You've still got a fairly expensive asset sitting idle.
Perhaps, but look outside any active distribution center and you'll find acres of idle trailers. I know Walmart even uses them as long term storage.
Then there's the extra labour to move one box at a time
If you're already moving one box at a time, because you're building the pallet, you may as well move one box at a time directly into the container. That was the whole point I was trying to make. There is no extra labor. The container itself is the unit of transport, rather than the pallet.
with ladders. You might be eight feet tall, but most people aren't.
Large molded plastic step stools, actually.
... two trips over one,
Unless the previous trailer just waits around until the next one is dropped off.
And where is this happening?
Anywhere you're shipping freight between two of your own facilities.
You can unload 3,000 cases of palletised goods far faster than two or three people stuck in the back of a semi-trailer can put them on a conveyer belt. It takes a warehouse 20 minutes to unload a full 26 pallet load semi-trailer, it takes 2hrs to unload 1500 cases on a conveyer belt.
That's only relevant if the driver and truck has to stay with the trailer. In a major distribution network where it's the same company on both ends, that does not apply.
Sure, pallets take some vertical space, but the amount of space taken is small compared to the ability for one person to move close to two tons of cargo single-handedly across smooth floors with no more than a jack.
That requires one person and one hand truck or fork lift to shuttle each pallet of two tons of cargo back and forth. It's cheap, but it's very low throughput, and it doesn't scale up to high throughput well. If you need high throughput, you're going to use conveyor. You use pallets for storage, for items that cannot be conveyed, or for things like LTL receiving where you can't keep the trailer, and don't want to hold up the driver while you hand unload.
Branson has a track record of seriously underestimating the difficulty of the challenges he picks. Plus he seems to believe he can replicate serious engineering achievements - eg space flight - on a shoestring budget.
You're overestimating the capability of SpaceShipOne/Two. It goes to space for all of a couple minutes. It does not go to orbit. The engineering requirements aren't nearly as tough. We've been sending unmanned vehicles up there since the early 40's, and manned ones up since the late 50's, back when NASA was still called NACA.
The Apollo programme was 4% of GDP, by itself
The Apollo program cost ~$20B, over the better part of a decade, during a time when the US GDP was rose from around $600B to $1T. So, it used roughly 0.3% of the GDP over that time period.
There's even a type of energy storage system you can make with superconductors - one of the highest power density and efficiency energy storage methods known to man.
The ultimate capacity of one of these systems is on the par with supercapacitors, and an order of magnitude lower than traditional chemical batteries. Their high power, low capacity, and functionally unlimited cycle life make them useful as a transient power filter, rather than a meaningful energy storage mechanism. Their sudden and nearly instantaneous quench makes them downright frightening as a sizable energy storage mechanism.