The energy required to get to the stratosphere (10km) is 10e6 tonnes * 9.8 (N/kg) * 10km =~ 10^15 joules. By my calculation that is more than twice the energy required for all 136 space shuttle missions (~4*10^12 joules each) over the entire duration of that project. Yes, they are balloons, but I would be that extracting hydrogen or helium takes some significant percentage of its lifting capacity.
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The energy required to get to the stratosphere (10km) is 10e6 tonnes * 9.8 (N/kg) * 10km =~ 10^15 joules. By my calculation that is more than twice the energy required for all 136 space shuttle missions (~4*10^12 joules each) over the entire duration of that project. Yes, they are balloons, but I would be that extracting hydrogen or helium takes some significant percentage of its lifting capacity.