Those Thunderhead balloons are fairly common in recent years. They carry a variety of payloads and can remain aloft for months, although most missions are around a week or two.
Here's a Thunderhead that I caught 3 years ago. At the time it was around 65,000 ft altitude and directly overhead. You can see the payload and its solar panels silhouetted against the envelope of the balloon. At that altitude the balloon is several hundred feet in diameter.
Very bright and obvious in the sky. Lots of UFO reports.

Here's what they look like being launched.

Here's a Thunderhead that I caught 3 years ago. At the time it was around 65,000 ft altitude and directly overhead. You can see the payload and its solar panels silhouetted against the envelope of the balloon. At that altitude the balloon is several hundred feet in diameter.
Very bright and obvious in the sky. Lots of UFO reports.

Here's what they look like being launched.

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