The Experts below are selected from a list of 207 Experts worldwide ranked by ideXlab platform
David H. Atkinson - One of the best experts on this subject based on the ideXlab platform.
-
titan s new pole implications for the huygens entry and Descent Trajectory and landing coordinates
Advances in Space Research, 2011Co-Authors: Bobby Kazeminejad, David H. Atkinson, Jeanpierre LebretonAbstract:Abstract The European Space Agency’s Huygens probe separated from the NASA Cassini spacecraft on 25 December 2004, after having been attached for a 7-year interplanetary journey and three orbits around Saturn. The probe reached the predefined NASA/ESA interface point on 14 January 2005 at 09:05:52.523 (UTC). It performed a successful entry and Descent sequence and softly landed on Titan’s surface on the same day at 11:38:10.77 (UTC) with a speed of about 4.54 m/s. Since the publication of the official project entry and Descent Trajectory reconstruction effort by the Descent Trajectory Working Group in 2007 (referred to as DTWG#4) various other efforts have been performed and published. This paper presents an overview of the most relevant reconstructions and compares their methodologies and results. Furthermore, the results of a new reconstruction effort (DTWG#5) are presented, which is based on the same methodology as DTWG#4 but takes into account new estimates of Titan’s pole coordinates which were derived from radar images of different Cassini Titan flybys. It can be shown that the primary effect can be observed in the meridional direction which is represented by a stark southward shift of the Trajectory by about 0.3 deg. A much smaller effect is seen in the zonal direction (i.e., less than 0.01 deg in the west to east direction). The revised probe landing coordinates are 192.335 deg W and 10.573 deg S. A comparison of these coordinates with results of recent landing site investigations using visual and radar images of the Cassini VIMS instrument shows excellent agreement of the two independently derived landing coordinates, i.e., longitude and latitude residuals of respectively 0.035 deg and 0.007 deg.
-
the huygens probe Descent Trajectory working group organizational framework goals and implementation
Planetary and Space Science, 2007Co-Authors: David H. Atkinson, Bobby Kazeminejad, J P Lebreton, Olivier Witasse, Miguel Perezayucar, Dennis L MatsonAbstract:Cassini/Huygens, a flagship mission to explore the rings, atmosphere, magnetic field, and moons that make up the Saturn system, is a joint endeavor of the National Aeronautics and Space Administration, the European Space Agency, and Agenzia Spaziale Italiana. Comprising two spacecraft - a Saturn orbiter built by NASA and a Titan entry/Descent probe built by the European Space Agency, Cassini/Huygens was launched in October 1997. The Huygens probe parachuted to the surface of Titan in January 2005. During the Descent, six science instruments provided in situ measurements of Titan’s atmosphere, clouds, and winds, and photographed Titan’s surface. To correctly interpret and correlate results from the probe science experiments, and to provide a reference set of data for ground-truth calibration of orbiter remote sensing measurements, an accurate reconstruction of the probe entry and Descent Trajectory and surface landing location is necessary. The Huygens Descent Trajectory Working Group was chartered in 1996 as a subgroup of the Huygens Science Working Team to develop and implement an organizational framework and retrieval methodologies for the probe Descent Trajectory reconstruction from the entry altitude of 1270 km to the surface using navigation data, and engineering and science data acquired by the instruments on the Huygens Probe. This paper presents an overview of the Descent Trajectory Working Group, including the history, rationale, goals and objectives, organizational framework, rules and procedures, and implementation.
-
huygens entry and Descent through titan s atmosphere methodology and results of the Trajectory reconstruction
Planetary and Space Science, 2007Co-Authors: David H. Atkinson, Bobby Kazeminejad, J P Lebreton, Miguel Perezayucar, Claudio SollazzoAbstract:Abstract The European Space Agency's Huygens probe separated from the NASA Cassini spacecraft on 25 December 2004, after having been attached for a 7-year interplanetary journey and three orbits around Saturn. The probe reached the predefined NASA/ESA interface point on 14 January 2005 at 09:05:52.523 (UTC) and performed a successful entry and Descent sequence. The probe softly impacted on Titan's surface on the same day at 11:38:10.77 (UTC) with a speed of about 4.54 m/s. The probe entry and Descent Trajectory was reconstructed from the estimated initial state vector provided by the Cassini Navigation team, the probe housekeeping data, and measurements from the scientific payload. This paper presents the methodology and discuss the results of the reconstruction effort. Furthermore the probe roll rate was reconstructed prior to the main entry phase deceleration pulse and throughout the entire Descent phase under the main and drogue parachute.
-
huygens probe entry and Descent Trajectory analysis and reconstruction techniques
EGS - AGU - EUG Joint Assembly, 2003Co-Authors: David H. Atkinson, Bobby Kazeminejad, V Gaborit, F Ferri, Jeanpierre LebretonAbstract:Abstract Cassini/Huygens is a joint National Aeronautics and Space Administration (NASA)/European Space Agency (ESA)/Agenzia Spaziale Italiana (ASI) mission on its way to explore the Saturnian system. The ESA Huygens Probe is scheduled to be released from the Orbiter on 25 December 2004 and enter the atmosphere of Titan on 14 January 2005. Probe delivery to Titan, arbitrarily defined to occur at a reference altitude of 1270 km above the surface of Titan, is the responsibility of the NASA Jet Propulsion Laboratory (JPL). ESA is then responsible for safely delivering the probe from the reference altitude to the surface. The task of reconstructing the probe Trajectory and attitude from the entry point to the surface has been assigned to the Huygens Descent Trajectory Working Group (DTWG), a subgroup of the Huygens Science Working Team. The DTWG will use data provided by the Huygens Probe engineering subsystems and selected data sets acquired by the scientific payload. To correctly interpret and correlate results from the probe science experiments and to provide a reference set of data for possible “ground-truthing” Orbiter remote sensing measurements, it is essential that the Trajectory reconstruction be performed as early as possible in the post-flight data analysis phase. The reconstruction of the Huygens entry and Descent Trajectory will be based primarily on the probe entry state vector provided by the Cassini Navigation Team, and measurements of acceleration, pressure, and temperature made by the Huygens Atmospheric Structure Instrument (HASI). Other data sets contributing to the entry and Descent Trajectory reconstruction include the mean molecular weight of the atmosphere measured by the probe Gas Chromatograph/Mass Spectrometer (GCMS) in the upper atmosphere and the Surface Science Package (SSP) speed of sound measurement in the lower atmosphere, accelerations measured by the Central and Radial Accelerometer Sensor Units (CASU/RASU), and the probe altitude by the two probe radar altimeters during the latter stages of the Descent. In the last several hundred meters, the altitude determination will be constrained by measurements from the SSP acoustic sounder. Other instruments contributing data to the entry and Descent Trajectory and attitude determination include measurements of the zonal wind drift by the Doppler Wind Experiment (DWE), and probe zonal and meridional drift and probe attitude by the Descent Imager and Spectral Radiometer (DISR). In this paper, the need for and the methods by which the Huygens Probe entry and Descent Trajectory will be reconstructed are reviewed.
-
titan wind effects on the Descent Trajectory of the esa huygens probe
Earth-like Planets and Moons, 2002Co-Authors: Bobby Kazeminejad, J P Lebreton, M K Bird, David H. AtkinsonAbstract:The Huygens Probe is the ESA-provided element of the joint NASA/ESA Cassini/Huygens mission to Saturn and Titan. The Cassini/Huygens spacecraft was launched on 15 October 1997 and will arrive at Saturn on the 1st of July 2004. The Huygens probe will be released on 24 December 2004 and enter the atmosphere of Titan on 14 January 2005. A recently discovered design flaw in the Huygens radio receiver onboard Cassini led to a significant redesign of the mission geometry by both the Huygens and Cassini project teams. In this new scenario the Orbiter will pass Titan at high altitude (i.e., 60,000 km) on the retrograde side of Titan and will trail the Probe by only about 2.1 hours instead of the originally planned 1250 km flyby altitude on the prograde side of Titan and a 4 hour delay time. Among the factors governing the duration and quality of the Cassini/Huygens communication window during the Descent is the Probe drift caused by zonal winds. Existing Titan wind models have been reevaluated and compared to recent ground-based observations. Simulations of the Probe entry and Descent show a drift from ∼300 km up to ∼430 km away from the “no wind” landing point, depending on the wind model. At the end of the nominal mission this difference in wind drift (assuming prograde winds) causes a difference of up to 1.7 dB (within a margin of 3 to 4 dB, resulting from the receiver design flaw) in the received signal-tonoise ratio. The high sensitivity of the received signal strength to zonal winds and their directions is due to the steep decrease of the Probe antenna gain when the Cassini spacecraft (with the Huygens receiver) as seen from the Probe moves to increasingly higher elevation angles. A simulation of the Probe atmospheric entry phase shows that the zonal wind direction also impacts the shape of the deceleration profile and its peak value. The deceleration profile will be accurately measured during the entry phase by accelerometers onboard the Probe. From this data set the density profile of the upper Titan atmosphere will be inferred. This will complement the orbiter instrument measurements planned during the early Titan flybys for validation of the upper Titan atmosphere model and evaluation of the drag force that will act on the Cassini spacecraft at subsequent low altitude Titan flybys (∼950 km).
Bobby Kazeminejad - One of the best experts on this subject based on the ideXlab platform.
-
titan s new pole implications for the huygens entry and Descent Trajectory and landing coordinates
Advances in Space Research, 2011Co-Authors: Bobby Kazeminejad, David H. Atkinson, Jeanpierre LebretonAbstract:Abstract The European Space Agency’s Huygens probe separated from the NASA Cassini spacecraft on 25 December 2004, after having been attached for a 7-year interplanetary journey and three orbits around Saturn. The probe reached the predefined NASA/ESA interface point on 14 January 2005 at 09:05:52.523 (UTC). It performed a successful entry and Descent sequence and softly landed on Titan’s surface on the same day at 11:38:10.77 (UTC) with a speed of about 4.54 m/s. Since the publication of the official project entry and Descent Trajectory reconstruction effort by the Descent Trajectory Working Group in 2007 (referred to as DTWG#4) various other efforts have been performed and published. This paper presents an overview of the most relevant reconstructions and compares their methodologies and results. Furthermore, the results of a new reconstruction effort (DTWG#5) are presented, which is based on the same methodology as DTWG#4 but takes into account new estimates of Titan’s pole coordinates which were derived from radar images of different Cassini Titan flybys. It can be shown that the primary effect can be observed in the meridional direction which is represented by a stark southward shift of the Trajectory by about 0.3 deg. A much smaller effect is seen in the zonal direction (i.e., less than 0.01 deg in the west to east direction). The revised probe landing coordinates are 192.335 deg W and 10.573 deg S. A comparison of these coordinates with results of recent landing site investigations using visual and radar images of the Cassini VIMS instrument shows excellent agreement of the two independently derived landing coordinates, i.e., longitude and latitude residuals of respectively 0.035 deg and 0.007 deg.
-
the huygens probe Descent Trajectory working group organizational framework goals and implementation
Planetary and Space Science, 2007Co-Authors: David H. Atkinson, Bobby Kazeminejad, J P Lebreton, Olivier Witasse, Miguel Perezayucar, Dennis L MatsonAbstract:Cassini/Huygens, a flagship mission to explore the rings, atmosphere, magnetic field, and moons that make up the Saturn system, is a joint endeavor of the National Aeronautics and Space Administration, the European Space Agency, and Agenzia Spaziale Italiana. Comprising two spacecraft - a Saturn orbiter built by NASA and a Titan entry/Descent probe built by the European Space Agency, Cassini/Huygens was launched in October 1997. The Huygens probe parachuted to the surface of Titan in January 2005. During the Descent, six science instruments provided in situ measurements of Titan’s atmosphere, clouds, and winds, and photographed Titan’s surface. To correctly interpret and correlate results from the probe science experiments, and to provide a reference set of data for ground-truth calibration of orbiter remote sensing measurements, an accurate reconstruction of the probe entry and Descent Trajectory and surface landing location is necessary. The Huygens Descent Trajectory Working Group was chartered in 1996 as a subgroup of the Huygens Science Working Team to develop and implement an organizational framework and retrieval methodologies for the probe Descent Trajectory reconstruction from the entry altitude of 1270 km to the surface using navigation data, and engineering and science data acquired by the instruments on the Huygens Probe. This paper presents an overview of the Descent Trajectory Working Group, including the history, rationale, goals and objectives, organizational framework, rules and procedures, and implementation.
-
huygens entry and Descent through titan s atmosphere methodology and results of the Trajectory reconstruction
Planetary and Space Science, 2007Co-Authors: David H. Atkinson, Bobby Kazeminejad, J P Lebreton, Miguel Perezayucar, Claudio SollazzoAbstract:Abstract The European Space Agency's Huygens probe separated from the NASA Cassini spacecraft on 25 December 2004, after having been attached for a 7-year interplanetary journey and three orbits around Saturn. The probe reached the predefined NASA/ESA interface point on 14 January 2005 at 09:05:52.523 (UTC) and performed a successful entry and Descent sequence. The probe softly impacted on Titan's surface on the same day at 11:38:10.77 (UTC) with a speed of about 4.54 m/s. The probe entry and Descent Trajectory was reconstructed from the estimated initial state vector provided by the Cassini Navigation team, the probe housekeeping data, and measurements from the scientific payload. This paper presents the methodology and discuss the results of the reconstruction effort. Furthermore the probe roll rate was reconstructed prior to the main entry phase deceleration pulse and throughout the entire Descent phase under the main and drogue parachute.
-
first application of the huygens Descent Trajectory working group Trajectory reconstruction algorithm to huygens data
2006Co-Authors: Bobby Kazeminejad, D H AtkinsonAbstract:The ESA Huygens probe performed a successful Entry, Descent, and Landing (EDL) sequence through Titan’s dense atmosphere on January 14, 2005. During all three phases, i.e., the supersonic entry phase, the Descent phase, as well as the impact and post impact phases, the probe performed measurements that were used for the reconstruction of its entry and Descent Trajectory. We first discuss the datasets relevant to the entry and Descent Trajectory reconstruction. We then provide an overview of the reconstruction strategy, and show preliminary results of the reconstructed entry and Descent Trajectory, including both position and velocity.
-
simulation and analysis of the revised huygens probe entry and Descent Trajectory and radio link modelling
Planetary and Space Science, 2004Co-Authors: Bobby Kazeminejad, J P Lebreton, Miguel Perezayucar, M Sancheznogales, M Bellomora, Nathan Strange, D Roth, L Popken, K Clausen, Patrice CouzinAbstract:The Cassini spacecraft will arrive at Saturn in 2004 carrying the Huygens probe. The beginning of the Cassini tour at Saturn has been redesigned to achieve a di:erent relative orbiter/probe geometry in order to compensate for the probe relay receiver design ;aw that was discovered during tests in February 2000. This paper presents a numerical simulation of the Huygens atmospheric entry and Descent Trajectory and the Cassini ;yby Trajectory during the probe mission. A variety of parameters that are crucial for the probe system and its scienti=c payload have been calculated and analyzed together with an assessment of their uncertainties. Furthermore the orbiter/probe relay link was simulated in order to assess any potential data loss on the basis of an analytical model of the actual Huygens receiver onboard the Cassini spacecraft. The redesigned Cassini/Huygens mission satis=es all science and engineering requirements and assures the best possible radio link for the entire nominal mission duration. ? 2004 Elsevier Ltd. All rights reserved.
Xu Tan - One of the best experts on this subject based on the ideXlab platform.
-
Descent Trajectory reconstruction and landing site positioning of chang e 4 on the lunar farside
Nature Communications, 2019Co-Authors: Jianjun Liu, Xin Ren, Wei Yan, He Zhang, Yang Jia, Xingguo Zeng, Wangli Chen, Xingye Gao, Dawei Liu, Xu TanAbstract:Chang’E-4 (CE-4) was the first mission to accomplish the goal of a successful soft landing on the lunar farside. The landing Trajectory and the location of the landing site can be effectively reconstructed and determined using series of images obtained during Descent when there were no Earth-based radio tracking and the telemetry data. Here we reconstructed the powered Descent Trajectory of CE-4 using photogrammetrically processed images of the CE-4 landing camera, navigation camera, and terrain data of Chang’E-2. We confirmed that the precise location of the landing site is 177.5991°E, 45.4446°S with an elevation of −5935 m. The landing location was accurately identified with lunar imagery and terrain data with spatial resolutions of 7 m/p, 5 m/p, 1 m/p, 10 cm/p and 5 cm/p. These results will provide geodetic data for the study of lunar control points, high-precision lunar mapping, and subsequent lunar exploration, such as by the Yutu-2 rover. The Chang’E-4 mission in January 2019 had the major challenge to land on the lunar far side without traditional radiometric techniques due to the missing line-of-sight. The authors here describe landing Trajectory reconstruction and positioning techniques based upon the Moon’s digital terrain model that allowed reproducing the entire process of a successful landing.
D H Atkinson - One of the best experts on this subject based on the ideXlab platform.
-
first application of the huygens Descent Trajectory working group Trajectory reconstruction algorithm to huygens data
2006Co-Authors: Bobby Kazeminejad, D H AtkinsonAbstract:The ESA Huygens probe performed a successful Entry, Descent, and Landing (EDL) sequence through Titan’s dense atmosphere on January 14, 2005. During all three phases, i.e., the supersonic entry phase, the Descent phase, as well as the impact and post impact phases, the probe performed measurements that were used for the reconstruction of its entry and Descent Trajectory. We first discuss the datasets relevant to the entry and Descent Trajectory reconstruction. We then provide an overview of the reconstruction strategy, and show preliminary results of the reconstructed entry and Descent Trajectory, including both position and velocity.
-
the esa huygens probe entry and Descent Trajectory reconstruction
ESASP, 2004Co-Authors: Bobby Kazeminejad, D H AtkinsonAbstract:Cassini/Huygens is a joint NASA/ESA mission on its way to explore the Saturnian system. The ESA Huygens probe is scheduled to be released from the Cassini spacecraft on December 25, 2004, will enter the atmosphere of Titan in January, 2005, and will descend to the surface of the planet using a sequence of different parachutes. To correctly interpret and correlate results from the probe science experiments and to provide a reference set of data for “ground-truthing” Orbiter remote sensing measurements, it is essential that the Trajectory reconstruction be performed as early as possible in the post-flight data analysis phase. The reconstruction of the Huygens entry and Descent Trajectory will be based primarily on the probe entry state vector provided by the Cassini Navigation Team, and measurements of acceleration, pressure, and temperature made by the Huygens Atmospheric Structure Instrument (HASI). Other datasets contributing to the entry and Descent Trajectory reconstruction include the mean molecular weight of the atmosphere measured by the probe Gas Chromatograph/Mass Spectrometer (GCMS) in the upper atmosphere and the Surface Science Package (SSP) speed of sound measurement in the lower atmosphere, and probe altitude by the two probe radar altimeters during the latter stages of the Descent. Measurements of the zonal wind drift by the Doppler Wind Experiment (DWE), and probe zonal and meridional drift, and probe altitude and Descent speed by the Descent Imager and Spectral Radiometer (DISR) will further constrain the probe Trajectory. This paper outlines the mathematical approach and computational flow of an algorithm that combines all the relevant measurements to retrieve the probe Trajectory most consistent with all data sets, and the probe Trajectory uncertainties.
Alvin Seiff - One of the best experts on this subject based on the ideXlab platform.
-
Deep winds on Jupiter as measured by the Galileo probe
Nature, 1997Co-Authors: David H. Atkinson, Andrew P. Ingersoll, Alvin SeiffAbstract:The Doppler Wind Experiment on the Galileo probe provided the first in situ data on wind speeds in Jupiter's atmosphere. Initial analysis^ 1 of the results indicated that wind speeds increase with depth, rather than decaying to zero below the cloud tops or remaining relatively constant as had previously been assumed^ 2 . But this earlier analysis was subject to several potential sources of error, as highlighted by the fact that wind speeds measured at the cloud tops did not seem to match those inferred from tracking clouds^ 3 in images obtained by the Voyager spacecraft. Here we report new analyses of the probe data that use a corrected treatment of the timing errors, adopt the measured^ 4 (rather than predicted) Descent Trajectory, and incorporate a new calibration of the instrumentation that takes into account the unexpectedly high temperatures encountered by the probe. We determine wind speeds at the cloud tops (700-mbar level) in the range 80–100 m s^−1, in agreement with the results of cloud tracking; the speed increases dramatically between 1 and 4 bar, and then remains nearly constant at ∼170 m s^−1down to the 21-bar level. The increase in wind speed implies a latitudinal density gradient of 0.5% per degree in the 1–2 bar altitude range, but whether these winds are driven by internal heat or absorbed sunlight remains uncertain.