The Hindenberg comes to Venus

Given last week's Return to Venus talk, here is a digression to discuss how a blimp floats above Venus' clouds (70 km). To spoil the argument - it can, and it will probably not explode; but you don't care.

We're following Zubrin's line of thought, with help from ballonsolaire.

Molecular weight of Venus is 43.45 g/mol; a little less than pure CO₂ (or Zubrin's Mars) but Venus does dilute the mix with some nitrogen. To displace 43.45 kg of Venus would take 2.016 kg of Earth-origin hydrogen gas (Venus hydrogen is heavier, but I hope to drain off some deuterium).

For air “fluid” density (ρ) at 70 km up, we have the Yeon Joo Lee dissertation figure 4.12f, below the Cold Collar. This graph is telling ρ slightly less than 100 gm^-3 but certainly more than Mars' 16. Let's say 90 gm^-3.

It happens that hydrogen AND water (18 g/mol) will cost money over Venus. Carbon monoxide is relatively cheap. That's 28 g/mol. So to displace 43.45 kg of Venus, we need 28 kg of CO. To displace 90 g of Venus, which at 70 km altitude is one cubic meter, takes 58 g of CO. This yields 32 gm^-3 of lift; or 0.32 Newtons / m³. By Newton himself, we plug in Venus' g force: at 70 km up, 8.87 * Math.Pow( 6052 / (6052+70) , 2 ) = about 8.666 ms^-2. Unheated CO may lift a mass of 37 g per m³ of balloon at this altitude over Venus. Hydrogen could lift 100 gm^-3.

But we’re helping hoist some turbines, like the GE90, at 8000 kg each. So damn the expense - full Hindenberg ahead!

Also we will be heating this balloon. With help from GE90, we fly underneath noon (or 11 AM) summer daylight every day. Gold leaf might be as pricey as water here, but (unlike how things work on Zubrin’s Mars) is hardly going to be scraped off in broad daylight soaring 70 km over Xibalba.

For sake of comparison I’ll be lifting a mainly cylindrical fuselage 20 m long and 2 m radius, pointed against the wind. That is 250 m³ volume. So: 25 kg lift if hydrogen. Heated to half-pressure: 50 kg.

Over the equator we get some help from the Hadley effect: hot air rises. This is most helpful where densest, at the lower altitudes. Mind you, there the balloon loses most of the sunlight, which is supposed to keep it hotter (and lighter) than the ambience.

CONCLUSION 7/27: A balloon is of negligible help to keep a craft aloft in sunlight over the equator. Over the poles, that's different.