World Reality

Here's one from the Explorer 2 balloon in 1935 from 72,395 ft.
it's the first picture to show the curvature.
The Explorer assents were US military.

Why no curvature in new video at higher altitudes from civilians?

A list of Early ballon missions.
This is actually the start of the space race between the US and USSR.

http://www.phenomena.org.uk/features/page139/page139.html

I found a few interesting points on the page

-Charles Green.
Nassau balloon.
September 10, 1838
Estimated assent of 26k ft.

The sun set just before the ascent, yet at 12,500 feet they were “once more within the sun's rays.”

I'll have to look into this further.

- P.Fredeseenko
Ossoaviakhim Syrius ballon
January 30, 1934
Soviet
Assent hight of 72,178 ft

"The sky colours recorded by the aeronauts changed from 'marine blue' at 5.28 miles, through dark blue, dark violet, dark violet-marine, dark violet-grey, to, at a height of 13.67 miles, black-grey."

You would think they would make some notes on seeing curvature.
I've been meaning to look for the original logs but so far only found this document

https://www.google.com.au/url…

I've also hope to get some time to look into the United States Air Force programme "Man High" which was a project to send one aeronaut for a protracted stay of at least a day in the stratosphere.

Man high 1
Sky at his maximum altitude of 96k ft described as “very dark blue, almost black. It's hard to describe the colour, whether it was black or blue-black.”

Man high 2
102k ft, At this height, blue sky reached about 10 degrees above the horizon, changing from white to pale blue to dark bluish purple; “...the sky was so heavily saturated with this bluish-purple colour that it was inescapable, yet its intensity was so low that it was hard to comprehend...” His horizon was 400 miles away.

But no curvature notes

Almost all Google search images show curvature
https://www.google.com.au/search…

To Research

Project Excelsior- High altitude jumps 1959-60

Such balloons were used for scientific research, most notably in the US Navy's SKYHOOK program,

Look at MOGUL(excuse fro roswell as it was a secret balloon program in 1947'

GOPHER was used to spy on USSR

MOBY DICK IN 1953 TO MAP HIGH ALTITUDE WIND CURRENTS

FLYING CLOUD used for a hydrogen filled attack balloon, like chemical or bio agents

GRANDSON for high alt photo reconosnce

source for "cold war balloon fights" to cover this section of orange text is below

http://www.airvectors.net/avbloon_3.html

Project Echo- balloon sat

http://history.nasa.gov/SP-4308/ch6.htm