[TruthInThoughtWordAndDeed]

I wish that I knew for certain, but I can only guess. NASA says we cannot get past the Van Allen radiation belts (3600 miles above earth), so the height of the firmament appears to be at or less than 3600 miles.

Here is the link where NASA admits to this 3600 mile high barrier: https://youtu.be/4O5dPsu66Kw?t=164

The Bible does not refer to Mars or Venus or the like as “planets.” It refers to a greater light (the Sun), a lesser light (the Moon), and the stars. No mention of planets. Genesis 1:16

When the Bible refers to the stars, it places them in the “sky” or “firmament” depending on how the underlying word is translated from Hebrew to English. Genesis 22:17

However, the Sun and the Moon appear to traverse courses that are entirely under the firmament.

[Svartalfiar]

I wish that I knew for certain, but I can only guess. NASA says we cannot get past the Van Allen radiation belts (3600 miles above earth), so the height of the firmament appears to be at or less than 3600 miles.

Did you watch the video? The guy didn't say there's a 3600 mile-away barrier, he said it's a difficult area to get through, due to radiation. Orion, the craft in the video, is talked about going out through the Van Allen belt, and then return back through it. And, it's been done before! That's how we got a man on the moon. And if planets aren't mentioned in the Bible, then how do we fit them in to this limited-firmament idea? And you need to work on your numbers, if the Sun and moon are in the firmament but the stars are outside of the line.
Earth to your 'firmament: 3.6M miles
Earth to Moon: ~240M miles.
Earth to the Sun: ~93MM miles
Earth to Saturn's moons: ~934MM miles
Earth to Voyager II: 11.2B miles
Earth to Voyager I: 13.5B miles

So, the farthest man-made objects are much farther out than your firmament would seem to let them. They're out past the heliosheath and into interstellar space.