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NASA NTRS2003

NASA Tech Briefs, September 2003

Topics include: Oxygen-Partial-Pressure Sensor for Aircraft Oxygen Mask; Three-Dimensional Venturi Sensor for Measuring Extreme Winds; Swarms of Micron-Sized Sensors; Monitoring Volcanoes by Use of Air-Dropped Sensor Packages; Capacitive Sensors for Measuring Masses of Cryogenic Fluids; UHF Microstrip Antenna Array for Synthetic- Aperture Radar; Multimode Broad-Band Patch Antennas; 164-GHz MMIC HEMT Frequency Doubler; GPS Position and Heading Circuitry for Ships; Software for Managing Parametric Studies; Software Aids Visualization of Computed Unsteady Flow; Software for Testing Electroactive Structural Components; Advanced Software for Analysis of High-Speed Rolling-Element Bearings; Web Program for Development of GUIs for Cluster Computers; XML-Based Generator of C++ Code for Integration With GUIs; Oxide Protective Coats for Ir/Re Rocket Combustion Chambers; Simplified Waterproofing of Aerogels; Improved Thermal-Insulation Systems for Low Temperatures; Device for Automated Cutting and Transfer of Plant Shoots; Extension of Liouville Formalism to Postinstability Dynamics; Advances in Thrust-Based Emergency Control of an Airplane; Ultrasonic/Sonic Mechanisms for Drilling and Coring; Exercise Device Would Exert Selectable Constant Resistance; Improved Apparatus for Measuring Distance Between Axles; Six Classes of Diffraction-Based Optoelectronic Instruments; Modernizing Fortran 77 Legacy Codes; Active State Model for Autonomous Systems; Shields for Enhanced Protection Against High-Speed Debris; Scaling of Two-Phase Flows to Partial-Earth Gravity; Neutral-Axis Springs for Thin-Wall Integral Boom Hinges.

Source record↗

NASA NTRS2013

Navigation Performance of Global Navigation Satellite Systems in the Space Service Volume

This paper extends the results I reported at this year's ION International Technical Meeting on multi-constellation GNSS coverage by showing how the use of multi-constellation GNSS improves Geometric Dilution of Precision (GDOP). Originally developed to provide position, navigation, and timing for terrestrial users, GPS has found increasing use for in space for precision orbit determination, precise time synchronization, real-time spacecraft navigation, and three-axis attitude control of Earth orbiting satellites. With additional Global Navigation Satellite Systems (GNSS) coming into service (GLONASS, Galileo, and Beidou) and the development of Satellite Based Augmentation Services, it is possible to obtain improved precision by using evolving multi-constellation receiver. The Space Service Volume formally defined as the volume of space between three thousand kilometers altitude and geosynchronous altitude ((is) approximately 36,500 km), with the volume below three thousand kilometers defined as the Terrestrial Service Volume (TSV). The USA has established signal requirements for the Space Service Volume (SSV) as part of the GPS Capability Development Documentation (CDD). Diplomatic efforts are underway to extend Space service Volume commitments to the other Position, Navigation, and Timing (PNT) service providers in an effort to assure that all space users will benefit from the enhanced capabilities of interoperating GNSS services in the space domain.

Force, Dale A.↗

NASA NTRS2015

Combined Global Navigation Satellite Systems in the Space Service Volume

Besides providing position, navigation, and timing (PNT) services to traditional terrestrial and airborne users, GPS is also being increasingly used as a tool to enable precision orbit determination, precise time synchronization, real-time spacecraft navigation, and three-axis attitude control of Earth orbiting satellites. With additional Global Navigation Satellite System (GNSS) constellations being replenished and coming into service (GLONASS, Beidou, and Galileo), it will become possible to benefit from greater signal availability and robustness by using evolving multi-constellation receivers. The paper, "GPS in the Space Service Volume," presented at the ION GNSS 19th International Technical Meeting in 2006 (Ref. 1), defined the Space Service Volume, and analyzed the performance of GPS out to seventy thousand kilometers. This paper will report a similar analysis of the signal coverage of GPS in the space domain; however, the analyses will also consider signal coverage from each of the additional GNSS constellations noted earlier to specifically demonstrate the expected benefits to be derived from using GPS in conjunction with other foreign systems. The Space Service Volume is formally defined as the volume of space between three thousand kilometers altitude and geosynchronous altitude circa 36,000 km, as compared with the Terrestrial Service Volume between 3,000 km and the surface of the Earth. In the Terrestrial Service Volume, GNSS performance is the same as on or near the Earth's surface due to satellite vehicle availability and geometry similarities. The core GPS system has thereby established signal requirements for the Space Service Volume as part of technical Capability Development Documentation (CDD) that specifies system performance. Besides the technical discussion, we also present diplomatic efforts to extend the GPS Space Service Volume concept to other PNT service providers in an effort to assure that all space users will benefit from the enhanced interoperability of GNSS services in the space domain. A separate paper presented at the conference covers the individual GNSS performance parameters for respective Space Service Volumes.

navigation satellites↗

NASA NTRS1997

Torsional Oscillations of the Earths's Core

Torsional oscillations of the Earth's liquid metallic outer core are investigated by diving the core into twenty imaginary e1qui-volume annuli coaxial with the axis of ratation of the Earth and determining temproal fluctuations in the axial component of angular memonetum of each annulus under the assumption of iso-rotation on cylindrical surfaces.

Torsional Oscillations Earth's core↗

NASA NTRS1996

Evidence for Excitation of Polar Motion by Fortnightly Ocean Tides

The second-degree zonal tide raising potential, which is responsible for tidal changes in the Earth's rotation rate and length-of-day, is symmetric about the polar axis and hence can excite the Earth's polar motion only through its action upon nonaxisymmetric features of the Earth such as the oceans. Ocean tidal excitation of polar motion in the diurnal and semidiurnal tidal bands has been previously detected and examined. Here, the detection of ocean tidal excitation of polar motion in the long-period tidal band, specifically at the Mf' (13.63-day) and Mf (13.66-day) tidal frequencies, is reported. Spectra of the SPACE94 polar motion excitation series exhibit peaks at the prograde and retrograde fortnightly tidal periods. After removing effects of atmospheric wind and pressure changes, an empirical model for the effect of the fortnightly ocean tides upon polar motion excitation is obtained by least-squares fitting periodic terms at the Mf and Mf' tidal frequencies to the residual polar motion excitation series. The resulting empirical model is then compared with the predictions of two hydrodynamic ocean tide models.

Gross, Richard S.↗

NASA NTRS1996

(abstract) Effect of Long Period Ocean Tides on the Earth's Rotation

tides oceans diurnal tidal bands Earth's rotation ↗

NASA NTRS1963

Earth Reflected Solar Radiation Incident upon an Arbitrarily Oriented Spinning Flat Plate

A general derivation is given for the earth reflected solar radiation input to a flat plate--a solar cell paddle, for example--which is spinning about an axis coincident with the axis of symmetry of the satellite to which it is affixed. The resulting equations are written for the general case so that arbitrary orientations of the spin axis with respect to the earth-satellite line and arbitrary orientations of the normal to the plate with respect to the spin axis can be treated. No attempt is made to perform the resulting integrations because of the complexity of the equations; nor is there any attempt to delineate the integration limits for the general case. However, the equations governing these limits are given. The appendixes contain: the results, in graphical form, of two representative examples; the general computer program for the calculation is given in Fortran notation; and the results of a calculation of the distribution of albedo energy on the proposed Echo II satellite. The value of the mean solar constant used is 1.395 times 10 (sup 4) ergs per centimeters-squared per second; the mean albedo of the earth is assumed to be 0.34; and the earth is assumed to be a diffuse reflector.

SOLAR RADIATION↗

NASA NTRS1960

Ranger Spacecraft

The thermal-control philosophy of the spacecraft currently under development by the Jet Propulsion Laboratory is design by passive means to maintain all components within the tolerances specified by cognizant engineers. Due to the complexity of the configurations, calculations are) of necessity, fairly generalized and final design is based upon tests in an environmental chamber. The Ranger series spacecraft is designed with a basic structure which is common to all models, with additional hardware to suit the individual mission. This basic structure of Rangers A-1 and A-2 is seen as the hexagonal instrument section, the erectable solar panels, the movable antenna, and the omniantenna. The Ranger A-1 and A-2 configuration is for engineering tests and space-exploration, with the scientific instrumentation isolation requirement dictating the spread-out design. The spacecraft stands 12 feet high, weighs 700 to 800 pounds, and has an internal power of 150 watts. Rangers A-3, A-4, and A-5 are designed to rough land a capsule on the moon. For these, a capsule and retrorocket replace the scientific instruments, occupying the space inside the tower structure. The spacecraft must survive many environments. Chronologically they are: 1) Folded configuration inside an aerodynamic shroud on the pad. 2) Thermal flux from shroud aerodynamically heated during boost phase. 3) Coasting up to 30 minutes attached to Agena stage after booster and shroud are separated. 4) Agena stage burning. 5) Coasting and tumbling after separation from Agena until it passes from earth's shadow. 6) Upon reaching sunlight, panels open and begin sun acquisition. 7) Antenna seeks earth after spacecraft locks onto sun. 8) Space phase- "steady state" with vehicle's vertical axis locked on sun, communicating with earth. The philosophy is to design for the sun-acquired mode, making allowances for the transient conditions.

Thostesen, T. O.↗

NASA NTRS1990

Evidence for flux ropes in the earth's magnetotail

Magnetic field reconnection is a fundamental process that occurs in the magnetotail during geomagnetic substorms. Some 2D reconnection models predict the formation of a plasmoid, or closed loop of magnetic field lines, in the noon-midnight meridional plane at those times. When the 3D magnetotail magnetic field is considered, it becomes clear that reconnection produces a flux rope with an axis transverse to the earth-sun line. Three signatures mark both 2D plasmoids and 3D flux ropes: (1) a bipolar magnetic field signature, (2) tailward flow of a hot plasma, and (3) convecting isotropic energetic particle distributions. Plasmoids and flux ropes may be distinguished by (4) the axial magnetic field that only flux ropes possess. All four signatures have been identified in near-earth, middle, and distant magnetotail observations, but their interpretation is disputed. Thus, the existence of magnetotail flux ropes remains a controversial subject.

Sibeck, David G.↗

NASA NTRS1980

Energetic particle bursts in the earth's magnetotail

The present review of observations of energetic particle bursts lead to the following conclusions: the time scales of acceleration range from less than 10 seconds to several tens of minutes; the energy extent of bursts ranges from less than 50 keV to 2 MeV; for impulsive highly anisotropic field-aligned bursts, inverse velocity dispersion has been observed; the source dimension along the x axis is less than 1 earth radius, and even as small as 2400 km; source movement is approximately 30 to 80 km/sec, while source size in the y direction can reach several earth radii; particle anisotropies are primarily directed earthward or tailward with a strong dawn-dusk component for protons.

Krimigis, S. M.↗

NASA NTRS1977

Lander Locations, Mars Physical Ephemeris, and Solar System Parameters: Determination from Viking Lander Tracking Data

Radio tracking data from the Viking landers have been analyzed to determine the parameters of the Mars physical ephemeris, the radii of Mars at the landing sites, and the lander locations. The orientation of the Mars rotation axis, referred to the 1950.0 earth mean equator, equinox, and epoch, was determined to be 317.340+/-0.003 degrees right ascension and 52.710+/-0.002degrees declination. The planet's rotation period was determined to be 24 h, 37 min, 22.663+/-0.002 s. Analyses indicate that the determination of the motions of the Mars rotation axis will require additional tracking data. The Mars radii at the sites of landers 1 and 2 are 3389.38+/-0.06 km and 3381.91+/-0.08 km, respectively. The areocentric location of lander 1 is 22.272+/-0.002 degrees N, 47.94+/-0.2 degrees W. The lander 2 location is 47.670+/-0.002 degrees N, 225.71+/-0.2 degrees W. The areocentric right ascensions of the landers are determined to be 277.314+/-0.002 degrees for lander 1 and 99.546+/-0.002degrees for lander 2 at 0000 hours, January 1, 1977 (Julian date 2443144.57). Possible determinations of relativity parameters, solar oblateness, asteroid mass, and variations of the universal gravitational constant, from their effects on the planetary motions, will require the additional tracking data of the Viking extended mission.

Mayo, A. P.↗

NASA NTRS1975

Past orientation of the lunar spin axis

The orientation of the lunar spin axis is traced from the early history of the earth-moon system to the present day. Tides raised on the earth by the moon have caused an expansion of the lunar orbit. Tides raised on the moon by the earth have de-spun the moon to synchronous rotation and driven its spin axis to a Cassini state - that is, in a coprecessing configuration, coplanar with the lunar orbit normal and the normal to the Laplacian plane (which is at present coincident with the normal to the ecliptic). This combination of events has resulted in a complex history for the lunar spin axis. For much of the period during which its orbital semimajor axis expanded between 30 and 40 earth radii, the obliquity of the moon was of order 25 to 50 deg. In fact, for a brief period the obliquity periodically attained a value as high as 77 deg; that is, the spin axis of the moon was only 13 deg from lying in its orbit plane.

Ward, W. R.↗

NASA NTRS1991

An extended Kalman filter for spinning spacecraft attitude estimation

An extended Kalman filter for real-time ground attitude estimation of a gyro-less spinning spacecraft was developed and tested. The filter state vector includes the angular momentum direction, phase angle, inertial nutation angle, and inertial and body nutation rates. The filter solves for the nutating three-axis attitude and accounts for effects due to principle axes offset from the body axes. The attitude is propagated using the kinematics of a rigid body symmetric about the principle spin axis; disturbance torques are assumed to be small. Filter updates consist only of the measured angles between celestial objects (Sun, Earth, etc.) and the nominal spin axis, and the times these angles were measured. Both simulated data and real data from the Dynamics Explorer -A (DE-A) spacecraft were used to test the filter; the results are presented. Convergence was achieved rapidly from a wide range of a priori state estimates, and sub-degree accuracy was attained. Systematic errors affecting the solution accuracy are discussed, as are the results of an attempt to solve for sensor measurement angle biases in the state vector.

Baker, David F.↗

NASA NTRS1987

Single-Axis Acoustic Levitator With Rotation Control

Rotation-control equipment simplified. Acoustic levitator with rotation control handles liquid and solid specimens as dense as steel in both low gravity and normal Earth gravity. Levitator is single-axis type.

Trinh, E. H.↗

NASA NTRS1979

Ocean tidal excitation of polar motion

An investigation was conducted to ascertain the response of the rotational motion of the earth to forcing functions produced by the water mass redistribution due to the ocean tides. In particular, the components of displacement of the rotation axis at the surface of the Earth were obtained. The investigation also addressed the larger question concerning the possibility of excitation of the Chandler wobble of the earth. In general, the results show the existence of a polar wobble as a response to each of the components of the ocean tides. The magnitude of the polar displacement depends on two factors: the amplitude of the tidal component and its period. The maximum periodic contributions are: the Doodson's component number 055.565 with a period of 18.613 years and 50 cm of polar displacement, the annual component 056.544 with 37 cm of polar displacement and the semi-annual 057.555 with 32 cm. The tidal components with daily and semi-daily periods yield very small polar displacements of the order of 0.01 cm. The combined effect of all the periodic components can yield as much as 90 cm of pole displacements. The changes produced by the ocean tides in the products of inertia are periodic and regular, therefore, they cannot be the source of excitation of the Chandler wobble.

Sanchez, B. V.↗

NASA NTRS1982

Comments on the long-term stability of the earth's obliquity

Continued tidal evolution of the earth-moon system will lengthen the day and expand the lunar orbit. Both of these changes increase the present 26,000-year equinoctial precession period. In less than two billion years, this period will become comparable to the approximately 49,000- and 69,000-year periods of important terms describing the precession of the earth's orbit plane due to planetary perturbations. These events occur when the lunar orbital semimajor axis drifts past approximately 66.5 and 68.0 earth radii, respectively, and will be accompanied by large oscillations of the obliquity and severe climatic alterations. The current rate of lunar recession implies that these resonances should have been encountered already, had present conditions been the norm throughout geologic time.

Ward, W. R.↗

NASA NTRSDate not supplied

Crucial Role of Thermal Gradients in MMS Fluxgate In-Flight Calibration

To meet the science goals of the Magnetospheric Multiscale (MMS) mission, the Fluxgate Magnetometer (FGM) must measure the ambient magnetic field with an accuracy of 0.1 nT. On a typical MMS orbit, the offsets (or zero levels) of the 3-axis FGM can vary by ~0.5 nT (exclusive of periods in Earth shadow). Previous studies have shown that these variations can be characterized as functions of sensor temperature, TS, and can thus be corrected to within 0.2 nT in the spin plane using in-flight calibration techniques (Bromund, et al., 2016, https://ntrs.nasa.gov/citations/20160014711). In that presentation, we noted two significant observations: A distinct function of TS must be used to characterize offsets during shadow: offsets at a given TScan differ by as much as 2 nT in shadow vs sunlight. Offsets change after maneuvers, without a commensurate change in TS . These changes can be as large as 2 nT. We now note a third, related observation: Offsets increase with proximity to the earth even when TS is constant, resulting in variations of ~0.2 nT at 4-5 Earth radii (RE) These effects are evidence that offsets are a multivariate function of TS and another factor, namely: thermal gradients. Due to the spacecraft spin, the Earth and the Sun each provide a relatively constant thermal input onto one instrument face while the opposite face remains in shadow, thus giving rise to thermal gradients. The thermal gradient depend on the orientation of the spin axis relative to the Earth or Sun. We observe that offsets vary by as much as 0.17 nT/degree as a function of the tilt of the spin axis towards the Sun. Thermal input from the Earth is dominated by Outgoing Longwave Radiation (OLR). Due to the proximity to Earth, the inverse proportion of the distance squared is a significant factor in the thermal gradient attributed to Earth OLR. We find that offsets can be corrected to <0.05 nT accuracy near perigee when accounting for these factors using empirically determined constants of proportionality that account for differences in emissivity of the top and bottom faces of the sensor to OLR (as well as other thermal effects). The changes in offset associated with thermal gradient are of the same order of magnitude as effects that were formerly attributed to sensor temperature alone, and thus both parameters are necessary to characterize the FGM offsets.

Kenneth R Bromund↗

NASA NTRS1986

The warped neutral sheet and plasma sheet in the near-earth geomagnetic tail

An analysis of ISEE 2 plasma and magnetic field data indicates that the plasma sheet and neutral sheet in the near-earth magnetotail are warped in such a manner that in summer (winter) the neutral sheet rises above (dips below) the solar magnetospheric equatorial plane near the center of the tail, but dips below (rises above) the equatorial plane along the tail flanks. In the near tail, the neutral sheet crosses the equatorial plane at about 12 earth radii from the aberrated X axis, considerably closer to the center of the tail than has been inferred from data obtained farther downstream. This increase in the warp with decreasing distance from the earth is consistent with theoretical predictions. In the near tail, the warp is sufficiently strong when the dipole tilt angle is large that even in quiet times the upper or lower edge of the plasma sheet can be found close to the solar magnetospheric equatorial plane along the tail flanks. The seasonal dependence of the warp can produce certain dawn-dusk asymmetries in satellite data which are more apparent than real.

Gosling, J. T.↗