The Experts below are selected from a list of 9435 Experts worldwide ranked by ideXlab platform
D.e. Smith - One of the best experts on this subject based on the ideXlab platform.
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summary of the results from the Lunar Orbiter laser altimeter after seven years in Lunar Orbit
Icarus, 2017Co-Authors: D.e. Smith, M S Robinson, Gregory A Neumann, Maria T Zuber, E Mazarico, F G Lemoine, J W Head, Paul G Lucey, O Aharonson, Xiaoli SunAbstract:In June 2009 the Lunar Reconnaissance Orbiter (LRO) spacecraft was launched to the Moon. The payload consists of 7 science instruments selected to characterize sites for future robotic and human missions. Among them, the Lunar Orbiter Laser Altimeter (LOLA) was designed to obtain altimetry, surface roughness, and reflectance measurements. The primary phase of Lunar exploration lasted one year, following a 3-month commissioning phase. On completion of its exploration objectives, the LRO mission transitioned to a science mission. After 7 years in Lunar Orbit, the LOLA instrument continues to map the Lunar surface. The LOLA dataset is one of the foundational datasets acquired by the various LRO instruments. LOLA provided a high-accuracy global geodetic reference frame to which past, present and future Lunar observations can be referenced. It also obtained high-resolution and accurate global topography that were used to determine regions in permanent shadow at the Lunar poles. LOLA further contributed to the study of polar volatiles through its unique measurement of surface brightness at zero phase, which revealed anomalies in several polar craters that may indicate the presence of water ice. In this paper, we describe the many LOLA accomplishments to date and its contribution to Lunar and planetary science.
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free space laser communication experiments from earth to the Lunar reconnaissance Orbiter in Lunar Orbit
Optics Express, 2013Co-Authors: Donald R. Skillman, Ronald S. Zellar, Jan F. Mcgarry, Evan D Hoffman, Wai H Fong, Michael A. Krainak, Gregory A Neumann, D.e. SmithAbstract:Laser communication and ranging experiments were successfully conducted from the satellite laser ranging (SLR) station at NASA Goddard Space Flight Center (GSFC) to the Lunar Reconnaissance Orbiter (LRO) in Lunar Orbit. The experiments used 4096-ary pulse position modulation (PPM) for the laser pulses during one-way LRO Laser Ranging (LR) operations. Reed-Solomon forward error correction codes were used to correct the PPM symbol errors due to atmosphere turbulence and pointing jitter. The signal fading was measured and the results were compared to the model.
B S Robinson - One of the best experts on this subject based on the ideXlab platform.
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the Lunar laser communication demonstration nasa s first step toward very high data rate support of science and exploration missions
Space Science Reviews, 2014Co-Authors: Don M Boroson, B S RobinsonAbstract:Future NASA missions for both Science and Exploration will have needs for much higher data rates than are presently available, even with NASA’s highly-capable Space- and Deep-Space Networks. As a first step towards this end, for one month in late 2013, NASA’s Lunar Laser Communication Demonstration (LLCD) successfully demonstrated for the first time high-rate duplex laser communications between a satellite in Lunar Orbit, the Lunar Atmosphere and Dust Environment Explorer (LADEE), and multiple ground stations on the Earth. It constituted the longest-range laser communication link ever built and demonstrated the highest communication data rates ever achieved to or from the Moon.
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the Lunar laser communication demonstration nasa s first step toward very high data rate support of science and exploration missions
Springer Netherlands, 2014Co-Authors: Don M Boroson, B S RobinsonAbstract:Future NASA missions for both Science and Exploration will have needs for much higher data rates than are presently available, even with NASA’s highly-capable Space- and Deep-Space Networks. As a first step towards this end, for one month in late 2013, NASA’s Lunar Laser Communication Demonstration (LLCD) successfully demonstrated for the first time high-rate duplex laser communications between a satellite in Lunar Orbit, the Lunar Atmosphere and Dust Environment Explorer (LADEE), and multiple ground stations on the Earth. It constituted the longest-range laser communication link ever built and demonstrated the highest communication data rates ever achieved to or from the Moon.
I Y Vasko - One of the best experts on this subject based on the ideXlab platform.
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hot ion flows in the distant magnetotail artemis observations from Lunar Orbit to 200 re
Journal of Geophysical Research, 2017Co-Authors: A V Artemyev, V Angelopoulos, A Runov, I Y VaskoAbstract:Plasma energization in Earth's magnetotail is supported by acceleration processes in (and around) magnetic reconnection regions. Hot plasma flows and strong electromagnetic waves, generated by magnetic energy release during reconnection, transport energy necessary for current system intensification and particle acceleration in the inner magnetosphere. Earth's magnetotail configuration includes two main reconnection regions (X lines): the near-Earth X line, which has been well studied by several multispacecraft missions, and the distant X line, which has been much less investigated. In this paper, we utilize the unique data set gathered by two ARTEMIS spacecraft in 2010 at radial distances between Lunar Orbit and ∼200 RE (Earth radii). We identify an X line at around ∼80 RE and collect statistics on hot plasma flows observed around and beyond this distance. Ion spectra within these flows are well fitted by a power law with the exponential tail starting above an energy ϵ0∼ 2–5 keV. Assuming that these spectra are originated at the distant X line, we examine the characteristics of the acceleration at the distant tail reconnection region.
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earth s distant magnetotail current sheet near and beyond Lunar Orbit
Journal of Geophysical Research, 2015Co-Authors: I Y Vasko, A V Artemyev, A A Petrukovich, R Nakamura, L M ZelenyiAbstract:We analyze the structure of the Earth magnetotail current sheet (CS) in middle, X∈[−50,−20] RE, and distant, X∈[−100,−80] RE, regions using data set of 573 CS crossings by Geotail in 1994–1995. For a subset of 213 CSs we determine the CS thickness L, average current density j0, and velocity vD=j0/en0 (n0 is the ion number density). We find similar dawn-dusk distributions of CS parameters for middle and distant tail: L is about 3000 km at the dusk flank and grows up to 12,000 km toward the dawn flank; j0 grows toward the dusk flank by a factor of 2–3; and the most intense CSs (with higher vD) are observed near midnight. We show that ion-scale CSs with the thickness of several ion thermal gyroradii (say less than seven) are observed in middle and distant tail in more than 50% of crossings. For observed CSs electrons likely provide the dominant contribution to the current density. We divide the subset into intense and weak CSs (using parameter vD). Weak CSs have thickness of about 20 ion thermal gyroradii and Bz of about 1.5 nT. Intense CSs have thickness of about 3–7 thermal gyroradii and much smaller Bz implying more stretched field line configuration. Intense CSs are accompanied by fast ion flows: vD is larger for larger amplitudes of ion bulk velocity vx that is likely due to larger contribution of Speiser ions. The properties of the CS in middle and distant tail are compared with those found for the near-Earth tail.
A V Artemyev - One of the best experts on this subject based on the ideXlab platform.
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hot ion flows in the distant magnetotail artemis observations from Lunar Orbit to 200 re
Journal of Geophysical Research, 2017Co-Authors: A V Artemyev, V Angelopoulos, A Runov, I Y VaskoAbstract:Plasma energization in Earth's magnetotail is supported by acceleration processes in (and around) magnetic reconnection regions. Hot plasma flows and strong electromagnetic waves, generated by magnetic energy release during reconnection, transport energy necessary for current system intensification and particle acceleration in the inner magnetosphere. Earth's magnetotail configuration includes two main reconnection regions (X lines): the near-Earth X line, which has been well studied by several multispacecraft missions, and the distant X line, which has been much less investigated. In this paper, we utilize the unique data set gathered by two ARTEMIS spacecraft in 2010 at radial distances between Lunar Orbit and ∼200 RE (Earth radii). We identify an X line at around ∼80 RE and collect statistics on hot plasma flows observed around and beyond this distance. Ion spectra within these flows are well fitted by a power law with the exponential tail starting above an energy ϵ0∼ 2–5 keV. Assuming that these spectra are originated at the distant X line, we examine the characteristics of the acceleration at the distant tail reconnection region.
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ion density and temperature profiles along xgsm and across zgsm the magnetotail as observed by themis geotail and artemis
Journal of Geophysical Research, 2017Co-Authors: A V Artemyev, V Angelopoulos, Heli Hietala, A Runov, Iku ShinoharaAbstract:Characteristics of the two-dimensional configuration of the magnetotail current sheet are important for modeling magnetotail motion/evolution and charged particle energization. Because of the magnetotail current sheet's dynamical nature, however, simultaneous plasma and magnetic field measurements at different radial distances are required to reveal this configuration. Simultaneous observations of the magnetotail current sheet from THEMIS D (around 10RE downtail), Geotail (around 30RE downtail), and ARTEMIS P1 (around 55RE downtail) are used to study distributions of plasma (ion) density and temperature along (Earth-Sun direction) and across (north-south direction) the magnetotail. Fourteen events (each including several current sheet crossings at different downtail distances) are studied. We demonstrate that the plasma temperature along and across the magnetotail varies more significantly than plasma density does. The temperature decrease from equatorial plane to current sheet boundaries is a major contributor to the cross tail pressure balance. The Alfven velocity VA,B calculated at the current sheet boundaries increases significantly towards the Earth from 700 km/s at Lunar Orbit ∼55RE to 2200 km/s around ∼10RE downtail. The corresponding energy EA=mpVA,B2(mp is the proton mass) is four times larger than the plasma temperature T0 in the magnetotail's equatorial plane, whereas the ratio EA/T0 is constant along the magnetotail. The plasma temperature T0 measured around Lunar Orbit in the magnetotail agrees well with the simultaneously measured energy of solar wind protons mpVSW2/2(VSW is the solar wind speed).
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earth s distant magnetotail current sheet near and beyond Lunar Orbit
Journal of Geophysical Research, 2015Co-Authors: I Y Vasko, A V Artemyev, A A Petrukovich, R Nakamura, L M ZelenyiAbstract:We analyze the structure of the Earth magnetotail current sheet (CS) in middle, X∈[−50,−20] RE, and distant, X∈[−100,−80] RE, regions using data set of 573 CS crossings by Geotail in 1994–1995. For a subset of 213 CSs we determine the CS thickness L, average current density j0, and velocity vD=j0/en0 (n0 is the ion number density). We find similar dawn-dusk distributions of CS parameters for middle and distant tail: L is about 3000 km at the dusk flank and grows up to 12,000 km toward the dawn flank; j0 grows toward the dusk flank by a factor of 2–3; and the most intense CSs (with higher vD) are observed near midnight. We show that ion-scale CSs with the thickness of several ion thermal gyroradii (say less than seven) are observed in middle and distant tail in more than 50% of crossings. For observed CSs electrons likely provide the dominant contribution to the current density. We divide the subset into intense and weak CSs (using parameter vD). Weak CSs have thickness of about 20 ion thermal gyroradii and Bz of about 1.5 nT. Intense CSs have thickness of about 3–7 thermal gyroradii and much smaller Bz implying more stretched field line configuration. Intense CSs are accompanied by fast ion flows: vD is larger for larger amplitudes of ion bulk velocity vx that is likely due to larger contribution of Speiser ions. The properties of the CS in middle and distant tail are compared with those found for the near-Earth tail.
Gregory A Neumann - One of the best experts on this subject based on the ideXlab platform.
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summary of the results from the Lunar Orbiter laser altimeter after seven years in Lunar Orbit
Icarus, 2017Co-Authors: D.e. Smith, M S Robinson, Gregory A Neumann, Maria T Zuber, E Mazarico, F G Lemoine, J W Head, Paul G Lucey, O Aharonson, Xiaoli SunAbstract:In June 2009 the Lunar Reconnaissance Orbiter (LRO) spacecraft was launched to the Moon. The payload consists of 7 science instruments selected to characterize sites for future robotic and human missions. Among them, the Lunar Orbiter Laser Altimeter (LOLA) was designed to obtain altimetry, surface roughness, and reflectance measurements. The primary phase of Lunar exploration lasted one year, following a 3-month commissioning phase. On completion of its exploration objectives, the LRO mission transitioned to a science mission. After 7 years in Lunar Orbit, the LOLA instrument continues to map the Lunar surface. The LOLA dataset is one of the foundational datasets acquired by the various LRO instruments. LOLA provided a high-accuracy global geodetic reference frame to which past, present and future Lunar observations can be referenced. It also obtained high-resolution and accurate global topography that were used to determine regions in permanent shadow at the Lunar poles. LOLA further contributed to the study of polar volatiles through its unique measurement of surface brightness at zero phase, which revealed anomalies in several polar craters that may indicate the presence of water ice. In this paper, we describe the many LOLA accomplishments to date and its contribution to Lunar and planetary science.
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simultaneous laser ranging and communication from an earth based satellite laser ranging station to the Lunar reconnaissance Orbiter in Lunar Orbit
Proceedings of SPIE, 2013Co-Authors: Donald R. Skillman, Ronald S. Zellar, Jan F. Mcgarry, Evan D Hoffman, Wai H Fong, Leva Mcintire, Frederic M Davidson, Michael A. Krainak, Gregory A Neumann, Maria T ZuberAbstract:We report a free space laser communication experiment from the satellite laser ranging (SLR) station at NASA Goddard Space Flight Center (GSFC) to the Lunar Reconnaissance Orbiter (LRO) in Lunar Orbit through the on board one-way Laser Ranging (LR) receiver. Pseudo random data and sample image files were transmitted to LRO using a 4096-ary pulse position modulation (PPM) signal format. Reed-Solomon forward error correction codes were used to achieve error free data transmission at a moderate coding overhead rate. The signal fading due to the atmosphere effect was measured and the coding gain could be estimated.
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free space laser communication experiments from earth to the Lunar reconnaissance Orbiter in Lunar Orbit
Optics Express, 2013Co-Authors: Donald R. Skillman, Ronald S. Zellar, Jan F. Mcgarry, Evan D Hoffman, Wai H Fong, Michael A. Krainak, Gregory A Neumann, D.e. SmithAbstract:Laser communication and ranging experiments were successfully conducted from the satellite laser ranging (SLR) station at NASA Goddard Space Flight Center (GSFC) to the Lunar Reconnaissance Orbiter (LRO) in Lunar Orbit. The experiments used 4096-ary pulse position modulation (PPM) for the laser pulses during one-way LRO Laser Ranging (LR) operations. Reed-Solomon forward error correction codes were used to correct the PPM symbol errors due to atmosphere turbulence and pointing jitter. The signal fading was measured and the results were compared to the model.
