The aircraft is able to climb under its own power. We have a diurnal energy cycle - charging the battery up through the day and deploying battery energy in the night. If we launch in the morning with a full battery, we have a whole day's worth of extra solar power to use to climb up to altitude.
Winds will be a bigger issue than energy when climbing. Up at 20 km (70k ft.) winds are quite calm, but we need to ascend through more turbulent winds as we climb. We’re sizing our MVP around this.
Winds up to 20 km are NOT quite calm. They can max out to 60 m/s at height of 10 km, which is more than 3 times than enough to blow a solar aircraft far-far away. You have to choose proper meteo conditions for climbing and descending and plan the trajectory taking into account those winds to be able to land at a given place.
I've been analyzing GFS data a couple of years ago for similar project. The problem is that lack of energy demands to design a really low speed aircraft for low densities that you can find in stratosphere. At 10 km winds are stronger than in stratosphere and density is higer.
You can find the results in https://journals.sagepub.com/eprint/GVXWXDABPE6A8PNRGTBU/ful....
The whole aircraft model probably is not like yours and is subject to many conservative estimates, but I am pretty much sure that wind model is accurate in this publication and generalizable to different regions.
I suppose an aircraft like this can climb like gliders do, using the streams of air that move upwards. This requires some planning, and likely a skilled glider pilot to help choose the course.
I'm similarly curious. Designing for a higher stall speed permits smaller wing area, lower drag, and lower weight. The cost is that takeoffs and landings become troublesome.
Other options that might work:
* Launch from the roof of a vehicle
* With a glider winch
* Towed by another aircraft
* Auxiliary engine / batteries that can be jettisoned & parachuted down
Climbing to altitude is the straightforward part. The transition from zero knots to the stall speed of the aircraft (minimum speed at which it can remain airborne) is the tricky bit. Designing for a lower stall speed necessitates wings which produce higher drag (by being larger) which requires more propulsion, which means bigger batteries and motors. So launching from a catapult or rocket or mothership or whatever means a lighter plane.
Launching by rocket means the plane would have to be pretty rugged to survive it. And that means more weight. You also have the issue of deployment. Folding wings means more weight and more things to go wrong.
Winds will be a bigger issue than energy when climbing. Up at 20 km (70k ft.) winds are quite calm, but we need to ascend through more turbulent winds as we climb. We’re sizing our MVP around this.