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(meteorobs) Excerpts from "CCNet DIGEST, 11 November 1998: LEONIDS SPECIAL"


------- Forwarded Message

From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet DIGEST 11/11/98
Date: Wed, 11 Nov 1998 14:11:55 -0500 (EST)

CCNet DIGEST, 11 November 1998: LEONIDS SPECIAL
-----------------------------------------------

(1) GODDARD SPACECRAFT PREPARED FOR ENCOUNTER WITH LEONID METEOR STORM
    Andrew Yee <ayee@nova.astro.utorontodot ca>=20

(2) RESEARCH AIRCRAFT FLY BELOW LEONID METEOR STORM
    Andrew Yee <ayee@nova.astro.utorontodot ca>=20

(3) LEONID METEOR SHOWER PROSPECTS FOR UK & EUROPE
    Andrew Yee <ayee@nova.astro.utorontodot ca>=20

(4) MIR COSMONAUTS DEPLOY 'METEORITE TRAP' DURING SPACEWALK
    CNN <http://cnn.com/TECH/space/9811/11/mir.01.ap/index.html>
...
(6) DUST EMISSION FROM COMET SWIFT-TUTTLE
    J. Sarmecanic et al., UNIVERSITY OF CALIFORNIA SAN DIEGO

==========================
(1) GODDARD SPACECRAFT PREPARED FOR ENCOUNTER WITH LEONID METEOR STORM

>From Andrew Yee <ayee@nova.astro.utorontodot ca>=20

Mark Hess/Jim Sahli
Goddard Space Flight Center				Nov. 9, 1998
Greenbelt, MD 20771
(Phone: 301-286-8955)
=20
RELEASE NO: 98-184
=20
GODDARD SPACECRAFT PREPARED FOR ENCOUNTER WITH LEONID METEOR STORM
=20
Flight controllers are laying plans to prepare an orbiting fleet of 22=20
Goddard spacecraft for the upcoming Leonid meteor storm, predicted to=20
be the fiercest in more than three decades.
=20
The annual Leonid shower -- this year a storm -- is expected to be=20
unusually intense because the Earth is crossing Comet Tempel-Tuttle's=20
orbital path at a time when the comet has recently passed by. This=20
happens once every 33 years when Tempel-Tuttle makes its closest=20
approach to the Sun. The Sun's radiation boils bits of dust and sand=20
off the comet, littering its path with debris.
=20
Where possible, controllers will change the orientation of satellites=20
to reduce the possibility that one of these tiny particles (1 to 100=20
microns in size, or about the size of a small sand grain) will strike=20
and disable a spacecraft. However, Leonid storms pose a greater than=20
usual threat to spacecraft not only because of the many tiny meteors=20
(thousands per hour) hitting our atmosphere, but also the tremendous=20
velocities of the particles.
=20
As the Earth moves across the comet's trail, Leonid particles will=20
enter the planet's atmosphere. Like two freight trains hurtling at one=20
another on the same track, the distance between the massive debris=20
cloud and the Earth closes at a mind-boggling 45 miles per second, or=20
over 200 times the speed of sound. In contrast, Perseid meteors reach=20
speeds of about 37 miles per second, and typical daily meteors achieve=20
velocities of about 12 miles per second.
=20
On spacecraft where it is practicable, high voltage systems that=20
supply instruments will be turned off, or ramped down, to safeguard=20
against the potential for electrical damage as a result of the=20
satellite's plunge into the debris cloud. The tiny meteors can hit the=20
spacecraft like a sandblaster and disintegrate, creating a cloud of=20
electrically charged plasma. Under the right conditions, this plasma=20
cloud can set off a chain reaction causing a massive short circuit.=20
The loss of the European Space Agency's Olympus communications=20
satellite in 1993 was attributed to a strike from the Perseid shower,=20
and the resulting plasma discharge that zapped the spacecraft's
delicate electronics.
=20
The 22 NASA spacecraft under Goddard's control -- from the 24,500=20
pound Hubble Space Telescope to the 25-year old, 800 pound IMP-8=20
satellite -- will be continuously monitored during the peak of the=20
storm, and some maneuvered to provide the greatest protection possible=20
from debris.
=20
"Each individual mission and project team reviewed its procedure for 
dealing with this annual phenomena, and has a specific implementation=20
plan for the Leonid meteor storm," said Philip E. Liebrecht, Associate=20
Director for Networks and Mission Services. "Each spacecraft has an=20
operating plan that balances the risk of taking specific defensive=20
measures against the risk of taking no action. We've had independent=20
review teams assess our plans, and I think we are doing everything=20
prudent and practicable to ensure the safety of our spacecraft."
=20
The Leonid meteor shower arrives every November. It takes its name=20
from the constellation Leo, the area of the sky where the meteors=20
appear to originate. The shower's small particles are completely=20
vaporized high in the Earth's atmosphere, and present no danger to the=20
Earth's surface or to aircraft.
=20
Historically, the most active Leonid showers occur during the first=20
two years following the comet's closest approach to the Sun. This last=20
occurred on Feb. 28, 1998. This year's outburst is projected to be=20
less severe than that observed in the last 33-year cycle, which=20
occurred in 1966. The peak time for the Leonid meteor storm will be=20
Nov. 17, sometime between 11:43 a.m and 5:43 p.m. Eastern Standard=20
Time.
=20
For the past several weeks, engineers at Goddard have been reviewing=20
the status of all the spacecraft under their control and developing=20
ways to reduce exposure to the meteor storm. In general, the health of=20
these spacecraft will be monitored before, during and after the storm,=20
and commands to a number of the spacecraft will be stopped or=20
curtailed during this period.
=20
The Hubble Space Telescope will be maneuvered so that its mirrors face=20
away from the storm. Its solar arrays will be rotated so only the=20
edges are exposed to oncoming particles. Controllers won't turn Hubble=20
off during the storm, but rather use the 10-hour period that Hubble is=20
maintained in this attitude to take a long-exposure picture (for more=20
on this, check out http://www.stscidot edu/ftp/proposer/leonid.html).
=20
Some spacecraft, like the Tropical Rainfall Measuring Mission, are=20
already in the ideal orientation for the storm, and only an adjustment=20
to position the solar arrays "edge on" to the storm will be needed.=20
The Rossi X-ray Timing Explorer's instruments will be turned off to=20
protect the spacecraft's high voltage devices from a potential massive=20
short circuit similar to what happened to Olympus.
=20
For the Advanced Composition Explorer, the solar arrays will be=20
rotated, and high voltage supplies for instruments will be ramped=20
down. Since the center of the Leonid stream is closer to the L-1 orbit=20
(1 million miles from the Earth toward the Sun) than to Earth, ACE=20
will see an even more intense storm than Earth-orbiting satellites.
=20
Risk reduction procedures will be followed for other spacecraft=20
including the Extreme Ultraviolet Explorer, Compton Gamma Ray=20
Observatory, Upper Atmosphere Research Satellite, Total Ozone Mapping=20
Spectrometer, Fast Auroral Snapshot, Solar Anomalous Magnetospheric=20
Particle Explorer, Transition Region and Coronal Explorer, WIND,=20
POLAR, Solar and Heliospheric Observatory, Interplanetary Monitoring=20
Platform and Earth Radiation Budget Satellite.
=20
The Tracking and Data Relay Satellites will be maintained in their=20
full operational mode, as these spacecraft are vital to provide the
communications link to and from other spacecraft during the peak storm
period.
=20
Flight control teams for all of Goddard's operational spacecraft have=20
been briefed on the meteor storm and have developed contingency plans=20
to react to any damage sustained during the storm. In addition, all=20
available command and control capabilities will be on alert for=20
possible use in an emergency, and subsystem engineers will be on=20
standby for consultation if there are any problems resulting from the=20
storm.
=20
More information on the Leonid meteor storm can be found at these web =
sites:
=20
   http://www.aero.org/leonid/index.html
=20
   http://www-space.arc.nasadot gov/~leonid/

   http://leroy.cc.ureginadot ca/~astro/Leonids/Leo_1.html

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(2) RESEARCH AIRCRAFT FLY BELOW LEONID METEOR STORM

>From Andrew Yee <ayee@nova.astro.utorontodot ca>=20

NOTE: The "Once-in-a-Century" claim in the release needs to be=20
clarified.
=20
*****
=20
National Science Foundation
Washington, D.C.
=20
Media contact:   Cheryl Dybas, NSF           (703) 306-1070 =
cdybas@nsfdot gov
Media contact:   Anatta, UCAR Communications (303) 497-8604 =
anatta@ucardot edu
Program contact: Cliff Jacobs, NSF           (703) 306-1521 =
cjacobs@nsfdot gov
=20
NSF PR 98-74				November 6, 1998
=20
Research Aircraft Fly Below Once-in-a-Century Leonid Meteor Storm
=20
Two research aircraft carrying new scientific observing instruments=20
and high-definition TV cameras will seize a once-in-a-lifetime=20
opportunity to observe the Leonids meteor shower on November 17, 1998.=20
Only once a century does Earth's orbit cross the dense part of the=20
tail of Comet Temple-Tuttle, which produces the storm.
=20
An L-188C Electra, owned by the National Science Foundation (NSF) and=20
operated by the National Center for Atmospheric Research (NCAR) in=20
Boulder, Colo. will be joined by an Air Force KC-135 in the night=20
skies over Okinawa, Japan, during the meteor storm.
=20
"The NSF Electra is an ideal platform to participate in the Leonids=20
meteor experiment," says Cliff Jacobs, program manager in NSF's=20
division of atmospheric sciences, which funds NCAR. "Its ability to=20
accommodate multiple state-of-the-art, upward-looking instruments will=20
provide an exceptional opportunity to study these meteors."
=20
The meteor storm will occur when Earth enters the dense debris behind=20
Temple-Tuttle on November 17, 1998, and again on November 18, 1999.=20
Although the comet returns every 33 years, its orbit crosses Earth's=20
only once every hundred years. This century's crossing offers=20
scientists a close look at the trails of unusually fresh and large=20
(millimeter- to centimeter-size) meteors entering the earth's=20
atmosphere at the fastest possible speeds -- 72 kilometers per second=20
(160,000 miles per hour). Best observations will be from East Asia=20
(China and Japan). Next year, Europe and North Africa will offer the=20
best viewing. From the ground, the source of the storm appears in
the constellation Leo.
=20
The National Aeronautics and Space Administration is heading the=20
experiment, which is the first mission in NASA's Astrobiology Program,=20
created to study the origin and prevalence of life in the universe.=20
The Leonid Multi-Instrument Aircraft Campaign is also supported by=20
NSF, the U.S. Air Force, and NHK Japanese television.
=20
The two aircraft are needed to take the observing instruments into=20
clear skies above the weather-laden lower atmosphere. The Air Force's=20
FISTA (Flying Infrared Signatures Technology Aircraft) will circle the=20
NSF/NCAR Electra in a racetrack pattern between 30,000 and 40,000 feet=20
while the Electra flies back and forth (north-south) about 10,000 feet=20
lower within the loop. At these altitudes (7 to 10 kilometers, or=20
roughly 4 to 6 miles) both planes will be safe from the meteors above,=20
which will burn up at 100 to 120 kilometers (60 to 75 miles) above the=20
ground.
=20
A major scientific goal of the mission is to determine how a meteor's=20
mass compares to its brightness. To date, scientists can only guess=20
how much material enters the atmosphere during a meteor shower. The=20
Electra will carry a dual-beam lidar (laser-based radar) built this=20
year to detect iron vaporized from the meteors in the upper=20
atmosphere. Says NCAR project manager Bruce Morley, "We know very=20
little about iron in the atmosphere and even less about the iron=20
contribution from meteors. Observing just one meteor accurately from=20
the sky would make a big difference to our understanding."
=20
                                    -NSF-
=20
Editors: High-resolution color photos of the Electra are available via=20
the Internet using anonymous ftp: Log on to ftp.ucardot edu, using the=20
userid: anonymous password: [your e-mail address] directory:=20
/communications [include the slash] filenames: elecnight1.tif,=20
elecnight2.tif, elecnight3.tif, elecnight4.tif, and electra.tif

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(3) LEONID METEOR SHOWER PROSPECTS FOR UK & EUROPE

>From Andrew Yee <ayee@nova.astro.utorontodot ca>=20

Royal Astronomical Society
=20
For immediate release: 10 November 1998
=20
Ref. PN 98/23
=20
Issued by:
=20
Dr Jacqueline Mitton
RAS Public Relations Officer
Office & home phone: Cambridge ((0)1223) 564914
Mobile phone: 0370 386133
FAX: Cambridge ((0)1223) 572892
E-mail: jmitton@dial.pipex.com
=20
and
=20
Peter Bond
Space Science Advisor
Phone: (0)1483-268672
Fax: (0)1483-274047
E-mail: 100604.1111@compuserve.com
=20
Leonid Meteor Shower Prospects for UK and Europe
=20
Professional and amateur skywatchers worldwide are awaiting the night=20
of 17th/18th November with considerable anticipation because of the=20
possibility that a spectacular meteor shower will take place. But what=20
can we really expect to see in the UK and rest of Europe?
=20
According to the best data available, Europe is likely to experience a=20
good meteor shower, but not a truly exceptional one -- perhaps up to=20
100 meteors per hour if we are lucky. The best time to look will be=20
between 1 a.m. and dawn in the early hours of 18th November. A storm=20
of many thousands of meteors per hour could occur, but it is much more=20
likely to be seen in the Far East -- China, Thailand, Japan -- than in=20
Europe.
=20
Forecasting Metoer Showers
=20
Predictions of a meteor storm in 1998 are based on the fact that=20
exceptional displays of the Leonid meteors -- so-called because they=20
appear to radiate from a point in the sky within the constellation Leo=20
- -- tend to recur every 33 years or so. There is not always a great=20
storm, however, such as the one in 1966 when observers in parts of the=20
USA for a short time saw meteors at a rate of 40 per second.
=20
But forecasting meteor showers is not a precise business, unlike=20
predicting eclipses, for example, for which the exact times and=20
circumstances can be calculated in advance. The time when a meteor=20
shower will peak, and the maximum rate at which meteors will appear to=20
rain down, can never be anticipated with great certainty. They are=20
something of a celestial lottery.
=20
For that reason, it is well worth looking out for meteors in the early=20
hours of the 18th, if skies are clear, even from the UK. There is a=20
slim chance of something exceptional, but a modest display at least is=20
on the cards, and meteors are easy to observe. They are best seen with=20
the naked eye and, during a shower, they can streak across almost any=20
part of the sky, as long as the radiant point is above the horizon.
=20
If a Leonid storm takes place, it is unlikely to last more than an=20
hour or so, but the gentler background shower carries on for a day or=20
two. According to the experts the expected peak time of any storm is=20
most likely to be about 7.45 p.m. (GMT). If this is correct, the storm=20
would be finished several hours before the constellation Leo rises=20
above the horizon in the UK.
=20
What Are Meteors?
=20
Meteors are caused by small fragments of material, mostly no larger=20
than a grain of sand, which burn up as they enter Earth's atmosphere=20
at high speed -- around 71 kilometres (45 miles) per second in the=20
case of the Leonids.
=20
Leonid meteors are dust particles that have come off Comet=20
Tempel-Tuttle. Most of this dust is still following the comet fairly=20
closely in space. The comet takes 33 years to complete an orbit around=20
the Sun, and planet Earth ploughs through its main dust cloud when the=20
comet returns to our vicinity every 33 years. In the years when this=20
happens, a strong shower or storm takes place. In the years in=20
between, a very small number of Leonid meteors are seen in=20
mid-November.
=20
Some meteor showers produce about the same rate of meteors around the=20
same date every year. Regular annual showers happen when the dust from=20
a comet has spread around the whole of the comet's orbit, something=20
that takes place gradually over a long period of time. An example is=20
the Orionids, a shower in late October each year caused by dust from=20
Halley's Comet.
=20
Looking ahead to 1999, Comet Tempel-Tuttle will still be relatively=20
nearby and some astronomers are predicting that the Leonid meteor=20
display could be better next year than this. If that were to happen,=20
then Europe is expected to be the ideal location.
=20
Do The Leonids Present Any Hazards?
=20
Most of the Leonids weigh about 1 millionth of a gram -- not much more=20
than a particle of cigarette smoke. Normally, objects this size would=20
pose no threat to spacecraft. However, when they are travelling many=20
times faster than a bullet from a high velocity rifle, the threat=20
increases significantly.
=20
Since the velocity of the meteor impacts is affected by a spacecraft's=20
motion as it orbits the Earth, hits could occur at any speed between=20
65 and 80 km (40 and 50 miles) per second. These could result in some=20
physical damage in sensitive areas as well as electrical short=20
circuits, plasma discharges, and computer malfunctions, which may be=20
sufficiently serious to disable a satellite. A form of sand-blasting=20
can erode outer surfaces such as thermal blankets, mirrors and solar=20
cells. Large impacting particles may even knock a satellite out of its=20
normal position, as happened to the European Space Agency's Giotto=20
spacecraft during its 1986 flyby of Halley's Comet.
=20
"These microparticles could penetrate a fairly weak spacecraft skin,"=20
said Professor Tony McDonnell of the Unit for Space Sciences and=20
Astrophysics at the University of Kent in Canterbury. However, the=20
most likely form of damage is to vulnerable power systems. "Perhaps a=20
handful of satellites could have unusual electrical anomalies," said=20
McDonnell.
=20
Past evidence suggests that the risks are fairly low. During the past=20
four decades, only one spacecraft, the European Space Agency's Olympus=20
satellite, is known to have been disabled by a (Perseid) meteor.=20
Furthermore, no spacecraft were damaged by the 1966 Leonid storm. On=20
the other hand, there are now more than 500 spacecraft orbiting the=20
Earth, over 10 times as many as in the mid-1960s.
=20
"The biggest uncertainty is the hourly rate (of arrival)," said=20
Professor McDonnell. "If this reaches 150,000 per hour, there will be=20
all sorts of damage, but there may only be 1,800 per hour."
=20
While the probability of any satellite being hit is thought to be less=20
than 0.1%, many spacecraft operators are taking no chances. The Space=20
Shuttle mission that carried John Glenn was deliberately timed to=20
avoid the Leonid shower. Cosmonauts on the Mir space station do not=20
have the luxury of choosing their flight window. While the Mir station=20
presents a large target for the Leonids, no serious damage is=20
expected. However, the two crewmen may play safe by moving into the=20
Soyuz lifeboat at the peak of the shower.
=20
Fortunately, the direction from which the particles approach the Earth=20
is almost perpendicular to the direction of the Sun. This means that=20
the chance of a direct hit will be substantially reduced since most=20
satellites will already have their solar panels aligned edge-on to the=20
shower.
=20
Further damage-limitation measures have been recommended by the=20
European Space Operations Centre operated by the European Space=20
Agency. These include turning spacecraft so that their most vulnerable=20
systems are not in the direct line of fire; switching off high voltage=20
systems; and putting a team of ground controllers on alert in case of=20
emergencies.
=20
In the case of the Hubble Space Telescope, its all-important mirror=20
will be turned away from the shower during observations of distant=20
galaxies. Most of the scientific instruments on the European ERS-1 and=20
ERS-2 Earth observation satellites and the Solar and Heliospheric=20
Observatory (SOHO) will be powered down and placed in 'sleep' mode=20
during the shower. SOHO and the American Advanced Composition Explorer=20
(ACE), which are located 1.5 million km sunward of the Earth, will be=20
particularly at risk since the main stream of meteors is expected to=20
pass much closer to them than any of their Earth-orbiting brethren.=20
Indeed, the trail of Leonids will actually travel between the Earth=20
and these two solar observatories.
=20
More Information about the Leonid Meteors may be found at the=20
following Web Sites:
=20
     Leonid '98 Meteor Outburst Mission Homepage (P. Jenniskens - NASA)
     http://www-space.arc.nasadot gov/~leonid/1998.html
=20
     Leonid Information for the Beginning and Advanced Meteor =
Enthusiast
     (G. Kronk)
     http://medicine.wustldot edu/~kronkg/leonids.html
=20
     SKY Online's Meteor Page (Sky & Telescope magazine)
     http://www.skypub.com/sights/meteors/meteors.html
=20
Visual Material
=20
Sky & Telescope magazine (based in Boston, USA) has available for=20
distribution:
=20
   * still images from the 1966 Leonid storm,
   * artistic renderings
   * video of the 1997 Perseid and Geminid meteor showers
   * a broadcast-quality, 1-minute animation of why the Leonids occur =
by
     artist Don Davis.
=20
Anyone wanting these for reproduction or broadcast can contact Irene=20
Szewczuk (irenes@skypub.com, phone 00 1 617-864-7360 x127) or Kelly=20
Beatty (kbeatty@skypub.com, phone 00 1 617-864-7360 x148). Fax for=20
both is 00 1 617-576-0336.

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
(4) MIR COSMONAUTS DEPLOY 'METEORITE TRAP' DURING SPACEWALK
=20
>From CNN <http://cnn.com/TECH/space/9811/11/mir.01.ap/index.html>
=20
November 11, 1998
=20
MOSCOW (AP) -- Two Russian cosmonauts on the Mir space station
successfully deployed a French-made device for catching and studying =20
small meteorite particles during a six-hour spacewalk that ended early
Wednesday.=20
=20
Cosmonauts Gennady Padalka and Sergei Avdeyev installed the "meteorite=20
trap," which should collect data on a barrage of particles expected to=20
peak around the Mir in mid-November, said Valery Lyndin, spokesman for=20
mission control.=20
=20
The device will stay attached to the Mir until 1999, when it will be=20
taken back to Earth for analysis by a French astronaut who will fly to=20
the station early next year.=20
=20
The "meteorite rain" doesn't pose a serious threat to the Mir because =20
it consists of tiny remnants, not full meteorites. To be safe,=20
however, the two cosmonauts will board the Soyuz escape capsule when=20
the shower reaches its peak.=20
=20
At the start of the spacewalk, Padalka and Avdeyev released a
satellite model made by schoolchildren from several countries. [...]=20
=20
Copyright 1998   The Associated Press

==========================
(6) DUST EMISSION FROM COMET SWIFT-TUTTLE

J. Sarmecanic*), M. Fomenkova, B. Jones: Modeling of mid-infrared dust=20
emission from P/Swift-Tuttle. PLANETARY AND SPACE SCIENCE, 1998,=20
Vol.46, No.8, pp.859-863

*) UNIVERSITY OF CALIFORNIA SAN DIEGO,CTR ASTROPHYS & SPACE SCI=20
0424,LA JOLLA,CA,92093

Comet P/Swift-Tuttle was observed at 11.7 mu m on 12 nights over the=20
course of three weeks in November 1992 using the UCSD mid-infrared=20
imaging camera (Fomenkova et nl., 1995). The large number of images=20
obtained and the overall high quality of the data permit the continued=20
study of the rich dust structures apparent in this active comet. We=20
present a model to interpret the features observed in these images=20
using olivine spheres (MgFeSiO4) as representative dust grains, and=20
illustrate the validity of the model by applying it to the image taken=20
on UT 9. 1 November. A fully three-dimensional Monte Carlo simulation
based on :the Finson-Probstein model (1968) is performed, and Mie=20
scattering theory is used to characterize the properties of the=20
grains. We found that the comet executes simple rotation about an axis=20
whose obliquity is 45 +/- 10 degrees. Our best-fit dust grain size=20
distribution in the size range from 0.6 to 10.0 mu m is of the form=20
f(a) similar to a(-beta) with beta =3D 2.5 +/- 0.5, not quite as steep=20
as the distribution (beta =3D 3.7) measured for comet P/Halley=20
(McDonnell er al., 1991). (C) 1998 Elsevier Science Ltd. All rights=20
reserved.


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