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Дата: 16 марта 1998 (1998-03-16)
От: Alexander Bondugin
Тема: Lunar Prospector Update - March 11, 1998
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Lunar Prospector Status Report #24
March 11, 1998
7:00 p.m. EST (4:00 p.m. PST)
The Lunar Prospector spacecraft continues to perform very well, and all
instruments continue to collect good data, according to Mission Control
at NASA's Ames Research Center. On Sat., March 7 (PST), mission
controllers sent commands to fire the spacecraft's thrusters to correct
its orbit. In addition, on Tues., March 10 (PST), two commands were
executed to tweak the gamma ray spectrometer's HV (high voltage) gain.
The current state of the vehicle (as of 4:00 p.m. (PST) on Wed., March
11, 1998), according to Mission Operations Manager Marcie Smith, is as
follows:
Spacecraft Orbit Number: 711
Data Downlink Rate: 3600 bps
Spin Rate: 12.18 rpm
Spin Axis Altitude Longitude: 281 degrees
Latitude: 87.6 degrees
Trajectory Periselene: 94 km
Aposelene: 106 km
Period: 118 minutes
Inclination: 90.7 degrees
Occultations: 44 minutes in duration
Eclipses: 45 minutes in duration
Last Saturday, mission controllers executed the first orbit trim
maneuver, in which two axial burns were fired: one to raise periselene
(closest distance from the Moon) and the other to lower aposelene
(furthest distance from the Moon). The target orbit (87 X 113 km) was
designed to be biased to compensate for periodic perturbations in order
to keep the actual orbit as close as possible to the desired 100
+ 20 km orbit for as long as possible. The
actual maneuver was very close to target, resulting in an orbit of 87.7
X 112.3 km. The precise command timeline was as follows:
Sat., March 7, 7:26 p.m. (PST) Thruster heaters on
Sat., March 7, 7:49 p.m. (PST) Thrusters A3 and A4 fired for 46.5 seconds
Sat., March 7, 7:50 p.m. (PST) Thruster parameters reset
Sat., March 7, 8:32 p.m. (PST) Thruster heaters on
Sat., March 7, 8:53 p.m. (PST) Thrusters A3 and A4 fired for 45.9 seconds
Sat., March 7, 8:54 p.m. (PST) Thruster parameters reset
Tues., March 10, 7:00 a.m. (PST) Gamma Ray Spectrometer command sent
On March 12 (PST), the Moon will see the Sun partially blocked by the
Earth. Mission controllers will carefully monitor this event to ensure
full battery recharging after normal once-per-orbit passages over the
nightside of the Moon. Also on that day, controllers plan to execute
small attitude and spin trim maneuvers.
Alison Davis
Lunar Prospector Mission Office
NASA Ames Research Center
Moffett Field, Calif. 94035
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=SANA=
Дата: 16 марта 1998 (1998-03-16)
От: Alexander Bondugin
Тема: Mars Surveyor 98 Update - March 13, 1998
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Mars Surveyor 98 Project Status Report
March 13, 1998
John McNamee
Mars Surveyor 98 Project Manager
Orbiter and lander integration and test activities are proceeding on
schedule with no significant problems. Orbiter electromagnetic
compatibility testing was completed successfully on March 9. The orbiter
spacecraft is being prepared for thermal vacuum testing scheduled to begin
on April 8. The lander vehicle was inserted into the backshell on March 12.
The lander/backshell combination will be mated with the cruise stage on
March 14 and the heat shield will be installed on March 19. The lander
spacecraft in full cruise configuration will be transported to the acoustics
lab at Lockheed Martin on March 20.
For more information on the Mars Surveyor 98 mission, please visit this
website:
http://mars.jpl.nasa.gov/msp98/
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=SANA=
Дата: 16 марта 1998 (1998-03-16)
От: Alexander Bondugin
Тема: Earth-Viewing Satellite Would Focus On Educational, Scientific Benefit
Subject: Earth-Viewing Satellite Would Focus On Educational, Scientific Benefit
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Douglas Isbell March 13, 1998
Headquarters, Washington, DC
(Phone: 202/358-1753)
RELEASE: 98-46
EARTH-VIEWING SATELLITE WOULD FOCUS ON EDUCATIONAL, SCIENTIFIC BENEFITS
Keying off a concept proposed by Vice President Al Gore, NASA
is developing plans for a small satellite which could provide
continuous views of the Earth by the year 2000.
NASA plans to issue educational, scientific and possibly
commercial announcements of opportunity within the next few weeks,
following the Vice PresidentХs call today for NASA to design,
build and launch the satellite by 2000.
"Vice President Gore has given us an exciting challenge,"
said NASA Administrator Daniel S. Goldin. "In the coming weeks,
we plan to solicit ideas from the academic, environmental,
scientific and commercial communities. We will synthesize these
ideas and communicate with the Congress as we go forward."
Goldin said NASA envisions "down-to-Earth" applications:
"This view of our planet can help us plan as fires ravage
wilderness areas, it may be able to save lives as we watch
hurricanes and typhoons form and threaten coastlines across the
grand sweep of ocean basins. Moreover, we think it is important
to inspire young minds, provide new perspectives on the planet for
our scientific community, and perhaps provide commercial
applications as well. We're going to pave the way for an Earth
Channel."
The satellite concept would place a high definition
television camera--paired with an eight-inch telescope--into an
orbit at a unique vantage point a million miles from Earth where
it could provide 24-hour views of the home planet. It would orbit
at a point in space where the gravitational attraction of the Sun
and the Earth essentially cancel one another out, allowing the
satellite to constantly view a fully sunlit hemisphere.
"We want to directly involve university students, teamed with
industry and government, in the design, development, operations
and data analysis from this unique venture," said Dr. Ghassem
Asrar, NASA Associate Administrator for Earth Science. "It would
allow scientists to track natural events such as hurricanes, large
fires and volcano plumes. We expect further innovative
applications to blossom as we let this singular view inspire the
imaginations of all the citizens of planet Earth."
Early plans envision a 330-pound satellite linked to Earth
through three simple, low cost ground stations equally spaced
around the globe to provide continuous downlink capability. One
new image would be downlinked every few minutes. The satellite
would be developed and launched within two years of a competitive
selection process. College students would participate in the
design and development of the spacecraft, and student teams would
operate the ground stations. The total mission cost, including
launch and operations, would not exceed $50 million.
- end -
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=SANA=
Дата: 16 марта 1998 (1998-03-16)
От: Alexander Bondugin
Тема: New Mars Global Surveyor Data Reveals Deeply Layered Terrain
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Douglas Isbell
Headquarters, Washington, DC March 13, 1998
(Phone: 202/358-1547)
Diane Ainsworth
Jet Propulsion Laboratory, Pasadena, CA
(Phone: 818/354-5011)
Cynthia M. O'Carroll
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-6943)
RELEASE: 98-45
NEW GLOBAL SURVEYOR DATA REVEALS DEEPLY LAYERED TERRAIN,
MAGNETIC FEATURES AND GENESIS OF A MARTIAN DUST STORM
For the first time in Mars exploration, a spacecraft has
captured the full evolution of a Martian dust storm. NASA's
Mars Global Surveyor mission also has returned new insights
into the deeply layered terrain and mineral composition of the
Martian surface, and to highly magnetized crustal features that
provide important clues about the planet's interior.
These findings are among the early results from the Mars-
orbiting mission being reported in today's issue of Science
magazine.
This first set of formal results comes from data obtained
in October and November 1997, while the spacecraft was just
beginning to use the drag of Mars' upper atmosphere to lower
and circularize its highly elliptical orbit in a process called
aerobraking. At the time, a dust storm was brewing on Mars and
had grown to about the size of the South Atlantic Ocean.
The Global Surveyor data suggest that the event began as a
set of small dust storms along the edge of the planet's
southern polar cap, according to Dr. Arden Albee of the
California Institute of Technology, Pasadena, CA, the Mars
Global Surveyor mission scientist. By Thanksgiving, it had
expanded into a large regional dust storm in Noachis Terra that
covered almost 180 degrees longitude, while spanning 20 degrees
south latitude to nearly the tip of the Martian equator.
"As this storm obscured the Martian landscape, we followed
it in detail using several instruments onboard Mars Global
Surveyor," Albee said. "The Thermal Emission Spectrometer
mapped the temperature and opacity of the atmosphere while the
camera followed the visual effects. The effects of the storm
extended to great heights of about 80 miles (130 kilometers)
and resulted in great increases in both atmospheric density and
variability from orbit to orbit. These atmospheric measurements
have great significance to future Mars missions that will be
using aerobraking techniques too."
Before the storm, atmospheric dust was generally
distributed very uniformly, Albee said. Observations of the
limb of the planet in the northern hemisphere revealed both
low-lying dust hazes and detached water-ice clouds at altitudes
of up to 34 miles (55 kilometers). Movement of these clouds was
tracked by the spectrometer as the planet rotated. Atmospheric turbulence
disrupted these cloud patterns as the small storms began to
rise and kick more dust into the air. As the storm began to
abate, small local storms began to crop up again along the
edges of the south polar cap, and ice clouds formed in
depressions as the carbon dioxide cap continued to retreat.
In addition to these unprecedented observations of a full-
blown Martian dust storm, measurements from the spacecraft's
Magnetometer and Electron Reflectometer have yielded new
findings about Mars' strong, localized magnetic fields. These
patches of the crust, which register high levels of magnetism,
are beginning to unlock some of the mysteries surrounding Mars'
internal dynamo and when it died, said Dr. Mario Acuna of
NASA's Goddard Space Flight Center, Greenbelt, MD.
"These locally magnetized areas on Mars could not form
without the presence of an overall global magnetic field that
was perhaps as strong as Earth's is today," says Acuna. "Since
the internal dynamo that powered the global field is extinct,
these local magnetic fields act as fossils, preserving a record
of the geologic history and thermal evolution of Mars."
Magnetic fields are created by the movement of electrically
conducting fluids, and a planet can generate a global magnetic
field if its interior consists of molten metal hot enough to
undergo convective motion, similar to the churning motion seen
in boiling water.
"The small size and highly magnetic nature of these crustal
features, which measure on the order of 30 miles (50
kilometers), are found within the ancient cratered terrain
rather than within the younger volcanic terrain," Acuna said.
"By correlating crustal age with magnetization, we have a
perfect window on Mars' past, which will help us to determine
when Mars' internal dynamo ceased operating."
High-resolution images of dunes, sandsheets and drifts also
are helping reveal earlier chapters of Martian history.
Landforms shaped by erosion are almost everywhere, according to
Albee, and many bear a striking resemblance to
Colorado's Rocky Mountains. Rocky ridges poke through the
Martian dust just as the jagged edges of cliffs pierce through
a blanket of snow in the Rockies. Martian dust appears to have
spilled down the sides of ridges just as fresh snow slides down
a ski slope.
"One almost expects to see ski tracks crisscrossing the
area," Albee added. "These images present a sharp contrast to
the images of boulder-strewn deserts found at the Viking and
Pathfinder landing sites."
Newly released images from the Mars Global Surveyor camera,
developed by principal investigator Dr. Michael Malin of Malin
Space Science Systems, Inc., San Diego, can be viewed on the
Internet at:
http://www.jpl.nasa.gov/marsnews or www.msss.com/
The Martian crust also exhibits much more layering at great
depth than was expected. The steep walls of canyons, valleys
and craters show the Martian crust to be stratified at scales
of a few tens of yards, which is an exciting discovery, Albee
noted. "At this point we simply do not know whether these
layers represent piles of volcanic flows or sedimentary rocks
that might have formed in a standing body of water," he said.
The Thermal Emission Spectrometer, led by principal
investigator Dr. Philip Christensen of Arizona State
University, is beginning to obtain a few infrared emission
spectra of the surface, although it is still too cold on the
surface for the best results. The best spectra clearly
indicate the presence of pyroxene and plagioclase, minerals
which are common in volcanic rocks, with a variable amount of
dust component. No evidence was found for carbonate minerals,
clay minerals or quartz. If present in these rocks, their
abundance must be less than about ten percent.
Their absence indicates that carbonates are not widespread
over the surface of the planet, but they may still be found in
specific locations that either favored their initial deposition
or their subsequent preservation. This finding could have
important implications for identifying areas that may preserve
signs of ancient life on Mars, since carbonate minerals are
commonly formed in biological processes, Albee said.
Striking results also have been obtained from Global
Surveyor's laser altimeter over Mars' northern hemisphere,
which is exceptionally flat with slopes and surface roughness
increasing toward the equator, according to principal
investigator Dr. David Smith of Goddard. The initial data for
this region helps scientists interpret a variety of landforms,
including the northern polar cap, gigantic canyons, ridges,
craters of all sizes and shield volcanoes. Most surprising are
views of extraordinarily mundane regions -- as flat as the
Bonneville Salt Flats in Utah - that extend over vast northern
regions of the planet.
Mars Global Surveyor will complete the first phase of its
two-part aerobraking strategy at the end of March, at which
time the science instruments will be turned on again for most
of the next six months. Over this period, the spacecraft will
stay in an 11 1/2-hour orbit and collect an additional bounty
of data at a closest approach of about 106 miles (170
kilometers) above the surface, much closer than the spacecraft
will pass over the planet once it has reached its formal
mapping orbit in March 1999. This closer orbit will allow the
science teams to take more detailed measurements of the Martian
atmosphere and surface without magnetic interference from the
solar wind.
"When we decided to slow the pace of aerobraking to reduce
the force on the solar panel that was damaged after launch, we
knew we would get a bonus -- the ability to collect much more
science data closer to the planet than will be possible during
the prime mapping mission," said Glenn E. Cunningham, Mars
Global Surveyor project manager at NASA's Jet Propulsion
Laboratory, Pasadena, CA. "Additionally, the six-month period
between the end of March and early September will yield an
extraordinary opportunity as the lowest point of the orbit
migrates over the northern polar cap. All of this information
that is coming back now is really icing on the cake, a
spectacular precursor to the global mapping data expected to
start flowing next year."
Mars Global Surveyor is part of a sustained program of Mars
explorationknown as the Mars Surveyor Program. The mission is
managed by the Jet Propulsion Laboratory for NASA's Office of
Space Science, Washington, DC. JPL's industrial partner is
Lockheed Martin Astronautics, Denver, CO, which developed and
operates the spacecraft. JPL is a division of the California
Institute of Technology.
-end-
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=SANA=
Дата: 16 марта 1998 (1998-03-16)
От: Alexander Bondugin
Тема: Sky & Telscope News Bulletin - March 13, 1998
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SKY & TELESCOPE'S NEWS BULLETIN
MARCH 13, 1998
NEAR-EARTH ASTEROID CAUSES COMMOTION
Although currently no known asteroids are on a collision course with the
Earth, there are nevertheless more than 100 bodies worrisome enough for the
Minor Planet Center to catalog them as "potentially hazardous objects." The
purpose of this list is to identify asteroids and comets that astronomers
should routinely check to refine their orbits.
On March 11th, Brian Marsden of the Central Bureau for Astronomical
Telegrams announced a new contender. The asteroid, designated 1997 XF11,
was discovered by University of Arizona asteroid hunter James Scotti on
December 6, 1997, as part of the Spacewatch project. Using additional
observations made over the next three months, Marsden calculated a
preliminary orbit for the 1.4- to 2.7-km-wide rock that showed it would
pass only 40,000 kilometers above Earth's surface on October 26, 2028.
However, the margin of error was still relatively large -- the only near-
certainty was that 1997 XF11 would pass by us at a distance closer than the
Moon.
The circumstances of the flyby seemed to continually change during the
following day as other astronomers made their own analyses. Orbital
calculations by Donald Yeomans and Paul Chodas (Jet Propulsion Laboratory)
showed that closest approach would be some 80,000 km, with errors only half
as great. Furthermore, the "target plane" of the asteroid did not intersect
the Earth, and thus the probability of impact was zero. Eleanor Helin (JPL)
reports finding a prediscovery image of the object. Incorporating positions
from this 1990 observation moved the nominal flyby distance out to a
comforting 950,000 km. Additional observations over the next weeks and
years will continue to firm up these figures.
ANCIENT CRATER CHAIN ON EARTH
The Earth already has many visible scars of cosmic collisions. Now
researchers have linked five impact features and suggest that they all
formed at the same time as a shattered comet or asteroid struck the Earth
-- much as the pieces of Comet Shoemaker-Levy 9 hit Jupiter in 1994. In the
March 12th NATURE, David Rowley (University of Chicago), John Spray
(University of New Brunswick), and Simon Kelley (The Open University)
explain how after moving the drifting continents back to their arrangement
214 million years ago, impact scars in France, Canada, Ukraine, and
Minnesota lined up. The largest of the craters is 100 km across. These
impacts are a likely influence on the mass extinction of life at the end of
the Triassic period, where 80 percent of the species then living on the
Earth disappeared.
NEW FARTHEST OBJECT
While some astronomers were worrying about very nearby cosmic objects,
others announced the most distant. Observations Arjun Dey (Johns Hopkins
University) and his colleagues using the 10-meter Keck II telescope atop
Hawaii's Mauna Kea picked up the faint light from a galaxy called
0140+326RD1 (RD1 for short). With a redshift of 5.34 -- the first object to
break the 5.0 "barrier" -- this young galaxy is seen as it was when the
universe was only 6 percent of its present age (about 820 million years
after the Big Bang). This is nearly 90 million light-years farther than any
previously discovered object. Details of the study will appear in
Astrophysical Journal Letters.
PATHFINDER R.I.P.
NASA scientists made a final try to contact Mars Pathfinder on March 10th.
The last full transmission from the lander came in on September 27th, but
signals were regularly sent to the lander in the faint hope that contact
would be restored. Those transmissions ended Tuesday, marking the official
end of the mission.
THIS WEEK'S "SKY AT A GLANCE"
Some daily events in the changing sky, from the editors of SKY &
TELESCOPE.
MARCH 15 -- SUNDAY
* Spica is to the right of the bright waning gibbous Moon after they
rise in midevening.
MARCH 16 -- MONDAY
* Telescope users in the Far East with good sky conditions can look for
Mercury passing barely north of the 6th-magnitude star 60 Piscium around
13:00 Universal Time -- so closely as to just miss occulting it.
MARCH 17 -- TUESDAY
* Look southwest in the evening this week for Orion. As winter gives way
to spring Orion moves lower toward the west, and its three-star Belt,
diagonal for most of the winter, becomes nearly horizontal.
MARCH 18 -- WEDNESDAY
* The eclipsing variable star Algol is at minimum light, magnitude 3.4
instead of its usual 2.1, for a couple hours centered on 8:53 p.m. EST. It
takes several additional hours before and after to fade and rebrighten. For
a complete schedule of Algol's eclipses, see
http://www.skypub.com/whatsup/algol.html.
MARCH 19 -- THURSDAY
* Mercury is at its greatest elongation in the west at dusk (19 degrees
east of the Sun).
MARCH 20 -- FRIDAY
* The March equinox occurs at 2:55 p.m. Eastern Standard Time. This is
when the Sun crosses the equator moving north, marking the start of spring
in the Northern Hemisphere and autumn in the Southern Hemisphere.
MARCH 21 -- SATURDAY
* Last-quarter Moon (exact at 2:38 a.m. EST). For tips on viewing our
nearest celestial neighbor, see "Touring the Moon with Binoculars" at
http://www.skypub.com/whatsup/moontour.html
============================
THIS WEEK'S PLANET ROUNDUP
============================
MERCURY and SATURN are low in the west as twilight fades. Mercury is the
brighter of the two. Early in the week Mercury is to Saturn's lower right.
By Thursday or Friday it's more directly to Saturn's right (about 5 degrees
from it) and fading.
VENUS shines brightly in the southeast during dawn.
MARS, quite faint, is disappearing into the sunset below Mercury.
JUPITER is hidden in the glare of sunrise.
URANUS and NEPTUNE are emerging from the glow of sunrise. They're far in
the background of brilliant Venus.
PLUTO, magnitude 13.8, is near the Ophiuchus-Scorpius border, well up in
the southeast by about 2 a.m.
(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.)
Full details, sky maps, and news of other celestial events appear each
month in SKY & TELESCOPE magazine. Clear skies!
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
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