Go higher. If you search for "high altitude wind" you'll get info from 20,000 feet, which is not at all the same as 20,000 meters. Past a point, the thinning atmosphere actually means less coupling and wind speed decreases. You'll note that tiny quote halfway through about it being difficult to get up to the required altitude of 20km. That's because the average wind speed bottoms out around 5 meters per second at an altitude between 20km and 25km [1]. Add in the thinning air reducing drag and, yeah, a solar-powered balloon can absolutely stationkeep at that altitude. Here's a wiki page with more links: https://en.wikipedia.org/wiki/Geostationary_balloon_satellit...

[1] https://www.researchgate.net/figure/Average-wind-speed-in-th...

I was wondering about this too. Then again, I don't know the air density difference. 130 knots at half the density (not that I know if half density is a feasible figure) would impart something like half the force, I imagine. Then again, lower density affects the ability of craft that use density for lift to operate.

> not that I know if half density is a feasible figure

1/15th - .08 kg/m^3 at 20km, 1.2 kg/m^3 at sea level. 20km is way the heck up there. And yes, it does make it difficult to build something buoyant enough, which is why the use case for this is something like a geostationary internet balloon rather than for transportation.

https://www.engineeringtoolbox.com/standard-atmosphere-d_604...

Density doesn't matter. As the density decreases the force of the wind does decrease, but the propulsive ability of propellers/wings also decreases. So the net effect is that the engines have to work equally hard.

Yup, that has been the Achille's heel of these types of vehicles. One work around is to have a bunch of vehicles and have them move to altitude, stay over the area of interest as long as possible and then change to a lower altitude without the winds to move back to the head of the line.

Apparently the craft is powered entirely by solar power, plus batteries, to work at night. A solar powered craft cannot maintain 130 knots.

Solar impulse 2 used 269.5 m2 of solar panels to produce 66 kW peak and do 75 knots.

That’s only ~1/2 the current max efficiency of solar panels. Suggesting many other improvements are at least possible and 130 knots are within reach if that’s what was being optimized for vs say cost.

The cool thing about this craft is that it’s a glider and doesn’t use solar power for direct propulsion. Instead it uses the solar power to make the ballon lighter than air. Once it reaches altitude it will start gliding by making the ballon heavier than air. While gliding it can reach very fast speeds. The question is though how many times it needs to refill the ballon during the night and if the stored power is enough.