Электронная библиотека астронома-любителя. RU.SPACE.NEWS

Электронная библиотека астронома-любителя. Книги по астрономии, телескопостроению, оптике.

главная

библиотека

архив RSN

ссылки

Ru.Space.News:

год:

Интернет-магазин
Любимых игрушек!

Обзоры оружия и снаряжения

m31.spb.ru

0.043

Архив RU.SPACE.NEWS за 01 декабря 1998

Дата: 01 декабря 1998 (1998-12-01) От: Alexander Bondugin Тема: Cassini Instrument Checkout - Day By Day [1/2] Привет всем! Вот, свалилось из Internet... 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] Привет всем! Вот, свалилось из Internet... 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 Привет всем! Вот, свалилось из Internet... 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