The lunar-solar effect on the orbital lifetimes of artificial satellites with highly eccentric orbits
Lunar solar perturbation effect on orbital lifetimes of artificial satellites with highly eccentric orbits
GRAVITATIONAL EFFECT↗
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Relativistic Electron Beams Accelerated By an Interplanetary Shock
Context: Collisionless shock waves have long been considered to be among the most prolific particle accelerators in the universe. Shocks alter the plasma they propagate through, and often exhibit complex evolution across multiple scales. Interplanetary (IP) traveling shocks have been recorded in situ for over half a century and act as a natural laboratory for experimentally verifying various aspects of large-scale collisionless shocks. A fundamentally interesting problem in both heliophysics and astrophysics is the acceleration of electrons to relativistic energies (> 300 keV) by traveling shocks. Aims: The reason for an incomplete understanding of electron acceleration at IP shocks is due to scale-related challenges and a lack of instrumental capabilities. This Letter presents the first observations of field-aligned beams of relativistic electrons upstream of an IP shock, observed thanks to the instrumental capabilities of Solar Orbiter. This study presents the characteristics of the electron beams close to the source and contributes to the understanding of their acceleration mechanism. Methods: On 25 July 2022, Solar Orbiter encountered an IP shock at 0.98 AU. The shock was associated with an energetic storm particle event, which also featured upstream field-aligned relativistic electron beams observed 14 min prior to the actual shock crossing. The distance of the beam’s origin was investigated using a velocity dispersion analysis (VDA). Peak-intensity energy spectra were analyzed and compared with those obtained from a semi-analytical fast-Fermi acceleration model. Results: By leveraging Solar Orbiter’s high temporal resolution Energetic Particle Detector (EPD), we successfully showcase an IP shock’s ability to accelerate relativistic electron beams. Our proposed acceleration mechanism offers an explanation for the observed electron beam and its characteristics, while we also explore the potential contributions of more complex mechanisms.
acceleration of particles↗
The effect of atmospheric drag on the design of solar-cell power systems for low Earth orbit
The feasibility of reducing the atmospheric drag of low orbit solar powered satellites by operating the solar-cell array in a minimum-drag attitude, rather than in the conventional Sun pointing attitude was determined. The weights of the solar array, the energy storage batteries, and the fuel required to overcome the drag of the solar array for a range of design life times in orbit were considered. The drag of the array was estimated by free molecule flow theory, and the system weights were calculated from unit weight estimates for 1990 technology. The trailing, minimum drag system was found to require 80% more solar array area, and 30% more battery capacity, the system weights for reasonable life times were dominated by the thruster fuel requirements.
Kyser, A. C.↗
Neptune Orbiters Utilizing Solar and Radioisotope Electric Propulsion
In certain cases, Radioisotope Electric Propulsion (REP), used in conjunction with other propulsion systems, could be used to reduce the trip times for outer planetary orbiter spacecraft. It also has the potential to improve the maneuverability and power capabilities of the spacecraft when the target body is reached as compared with non-electric propulsion spacecraft. Current missions under study baseline aerocapture systems to capture into a science orbit after a Solar Electric Propulsion (SEP) stage is jettisoned. Other options under study would use all REP transfers with small payloads. Compared to the SEP stage/Aerocapture scenario, adding REP to the science spacecraft as well as a chemical capture system can replace the aerocapture system but with a trip time penalty. Eliminating both the SEP stage and the aerocapture system and utilizing a slightly larger launch vehicle, Star 48 upper stage, and a combined REP/Chemical capture system, the trip time can nearly be matched while providing over a kilowatt of science power reused from the REP maneuver. A Neptune Orbiter mission is examined utilizing single propulsion systems and combinations of SEP, REP, and chemical systems to compare concepts.
Fiehler, Douglas I.↗
A Comparison of Structurally Connected and Multiple Spacecraft Interferometers
Structurally connected and multiple spacecraft interferometers are compared in an attempt to establish the maximum baseline (referred to as the "cross-over baseline") for which it is preferable to operate a single-structure interferometer in space rather than an interferometer composed of numerous, smaller spacecraft. This comparison is made using the total launched mass of each configuration as the comparison metric. A framework of study within which structurally connected and multiple spacecraft interferometers can be compared is presented in block diagram form. This methodology is then applied to twenty-two different combinations of trade space parameters to investigate the effects of different orbits, orientations, truss materials, propellants, attitude control actuators, onboard disturbance sources, and performance requirements on the cross-over baseline. Rotating interferometers and the potential advantages of adding active structural control to the connected truss of the structurally connected interferometer are also examined. The minimum mass design of the structurally connected interferometer that meets all performance-requirements and satisfies all imposed constraints is determined as a function of baseline. This minimum mass design is then compared to the design of the multiple spacecraft interferometer. It is discovered that the design of the minimum mass structurally connected interferometer that meets all performance requirements and constraints in solar orbit is limited by the minimum allowable aspect ratio, areal density, and gage of the struts. In the formulation of the problem used in this study, there is no advantage to adding active structural control to the truss for interferometers in solar orbit. The cross-over baseline for missions of practical duration (ranging from one week to thirty years) in solar orbit is approximately 400 m for non-rotating interferometers and 650 m for rotating interferometers.
Surka, Derek M.↗
Testing for Dark Matter Trapped in the Solar System
We consider the possibility of dark matter trapped in the solar system in bound solar orbits. If there exist mechanisms for dissipating excess kinetic energy by an amount sufficient for generating bound solar orbits, then trapping of galactic dark matter might have taken place during formation of the solar system, or could be an ongoing process. Possible locations for acumulation of trapped dark matter are orbital resonances with the planets or regions in the outer solar system. It is posible to test for the presence of unseen matter by detecting its gravitational effects. Current results for dynamical limits obtained from analyses of planetary ephemeris data and spacecraft tracking data are presented. Possible future improvements are discussed.
dark matter bound solar orbits galactic dark matte↗
Optimization of a solar-electric-propulsion planetary orbiter spacecraft.
Solar electric propulsion spacecraft design for 1971 Mars orbital rendezvous, optimizing net spacecraft mass with respect to several constraints
Sauer, C. G., Jr.↗
Effects of solar radiation pressure on the orbit of the Solar Power Satellite
The surface area-to-weight ratio of the Solar Power Satellite (SPS) is of the order of sq m/kg. Therefore, solar radiation pressure will be an important perturbation on the orbit, causing large variations in eccentricity. An analytical solution is developed for the motion of eccentricity and the line of apsides. Included is a secular term due to the earth's orbital eccentricity. Several initial conditions are considered. For some cases, the eccentricity is nearly constant over a few years. General characteristics of the motion are discussed. Long-term (30 years) effects of gravity are investigated by using a numerical integration method. Eccentricities of approximately 0.08 can be expected for uncorrected SPS orbits.
Graf, O. F., Jr.↗
Shielding materials for highly penetrating space radiations
Interplanetary travel involves the transfer from an Earth orbit to a solar orbit. Once outside the Earth's magnetosphere, the major sources of particulate radiation are solar cosmic rays (SCR's) and galactic cosmic rays (GCR's). Intense fluxes of SCR's come from solar flares and consist primarily of protons with energies up to 1 GeV. The GCR consists of a low flux of nuclei with energies up to 10(exp 10) GeV. About 70 percent of the GCR are protons, but a small amount (0.6 percent) are nuclei with atomic numbers greater than 10. High energy charged particles (HZE) interact with matter by transferring energy to atomic electrons in a Coulomb process and by reacting with an atomic nucleus. Energy transferred in the first process increases with the square of the atomic number, so particles with high atomic numbers would be expected to lose large amounts of energy by this process. Nuclear reactions produced by (HZE) particles produce high-energy secondary particles which in turn lose energy to the material. The HZE nuclei are a major concern for radiation protection of humans during interplanetary missions because of the very high specific ionization of both primary and secondary particles. Computer codes have been developed to calculate the deposition of energy by very energetic charged particles in various materials. Calculations show that there is a significant buildup of secondary particles from nuclear fragmentation and Coulomb dissociation processes. A large portion of these particles are neutrons. Since neutrons carry no charge, they only lose energy by collision or reaction with a nucleus. Neutrons with high energies transfer large amounts of energy by inelastic collisions with nuclei. However, as the neutron energy decreases, elastic collisions become much more effective for energy loss. The lighter the nucleus, the greater the fraction of the neutron's kinetic energy that can be lost in an elastic collision. Thus, hydrogen-containing materials such as polymers are most effective in reducing the energy of neutrons. Once neutrons are reduced to very low energies, the probability for undergoing a reaction with a nucleus (the cross section) becomes very high. The product of such a reaction is often radioactive and can involve the release of a significant amount of energy. Thus, it is important to provide protection from low energy neutrons during a long duration space flight. Among the light elements, lithium and boron each have an isotope with a large thermal neutron capture cross section, Li-6 and B-10. However, B-10 is more abundant in the naturally-occurring element than Li-6, has a thermal neutron capture cross section four times that of Li-6, and produces the stable products, He-4 and Li-7 in the interaction while Li-6 produces radioactive tritium (H-3). Thus, boron is the best light-weight material for thermal neutron absorption in spacecraft. The work on this project was focused in two areas: computer design where existing computer codes were used, and in some cases modified, to calculate the propagation and interactions of high energy charged particles through various media, and materials development where boron was incorporated into high performance materials.
Kiefer, Richard L.↗
Effect of an oxygen plasma on uncoated thin aluminum reflecting films
Thin aluminum films were considered for use as a reflective surface for solar collectors on orbiting solar dynamic power systems. A matter of concern is the durability of such reflective coatings against oxidative attack by highly reactive neutral atomic oxygen, which is the predominate chemical specie in low Earth orbit. Research to date was aimed at evaluating the protective merit of thin dielectric coatings over the aluminum or other reflective metals. However, an uncoated aluminum reflector may self-protect by virtue of the oxide formed from its exposed surface, which constitutes a physical barrier to further oxidation. This possibility was investigated, and an attempt was made to characterize the effects of atomic oxygen on thin Al films using photomicrographs, scanning electron microscopy, spectrophotometry, Auger analysis, and mass measurements. Data collected in a parallel effort is discussed for its comparative value. The results of the investigation of uncoated aluminum supported the self-protection hypothesis, and importantly, it was found that long term specular reflectance for uncoated aluminum exceeded that of Al and Ag reflectors with dielectric coatings.
Parsons, Roger L.↗
Analysis of Cislunar Transfers Departing from a Near Rectilinear Halo Orbit Using Solar Electric Propulsion
An analysis is completed to support the design of optimized trajectories of a massive spacecraft from an L2 Southern NRHO to a Distant Retrograde Orbit and a L2 Northern NRHO using a Solar Electric Propulsion System (SEP). An optimized trajectory is developed for each transfer for a 54t spacecraft utilizing a 26.6kW SEP system. A parameterization is developed for each reference transfer to allow analysis of the sensitivity of the trajectory to changes in vehicle mass, SEP power, and Ion Propulsion System (IPS) performance. Required Dv for each transfer is characterized by the initial acceleration of the spacecraft, thus allowing trajectories to be assessed over a wide range of vehicle mass and SEP power inputs. This approach is shown to be useful in identifying optimal IPS configurations for minimizing propellant requirements for the reference transfers. Additionally, the analysis identifies regions where increases in SEP power do not immediately result in a corresponding decrease in required propellant as well as highlights the relative sensitivities of propellant requirements to changes in IPS thrust and specific impulse.
low thrust↗
A spectrometer for observations of the solar extreme ultraviolet from the OSO-I satellite
EUV solar spectrometer in orbiting solar observatory /OSO-1/, describing satellite, optics and detector, data coding, etc
Behring, W. E.↗
Astrophysics
The instrumentation, accomplishments and future activities in space astrophysics observations are explored. The Solrad, Orbiting Solar Observatory, Solar Maximum Mission, Orbiting Astronomical Observatory, Extreme Ultraviolet Explorer, Uhuru, HEAO-2, IRAS and ESA SAS spacecraft missions and data are summarized. Observations which identified the black hole in Cygnus-1 are described and known gravity-controlled phenomena in the universe are reviewed. Observations at different electromagnetic wavelengths and by particle detectors are outlined, and proposed gravity wave and neutrino detectors are discussed. The implications of the angular, spectral and temporal resolution, polarization, spectral range and observational limits of the instrumentation and data are considered. Current topics of interest in studies of the cosmic background radiation, distance scales, quasars and pulsars, star formation, and coronal heating are outlined. Finally, the design features and observational goals of the NASA Great Observatories space platforms are described.
Gilman, David A.↗
Near-Term Interstellar Sailing
A number of techniques are investigated that allow the possibility of near- ecliptic exploration beyond the Sun's heliopause (200 AU) using contemporary solar-sail spacecraft (with areal mass thickness about 0.0082 kilograms per square meters). Maximum mission duration to the heliopause was defined as one human working lifetime; missions to the Sun's gravity focus at 550 AU from the sun must take less time than one human lifetime. Options include unfurling the sail at the 0.2-AU perihelion of a parabolic solar orbit, unfurling the sail at the 0.2-AU perihelion of a 2.5-AU aphelion solar orbit, and performing a grazing gravity-assist flyby of Jupiter. Although these techniques are capable of performing the defined mission, higher-technology sails are faster.
Matloff, Gregory L.↗
Solar flare hazard to earth-orbiting vehicles
Solar flare hazard to earth orbiting vehicles
RADIATION HAZARD↗
High intensity solar irradiation testing of UV optics
The Orbiting Solar Observatory-I (OSO-8 in orbit) incorporates two high resolution solar pointing spectrometers operating from 1000 A to 4000 A. Energy from the sun enters a Cassegrainian telescope and is focused on a slit while the solar disk is scanned to one arc-second resolution. The stability of the secondary mirrors reflectance was of concern since they would be exposed to intense focused solar energy up to 27 suns. A test program was initiated to simulate this energy input on sample UV mirrors of the MgF2 and LiF types and to evaluate their performance after irradiation. Tests were conducted to simulate the solar spectrum at high intensities (25 suns) and at a single wavelength near Lyman-alpha, but with twenty times the solar intensity at Lyman-alpha. Post-test measurements after every exposure were made at wavelengths from 1025 A to 1849 A. After 75 simulated 'orbits', reflectance changes due to temperature effects were noted to be less than 10%. Reductions in reflectance under high intensity solar radiation were generally greater than 10%. Polymerization of surface contaminations on the LiF mirrors reduced reflectances at short wavelengths by 40%.
Greyerbiehl, J. M.↗
Nuclear electric power and propulsion system for earth orbital and solar system exploration applications
This paper discusses the design of a Nuclear Electric Propulsion (NEP) system, selection of thrusters and propellant. Outer planet exploration requirements are compared to earth orbital power requirements and a nuclear electric power system with a power level of 200 to 250 kWe is recommended. Current technology appears capable of accomplishing the early missions and growth potential exists for accomplishing more difficult later missions without significant changes in the basic system.
Phillips, W. M.↗
The Road to Launch and Operations of the Spitzer Space Telescope
Spitzer Space Telescope, the fourth and final of NASA's Great Observatories, and the cornerstone to NASA's Origins Program, launched on 25 August 2003 into an Earth-trailing solar orbit to acquire infrared observations from space. Spitzer has an 85cm diameter beryllium telescope, which operates near absolute zero utilizing a liquid helium cryostat for cooling the telescope. The helium cryostat, though designed for a 2.5 year lifetime, through creative planning now has an expected lifetime of 5.5 years. Spitzer has completed its in-orbit checkout/science verification phases and the first two years of nominal operations, becoming the first mission to execute astronomical observations from a solar orbit. Spitzer was designed to probe and explore the universe in the infrared utilizing three state of the art detector arrays providing imaging, photometry, and spectroscopy over the 3-160 micron wavelength range...
infrared↗