Can sunlight alone keep it up for a year?
Does the loop close?
Solar collection integrated over the real hull surface, a fuel cell and electrolyzer round trip, and a day-by-day mission integration that reports the day it fails rather than an average that hides it.
Does the loop close?
Regime A is the project's thesis: sunlight in, electrolysis to store, fuel cell to convert back, engines cold, endurance bounded by component life rather than by energy. The balance is run day by day through a year, because an annual average hides the ship that banks a surplus in June and runs a deficit in December.
Where the energy goes, annualised
The finding: energy is not the binding constraint
It is not close to being one. Lift makeup, the term that sounds like it should dominate a hydrogen airship, is 1.9% of demand. Station keeping is 88% and it is cubic in wind speed, so the real question this vehicle faces is not whether it can power itself but what weather it can live in. Whether it can carry its own structure is phase 3, and that is where the answer is likely to get hard.
| Design point | Length | Volume | Gross lift | Leak | Hold | Max wind | Regime A |
|---|---|---|---|---|---|---|---|
| Baseline | 115 m | 32,968 m³ | 37.6 t | 1.08%/a | 8 m/s | 12.2 m/s | CLOSES |
| Minimum viable | 65 m | 5,953 m³ | 6.8 t | 1.57%/a | 6 m/s | 14.9 m/s | CLOSES |
| Stretch | 125 m | 42,338 m³ | 48.3 t | 1.08%/a | 12 m/s | 11.4 m/s | FAILS |
The stretch ship does not close, and it is left that way rather than tuned until it passes. It fails on day 354 by 16 percent while showing a comfortable 12.5 percent annual surplus, which is exactly the trap a day-by-day balance exists to catch. The cause is the battery, not the hull: on the shortest day the pack saturates and the overflow spills into the hydrogen path at about a third round-trip efficiency, so those kilowatt hours cost three times as much collection.
What should the engine burn?
Comparing fuels by energy per kilogram is the habit of every other vehicle and it is the wrong metric here. On an airship the scarce resource is not mass, it is lift: every kilogram of fuel aboard is a kilogram of payload that is not, and every cubic metre inside the hull is a cubic metre that is not lifting. Ranked by energy stored per kilogram of lift given up, the order inverts.
| Fuel | MJ/kg | Lift cost | MJ per kg of lift | Water recovery needed |
|---|---|---|---|---|
| Modern air-density gas blend, 46 mol% propane / 54 mol% methane | 46.5 | 0.93 | 50.0 | none |
| Blaugas, as carried by LZ-127 Graf Zeppelin | 48.0 | 0.97 | 49.6 | none |
| Jet-A with exhaust water recovery | 42.8 | 1.05 | 40.6 | 81% |
| Hydrogen drawn from the lift cells | 120.0 | 13.40 | 9.0 | impossible |
| Hydrogen in 700 bar Type IV storage | 120.0 | 19.40 | 6.2 | 11% |
You cannot burn the lifting gas
“One gas for lift and fuel” is the most attractive idea in the propulsion module and it does not survive the buoyancy budget. Removing 1 kg of hydrogen from a cell removes 1 kg of weight and about 13.4 kg of gross lift, so the ship goes 12.4 kg heavy per kilogram burned, while combustion returns only 8.94 kg of water. No recovery fraction can hold trim, and recovering the water makes it worse rather than better: 21.3 kg heavy instead of 12.4.
A modern buoyancy-neutral blend is trivial to formulate and better than the historical one: 46.1 mol% propane with 53.9 mol% methane is exactly air density, 46.6 MJ/kg, both commodity fuels obtainable anywhere. Blaugas itself was not air density, despite what every popular source says: relative density 0.963, so consuming Graf Zeppelin’s full load made it about 1,316 kg heavier.
Which resource runs out first?
The energy balance said energy does not bind. This steps a day at a time through a multi-year mission tracking gas mass and purity, water, food and consumables, to find out what does. The answer is a legal interval, and the thing everyone expects to bind turns out not to.
| Resource, on its own | Days | Years |
|---|---|---|
| condition inspection | 365 | 1.00 |
| food | 400 | 1.10 |
| food shelf life | 5,479 | 15.00 |
Water was expected to bind. It does not.
A 90 m hull presents about 1,170 m² of plan area to the rain. In the trade wind belt at a metre of annual rainfall, even a poor 40 percent collection efficiency gathers 2,086 kg/day against a net loss of 9.3 kg/day for two people at 85 percent recycling. Catchment covers the loss 224 times over, and still covers it more than fifteen times at the most pessimistic end of every assumption.
The vehicle is water rich. Ballast is free, electrolyzer feedstock is free, and the hygiene allowance that looked like the largest lever in the life support budget is not a lever at all. That makes water a station-choice question rather than an equipment one: parked under a subtropical high instead of in the trade winds, the catchment term collapses and the whole analysis changes.
What is plumbed to what
A day-by-day integration answers whether the loop closes. It cannot answer whether the vehicle has one bus whose failure kills everything, or a water loop whose only source stops working in the doldrums. These are the schematics, and the checks are connectivity questions rather than budget ones.
Power
Nothing drives a propeller mechanically. Every source feeds one DC bus and every load takes from it, which is what lets the engine sit aft for the exhaust rule while the propulsors sit where they are aerodynamically useful. It costs a conversion stage and it buys the entire arrangement.
PASSHabitat and avionics has two independent paths to a source.
4 independent sources upstream: array, generator, fuel-cell, battery. Losing any one leaves the load fed.
Water
The fuel cell and the electrolyzer are a closed water loop with each other: nine kilograms of water per kilogram of hydrogen, both ways. The hydrogen store is therefore also a water store, and the two inventories cannot be reasoned about separately. What is not closed is the crew’s own consumption, which is why the recycling fraction and the catchment decide the endurance rather than the tank size.
PASSThe water loop closes on the annual average.
2086 kg/day of catchment plus 53 recovered and 2 from the fuel cell, against 62 kg/day of consumption. That is a surplus of 34 TIMES on catchment alone, because the hull presents a plan area of nearly two thousand square metres and two people drink very little of what lands on it. WATER IS NOT THE BINDING RESOURCE and it is worth saying so plainly: the interesting constraints on this vehicle are food, hydrogen inventory and the structure, and a water budget that looks tight has almost certainly double counted the electrolyzer.
PASSThe tanks carry a 30 day dry spell with no catchment at all.
213 kg drawn down over 30 dry days against 2500 kg of capacity. Recycling and fuel cell product carry 89 percent of consumption without any rain at all.
PASSElectrolyzer feedstock is counted as circulation, not consumption.
2.2 kg/day goes to the electrolyzer and 2.2 kg/day comes back from the fuel cell. Nine kilograms of water per kilogram of hydrogen, both ways. Counting the outbound leg as consumption would double count the largest flow in the loop and make the water budget look impossible.