In 1983, Divine presented a comprehensive model of the Jovian charged particle environment that has long served as a reference for missions to Jupiter. However, in situ observations by Galileo and ...synchrotron observations from Earth indicate the need to update the model in the inner radiation zone. Specifically, a review of the model for 1 MeV < E < 100 MeV trapped electrons suggests that, based on the new synchrotron observations, the pitch angle distributions within L < 4 need to be updated by introducing two additional components: one near the Jovian magnetic equator and one at high magnetic latitudes. We report modifications to the model that reproduce these observations. The new model improves the fit to synchrotron emission observations and remains consistent with the original fit to the in situ Pioneer and Voyager data. Further modifications incorporating observations from the Galileo and Cassini spacecraft will be reported in the future.
High-energy, trapped electron and proton environments around the outer planets can pose a serious threat to spacecraft operations. For example, high-energy electrons are a critical source for a ...phenomenon called internal electrostatic discharge (IESD) which is believed to be the number one cause of spacecraft anomalies in the space radiation environment. Several missions are being considered by NASA that will go to the outer planets (Jupiter, Saturn, Uranus, and Neptune). Indeed, NASA currently has plans to send two spacecraft to Jupiter: one as an orbiter that will perform multiple flybys of Europa and another as a Europa Lander. Of the mission concepts selected for the latest New Frontier Competition, one is to visit Titan, the largest moon of Saturn. Similarly, NASA also has identified missions to Uranus and/or Neptune as potential flagship missions in the last decadal survey. For all of these missions, radiation dose and IESD are potentially critical design parameters. Understanding the trapped election and proton environments at these planets to be able to specify the radiation and IESD design environments for them is an important prerequisite in mitigating these potential hazards. In this paper, we will compare the trapped high-energy electron (<inline-formula> <tex-math notation="LaTeX">E > 1 </tex-math></inline-formula> MeV) and proton (<inline-formula> <tex-math notation="LaTeX">E > 5 </tex-math></inline-formula>-10 MeV) environments at Jupiter, Saturn, Uranus, and Neptune to that at the earth using the latest trapped particle models developed at JPL: GIRE3 for Jupiter, SATRAD for Saturn, UMOD for Uranus, and NMOD for Neptune. The global structure of the electron and proton belts and the dose profiles for possible mission scenarios will be presented and compared.
MOST northern Europeans have only the normal M form of the plasma protease inhibitor α1,-antitrypsin, but some 4% are heterozygotes for the Z deficiency variant1. For reasons that have not been ...well-understood, the Z mutation results in a blockage in the final stage of processing of antitrypsin in the liver2such that in the Z homozygote only 15% of the protein is secreted into the plasma. The 85% of the α1, -antitrypsin that is not secreted accumulates in the endoplasmic reticulum of the hepatocyte; much of it is degraded but the remainder aggregates to form insoluble intracellular inclusions. These inclusions are associated with hepatocellular damage, and 10% of newborn Z homozygotes develop liver disease which often leads to a fatal childhood cirrhosis. Here we demonstrate the molecular pathology underlying this accumulation and describe how the Z mutation in antitrypsin results in a unique molecular interaction between the reactive centre loop of one molecule and the gap in the A-sheet of another. This loop–sheet polymerization of Z antitrypsin occurs spontaneously at 37 °C and is completely blocked by the insertion of a specific peptide into the A-sheet of the antitrypsin molecule. Z antitrypsin polymerized in vitro has identical properties and ultra-structure to the inclusions isolated from hepatocytes of a Z homozygote. The concentration and temperature dependence of this loop–sheet polymerization has implications for the management of the liver disease of the newborn Z homozygote.
A two-stage mission to place a spacecraft (SC) below the Jovian radiation belts, using a spinning bare tether with plasma contactors at both ends to provide propulsion and power, is proposed. Capture ...by Lorentz drag on the tether, at the periapsis of a barely hyperbolic equatorial orbit, is followed by a sequence of orbits at near-constant periapsis, drag finally bringing the SC down to a circular orbit below the halo ring. Although increasing both tether heating and bowing, retrograde motion can substantially reduce accumulated dose as compared with prograde motion, at equal tether-to-SC mass ratio. In the second stage, the tether is cut to a segment one order of magnitude smaller, with a single plasma contactor, making the SC to slowly spiral inward over several months while generating large onboard power, which would allow multiple scientific applications, including in situ study of Jovian grains, auroral sounding of upper atmosphere, and space- and time-resolved observations of surface and subsurface.
Hubble Asteroid Hunter García-Martín, Pablo; Kruk, Sandor; Popescu, Marcel ...
Astronomy and astrophysics (Berlin),
03/2024, Letnik:
683
Journal Article
Recenzirano
Odprti dostop
Context . Determining the size distribution of asteroids is key to understanding the collisional history and evolution of the inner Solar System. Aims . We aim to improve our knowledge of the size ...distribution of small asteroids in the main belt by determining the parallaxes of newly detected asteroids in the Hubble Space Telescope (HST) archive and subsequently their absolute magnitudes and sizes. Methods . Asteroids appear as curved trails in HST images because of the parallax induced by the fast orbital motion of the spacecraft. Taking into account the trajectory of this latter, the parallax effect can be computed to obtain the distance to the asteroids by fitting simulated trajectories to the observed trails. Using distance, we can obtain the absolute magnitude of an object and an estimation of its size assuming an albedo value, along with some boundaries for its orbital parameters. Results . In this work, we analyse a set of 632 serendipitously imaged asteroids found in the ESA HST archive. Images were captured with the ACS/WFC and WFC3/UVIS instruments. A machine learning algorithm (trained with the results of a citizen science project) was used to detect objects in these images as part of a previous study. Our raw data consist of 1031 asteroid trails from unknown objects, not matching any entries in the Minor Planet Center (MPC) database using their coordinates and imaging time. We also found 670 trails from known objects (objects featuring matching entries in the MPC). After an accuracy assessment and filtering process, our analysed HST asteroid set consists of 454 unknown objects and 178 known objects. We obtain a sample dominated by potential main belt objects featuring absolute magnitudes (H) mostly between 15 and 22 mag. The absolute magnitude cumulative distribution log N ( H > H 0 ) ∝ α log( H 0 ) confirms the previously reported slope change for 15 < H < 18, from α ≈ 0.56 to α ≈ 0.26, maintained in our case down to absolute magnitudes of around H ≈ 20, and therefore expanding the previous result by approximately two magnitudes. Conclusions . HST archival observations can be used as an asteroid survey because the telescope pointings are statistically randomly oriented in the sky and cover long periods of time. They allow us to expand the current best samples of astronomical objects at no extra cost in regard to telescope time.
Recent measurements of the high-energy, omni-directional electron environment by the Galileo spacecraft Energetic Particle Detector (EPD) have been analyzed in the range from 7 to 28 Jupiter radii. ...10-min averages of these data between Jupiter orbit insertion in 1995 to the end of the mission have been analyzed to provide estimates of the electron differential fluxes at 1.5, 2, and 11 MeV in the jovian equatorial plane as a function of radial distance. These data provide a long term picture of the variations in the high-energy electron environment over the ∼8 years of the Galileo mission. This paper reviews those measurements and the statistics associated with them for the 8 year period. In general, the data variations are well behaved with variations being within a factor of ∼2 of a median value at a given distance from Jupiter. These results are analyzed in detail and the orbit variations discussed in the context of the overall data set. The results of this analysis of the long-term statistical variations in high-energy electron fluxes are directly applicable to models that estimate the effects of the radiation environment on Jupiter's moons and their atmospheres as they permit estimates of the possible range of radiation effects that might be expected.
We present an empirical model of Jupiter's electron radiation environment and its application to the design of the future NASA mission to Europa. The model is based on data from the Galileo ...spacecraft. Measurements of the high-energy, omni-directional electrons from the Energetic Particle Detector (EPD) and magnetic field from the Magnetometer (MAG) onboard Galileo are used for this purpose. Ten-minute averages of the EPD data are used to provide an omni-directional electron flux spectrum at 0.238, 0.416, 0.706, 1.5, 2.0, and 11.0 MeV. Additionally, data from the Geiger Tube Telescope onboard Pioneer 10 and 11 are used to calculate the flux of 31 MeV electrons. The Galileo Interim Radiation Electron model v.2 (GIRE2) combines these datasets with the original Divine model and synchrotron observations to estimate the trapped electron radiation environment. Unlike the original Divine model, which was based on flybys of the Voyager and Pioneer spacecraft, the new GIRE2 model covers about 7 years of data and more than 30 orbits around Jupiter from the Galileo spacecraft. The model represents a step forward in the study of the Jovian radiation environment and is a valuable tool to assist in the design of future missions to Jupiter. This paper gives an overview of GIRE2 and focuses on its application to the design of the future NASA mission to Europa. The spacecraft will orbit Jupiter and perform multiple flybys of the moon Europa, which is embedded in the middle of a very strong radiation environment. The radiation environment surrounding the moon as well as along the trajectory are described in the paper together with the implications of this environment on the design of a mission.
A well-known concern for polar orbiting spacecraft at the Earth is spacecraft charging due to the aurora. Studies of Jupiter reveal the presence of a variety of similar auroral phenomena. In ...particular, three regions have been identified-a narrow auroral zone at high latitudes, a complex and variable environment over the poles, and auroralike features associated with the main jovian moons and their magnetic flux tubes. These auroral structures are, like their earthly counterparts, expected to be sources of charging. This paper reviews the observational data and models of the jovian aurora zone and polar regions. In combination with models of the jovian plasma environment, the ambient charging currents are then computed with the intention of providing realistic estimates of spacecraft potentials at Jupiter. These are of particular importance to the Juno mission as it is a Jupiter polar orbiter and will pass through the jovian auroral zones near the planet. Of special concern, unlike previous missions to Jupiter, Juno will utilize large solar arrays. While previous missions (e.g., the Voyagers and Galileo) utilized RTGs and were carefully designed to avoid differential surface charging, the Juno mission's solar arrays may make it more sensitive to surface charging. Although the jovian aurora is a possibly serious threat to Juno and similar missions, as will be discussed, an understanding of the environment and proper mitigation techniques should limit their effects.
The WFPC2 was installed in the Hubble Space Telescope (HST) in 1993 December. Since then, the instrument has been providing high-quality images. A significant amount of calibration data has been ...collected to aid in the understanding of the on-orbit performance of the instrument. Generally, the behavior of the camera is similar to its performance during the system-level thermal vacuum test at JPL in 1993 May. Surprises were a significant charge-transfer-efficiency (CTE) problem and a significant growth rate in hot pixels at the original operating temperature of the CCDs (– 76 °C). The operating temperature of the WFPC2 CCDs was changed to –88 °C on 1994 April 23, and significant improvements in CTE and hot pixels are seen at this temperature. In this paper we describe the on-orbit performance of the WFPC2. We discuss the optical and thermal history, the instrument throughput and stability, the PSF, the effects of undersampling on photometry, the properties of cosmic rays observed on-orbit, and the geometric distortion in the camera. We present the best techniques for the reduction of WFPC2 data, and describe the construction of calibration products including superbiases, superdarks, and flat fields.
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