[meteorite-list] Earth Orbiting Satellites Brace for Leonid Meteor Shower

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:47:09 2004
Message-ID: <200111071645.IAA11141_at_zagami.jpl.nasa.gov>

http://www.space.com/businesstechnology/technology/leonids_satellites_011107-1.html

Earth Orbiting Satellites Brace for Leonid Meteor Shower
By Jim Banke
space.com
07 November 2001

CAPE CANAVERAL, Fla. -- Satellite operators will keep a close eye on their
Earth-orbiting spacecraft during the upcoming Leonid meteor shower, and
though the risk of damage from a stray speck of dust is greater than normal,
officials are confident there will be no natural disasters in space.

Nevertheless, if a Leonid meteoroid hits a satellite, the small grain can
destroy an imaging mirror or plow through fragile parts such as an
electricity-generating solar panel, possibly creating electrical shorts that
can disable the craft. Just the momentum imparted by an impact can throw a
satellite off course.

Especially sensitive at this time -- but not necessarily vulnerable -- are
the nation's reconnaissance, communications, navigation and weather
forecasting satellites, which are playing a key role in the United States'
efforts to combat terrorism in Afghanistan, and around the globe.

Not to worry, officials say.

"Satellites are designed with information about past storms and other things
that can happen in space," said Capt. Adriane Craig, a spokesperson for the
U.S. Air Force Space Command at Peterson Air Force Base near Colorado
Springs, Colo.

"Our satellites are robust and in the event that there is a problem we have
backup systems and contingency plans to help get them back online."

Air Force controllers at Peterson are responsible for monitoring the various
constellations of military satellite systems around the clock, Craig said,
but she wouldn't say exactly what additional measures -- if any -- are being
taken to minimize the threat from the Leonids.

"For the Leonids we have models that help us predict when the storm will
peak, so certainly (the satellite operators) can be more attentive during
that time, but we monitor the spacecraft pretty vigilantly every day of the
year," she said, politely refusing to elaborate. "I will not reveal anything
operationally about any actions we might or might not take."

The story is the same at the National Reconnaissance Office (NRO), which is
responsible for operating the many clandestine spy satellites responsible
for so much of the nation's space-based intelligence gathering efforts.

"We're working closely with the Air Force to fully understand the
implications of the Leonid storm, and we'll take precautions that we feel
are appropriate," said Art Haubold, a spokesman for the National
Reconnaissance Office. "However, we don't discuss operational details of our
satellites."

It's possible that in some cases a satellite may be turned off as the best
defense against being struck by a Leonid meteoroid. However, industry
observers and others agree that military and NRO spacecraft are constructed
with extra shielding and back up systems inside the spacecraft itself,
allowing continuing operation no matter what.

"Military satellites are much more hardened and much more capable of
surviving such things than normal satellites," said Bill Cooke, a meteor
forecaster at NASA's Marshall Space Flight Center in Huntsville, Ala.

So to, Cooke said, is the International Space Station, where the current
Expedition Three crew of Frank Culbertson, Vladimir Dezhurov and Mikhail
Turin are wrapping up a four-month stay in space. Shuttle Endeavour is to be
launched Nov. 29 -- long after the Leonid's peak -- to bring up a new crew
and then return to Earth on Dec. 10.

"The space station has armor to protect it against stuff as much as an inch
across," Cooke said. "We're not expecting anything that big from this year's
Leonids."

Remnants from the icy comet Tempel-Tuttle, the Leonid meteor shower will
result when planet Earth sweeps through the comet's trail of debris next
week and the tiny particles encounter our atmosphere and burn up, sparking
what are commonly called shooting stars.

Earth will enter the heavier parts of the stream at about 11 p.m. EST on
Nov. 17 (0400 GMT Nov. 18). Activity will peak around 5 a.m. EST Nov. 18
(1000 GMT), when as many as 13 meteors per minute could be visible, likely
for a stretch of time that lasts less than one hour.

No larger than a grain of sand, the Leonid meteroids tend to vaporize at
about 60 miles (100 kilometers) above the surface. Satellites, however, are
orbiting the planet much higher and so could be hit by the bits before they
burned up.

Satellites that orbit between 200 and 600 miles (325 and 965 kilometers)
above Earth will face meteor rates roughly the same as what is expected to
be seen from the ground, Cooke said.

However, high-flying geostationary satellites, which sit 22,300 miles
(35,900 kilometers) above the planet will be closer to the densest part of
the debris stream. Moreover, geostationary satellites in the Western
Hemisphere would be at the greatest risk, Cooke said.

Because Tempel-Tuttle orbits the Sun in the opposite direction compared to
Earth -- a backward motion called retrograde -- its debris would hit a
satellite with much greater velocity than other meteors created by the
debris from other comets.

"It's like two cars hitting head-on," Cooke said, adding that the
penetration power is 16 times that of a normal meteor.

The greatest danger, Cooke says, is the generation of a plasma cloud -- a
byproduct of high-speed impacts that could cause an electrical short
circuit.

When a meteor as fast as a Leonid strikes something, it vaporizes, creating
a cloud of plasma, or electrically charged particles. An electrical current
can then flow from one part of the craft, through the plasma cloud, and then
destroy an instrument on another part of the craft.

Few such instances have been documented.

In 1993, during the August Perseid meteor shower, a meteor hit an Olympus
communications satellite. The impact formed a plasma cloud, and the craft's
attitude control system was zapped. By the time operators could stabilize
it, they had depleted all of its attitude-control propellant and the
satellite was lost.
Received on Wed 07 Nov 2001 11:45:03 AM PST