On 28Nov2019 0204, Cian Witherspoon wrote:

> But on your other point, cargo sections are tiny. A fully loaded 40’
> container has an average density of about 350kg/m3, which is honestly about
> half the density of wheat grain. volumetric ship design gives us literal
> dTons of waste space if we try and reconcile mass based performance with
> current designs.

Per wikipedia (which I figure should be good enough for this), a 40'
container has an interior volume of 67.5 m^3, an exterior volume of 77.0
m^3. It's max gross weight is 30 tonnes, so maximum density is 0.39
t/m^3. A 20' container has a maximum density of twice that, or 0.78 t/m^3.

A traditional volumetric ton is 100 cubic feet, for a density of
0.26-0.29 t/m^3, depending on what kind of 'ton' you use for mass. This
was considered a good rule of thumb for loose cargo, break-bulk, etc.

Modern aircraft tend to have much lower maximum densities - a 767's
cargo spaces can handle all of 7.68 pounds/cubic foot (0.123 t/m^3).

If spaceships are set up for containers, they'll have fairly small cargo
spaces. If they're set up for loose cargo and break bulk they'll have
larger cargo spaces. If they expect low-density cargo they'll be like
aircraft, and any high-density cargoes will mean a few pallets of cargo
sitting in a 'near-empty' hanger. A dedicated ore hauler will be the
opposite, of course - small bays filled with dense ore.

In general I prefer to use the traditional rule of thumb, as it still
works fairly well today, and also works fairly well for overall ship
volumes, and as Traveller spaceships seem to be built more like water
vessels than modern aircraft or spacecraft it seems a good rule of thumb
(hydrogen fuel tanks excepted, of course).

--
Rupert Boleyn <xxxxxx@gmail.com>