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تسجيل مستخدم جديدExploration of trans-Neptunian objects using the Direct Fusion Drive
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The Direct Fusion Drive (DFD) is a nuclear fusion engine that will provide thrust and electrical power for any spacecraft. It is a compact engine, based on the D -$^{3}$He aneutronic fusion reaction that uses the Princeton field reversed configuration for the plasma confinement and an odd parity rotating magnetic field as heating method to achieve nuclear fusion (Cohen et al., 2019), which will heat the deuterium, also used as propellant. par In this work we present possibilities to explore the solar system outer border using the DFD. The objective is to reach some trans-Neptunian object, such as the dwarf planets Makemake, Eris and Haumea in less than 10 years with a payload mass of at least of 1500 kg, so that it would enable all kind of missions, from scientific observation to in-situ operations. For each mission a thrust-coast-thrust profile is considered. For this reason, each mission is divided into 3 phases: i. the spiral trajectory to escape Earth gravity; ii. the interplanetary travel, from the exit of Earth sphere of influence to the end of the coasting phase; iii. maneuvers to rendezvous with the dwarf planet. Propellant mass consumption, initial and final masses, velocities and $Delta V$ for each maneuver are presented. Calculations to reach a vicinity at 125 AU for the study of Sun magnetosphere as well as Eris via flyby are also presented, with interest on the influence of different acceleration phases. Our calculations show that a spacecraft propelled by DFD will open unprecedented possibilities to explore the border of the solar system, in a limited amount of time and with a very high payload to propellant masses ratio.
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The main purpose of this work is to perform an analysis of realistic new trajectories for a robotic mission to Saturns largest moon, Titan, in order to demonstrate the great advantages related to the Direct Fusion Drive (DFD). The DFD is a D -$^3$He
fuelled, aneutronic, thermonuclear fusion propulsion system. This fusion propulsion concept is based on a magnetically confined field reversed configuration plasma, where the deuterium propellant is heated by fusion products, and then expanded into a magnetic nozzle, providing both thrust and electrical energy to the spacecraft [1]. The trajectories calculations and analysis for the Titan mission are obtained based on the characteristics provided by the PPPL [1]. Two different profile missions are considered: the first one is a thrust-coast-thrust profile with constant thrust and specific impulse; the second scenario is a continuous and constant thrust profile mission. Each mission study is divided into four different phases, starting from the initial low Earth orbit departure, the interplanetary trajectory, Saturn orbit insertion and the Titan orbit insertion. For all mission phases, maneuver time and propellant consumption are calculated. The results of calculations and mission analysis offer a complete overview of the advantages in term of payload mass and travel time. It is important to emphasize that the deceleration capability is one of the DFD game changer: in fact, the DFD performance allows to rapidly reach high velocities and decelerate in even shorter time period. This capability results in a total trip duration of 2.6 years for the thrust-coast-thrust profile and less than 2 years considering the continuous thrust profile. The high payload enabling capability, combined with the huge electrical power available from the fusion reactor, leads to a tremendous advantage compared to present technology.
It is demonstrated that the development of a nuclear fusion rocket engine based on a D $-$ $^{3}$He (Deterium-Helium 3) technology will allow to travel in the solar system and beyond. The Direct Fusion Drive (DFD) is the D $-$ $^{3}$He-fueled, aneutr
onic, thermonuclear fusion propulsion system that is under development at Princeton University Plasma Physics Laboratory [1]. It is considered and analyzed the Earth-Mars mission using the DFD. It is shown that one-way trips to Mars in slightly more than 100 days become possible and also journeys to the asteroid belt will take about 250 days [2]. It is presented an analysis of realistic new trajectories for a robotic mission to Saturns largest moon, Titan, to demonstrate the great advantages related to the thermonuclear DFD. The trajectories calculations and analysis for Saturns largest moon Titan different profile missions are given based on the characteristics of a 2 MW class DFD engine. This capability results in a total trip duration of 2.6 years for the thrust-coast-thrust profile and less than 2 years for the continuous thrust profile [3]. Using the same 2 MW class DFD engine one can reach some trans-Neptunian object, such as the dwarf planets Makemake, Eris, and Haumea in less than 10 years with a payload mass of at least 1500 kg, so that it would enable all kind of missions, from scientific observation to in-situ operations [4]. We consider for each mission a Thrust-Coast-Thrust profile. For this reason, each mission is divided into 3 phases: i. the trajectory to escape Earth gravity influence; ii. the interplanetary travel, from the exit of Earth sphere of influence to the end of the coasting phase; iii. maneuvers to rendezvous with a target object. We present calculations to reach a vicinity at 125 AU.
The thermal emission of transneptunian objects (TNO) and Centaurs has been observed at mid- and far-infrared wavelengths - with the biggest contributions coming from the Spitzer and Herschel space observatories-, and the brightest ones also at sub-mi
llimeter and millimeter wavelengths. These measurements allowed to determine the sizes and albedos for almost 180 objects, and densities for about 25 multiple systems. The derived very low thermal inertias show evidence for a decrease at large heliocentric distances and for high-albedo objects, which indicates porous and low-conductivity surfaces. The radio emissivity was found to be low ($epsilon_r$=0.70$pm$0.13) with possible spectral variations in a few cases. The general increase of density with object size points to different formation locations or times. The mean albedos increase from about 5-6% (Centaurs, Scattered-Disk Objects) to 15% for the Detached objects, with distinct cumulative albedo distributions for hot and cold classicals. The color-albedo separation in our sample is evidence for a compositional discontinuity in the young Solar System. The median albedo of the sample (excluding dwarf planets and the Haumea family) is 0.08, the albedo of Haumea family members is close to 0.5, best explained by the presence of water ice. The existing thermal measurements remain a treasure trove at times where the far-infrared regime is observationally not accessible.
Since 2013, dense and narrow rings are known around the small Centaur object Chariklo and the dwarf planet Haumea. Dense material has also been detected around the Centaur Chiron, although its nature is debated. This is the first time ever that rings
are observed elsewhere than around the giant planets, suggesting that those features are more common than previously thought. The origins of those rings remain unclear. In particular, it is not known if the same generic process can explain the presence of material around Chariklo, Chiron, Haumea, or if each object has a very different history. Nonetheless, a specific aspect of small bodies is that they may possess a non-axisymmetric shape (topographic features and or elongation) that are essentially absent in giant planets. This creates strong resonances between the spin rate of the object and the mean motion of ring particles. In particular, Lindblad-type resonances tend to clear the region around the corotation (or synchronous) orbit, where the particles orbital period matches that of the body. Whatever the origin of the ring is, modest topographic features or elongations of Chariklo and Haumea explain why their rings should be found beyond the outermost 1/2 resonance, where the particles complete one revolution while the body completes two rotations. Comparison of the resonant locations relative to the Roche limit of the body shows that fast rotators are favored for being surrounded by rings. We discuss in more details the phase portraits of the 1/2 and 1/3 resonances, and the consequences of a ring presence on satellite formation.
Context: Accurate measurements of diameters of trans-Neptunian objects are extremely complicated to obtain. Thermal modeling can provide good results, but accurate absolute magnitudes are needed to constrain the thermal models and derive diameters an
d geometric albedos. The absolute magnitude, Hv, is defined as the magnitude of the object reduced to unit helio- and geocentric distances and a zero solar phase angle and is determined using phase curves. Phase coefficients can also be obtained from phase curves. These are related to surface properties, yet not many are known. Aims: Our objective is to measure accurate V band absolute magnitudes and phase coefficients for a sample of trans-Neptunian objects, many of which have been observed, and modeled, within the TNOs are cool program, one of Herschel Space Observatory key projects. Methods: We observed 56 objects using the V and R filters. These data, along with those available in the literature, were used to obtain phase curves and measure V band absolute magnitudes and phase coefficients by assuming a linear trend of the phase curves and considering magnitude variability due to rotational light-curve. Results: We obtained 237 new magnitudes for the 56 objects, six of them with no reported previous measurements. Including the data from the literature we report a total of 110 absolute magnitudes with their respective phase coefficients. The average value of Hv is 6.39, bracketed by a minimum of 14.60 and a maximum of -1.12. In the case of the phase coefficients we report 0.10 mag per degree as the median value and a very large dispersion, ranging from -0.88 up tp 1.35 mag per degree.
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