Starship Sizes

I worked on space ship design and economics yesterday. Turns out, even the very basics are utterly fascinating: How big would an interstellar spaceship be in my universe?

Since we do not have “real” spaceships, except for a few fairly small and primitive vehicles, I can’t just look up some numbers in an almanac. But I can look at what previous Science Fiction settings have done – as good a starting point as any – do some sanity checking on those numbers and then pick my own scale based on the results.

My two starting points will be Piper and Traveller. Both use volume to describe ships, rather than mass (which is a topic for a later discussion).

H. Beam Piper, who wrote some of my favorite Science Fiction stories, generally uses spherical hyperdrive ships. In Space Viking, a few ship classes as named as 1000, 1500, and 2000 foot ships.

Traveller assumes ships sized 100-2000 displacement tons in its basic rules; where a ton is defined as the volume of a 1000kg of liquid hydrogen, or roughly 14.28 cubic meters. Extended rules let you design ships up to one million tons.

H. Beam Piper’s ships in numbers:

Diameter (ft) Diameter (m) Volume m^3 Traveller tons
1000 304,8 14826666,2 1038281,95
1500 457,2 50039998,44 3504201,57
2000 609,6 118613329,64 8306255,58

And I must admit, I underestimated the size of those ships. It turns out, Traveller’s ships end where Piper’s begin.

Diameter (ft) Diameter (m) Volume m^3 Traveller tons
45,84 13,97 1428 100
98,76 30,1 14280 1000
363,82 110,89 714000 50000
458,38 139,72 1428000 100000
783,82 238,91 7140000 500000
987,56 301,01 14280000 1000000

H. Beam Piper’s ships are positively huge when viewed from a Traveller perspective. As an aside, the 800t Broadsword-class “Mercenary cruiser” has a diameter of 91 feet (27.94m) – quite a difference from the Space Viking’s 2000 foot Nemesis and Enterprise that inspired the Traveller ship!

Now, for real-world comparisons.

The space shuttle has a habitable volume in the front section of 65 cubic meters (includes flight deck), or about 4.6 Traveller-tons; the shuttle’s external fuel tank holds a volume of 2 million liters of fuel – about 140 Traveller-tons. The space shuttle orbiter is 17.27m high and 37.24m long. Yes, the orbiter is longer than the diameter of the Mercenary cruiser.

Also incidentally, a 2000 ft Piper ship has about the same volume as an Imperial Star Destroyer.

The Empire State Building is 443m tall, the Burj Khalifa in Dubai is 828 meters tall. 457 meters, or 1500 feet, is the height of the John Hancock Center in Chicago. Piper’s space viking ships would dwarf most of Earth’s tallest skyscrapers – you have to remember that those ships actually do land on planets, thanks to contragravity technology.

An A380 seems to have a fuselage volume of something on the order of 2500m^3, which works out to 175 Traveller-tons. The new US supercarrier class, the Gerald R. Ford, will have a displacement of just over 100,000 tons – this works out to a volume of 7000 Traveller tons. Of course displacement just shows us how much volume of the Ford is under water, and how much she masses; but volume figures for ships is surprisingly hard to obtain.

For submarines, though, submerged displacement automatically tells us the total volume of the ship. For a Los Angeles class nuclear submarine, that’s 6927 tons, equivalent to 485 Traveller-tons. Yes, that’s a fairly big submarine, 110m.

Size Comparison
Size Comparison

Image credits: Eiffel Tower, by Alexander.stohr; Los Angeles submarine by Voytek S; STS Orbiter by NASA. Size comparison image released under cc-by-sa.

Traveller3d has a pretty good Traveller ship size comparison graphic as well, and it seems to match mine.

So, what do we make of all this?

  • The Space Shuttle was already fairly large – this probably has implications for the future. I guess it kind of makes sense; after all you have to have a lot more protective gear, reaction mass, and whatnot in comparison to planet-side vehicles.
  • Traveller ships really are not all that big. Yes, they are massively bigger than anything we can build in space, but they are fairly manageable – certainly nothing on the scale of some other sci fi ships.
  • H. Beam Piper’s ships are more in line with said other ships, that is, his ships are huge compared to Traveller.

Personally, I prefer “tramp freighter” ships. Something that is big enough to be versatile, but not so big as that it requires 50,000 crew men and becomes unreasonable to manage. When looking at the comparisons, the comparison to the A380 strikes me – that’s a big airplane!

On the other hand, big ships have a certain coolness factor of their own, and there’s definitely a “market” for them, so excluding huge ships completely seems like a mistake to me.

For Naval equivalents, we need to keep in mind that the United States maintains about a dozen of aircraft carriers in service, and they have the largest military budget in the world. Huge civilian ships are more common, but they are still a tiny percentage of the overall number of ships in operations. Even if big ships exist, they will be few and far between. After all someone will have to pay for all those big ships, staff them, maintain them, and so on.

For my universe, I should simply pick the best of both worlds. Most ships are “small” – 1000 Traveller tons or less – but some really big ships exist. A million Traveller-tons is probably a good conservative upper limit; a sphere of 300m diameter is notable, but it’s not in the Deathstar league. Non-Spherical ships will be larger, of course, and I see no reason why space stations couldn’t be even bigger.

But, I think it’s vitally important to keep things plausible. Thus, really big warships are used for “gunboat diplomacy” as much as anything else; in wartime they will be tasked to take – or defend – the most crucial systems. They are way too important, way too expensive to be wasted on tracking down some small group of smugglers.

Likewise, huge bulk freighters exist – but only in situations where the profits justify their expense.

I am beginning to sense that my universe will need at least a basic economic model.

Update, 2012-11-05: The space shuttle is/was sometimes transported on a special Boeing 747. Awesome photos such as this provide a nice reality check for that at least that part of my size comparison.



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4 thoughts on “Starship Sizes

  1. I love the size comparison chart.

    I would imagine that the size of space ships would be dictated by where they are built or more accurately where the material to build them comes from. If it’s from earth, the gravity means lifting a lot of material into orbit thus small ships. If the material comes from the moon, (titanium etc) they could be larger because of the lower cost to lift materials out of the gravity well. Big ships would likely be built of materials from asteroids.

    There is a post on gizmag about the largest yet container ship being built and had some stats if you want another reference. I found it interesting that they used a cargo capacity measurement that I had never heard of the “Teu” which is the capacity to carry a 20 ft container.

  2. Yeah – this is purely a "look and feel" decision. Economics do not figure into it; in my mind I can always make the economy work (Traveller and Piper both have contragravity, which should make launches of material, even from a planet, dirt cheap. Yes, neither is exactly "hard" sci fi). Come to think of it, if one is to have large-scale interstellar travel then assuming really, really cheap launches is probably a given. Creating a consistent economy sounds like fun, by the way. Not that I know much about economic theory, but I'll give it a shot.

    I actually knew about the TEU, but that may be down to being born and raised in a big port city (Hamburg). There's also a bigger version ("2 Teu"). In any interstellar setting, they'd almost certainly have something similar to an ULD, which is the air freight equivalent to a TEU container:

  3. Love the size comparison graphic too! I knew Piper's ships were big but this gives them some remarkable perspective. Thanks.

    (Nice observation too on the way Traveller's ~Broadsword~ ships didn't even begin to match their Space Viking inspirations in size.)

    P.S. If I recall correctly, a standard flatbed railcar can carry two "TEU." Two TEU on a railcar is about the size of (or slightly larger than) a traditional rail "boxcar." The Shuttle cargo bay happens to be just about the size of a boxcar, thus making its "cargo capacity" about two TEU.

  4. Just to follow up on this: Payload bay of the Space Shuttle is 4.6 m by 18.3 m and is roughly cylindrical; so that’s about 304 cubic meters of payload volume. Payload mass seems to vary, but is usually listed as just under 30 tons. Incidentally, 304 cubic meters are about 21-22 Traveller displacement tons of cargo space.

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