) when cell phones (maneuver drives) are available, what about the fact that the a) some worlds have 1G or higher gravity, and b) probably MOST maneuver drives are 1G (just like most cars have 4- or 6-cylinder engines). While Traveller hand waves the fact that technically a 1G maneuver drive could not escape the gravity of a 1G or higher world without a feat of engineering heroism (e.g., pressing the drive to overperform), discriminating referees might take issue with that. Not everyone is going to have a 2G or higher maneuver drive. So wouldn't it make sense that a space elevator would be an alternative form of transportation on such worlds?
"Spacers lead a sedentary life. They live at home, and their home is always with them—their starship, and so is their country—the depths of space."
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Re: Starship Hull design

Postby Condottiere » Mon May 29, 2017 8:07 am

Image

Let's be fair, there's always someone who'll want to build the Burj Khalifa, or their version of it.

I could imagine one emblazoned in mile high letters with the words Trump Tower.

But pragmatically, you need to make an economic case for it, and overcome NIMBYism.
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Re: Starship Hull design

Postby Nobby-W » Mon May 29, 2017 9:02 am

paltrysum wrote:
Mon May 29, 2017 5:16 am
[ . . .]What about the fact that the a) some worlds have 1G or higher gravity, and b) probably MOST maneuver drives are 1G (just like most cars have 4- or 6-cylinder engines).
[ . . .]
A ship with airfoil surfaces (i.e. a spaceplane), could get to orbit with less than 1G of thrust - in KSP, spaceplanes with more than 1G of thrust are unusual, although you often have to hold your head just right to get the right course to get into orbit without running out of fuel. Although the original designs for the Type-A didn't have airfoil structures, the Type-R illustrations certainly do. Maybe, with a bit of handwavium, you could cast the Type-A as a lifting body. :wink:

I think, however, that the circumstances in which a J1/1G streamlined ship make sense are pretty limited. Unless you have favourable conditions like the spinward main then you might expect to see a lot more J2-J4 traffic - and the J1 traffic is likely to just be confined to those routes where a back/forth service or circuit around a cluster of worlds carries a lot of trade. Certainly relevant economically, but somewhat boring as an adventure.

From a game balance perspective, though, a J1 ship makes sense if you want to have a small setting with a couple of subsectors and run a trading sandbox game without having to roll up a whole sector. It's a sort of mechanic of convenience.
paltrysum wrote:
Mon May 29, 2017 5:16 am
So wouldn't it make sense that a space elevator would be an alternative form of transportation on such worlds?
If you want beanstalks in your 'verse then they could make sense if you have a large traffic volume - i.e. the throughput makes the capital outlay cost-effective. From a gaming perspective I don't see them as particularly interesting - Once you've done the terrorist plot to destroy the beanstalk then you've pretty much exhausted its potential as an adventure seed.

A clean, shiny, efficient high port is also a fairly boring place, but an older, decadent, seedy highport with a history and a seamy underside is somewhere with plenty of scope for adventures. Freeside from Neuromancer, Cloud City (Bespin) from the Empire Strikes Back or the mining base from Outland are a much better archetype for a space station that's fun to adventure on.
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Re: Starship Hull design

Postby AndrewW » Mon May 29, 2017 9:27 am

Nobby-W wrote:
Mon May 29, 2017 9:02 am
From a gaming perspective I don't see them as particularly interesting - Once you've done the terrorist plot to destroy the beanstalk then you've pretty much exhausted its potential as an adventure seed.
Nope, could always do the carrier stuck on the beanstalk rescue mission, have to get your ship into place and retrieve the carrier before it falls.

There's an assassin onboard but you don't know who it is.

A noble throws a party on one, of course nothing ever goes wrong at those.

Bomb in one of the carriers you have to find and disarm it before it goes off (not enough to destroy the beanstalk).

Aliens are taking people from the beanstalk and replacing them, but nobody believes you.
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Re: Starship Hull design

Postby Nobby-W » Mon May 29, 2017 9:56 am

AndrewW wrote:
Mon May 29, 2017 9:27 am
Nobby-W wrote:
Mon May 29, 2017 9:02 am
From a gaming perspective I don't see them as particularly interesting - Once you've done the terrorist plot to destroy the beanstalk then you've pretty much exhausted its potential as an adventure seed.
Nope, could always do the carrier stuck on the beanstalk rescue mission, have to get your ship into place and retrieve the carrier before it falls.

There's an assassin onboard but you don't know who it is.

A noble throws a party on one, of course nothing ever goes wrong at those.

Bomb in one of the carriers you have to find and disarm it before it goes off (not enough to destroy the beanstalk).

Aliens are taking people from the beanstalk and replacing them, but nobody believes you.
None of those are peculiar to a beanstalk, though. You could do any of them on a variety of locations, and the only one where you might actually interact with the specific characteristics of a beanstalk is the first. However, in the first example, you've also just described the plot of nearly every episode of Thunderbirds - and none of those took place on a beanstalk at all.

I know this because I am actually old and crusty enough to have watched Thunderbirds on TV and even used to have a Thunderbird 2 Dinky toy (sadly, now lost to the ravages of time, and it would never have been in a remotely collectible condition).
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Re: Starship Hull design

Postby AndrewW » Mon May 29, 2017 2:24 pm

Nobby-W wrote:
Mon May 29, 2017 9:56 am
None of those are peculiar to a beanstalk, though. You could do any of them on a variety of locations, and the only one where you might actually interact with the specific characteristics of a beanstalk is the first. However, in the first example, you've also just described the plot of nearly every episode of Thunderbirds - and none of those took place on a beanstalk at all.


Never actually watched it myself. But doing them on a beanstalk adds different elements then elsewhere. Yes they could be done elsewhere, but so could your example. Just offering up more possibilities.
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Re: Starship Hull design

Postby phavoc » Mon May 29, 2017 2:36 pm

Nobby-W wrote:
Mon May 29, 2017 9:02 am
If you want beanstalks in your 'verse then they could make sense if you have a large traffic volume - i.e. the throughput makes the capital outlay cost-effective. From a gaming perspective I don't see them as particularly interesting - Once you've done the terrorist plot to destroy the beanstalk then you've pretty much exhausted its potential as an adventure seed.

A clean, shiny, efficient high port is also a fairly boring place, but an older, decadent, seedy highport with a history and a seamy underside is somewhere with plenty of scope for adventures. Freeside from Neuromancer, Cloud City (Bespin) from the Empire Strikes Back or the mining base from Outland are a much better archetype for a space station that's fun to adventure on.
Stealing a Free Trader and crashing it into your target city while on orbital approach would be far more of a destructive act for a terrorist group. And there are millions of those lying around, and piracy is rampant in space, just look at all the armed ships. Both ideas are bit far-fetched because if both were taken to fruition then there wouldn't be star nations, just a lot of planets with smoking holes in them.

Your clean, shiny highport can be connected to that beanstalk so all that bulk cargo can travel up the beanstalk cheaply and efficiently. Not every world is going to build one, or would need one - it would take a specific need (like a breadbasket world, a manufacturing world or a mining world) that generated enough product to justify such a thing. Or, in reverse, a planet that had huge appetites for all of the above would want to efficiently bring all that down from orbit. Efficiency is what drives mercantilism and capitalism.
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Re: Starship Hull design

Postby Nobby-W » Mon May 29, 2017 6:24 pm

phavoc wrote:
Mon May 29, 2017 2:36 pm
Stealing a Free Trader and crashing it into your target city while on orbital approach would be far more of a destructive act for a terrorist group.
[ . . . ]
After the first few successful attempts, I dare say that sales of point defence weapon systems, SDBs and heavy fighters would take a marked spike. It's too obvious a movie plot threat for governments not to have to build defences against it - if only to shut up the local tabloid press.

If you're interested in the physics, the Chelyabrinsk meteor is estimated to have weighed something like 12,000 tons, and was completely vapourised when it entered the atmosphere at approximately 20km/sec. The Tunguska meteor of 1908 made a much bigger bang (estimated about 30MT), but is estimated to have been more like a million tons or so.

From this, we can infer that te-entry at 20km/sec will almost certainly vapourise a starship hull in the upper atmosphere before it does any harm, so there is a practical upper limit on how fast you could actually be travelling when you do this. If you make an assumption in the region of (say) 10km/sec, or a little over the velocity of an unpowered re-entry, you get an upper limit on how much damage can actually be done, and how long you have to respond.

At 10km/sec, the kinetic energy of a 200 ton object is equivalent to a couple of kilotons or so, enough to trash the CBD of a major city and therefore be interesting as a terror weapon.

Now, say you had a kinetic surface-air missile that could accelerate at 100g like the 1960's Sprint ABM system. In 10 sec, it could reach 10km/sec, having travelled about 50km during that 10 second burn. Setting aside the possibility of equipping it with a small nuclear warhead for the moment, a missile of that spec weighing 1 ton would have a closing kinetic energy equivalent to travelling at 20km/sec, and kinetic energy has a quadratic relationship to speed. The kinetic energy on impact would be equivalent to nearly 50 tons of TNT.

This is enough to break up the hull into fragments that will burn up harmlessly in the atmosphere.

In summary, this particular threat is somewhat overrated. Nevertheless, it won't stop the tabloid press clamouring for yet more budget for COACC SDB squadrons and stronger controls to keep tabs on those nasty immigrant Geonee.

On a side note, a vacuum world will be more vulnerable to this as you could crash a ship travelling more quickly - there's no atmosphere to burn it up. However, explosive effects propogate much less in a vacuum, and this event would have no radiation flash, which is by far the most lethal effect of a nuclear explosion in a vacuum. A vacuum world facility would be more vulnerable, but the effects of the explosion would be a lot less damaging than in an atmosphere.

As a consequence, one might find that vacuum worlds in regions where this might be a threat may tend towards more dispersed settlements. However, all things being equal, a SAM battery may be sufficient defence to protect against this type of attack.

TL;DR: If a 12,000 ton meteorite can't enter the atmosphere without being vapourised in mid-air, neither can a free trader.
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Re: Starship Hull design

Postby h1ro » Mon May 29, 2017 7:39 pm

I don't really want to get into an argument about flying starships into cities. No doubt it could happen, no doubt there could be people sick enough to think it will advance their cause. I don't care. Traveller was envisioned in a pre 9/11 world. For the most part it's stayed firmly in it's epoch.

I am not the best at this kind of argument, I'm far from an engineer. Is yours a strawman argument? I don't know.

We have no idea how much a starship weighs. The 200 tons you use as an example, is that the ship's displacement or mass? Where did the mass come from? By way of comparison, a 767 has a max TO weight of 158 tonnes, we know what that can do on impact with a building at a relatively low speed.

You choose not to mention the angle the Chelyabinsk Meteor struck the atmosphere at. Nor the 1500 casualties caused indirectly by it's breaking up in the atmosphere. It was estimated at 20m in diameter, probably smaller than our fictional starships but probably greater in mass.

If you know your ship is gonna break up on interaction with the atmosphere at X speed, you choose not to go that fast. If there's no warhead on the ship and you're going for a kinetic strike, you maximise the speed at which the ship will retain it's integrity. Maybe the shotgun effect would work to? Who knows? There's also the small matter of the active fusion power plant on board. I don't know what would happen to the power plant at the point of impact.

With even the simplest of starships able to sustain acceleration at rates significantly greater than anything we currently make of a similar size there is no need accumulate speed beyond the atmosphere, nor do we know the G loading or temperature the ship's surface can tolerate. So many unknowns.

Where do you get your Sprint ABM numbers from? Wiki has the max speed of 12,500km/h or 3.4 km/s. With our current technology, we need to launch 3 Patriot missiles to get an 87% chance of intercepting a Scud missile. Maybe. Seems there are people who dispute the numbers, some say the intercept rate was zero. That's against a ballistic missile, it isn't manoeuvring. OK, advance a few TLs but then throw in your target doing random high G manoeuvres. Missiles aren't gonna be your best bet for an interception, and unless you can guarantee vapourising the target, might not be a lot of help even if they do hit. Isn't it odd how, having achieved such a high velocity your 1 ton of missile hasn't broken up into pieces?

Maybe I should have ignored the post, like I said at the start, I don't care to get into an argument about random acts of violence, especially not today, Memorial Day and yes, I know we've wandered off topic but really, what's your post got to do with the thread?
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Re: Starship Hull design

Postby Nobby-W » Mon May 29, 2017 9:10 pm

h1ro wrote:
Mon May 29, 2017 7:39 pm
I am not the best at this kind of argument, I'm far from an engineer. Is yours a strawman argument? I don't know.
A straw man fallacy (https://en.wikipedia.org/wiki/Straw_man) is based on deliberately misinterpreting an opponent's proposition. I called pHavoc out on this when he implied that I was talking about launching space station parts into orbit on rockets KSP style (in fact, he did this twice). There's an enormous list of logical fallacies on Wikipedia - most of which I'd never even heard of. You might be able to find something about incompleteness of an argument or basing it on incompletely stated assumptions (which is quite hard not to do in a forum about role playing games), but it's definitely not a straw man fallacy.

My argument is just some maths - 6th form physics plus a bit of stuff I learned playing Kerbal Space Program. Atmospheric heating puts a practical upper limit on how fast you could re-enter; The Chleyabinsk Meteor was estimated at 12,000 tons, and entered the atmosphere at about 20km/sec. The mass and density was definitely much greater than a small starship but it still vapourised in the atmosphere.

As to whether you could just aim straight down - if you assume that orbital mechanics and 'sensible' orbits apply, it would be a very strange trajectory to approach a world on, and it would require somewhat precise timing to hit where you intended to. If you think in terms of real or realistic space travel, anybody intending to land on a world would first aim for a capture orbit (https://en.wikipedia.org/wiki/Orbit_insertion), burn at periapsis to slow down and circularise the orbit, then make any adjustments to inclination needed to fly to their destination on the surface. The only sane exception to that would be if you intended to do an atmospheric braking manoeuvre, in which case your capture orbit would have a periapsis inside the atmosphere but still above ground level.

Trajectories that hit the ground (sometimes known as Lithobraking) are not generally sensible orbits. Ergo, it would be fairly obvious that something was amiss if a starship was approaching on such a trajectory at speed. Scrambling a SDB or some fighters to intercept as soon as it was detected is probably not an unreasonable response.

I'd like to say Kerbal Space Program is not rocket science (OK, I'll see myself out), but for anyone who fancies themselves as a space nerd, I can't recommend it enough as a rough and ready education about the basics of orbital mechanics and space flight. Try it - once you have some grasp of orbital mechanics, you too can become a miserable, intolerant old grognard about this stuff, just like me.
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Re: Starship Hull design

Postby h1ro » Mon May 29, 2017 10:10 pm

Nobby-W wrote:
Mon May 29, 2017 9:10 pm
I'd like to say Kerbal Space Program is not rocket science (OK, I'll see myself out), but for anyone who fancies themselves as a space nerd, I can't recommend it enough as a rough and ready education about the basics of orbital mechanics and space flight. Try it - once you have some grasp of orbital mechanics, you too can become a miserable, intolerant old grognard about this stuff, just like me.
For the record, I don't think you're being a "miserable, intolerant old grognard"

I do think that you're assuming that ships with anti gravity/contragrav/lifters/whatever the hell you want to call them will interact with planets as the spacecraft and satellites we have today do.

That doesn't mean they will rewrite the rules of physics as they pertain to orbital mechanics, not at all. Craft in the Traveller universe will still orbit in ways you've described but I do think that they will re enter differently. That their manipulation of gravity will mean they can choose ways different from what we have to deorbit. How different is a good question and that's what I'm interested in writing about/discussing.
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Re: Starship Hull design

Postby Nobby-W » Mon May 29, 2017 10:53 pm

h1ro wrote:
Mon May 29, 2017 10:10 pm
I do think that you're assuming that ships with anti gravity/contragrav/lifters/whatever the hell you want to call them will interact with planets as the spacecraft and satellites we have today do.
You're right. I am. I think the point that I haven't made clear is that I don't think that this sort of tech actually makes any difference to the way spaceships behave in interplanetary travel or travel around a planet, and I don't think it makes the notion of putting something into an orbit obsolete either. It also doesn't significantly affect the mechanics of travelling between a planet's surface and orbit. Cannae change the laws of physics and all that.

So, I am assuming this, but for a good reason - I don't think this tech materially affects the way spacecraft behave in orbital, suborbital or interplanetary manoeuvring. I'm also assuming that takeoff and landing is not a core function of a satellite designed for a mission where it sits in orbit doing something for years on end. Therefore, fitting a large power plant and anti-grav system is a waste of money when you can just place the satellite into orbit using a fairly ordinary small craft such as a pinnace. Not to mention that managing heat buildup in spacecraft is quite a performance so a large, powerful fusion reactor isn't necessarily a desirable thing to have on a satellite in the first place.
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Re: Starship Hull design

Postby phavoc » Tue May 30, 2017 3:21 pm

Nobby-W wrote:
Mon May 29, 2017 9:10 pm
A straw man fallacy (https://en.wikipedia.org/wiki/Straw_man) is based on deliberately misinterpreting an opponent's proposition. I called pHavoc out on this when he implied that I was talking about launching space station parts into orbit on rockets KSP style (in fact, he did this twice). There's an enormous list of logical fallacies on Wikipedia - most of which I'd never even heard of. You might be able to find something about incompleteness of an argument or basing it on incompletely stated assumptions (which is quite hard not to do in a forum about role playing games), but it's definitely not a straw man fallacy.

My argument is just some maths - 6th form physics plus a bit of stuff I learned playing Kerbal Space Program. Atmospheric heating puts a practical upper limit on how fast you could re-enter; The Chleyabinsk Meteor was estimated at 12,000 tons, and entered the atmosphere at about 20km/sec. The mass and density was definitely much greater than a small starship but it still vapourised in the atmosphere.
You continually deflect the issue of contragravity (mayhaps you have a strawman argument of your own here as you continually state others have?). It will NOT operate the same way reaction thrusters do. And as much as you keep pushing KSP, it, too, uses existing reaction-based thrust as it's primary baseline. IF Traveller ships operated in that manner then this wouldn't be an issue. However, I don't think that is the case. And once you introduce a technology that operates outside the existing models then the assumptions you are making are no longer valid. An open question would be around what sort of orbital velocity an object release in orbit would have assuming you left the planet on anti-grav and ended up in orbit. Would you be able to easily change your orbital speeds to whatever you desired? Would you only have the orbital velocity of the area of the planet you left from?? Somewhere in between??? All questions we have no clue on answering because we have no model to operate from.

As you pointed out, orbital velocity is an issue in maintaining your position relative to the planetary body that you are orbiting below. Beyond that your orbital velocity isn't terribly important if you don't care where your orbit takes you relative to the planetary body. We've yet to bring into the conversation the other aspects of being in orbit that can affect your orbital altitude. So long as you have the tech existing in Traveller that's really not much of an issue.

As to why any spaceship would follow the model you are stating here is odd. Traveller ships have sufficient thrust to enter atmosphere at a relatively sedate speed. Lower speeds mean less heat and less stress on the hull - which is great considering these ships are designed to operate for decades. They wouldn't need to use atmospheric braking - at least as a normal operational aspect. It's the same as helicopters not needing to use auto-rotation to land. You don't plan that your engine(s) is going to fail on a regular basis.

Personally I prefer using NASA tools for orbital planning. There is a free tool that you can use to play around with this. It's called the General Mission Analysis Tool (GMAT). It's located here - https://gmat.gsfc.nasa.gov/. It's fun to play around with. It's not as fun as KSP (who doesn't like burning their Kerbals up on re-entry?), but it's rooted in pure science, and, well, NASA!

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