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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