It's a joke.

Relax, he was just poking fun at your error in using 'sudo' (the linux super-user command) instead of 'pseudo' (the prefix meaning counterfeit).

Not sure if this is a response to the joke or not, though...

I ... think it might have been intentional. Notice the xkcd comic.

Right click on the files/folders you want to share read-only, go to the Dropbox sub-menu, and click "get shareable link". I use it all the time. I think it's exactly what you're describing?

I only see "Browse on Dropbox website..." and "Share this folder..." in the contextual menu.

I don't doubt you at all – I can see in their documentation that the feature exists. I just can't seem to make it happen.

Update: Looks like this only works for files that are already public, as far as I can tell. I managed to find "Copy public link..." if I right click in the Public folder.

Update 2: What a mess! Here's the doc that explains this buried feature: https://www.dropbox.com/help/167 I was able to switch to the "new sharing model", whatever that means. I still can't generate the link, though.

http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation Delta-V = v_exhaust * ln( mass_initial / mass_final )

It's bit more complicated than that. The balloon lift will decrease with pressure, which will decrease with altitude but so will aerodynamic drag. Ion engines design for satellite operation also prioritize low reaction mass usage and I am not sure the low thrust is a hard limit or a design choice. The device could also use vertical thrust to compensate for the loss of lift and then gradually rotate until it reaches orbital speeds.

It's probably impossible with current propulsion technology, but it would be useful to have a number when it starts to be possible.