Density of star ships

Discussion in 'Trek Tech' started by Chuck4, Nov 5, 2013.

  1. Chuck4

    Chuck4 Ensign Red Shirt

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    TOS and TMP enterprise were suppose to be around 300 metered long, and mass 300,000 metric tons. This would make it approximately as long as an large aircraft carrier but three times as massive. I haven't actually worked out the volume of the star ship, but eyeballing it tells me it's a pretty space inefficient design, meaning it has a lot of dimension and surface ares for not much interior volume. The primary hull is on average maybe 3 decks thick. The secondary hull has at most 1/8 the volumn of an aircraft carrier hull. The hull of a large aircraft carrier almost certainly has much more interior volume in total than the TOS enterprise.

    So, this means overall, the enterprise is an extraordinarily dense structure, far denser than modern ships, planes, or submarines. Possibly 3-6 times denser. Enterprise is certainly denser than water and would sink like a stone if it had to ditch.

    Since most of the enterprise's primary and seconary hills are empty space just like shipand assuming 2 centuries of progress in material science would allow the ship's structural weight to stay under control, this suggests most of the ship's mass must be in those two big engine nacelles.

    What do you think?
     
  2. C.E. Evans

    C.E. Evans Admiral Admiral

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    I think a lot of people have placed the bulk of a ship's weight in the nacelles with the idea that the warp coils, antimatter pods, or whatever you think is in there are extremely heavy. In that capacity, the nacelle struts are not so much supporting the nacelles as attaching the rest of the ship to them.
     
  3. Nob Akimoto

    Nob Akimoto Captain Captain

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    There's not a lot that supports the "300,000" metric ton figure other than fanon. The numbers more usually bandied about outside of that are closer to a million metric tons. Usually in the 700,000-1,000,000 metric ton range. The internal volume of the TOS Ent is about 215,000 cubic meters.
     
  4. Saturn0660

    Saturn0660 Rear Admiral Rear Admiral

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    Indeed I'd also agree that the Nacelles are likely by far the "heaviest" part of the ship. I get the feeling that those warp coils are ultra dense. I also get that feeling that they are made that way on purpose as to last longer.
     
  5. CorporalCaptain

    CorporalCaptain Admiral Admiral

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    I'm not aware of any canonical references that quote the mass of any starship aloud. If there are any, I'd sure like to know what episodes they're in. Ditto for length figures and other size measurements.

    Size is easier to estimate than mass, because we have geometry at our disposal, and objects of known size (i.e. people) to make comparisons.

    To estimate mass, we have to be more indirect. Starships don't gravitationally disrupt the planetary systems they pass through, so they can't be too heavy. Additionally, those that land on planet surfaces (e.g., Bounty and Voyager) can't be so heavy that they sink into the ground.

    For reference, the displacement of the real-world aircraft carrier USS Enterprise (CVN-65) is on the order of 95,000 tons, nearly one-third of the quoted 300,000 metric tons for the starship. Given what the starship does, I've always thought that therefore that's just too light a figure for the starship's mass. How heavy it could get before it started interfering with the orbits of planetary satellites, I don't know, but I'd imagine it to be as heavy as it could get without being disruptive (when all its power systems are turned off).

    I agree that the nacelles are probably the densest parts.

    Just my two cents.
     
  6. Green Shirt

    Green Shirt Rear Admiral Rear Admiral

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    Scotty in Mudd's Women "almost a million gross tons".
     
  7. BK613

    BK613 Fleet Captain Fleet Captain

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    One thing to remember is that ocean-going vessels must by design have a density that is less than that of surface seawater: starships do not.
     
  8. Nob Akimoto

    Nob Akimoto Captain Captain

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    Scotty mentions the ship's about a million gross tons (probably meaning long ton here) in "Mudd's Women", while Voyager is noted as being "15 decks thick, and 700,000 metric tons" several times in the series. (There's a little bit of a comparison and analysis here: http://www.trekbbs.com/showthread.php?t=227710 )

    We're talking about a hull that needs to withstand extremes of temperature and kinetic stresses that would tear anything built to CVN-65's standards to pieces. The density's going to be higher as a matter of course.
     
  9. CorporalCaptain

    CorporalCaptain Admiral Admiral

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    Ah, thanks! :techman:
     
  10. Chuck4

    Chuck4 Ensign Red Shirt

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    If enterprise has a volume of 215000 cubic meters and a mass of a million tons, that means the ship is denser overall then if it were made of solid titanium without any cavities inside.

    If let's say 3/4 of that mass is in those nacelles, then those nacelles would have to be far denser than solid lead, gold, or uranium, amongst the densest materials under normal temperature and pressure known to science.

    This suggests the script writers didn't think about what they were talking about, or the enterprise must have quite an amount of exotic ultradense substances as yet completely unknown to science onboard.

    Now very approximately, TOS and TMP enterprise is roughly the same size as USS Nimitz, or about 4 times the size of the largest modern cargo plane, the an-225.

    The Nimitz weigh 100,000 ton full load, so it's structural weight would roughly be in the 50,000-70,000 ton range, sans reactor, store, planes, crew, aviation fuel, munition. An-225 weigh about 250 tons empty. Scale up by a factor of 4 would make it 64 times heavier, or roughly 18,000 tons.

    I think given 2 centuries of advancements in material science, with new thinks like structural integrity fields, etc, it is reasonable to suppose star ship builders should be able to keep structural weights of the enterprise very broadly in line with the weights of these 20 century structures of comparable size. So 20,000 - 70,000 ton would seem a fair and reasonable estimate for how much enterprise's structure ought to weigh. Double that for doubt, I think enterprise's structure would weight 140,000 ton, tops.

    In light of this, a total weight or mass of 300,000 tons would seem much more reasonable. In this case, enterprise would already be far denser than water and would sink like a stone.

    1,000,000 ton would just be very hard to support, unless we posit somewhere on the ship these are 800,000 tons of some truly exotically dense material.

    If these is a small black hole somewhere in the ship's innards to help power it, then I would believe the figure of 1,000,000 tons. Otherwise the ship wouldn't be that heavy if it were cast in solid metal.
     
    Last edited: Nov 6, 2013
  11. Green Shirt

    Green Shirt Rear Admiral Rear Admiral

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    You're welcome. :)
     
  12. Nob Akimoto

    Nob Akimoto Captain Captain

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    A 210,000 m*³ ship at a million metric tons is only a density of 5,000 kg/m³. That's dense, but it's not unbelievably dense.

    A more useful metric is probably taking the surface area of the ship and multiplying it by a small amount to get a overall "outer hull" volume. Here we're talking about 60,000 m². With a 2m thick outer hull, we'd fudge it and say there's 120000m³ of hull plating volume. That's a density requirement of about anywhere from 5,000 - 8,000 kg/m³ depending on how we define "nearly a million gross tons of ship". Presumably stuff like duranium, rodinium or trititanium is going to be much denser than titanium, and probably closer to stuff like tungsten(19,000 kg/m³) or nickel (8,900 kg/m³).

    If we made it so half of the ship is made up of some sort of carbon molecule similar to diamond, and the other half out of a dense metal, then somewhere in the high 6 figures would make sense for a starship's overall mass.
     
  13. Chuck4

    Chuck4 Ensign Red Shirt

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    A 2 meter thick hull would be difficult to justify given the large number of windows.
     
  14. Chuck4

    Chuck4 Ensign Red Shirt

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    A 2 meter thick hull would be difficult to justify given the large number of windows.

    Also, if the ship indeed need a dense hull 2 meters thick, resulting in an outer shell that is a big part of the ship's mass, then any decent engineer would have economized on both total weight and the use the this dense material by giving the ship a more volume efficient shape, in other words, adopt a shape that had less surface area for a given amount internal volume.

    As it is enterprise is hardly shape that maximize internal volume for a given surface area and shell weight. It is a shape that only makes sense if structure itself is cheap, light and very strong.
     
  15. Masao

    Masao Fleet Captain Fleet Captain

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    I've always disregard the "million gross tons" figure for Enterprise. Sometimes common sense should prevail over onscreen evidence. As has been discussed in this forum before, "gross ton" can be a unit of weight (the same as "long ton") or can be a unit of volume. If we use Nob's figure of 215,000 m^3 for volume and a commonly quoted displacement of 190,000 metric tons, we get an overall density of about 0.9 metric tons per cubic meter, which is a bit less than water. Of course, that's an overall figure, and some parts of the ship are denser and some are less dense. I've always thought that advances in material science would lead to starships being less dense (lighter yet stronger) then present day ships.

    Voyager/Intrepid has a volume of 626,000 m^3, so with a weight of 700 kmt, it has a density a bit higher than water but in the same ball park.
     
    Last edited: Nov 6, 2013
  16. Nob Akimoto

    Nob Akimoto Captain Captain

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    I'm curious why a starship should be compared to a conventional naval vessel for density. Is there some reason it needs to have a density of less than water? If we're going to talk about common sense, the material descriptions we're given about starships is that they're designed to withstand weapon impacts that destroys relatively dense things like iron-nickel asteroids with ease. Even assuming that say torpedo technology evolved significantly between 2293 and 2370, an unshielded Enterprise-A was taking torpedo hits that would presumably destroyed much larger asteroids with relative ease. In which case the hull materials being less dense than a combination of nickel and iron doesn't make a lot of sense. Indeed the requirements for a starship constructed in space (contra the absurdity of ST09) are probably more toward better thermal properties and maybe radiation shielding over things like lightness. There's simply no need for a starship that uses mass reduction technology to worry all that much about using high density materials for its hull.

    There's nothing in canon or even official sources that suggest a 190,000 ton Enterprise, and there's evidence to suggest ships are, in general, heavier than water. There's no real reason for the compromises that naval vessels have to deal with in terms of hull density on a starship.
     
  17. Crazy Eddie

    Crazy Eddie Vice Admiral Admiral

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    Good point.

    Personally, I prefer to compare starships to real-world spacecraft like the Soyuz or the Apollo CSM/LM. Been a long time since I did the work, but I figured out that the entire Apollo stack had a density of about 290kg/m^3, while the space shuttle was closer to 170 and Soyuz was around 210. Most newer spacecraft -- the Dragon, Cygnus, HTV and ATV cargo ships, for example -- have similar densities between about 150 and 250kg/m^3.

    With a volume of 215,000m^3, that would give the Enterprise-A a mass of 32,250 to 52,500 tons.

    You're assuming that density is equivalent to physical resilience, which is not always (or even usually) the case. A starship with a 2-meter thick hull of deleted uranium isn't going to be more resistant to impact damage than a starship with 10 aluminum whipple shields 20cm apart. Add kevlar between the shields, you double its resistance; add trek-style forcefields between the shields, you make it virtually indestructible. Far more importantly, a 2-meter shell of depleted uranium is a lot harder to repair or replace or even service than a stack of thin wipple shields bolted to a frame; a photon torpedo may peel six of ten layers of your hull plating, but since it's just thin aluminum plate you can just unbolt the damaged sections and slap new ones in its place (whereas depleted uranium will crack/spall and possibly shatter as huge chunks of it are propelled into the inner hull at tremendous speeds).

    Something to remember in space is that kinetic impacts are an action-reaction relationship. Putting more mass in front of a projectile simply creates more mass that can be thrown towards you when it hits. You want to DEFLECT the projectile, not stop it cold. Starships use deflector shields for this purpose, but their hull plating probably works in a similar way, in which case it is probably VERY low density and a lot more elastic than most of us would believe.

    Mass reduction costs energy. The less you have to reduce your mass to maneuver at impulse power, the more energy you have available for things like phasers, shields and sensors. As with real-world spacecraft: a heavier ship has a certain mass penalty as it burns through its fuel that much faster to get the same performance.

    What's more, radiation shielding isn't accomplished (normally) with high density materials. Protection from radiation usually requires some material with a lot of hydrogen; LH2 and distilled water work exceptionally well, as does parafin or other forms of hydrocarbons. A ship with forcefield technology wouldn't have as much of a need.

    Naval vessels don't have to make much of a compromise, actually. They just have to displace more water than their own mass, which means there's a minimum size their hull components must be built to in order to achieve the needed displacement for their intended fittings.

    Space ships start with completely different design assumptions. You start with mission capabilities, and then you go through a catalog to see what systems can provide those capabilities. Choose your payload, then choose a bus type (e.g. the physical body of the spacecraft) and then put it all together. The selection of the bus usually has a lot to do with what kind of propulsion system you have available, and a lighter bus gives you more propulsion options than a heavier one.

    A lighter starship, by the same token, can get away with using a smaller impulse engine and a more efficient warp drive. Reducing the mass further might actually improve its combat maneuverability, and could also improve its thermal characteristics if the lighter materials absorb less heat.
     
  18. T'Girl

    T'Girl Vice Admiral Admiral

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    The show spoke of "Duranium" being used for the hull, or as part of the hull. If duranium refers to depleted uranium (with their science completely depleted) that would make the outer shell of the ship responsible for a health percentage of the ship's mass. Combine that with the warp coils, the impulse engines, and things like the M/AM reactor and the majority of the ship might not be unusually "dense."


    :)
     
  19. Crazy Eddie

    Crazy Eddie Vice Admiral Admiral

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    I figure duranium is actually the trade name for an alloy that uses a combination of rare metals (titanium, nickel, platinum etc) that are only plentiful in asteroids. Nickel-platinum alloys, for example, have shape-memory properties that allow them to deform hugely under mechanical stress only to return to their original shape when heated beyond a threshhold point; if Starfleet is using something like this in their hull plating, then "polarizing" it with an electric field might be a sneaky way of forcing those hull materials to constantly return to their original shape when subjected to mechanical stress. Better yet, an open-cell metal foam of nickel-platinum alloy would give you a material 90% lighter than solid metal while retaining almost all of its strength in the same volume, plus the benefit of being better able to deflect projectiles in hyper-velocity collisions (rather than shatter/spall into the compartment).

    Even better, an alloy of nickel-titanium-palladium would have a mindblowing strength-to-weight ratio in addition to being able to trap some hydrogen in the matrix (palladium hydride) which would make it an ideal radiation shielding material. The same material in an open-cell foam could be fashioned into hull plates several feet thick that are still no heavier than ordinary sheetmetal.

    Besides, we know that Starfleet uses a lot of tritanium in their construction too, which I can only assume is an allotrope of titanium (probably a glass).
     
  20. CorporalCaptain

    CorporalCaptain Admiral Admiral

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    My only purpose in bringing up CVN-65 was simply to point out that the 300,000 metric ton figure given for the starship in the OP seems (IMO) implausibly too light (as is the 190,000 metric ton figure that FJ gave), because it's too close to the mass of a real world naval vessel of similar size.

    The almost-million-ton figure given in Mudd's Women, that I'd forgotten about, sounds better, at the very least because it's larger than 190,000 metric tons.