Standard Cargo Units need to be modified in some way.

[Yaffle]

Strictly speaking, neither mass nor weight explains why a child can't push a shipping container around on Earth. That's due to friction with the floor. Put it up on air bearings and a child will move it just fine, although it will accelerate quite slowly (and definitely don't get between it and a hard place once it's moving).

In the same way a human can push/pull a multiple-thousand tonne ship at the dockside, albeit needing a reasonable time to exert the force to see any movement.

 

[Morbad]

Methinks you may be confusing energy density with amount of hydrogen in these statements.
Gasoline is full of lots of other stuff than hydrogen, thus it has less hydrogen than pure liquid hydrogen.

No, most hydrocarbons and water have greater volumetric hydrogen density than L2 because L2's density is extremely low.

A liter of liquid L2 is a grand total of 71 grams, all hydrogen.

A liter of gasoline is only ~14% hydrogen, but since a liter of gasoline is about 750 grams, that's still more hydrogen (over 100g) than a liter of L2.

A liter of water is ~1000g, obviously, and is about 11.2% hydrogen, by mass, or 112 grams of hydrogen per liter.

Citation?

I googled the densities and molar concentrations then extrapolated, but it's common knowledge that liquid hydrogen has horrible volumetric energy density because it's so light.

Liquid hydrogen's energy density per unit of mass is quite good and obviously it's hydrogen density per unit of mass is as high as it gets, but volume is quite often the limiting factor in hydrogen storage and many compounds have superior volumetric hydrogen density.

It's highly unlikely that liquid hydrogen would be in a canister of "hydrogen fuel" for this, and other reasons (it would need to be highly pressurized or refrigerated, either of which would require a stronger canister and more careful handling). If I had to guess, I'd say it's probably just diesel fuel or some sort of metallic hydride powder, because those would be the best density/convenience options and water is it's own commodity.

Further reading:

https://pdfs.semanticscholar.org/b781/192e2624db103d1b615502dd44354eff9b52.pdf -- good hydrogen density chart on page 4.
https://www.energy.gov/eere/fuelcells/metal-hydride-storage-materials
https://en.wikipedia.org/wiki/Hydrogen_storage

Well, if we can imagine suitably strong canisters, we could be transporting slugs of metallic hydrogen. That has a density up to a couple times the density of water. Probably need to keep it pressurized to a few million atmospheres though!

I can't reconcile such canisters with how fragile they are in game. Far easier to think of a ton of hydrogen fuel as just a ~100-120kg of hydrogen bound up in just under a ton of hydride or hydrocarbon and poured into a barrel.

 

[varonica]

No, the child would move.

Only if you didn't nail it to the ground

But seriously now, in zero gravity they would both move and the amount of motion can be calculated quite easily given we know the mass of each and the force exerted, but the fact is the child can grab hold of a rail to stop itself, but the container would continue moving slowly until it encountered a reciprocal stopping force, so yes the child could load the ship by hand....granted very slowly, as long as said child exerted force in the correct direction.

 

[varonica]

I can't reconcile such canisters with how fragile they are in game. Far easier to think of a ton of hydrogen fuel as just a ~100-120kg of hydrogen bound up in just under a ton of hydride or hydrocarbon and poured into a barrel.

One of the mistakes many people make is that by itself hydrogen just isn't a useful fuel. If you put on a breathing mask and stepped into a container full of hydrogen gas and nothing else and struck a match nothing would happen, because pure hydrogen doesn't burn, it has to be mixed with a catalyst at the correct concentrations, sometimes LOX is used. Combining hydrogen with a catalyst that ignites and burns with a spark or applied heat and therefore doesn't need an external catalyst may be the way to go, but all you really end up with is a bomb, keeping fuel and catalyst separate until needed is the better way to go. Solid rocket boosters employ a combined fuel and catalyst, but of course once you touch a match to one of them it doesn't go out until it's all burnt, so not so useful when trying to dock.

It is indeed quite likely that our hydrogen fuel isn't pure hydrogen but actually a compound since I don't see big tanks of LOX anywhere on any of my ships and it's just called hydrogen fuel for convenience!

 

[Morbad]

One of the mistakes many people make is that by itself hydrogen just isn't a useful fuel.

For a fusion reactor it would be.

 

[Bob Lighthouse]

Only if you didn't nail it to the ground

But seriously now, in zero gravity they would both move and the amount of motion can be calculated quite easily given we know the mass of each and the force exerted, but the fact is the child can grab hold of a rail to stop itself, but the container would continue moving slowly until it encountered a reciprocal stopping force, so yes the child could load the ship by hand....granted very slowly, as long as said child exerted force in the correct direction.

The child's relative mass and strength would not be enough to do jack.
And no, go try to help dock a ship sometime.
Mass matters a whole lot more than you seem to be giving credit for.

Poor kid would still get smashed.

 

[Bob Lighthouse]

In the same way a human can push/pull a multiple-thousand tonne ship at the dockside, albeit needing a reasonable time to exert the force to see any movement.

They need the Earth and gravity.
There's no way a child can do that either.
Have you ever worked dockside?

A single human cannot do that in any practical sense.

 

[Sylow]

For a fusion reactor it would be.

And as long as it's volume is not a crippling limiting factor, actually a quite good one.