I remember reading an article in Aviation Week, when I was in grad school (ca. 1980), about the author getting a ride in an SR-71. One thing that stood out vividly at the time, and remains with me to this day, is his account of powering the aircraft up. When the star tracker came on, he wrote, it immediately began picking up stars <i>while on the ground</i>. I have never been able to find independent corroboration of this. It's a shame that I never asked all of the SR-71 pilots I knew up at Dryden about it, but it wasn't something that came to mind (it wasn't "top of mind", as everyone always says).
On Apr 1, 2023, at 9:27 PM, whitney bayourat.com <whitney@xxxxxxxxxxxx> wrote:
The SR71 star tracker worked great, day and night. Read the book "Skunk Works" by: Ben Rich
Whitney Richard
Secretary Tripoli Louisiana
President South Louisiana Rocketry
whitney@xxxxxxxxxxxx
-----Original Message-----
From: arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> On Behalf Of Jim Davis
Sent: Saturday, April 1, 2023 12:41 PM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Star trackers at high altitude
I was reading Scott Lowther's "Origins and Evolution: Lockheed SR-71 Blackbird" (highly recommended, by the way) and came across this statement referring to the SR-71's astro-inertial navigation system:
"For an aircraft operating about 80,000ft, stars would be visible at all hours of the day. At that altitude the sky is black, not blue; the aircraft appears to be in space."
My first thought was that this couldn't be right; I was reminded of claims by moon hoaxers of why no stars were visible in photos taken on the moon. The lunar surface is so bright during the lunar day that it drowns out any starlight.
Thinking on this further I began to have doubts. At 80,000 ft there is no dust to scatter sunlight and perhaps the aircraft would be far enough above the earth that the reflected light from the surface wouldn't be that bright.
Can stars be tracked at that altitude during the daylight hours? If so, at what altitude does this become practical?
Jim Davis
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