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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Does the orbit-averaged theory require a scale separation between periodic orbit size and perturbation correlation length?

Using the canonical perturbation theory, we show that the orbit-averaged theory only requires a time-scale separation between equilibrium and perturbed motions and verifies the widely accepted notion that orbit averaging effects greatly reduce the microturbulent transport of energetic particles in a tokamak. Therefore, a recent claim [Hauff and Jenko, Phys. Rev. Lett. 102, 075004 (2009); Jenko et al., ibid. 107, 239502 (2011)] stating that the orbit-averaged theory requires a scale separation between equilibrium orbit size and perturbation correlation length is erroneous.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Symmetry of reentrant tetragonal phase in Ba 1 - x Na x Fe 2 As 2 : Magnetic versus orbital ordering mechanism

Magnetostructural phase transitions in Ba 1-x A x Fe 2 As 2 (A = K, Na) materials are discussed for both magnetically and orbitally driven mechanisms, using a symmetry analysis formulated within the Landau theory of phase transitions. Both mechanisms predict identical orthorhombic space-group symmetries for the nematic and magnetic phases observed over much of the phase diagram, but they predict different tetragonal space-group symmetries for the newly discovered reentrant tetragonal phase in Ba 1-x Na x Fe 2 As 2 (x similar to 0.24-0.28). In a magnetic scenario, magnetic order with moments along the c axis, as found experimentally, does not allow any type of orbital order, but in an orbital scenario, we have determined two possible orbital patterns, specified by P4/mnc1' and I4221' space groups, which do not require atomic displacements relative to the parent I4/mmm1' symmetry and, in consequence, are indistinguishable in conventional diffraction experiments. We demonstrate that the three possible space groups are, however, distinct in resonant x-ray Bragg diffraction patterns created by Templeton & Templeton scattering. This provides an experimental method of distinguishing between magnetic and orbital models.

Khalyavin, D. D.↗
NASA NTRS1992

Orbiter-orbiter and orbiter-lander tracking using same-beam interferometry

Two spacecraft orbiting Mars will subtend a small angle as viewed from Earth. This angle will usually be smaller than the beam width of a single radio antenna. Thus the two spacecraft may be tracked simultaneously by a single Earth-based antenna. The same-beam interferometry (SBI) technique involves using two widely separated antennas, each observing the two spacecraft, to produce a measurement of the angular separation of the two spacecraft in the plane of the sky. The information content of SBI data is thus complementary to the line-of-sight information provided by conventional Doppler data. The inclusion of SBI data with the Doppler data in a joint orbit estimation procedure can desensitize the solution to gravity mismodeling and result in improved orbit determination accuracy. This article presents an overview of the SBI technique, a measurement error analysis, and an error covariance analysis of some examples of the application of SBI to orbit determination. For hypothetical scenarios involving the Mars Observer and the Russian Mars '94 spacecraft, orbit determination accuracy improvements of up to an order of magnitude are predicted, relative to the accuracy that can be obtained by using only Doppler data acquired separately from each spacecraft. Relative tracking between a Mars orbiter and a lander fixed on the surface of Mars is also studied. Results indicate that the lander location may be determined to a few meters, while the orbiter ephemeris may be determined with accuracy similar to the orbiter-orbiter case.

Folkner, W. M.↗
NASA NTRS1973

Space shuttle: Preliminary pressure distributions on the 049 orbiter, orbiter in presence of H/O tank and orbiter in launch configuration

The 049 orbiter and launch configurations were tested in a trisonic wind tunnel to obtain preliminary loads information on the orbiter alone, orbiter in presence of the H/O tank and orbiter in the full launch configuration. The orbiter consisted of the baseline 049 double-delta wing, twin vertical stabilizers, seven degrees of dihedral and included abort rockets. The orbiter was mounted at minus 1.50 degree of incidence (fuselage centerline relative to H/O tank centerline) in the launch configuration. The solid rocket motors were mounted at a radial location of 21 degrees from the horizontal centerline of the H/O tank. The test was conducted over a Mach number range of 0.6 to 4.96. Nominal angle of attack and angle of sideslip ranges of minus 6 to plus 6 degrees were tested. In addition, the orbiter alone was tested over an angle of attack range of minus 6 to plus 26 degrees.

Hamilton, J. T.↗
NASA NTRS1990

Orbiter-orbiter and orbiter-lander tracking using same-beam interferometry

Two spacecraft orbiting Mars may be tracked simultaneously by a single earth-based antenna. Same-beam interferometric techniques, using two widely separated antennas, produce a spacecraft-spacecraft measurement in the plane of the sky, complementary to the line-of-sight Doppler information. This paper presents an overview of the same-beam interferometric measurement technique, a measurement error analysis, and examples of the application of same-beam interferometry to orbit determination. For the case of Mars Observer and the Soviet Mars '94 mission, orbit determination improvement up to an order of magnitude is found. Relative tracking between a Mars orbiter and a lander fixed on the surface of Mars is also studied. The lander location may be determined to a few meters, while the orbiter ephemeris may be determined with accuracy similar to the orbiter-orbiter case.

Folkner, W. M.↗
NASA NTRS1992

Analysis of orbital perturbations acting on objects in orbits near geosynchronous earth orbit

The paper presents a numerical investigation of orbital evolution for objects started in GEO or in orbits near GEO in order to study potential orbital debris problems in this region. Perturbations simulated include nonspherical terms in the earth's geopotential field, lunar and solar gravity, and solar radiation pressure. Objects simulated include large satellites, for which solar radiation pressure is insignificant, and small particles, for which solar radiation pressure is an important force. Results for large satellites are largely in agreement with previous GEO studies that used classical perturbation techniques. The orbit plane of GEO satellites placed in a stable plane orbit inclined approximately 7.3 deg to the equator experience very little precession, remaining always within 1.2 percent of their initial orientation. Solar radiation pressure generates two major effects on small particles: an orbital eccentricity oscillation anticipated from previous research, and an oscillation in orbital inclination.

Friesen, Larry J.↗
DOE OSTI2015

Influence of single particle orbital sets and configuration selection on multideterminant wavefunctions in quantum Monte Carlo

Multideterminant wavefunctions, while having a long history in quantum chemistry, are increasingly being used in highly accurate quantum Monte Carlo calculations. Since the accuracy of QMC is ultimately limited by the quality of the trial wavefunction, multi-Slater determinants wavefunctions offer an attractive alternative to Slater-Jastrow and more sophisticated wavefunction ansatz for several reasons. They can be efficiently calculated, straightforwardly optimized, and systematically improved by increasing the number of included determinants. In spite of their potential, however, the convergence properties of multi-Slater determinant wavefunctions with respect to orbital set choice and excited determinant selection are poorly understood, which hinders the application of these wavefunctions to large systems and solids. In this paper, by performing QMC calculations on the equilibrium and stretched carbon dimer, we find that convergence of the recovered correlation energy with respect to number of determinants can depend quite strongly on basis set and determinant selection methods, especially where there is strong correlation. We demonstrate that properly chosen orbital sets and determinant selection techniques from quantum chemistry methods can dramatically reduce the required number of determinants (and thus the computational cost) to reach a given accuracy, which we argue shows clear need for an automatic QMC-only method for selecting determinants and generating optimal orbital sets.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2014

Maintaining Aura's Orbit Requirements While Performing Orbit Maintenance Maneuvers Containing an Orbit Normal Delta-V Component

The Earth Observing System (EOS) Afternoon Constellation consists of five member missions (GCOM-W1, Aqua, CALIPSO, CloudSat, and Aura), each of which maintain a frozen, sun-synchronous orbit with a 16-day repeating ground track that follows the Worldwide Reference System-2 (WRS-2). Under nominal science operations for Aura, the propulsion system is oriented such that the resultant thrust vector is aligned 13.493 degrees away from the velocity vector along the yaw axis. When performing orbit maintenance maneuvers, the spacecraft performs a yaw slew to align the thrust vector in the appropriate direction. A new Drag Make Up (DMU) maneuver operations scheme has been implemented for Aura alleviating the need for the 13.493 degree yaw slew. The focus of this investigation is to assess the impact that no-slew DMU maneuver operations will have on Aura's Mean Local Time (MLT) which drives the required along track separation between Aura and the constellation members, as well as Aura's frozen orbit properties, eccentricity and argument of perigee. Seven maneuver strategies were analyzed to determine the best operational approach. A mirror pole strategy, with maneuvers alternating at the North and South poles, was implemented operationally to minimize impact to the MLT. Additional analysis determined that the mirror pole strategy could be further modified to include frozen orbit maneuvers and thus maintain both MLT and the frozen orbit properties under noslew operations.

Aqua↗
NASA NTRSDate not supplied

Shadow Chaser: a SmallSat Mission Concept to Measure the Upper Atmosphere of Uranus from Earth Orbit, and Enabling Aerocapture Orbit Insertion Benefits for Uranus Orbiter and Probe

We present the latest design of the Shadow Chaser mission concept that will measure the upper atmosphere of Uranus from Earth orbit using the stellar occultation technique. Upcoming stellar occultations by Uranus represent valuable opportunities to prepare for a potential aerocapture orbit insertion to be incorporated in the Uranus Orbiter and Probe (UOP) Flagship mission, the highest-priority new mission recommended by the 2022 Planetary Science Decadal Survey. An aerocapture maneuver enables faster interplanetary trajectories that do not depend on Jupiter gravity assist, and offer annual launch windows for UOP. However, an aerocapture maneuver’s precision depends on a-priori knowledge of the upper atmosphere, which today primarily comes from the highly uncertain Voyager 2 stellar occultations recently shown to be inconsistent with ground-based occultation measurements during the same era. To improve upper atmospheric characterization, the Shadow Chaser will observe the occultations by Uranus on February 15, 2031, October 9, 2031 and February 6, 2032 from Earth orbit. Together with the occultation on April 8, 2025 (which we are planning to observe from the ground), these events represent the best opportunities to characterize the Uranian upper atmosphere before UOP arrival. We present the Shadow Chaser’s latest spacecraft and measurement design. We will also present results of analyses funded by NASA Space Technology Mission Directorate to establish the viability of aerocapture for UOP, quantify the benefits of reducing Uranian upper atmospheric uncertainties to improve the aerocapture design, and demonstrate that anticipated new stellar occultation data can be incorporated into the engineering design of aerocapture.

Uranus↗