How does it deal with expanding gases at higher altitudes?

probably the same way they deal with it today, either a compressor and tank that can be filled from the gasses in the balloon as it rises and released at it descends or you just calculate the rate of expansion and make sure your balloon has enough excess space and elasticity to compensate for it.

A 90 kg payload might be too little for much of a radar, but enough for an InfaRed Search & Track system & a telescope.

Airship can beam comm from shore to ship, Internet or from HI to Mainland US & Alaska alone for Communications. & aid Search & rescue IE MH370.

Nice but I would prefer to see it powered by a ground based laser.

Another great advantage is there will be no space junk floating around at high speeds. Also no aircraft will ever encounter the blimps because they are operating at altitudes most aircraft engines would cease to function at.

So, why the convoluted power system? Solar → electrolysis → hydrogen fuel cells → electric propulsion motors... why not directly from Solar to motors? You would need an intermediate storage cell array of course, but surely a battery or capacitor system able to last through the night wouldn't weigh much more than all that extra hi-tech conversion (read inefficient) of power via water/hydrogen? Too much to go wrong, I'd think.

Less than 100kg payload for something that size seemed a bit low, but with 15,000-30,000 cubic meters of lift gas and a lift of about 9.5g/m^3 at 20km and outside air 20K above normal temp., they have a gross lift of only 1400 - 2800 kg, which is not really enough for the craft.
Going down to 55kft / 17km gives 63% more lift, and is still well above air traffic - but getting down to 36kft/11km would give 4x the lift at 20km. Airships work much, much better at lower altitudes.

@ MzunguMkubwa They probably think that the hydrogen system will last longer than batteries but they might plan to have the waste heat from the fuel cells warm the lift gas through the night stabilizing the lift.

@ EH The system will not work at lower altitudes due to wind speed. At approximately 70,000 ft (actual altitude varying by latitude and season and not at all at high latitudes) there is a very sweet spot in terms of annual average wind speed (about 12 kph). This is where the energy required for station keeping is absolutely lowest. This band of nullified wind is also relatively thin, only a couple thousand feet thick. If you are above or below this very much then annual average wind speeds are significantly higher.
Any system intended to operate here also has to be able to fairly tightly stabilize altitude against daytime heating and nighttime cooling of the lift gas.