Today, government secrecy sabotages an early
satellite. The University of Houston's College of
Engineering presents this series about the machines
that make our civilization run, and the people
whose ingenuity created them.
In 1985 Peter
Likins, then President of Lehigh University, told
an intriguing tale about the first satellites that
orbited Earth. The Russian Sputniks I and
II flew in October and November 1957. The
American Explorer I flew in January 1958.
The two Sputniks were not quite
spherical. But Explorer I was long and
narrow like a pencil. It was supposed to rotate
around its own centerline, like a pencil spinning
about its lead. It was definitely not supposed to
rotate end over end like an airplane propeller or a
Technically speaking, we say a pencil spinning
about its lead is in its minimum moment of
inertia mode. The windmilling pencil is in its
maximum moment of inertia mode, and it spins
A radio astronomer named Ronald Bracewell, at
Stanford University, tracked the first
Sputnik and determined that it was
spinning in its maximum moment of inertia mode. As
its antennae flexed, it dissipated a small amount
of rotational energy. That'd destabilized any
rotation that was not in the maximum moment
of inertia mode.
Bracewell knew about that behavior because that's
how galaxies behave. What he knew, and
Explorer's engineers didn't,
was that Explorer I's rotation would
be unstable. It would soon flip over and start
windmilling through space. That's what a spinning
coin does. It starts out spinning about one of its
diameters. Then, as it spends its energy, the
rotation flattens out. It tries to go horizontal
and spin like a turntable.
So Bracewell called engineers at the Jet Propulsion
Laboratory to warn them. But people in charge of
security wouldn't let him talk with the engineers.
He had to get the word out by publishing a paper in
the open literature. It came out seven months after
Explorer I was launched. Once up,
Explorer I made just one earth orbit.
Then it flipped over, and from then on it
windmilled across the heavens.
Actually, in 1957 another engineer named Landon
described that kind of instability in laboratory
notes at RCA. But he didn't publish them, nor was
he aware of the Explorer problem.
Information that isn't public can't do anyone much
There can, I suppose, be good reasons for secrecy
in technology. But make no mistake, secrecy is an
enemy of progress. Creativity, freedom, and
openness are natural bedfellows.
Ten years ago, a Russian engineer pointed out why
we stayed ahead of Russia in computer development.
Once we'd established a lead, he said, Russia tried
to keep up by copying what we'd already done. They
had plenty of ways to break through our security.
But, being forced by their system to play that
game, instead of being allowed to trust their own
inventive genius, they were trapped in a technology
that was doomed to stay one step behind us.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
Likens, P., Spacecraft Attitude Dynamics and Control
-- A Personal Perspective on Early Developments.
Invited Lecture preprint, American Institute of
Aeronautics and Astronautics, 1985.
Bracewell, R. N., and Garriot, O. K., Rotation of
Artificial Earth Satellites. Nature, Vol.
182, Sept. 20, 1958, pp. 760 et seq.
This is a revised version of Episode 47. I am grateful to James
Casey, University of California at Berkeley, for
suggesting this topic and for considerable counsel
on the subject.
For another illustration of the stability
phenomenon we describe here, see Episode 1313 and especially the
discussion of the rattleback in the
For more on Explorer I, see the website:
For a full size schematic
diagram of Explorer I click on the thumbnail
Images of Explorer I, courtesy of
The Engines of Our Ingenuity is
Copyright © 1988-2017 by John H.
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