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Дата: 10 апреля 1998 (1998-04-10)
От: Alexander Bondugin
Тема: Galileo Update - April 9, 1998
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MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov
GALILEO EUROPA MISSION STATUS
April 9, 1998
The Galileo spacecraft successfully completed its most recent flyby of
Jupiter's moon Europa on March 29, and indications are there was no change
to the gyroscope performance. Because one of the two gyros had been acting
up, the closest approach to Europa was carried out in cruise mode, with the
gyros turned off; the spacecraft used only <b style="color:black;background-color:#ffff66">stars</b> to orient itself and point
its instruments. However, an attitude-control system performance test
showed that the gyros did not degrade further during this latest pass
through Jupiter's intense radiation environment. Galileo project engineers
have pinpointed a single computer chip as the cause of the anomalous
behavior. This particular chip has received more radiation exposure than
other similar chips in the gyro electronics.
This week, Galileo transmitted to Earth pictures and other science
information gathered during the latest Europa flyby. This includes one of
three observations by the photopolarimeter radiometer designed to refine
temperature variation maps of Europa's surface. This will help scientists
understand surface ages and composition and the process that may have
formed the surface. In addition, there is information from instruments
that study magnetic fields and charged particles on the interaction between
Europa and Jupiter's magnetic and electric field environment. The camera
and the near infrared mapping spectrometer have returned information on a
region of dark lines and the Mannann'an crater on Europa. Data gathered by
the spectrometer of the south pole of Jupiter's volcanic moon, Io, provides
the spacecraft's best view of the area until late 1999.
On Friday, April 10, the spacecraft will perform regular propulsion
system maintenance and perform a turn to keep its radio antenna pointed toward
Earth.
Galileo's next Europa flyby will take place on May 31, 1998, at an
altitude of 2,521 kilometers (1,566 miles). The spacecraft successfully
completed its primary mission in December 1997 and is now in its two-year
extension, the Galileo Europa Mission. Current plans include four more
Europa flybys after the May encounter, four Callisto flybys, and one or two
of Io, depending on spacecraft health.
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Дата: 10 апреля 1998 (1998-04-10)
От: Alexander Bondugin
Тема: Mars Global Surveyor Update - April 9, 1998
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From the Mars Global Surveyor home page:
http://mars.jpl.nasa.gov/mgs/target/update4-9.html
SUMMARY OF CLUSTER 1 TARGETED IMAGING
09-APR-98 3:30 PM PDT
Mars Global Surveyor has completed the first of three sets (clusters) of
specially targeted imaging opportunities during its current hiatus in
aerobraking. While it was estimated that probability of successfully
accomplishing this imaging would be on the order of 30-50% for each of the
images, owing to navigation, spacecraft attitude control and map location
uncertainties, it appears that we have done somewhat better.
On April 3, 1998, at 0958 UTC, MGS pointed the Mars Orbiter Camera toward
the Viking Lander 1 site in Chryse Planitia. The area was covered with a
thin cloud layer and patchy thick clouds, reducing but not eliminating
surface visibility. The narrow angle image had relatively low contrast but
the contrast was sufficient for adequate feature identification. This
analysis showed that the targeted spot for the Viking Lander 1 sites was
approximately 40 pixels or 150 m off the western edge of the image, although
it was well centered in the north to south direction. We came very close,
and the pointing performance was well within the expected variations of the
spacecraft's attitude control system, and we'll count this as a miss.
Because the Lander was not in the picture, we won't release the image at
this time.
Viking Lander 2 is located in Utopia Planitia, further north and on the
other side from Mars from Viking Lander 1. When MGS imaged this area on
April 3, at 2137 UTC, on the orbit following the Viking Lander 1
observation, it found the area in heavy overcast, with clouds and haze
severely reducing the surface visibility by over 70-80%. These clouds and
possible surface frost led to a scene substantially brighter than
anticipated, and thus much of the image data was saturated bright.
Aggressive application of image processing techniques enhanced faint
brightness variations, rendering a small number of surface features visible.
These features were used to attempt to determine the success of the
targeting. It is believed that the Viking-era landing location may be with
the extreme south-west portion of the image and the western-most of three
new estimated positions, more recently determined, may be in the lower
south-eastern portion of the image. The location of Viking Lander 2 is the
least well known of the sites being imaged. So, we'll count this attempt as
a hit, however, because the image is mostly clouds, we won't release it at
this time.
Mars Pathfinder, the Sagan Memorial Station, and the Sojourner rover are
located in Ares Vallis. On April 4th, at 0916 UTC, the spacecraft was
successful in targeting the point that it was directed to, however, a
controversy has arisen as to the true coordinates of the real landing site.
It appears that, after some reevaluation of the targeting information used
with the Mars Pathfinder project, we have used the wrong coordinate
references for our target point. Better information will be used in the next
opportunity. Because it appears that Mars Pathfinder is not in the image, we
won't release the image at this time.
The feature known as the "Face on Mars" in the Cydonia region was imaged
quite successfully on April 5th and its image was released in raw form and
in an enhanced form on April 6th. The picture was acquired 375 seconds after
the spacecraft's 220th closest approach to Mars. At that time, the "Face",
located at approximately 40.8 degrees N, 9.6 degrees W, was 275 miles (444 km)
from the
spacecraft. The "morning" sun (about 10 AM local solar time) was 25 degrees
above
the horizon. The picture has a resolution of 14.1 feet (4.3 meters) per
pixel, making it ten times higher resolution than the best previous image of
the feature, which was taken by the Viking Orbiter 1 in 1976. The full image
covers an area 2.7 miles (4.4 km) wide and 25.7 miles (41.5 km) long.
Since winter clouds cover much of the northern hemisphere of Mars above 40
degrees
N latitude at this time of the Martian year, the raw image of the "Face" was
of very low contrast, that is, variations in brightness of the picture
elements cover a very small range compared to the ultimate capability of the
camera. Thus, the "raw" image appears very dark and flat. This very washed
out appearance of the northern hemisphere of Mars can be readily seen in the
wide angle image taken at the same time as the narrow angle picture that
contains the "Face" (see
http://mars/mgs/msss/camera/images/4_6_face_release/index.html). The
enhanced version of the raw data has made the feature visible. The enhanced
version also flipped the image left to right to make it appear in the same
orientation as the familiar Viking image.
The targeting was very good for this attempt and is clearly a hit. The
"Face" was nearly exactly in the center of the image. A portion of another
feature in the area, the "D&M Pyramid", is the bottom left-hand corner of
the image.
The Mars Surveyor Operations Project assesses the results of the first
cluster of targeted imaging to have been quite successful. The results have
provided information useful in fine tuning the processes for the second
cluster of images that will be taken starting on April 12th.
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