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<p><font size="2" face="Verdana,Helvetica,Arial" color="white"><b><font size="3">Manmade
Meteors</font><br>
by James Oberg</b></font> </p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white"><b> </b></font>
</p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">One of the
most thrilling surprises for a skywatcher is a bright fireball. Aside
from the unexpected shock, there's the visual variety of colors, flares,
a trail, and perhaps even sounds. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">Sometimes
the fireball is manmade, a falling satellite or on occasion a deliberately
descending manned spacecraft. Their special features include a flatter
flight path and a wider variety of materials to burn (and occasionally
explode) spectacularly. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">These artificial
fireballs may be a treat when viewed from the ground. But the view from
inside the manmade meteor is even better, and may provide even more unique
testimony about details of the atmospheric entry heating process that
all objects--natural and artificial--endure. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">These close-up
views include bizarre colors, shapes, and motions of the flames. And they
provide some intriguing new mysteries, too. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">Several hundred
people--astronauts and cosmonauts--have ridden descending spacecraft through
the flames of atmospheric entry. Mostly this happened over the sunlit
side of the Earth, since the spaceships wanted to land in daylight. In
those cases, the fiery outside patterns were subdued, and often the crew
had other things to concentrate on, or they weren't near convenient windows.
</font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">But sometimes
they glance outside. Based on interviews with John Glenn, National Geographic
writer Robert Voas described what America's first man in orbit saw during
his Mercury-6 entry in 1962: "All around him glows the brilliant orange
color. Behind, visible through the center of the window, is a bright yellow
circle. He sees that it is the long trail of glowing ablation material
from the heat shield, stretching out behind him and flowing together."
Glenn's own comments over the radio were pithier: "This is Friendship
7," he had reported. "A real fireball outside!" </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">Later, Gemini
and Apollo astronauts viewed and sometimes filmed the fiery trail behind
them, since these spacecraft had small backwards-facing windows (Russian
manned space vehicles do not have windows in these positions). But none
of the reports from these small capsules prepared engineers for what astronauts
were able to see out of the bigger windows of the much bigger space shuttle
vehicle. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">It's important
to realize that the shuttle enters the atmosphere at a high "angle of
attack"--in earthside terms, it's making a big "belly flop" with its nose
very high in relation to its forward motion. The compression shock wave
covers the entire underside of the spacecraft, but is hottest at the leading
edges of the wing and under the nose. The fireball trail streams backwards
in about the same direction the shuttle's tail is facing. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">The shuttle's
windows face in many directions. Forward, the six windows allow the pilots
more than 240 degrees of view. Overhead, two windows at the back of the
cabin allow observation of targets in space which the shuttle is docking
to. Aft-facing windows show the payload bay--but of course, during landing
the payload bay doors are closed so no external scenes are visible through
them. On the middeck, there is a large window in the main hatch on the
spaceship's left side. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">The first
shuttle entry partially in darkness was STS-5 in November 1982. Gazing
forward, mission commander Vance Brand later described how "the sky turned
rust-colored." Copilot Bob Overmyer compared the view to "leaning into
a blast furnace." Watching the lights from the middeck, Joe Allen recalled
how "it's like being inside a neon sign--we could see this rose-colored
glow for a long time." </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">The first
shuttle night landing was STS-8 in September 1983, so they had darkness
the entire length of their atmospheric descent. All five astronauts got
good views of the flames surrounding their spaceship. Commander Dick Truly
described how the color started out as "salmon-colored," then shifted
to "white hot." </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">But astronaut
Dale Gardner--sitting in the aft right seat that had been installed after
the flight of STS-5--noticed something entirely different. He recalled
being puzzled by light flashes from above and behind the Orbiter, coming
in through the overhead windows. "I leaned forward and craned my neck
around," he recalled, "but I never could get in the right position to
see anything." Instead, Gardner held a 16-mm camera up, pointed it "in
the blind" towards the light, and triggered off several seconds of exposures.
</font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">The film
captured a bizarre glowing structure, just like the inside of Joe Allen's
"neon tube" extending backwards (downstream) from the Orbiter. On a later
flight, as two crewmen deliberately stayed out of their seats to watch
the apparition, it reminded them of a glowing Easter Island statue. "Should
we photograph it," one wondered out loud, "or bow down to it?" </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">The "light
show" clearly progressed through stages. At the end of his first space
flight, aboard STS-11 in February 1984, "Hoot" Gibson kept careful track
of the show. The color surrounding the Orbiter changed from dull pink
to a bright orange pink, which then became supplemented with a bright
white flickering from behind. The period ranged from one to three seconds.
Looking backwards from his seat, through the overhead window, Gibson recalled
seeing "two sheets of flame interacting, moving back and forth from one
side to the other." </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">Describing
a video sequence out the overhead window during the STS-94 entry in July
1997, Don Thomas reported: "It starts off just as bright flashes like
a giant flame." After about five minutes, the "Easter Island statue" appears:
"It changes into this little inverted mushroom structure you can see glowing
there," he explained. Finally the trail widens into a bright yellow-white
"structure," then slowly fades. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">What the
astronauts were probably seeing was the unstable transition between laminar
and turbulent regimes, as the airflow flip-flopped back and forth at a
certain point during the descent. It was a totally unexpected visual phenomenon.
</font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">From an entirely
different perspective, ground viewers also saw the shuttle flames first
flickering, then growing steady, and finally dying out--but over a track
thousands of kilometers long, so no single observer could see the entire
sequence as the crew could. For example, the STS-72 entry (January 20,
1996) was entirely across the dark side of Earth, and clear weather allowed
alerted observers to watch the entire length of the glowing portion. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">From Maui
in the Hawaiian Islands (with the shuttle near orbital velocity at an
altitude of116 km), observer Ken Harris reported: "The glow was barely
visible, but I could see bright flashes of light." From Tucson, Arizona
(the shuttle was at mach 22 at 70 km), Alan Varner wrote: "There was an
orange spot that came out of the west with a very bright trail streaming
behind it. The light from the shuttle was bright white in the center and
deep red at the edges." Added observer Carl Holmberg: "The glow of the
trail was florescent white, while the fireball was orange." </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">South of
Dallas, Texas (with the shuttle at mach 16 at 60 km altitude), Jerry Matulka
had loaded three generations of his family into a van for a midnight road
trip to see the shuttle's fireball, and none of them was disappointed.
"The trail stayed illuminated for some time," he reported, adding he thought
its color was orange. "It was like a huge neon tube from horizon to horizon."
Other observers also noted that the trail ("white with a slight orange
hue" or "maybe a tint of yellow") tended to broaden (to half a degree,
according to one) and then slowly fade. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">By the time
it passed Bay St. Louis on Mississippi's Gulf Coast (at Mach 11 at 52
km), the trail had shortened to about 60 degrees, but the fireball was
still leaving an "incredibly bright orange-yellow streak," according to
a report from observer Terry Jones. Further, "the pulsing of the light
at the heat shield was clearly visible." From Pensacola, Florida (mach
9 at 48 km), Ted Kirchharr saw the shuttle as "a blinking star" ("there
was a bit of yellow tint in the light"), while the trail "was only visible
through binoculars." By this point, the fireball phase was clearly drawing
to a close. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">This yellow-orange
light--I've seen it myself and described it as a "golden spark"--is a
common description of the trail from all the way back to John Glenn's
first flight. Why should it be that color? </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">In describing
visual effects associated with spacecraft entries, observational astronomer
Paul Maley concluded that "the best candidate" was the combination of
nitrous oxide (NO) formed by the shock wave and naturally-occurring ozone
(O3), to form stable nitric oxide (NO2). In the laboratory, that reaction
"produces a yellow color, although initially it appears to be orange."
</font><font size="2" face="Verdana,Helvetica,Arial" color="white">That's
in small amounts--but on a shuttle entry, up to six tons of nitrous oxide
are produced along its entry path. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">"As the reentry
wake grows with time," Maley wrote, "it moves outward into ozone already
present in the air. The wake forms a cylinder which spreads laterally
from the flight path." This is exactly what returning spacefarers have
noticed since the Mercury days. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">Just why
the trailing "neon tube" should thicken into the "mushroom cap" (or "Easter
Island statue effect") reported by shuttle astronauts is still not clear.
It remains a puzzle for the "fluid dynamics" experts. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">There's one
more mysterious physical process involved in high-speed atmospheric entry,
and space vehicles may have accidentally helped solve one of astronomy's
most baffling mysteries. This is the puzzle of "electrophonic meteor sounds."
</font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">During atmospheric
entry, the plunging object literally smashes apart the gas atoms it runs
into. Electrons are torn loose, creating super-hot ions. This creates
the "plasma sheath" which blocks radio transmissions due to its electrical
conductivity. It also apparently does something far, far stranger. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">For at least
two hundred years, astronomers have documented eyewitness reports of bright
meteor falls in which people insist they heard noises from the fireball
in real time. Even though the object may have been a hundred kilometers
away or more, many people described instantaneous "hissing" or "whooshing"
sounds. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">Most scientists
dismissed these accounts as imaginary delusions conjured up by perceptual
parallels with fireworks. But others weren't so quick to disregard them,
even if there was no known physical explanation. Some accounts described
witnesses first hearing the sounds in a house, then coming outside to
see the fireball. Since this perception, if real, had to be caused by
something moving at the speed of light, it was dubbed "electrophonic sound"--but
without any true understanding of the physical basis for it. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">Then, in
the mid-1980s, as space shuttles began landing in Florida after a fiery
entry across the southern U.S., thousands of people in Texas deliberately
went outside to watch the scheduled overflights, especially when it happened
in darkness. They thrilled to the sight of the manmade meteor and the
knowledge there were humans inside the fireball. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">And many
of them heard the same instantaneous hissing noise that had baffled meteor
experts for centuries. It was variously described like "a skier moving
down a slope," or a "motorboat cutting through water." The sound, furthermore,
did not come from the object in the sky, it seemed to emanate from all
around the observer. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">Many of these
observers "knew" it was impossible to hear sounds from space, and some
thought they were crazy. One man called the NASA public affairs office
in Houston to describe how the shuttle overflight "nearly shook the leaves
off the trees," and the press official who talked to him--I was standing
nearby and accidentally overheard the conversation--thanked him for the
description, hung up, and then laughed out loud to his colleagues about
the "idiotic redneck delusion." Since the reported phenomenon was known
to be impossible, many assumed it could not have happened. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">But the phenomenon
was real, and the shuttle entries unexpectedly helped find the explanation
at last. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">It turned
out that the bright natural meteor fireballs--and entering space shuttles
too--can produce random bursts of radio noise in the 5 to 8 kilohertz
radio spectrum. These signals move outwards at the speed of light, and
are sometimes powerful enough to vibrate physical objects near ground
observers, which creates the hitherto mysterious sounds. The physical
origin of the radio noise is still obscure--it probably is connected with
distortions to Earth's magnetic field and subsequent collapse back to
normal conditions--but the radio noise has now been recorded, and its
auditory effect on objects has been reproduced in laboratories. Leaves
and pine needles are especially noisy, along with dry hair, eyeglasses,
metal and metal foil, and other materials often near unsuspecting witnesses.
That's where the sound was really coming from. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">So one more
aspect of meteors that most people assumed was true--that the reported
sounds were delusions--was actually false. And artificial meteors helped
explain the mystery. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">And as with
fireballs throughout history, such mysteries add to the thrill of those
who watch them from the ground, and to the thrill of those who actually
ride these manmade meteors through the sky. </font></p>
<p><font size="2" face="Verdana,Helvetica,Arial" color="white">James Oberg
is a 22-year veteran of Mission Control in Houston, and a lifelong sleuth
of Soviet space secrets. He is now a full-time writer and consultant.
His home page is www.jamesoberg.com.</font><font size="2" face="Verdana,Helvetica,Arial" color="white">
<br>
</font></p>
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