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Дата: 10 ноября 1998 (1998-11-10)
От: Alexander Bondugin
Тема: Cassini Update - November 6, 1998
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Cassini Significant Events
for 10/30/98 - 11/05/98
Spacecraft Status:
The most recent Spacecraft status is from the DSN tracking pass on
Wednesday, 11/04, over the Goldstone tracking station. The Cassini
spacecraft is in an excellent state of health and is executing the C10
sequence normally. The speed of the spacecraft can be viewed on the
"Where is Cassini Now?" web page (http://www.jpl.nasa.gov/cassini/today/).
Spacecraft Activity Summary:
On Monday, 11/02, three activities were performed: the Delta-V Estimator
Flight Software Update was sent up to the spacecraft, the Solid State
Recorder (SSR) record and playback pointers were reset, and the AACS High
Water marks were cleared.
On Tuesday, 11/03, Part 1 of the SSR-A Power Off was performed. Powering
off the SSR will enhance the overall life expectancy of the unit. Part one
consisted primarily of a complete memory test prior to the power off
commands.
On Wednesday, 11/04, Part two of the SSR-A Power Off was performed and the
VIMS Decontamination Heaters were powered up for a 24 hour period.
Upcoming events:
Activities scheduled for the week of 11/06-11/12 include SSR FSW Partition
Maintenance on 11/06, uplink of the C11 sequence on 11/07, and AACS
Attitude Estimator Memory Readout and SSR Pointer Reset on 11/09.
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=SANA=
Дата: 10 ноября 1998 (1998-11-10)
От: Alexander Bondugin
Тема: Automated Rendezvous & Docking Component Completes Successful Test Abo
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June Malone
Media Relations Office
Marshall Space Flight Center
Huntsville, AL 35812
(256) 544-0034
june.malone@msfc.nasa.gov
http://www.msfc.nasa.gov/news
For Release: Nov. 5, 1998
RELEASE: 98-229
Automated Rendezvous & Docking Component Completes Successful Test Aboard
STS-95
The STS-95 Space Shuttle crew completed a series of successful tests on a
new video guidance sensor component Tuesday, Nov. 3. The component -- part
of the Automated Rendezvous and Capture System -- will allow spaceships to
locate each other and rendezvous without human intervention. The sensor
will be used by the International Space Station to simplify routine supply
dockings and separations.
The video guidance sensor, developed by NASA's Marshall Space Flight Center
in Huntsville, Ala., uses a combination of lasers, video and reflectors to
measure the relative position and distance between spacecraft. For testing,
reflectors were mounted on the SPARTAN solar observatory satellite that was
carried into orbit by Discovery Oct. 29. During the STS-95 mission, the
Shuttle-mounted video guidance sensor measured reflected laser light from
SPARTAN to gather rendezvous data.
The satellite was deployed from the Shuttle's payload bay on Sunday, Nov. 1.
The STS-95 crew used the Shuttle's robot arm to position SPARTAN 33 feet, or
10 meters, in front of the video guidance sensor mounted in the payload bay.
The Shuttle's robot arm moved SPARTAN as close as 13 feet, or 4 meters, to
the sensor to gather detailed tracking information prior to releasing SPARTAN
into space for a two-day solar science mission.
On Nov. 3, after a successful SPARTAN science mission, the STS-95 crew began
long-range testing of the Video Guidance Sensor during manual rendezvous and
retrieval operations.
The video guidance sensor was activated and made contact when the Shuttle
moved to within 480 feet, or 146 meters, of the satellite. During approach,
at 360 feet, or 110 meters, the crew performed attitude maneuvers -- changing
the position of the Shuttle to determine the width of the sensor's field of
view. "The video guidance sensor locked-on at 480 feet. That's 120 feet better
than we designed the system to achieve," said Gene Beam, project manager for
the video guidance sensor at Marshall Center.
The crew stopped attitude maneuvers at 246 feet, or 75 meters, from SPARTAN
during the brief orbital nighttime to maintain observation of the nearby
satellite. The Shuttle then moved away to a distance of 600 feet, or 82
meters, to gather more information on the maximum limits of long-range
tracking. Completing the maneuver, the crew moved back into robot arm range
of SPARTAN and successfully captured and re-stowed it in the Shuttle payload
bay for return to Earth.
During long-range testing, data from the Shuttle's hand-held laser range
finder was compared to information from the video guidance sensor. "The
difference in readings between the hand-held laser and the sensor was well
within acceptable levels," said an STS-95 crew member. "The data we collected
looks comparable to the data from the earlier STS-87 mission where we first
tested this sensor." The Space Shuttle Columbia carried the first test into
orbit in November 1997. The operational version of the Automated Rendezvous
and Capture System is expected to be accurate within one-tenth of an inch.
##
Editor's Note: For more information call June Malone at the Marshall Space
Flight Center Media Relations Office at (256) 544-0034 or visit the Marshall
Space Flight Center News Room website at: http://www.msfc.nasa.gov/news
Andrew Yee
Ayee@nova.astro.utoronto.ca
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=SANA=
Дата: 10 ноября 1998 (1998-11-10)
От: Alexander Bondugin
Тема: WDC-A R&S Launch Announcement 12976: Iridiums 2 and 83-86
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COSPAR/ISES
WORLD WARNING AGENCY FOR SATELLITES
WORLD DATA CENTER-A FOR R & S, NASA/GSFC
CODE 633, GREENBELT, MARYLAND, 20771. USA
SPACEWARN 12976
COSPAR/WWAS USSPACECOM NUMBER
SPACECRAFT INTERNATIONAL ID (CATALOG NUMBER) LAUNCH DATE,UT
IRIDIUM 02 1998-066A 25527 06 NOVEMBER 1998
IRIDIUM 86 " 066B 25528 "
" 85 " 066C 25529 "
" 84 " 066D 25530 "
" 83 " 066E 25531 "
DR. JOSEPH H. KING, DIRECTOR, WDC-A-R&S.
[PH: (301) 286 7355.
E-MAIL: KING@NSSDCA.GSFC.NASA.GOV
06 NOVEMBER 1998 19:30 UT]
Further details will be in a forthcoming SPACEWARN Bulletin
Dr. Edwin V. Bell, II
_/ _/ _/_/_/ _/_/_/ _/_/_/ _/_/ Mail Code 633
_/_/ _/ _/ _/ _/ _/ _/ _/ NASA Goddard Space
_/ _/ _/ _/_/ _/_/ _/ _/ _/ Flight Center
_/ _/_/ _/ _/ _/ _/ _/ _/ Greenbelt, MD 20771
_/ _/ _/_/_/ _/_/_/ _/_/_/ _/_/ +1-301-286-1187
ed.bell@gsfc.nasa.gov
SPACEWARN home page: http://nssdc.gsfc.nasa.gov/spacewarn/
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=SANA=
Дата: 10 ноября 1998 (1998-11-10)
От: Alexander Bondugin
Тема: 1998 Leonid Model Prediction
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1998 Leonid Model Prediction
By Peter Brown, UWO Meteor Group. Issued
November 5th, 1998.
Using a total of 12 different models for the ejection of meteoroids from
comet Tempel-Tuttle, a preliminary "best" guestimate for the location of
the strongest peak in activity and its associated ZHR for the 1998
Leonids has been found.
The 12 model approach involves using three major variations in meteoroid
density (0.1, 0.8 and 4.0 g/cm^3 for bulk density of the
meteoroid). For each of these three densities, four different variations
in the initial ejection velocities are also employed - one follows
the distributed production model of Crifo which produces broad
distributions in initial ejection velocity which
has a mean velocity lower than the classical Whipple/Jones ejection
model. In addition to Crifos distributed production model, a
Whipple/Jones ejection velocity model is used, as well as a second
variant of the same with a heliocentric velocity dependance of
r^-0.5 in place of the usual r^-1. The fourth model is again a variant
on the Jones/Whipple model in which the ejection velocity at a
given heliocentric distance is not single-valued in the monte carlo
generating routine, but rather has a parabolic distribution of
probable velocities about the average Jones/Whipple velocity for the
chosen heliocentric distance. See Brown and Jones (1998), Icarus, v.
133, pp. 36 - 68 for more details.
The results of the modelling for the Leonids, using ejections at all
perhelion passages of the comet back to 1499 AD (ie 15
revolutions of the comet prior to the current epoch). A simple summation
of the meteoroids which are then visible at Earth at the
present time from this ensemble and which would produce visually
observable meteors (mass 1 mg) was then computed from all
ejecta. A meteoroid is defined as being Earth-intersecting if its nodal
radius is within 0.005 AU of Earth at the longitude of its
descending node. All models suggested a steep increase in activity
beginning in December, 1997/early 1998 accompanying the
passage of Tempel-Tuttle. The resolution of the modelling is of order 2
months and thus all models suggest that this November will
show significantly increased activity relative to 1997 (when the peak
ZHR reached just short of 100), and likely activity approaching meteor
storm levels (ZHRs of order 1000). Using 1997 as a baseline and taking
the peak ZHR to have been 96 +/- 13 at 235.22 +/- 0.02 (J2000) in 1997
we have extrapolated the relative model difference between the activity
strength predicted by the model in 1997 to that observed and that
predicted for 1998. Using a mean of all models, produces a predicted
location for the peak in 1998 of 235.26 +/- 0.04 (J2000) with a peak ZHR
of 1200 +/- 280. This solar longitude corresponds to Nov 17 at 19:20 UT
with a 1-sigma uncertainty of 60 minutes. We emphasize that due to the
model results sensitive dependance on density of the meteoroids, the
range of possible ZHRs extends from slightly lower than the bound given
above to nearly 10 000 (the higher values associated with the models
using the least dense meteoroids and lowest ejection velocities).
The use of relative modelling difference between 1997 and 1998 implies
that the veracity of the prediction in 1998 relies entirely on the
accuracy of the magniude of the ZHR reported in 1997 under full moon
conditions. As well as the above, the models suggest that broad
activity, persisting for of order a full day centred about this peak
should be noticeably above normal Leonid background levels and should be
rich in larger meteoroids in 1998 most notably after the time of the
peak. The model suggests ZHRs of order 100 or greater in the 3-4 hour
window prior to the peak and ZHRs of order 100-200 persisting for many
hours after the peak.
The mass index near the time of the peak over the visual magnitude range
will be near 1.6 +/- 0.1. It is worth noting that a significant decrease
in the mass index from 1.8 +- 0.1 several hours prior to the peak to
this lower value and then upward again after the peak is visible in most
models.
*********************************************************************
Peter Brown
Meteor Physics Lab
Department of Physics and Astronomy
University of Western Ontario
London, Ontario
N6A 3K7
Canada
Voice:1-519-679-2111 x6458
Fax:1-519-661-2033
*********************************************************************
Hа сегодня все, пока!
=SANA=
Дата: 10 ноября 1998 (1998-11-10)
От: Alexander Bondugin
Тема: Leonid Meteor Shower, Special Lecture At Griffith Observatory
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Griffith Observatory Press Releases
Leonid Meteor Shower
There may be a significant meteor shower on the morning of Tuesday,
November 17 (or, less likely, on the morning of November 18).
Every November 17, when the earth passes near the orbit of Comet
Tempel-Tuttle, we pass through a sparse swarm of comet debris and
experience a minor meteor shower that generally goes unnoticed. Every 33
years, however, the earth passes through a dense knot of this cometary
material, and there is the possibility of a dramatic meteor storm when the
sky might fill with thousands of "falling stars." This year there may be
such a brief meteor storm lasting no more than a few hours. Although the
shower is predicted to be strongest over Asia, enough meteors may fall over
California to make the night very interesting. This is a meteor shower that
sky watchers should not miss.
The best time to observe the shower from the United States will be the few
hours before dawn on Tuesday morning, November 17. There is less likelihood
of a shower on the morning of the 18th. Few meteors will fall before 1 a.m.
Although it is difficult to estimate the actual rate, an observer in a dark
location will likely see dozens of meteors per hour. There may be brief
periods lasting several minutes when quite a few meteors fall, followed by
periods of relative calm.
The meteors radiate from the direction of Leo, the Lion, and for that
reason they are called the Leonids. Leo is low in the east before dawn, but
the meteors will appear all over the sky. Leonid meteors strike the earth's
atmosphere at high speed, 44 miles per second, and often leave smoke
trails. The moon is almost new and out of the way.
Because of the early hour, Griffith Park will not be open for meteor
observing. Observers should plan to be far from city lights. The
Observatory is often asked to recommend an observing location, but the
answer is -- go away from the city to where it is dark.
For additional information on the Leonid meteors please visit these web sites:
International Meteor Organization: http://www.imo.net
Leonid 98: http://www-space.arc.nasa.gov/~leonid.html
Meteor Storm Hazard:
http://leroy.cc.uregina.ca/~astro/Leonids/Leo_1.html
Media i Corporation (live CCD images from Japan):
http://www.media-i.com/www/Milkyway/index.html
Special Lecture at Griffith Observatory on Monday, November 16
On Monday, November 16, 1998, Griffith Observatory will host a special
lecture by Dr. Amir Aczel on "Why There Must Be Intelligent Life in the
Universe."
For thousands of years visionaries and writers have argued that we cannot
be alone -- that there must be intelligent life in the universe. Now, with
the latest information from Mars, the latest discoveries from the Hubble
telescope, and the knowledge about life at the extremes, scientists are
taking up where the visionaries left off.
Dr. Amir Aczel, author of Fermat's Last Theorem, pulls together everything
that science has discovered and mixes in probability theory to argue the
case for the existence of intelligent life beyond our planet.
Dr. Aczel's new book "Why There Must Be Intelligent Life in the Universe"
will be on sale following the lecture, which Dr. Aczel will autograph.
The lecture will be at 7:30 p.m. on Monday, November 16, 1998. The
Observatory will open, and tickets will go on sale at 7:00 p.m. Ticket
prices are $4.00. Children under five are not admitted.
*********************************************************************
Griffith Observatory Griffith phone: (323) 664-1181
2800 East Observatory Road Griffith fax: (323) 663-4323
Los Angeles, California 90027 USA http://www.GriffithObs.org
mailto:list@GriffithObs.org
*********************************************************************
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=SANA=
Дата: 10 ноября 1998 (1998-11-10)
От: Alexander Bondugin
Тема: Sky & Telescope News Bulletin - November 6, 1998
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SKY & TELESCOPE'S NEWS BULLETIN
NOVEMBER 6, 1998
AS THE KBO TURNS
Astronomers at the European Southern Observatory (ESO) announced that they
determined the rotation period of one of the most distant objects in the
solar system. Olivier Hainaut and his four colleagues from La Silla, Chile,
and Paris Observatory took 50 images of minor planet 1996 TO66 -- a bright
member of the class of body called trans-Neptunian objects, or Kuiper Belt
objects (KBO). The astronomers used ESO's 3.6-meter New Technology
Telescope (NTT) to observe 1996 TO66 in August and October 1997 when it was
about 45 astronomical units (6.7 billion kilometers) away from the Sun and
shining feebly at 21st magnitude. The object's light curve suggests that it
rotates every 6 hours 15 minutes. Discussing their finding at a conference
on small bodies in the outer solar system at ESO's Garching, Germany,
headquarters this past week, the astronomers explain that 1996 TO66's
rotation period probably dates from the birth of the solar system. They
note that minor planet 2060 Chiron, which orbits between Saturn and Uranus
but likely originated much farther out, also rotates with a period near 6
hours.
CLUMPS IN WINDY NEBULA
A new image released from the Space Telescope Science Institute on Thursday
reveals the effects of strong stellar winds. The nebula M1-67 is being
shaped by the outflow from the exceptionally hot and luminous star QR
Sagittae. Most of the nebula probably consists of ejecta that the star cast
off during an earlier phase of its evolution. The picture shows many small,
bright knots that may be the first direct images of clumps flying outward
in the stellar wind of a hot star. Details are in *Astrophysical Journal
Letters* for October 20, 1998.
AURORA FOR THE WEEKEND?
Patrick S. McIntosh (HelioSynoptics Inc.) reports that on November 5th a
flare was ejected from an active area on the Sun that may provide a display
of aurora (northern and southern lights). His electronic announcement to
*Sky & Telescope* notes that we should expect major geomagnetic storm
conditions by late November 7th, which should continue through most of the
following day.
COMET GIACOBINI-ZINNER IN AQUILA
Viewing of Comet 21P/Giacobini-Zinner will improve this week, as the bright
Moon leaves the early evening sky. The comet remains at about 9th
magnitude, but may brighten a bit more by the end of the month. This week,
the comet continues its trek through Aquila. It lies about 20 to 40 degrees
above the southwestern to western horizon, depending on your latitude, at
the end of evening twilight. For a finder chart, see page 107 of the
November *Sky & Telescope.* Here are positions for Comet Giacobini-Zinner
for 0 hours Universal Time (2000.0 coordinates) for the coming week:
R.A. Dec.
November 7 19h 23m -06.8 deg.
November 9 19h 32m -07.8 deg.
November 11 19h 41m -08.8 deg.
WINTER STAR PARTY BLOWN AWAY
Every February hundreds of skygazers head to the Florida Keys for the
Winter Star Party, one of the United States's major annual astronomical
conventions. However, WSP's venue, a Girl Scout camp right at the water's
edge, was heavily damaged by Hurricane Georges, which blew through the Keys
in late September. Tippy D'Auria, WSP founder and chairman, originally
thought the damage could be repaired before the February 1999 gathering.
But "in spite of heroic efforts," he says, "it appears that the camp will
not be ready in time." Thus, the event has been cancelled. However, Tom
Clark and Jack Newton are making arrangements to host an alternative to WSP
for the week of February 14, 1999, at Chiefland, Florida. For details,
visit the Calendar of Star Parties in the Resources section of *Sky &
Telescope*'s Web site.
INTRODUCTING THE NEW SKYPUB.COM
And speaking of our Web site, it has a new look! We unveiled Sky &
Telescope's new home page this week. Point your Web browser to
http://www.skypub.com/ to see the improvement. All of your favorite pages
from the old SKY Online Web site are here in an easier-to-use format. The
site is divided into five major categories: NEWS, SIGHTS, TIPS, IMAGING,
and RESOURCES. There are over 30,000 active links on this new site spread
across more than 500 Web pages. You'll also be able to order from among the
more than 200 quality astronomical books and products found in the 1999 Sky
Publishing Catalog using our new online store. Please note that many of our
pages' URLs have changed, so you may need to alter your bookmarks and
Web-page links.
THIS WEEK'S "SKY AT A GLANCE"
Some daily events in the changing sky, from the editors of SKY &
TELESCOPE.
NOV. 8 -- SUNDAY
* Mercury and Antares appear 2 degrees apart this evening and tomorrow
evening. Look with binoculars just above the southwest horizon a half hour
after sunset. Antares is the fainter one, on the lower left.
* Jupiter's Great Red Spot should cross the planet's central meridian
around 9:42 p.m. Eastern Standard Time. Lately the spot has been very pale
tan with a dark outline and a small, reddish-brown patch in its south side.
For a list of all predicted Red Spot transit times this observing season,
see http://www.skypub.com/sights/moonplanets/redspot.html.
* The eclipsing variable star Algol should be in one of its periodic
dimmings, magnitude 3.4 instead of its usual 2.1, for a couple hours
centered on 11:34 p.m. EST. Algol takes several additional hours to fade
and brighten. For a list of its predicted minima through next winter, see
http://www.skypub.com/sights/variables/algol.html.
NOV. 9 -- MONDAY
* The red long-period variable star Chi Cygni in the Northern Cross
should be at maximum brightness, 5th magnitude, around this date. See the
chart in the November Sky & Telescope, page 100.
NOV. 10 -- TUESDAY
* Last-quarter Moon (exact at 7:28 p.m. EST).
* Mercury is at greatest elongation in the evening sky, 23 degrees east
of the Sun.
* Saturn's largest moon, 8th-magnitude Titan, appears four ring-lengths
to Saturn's east tonight through Thursday night. A small telescope will
show it.
* Jupiter's Red Spot should transit around 11:21 p.m. EST.
NOV. 11 -- WEDNESDAY
* Algol should be at minimum brightness for a couple hours centered on
8:23 p.m. EST.
* Jupiter's Red Spot should transit around 7:12 p.m. EST.
NOV. 12 -- THURSDAY
* Ceres, the largest minor planet (asteroid), is drifting near Aldebaran
in the late-evening sky. You can pick it up in binoculars; it's about
magnitude 7.5. Use the finder chart in the November Sky & Telescope, page
109.
* Users of medium-size and large telescopes from Texas to the Great Lakes
have a chance to catch the faint asteroid 145 Adeona occulting a
10.0-magnitude star just south of Capricornus this evening. The occultation
could last for 7 seconds around 1:24 Universal Time November 13th (7:24
p.m. Central Standard Time on the 12th). For a finder chart and any late
updates, see http://www.skypub.com/sights/occults/occults.html.
* Mars appears near the thick waning crescent Moon in the east before
dawn Friday morning.
NOV. 13 -- FRIDAY
* Jupiter's Red Spot should transit around 8:51 p.m. EST.
NOV. 14 -- SATURDAY
* Some doorstep astronomy: Look low in the northeast after dark for
bright Capella. Later in the evening it rises higher in the sky. Well to
Capella's right, in the east, is the Pleiades cluster. Orange Aldebaran
twinkles down below the Pleiades.
THIS WEEK'S PLANET ROUNDUP
MERCURY is very low in evening twilight. Using binoculars, look for it
barely above the southwest horizon about 30 minutes after sunset. Appearing
near it early in the week is Antares, somewhat fainter.
VENUS is hidden in the glare of the Sun.
MARS, in Leo, shines in the southeast before and during dawn.
JUPITER is the big, brilliant "star" high in the south during evening. You
can't miss it! Jupiter moves to the southwest in late evening, and it sets
after midnight.
SATURN is the bright "star" far to Jupiter's lower left after dusk,
directly left of Jupiter by midevening, and to Jupiter's upper left as the
night grows late. The two planets appear 40 degrees apart (about 4
fist-widths at arm's length), on opposite ends of Pisces.
URANUS and NEPTUNE, magnitudes 5.8 and 7.9 respectively, are in (or very
near) Capricornus in the south-southwest just after dark. See the finder
chart for them in the September Sky & Telescope, page 110, or at
http://www.skypub.com/sights/moonplanets/urnepplu.html.
PLUTO is hidden in the sunset.
(All descriptions that relate to the horizon or zenith are written for the
world's midnorthern latitudes. Descriptions that also depend on longitude
are for North America. Eastern Standard Time, EST, equals Universal Time
minus 5 hours.)
More details, sky maps, and news of other celestial events appear each
month in SKY & TELESCOPE, the essential magazine of astronomy. See our
enormous Web site at http://www.skypub.com/. Clear skies!
SKY & TELESCOPE, P.O. Box 9111, Belmont, MA 02478 * 617-864-7360 (voice)
Copyright 1998 Sky Publishing Corporation. S&T's Weekly News Bulletin and
Sky at a Glance stargazing calendar are provided as a service to the
astronomical community by the editors of SKY & TELESCOPE magazine.
Widespread electronic distribution is encouraged as long as these
paragraphs are included. But the text of the bulletin and calendar may not
be published in any other form without permission from Sky Publishing
(contact permissions@skypub.com or phone 617-864-7360). For updates of
astronomical news, including active links to related Internet resources,
are available via SKY & TELESCOPE's site on the World Wide Web at
http://www.skypub.com/.
In response to numerous requests, and in cooperation with the Astronomical
League (http://www.mcs.net/~bstevens/al/) and the American Association of
Amateur Astronomers (http://www.corvus.com/), S&T's Weekly News Bulletin
and Sky at a Glance are available via electronic mailing list too. For a
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SKY & TELESCOPE, the Essential Magazine of Astronomy, is read by more than
200,000 enthusiasts each month. It is available on newsstands worldwide.
For subscription information, or for a free copy of our catalog of fine
astronomy books and products, please contact Sky Publishing Corp., 49 Bay
State Rd., Cambridge, MA 02138-1200, U.S.A. Phone: 800-253-0245 (U.S. and
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custserv@skypub.com. WWW: http://www.skypub.com/. Clear skies!
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=SANA=
Дата: 10 ноября 1998 (1998-11-10)
От: Alexander Bondugin
Тема: Air-breathing Rocket Engine Tests Successfully Completed (Forwarded)
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June Malone
Media Relations Office
Marshall Space Flight Center
Huntsville, AL 35812
(256) 544-7061/0034
June.Malone@msfc.nasa.gov
http://www.msfc.nasa.gov/news
For Release: Nov. 6, 1998
RELEASE: 98-231
Air-breathing Rocket Engine Tests Successfully Completed
NASA has successfully completed two years of testing radical, new rocket
engines that could change the future of space travel. NASA and its industry
partners have ground tested rocket engines that "breathe" oxygen from the air.
"Air-breathing rocket engine technologies have the potential of opening the
space frontier to ordinary folks," said Uwe Hueter of NASA's Marshall Space
Flight Center in Huntsville, Ala. "We've proven the technologies on the
ground with extensive testing of complex and technically challenging system
components. Now, I believe we're ready to demonstrate the technologies in
flight."
Air-breathing rocket engines could make future space travel like today's air
travel, said Hueter, manager of NASA's Advanced Reusable Technologies project.
The spacecraft would be completely reusable, take off and land at airport
runways, and be ready to fly again within days.
An air-breathing rocket engine inhales oxygen from the air for about half the
flight, so it doesn't have to store the gas onboard. So at take-off, an air-
breathing rocket weighs much less than a conventional rocket, which carries
all of its fuel and oxygen onboard. Getting off the ground is the most
expensive part of any mission to low-Earth orbit, and reducing a vehicle's
weight decreases cost significantly.
An air-breathing engine (called a rocket-based, combined cycle engine) gets
its initial take-off power from specially designed rockets, called air-
augmented rockets, that boost performance about 15 percent over conventional
rockets. When the vehicle's velocity reaches twice the speed of sound, the
rockets are turned off and the engine relies totally on oxygen in the
atmosphere to burn the hydrogen fuel. Once the vehicle's speed increases to
about 10 times the speed of sound, the engine converts to a conventional
rocket-powered system to propel the vehicle into orbit.
This unconventional approach to getting to space is one of the technologies
NASA's Advanced Space Transportation Program at the Marshall Center is
developing to make space transportation affordable for everyone from business
travelers to tourists. NASA's goal is to reduce launch costs from today's
price tag of $10,000 per pound to only hundreds of dollars per pound.
GASL, a small aerospace company in Ronkonkoma, N.Y., has conducted most of
the air-breathing rocket engine testing at its facilities on Long Island.
GASL's unique facility is capable of testing across a wide range of speeds
and modes the rocket engine must achieve in flight.
NASA's industry partners in developing air-breathing rocket technologies are:
Aerojet Corp. of Sacramento, Calif.; Rocketdyne of Canoga Park, Calif.;
Astrox Corp. of Rockville, Md.; Pennsylvania State University of University
Park; and the University of Alabama in Huntsville.
- end -
Note to Editors: Interviews, photos and video supporting this release are
available to media representatives by contacting June Malone, Media Relations
Office, Marshall Space Flight Center, (256) 544-0034. For an electronic
version of this release, photos, QuickTime movie or more information, visit
Marshall's new Virtual NewsRoom: http://www.msfc.nasa.gov/news
For more information on the Advanced Space Transportation Program, visit its
Web site: http://stp.msfc.nasa.gov
[NOTE:
Images supporting this release are available at
http://www1.msfc.nasa.gov/NEWSROOM/news/photos/1998/photos98-231.htm
QuickTime movies supporting this release are available at
http://www1.msfc.nasa.gov/NEWSROOM/news/video/video98-231.htm]
Andrew Yee
ayee@nova.astro.utoronto.ca
Hа сегодня все, пока!
=SANA=
Дата: 10 ноября 1998 (1998-11-10)
От: Alexander Bondugin
Тема: Mars Express wins unanimous support (Forwarded)
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European Space Agency
Press Release No. 47-98
Paris, France 5 November 1998
Mars Express wins unanimous support
All fourteen national delegations in the European Space Agency's Science
Programme Committee have backed the project to send a spacecraft to
Mars in 2003. Support for Mars Express, as this exciting mission is called,
is qualified by concern about the long-term budget of ESA's science
programme. At its meeting in Paris on 2 and 3 November, the Science
Programme Committee made its approval of the implementation of Mars
Express conditional on sufficient funding for the science programme and
no impact on previously approved projects.
"The green light for Mars Express shows that Europe is perfectly capable
of seizing special chances in exploring space," said Roger Bonnet, ESA's
director of science. "At a cost to ESA of 150 million ECU, Mars Express
is the cheapest Mars mission ever, yet its importance and originality
are far greater than the price tag suggests."
Bonnet continued: "Mars Express has been advertised by the Science
Programme Committee as a test case for new approaches in procuring
and managing future science projects, with a view to achieving major
savings. In the international arena, Mars Express will confirm Europe's
interest in a major target for space research in the new century, when
we make our forceful debut at the Red Planet. In fact, Mars Express is
designed to be a pivotal element of an international multi-mission,
global effort for the exploration of Mars."
Development of the spacecraft will now proceed swiftly, to meet the
deadline of an exceptionally favourable launch window early in June
2003. Mars Express will go into orbit around Mars at Christmas 2003.
Seven scientific instruments on board will include a high-resolution
camera, a range of spectrometers, and a radar to penetrate below the
surface. For the first time in the history of the exploration of the Red
Planet, scientists can hope to detect sub-surface water, whether it
exists in the form of undergound rivers, pools, glaciers or permafrost.
Signs of life on Mars, whether extinct or continuing today, may reveal
themselves to a lander carried by Mars Express. This is Beagle 2, a
project led by the Open University in the United Kingdom, with
contributions from many other European countries. The lander also
promises invaluable information about the chemistry of the Martian
surface and atmosphere. Beagle 2 is to be independently funded. Some of
the necessary funds have already been raised and ESA has agreed with the
principal investigator to keep a place for Beagle 2 aboard Mars Express.
The financial situation will be verified at a date to be agreed with the
mission's prime contractor.
For more details about the mission visit the Mars Express web site on:
http://sci.esa.int/marsexpress/
For further information, please contact:
ESA Public Relations Division
Tel: +33(0)1.53.69.71.55 Fax: +33(0)1.53.69.76.90
Andrew Yee
ayee@nova.astro.utoronto.ca
Hа сегодня все, пока!
=SANA=
Дата: 10 ноября 1998 (1998-11-10)
От: Alexander Bondugin
Тема: ESA's experts are ready for a storm of comet dust (Forwarded)
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ESA Science News
http://sci.esa.int
6 Nov 1998
ESA's experts are ready for a storm of comet dust
When the Earth crosses the wake of Comet Tempel-Tuttle on 17 November,
European scientists will use the NASA-ESA Hubble Space Telescope to detect
impacts of cosmic dust. ESA's European Space Operations Centre (ESOC) has
sent out a warning to spacecraft operators about risks to all satellites in
the Earth's vicinity on that day, from the Leonid meteor storm. Countless
dust grains thrown out by the comet will slam into the Earth's atmosphere
at 71 kilometres per second. The Leonids, as they are called, may produce
the most spectacular shower of meteors, or "shooting stars", seen since
1966.
Minute grains of dust create the glowing heads and tails that make comets
famous. A trail of dust traces the orbit of each comet, and when the Earth
encounters a comet trail the result is a meteor shower. Comet Tempel-Tuttle
has just refreshed its dust trail on a visit to the Sun's vicinity, which
it makes every 33 years.
The Leonids approach the Earth from the direction of the constellation Leo.
As a precaution, the Hubble Space Telescope will turn its back on Leo for
ten hours around the predicted peak of the Leonid event, which is at about
20:30 CET on 17 November. Astronomers will take the opportunity to look for
undiscovered galaxies in the opposite direction in the sky. Any disturbances
caused to the 11.6-tonne Hubble spacecraft by the Leonid dust impacts will
be recorded for analysis by dust specialists. One of the teams chosen for
this study includes ESA and UK scientists and is headed by John Zarnecki of
the University of Kent.
Zarnecki comments: "It seems like doing an experiment with the crown jewels.
But Hubble is a fantastically accurate star pointer, so we should detect
wobbles due to quite small impacts. We hope to check our theories about the
numbers of grains of different masses. But I'd hate to see any harm come to
Hubble," Zarnecki adds. "Or any other spacecraft for that matter."
Taking account of the risk to spacecraft
This year Comet Tempel-Tuttle passed within 1.2 million kilometres of the
Earth's orbit, which is very near by astronomical standards. Similar close
encounters have produced widely differing results in the past. In 1932 the
count of visible meteors in the Leonids reached an unremarkable rate of 240
per hour, compared with a normal background of about 10-20 sporadic meteors
per hour at quiet times. Yet in 1966 the count-rate for the Leonids was
15,000 per hour, or 4 per second, and some observers reported even higher
rates.
If the rate is again 15,000 per hour, a spacecraft presenting a target of 10
square metres to the Leonid storm is likely to receive one hit penetrating
aluminium to a depth of 0.4 millimetre. A larger spacecraft has a greater
chance of being hit by a more penetrating dust grain. Operators are therefore
advised to turn their spacecraft to present as small a target as possible,
and to try to ensure that sensitive parts do not face the meteor stream.
"Bullet-like damage caused by large particles is only part of the story,"
says Walter Flury of ESOC's mission analysis section. "Fine grains are far
more numerous and can sand-blast optical systems, thermal blankets and solar
cells. And in a cloud of charged particles created by the impacts, lightning-
like discharges can cause faults in the electronic systems of the spacecraft.
The very high speed of the Leonids aggravates that risk, so it may be
advisable to switch off sensitive equipment. Damage due to electrical
discharges may be the most serious hazard from the Leonids."
Predictions are very uncertain and effects are very chancy, so one
recommendation is simply to reinforce the spacecraft operation teams on 17
November, to cope with any emergency that arises. The direction of arrival
of the Leonids is favourable for satellites in one respect. The dust grains
will come from a direction almost at right angles to the direction of the
Sun. Flat solar panels in their normal orientation, facing the Sun, present
only a narrow edge as a target for the Leonids.
Controllers of ESA's Earth observation satellites ERS-1 and ERS-2 will switch
off the instruments during the hazardous period to reduce the risk of
electrically-induced damage. ESA's solar spacecraft SOHO, stationed 1.5
million kilometres out in space, is likely to experience an even stronger
storm of Leonids than satellites in the Earth's vicinity. Measures to reduce
the hazard may include rotating the spacecraft to screen vital equipment,
and switching off scientific instruments.
The view from the ground
When the Leonids are at their peak, Leo will just be rising on Europe's
eastern horizon. Nevertheless, observers in Europe watching out between
midnight and dawn, on 17 and 18 November, may see unusual numbers of meteors.
The best view will be from east Asia, where Leo will be high in the night
sky at the time of the expected maximum. ESA has joined with other space
agencies in sponsoring a Canadian expedition to Mongolia to observe the
Leonids with video cameras equipped with image intensifiers. The same
Canadian initiative will use radars in northern Australia to detect the
meteors. Real-time information on the intensity and duration of the dust
storm will help spacecraft operators to judge when the risk has passed.
Next year's appearance of the Leonids, in November 1999, will be best seen
from Europe, and it could be bigger than this year's event. For the same
reason, the risk posed by the Leonids to spacecraft will recur at that time.
ESA scientists will be rehearsing this year for ground-based observations
of the Leonids next year, from southern Spain.
Historical note on dust damage
ESA has brutal experience of cosmic dust storms. In March 1986, its Giotto
spacecraft flew deep into the dusty head of Halley's Comet, where it obtained
amazing pictures of the nucleus. A dust particle no bigger than a grain of
rice slammed into the spacecraft at 68 kilometres per second with the force
of a hand grenade, and set it wobbling. A sand-blast of smaller grains,
recorded as a continous drumbeat by dust detectors on Giotto, disabled
the camera and caused other damage. Nevertheless the ESA operations team
recovered control of the spacecraft and even managed to fly Giotto on an
extended mission that took it to Comet Grigg-Skjellerup six years later.
Controllers were less lucky in August 1993 when a dust grain from Comet
Swift-Tuttle, in the Perseid meteor stream, was probably to blame for
knocking out ESA's Olympus telecommunications satellite after four years of
operation. Although it remained intact, Olympus lost so much thruster fuel
in trying to correct its attitude that it became unmanageable. More direct
knowledge of dust impacts on spacecraft came from examining part of the
original solar array of the Hubble Space Telecope, provided by ESA, which
was returned to Earth in the first refurbishment mission in December 1993.
The solar cells were pitted by many small dust impacts.
The Leonids on the Internet
For the ESA/ESOC report "The Leonid 1998 Meteor Shower: information for
spacecraft operators":
http://www.estec.esa.nl/spdwww/leonids/
For a brief video clip of telescope images of meteor trails, see:
http://www.so.estec.esa.nl/planetary/meteors/animation/
For general information see the Leiden Leonid site (mirroring a NASA site)
and the home page of the International Meteor Organization, both of which
have leads to abundant material:
http://strw.leidenuniv.nl/~leonid/
http://www.imo.net
For updates on the Leonid event as it affects ESA science activities, watch
the ESA science site:
http://sci.esa.int
For further information please contact:
ESA Public Relations Division
Tel: +33(0)1.53.69.7155 Fax: +33(0)1.53.69.7690
At ESA's Satellite Operations Centre (ESOC), Darmstadt (Germany), you may
contact:
Walter Flury -- Tel: +49(0)6151.2270
The following specialists at ESA's Technical and Research Centre (ESTEC)
can give more detailed information in various languages:
Dutch: Hakan Svedhem -- Tel: +31(0)71.565.3370
English: Trevor Sanderson -- Tel: +31(0)71.565.3577
John Zarnecki -- Tel: +31(0)71.565.3423
French: Jean-Pierre Lebreton -- Tel: +31(0)71.565.3600
Bernard Foing -- Tel: +31(0)71.565.5647
German: Detlef Koschny -- Tel: +31(0)71.565.4828
Gerhard Schwehm -- Tel +31(0)71.565.3539
Italian: Francesca Ferri -- Tel: +31(0)71.565.5634
Spanish: Luisa Lara Lopez -- Tel: +31((0)71.565.4893
Swedish: Hakan Svedhem -- Tel: +31(0)71.565.3370
USEFUL LINKS FOR THIS STORY
ESOC report on Meteor showers
http://www.estec.esa.nl/spdwww/leonids/
Meteor trail animation
http://www.so.estec.esa.nl/planetary/meteors/animation/
Leiden univ. Leonids site
http://strw.leidenuniv.nl/~leonid/
International meteor organisation
http://www.imo.net
Andrew Yee
ayee@nova.astro.utoronto.ca
Hа сегодня все, пока!
=SANA=
Дата: 10 ноября 1998 (1998-11-10)
От: Alexander Bondugin
Тема: This Week On Galileo - November 9-15, 1998
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THIS WEEK ON GALILEO
November 9-15, 1998
With only two weeks until Galileo's next encounter with Europa,
Jupiter's icy moon, the spacecraft spends most of the week returning
science data stored on its onboard tape recorder. The data were
acquired during Galileo's previous flyby of the icy moon, back in
September. Data processing and transmission is suspended twice this
week so the spacecraft can perform regular maintenance on its
propulsion system, and perform a standard gyroscope performance test.
This week's playback time is used to fill gaps in previously returned
data, select new data, or to re-process data with different parameters.
Data from fifteen observations, all describing Europa, are returned by
the spacecraft camera, near-infrared mapping spectrometer and
ultraviolet spectrometer.
The spacecraft camera returns the majority of observations this week,
12 of the 15 planned. The first observation is a mosaic of images
taken near Europa's terminator. The observation cuts across various
terrain types that are considered to be the best evidence for the
existence of a liquid layer under Europa's surface. Three sets of
images, some in color, are returned this week showing Europa's Agenor
Linea. Agenor Linea's brightness is believed to be an indication that
the feature is fairly young. A single observation is returned of
Thrace Macula. The images are expected to clarify the nature of a
large dark area that may be similar to other regions which have been
found to contain iceberg-like fragments of older crust. The remaining
seven observations returned by the camera this week contain images of
Libya Linea, Thynia Linea, Europa's south polar region, pull-apart
wedges, dissected terrain, a strike-slip fault, and regions of
unexplored terrain.
The remaining three observations are returned by the near-infrared
mapping spectrometer together with the ultraviolet spectrometer. All
three observations aim to provide more information on the spectral
characteristics of Europa's surface, which will help scientists
understand more about its composition. Two of the observations have a
special emphasis on detecting non-ice components.
For more information on the Galileo spacecraft and its mission
to Jupiter, please visit the Galileo home page:
http://www.jpl.nasa.gov/galileo
Hа сегодня все, пока!
=SANA=
Дата: 10 ноября 1998 (1998-11-10)
От: Alexander Bondugin
Тема: Mars Surveyor 98 Update - November 7, 1998
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1998 MARS SURVEYOR PROJECT STATUS REPORT
November 7, 1998
John McNamee
Mars Surveyor 98 Project Manager
Mars Climate Orbiter: Launch -33 days
Successfully completed the launch/init Mission Systems Test (MST) - final
time this will be run on the orbiter prior to launch. An anomaly was
observed in the flight Pyro Initiation Unit (PIU) during the start of the
launch/init run with symptoms similar to that observed, and thought to be
resolved, on the ATLO Test Unit (ATU) PIU. Troubleshooting is in progress.
Ordnance was installed on the orbiter. Troubleshooting of various open
items was accomplished on the spacecraft. The harness/prop final
walkdown was completed.
Mars Polar Lander: Launch -57 days
A procedural error cause the scipted attitude determination Entry, Descent
and Landing (EDL) MST to abort prior to completion. The cause is understood
and the test will be repeated next week.
For more information on the Mars Surveyor 98 mission, please visit
our website at:
http://mars.jpl.nasa.gov/msp98
Hа сегодня все, пока!
=SANA=
Дата: 10 ноября 1998 (1998-11-10)
От: Alexander Bondugin
Тема: Mars Global Surveyor Aerobraking Update - November 5, 1998
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Mars Global Surveyor Aerobraking Status Report
Thursday, November 5 (DOY 304/19:00:00 to DOY 309/19:00:00 UTC)
Last Orbit Covered by this Report = 685
Total Phase I Aerobraking orbits accomplished = 180
Total Phase II Aerobraking orbits accomplished = 112
Total Science Phasing orbits accomplished = 290
Apoapsis altitude = 10669 km
Apoapsis altitude decrease since start of aerobraking = 43357 km
Periapsis altitude = 112.6 km
Current Orbit Period = 06:56:04
Orbit Period decrease since start of aerobraking = 38:03:29
Starting Phase II orbit period = 11:38:02
RECENT EVENTS:
The Mars Global Surveyor spacecraft maintains excellent health and
performance as aerobraking operations have reduced the orbit period to less
than 7 hours. The last 16 drag passes have removed 32 minutes from the orbit
period. The 6-orbit running mean is currently 0.295 N/m2 but should start to
decrease dramatically since the desired drag corridor has been reduced in
force. Results presented at this week's reset meeting shows the period
deficit (suffered due to the late start of Phase 2) has been nearly
eliminated. Two periapsis raise maneuvers were executed during this period
to reduce the drag force and to average about 0.20 N/m2. A new target
corridor, 0.17 - 0.23 N/m2, has been established to slow aerobraking. It is
desired to keep the period reduction rate close to the baseline plan to
maintain the orbit phasing and inclination desired for the mapping orbit.
Sequence P684 is currently controlling S/C activities through the remainder
of orbit 686. The reset 10 parameter selections further reduce the MOLA
warming maneuver to 45 minutes and calls for all drag sequences to be built
using 4 primary orbits and 2 backup orbits. This is an increase of 1 primary
orbit and will allow the flight team to continue building only 1 drag
sequence per day. The primary charger connect time has been increased to
maintain margin. P687 will take control of spacecraft activities later
tonight and will continue control through orbit 690. All timing estimations
have been well within the 232s, excessive fuel use limit. Due to a sequence
generation problem, P679 was not built in time to uplink to the S/C. Orbit
679 activities were commanded as a backup orbit from sequence P676. A P680
sequence was built to execute orbits 680, 681 and 682.
All subsystems report excellent S/C health with no performance concerns. The
-Y solar array yoke has shown no changes in structural performance. Attitude
knowledge has been maintained throughout the period with excellent star
processing. The power subsystem reports strong performance with 11.0 %
battery discharge depths each orbit. There is now 15 minutes of primary
charger re-charge margin. The minimum MOLA laser temperature observed this
period was 12.1њC. The largest temperature increase due to aero-heating seen
was 66њC on the -Y solar array, cell side. The telecommunications subsystem
continues solid performance.
The System Test Lab (STL) has been repaired. Testing will return to the lab
tomorrow. Tests to be completed are, aerobraking pop-up re-verification, 2
am mapping flight software update validation, and nominal 2 am mapping
sequence testing. About 3.5 weeks has been lost in the schedule. The revised
test schedule will likely require 7 days per week operations.
The Thermal Emissions Spectrometer (TES) was powered off this week for the
duration of aerobraking.
UPCOMING EVENTS:
Periapsis for Orbit 686 DOY309/20:14:20 UTC Through
Periapsis for Orbit 700 DOY313/18:44:53 UTC
(Note: MST = UTC-7 hours DOY309=11/5)
SPACECRAFT COMMANDING:
There were 18 command files radiated to the S/C during this period. The
total files radiated since launch is now 2945. These commands were sent in
support of the following activities:
TES power off
Nominal drag pass sequences (P670, P673, P676, P680, P683, P684)
Nominal corridor control maneuver sequences (A682, A685)
Command loss timer reset
Nominal star catalog and ephemeris file updates
Hа сегодня все, пока!
=SANA=
Дата: 10 ноября 1998 (1998-11-10)
От: Alexander Bondugin
Тема: Mars Global Surveyor Update - November 6, 1998
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Mars Global Surveyor
Project Status Report Overview
Prepared by Mars Surveyor Operations Project Manager
NASA Jet Propulsion Laboratory
Friday 6 November 1998
Aerobraking by the MGS spacecraft is proceeding smoothly. The spacecraft
health is excellent. The atmosphere is stable and, in general, periapsis
density levels have been very predictable. After six weeks (90 periapsis
passes), the orbital period has been reduced to 7.0 hours and the difference
from the planned period reduction path due to the late start for this phase
has been completely made up. A periapsis raise maneuver was performed on
revolution P686 to reduce the average aerobraking pressure from 0.28 n/m2 to
0.2 n/m2 by increasing the altitude at periapsis by 2 km to 116 km. This
level of resistance or lower will be targeted for most of the remainder of
the aerobraking phase to follow a "glide-path" reduction rate which will
arrive at a two hour period next February just when the orbit plane
precession reaches the 2 AM lighting geometry.
On November 2, the TES instrument was turned off to conserve the backup
interferometer fringe counting lamp for the mapping phase beginning next
March. On November 6, the Project Manager briefed Code S program management
on the MGS high gain antenna deployment strategy at the start of the mapping
phase. A three week pre-deployment, contingency science period has been
created in the new Mission Plan.
A telecom analysis review, held on November 4, confirmed that with minor
modification to the Stanford 46 m radio antenna, it will be possible to
detect the beacon signals from both MGS and MCO spacecraft relay antennae
and from the DS2 landed station uplink carriers during the M'98 relay
operation.
Operations personnel participated Mars Polar Lander system data flow tests
and the TMOD Launch Readiness Review for the M'98 mission held on Friday,
11/6/98.
Hа сегодня все, пока!
=SANA=
Дата: 10 ноября 1998 (1998-11-10)
От: Alexander Bondugin
Тема: Astronomers in Arizona aim for shortest submillimeter wavelengths (For
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News Services
University of Arizona
Contact(s):
Thomas L. Wilson, 520-621-5505
November 9, 1998
Astronomers in Arizona aim for shortest submillimeter wavelengths
Astronomers plan soon to make observations at the shortest, highest-frequency
submillimeter wavelengths ever detected from Earth -- with a telescope that
satellite holography recently proved to be the most accurate of its kind in
the world.
If they succeed, they pave the way for ground-based astronomy at the shortest
possible submillimeter, or microwave, wavelengths. Until astronomers complete
this gap between radio and infrared/optical astronomy, they cannot piece
together a coherent, comprehensive picture of the universe.
The telescope is the 10-meter Heinrich Hertz Submillimeter Telescope (HHT),
a joint project of The University of Arizona Steward Observatory in Tucson
and the Max Planck Institute for Radioastronomy (MPIfR) in Bonn, Germany.
Astronomers from the UA and the Harvard-Smithsonian Center for Astrophysics
(CfA) in Cambridge, Mass., this month will install a unique receiver at the
$10 million telescope on Mount Graham, Ariz.
The surface shape of the telescope's primary reflector must be incredibly
accurate to observe very high-frequency submillimeter wavelengths, said
Thomas L. Wilson, director of the Submillimeter Telescope Observatory. The
observatory, which consists of the HHT and its co-rotating enclosure, is
staffed by 15 Arizona and German researchers. Wilson became observatory
director in September 1997.
This fall, observatory staff measured and adjusted the accuracy of the 60
panels in the 10-meter (33-foot) primary reflector by a technique called
satellite holography. It involved scheduling time on a communications
satellite operated by the MIT Lincoln Laboratory for the U.S. Defense
Department. Observatory staff used signals from the satellite's radio
beacon and a special receiver from the National Radio Astronomy Observatory
in Tucson to map the shape of the reflector twice each night. They then made
fine adjustments by moving panels in or out, or tilting panels left or right.
After about three weeks of measuring and mapping, the HHT reflector was
brought to an accuracy within 12 microns -- about half the thickness of a
human hair, or one part in a million of the diameter of the telescope. "If
the HHT dish were a mile across, no surface irregularity would be greater
than a few widths of a fingernail. That makes this telescope THE most
accurate telescope in the radio range," Wilson said. The feat is all the
more remarkable because it was done on a reflector in an open telescope on
a 10,425-foot (3,200-meter) mountaintop, not in a laboratory, he added.
The Harvard-Smithsonian Center for Astrophysics developed the new technology
submillimeter receiver to be installed at the HHT later this month. The new-
type "HEB" receiver, or Hot Electron Bolometer, incorporates a new material
called nobium nitride. The receiver was first tested on a telescope -- the
HHT -- during three weeks last March. Astronomers measured spectra at the
high frequency bands they aimed for -- the 690 GigaHertz (500 micron
wavelengths) and 810 GigaHertz (350 micron wavelengths) bands. (A hertz is
a unit of frequency, one cycle per second. A GigaHertz is a billion Hertz.)
"We believe these are the first astronomical spectra ever reported with an
HEB system on a telescope," Wilson said. "This has very great promise for
studies at really high frequency wavelengths -- 200 microns or shorter."
Wavelengths this short approach one TeraHertz (trillion Hertz) frequencies --
about 10,000 times higher frequency than an FM radio receives. Such high-
frequency wavelengths -- which border far infrared wavelengths -- cannot be
detected with conventional, superconducting receivers currently used, Wilson
said.
Submillimeter, or microwave, astronomy covers the wavelength range between
300 microns and 1,000 microns (three-tenths of a millimeter and one
millimeter). Longer wavelengths fall in the radio region of the
electromagnetic spectrum; shorter wavelengths are in the far infrared region.
The submillimeter region is regarded by many to be astronomy's last wholly
unexplored wavelength frontier. It is essential in understanding the process
of star and planet formation, both in our own Milky Way Galaxy and in other
galaxies throughout the universe.
One major target for submillimeter astronomy is to study the cool, molecular
clouds of dust and gas that exist 100 light years or more from our sun,
Wilson said. (Astronomers theorize that a supernova explosion swept away the
molecular material closer to the sun, which at the time already had formed
its solar system.) Astronomers need a better understanding of the physical
conditions within molecular clouds to better understand why stars form, and
why some stars give rise to planets, while other stars do not.
Submillimeter astronomy has remained terra incognita because of the sheer
complexity of its astronomical instrumentation and a dearth of extremely
good observing sites since water vapor in Earth's atmosphere absorbs
submillimeter radiation. Only the driest atmosphere is sufficiently
transparent to submillimeter radiation.
"Weather plays a big role in submillimeter astronomy," Wilson said. "I think
a fair statement is that if you want to observe at submillimeter wavelengths,
you have to reckon that half the time is lost to other-than-optimal weather.
Then, during the other half of the time, there can be problems with the
receiver or the telescope. The receivers which we use are really very
complex. They really are cutting-edge physics in themselves."
The Steward Observatory Radio Astronomy Lab headed by Christopher Walker, the
MPIfR Heterodyne Receiver Group and the MPIfR Bolometer Group have provided
much of the HHT instrumentation available to the astronomical community.
Wilson said the Submillimeter Telescope Observatory has started developing
a suite of receivers in collaboration with the National Radio Astronomy
Observatory and the Harvard-Smithsonian CfA.
The HHT is the only large submillimeter telescope that astronomers can use
both day and night. It owes this unique capability to the fact that it is
made of a carbon-fiber reinforced plastic that is 20 times less sensitive to
temperature change than most metals, and to that fact that it is located at
a high-altitude site that is generally very dry. The world's other two large
submillimeter telescopes -- the 10-meter Caltech Submillimeter Telescope and
the 15-meter James Clerk Maxwell Telescope -- are both located on Mauna Kea,
Hawaii, a mountain surrounded by ocean so that it trails off clouds of water
vapor when heated by daily sunshine. The HHT is shut down during the Arizona
summer monsoons, but is free of the local diurnal effect that plagues the
Hawaiian-based telescopes.
A small, millimeter-wavelength radio receiver mounted on the HHT enclosure
measures atmospheric conditions. UA and CfA astronomers will observe at the
shortest, highest-frequency wavelengths this winter when the weather is
extremely good -- usually right after a big snowstorm, after the water has
fallen from the sky and temperatures turn very cold, Wilson said.
"I think the chance of finding something new is much better the shorter
wavelengths, where little astronomy has been done," Wilson said. "We're
hoping for a big surprise, something really spectacular."
Prior to becoming director of the Submillimeter Telescope Observatory, Wilson
was a staff scientist for the MPIfR in Bonn. His work there involved helping
to start a 100-meter telescope in Effelsberg, Germany, and a 30-meter
telescope in Spain, as well as the 10-meter HHT in Arizona. His more than 220
publications and three books include the book, "Tools of Radio Astronomy,"
about to published in 3rd edition. Wilson completed his doctorate in physics
in 1969 at the Massachusetts Institute of Technology, where his thesis
adviser was Bernard F. Burke. Burke was in Tucson last Friday to receive the
33rd Karl G. Jansky award for his pioneering work in radio astronomy.
LINKS:
http://maisel.as.arizona.edu:8080/
Andrew Yee
ayee@nova.astro.utoronto.ca
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Дата: 10 ноября 1998 (1998-11-10)
От: Alexander Bondugin
Тема: Hubble Sees Bright Knots Ejected From Brilliant Star
Привет всем!
Вот, свалилось из Internet...
FOR RELEASE: 9:00 a.m. (EST) November 5, 1998
CONTACT: Yves Grosdidier
Universitie de Montreal, Montreal, Canada
(Phone: 514-343-6111, x5245)
(e-mail: yves@astro.umontreal.ca)
PHOTO NO.: STScI-PRC98-38
GREAT BALLS OF FIRE!
HUBBLE SEES BRIGHT KNOTS EJECTED FROM BRILLIANT STAR
Resembling an aerial fireworks explosion, this dramatic NASA Hubble
Space Telescope picture of the energetic star WR124 reveals it is
surrounded by hot clumps of gas being ejected into space at speeds of
over 100,000 miles per hour.
Also remarkable are vast arcs of glowing gas around the star, which are
resolved into filamentary, chaotic substructures, yet with no overall
global shell structure. Though the existence of clumps in the winds of
hot stars has been deduced through spectroscopic observations of their
inner winds, Hubble resolves them directly in the nebula M1-67 around
WR124 as 100 billion-mile wide glowing gas blobs. Each blob is about 30
times the mass of the Earth.
The massive, hot central star is known as a Wolf-Rayet star. This
extremely rare and short-lived class of super-hot star (in this case
50,000 degrees Kelvin) is going through a violent, transitional phase
characterized by the fierce ejection of mass. The blobs may result from
the furious stellar wind that does not flow smoothly into space but has
instabilities which make it clumpy.
The surrounding nebula is estimated to be no older than 10,000 years,
which means that it is so young it has not yet slammed into the gasses
comprising the surrounding interstellar medium.
As the blobs cool they will eventually dissipate into space and so
don't pose any threat to neighboring stars.
The star is 15,000 light-years away, located in the constellation
Sagittarius. The picture was taken with Hubble's Wide Field Planetary
Camera 2 in March 1997. The image is false-colored to reveal details in
the nebula's structure.
Credit: Yves Grosdidier (University of Montreal and Observatoire de
Strasbourg), Anthony Moffat (Universitie de Montreal), Gilles Joncas
(Universite Laval), Agnes Acker (Observatoire de Strasbourg), and NASA
EDITORS: Image files and photo caption are available on the Internet at
http://oposite.stsci.edu/pubinfo/1998/38 and via links in
http://oposite.stsci.edu/pubinfo/pictures.html and
http://oposite.stsci.edu/pubinfo/latest.html.
Higher resolution image files are available at
http://oposite.stsci.edu/pubinfo/tiff/1998/9838.tif
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