Zwicky's Pellets
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On 1957 Oct 17 at 0505 UTC the US Air Force launched a sounding rocket,
Aerobee USAF-88, from Holloman Air Force Base in New Mexico to an apogee of
114 km.
The ejected rocket nose cap carried three explosive devices (loosely, 'grenades')
which were detonated at about 80 km altitude. Charge A, built by Thomas Poulter
of Stanford, was expected to accelerate about 0.1 gram of material to very
high velocities of order 14 km/s; Charge B, developed by John Rinehart of Smithsonian
Astrophysical Observatory (SAO) in collaboration with Poulter, was designed to
accelerate a slightly higher mass of particles to somewhat lower speed; Charge C,
built by Fritz Zwicky of CalTech, used an iron oxide/aluminium thermite mixture
that was intended to accelerate self-luminous material to velocities above 11 km/s.
In the event two meteor trails were seen emanating from the explosion of the
nose cone. Zwicky claimed that his pellet had reached Earth escape velocity
and gone into orbit around the Sun (Engineering and Science, Jan 1958, p 20).
This claim is often repeated uncritically, most recently in a fun article by
Nick D'Alto in Smithsonian's Air and Space magazine:
http://www.airspacemag.com/daily-planet/1957-two-tiny-pellets-were-first-man-made-objects-escape-earths-gravity-180954622/

However, Zwicky was a genius, but also very much a self-promoter.
He never published a science paper on the experiment. The only serious analysis I've
seen is by R. McCrosky of SAO (Observations of Simulated Meteors,
Smithsonian Contributions to Astrophysics, 5, 29 (1961) which
can be found at http://adsabs.harvard.edu/abs/1961SCoA....5...29M
indicates that the observed meteor trails were from charges A and B, which were not
self-luminous and so would only glow as they reentered the atmosphere heading down
and burning up. A's speed was measured at 14.4 km/s (Earth-relative) while B's was
in the range of 5 to 9 km/s.  McCrosky doesn't say so explicitly,
but the implication is that Zwicky's grenade didn't work.

We may conclude that Poulter's Charge A pellet, with a mass around 0.1 grams,
was (briefly) the first artifact to reach escape speed - but not escape velocity (i.e.
it was going in the wrong direction). I really wanted the story of Zwicky's
solar orbit pellets to be true, but it doesn't look good. Maybe McCrosky's analysis
was wrong - I'm going to check if the relevant tracking plates are in the Harvard Plate Stacks
but I doubt it, the plates from the NMSU ballistic cameras would probably have stayed
in McCrosky's possession and probably no longer exist.

[Edit, Oct 2017: At an altitude of 80 km, I suspect the air density is
high enough that the pellets would probably have become meteors and
melted, even if they were headed up instead of down. But I don't know
how to do that calculation.]

I conclude that Zwicky's claim is unlikely to be true and, sadly, should not be
accepted as historical fact.

- Jonathan McDowell, May 2017