[masklinn]

> 250 tonnes is A LOT to lift. Look how big a hot air balloon needs to be to lift a few passengers in a basket. Sure helium has more lifting power but it doesn't create miracles. That means the balloon would have to be absolutely massive.

Agreed, per my calculations it'll need to be around 120m wide, and 30 deep (lifeisstillgood comes up with slightly smaller numbers of 100 x 25, possibly because they used 1.1kg / m3 where I used 1 for the lifting power of helium). That's more or less a baseball field.

And it's just for the naked payload, you still need to account for the envelope itself, the solar panels, the cabin, the engines, the batteries, and the fuel (as, per site, it has a biofuel backup). That probably adds a dozen tonnes at least (the solar panels alone would be 5-10 depending how much of the top's surface is covered). By the end you're probably looking at a men's cricket field, one on the large size.