Yeah, ballasting is often forgotten when people talks about huge cargo airships.
Yes, it can drop a huge generator into the middle of nowhere for your construction project, but unless you do something it will then shoot up to the stratosphere due to all the extra lift.
Still, its solvable with either some rudimentary infrastructure (pump water aboard as you unload cargo) or by removing some of the lifting gas (much less of an issue with hydrogen).
There is (was?) an effort to restart Airships for cargo traffic. They solved the ballast issue with onboard compressors. If understood it correctly that solved this problem complete with [effectively?] no loss of lift gas.
Interesting! Setting the weight of the compressors and the energy requirements (I guess you could supply that ground side if possible) it really does solve the issue of loosing helium. :)
For hydrogen you I guess you could either let it go or also use the compressors in case there is no way to replenish the lifting gas & you might need the extra lift before returning to your primary maintenance base.
Right but now you're consuming energy to run those compressors, making the energy-savings moot. If you look at the history of airship development (which admittedly is ancient by modern technological standards), there were several incidents of airships floating away from their mooring. Mooring an airship is actually a fairly difficult problem.
Energy usage for compression is tiny compared to actually transiting, and you can get some of the energy back. Or if it was hydrogen fueled, just run your engines for a short time.
Or, just have the compressor ready at the dock, and wait with the unloading until the hydrogen has been compressed.
But yeah, simply running a compressor powered by hydrogen should suffice. I assume the airships would require some surplus hydrogen anyway, in case there's a mid-flight leak or something.
Fair enough you're probably right. And if you have a battery onboard and charge it using solar cells on the ship, you should have enough energy generated to at least run the compressor and dock the ship.
This might be slow, but what about using the lift gas in a fuel cell with atmospheric O2 for extra efficiency? You reduce the lift gas in the bags, and if you store the water aboard then you get extra ballast. You could even “unload” the extra electricity for use groundside.
The corollary pipe dream here is to line the entire interior of the envelope as a fuel cell membrane and use the airship as a portable battery.
IIRC some military airships condensed water from their their engine exhaust to keep better control over their balance (the ship otherwise gets lighter as you burn fuel and you might have to release some of the irreplaceable lifting gas instead).
This is only really an issue with Helium. When Hydrogen is your lifting gas, you can use it with fuel cells to power the cranes, producing water as a further ballast.
Yes, it can drop a huge generator into the middle of nowhere for your construction project, but unless you do something it will then shoot up to the stratosphere due to all the extra lift.
Still, its solvable with either some rudimentary infrastructure (pump water aboard as you unload cargo) or by removing some of the lifting gas (much less of an issue with hydrogen).