What is the working life time of a space craft?
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There's constant abrasion from solar and galactic winds, microasteroidal rocks, and constant thermal stress... only one side is heated by the star.
creativehum
SOC-14 1K
Not to mention wear and tear from flights through atmospheres for streamlined ships, as well as ships that spend time in atmospheres full of corrosive or exotic gasses.
creativehum
SOC-14 1K
They don't have to in your setting. Not mine.
well, ask and ye shall receive.
http://www.space.com/34511-another-u-s-air-force-weather-satellite-just-broke-up-in-orbit.html
oh, well there's that.
let's see, twice a month x (say) 10 years = 240 re-entries. that's a lot of heat stress.
http://www.space.com/34511-another-u-s-air-force-weather-satellite-just-broke-up-in-orbit.html
oh, well there's that.
let's see, twice a month x (say) 10 years = 240 re-entries. that's a lot of heat stress.
Yes, there is.
7mm chunk taken out of a window: http://www.popsci.com/paint-chip-likely-caused-window-damage-on-space-station
We have thrust induced oscillation damage: http://www.universetoday.com/24571/has-the-iss-suffered-structural-damage/
Keep in mind: the ISS is doing 27600 km/h. A typical Traveller ship is doing that or faster in 20 minutes, and will be doing so outside the magentospheric protection that the ISS enjoys.
Plus, the ISS needs regular thrust applications to maintain a steady orbit - it's still in atmosphere.
Drakon
SOC-14 1K
You pressure cycle the hull every time you land on a planet. The outside pressure goes from zero to, well, it can be a lot. You need a minimum of 5 PSI internal for living, so the hull will take most of the flexing.
And you have temperature changes, going from the frozen reaches of space to whatever weather you have at the air port. If you enter planetary atmospheres hot, hull temps can get quite warm.
Something that occurs to me is that the hull is really your biggest hurdle in keeping a ship running for longer than 120 years. Wiring and systems aboard ship can be swapped out for new upgraded equipment. It might be possible to create a modular hull and frame system and replace components as needed as metal fatigue renders some components dangerous to use.
Average passenger liners don't pressurize at more than about +0.6 Bar. Remember that the skin stress factor isn't a linear function, either. (It involves both area and linear measures, including linear distance between reinforcements, and the area unreinforced...)
Cabin pressure is lowered to 0.8 bar (sometimes to 0.7 bar), typically, and cruise height seldom crosses 15 km (about 49,000') and about 0.1 bar, and typically is around 10 km (and 0.3 bar) external, for about 0.5 atm pressure flex.
The Aircraft pressure envelope is also not the structural member. For Traveller spacecraft, it often appears to be.
Further still, a failure of the pressure envelope on an aircraft is usually non-catastrophic, and at most a minor health risk; unusual but spectacular failures (Aloha 243, United 811) are the rare exceptions, and most failures occur shortly after takeoff and get noticed before dangerous differentials. (I've had to change planes twice because of pressure failures detected on the ground...) And those pressure changes are much more gradual than the listed rates for Traveller ships launch/land cycles.
That pressure vessel stress is pretty minor. But it adds up, especially when combined with the potential for thermal shocks to cumulate with it.
I agree it isn't a major issue, but it IS an issue.
Enoki
SOC-14 1K
Throw in changes in gravitational stress, flexion of the ship (particularly if larger) due to maneuvering and such, wear and tear on the machinery and systems.
That last is just like any piece of complex machinery. At some point so many components, often minor ones, have worn out to the point that the overall cost of replacing them is more than the cost of simply buying new.
Something as simple as the decking material gets worn out. You have a certain standard of expectation by passengers that for their 10,000 Cr high passage they're going to be staying in a stateroom that isn't a fleabag hotel room on the interstellar interstate...
Valves wear out. Motors and controllers wear out. Wiring works loose. Plumbing and piping fittings are worked where they leak.
Even pressurizing the ship and having it in different external pressures will stress the hull over time no different from a pressurized airplane or submarine.
All the accumulated issues get to a point where the ship simply isn't worth bringing back up to standard.
I could easily see there being "Used ship dealers" who specialize in salvage title ships, ones that are thrashed into "beaters," and such. And, I can see there being individuals with a dream and little cash buying them on the expectation they'll "fix them up" when in reality they are operating on the edge of disaster instead.
That last is just like any piece of complex machinery. At some point so many components, often minor ones, have worn out to the point that the overall cost of replacing them is more than the cost of simply buying new.
Something as simple as the decking material gets worn out. You have a certain standard of expectation by passengers that for their 10,000 Cr high passage they're going to be staying in a stateroom that isn't a fleabag hotel room on the interstellar interstate...
Valves wear out. Motors and controllers wear out. Wiring works loose. Plumbing and piping fittings are worked where they leak.
Even pressurizing the ship and having it in different external pressures will stress the hull over time no different from a pressurized airplane or submarine.
All the accumulated issues get to a point where the ship simply isn't worth bringing back up to standard.
I could easily see there being "Used ship dealers" who specialize in salvage title ships, ones that are thrashed into "beaters," and such. And, I can see there being individuals with a dream and little cash buying them on the expectation they'll "fix them up" when in reality they are operating on the edge of disaster instead.
kilemall
SOC-14 5K
IMTU I have an aggressive TL increase assumed, approximately 40-50 years per TL with the Great Plague interruption, so I don't subsume a 1000 year plus technological/economic entity.
Since 100 years gets into TL8 territory, I have fission power plants and the issue of neutron embrittlement, and that has a lot to do with why most ships are younger.
Fusion is initially the He3 kind and so aneutronic fusion means a lot less of that sort of issue, along with shielding weight and bulk. The fuel cost though is driving most to adopt the relatively new muon-catalyzed fusion set (I guess my Fusion +, huh) which has a little of that but not like fission.
I've also got that tailsitter/G-compensator TL thing going on, so the 'newer' TL10 craft are generally more desirable if they are more then 1G.
I would expect something like this TNE wear factor counts too, at a certain point it just takes too much to keep the old boat in the air even though it's pure profit otherwise to operate.
Past a certain safety point planets would not want a questionable ship overhead that might crash or leak, or the TC/Imperium equivalent to have to deal with a space lane hazard. So off to the boondocks with the last leg ships- in my case the Oort Clouds.
Bottom line, there are quite a few 30-60 year old craft, but not a lot past that point that don't have serious deficiencies.
Heh, just had a random thought- treat ship aging like character aging.
When they hit the aging time, roll every four years.
STR= Hull/Weapons/Cargo/Staterooms
DEX= M-Drive/J-Drive
END= Power plant/Fuel System
INT= Computer/Bridge/Sensor systems
Every failed roll inflicts a 'hit' on a ship system. For CT ships, that might be a downgrading on the letter drive, or flatout failure if there are no lower drive values- for HG that might be a system value.
If the system is then replaced it goes on the same aging cycle as year 0, but something else in the category can break on the next aging roll.
You can also 'age' the ship if it goes through some extraordinary pounding like a battle, a meteor shower or a solar flare, or conversely not age if it has been mothballed.
'Feels' like about the right time frame and consistency, and means holding onto that ship might be more an act of stubbornness, sentiment or willfulness rather then a considered financial strategy. But if the ship has a 'reputation', it may all be worth it.
Heh, may also be a 'strategy' the banks worked out with the shipyards- have the ships designed for planned obsolescence at the 38 year mark, a percentage of the owners won't be able to replace the failed parts and default on their loans, banks repo ships and get a resale value AND all that profit from decades of financing.
Since 100 years gets into TL8 territory, I have fission power plants and the issue of neutron embrittlement, and that has a lot to do with why most ships are younger.
Fusion is initially the He3 kind and so aneutronic fusion means a lot less of that sort of issue, along with shielding weight and bulk. The fuel cost though is driving most to adopt the relatively new muon-catalyzed fusion set (I guess my Fusion +, huh) which has a little of that but not like fission.
I've also got that tailsitter/G-compensator TL thing going on, so the 'newer' TL10 craft are generally more desirable if they are more then 1G.
I would expect something like this TNE wear factor counts too, at a certain point it just takes too much to keep the old boat in the air even though it's pure profit otherwise to operate.
Past a certain safety point planets would not want a questionable ship overhead that might crash or leak, or the TC/Imperium equivalent to have to deal with a space lane hazard. So off to the boondocks with the last leg ships- in my case the Oort Clouds.
Bottom line, there are quite a few 30-60 year old craft, but not a lot past that point that don't have serious deficiencies.
Heh, just had a random thought- treat ship aging like character aging.
When they hit the aging time, roll every four years.
STR= Hull/Weapons/Cargo/Staterooms
DEX= M-Drive/J-Drive
END= Power plant/Fuel System
INT= Computer/Bridge/Sensor systems
Every failed roll inflicts a 'hit' on a ship system. For CT ships, that might be a downgrading on the letter drive, or flatout failure if there are no lower drive values- for HG that might be a system value.
If the system is then replaced it goes on the same aging cycle as year 0, but something else in the category can break on the next aging roll.
You can also 'age' the ship if it goes through some extraordinary pounding like a battle, a meteor shower or a solar flare, or conversely not age if it has been mothballed.
'Feels' like about the right time frame and consistency, and means holding onto that ship might be more an act of stubbornness, sentiment or willfulness rather then a considered financial strategy. But if the ship has a 'reputation', it may all be worth it.
Heh, may also be a 'strategy' the banks worked out with the shipyards- have the ships designed for planned obsolescence at the 38 year mark, a percentage of the owners won't be able to replace the failed parts and default on their loans, banks repo ships and get a resale value AND all that profit from decades of financing.
sure those stresses exist, but they're minor in comparison to the stresses faced by an ocean-going ship, and those will last 40 years if cared for at all.
https://www.youtube.com/watch?v=rx2OhSPserM
sure. just don't see how any plausible stress load on a space ship can wear it down to that level in 40 years, or 80 for that matter.
heh. I was wondering if anyone would get to that. can't speak to that directly without violating security issues, but suffice to say that in response to neutron embrittlement one does not replace the entire hull.
Many don't last 40 years. Also, keep in mind transient loading on a wet naval ship seldom exceeds 0.5G, pressure loading seldom exceeds 0.1 bar in condition Z (Fully buttoned up), and the ships making 40 years are getting major overhauls every 4-6 years, including complete hull resurfacing (remove all the paint, check for damage, replace damaged sections, then repaint; paint is actually a sacrificial protectant for the metal).
2 G-hours thrust exposes the ship to abrasive damage (72000m/s) exposes each square meter to major abrasive risks. average particle size is around 10e-6 to 10e-8 kg (Hajuk, 1991) at a rate of 1 particle per cubic kilometer, which means once per 3.6 hours being hit by a particle which, ignoring its intrinsic velocity, is getting some 0.5kJ. Fortunately, most of our current encounters with such particles are in cases where their intrinsic velocity reduces collision energy as they've fallen into orbital patterns; Traveller ships don't. Note that interplanetary flights can be considerably higher - one or more per hour, given 6 G-hours thrust. Pretty much nothing we've done to space exceeds 16 km/s... just over 1/5 these velocities (and thus 1/25 the energy). A .22LR imparts 125 J...
Note also: most such impacts are grains of sand. They and the material hit VAPORIZE. The steel getting 0.25 kJ is going to lose about 0.1 µL (0.0001 mL) IIRC. That's mass losses by abrasion.
The average flight time in this regime is sufficient to get one such hit per Sortie (takeoff to landing), plus atmospheric issues. Paint isn't going to be thick enough to account for that.
The thrust flexations for a 1G ship, which may be (canonically) up to 0.25 G @ 90° off ship's axis, are roughly 4x the maximum energy a wet naval ship experiences, and unlike the navy, are routine operations. (Note that Icebreakers take 0.9G transient loads routinely, and the USCG wants to replace them every 20 years.)
The typical naval ship has under 0.25G thrust, and uses it about half the time.
So, since the energy involved is square of thrust... call it 0.0625 stress units per year 20 work years of a 40 year life, giving a final of 1.25 thrust stress units
Tye typical Traveller vessel experiences 1G for 1/7th of its operational life, which we can assume is an average of a bit over 40 years. (Mostly because mortgages for ships are usually pushed to average –1 sigma). So 5.714 thrust stress units. As a rough guess, that's good enough - about 4.6x the stress damage, even given only 2 days per 14 under thrust.
Then, there's high energy particulate damage. Which is what's doing most of the damage to solar panels in space. It cumulates, embrittles metal, cracks silicates, and changes chemistry...
again, only about 5.714 years worth in 40 years. Still, that adds up.
And we don't have canonical commentary on the effects of J-Space on hulls inside a jump bubble; we know that outside the bubble, the effect is utterly catastrophic. We do have canon that life inside the bubble is not 100% protected - see also TNE's various effects of anagathics for that, as well as the Jagd-il-jgd writeup in JTAS. (Jagd cannot survive jump.) So, some stress is happening there, but we don't know exactly what. We can presume it affects ships as well as people.
kilemall
SOC-14 5K
Well, that's at least the power plant replacement, which ain't casual, and then have to think solar flares will be a similar event to the hull, only concentrated.
Oh hey, look at this while I was looking up neutron embrittlement, looks like hydrogen AND cryogenic embrittlement may also be a factor for our ships-
https://en.wikipedia.org/wiki/Embrittlement
The hull of commercial ships will usually outlive their commercial value.
That is: evolution of trade or technology make liners optimized for a trade less competitive over time and: a) withdrawn awaiting a demand surge that will allow profitable freight b) reassign to alternative trade where they may find a living c) sold cheap to whomever can make money given a very low capital investment d) scrapped.
The point is not to be exhaustive in wet/space comparison but to point to the "static" nature of the trade system in traveller. Market Specific Design, an aspect that determine a lot the actual duration of a ship's life is largely absent in Traveller.
Dont shoot, I enjoy this debate on durability of space ship and keep having fun with it, just don't forget that aging ships have to earn a living in a changing world, not just extra maintenance cost.
have fun
Selandia
That is: evolution of trade or technology make liners optimized for a trade less competitive over time and: a) withdrawn awaiting a demand surge that will allow profitable freight b) reassign to alternative trade where they may find a living c) sold cheap to whomever can make money given a very low capital investment d) scrapped.
The point is not to be exhaustive in wet/space comparison but to point to the "static" nature of the trade system in traveller. Market Specific Design, an aspect that determine a lot the actual duration of a ship's life is largely absent in Traveller.
Dont shoot, I enjoy this debate on durability of space ship and keep having fun with it, just don't forget that aging ships have to earn a living in a changing world, not just extra maintenance cost.
have fun
Selandia
traveller civilian ships spend the majority of their careers in jump or in atmo. I think modern civilian airliners get more radiation than a traveller ship would.
heh. maybe jump is corrosive ....
seems the biggest factor, but imtu fuel tanks are gravity-lined, so the fuel doesn't touch the metal. (actually that's a retro, occurred to me last year and I posted it and said I should get reputations points for the idea, but got negative reputation instead. bummer.)
our rw, sure. what's not at all clear is why that would happen in the world posited in traveller.
oh, stupid me, just realized what you said.
imtu high-tech construction is taken up almost exclusively by the navy, leaving low-tech building to the civvies, so it's fairly stable in that regard. the big hurdle is affording a ship at all, not the transition from tech 11 to tech 12.
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Enoki
SOC-14 1K
Just the fact that even the smallest ship will have dozens of pumps, electric motors, servos, actuators, as well as literally hundreds, possibly thousands, of relays, switches, and other moving parts of various sorts says that stuff over time being in use will wear out.
The vibration and stress of the ship in general will loosen parts like electrical connections and pipe fittings.
In those terms, not even considering the hull and other structure, starships will be as or more complex than any aircraft today is. Consider just a far or free trader. The plumbing alone for the freshers / heads / bathrooms is going to be a complex item on the order of a commercial building today. The water has to come from somewhere and the waste has to go somewhere. Treatment might be necessary as well. That stuff doesn't work on PFM in reality.
Every automatic hatch on a ship has to have motors and controls to open and close it. It likely needs a number of safety relays to monitor it's state, prevent it closing on someone or thing in the way, possibly remote status indication on the bridge or elsewhere.
Let's say that it requires (by the manual) periodic inspection, cleaning, and lubrication. Maybe on a ship that's short handed or with a crew that is lazy that doesn't get done until the hatch doesn't work. How common is something like that?
Modifications are another issue. Unauthorized and improperly engineered ones are going to occur, particularly on commercial and privately owned vessels. Say, the Captain wants the equivalent of cable TV in his stateroom. The ship's "engineer" drills holes in a couple of what were supposed to be airtight bulkheads to install that. The Captain's happy, the ship's integrity is compromised...
It's often lots and lots of little things that add up to big problems on complex systems.
If I were devising a table of time, cost, and frequency of repairs and maintenance I'd use not just age but how close to the technological edge equipment comes.
Stuff that's cutting edge technology is going to be less reliable than proven, repeatedly engineered stuff. It's just as prone as old technology to have issues in many cases.
I'd think on starships stuff that's TL 12 to 13 is very reliable. TL 15+ stuff is less reliable due to it's cutting edge nature. It's harder to find parts for since the stocks haven't been made yet. The tech manuals and systems often are inaccurately documented or the procedures have errors in them. That'll get worked out, in part at your expense...
Then, old stuff that's been running for decades is the same way. It's prone to break and harder to fix in many cases because nobody carries stuff that ancient... "You might have better luck over at the salvage yard" the parts guy might tell you...
The vibration and stress of the ship in general will loosen parts like electrical connections and pipe fittings.
In those terms, not even considering the hull and other structure, starships will be as or more complex than any aircraft today is. Consider just a far or free trader. The plumbing alone for the freshers / heads / bathrooms is going to be a complex item on the order of a commercial building today. The water has to come from somewhere and the waste has to go somewhere. Treatment might be necessary as well. That stuff doesn't work on PFM in reality.
Every automatic hatch on a ship has to have motors and controls to open and close it. It likely needs a number of safety relays to monitor it's state, prevent it closing on someone or thing in the way, possibly remote status indication on the bridge or elsewhere.
Let's say that it requires (by the manual) periodic inspection, cleaning, and lubrication. Maybe on a ship that's short handed or with a crew that is lazy that doesn't get done until the hatch doesn't work. How common is something like that?
Modifications are another issue. Unauthorized and improperly engineered ones are going to occur, particularly on commercial and privately owned vessels. Say, the Captain wants the equivalent of cable TV in his stateroom. The ship's "engineer" drills holes in a couple of what were supposed to be airtight bulkheads to install that. The Captain's happy, the ship's integrity is compromised...
It's often lots and lots of little things that add up to big problems on complex systems.
If I were devising a table of time, cost, and frequency of repairs and maintenance I'd use not just age but how close to the technological edge equipment comes.
Stuff that's cutting edge technology is going to be less reliable than proven, repeatedly engineered stuff. It's just as prone as old technology to have issues in many cases.
I'd think on starships stuff that's TL 12 to 13 is very reliable. TL 15+ stuff is less reliable due to it's cutting edge nature. It's harder to find parts for since the stocks haven't been made yet. The tech manuals and systems often are inaccurately documented or the procedures have errors in them. That'll get worked out, in part at your expense...
Then, old stuff that's been running for decades is the same way. It's prone to break and harder to fix in many cases because nobody carries stuff that ancient... "You might have better luck over at the salvage yard" the parts guy might tell you...
Enoki
SOC-14 1K
I've always though of the liquid hydrogen tanks as being made like dewers (thermos bottles) only with much better technology. They might even have something like carbon nanotubes or foam stuffed inside to prevent the fuel from shifting.
I can't see their needing something that's powered because that means the ship has to remain running or have a off ship power connection at all times to maintain the fuel tank integrity.
That technology has been around a long time even on present day Earth and works well. If the tanks were designed to be removable and replaced, then that can be done as they wear out, if they wear out.
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