Equatorial wind speed at 60,000 feet?
 

Google is buying Titan Aerospace, a company which plans to make solar-powered drones that can loiter for up to five years (they say, six months is probably more like it) at a target altitude of 60,000'. Google says that it's interested in this for, among other things, bringing broadband to developing countries.

A quick look at the specs for these beasts says that they will be able to do around 65 mph. Which doesn't sound much... but apart from the small business of getting up and down safely, is that enough for station keeping for months at a time at that altitude over, say, Africa?

Lots of TRWs in lower latitudes go above 60,000.

As with all these things it is not a case of average winds, it is what happens at the extremes. The stratosphere is a relatively peaceful place in average winds terms but there would only need to be a week of 100Kt winds and the UAS is a few hundred miles away possibly unable to get back.

However, the more difficult weather to deal with could be vertical windshear in convective storms. The tropopause is not a neat flat layer at 36,000ft it is literally the local altitude at which convection stops. Near the poles it can be as low as 15,000ft and at the equator up to 70,000ft waves form and break in the tropopause its like a giant lava lamp in some regards. In the tropics and especially the Inter-Tropical Convergence Zone, the lines of storms around the equator, storms may reach up to 70,000 ft and the vertical updrafts may be at more than 100kts vertical speed. This would not be a safe environment for a widebody let alone a lightweight UAS.

So it might work - but engineers may have a different view of the reliability than scientists or software engineers.

Loitering a drone at 65000 ft is just the beginning, even if it has the battery power needed to carry it through the night.
The payload must provide adequate bandwidth and power, even though the power is only what the solar cells can provide and the send/receive antenna size and shape are constrained by aerodynamics. That makes for a ferocious engineering problem.
Getting a bus, as Google has done with the Titan purchase, is a very long way from having a product.

I've done some more digging, and found a range of results that suggest average windspeeds at those latitudes and heights between 5 and 20 knots. Which is quite a variation, quite apart from excursions. The UAV manufacturers say "There's no weather up there": I expect if any of them are successful we'll learn a lot more about how much weather there isn't.

As for the feasibility of the whole enterprise, as etudiant says getting the platform up there is one thing, having a useful payload is quite another. I haven't got exact figures, but the radio side of an LTE base station alone takes around 400w (that's the customer-side, ignoring backhaul). LTE cells aren't at FL 600, the Titan Aerospace UAV only generates 100w (and needs all of that to stay aloft) and has a payload of 32kg. Bigger models are planned with higher power budgets, and the basic plan seems to be to have lots and lots of low-power infrastructure rather than a few soaring behemoths, but I rather fear physics (and the lessons of Iridium) are agin them.

Check it out here with this amazing real time wind visualisation: earth.nullschool.net

It seems to be doable over most of Africa.

I have an LTE base station on my desk at work that draws...oh, around 25W total excluding only the RF power AMP, and weighs, oh, something less than 1KG. The comms aren't the tough part of this particular concept.

Wow, is big brother expecting launches of mangoes and bananas anytime soon?


-and, Arterpster, right - ITCZ city!