Дата: 01 декабря 1998 (1998-12-01)
От: Alexander Bondugin
Тема: Cassini Instrument Checkout - Day By Day [1/2]
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Cassini Instrument Checkout Day By Day
http://www.jpl.nasa.gov/cassini/msnstatus/ico_byday.html
What is Instrument Checkout?
Instrument Checkout (or ICO) is a fully integrated checkout of the
Cassini spacecraft's 12 science instruments. During the 25-day period of
ICO, all 12 instruments will be performing tests to verify that the
equipment is in good working order. In addition, tests will be conducted to
see if any instrument components can be "heard" by other instruments. In
order to maximize science data return, engineers need to understand if any
of the instruments' operating schemes causes noise in any of the other
instruments. Noise generated by one instrument and heard by another is
similar to hearing static on the car radio generated by the engine.
Instrument to instrument noise can cause degradation of the data.
Why is Instrument Checkout Scheduled When It Is?
On January 9, 1999, the spacecraft will be at "opposition" with
respect to Earth. Opposition describes the period when the angle between the
Earth and the Sun, as seen from the spacecraft, is close to zero degrees.
Viewers on Earth would see the Sun and spacecraft in diametrically opposite
parts of the sky. Because this angle is so small, the high gain antenna can
be moved to point at Earth and still provide a large degree of shading for
the onboard instrumentation.
The spacecraft is designed for operation at Saturn, which is 9 times
further away from the Sun than Earth. As a result, while Cassini is
travelling in the inner Solar System, the delicate electronics and
instrumentation need to be kept cool. The spacecraft's high gain antenna is
being used as an umbrella to shade these delicate electronics during this
part of Cassini's journey to Saturn. This is accomplished by pointing the
high gain antenna toward the Sun. Communications between Cassini and Earth
is done through the spacecraft's low gain antennae when the high gain
antenna is being used as a sun shade.
The low gain antennas onboard the spacecraft can communicate with
Earth, providing low rate data (no greater than 948 bits per second) to
engineers on the ground. These low data rates can be used to communicate
spacecraft commands, spacecraft and instrument health, and navigation and
tracking data. However, the science instruments need to have higher data
rates in order to send the multitude of science information to Earth. This
means that in order to collect the data from the science instruments and
send it to the ground, instrument checkout needs to be performed on the
spacecraft's high gain antenna.
Engineers who specialize in studying the different thermal (heating)
environments for Cassini spent a great deal of time analyzing the Sun
exposure that the spacecraft would receive during this period of time. After
careful analysis, it was decided that a period of 25 days, centered around
spacecraft opposition, would be the maximum allowable time that the high
gain antenna could point at the Earth and still keep the instrumentation
cool.
Therefore, since opposition is occurring on 9 January 1999, instrument
checkout extends from 28 December 1998 through 21 January 1999. During this
time period, the spacecraft is 0.5 astronomical units (half the distance
from the Sun to the Earth). This means that the time it takes for a command
to travel from Earth to Cassini is 5 minutes. In comparison, the current
time it takes for a command from the ground to reach the Voyager (currently
at approximately 70 astronomical units from the Sun) spacecraft is 18 hours!
Day 1 - 28 December 1998
This is the first day of ICO. This day is devoted to turning the
spacecraft such that the high gain antenna points at Earth, verifying that
the high data rates are working correctly, and that communication with the
spacecraft is stable. Once the Flight Systems engineers check out the high
gain antenna's data links, ICO is ready to go.
The main objective of day 1 will be to play back data stored on the
spacecraft's solid state recorder. These data consist of engineering and
health data on the Huygens probe. The Huygens probe will be performing its
bi-annual "probe checkout" on 22 December 1998. Data from this probe
checkout will be stored on the tape recorder and played back when the link
has been established with the high gain antenna. This greatly reduces the
amount of time necessary to play back these data. Using the low gain
antenna, play-back of probe checkout data would take several hours. However,
with the high gain antenna, this play-back will take only 1 to 2 hours.
Day 2 - 29 December 1998
Today will be the first checkout test for the Radio Science
instrument. Radio science combines the use of onboard instrumentation with
the Deep Space Network to study atmospheres and ionospheres of Saturn and
Titan, rings, gravity fields of Saturn and its satellites, and low frequency
gravitational waves in the Solar System. The Cassini spacecraft can
communicate at 3 different wavelengths: X-band (frequency 8.4 GHz), S-band,
and Ka-band.
Radio Science will perform a 3 hour test of the >Ultra-Stable
Oscillator which tests the downlink of Ka-band, S-band, and X-band signals.
This will be followed by a 2-hour test which tests the downlink of both the
X-band and S-band wavelengths. Both of these tests will be performed in
real-time. This means that the Deep Space Network will be communicating with
the spacecraft while the tests are being performed and the data from these
tests will be sent to the ground in real-time.
Day 3 - 30 December 1998
The first onboard activity today will be the primary checkout for the
Radio and Plasma Wave Science (RPWS) instrument. At Saturn RPWS will study
plasma waves, radio emissions, and dust in the Saturn system. The RPWS
checkout is scheduled to take 7 hours and will involve collecting data at
different onboard telemetry rates and sending that data to the ground in
real-time.
At the conclusion of the 7-hour RPWS checkout, the Magnetometer (MAG)
instrument will perform a 24-hour checkout. MAG studies planetary magnetic
fields and their interactions with the solar wind. The first 2 hours of the
MAG checkout will be performed over a Deep Space Network pass. The final 8
hours of the 24-hour MAG checkout will also be performed over a Deep Space
Network pass. During the time between the 2 DSN passes, the MAG checkout
will continue. Data will be stored on the spacecraft's solid state recorder
for play-back during the next DSN pass. During the 24-hour MAG checkout, the
instrument will collect data in all of its various science data modes. This
will provide scientists on the ground the ability to verify that all of the
data modes are functioning correctly for the instrument.
Day 4 - 31 December 1998
Today MAG completes its 24-hour active checkout. MAG will remain
turned on following this checkout in order to "watch" other instruments'
activities. MAG is particularly sensitive to interference from other onboard
electronics. Therefore, scientists want to determine if any interference for
MAG is caused by other instruments so that plans can be made during the
Saturn Tour, and earlier, to minimize the effects of this interference on
MAG science data.
After MAG completes its 24-hour active checkout, the Cosmic Dust
Analyzer (CDA) will be turned on. CDA collects ice, dust, and other small
particles as the spacecraft travels through the Solar System. The
concentration and size distribution of these particles allows scientists to
determine the density and composition of particles in the solar system and
Saturn system. After completing its 3-hour checkout, CDA will remain on
through the remainder of ICO.
Day 5 - 1 January 1999
Happy New Year! While the Tournament of Roses Parade and Rose Bowl
game go on in Pasadena, engineers at JPL will continue to monitor the
Cassini spacecraft. While no active checkouts are scheduled for today, RPWS,
MAG, and CDA will continue collecting data in their monitoring modes.
Day 6 - 2 January 1999
Today's first job is to playback the data that were collected
yesterday. After all of these monitoring data are safely on the ground,
Radio Science will conduct another test. This time, the instrument and Deep
Space Network will link up for 4 hours to perform a test of X-band and
S-band downlink with X-band uplink.
Day 7 - 3 January 1999
Today the Magnetospheric Imaging Instrument (MIMI) will begin a 3-day
intensive checkout. MIMI's objective is global magnetospheric imaging as
well as measurements of Saturn's magnetosphere and solar wind interactions.
The first 8 hours of MIMI's checkout today will be performed over a Deep
Space Network pass. This allows scientists to interact with the instrument.
Based on data scientists will receive, they will send commands back to the
instrument.
Hа сегодня все, пока!
=SANA=
Дата: 01 декабря 1998 (1998-12-01)
От: Alexander Bondugin
Тема: Cassini Instrument Checkout - Day By Day [2/2]
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Day 8 - 4 January 1999
Today is the second day of MIMI's active checkout. Over an 8-hour Deep
Space Maneuver pass today, voltage levels will be gradually stepped up on
the instrument. Scientists on the ground will closely monitor these voltage
step ups and, if the instrument voltage gets too high, scientists will issue
a real-time command to stop the voltage from further increasing. This will
minimize any possible damage to the instrument while giving scientists an
opportunity to interact with the instrument in real-time.
In addition, today the Cassini Plasma Spectrometer (CAPS) will begin a
3 day active checkout that is very similar to MIMI's checkout. Voltages will
be gradually increased in the instrument while scientists on the ground
monitor CAPS in real-time. Upon arrival at Saturn, CAPS will study plasmas
within and near Saturn's magnetosphere.
Finally today, the Ion and Neutral Mass Spectrometer (INMS) will be
powered on. INMS will be studying compositions of neutral and charged
particles within Saturn's magnetosphere. While INMS's cover will remain on
until Saturn Orbit Insertion, scientists will be checking that the
instrument is healthy and collecting data at the proper intervals.
Day 9 - 5 January 1999
Today is devoted to the continuing CAPS and MIMI checkouts. Today is
the final day of MIMI's active checkout and the second of three days for
CAPS. Upon completion of MIMI's active checkout, the MIMI instrument will be
switched into a monitoring mode and will be collecting data as other
instruments perform their checkout activities.
The decontamination heaters for the Visible and Infrared Mapping
Spectrometer (VIMS) will also be powered off today in preparation for VIMS
activities. These heaters stay powered on throughout flight to keep the
delicate surfaces of the VIMS optical surface free of exhaust condensation.
The last activity for today will be the INMS checkout activities. INMS
will perform a 3-hour checkout of its different equipment modules.
Day 10 - 6 January 1999
Today CAPS will complete its 3-day active checkout and be switched
into a monitoring mode.
Day 11 - 7 January 1999
First up today is Radio Science which commences with a 3 hour
Ultra-Stable Oscillator test that is identical to the test performed on Day
2 (29 December 1998). After this test, radio science continues with a 4-hour
test of X-band and Ka-band downlink combined with X-band uplink.
Following Radio Science, the Ultraviolet Imaging Spectrograph (UVIS)
will perform a 1-hour checkout to verify that the instrument is functioning
correctly. UVIS will be producing spatial ultraviolet maps, mapping the ring
radial structure, and determining the hydrogen/deuterium ratios at Saturn.
Deuterium is a heavy form of hydrogen. The ratio of hydrogen to deuterium is
a sensitive indicator of conditions during the formation of the universe
during the Big Bang.
Day 12 - 8 January 1999
Today is an exciting day for Cassini scientists and engineers. The
spacecraft will perform a maneuver that will align the CAPS instrument such
that it can measure the solar wind. Then the spacecraft will be maneuvered
again to allow one of the MIMI sensors to collect data. The functionality of
this sensor can only be verified if the spacecraft is rolled and data are
collected during this roll. After all the maneuvers are complete, the
spacecraft will be sent back to its normal "attitude" for ICO with the high
gain antenna pointed at Earth. The combination of these rolls will take a
few hours to complete. Since the high gain antenna will be pointed away from
Earth during this time, the data collected will be stored on the solid state
recorder. These data will be played back when the high gain antenna is
pointed back at the Earth at the conclusion of this activity.
Once the spacecraft is back to its normal attitude, the Composite
Infrared Spectrometer (CIRS) will be turned on and a 3-hour checkout of the
instrument will take place. At Saturn, CIRS will be performing spectral
mapping to study temperature and composition of surfaces, atmospheres, and
rings.
After CIRS has completed its checkout, the decontamination heaters on
the Imaging Science Subsystem (ISS) will be turned off and the instrument
will be turned on. ISS, the cameras onboard Cassini, will be performing
multi-spectral imaging of Saturn, Titan, rings, and Saturn's small
satellites.
Finally, there will be an interference test between RPWS and CAPS
today.
Day 13 - 9 January 1999
Today ISS will be performing its checkout. This will take 3 hours to
complete. Following the ISS checkout, VIMS will be powered on and the
instrument's functional checkout will be performed. The combination of VIMS
activities will take 6 hours today. At the conclusion of today's activities,
all of Cassini's instruments with the exception of RADAR, Radio Science, and
the Probe, will be on.
Day 14 - 10 January 1999
Today is devoted to performing an instrument to instrument
interference test. Each instrument will take turns cycling through filters,
shutters, and electronics while the other instruments listen for possible
interference. This test involves all instruments except RADAR and the Probe
and will be performed 3 times. The first 2 times, all instruments will
participate with the exception of Radio Science. It is done twice so that 2
different data collection modes can be used. This maximizes the ability of
each instrument to study the other instruments' effects on them. The third
time through the test, Radio Science will be turned on and CIRS, ISS, UVIS,
and VIMS will not participate.
These tests will take over 6 hours to complete. When finished, CAPS,
MIMI, CDA, MAG, and RPWS will remain in their monitoring modes. The other
instruments will be placed in a quiet state.
Day 15 - 11 January 1999
Today Radio Science will be testing their Ka-band uplink and downlink.
This test is scheduled to take 2 hours. Due to hardware limitations at the
Deep Space Network, this 2-hour test will be performed using a Deep Space
Network antenna that is reserved for research and development. Cassini is
using this antenna because it is one of the few antennas that has Ka-band
uplink and downlink capability.
Day 16 - 12 January 1999
Today Radio Science is up again. First will be another 3-hour test of
the Ultra-Stable Oscillator. Following that test, a 2-hour test of X-band,
S-band, and Ka-band downlink will be performed.
Following the Radio Science test, there is a 2 hour opportunity for
CIRS to repeat any or all of their active checkout activities. If their
primary activities on day 12 (8 January, 1999) went smoothly, this 2 1/2
hour window will not be used. At the conclusion of this window, the CIRS
instrument will be turned off and its participation in Instrument Checkout
will be complete.
Day 17 - 13 January 1999
Today is reserved for repeating activities for which adequate results
were not obtained. This opportunity is also in the schedule to allow for a
test to be repeated in the event that communication with the spacecraft was
lost during a checkout activity. Occasionally a tracking pass is lost due to
bad weather conditions or mechanical or electronic problems. Deep Space
Network passes may also be lost by Cassini in the event of another
spacecraft's emergency. In such a situation, Cassini could lose a pass in
support of the other spacecraft's recovery efforts.
There is a 1-hour opportunity for UVIS followed by a 2 hour
opportunity for INMS to repeat a failed or compromised activity.
Day 18 - 14 January 1999
Today is the first of two days reserved for CAPS and MIMI to repeat
portions of their active 3-day checkouts.
Day 19 - 15 January 1999
Today is the second of two days reserved for CAPS and MIMI to repeat
portions of their active 3-day checkouts. At the conclusion of this 2-day
period, both MIMI and CAPS will be powered off.
Day 20 - 16 January 1999
Today there will be another spacecraft maneuver. This time, the
spacecraft will be moved so that the star Alpha Virginis (Spica) is in the
field of view for ISS, UVIS, and VIMS. These 3 instruments will capture
images of Spica and the data will be played back. Spica is a prominent,
bluish star easily seen in the southeastern sky during the evening in
springtime.
Day 21 - 17 January 1999
The Spica imaging will conclude early today. At the conclusion of
these activities, ISS and VIMS will be turned off and their decontamination
heaters will be turned on. UVIS will also be powered off.
Day 22 - 18 January 1999
Today, Radio Science will perform its last test of the Ultra-Stable
Oscillator. Following Radio Science, the RADAR instrument will be powered
on. RADAR will perform an 8-hour checkout designed to simulate RADAR
operations at Titan. INMS, which is particularly sensitive to RADAR's
electronics, will be listening for interference during this test. At the
conclusion of the RADAR checkout, both RADAR and INMS will be powered off.
RADAR will be mapping the cloud-shrouded surface of Titan upon arrival at
Saturn.
Day 23 - 19 January 1999
RPWS and MAG will also be powered off after the RADAR checkout is
complete.
Day 24 - 20 January 1999
Today Radio Science has a 4-hour period when any Radio Science test
can be repeated except for the Ka-band uplink and downlink test. Following
this period, there is a 4 hour opportunity with the special Deep Space
Network antenna to repeat the Ka-band uplink and downlink test.
Day 25 - 21 January 1999
Today is the final day of instrument checkout. RADAR has an 8 hour
opportunity to repeat portions of their checkout activity if their checkout
on day 23 (19 January 1999) failed. At the conclusion of the RADAR checkout,
RADAR and CDA will be powered off. At this time, all 12 instruments will be
off.
The final activity in instrument checkout is to re-point the high gain
antenna at the Sun and re-establish the telemetry link through the low gain
antenna.
Hа сегодня все, пока!
=SANA=
Дата: 01 декабря 1998 (1998-12-01)
От: Alexander Bondugin
Тема: Sky & Telescope News Bulletin - November 27, 1998
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SKY & TELESCOPE'S NEWS BULLETIN
NOVEMBER 27, 1998
ANOTHER STEP FORWARD FOR SUBARU
Japan's Subaru Telescope took another step toward first light earlier this
month
when its 8.3-meter-diameter primary mirror was successfully aluminized. The
giant optic arrived at the summit of Mauna Kea, Hawaii, on November 5th. It was
immediately transferred to a giant vacuum chamber, where an ultrathin film of
highly reflective aluminum was deposited on its concave surface. On November
8th
telescope director Norio Kaifu proudly declared the operation a success. Plans
call for the newly finished mirror to be installed in its cell, and the cell in
turn to be installed into the telescope structure, in early to mid-December.
First light is expected by the end of January.
ION ENGINE: FULL AHEAD
While it got off to a slow start, NASA's Deep Space 1 is finally on its way at
full speed. DS 1 -- launched on October 24th -- is the first spacecraft to use
a
beam of electrically accelerated xenon ions as its main propulsion system. The
craft is expected to use this "ion drive" to modify its orbit around the Sun
for
a flyby of the high-inclination Mars-crossing minor planet 1992 KD next July.
However, during its first trial on November 10th, the drive switched itself off
after only 4=AB minutes. Engineers suspect that the shutdown occurred because
of a
contaminant between two high-voltage elements that has since vaporized. The
engine was restarted on November 24th at 5:53 p.m. Eastern Standard Time and
ran
smoothly throughout the night. Today flight controllers commanded the engine to
increase thrust. The engine will be left running over the U.S. Thanksgiving
holiday weekend.
EXTRASOLAR PLANET IN BINARY SYSTEM
Swiss astronomers at the European Southern Observatory (ESO) announced today
their discovery of an extrasolar planet orbiting a binary star. The new 1.2-
meter Leonard Euler Telescope -- built expressly for finding planets around
other stars -- found the signature of a substellar companion around Gliese 86
(HD 13445), located 35 light-years away in Eridanus. The star, a 6th-magnitude
dwarf with a mass of about 0.8 Sun, is itself a long-period binary. Astronomers
used the telescope to record the changing radial velocity of the primary star
and deduced a 15.83-day period. Their data corresponds to a planet with a mass
of at least 5 Jupiters in a circular orbit 16.5 million kilometers in radius.
The Euler Telescope will be used to search for planets around 1,000 nearby
stars.
DEEP IN THE HEART OF TUCANA
Astronomers at the Space Telescope Science Institute unveiled today the results
of their second marathon observing session -- the Hubble Deep Field South. The
first Hubble Deep Field was a 10-day-long composite exposure in 1995 of a
nearly
blank piece of sky in Ursa Major. Taken with the Hubble Space Telescope's Wide
Field and Planetary Camera 2 (WFPC2), it uncovered more than 3,000 objects,
some
as faint as 30th magnitude. In October 1998 Hubble used three instruments in
tandem to stare at the southern circumpolar constellation Tucana. WFPC2 viewed
the sky in several visible and near-ultraviolet bands and captured hundreds of
faint galaxies. The Space Telescope Imaging Spectrograph (STIS) was trained on
a
17th-magnitude quasar. And the Near-Infrared Camera and Multi-Object
Spectrometer (NICMOS) looked at three small patches of sky nearby. The result
of
this 10-day composite is an equally galaxy-packed view, which astronomers will
now pick apart and study in detail.
COMET C/1998 U5 (LINEAR)
Comet LINEAR continues to put on a surprisingly good show. Discovered in late
October by MIT's Lincoln Laboratory Near Earth Asteroid Research (LINEAR) Team
and later identified as a comet by team member Frank Shelly, it was not
expected
to brighten beyond magnitude 10.5. But the comet underwent an outburst in the
second week of November that brought this fast-moving object within the range
of
small telescopes and binoculars. Recent estimates put it at roughly 9th
magnitude. Here are positions for the coming week at 0:00 Universal Time in
2000.0 coordinates:
Date R.A. Dec.
Nov 28 22h 22.0m +42d 02'
Nov 30 22h 08.0m +38d 43'
Dec 02 21h 57.3m +35d 49'
Dec 04 21h 48.8m +33d 18'
THIS WEEK'S "SKY AT A GLANCE"
Some daily events in the changing sky, from the editors of SKY & TELESCOPE.
NOV. 29 -- SUNDAY
* Some doorstep astronomy: The brightest star in the northeast these evenings
is Capella. Far to its right, and perhaps a bit higher, are the Pleiades. Down
below the Pleiades is orange Aldebaran.
* Saturn shines to the Moon's left early this evening. It's to the Moon's
upper left later in the night.
NOV. 30 -- MONDAY
* Look for Saturn to the Moon's upper right in early evening, and directly to
its right later at night.
* Seen in a medium-sized telescope, Jupiter's Great Red Spot should cross the
planet's central meridian (the imaginary line down the center of Jupiter's disk
from pole to pole) around 8:00 p.m. Eastern Standard Time. Lately the spot has
been very pale tan with a darker reddish mark in its south side. For a list of
all predicted Red Spot transit times, see
http://www.skypub.com/sights/moonplanets/redspot.html.
DEC. 1 -- TUESDAY
* Comet Giacobini-Zinner is still in good view in Capricornus just after dark
this week. It is a dim fuzzball glowing at about 9th magnitude (in reach of
most
amateur telescopes) with hints of a tail. See the finder chart in the November
Sky & Telescope, page 107, or at
http://www.skypub.com/sights/comets/Giacobini/gz_1998.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 10:06
p.m. EST. Algol takes several additional hours to fade and brighten. For a list
of all its predicted minima see
http://www.skypub.com/sights/variables/algol.html.
DEC. 2 -- WEDNESDAY
* The Moon occults Aldebaran before sunup Thursday morning as seen from the
northwestern U.S.
* Jupiter's Red Spot should transit around 9:39 p.m. EST.
DEC. 3 -- THURSDAY
* Full Moon (exact at 10:19 a.m. EST).
DEC. 4 -- FRIDAY
* Earliest nightfall of the year (as seen from latitude 40 degrees north).
* Jupiter's Red Spot should transit around 11:18 p.m. EST.
* Algol should be at minimum light for a couple of hours around 6:55 p.m.
EST.
DEC. 5 -- SATURDAY
* Jupiter's Red Spot should transit around 7:09 p.m. EST.
THIS WEEK'S PLANET ROUNDUP
MERCURY and VENUS are hidden in the glare of the Sun.
MARS, magnitude +1.4, shines high in the southeast before and during dawn.
Spica
is the star well to its lower left. Brighter Arcturus shines farther to Mars's
left.
JUPITER, magnitude -2.5, is the big, brilliant "star" high in the south during
the evening. You can't miss it! Jupiter moves to the southwest in late evening
and sets around midnight.
SATURN, magnitude +0.1, is the yellowish "star" far to Jupiter's left just
after
dark, and to Jupiter's upper left later in the evening. The two planets appear
39 degrees apart (about 4 fist-widths at arm's length), on opposite ends of
Pisces.
URANUS and NEPTUNE are getting low in the southwest just after dark. See the
finder chart in the September Sky & Telescope, page 110, or at
http://www.skypub.com/sights/moonplanets/urnepplu.html.
PLUTO is hidden behind the glare of the Sun.
(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
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(contact permissions@skypub.com or phone 617-864-7360). For updates of
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Hа сегодня все, пока!
=SANA=
Дата: 01 декабря 1998 (1998-12-01)
От: Alexander Bondugin
Тема: First Images and Spectra from ISAAC on VLT UT1 (Forwarded)
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ESO Education and Public Relations Dept.
Text with all links is available on the ESO Website at URL:
http://www.eso.org/outreach/press-rel/pr-1998/pr-19-98.html
ESO Press Release 19/98
For immediate release: 26 November 1998
First Images and Spectra from ISAAC on UT1
New VLT Instrument Delivers Spectacular Infrared Views of the Southern Sky
The VLT Infrared Spectrometer And Array Camera (ISAAC) [1] was installed at
the first 8.2-m VLT Unit Telescope (UT1) on November 14, 1998, cf. ESO PR
Photos 42a-h/98. ISAAC is the second major VLT instrument to be installed at
the VLT and the first to be fully designed and developed at ESO within its
Instrumentation Division.
Following evacuation of its large vacuum vessel, cooling to cryogenic
temperature and alignment with the telescope according to the planned
schedule, it successfully achieved technical first light during the night
between November 16 and 17, 1998.
ESO PR Photo 46a/98
PR Photo 46a/98 shows ISAAC as it is now mounted at the UT1 Nasmyth B
adaptor-rotator (right; blue colour). The co-rotator system (left) through
which the various cables are fed to the instrument, is also well visible.
(Photo obtained on November 16, 1998).
The first focus tests on stars yielded images of excellent sharpness, around
0.45 arcsec full-width-half-maximum (FWHM). During the following nights,
even better images, as small as 0.25 arcsec in relatively short exposures,
were obtained, testifying to the quality of the site as well as the optical
quality of both the telescope and instrument. Observations were executed
using the new VLT Control and Data Flow Systems which are driven by
Observation Blocks that define all details of the required astronomical
exposures.
In addition to direct images in various infrared colours (selected with
different optical filters), spectroscopic observations were also made during
the first few nights of operation.
This Press Release is accompanied by several images and spectra which
illustrate some of the exceptional new astronomical capabilities offered by
this instrument.
Star-Forming Region RCW38 in the Milky Way
ESO PR Photo 46b/98
PR Photo 46b/98 displays a spectacular three-colour composite image of
RCW38, obtained through three near-infrared filters. This is a region in
the Milky Way at a distance of about 5,000 light years, where stars which
have recently formed in clouds of gas and dust are still heavily obscured
and cannot be observed in the visible part of the spectrum. Contrarily, as
this image shows, they are very well seen at infrared wavelengths where
the obscuration is substantially lower. The diffuse radiation is a mixture
of starlight scattered by the dust and gas in the area, and atomic and
molecular hydrogen line emission.
Technical Information: The photo is a combination of three exposures
through Z (centred at 0.90 micron), H (1.65 micron) and Ks filters
(2.16 micron) and with exposure times of 160, 320 and 210 seconds,
respectively, The field measures 2.5 x 2.5 arcmin with North at the top
and East to the left. The seeing was 0.4 arcsec.
Distant Radio Galaxy MRC0316-257
ESO PR Photo 46c/98
PR Photo 46c/98 is a Ks (2.16 micron) image, centred on the distant radio
galaxy MRC0316-257 (redshift z = 3.14). It was obtained primarily to
locate other distant galaxies for future spectroscopic observations with
ISAAC.
Technical Information: This image was obtained by combining 45 1-min
exposures, taken with the telescope randomly offset by small amounts in
between ("jittering") to allow subtraction of the bright sky emission at
this wavelength. The seeing was 0.5 arcsec and the limiting magnitude is
around Ks = 22. The field measures 2.5 x 2.5 arcmin with N at the top and
E to the left.
Galaxy Cluster CL2244-02 with Gravitational Arcs
ESO PR Photo 46d/98
PR Photo 46d/98 is a colour composite image of the galaxy cluster
CL2244-02 (redshift z = 0.3), combining a 20 min jittered ISAAC Ks
(2.16 micron) exposure with 15 min V (green-yellow) and R (red) exposures,
obtained with the VLT Test Camera at the UT1 Nasmyth focus. In addition to
the prominent blue arc, produced by gravitational lensing of a galaxy at
redshift z = 2.24, there are also notable, very red arcs, both closer to
the centre and further out. They were only detected in the infrared image
and are probably due to lensing of a much more distant galaxy.
Technical Information:The field size is about 1.5 x 1.5 arcmin with N at
the top left and E at the lower left corner. The seeing was between 0.46
and 0.65 arcsec in the different images.
Center of Merging Galaxy System ESO202-G23
ESO PR Photo 46e/98
PR Photo 46e/98 is a colour composite image of the merging galaxy system
ESO202-G23 made by combining an ISAAC H (1.65 micron) exposure with
(blue) and R (red) exposures made with the VLT Test Camera at Nasmyth
focus. At least one of the two nuclei is obviously an Active Galaxy Nucleus
(AGN) whose partially collimated ultraviolet radiation is exciting the
surrounding gas to the North. Also visible is a blue star-forming complex
to the South of the centre and a complicated pattern of gas emission due
to the combination of arms resulting from the merger, as well as heavy
dust extinction. Of additional interest is the arc of very red objects in
the lower part of the image which are more distant galaxies.
Technical Information:Exposure times in the H, B and R filters were 1200,
1800 and 900 seconds, respectively. The field measures about 1.5 x 1.5
arcmin, with N at the top left and East at the lower left corner. The
seeing was about 0.4 arcsec.
Lensed Quasar MG0414+0534
ESO PR Photo 46f/98
PR Photo 46f/98 is an infrared colour composite of the quadruply lensed
quasar system MG0414+0534 made by combining 20 min ISAAC J (1.25
micron) and Ks (2.16 micron) exposures. This complex of images is only
about 2 arcsec across. At the centre is the red galaxy at redshift z = 0.96
which is responsible for the four (of which two are not completely
resolved) gravitationally lensed images of a z = 2.64 quasar plus a faint
arc.
Technical Information: N is at the top and E to the left. The seeing was
0.4 arcsec.
Herbig-Haro Object HH212
ESO PR Photo 46g/98
PR Photo 46g/98 shows a long-slit (2 arcmin) spectrum in the 2 - 2.5 micron
spectral region of the Herbig Haro object HH212. The spectral resolution
is about 500. It is believed that a protostar -- that is invisible even at
infrared wavelengths -- is responsible for the two pulsed jets seen in this
spectral image. They are remarkable because of the high degree of symmetry
of the 'blobs' which have been ejected in opposite directions (up and down
in this image). Each of the individual 'images' shows the jets in a
different spectral line emitted by molecular hydrogen that has been shock
excited by the impact of the ejected gas.
Starforming Galaxy at Redshift 0.62
ESO PR Photo 46h/98
PR Photo 46h/98 is an infrared spectrum showing the Hydrogen-alpha
(0.6563 micron) emission line (indicated with an arrow), shifted to 1.06
micron in a star-forming galaxy at redshift z = 0.62, discovered in the
CFRS survey. The total integration time with ISAAC was only 1 hour.
Note:
[1] ISAAC is a cryogenic infrared imager and spectrometer (spectral region
0.9 - 5 micron) installed at the Nasmyth B focus of UT1. It has two arms, one
for the Short Wavelength (SW) spectral domain (0.9 - 2.5 micron), and one for
the Long Wavelength (LW) spectral domain (2.5 - 5 micron), both equipped with
state-of-the-art detectors. ISAAC has a variety of imaging and spectroscopy
modes in both of the arms. It is controlled via a panoply of software
templates for defining and executing sequences of operations for
Acquisition, Observation and Calibration. As any other VLT instrument,
ISAAC can be used in Service or Visitor Mode.
ESO Press Photos may be reproduced, if credit is given to the European
Southern Observatory.
Andrew Yee
ayee@nova.astro.utoronto.ca
Hа сегодня все, пока!
=SANA=
Дата: 01 декабря 1998 (1998-12-01)
От: Alexander Bondugin
Тема: First Results from the VLT UT1 Science Verification Programme [1/2]
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ESO Education and Public Relations Dept.
Text with all links is available on the ESO Website at URL:
http://www.eso.org/outreach/press-rel/pr-1998/pr-20-98.html
ESO Press Release 20/98
For immediate release: 26 November 1998
First Results from the UT1 Science Verification Programme
Performance verification is a step which has regularly been employed in
space missions to assess and qualify the scientific capabilities of an
instrument. Within this framework, it was the goal of the Science
Verification program to submit the VLT Unit Telescope No. 1 (UT1) to the
scrutiny that can only be achieved in an actual attempt to produce
scientifically valuable results. To this end, an attractive and diversified
set of observations were planned in advance to be executed at the VLT.
These Science Verification observations at VLT UT1 took place as planned in
the period from August 17 to September 1, 1998, cf. the September issue of
the ESO Messenger (No. 93, p. 1) and ESO PR 12/98 for all details. Although
the meteorological conditions on Paranal were definitely below average, the
telescope worked with spectacular efficiency and performance throughout the
entire period, and very valuable data were gathered.
After completion of all observations, the Science Verification Team started
to prepare all of the datasets for the public release that took place on
October 2, 1998. The data related to the Hubble Deep Field South (now
extensively observed by the Hubble Space Telescope) were made public
world-wide, while the release of other data was restricted to ESO member
states. With this public release ESO intended to achieve two specific goals:
offer to the scientific community an early opportunity to work on valuable
VLT data, and in the meantime submit the VLT to the widest possible
scrutiny.
With the public release, many scientists started to analyse scientifically
the VLT data, and the following few examples of research programmes are
meant to give a sample of the work that has been carried out on the Science
Verification data during the past two months. They represent typical
investigations that will be carried out in the future with the VLT. Many of
these will be directed towards the distant universe, in order to gather
insight on the formation and evolution of galaxies, galaxy clusters, and
large scale structure. Others will concentrate on more nearby objects,
including stars and nebulae in the Milky Way galaxy, and some will attempt
to study our own solar system.
The following six research programmes were presented at the Press Conference
that took place at the ESO Headquarters in Garching (Germany) today.
Deep Galaxy Counts and Photometric Redshifts in the HDF-S NIC3 Field
The goal of this programme was to verify the capability of the VLT by
obtaining the deepest possible ground-based images and using multicolour
information to derive the redshifts (and hence the distances) of the
faintest galaxies. The space distribution, luminosity and colour of these
extreme objects may provide crucial information on the initial phases of
the evolution of the universe. The method is known as photometric redshift
determination.
The VLT Test Camera was used to collect CCD images for a total of 16.6 hours
in five spectral filters (U, B, V, R and I) in the so-called HDF-S NIC3
field. This is a small area (about 1 arcmin square) of the southern sky
where very deep observations in the infrared bands J, H and K (1.1, 1.6 and
2.2 micron, respectively) have been obtained by the Hubble Space Telescope
(HST).
The observations were combined and analyzed by a team of astronomers at ESO
and the Observatory of Rome (Italy). Galaxies were detected in the field
down to magnitude approx. 27-28. In most colours, the planned limiting values
of the fluxes were successfully reached.
ESO PR Photo 48a/98
PR Photo 48a/98 shows some examples of photometric redshift determination
for faint galaxies in the HDF-S NIC3 field. The filled points are the
fluxes measured in the five colors observed with the VLT Test Camera (U,
B, V, R and I) and in the infrared H spectral band with the NICMOS
instrument on the Hubble Space Telescope. The curves constitute the best
fit to the points obtained from a library of more than 400,000 synthetic
spectra of galaxies at various redshifts (Fontana et al., in preparation).
For most of these very faint sources, it is not possible to collect enough
photons to measure the recession velocity (the redshift) by spectroscopy,
even with an 8-m telescope. The redshifts and the main galaxy properties are
then determined by comparing the colour observations with synthetic spectra
(see PR Photo 48a/98). This has been done for more than one hundred galaxies
in the field brighter than magnitude 26.5. Around 20 are found to be at
redshifts larger than 2. The brighter ones are excellent candidates for
future detailed studies with the UT1 instruments FORS1 and ISAAC.
The scientists involved in this study are: Sandro D'Odorico, Richard Hook,
Alvio Renzini, Piero Rosati, Rodolfo Viezzer (ESO) and Adriano Fontana,
Emanuele Giallongo, Francesco Poli (Rome Observatory, Italy).
A Gravitational Einstein Ring
Because the gravitational pull of matter bends the path of light rays,
astronomical objects -- stars, galaxies and galaxy clusters -- can act like
lenses, which magnify and severely distort the images of galaxies behind
them, producing weird pictures as in a hall of mirrors.
In the most extreme case, where the foreground lensing galaxy and the
background galaxy are perfectly lined up, the image of the background galaxy
is stretched into a ring. Such an image is known as an Einstein ring,
because the correct formula for the bending of light was first described by
the famous phycisist Albert Einstein.
ESO PR Photo 48b/98 ESO PR Photo 48c/98
PR Photo 48b/98 (left) shows a new, true colour image of an Einstein ring
(upper centre of photo), first discovered at ESO in 1995. The ring, which
is the stretched image of a galaxy far out in the Universe, stands out
clearly in green, and the red galaxy inside the ring is the lens. The
discovery image was very faint, but this new picture, taken with the VLT
during the Science Verification Programme allows a much clearer view of
the ring because of the great light-gathering capacity of the telescope
and, not least, because of the superb image quality. In Photo 48c/98
(right), four images illustrate the deduced model of the lensing effect.
In the upper left, the observed ring has been enlarged and the image of
the lensing galaxy removed by image processing. Below it is a model of the
gravitational field (potential) around this galaxy along with the "true"
image of the background galaxy shown. At the lower right is the resulting
gravitationally magnified and distorted image of the background galaxy,
which to the upper right has been de-sharpened to the same image quality
as the observed image. The similarity between the two is most convincing.
The picture shows a new, true colour image of an Einstein ring, first
discovered at ESO in 1995. The ring, which is the stretched image of a
galaxy far out in the Universe, stands out clearly in green, and the red
galaxy inside the ring is the lens. The discovery image was very faint, but
this new picture, taken with the VLT during the Science Verification
Programme allows a much clearer view of the ring because of the great
light-gathering capacity the telescope and, not least, because of the superb
image quality.
Gravitational lensing provides a very useful tool with which to study the
Universe. As "weighing scales", it provides a measure of the mass within the
lensing body, and as a "magnifying glass", it allows us to see details in
objects which would otherwise be beyond the reach of current telescopes.
This new detailed picture has allowed a much more accurate measurement of
the mass of the lensing galaxy, revealing the presence of vast quantities of
"unseen" matter, five times more than if just the light from the galaxy is
taken into account. This additional material represents some of the
Universe's dark matter. The gravitational lens action is also magnifying the
background object by a factor of ten, providing an unparalleled view of this
very distant galaxy which is in a stage of active star-formation.
The scientists involved in this study are: Palle Mxller (ESO), Stephen J.
Warren (Blackett Laboratory, Imperial College, UK), Paul C. Hewett
(Institute of Astronomy, Cambridge, UK) and Geraint F. Lewis (Dept. of
Physics and Astronomy, University of Victoria, Canada).
Hа сегодня все, пока!
=SANA=
Дата: 01 декабря 1998 (1998-12-01)
От: Alexander Bondugin
Тема: First Results from the VLT UT1 Science Verification Programme [2/2]
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An Extremely Red Galaxy
One of the main goals of modern cosmology is to understand when and how the
galaxies formed. In the very last years, many high-redshift (i.e. very
distant) galaxies have been found, suggesting that some galaxies were
already assembled, when the Universe was much younger than now. None of
these high-redshift galaxies have ever been found to be a bona-fide red
elliptical galaxy. The VLT, however, with its very good capabilities for
infrared observations, is an ideal instrument to investigate when and how
the red elliptical galaxies formed.
The VLT Science Verification images have provided unique multicolour
information about an extremely red galaxy that was originally (Treu et al.,
1998, A&A Letters, Vol. 340, p. 10) identified on the Hubble Deep Field
South (HDF-S) Test Image. This galaxy is shown in PR Photo 48d/98 that is an
enlargment from ESO PR Photo 35b/98. It was detected on near-IR images and
also on images obtained in the optical part of the spectrum, at the very
faint limit of magnitude B ~ 29 in the blue. However, this galaxy has not
been detected in the near-ultraviolet band.
ESO PR Photo 48d/98 ESO PR Photo 48e/98
PR Photo 48d/98 (left) shows the very red galaxy (at the arrow) in the
Hubble Deep Field South, discussed here. Photo 48e/98 (right) is the
spectrum of a typical elliptical galaxy, redshifted to z = 1.8 and
compared with the brightness of the galaxy in different wavebands
(crosses), as measured during the VLT SV programme and the Hubble Deep
Field South Test Program (the cross to the right). The arrow indicates the
upper limit by the VLT SV in the ultraviolet band. It can be seen that
these observations are fully consistent with the object being an old,
elliptical galaxy at the high redshift of z=1.8, i.e. at an epoch, when
the Universe was much younger than now. The new ISAAC instrument at VLT
UT1 will be able to obtain an infrared spectrum of this galaxy and thus
to affirm or refute this provisional conclusion.
The colours measured at the VLT and on the HST Test Image are very well
matched by those of an old elliptical galaxy at redshift z ~ 1.8; see Photo
48e/98. All the available evidence is thus consistent with this object being
an elliptical galaxy with the highest-known redshift for this galaxy type. A
preliminary analysis of Hubble Deep Field South data, just released, seems
to support this hypothesis.
If these conclusions are confirmed by direct measurement of its spectrum,
this galaxy must already have been "old" (i.e. significantly evolved) when
the Universe had an age of only about one fifth of its present value. A
spectroscopic confirmation is still outstanding, but is now possible with
the ISAAC instrument at VLT UT1. A positive result would demonstrate that
elliptical galaxies can form very early in the history of the Universe.
The scientists involved in this study are: Massimo Stiavelli, Tommaso Treu
(also Scuola Normale Superiore, Italy), Stefano Casertano, Mark Dickinson,
Henry Ferguson, Andrew Fruchter, Crystal Martin (STSci, Baltimore, USA),
Piero Rosati and Rodolfo Viezzer (ESO), Marcella Carollo (Johns Hopkins
University, Baltimore, USA) and Henry Tieplitz (NASA, Goddard Space Flight
Center, Greenbelt, USA).
Lyman-alpha Companions and Extended Nebulosity around a Quasar at Redshift
z=2.2
In current theories of galaxy formation, luminous galaxies we see today
were built up through repeated merging of smaller protogalactic clumps.
Quasars, prodigious sources pouring out 100 to 1000 times as much light as
an entire galaxy, have been used as markers of galaxy formation activity
and have guided astronomers in their hunting of primeval galaxies and
large-scale structures at high redshift. A supermassive black-hole,
swallowing stars, gas and dust, is thought to be the engine powering a
quasar and the interaction of the galaxy hosting the black-hole with
neighboring galaxies is expected to play a key role in "feeding the
monster".
At intermediate redshift, a large fraction of radio-loud quasars and radio
galaxies inhabit rich clusters of galaxies, whereas radio-quiet quasars are
rarely found in very rich environments. Furthermore, tidal interaction
between quasars and their nearby companions is also the favoured explanation
for the presence of large gaseous nebulosities associated with radio-loud
quasars and radio galaxies. At high redshift, searches for Lyman-alpha
quasar companions and emission-line nebulosities show strong similarities
with those seen at lower redshift, although the detection rate is lower.
ESO PR Photo 48f/98 ESO PR Photo 48g/98
PR Photo 48f/98 (left) is a false-colour reproduction of a B-band image of
the field around the radio-weak quasar J2233-606 in the Hubble Deep Field
South (HDF-S). Photo 48g/98 (right) represents emission from the same
direction at a wavelength that corresponds to Lyman-alpha emission at the
redshift (z = 2.2) of the quasar. Three Lyman-alpha candidate companions
are indicated with arrows. Note also the extended nebulosity around the
quasar.
A search for Lyman-alpha companions to the radio-weak quasar J2233-606 in
the Hubble Deep Field South (HDF-S) was conducted during the VLT UT1 SV
programme in a small field of 1.2 x 1.3 arcmin2, centered on the quasar.
Candidate Lyman-alpha companions were identified by subtracting a broad-band
B (blue) image, that traces the galaxy stellar populations, from a
narrow-band image, spectrally centered on the redshifted, narrow Lyman-alpha
emission line of the quasar (z = 2.2).
Three Lyman-alpha candidate companions were discovered at angular distances
of 15 to 23 arcsec, or 200 to 300 kpc (650,000 to 1,000,000 light-years) at
the distance corresponding to the quasar redshift. The emission lines are
very strong, relative to the continuum emission of the galaxies -- this could
be a consequence of the strong ionizing radiation field of the quasar. These
companions to the quasar may trace a large-scale structure which would
extend over larger distances beyond the observed, small field.
Even more striking is the presence of a very extended nebulosity whose size
(120 kpc x 160 kpc) and Lyman-alpha luminosity (3 x 10**44 erg/cm2/s) are
among the largest observed around radio galaxies and radio-loud quasars,
but rarely seen around a radio-weak quasar. Tidal interaction between the
northern, very nearby companion and the quasar is clearly present: the
companion is embedded in the quasar nebulosity, most of its gas has been
stripped and lies in a tail westwards of the galaxy.
The scientists involved in this study are: Jacqueline Bergeron (ESO),
Stefano Cristiani, Stephane Arnouts, Gianni Fasano (Padova, Italy) and
Patrick Petitjean (Institut d'Astrophysique, Paris, France).
Very Distant Galaxy Clusters
During the past years, it has become possible to detect and subsequently
study progressively more distant clusters of galaxies.
For this research programme, UT1 Science Verification data were used, in
combination with data obtained with the SOFI instrument at the ESO New
Technology Telescope (NTT) at La Silla, to confirm the existence of two very
distant galaxy clusters at redshift z ~ 1, that had originally been detected
in the ESO Imaging Survey. This redshift corresponds to an epoch when the
age of the Universe was only two-thirds of the present.
ESO PR Photo 48h/98
PR Photo 48h/98 (left) is a colour composite that shows the now confirmed
cluster EIS0046-2930. The image has been produced by combining the V
(green-yellow), R (red) and I (Near-IR) exposures with the Test Camera
obtained during the VLT-UT1 Science Verification. The yellow-orange
galaxies are the cluster members and the bluer objects are galaxies
belonging to the general field population. The cluster center is at the
location of the largest (yellow-orange) cluster galaxy to the left of the
center of the image. The field measures 90 x 90 arcsec.
This was achieved by the detection of a spatial excess density of galaxies,
with measured colour equal to that of elliptical galaxies at this redshift,
as established by counts in the respective sky areas. The field of one these
clusters is shown in PR Photo 48h/98.
These new data show that the VLT will most certainly play a major role in
the studies of the cluster galaxy population in such distant systems. This
will contribute to shed important new light on the evolution of galaxies.
Furthermore, the VLT clearly has the potential to identify and confirm the
reality of many more such clusters and thereby to increase considerably the
number of known objects. This will be important in order to determine more
accurate values of the basic cosmological constants, and thus for our
understanding of the evolution of the Universe as a whole.
The presentation was made by Lisbeth Fogh Olsen (Copenhagen Observatory,
Denmark, and ESO) on behalf of the scientists involved in this study.
Icy Planets in the Outer Solar System
Observations with large optical telescopes during the past years have begun
to cast more light on the still very little known, distant icy planets in
the outer solar system. Until November 1998, about 70 of these have been
discovered outside the orbit of Neptune (between 30 and 50 AU, or 4,500 to
7,500 million km, from the Sun). They are accordingly referred to as
Trans-Neptunian Objects (TNOs).
Those found so far are believed to represent the "tip of the iceberg" of a
large population of such objects belonging to the so-called Kuiper Belt.
This is a roughly disk-shaped region between about 50 and 120 AU (about
7,500 to 18,000 million km) from the Sun, in which remnant bodies from the
formation of the solar system are thought to be present.
From their measured brightness and the distance, it is found that most known
TNOs have diameters of the order of a few hundred kilometres. About half of
those known move in elongated Pluto-like orbits, the others move somewhat
further out in stable, circular orbits.
During the two-week Science Verification programme, approximately 200
minutes were spent on a small observing programme aimed at obtaining images
of some TNOs in different wavebands (B, V, R and I). Since this programme
was primarily designed as a back-up to be executed during less favourable
atmospheric conditions, some of the observations could not be used. However,
images of three faint TNOs were recorded during an excellent series of 1-10
min exposures.
From these data, it was possible to measure quite accurate magnitudes (and
thus approximate sizes) and to determine their colours. One of them, 1996
TL66, was among the bluest TNOs ever observed. It is believed that this is
because its surface has undergone recent transformation, possibly due to
collisions with other objects or the breaking-off of small pieces from the
surface, in both cases revealing "fresh" layers below.
The combination of all available exposures made it possible to look for
faint and tenous atmospheres around these TNOs, but none were found.
These results show that it is possible, with little effort and even under
quite unfavourable observing conditions, to obtain valuable information with
the VLT about icy objects in the outer solar system. Of even greater
interest will be future spectroscopic observations with FORS and ISAAC that
will allow to study the surface composition in some detail, with the
potential of providing direct information about (nearly?) pristine material
from the early phases of the solar system.
The scientists involved in this study are: Olivier Hainaut, Hermann
Boehnhardt, Catherine Delahodde and Richard West (ESO) and Karen Meech
(Institute of Astronomy, Hawaii, USA).
ESO Press Photos may be reproduced, if credit is given to the European
Southern Observatory.
Andrew Yee
ayee@nova.astro.utoronto.ca
Hа сегодня все, пока!
=SANA=
Дата: 01 декабря 1998 (1998-12-01)
От: Alexander Bondugin
Тема: No major changes seen in stability of Antarctic ice sheet (Forwarded)
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Ohio State University
Contact: C.K. Shum (614) 292-7118; CKShum@osu.edu
Written by Earle Holland, (614) 292-8384; Holland.8@osu.edu
11/23/98
NO MAJOR CHANGES SEEN IN STABILITY OF ANTARCTIC ICE SHEET
COLUMBUS, Ohio -- The interior of the West Antarctic ice sheet -- the
largest grounded repository of ice on the planet -- isn't melting rapidly,
is reasonably stable and has been so for more than a century.
That's the conclusion drawn by an international team of scientists who
analyzed five years of satellite radar measurements covering a large part
of the southernmost continent. Their report was published in a recent issue
of the journal Science.
The study is important in that it offers one of the best investigations so
far of possible mass balance changes in the ice covering Antarctica. While
global warming has been blamed for possible reductions in the Antarctic ice
sheet, scientists have argued over whether there was definitive evidence of
such ice loss. It's also unclear whether the west Antarctic ice sheet would
be unstable in a warmer world.
The new study suggests that the answer is no, at least for the middle of the
ice sheet.
"Based on our short, five-year period of observation of the interior of
Antarctica, we do not seem to detect that the ice is melting more than one
centimeter per year," explained C.K. Shum, an associate professor of civil
and environmental engineering and geodetic science at Ohio State University.
"That would mean that the interior Antarctic ice sheet does not seem to be
contributing to sea level rise more than 1 millimeter per year." Shum said
that a one-centimeter (0.4 inch) decrease in Antarctic ice sheet volume
roughly converts into a one-millimeter (0.04 inch) rise in global sea level.
Shum, along with other scientists from University College in London and the
Delft University of Technology in the Netherlands, analyzed radar altimetry
data retrieved from two European Space Agency remote sensing satellites --
ESA-1 and ESA-2 -- used to measure ice altitudes from 1992 through 1996.
The orbits of the satellites reached to 81.5 degrees N, allowing them to
regularly monitor at least 60 percent of the continent's grounded ice.
The majority of the West Antarctic ice sheet sits atop dry land while the
East Antarctic ice sheet is grounded below sea level. Changes in the East
Antarctic sheet would have little effect on sea level since the ice displaces
sea water. But a complete melt of West Antarctic ice would pour new water
into the oceans, raising sea levels.
"We assume that global warming is underway now," Shum says, "and it may be
enhanced by human activities but, until now, its effect on ice loss in
Greenland and the Antarctic has been mostly speculation. We wanted to look
at ice sheets to see how they contribute to sea level rise."
Researchers understand some causes for sea level rise, Shum said, but the
role ice sheets may play "remains an uncertainty." During the last ice
age -- 18,000 years ago -- sea levels were at least 100 meters lower than
they are today.
Shum and his colleagues turned to the ESA satellites to look for ice sheet
growth. The two, circling the globe in 800-kilometer (497-mile) orbits, were
able to measure the height of the ocean surface to an accuracy of about 5
centimeters (two inches).
"But over ice, the readings are less accurate," Shum said. "The satellites
also have problems accurately measuring coastal ice regions."
The researchers had to devise new algorithms to decipher the raw, ice sheet
altimetry data and correct for several variables such as radar penetration
below the ice surface and snow accumulation. Even with these limitations,
the study represents the longest time series for which data is available.
Shum said the National Aeronautics and Space Administration is planning
a new mission for the year 2001 called ICESAT. It would position a new
satellite in a near-polar orbit, increasing the amount of ice sheet
coverage, and use a more accurate laser altimeter to take measurements.
These, combined with the radar altimetry data, would give a much better
assessment of mass balance changes, if any, in the Antarctic ice sheets.
This project was supported in part by the NASA Physical Oceanography Program
and the United Kingdom Natural Environment Research Council.
Andrew Yee
ayee@nova.astro.utoronto.ca
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Дата: 01 декабря 1998 (1998-12-01)
От: Alexander Bondugin
Тема: Smart materials provide for self-adjusting satellite antennas
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Ohio State University
Contact: Gregory Washington, (614) 292-8486; Washington.88@osu.edu
Written by Pam Frost, (614) 292-9475; Frost.18@osu.edu
11/23/98
SMART MATERIALS PROVIDE FOR SELF-ADJUSTING SATELLITE ANTENNAS
COLUMBUS, Ohio -- Researchers at Ohio State University have taken the first
step toward developing adjustable antennas for satellite communications.
Such an antenna could change the shape of its reflector while in orbit to
improve signal quality. It could also replace several traditional antennas
by delivering a variety of signals for cellular phones, pagers, and global
positioning systems.
Scientists had previously found that adjustable reflectors made of plastic
were light enough for use in space, but they were too flexible to afford
good shape control.
Gregory Washington, assistant professor of mechanical engineering, and
Hwan-Sik Yoon, a graduate student, have proven through computer simulations
that thin piezoceramic patches spaced around the back of a reflector will
reinforce the plastic while controlling its shape. The research appeared
in a recent issue of the journal Smart Materials & Structures.
A piezoceramic material is a ceramic that changes shape when a voltage is
applied to it, or releases a voltage when its shape is changed manually.
Researchers sometimes call these "smart" materials. "When we attach this
piezoceramic material to another surface and it expands, the surface bends.
When it contracts, the surface bends the other way. With that movement,
we're able to change the overall shape of a structure. In this case, the
shape change alters the properties of the reflector or antenna itself,"
explained Washington.
Satellites normally must move the entire mechanism beneath an antenna
to change its direction. "It's as if our eyes could only stare straight
forward -- to see other directions we'd have to turn our whole head," said
Washington. "But an adjustable antenna can make fine movements on its own,
like we do when we look around with our eyes."
When satellites move to adjust the direction of standard antennas, they
create inertial forces that throw off the orientation of the entire satellite.
But an adjustable antenna with actuators made of plastic and piezoceramic
material would be light enough to generate very little inertia.
"That's one of the significant benefits -- the satellite wouldn't have to
constantly reorient itself," said Washington. "Plus, instead of having three
or four antennas on a satellite, we could have one or two multifunctional
antennas."
Washington and Yoon developed a series of lengthy and complex equations to
model the movement of the piezoceramic actuators. Then they put those
equations into a computer code called POMESH, short for Physical Optics Mesh.
Researchers at the Jet Propulsion Laboratory in Pasadena, CA, previously
developed POMESH to model the radiation pattern of rigid antenna reflectors.
Washington and Yoon modified the code to suit an antenna that changes shape.
Through computer simulations with POMESH, Washington and Yoon found that
the plastic reflector materials must be molded to a particular shape and
the actuators must be bonded to the structure at specific temperatures and
pressures for the design to work. The researchers have now obtained a series
of molds to begin making adjustable antennas. "Nobody has ever tried to
build these antennas before, so we're doing everything from the ground up,"
said Washington.
He and Yoon have also written control algorithms by which these new antennas
will be able to self-tune in response to commands from Earth. "Let's say
someone wants to find a shape that gives maximum power to a signal in the
presence of atmospheric disturbances," said Washington. "An adjustable
antenna could configure itself to send out the maximum amount of
information."
The ability for antennas to change shape solves certain problems. For
instance, sunlight heats antenna materials and warps them; when that
happens, adjustable antennas could simply self-correct.
Another common problem: Earth's atmosphere scatters satellite signals the
same way water scatters a beam of light. For this reason, not all transmitted
information reaches a target. Standard antennas can't correct for that,
but an adjustable antenna could even navigate signals through turbulent
atmospheric conditions like storms. It could deliver more information using
the same amount of power.
The technology may also lead to advanced membrane optics for telescopes and
microscopes -- that is, thin and flexible lenses and mirrors that change
shape to change focus.
Currently Washington and Yoon are working with Willie Theunissen, an
engineering graduate student at the University of Pretoria, South Africa,
to continue to modify and develop physical and geometric optics code for
advanced antennas. "We're generating new code because we want to be able to
choose the right amount of actuators and find out just where to place them
for the different shapes we want to obtain," said Washington.
This work was funded by a grant from the National Science Foundation and the
U.S. Army Research Office. In the future, the researchers may work with NASA
on smart, adjustable antennas for wireless communications networks. Such
networks could transmit signals for telephones, televisions, and faxes
without the need for cables and phone lines. Washington hopes they will be
able to finish building an antenna by March 1999, when the space agency will
run a series of field tests.
Andrew Yee
ayee@nova.astro.utoronto.ca
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