This was an autonomous, solar-powered aircraft intended to be a prototype for “atmospheric satellites” which would orbit at high altitudes. The Helios prototype crashed in the Pacific during testing. Was the whole program scrapped? Are atmospheric satellites a good idea? If not, what’s wrong with them?
Most NASA projects have a limited budget. When the money runs out they stop; regardless of whether they’ve achieved success, failure, or only partial progress to their goals. Aeronautical research is the generally the runt of the NASA litter when it comes to suckling at the Congressional money teat. Helios’ money ran out.
Helios / Pathfinder was quite awhile ago: https://en.wikipedia.org/wiki/NASA_Pathfinder
In general NASA’s research goals are to tackle the very early proof of concept & risk reduction stuff; to ensure an idea can pass the laugh test with current or near future tech. Helios succeeded at that.
The next step is for private industry to pick up the ball and run with it. Since that time there have been a number of private efforts to develop practical long duration high altitude UAVs serving as “atmospheric satellites”. The favored configuration is solar powered low speed aircraft, although there are still some folks pursuing buoyant lift as at least part of the total package.
My feeble memory is not dragging up the names of some of the projects I’ve read about in the aerospace trade press. But there are several in the works right now. If I stumble on a name or two in my reading I’ll post back.
A private group seems to be attempting to fly around the world (in 13 separate legs) using a solar powered airplane. It just completed it’s most recent leg which involved being aloft for 118 hours straight, using only solar power. This plane is manned, so that’s probably the main limit on how long it can remain in the air at once. A drone version could conceivably stay longer.
This isn’t an atmospheric satellite exactly, but at least it kind of shows the general direction this technology has traveled since NASA dropped it.