Played in browser (firefox) with no apparent issues in my case...
Impressive visuals, with moving shadows as the balloon ascends, everything is there and everything has a good reason to be there. At first I thought the meters were just static, I coudn't believe how good they do react. It really made me feel inside. SFX are amazing, clock sound is 3D!! (probably other sounds too, didnt check). Mechanics feel very organic. I tried a couple of times and always got a "burst in the stratosphere", but I got a lot of fun. I clearly need to fully understand how to pilot that thing, so I will keep trying.
Despite taking place before what is actually considered the space race, you really delivered an amazing scope for such a short time, congrats.