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The Gravity Recovery and Interior Laboratory (GRAIL) mission [1] has provided lunar gravity with unprecedented accuracy and resolution. GRAIL has produced a high-resolution map of the lunar gravity field [2,3] while also determining tidal response. We present the latest gravity field solution and its preliminary implications for the Moon's interior structure, exploring properties such as the mean density, moment of inertia of the solid Moon, and tidal potential Love number k(sub 2). Lunar structure includes a thin crust, a thick mantle layer, a fluid outer core, and a suspected solid inner core. An accurate Love number mainly improves knowledge of the fluid core and deep mantle. In the future, we will search for evidence of tidal dissipation and a solid inner core using GRAIL data.

Variations in rotation and orientation of the Moon are sensitive to solid-body tidal dissipation, dissipation due to relative motion at the fluid-core/solid-mantle boundary, tidal Love number k2, and moment of inertia differences. There is weaker sensitivity to flattening of the core/mantle boundary (CMB) and fluid core moment of inertia. Accurate Lunar Laser Ranging (LLR) measurements of the distance from observatories on the Earth to four retroreflector arrays on the Moon are sensitive to variations in lunar rotation, orientation and tidal displacements. Past solutions using the LLR data have given results for Love numbers plus dissipation due to solid-body tides and fluid core. Detection of the fluid core polar minus equatorial moment of inertia difference due to CMB flattening is weakly significant. This strengthens the case for a fluid lunar core. Future approaches are considered to detect a solid inner core.

The Gravity Recovery and Interior Laboratory (GRAIL) mission has provided lunar gravity with unprecedented accuracy and resolution. GRAIL has produced a high-resolution map of the lunar gravity field while also determining tidal response. We present the latest gravity field solution and its preliminary implications for the Moon's interior structure, exploring properties such as the mean density, moment of inertia of the solid Moon, and tidal potential Love number k2. Lunar structure includes a thin crust, a deep mantle, a fluid core, and a suspected solid inner core. An accurate Love number mainly improves knowledge of the fluid core and deep mantle. In the future GRAIL will search for evidence of tidal dissipation and a solid inner core.

Variations in rotation and orientation of the Moon are sensitive to solid-body tidal dissipation, dissipation due to relative motion at the fluid-core/solid-mantle boundary, and tidal Love number k2 [1,2]. There is weaker sensitivity to flattening of the core-mantle boundary (CMB) [2-5] and fluid core moment of inertia [1]. Accurate Lunar Laser Ranging (LLR) measurements of the distance from observatories on the Earth to four retroreflector arrays on the Moon are sensitive to lunar rotation and orientation variations and tidal displacements. Past solutions using the LLR data have given results for dissipation due to solid-body tides and fluid core [1] plus Love number [1-5]. Detection of CMB flattening has been improving [3,5] and now seems significant. This strengthens the case for a fluid lunar core.

Variations in rotation and orientation of the Moon are sensitive to solid-body tidal dissipation, dissipation due to relative motion at the fluid-core/solid-mantle boundary, and tidal Love number k2 [1,2]. There is weaker sensitivity to flattening of the core-mantle boundary (CMB) [2,3,4] and fluid core moment of inertia [1]. Accurate Lunar Laser Ranging (LLR) measurements of the distance from observatories on the Earth to four retroreflector arrays on the Moon are sensitive to lunar rotation and orientation variations and tidal displacements. Past solutions using the LLR data have given results for dissipation due to solid-body tides and fluid core [1] plus Love number [1-5]. Detection of CMB flattening, which in the past has been marginal but improving [3,4,5], now seems significant. Direct detection of the core moment has not yet been achieved.

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Observationally determined values of the Love number k2 are larger than existing models of the lunar interior predict. The region between the deep moonquakes and core may be a low velocity zone from a partial melt. Additional information is contained in the original extended abstract.

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Analysis of Lunar Laser Ranges gives information on lunar tidal dissipation and a molten core. For the ancient moon tidal heating of the interior and heating at the core-mantle boundary could have rivaled radiogenic heating.

Laser ranges between observatories on the Earth and retroreflectors on the Moon started in 1969 and continue to the present. Recent range accuracies are 2 cm while earliest ranges are an C, order of magnitude less certain. Four retroreflectors are ranged: three located at the Apollo 11, 14, and 15 sites and one on the Lunakhod 2 rover. Accurate analysis of the range data determines a number of lunar science parameters. The lunar interior variables include a fluid core parameter. The Lunar Laser Ranging effort is reviewed elsewhere. Many parameters are detected through their influence on rotation. Also detected are solid-body tides and accurate selenocentric reflector locations. Determined through the rotation are moment-of-inertia differences, gravitational harmonics, potential Love number, and dissipation effects due to tides and molten core. The rotation of the Moon is not at its minimum energy state; some recently active process has caused free librations. The moment differences contributed to the recent improvement of the Moon's moment of inertia from the Lunar Prospector gravity field. The Love numbers provide bulk elastic properties. Future possibilities for measurement include oblateness of the core-mantle boundary and core moment. A study of dissipation signatures in the rotation determines tidal Q vs. frequency and concludes that the Moon has a molten core. At 1 month the tidal Q is 37 and at 1 yr it is 60. The core radius is < or = 352 km for Fe and < or = 374 km for the Fe-FeS eutectic. The core detection exceeds 3x its uncertainty. The spin of the core is not aligned with the spin of the mantle and torque arises from the velocity difference at the boundary. Yoder's turbulent boundary layer theory is used to compute the radii. The present heat generation from tides and core interaction is minor compared to radiogenic heating. The heating for ancient times is more interesting. Peale and Cassen investigated lunar tidal heating while the lunar orbit expanded due to tides on Earth. Their calculations predate the measurement of Q and should be multiplied by 3.45 to match the lunar-laser-determined Love number and monthly Q. Tidal-heating computations depend on how fast the lunar orbit evolved and whether the tidal dissipation is localized. Neither is known, but plausible assumptions lead to early central region temperature increases of several hundred degrees. Most of the energy is deposited early in the Moon's history. The turbulent boundary layer theory allows a prediction of energy dissipated at the core-mantle boundary during orbit evolution. Under the assumption that the properties of the early core are the same as at present, the energy dissipated by core-mantle interaction is about the same as for tidal dissipation, but it is deposited in a smaller volume. This source of energy is capable of promoting convection in an early fluid core and driving a dynamo. This is a transient phase with a duration depending on the rate of orbit evolution. Plausible assumptions lead to a duration of a few hundred million years. Thus, the remnant magnetization of many lunar rocks is compatible with a brief global magnetic field powered by dynamical energy dissipation. Analysis of the lunar laser ranges is providing information on lunar geophysics. Future data will improve accuracies of present solution parameters, and several more interior effects should be detectable.

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Non-steady differential rotation drive by bouyancy forces within the Earth's liquid outer core (OC) plays a key role not only in the generation of the main geomagnetic field by the magnetohydrodynamic (MHD) dynamo process but also in the excitation of irregular fluctuations in the angular speed of rotation of the overlying solid mantle, as evidenced by changes in the length of the day (LOD) on decadal and longer timescales (1-8).

The rotation of the Moon is influenced by solid-body tides and interaction at a liquid-core/solid-mantle boundary. The Lunar Laser Ranging (LLR) data are sensitive to variations in lunar rotation. Analysis of those ranges reveals four dissipation periodicities in the rotation. These signatures can be explained with the combined effects of tide plus core, but not with either alone. The fluid core detection exceeds three times its uncertainty. The inferred core radius has a 1 -sigma upper limit of 352 km for iron and up to 374 km if sulfur is present. The tidal dissipation is strong, Q at one month is 37 +/- 5 .Q increases for longer periods and is 60 (-15, +40) at one year.Dynamical evidence for a fluid lunar core has previously been presented. These-earlier solutions included three dissipation parameters. New solutions benefit from additional LLR data and an improved gravity field from Doppler tracking of Lunar Prospector. Five dissipation parameters are now solved for. There are several options for dissipation parameters: a core coupling parameter, a time delay for tidal distortion of the moments of inertia, and five periodic terms in the rotation angles. Solutions with different combinations of these are compatible (a theory relates K/C and time delay to a series of periodic terms). The solutions used K/C, time delay, and one periodic term. When dissipation signatures at five rotation frequencies are solved for, four amplitudes (4 to 263 milliarcseconds) are detected above the noise. Attempts to explain these results using either tides alone or core alone fail (less than 3(sigma) discrepancy for the former and 9(sigma), for the latter). A combination of tides and liquid core matches the results well.

A description is given of the operational JPL project to measure, combine, and predict Earth rotation parameters in support of spacecraft navigation.

The 1982-1983 El Nino/Southern Oscillation (ENSO) event was accompanied by the largest interannual variation in the Earth's rotation rate on record. In this study we demonstrate that atmospheric forcing was the dominant cause for this rotational anomaly, with atmospheric angular momentum (AAM) integrated from 1000 to 1 mbar (troposphere plus stratosphere) accounting for up to 92% of the interannual variance in the length of day (LOD). Winds between 100 and 1 mbar contributed nearly 20% of the variance explained, indicating that the stratosphere can play a significant role in the Earth's angular momentum budget on interannual time scales. Examination of LOD, AAM, and Southern Oscillation Index (SOI) data for a 15-year span surrounding the 1982-1983 event suggests that the strong rotational response resulted from constructive interference between the low-frequency (approximately 4-6 year) and quasi-biennial (approximately 2-3 year) components of the ENSO phenomenon, as well as the stratospheric Quasi-Biennial Oscillation (QBO). Sources of the remaining LOD discrepancy (approximately 55 and 64 microseconds rms residual for the European Centre for Medium-Range Forecasting (EC) and U.S. National Meteorological Center (NMC) analyses) are explored; noise and systematic errors in the AAM data are estimated to contribute 18 and 33 microseconds, respectively, leaving a residual (rms) of 40 (52) microseconds unaccounted for by the EC (NMC) analysis. Oceanic angular momentum contributions (both moment of inertia changes associated with baroclinic waves and motion terms) are shown to be candidates in closing the interannual axial angular momentum budget.

Difficulties related to the paucity of weather observation data regarding oceans were potentially alleviated for three summer months in 1978 when NASA's Seasat telemetered data from three wind-measuring instruments. The present study is concerned with one of these instruments, the Seasat A Scatterometer System (SASS). Attention is given to an internal consistency check of the SASS 1 model, comparisons of SASS 1 and other model-predicted winds with in situ winds, and a brief summary of the principal findings. It is found that a new wind retrieval system is required if SASS wind data are to be globally applicable and, at the same time, are to meet the required performance specifications. The sum-of-squares (SOS) technique for inverting SASS NRCS (normalized radar cross section) measurements results in the discarding of valuable data in low-speed areas and for higher incidence angles.

The power law form of the SEASAT A Scatterometer System (SASS) empirical backscatter-to-wind model function does not uniformly meet the instrument performance over the range 4 to 24 /ms. Analysis indicates that the horizontal polarization (H-Pol) and vertical polarization (V-Pol) components of the benchmark SASS1 model function yield self-consistent results only for a small mid-range of speeds at larger incidence angles, and for a somewhat larger range of speeds at smaller incidence angles. Comparison of SASS1 to in situ data over the Gulf of Alaska region further underscores the shortcomings of the power law form. Finally, a physically based empirical SASS model is proposed which corrects some of the deficiencies of power law models like SASS1. The new model allows the mutual determination of sea surface wind stress and wind speed in a consistent manner from SASS backscatter measurements.

The first global wind fields from SEASAT-A scatterometer (SASS) data were produced. Fifteen days of record are available on tape, with unique wind directions indicated for each observation. The methodology of the production of this data set is described, as well as the testing of its validity. A number of displays of the data, on large and small scales, analyzed and gridded, are provided.

A description is given of the algorithm used to convert Seasat-A satellite microwave scatterometer measurements of ocean normalized radar cross section to the neutral stability vector wind at 19.5 m height, as well as to compare these winds with high-quality surface observations. The wind vector algorithm used an empirical normalized radar cross section model function to describe the ocean normalized radar cross section's dependence on the 19.5-m neutral stability wind vector. In addition, two model functions were evaluated by means of an independent set of in situ surface wind observations from the Joint Air Sea Interaction experiment (JASIN). Better results were produced by these comparisons than the stipulated Seasat wind speed and direction accuracy specifications of + or - 2 m/sec and + or - 20 deg, respectively, over the 0-16 m/sec range of winds observed during JASIN.

The Seasat-A Satellite Scatterometer (SASS) ocean normalized radar cross section (NRCS) dependence on the 19.5-m neutral stability wind vector may be specified as a function of radar incidence angle, the angle between wind direction and radar azimuth, and the neutral stability wind speed expressed in m/sec at a height of 19.5 m. An account is given of the development of models both expressing this relationship and providing the basis of inversion of NRCS to SASS winds, from initially aircraft scatterometer measurement-based forms to three Seasat field-validation experiments which furnish model NRCS versus surface windspeed data for comparison with SASS data.

Surface wind velocities have been derived from backscatter measurements of the ocean surface made by a satellite-borne, microwave sensor. Comparisons with high-quality surface-based measurements obtained during the Joint Air-Sea Interaction experiment are described. The accuracy of the scatterometer winds at this mid-latitude site, + or 1.6 m/s in speed and + or - 18 deg in direction, for winds between 3 and 16 m/s is within the design specification.

This paper describes the algorithms used to convert engineering unit data obtained from the Seasat-A satellite scatterometer (SASS) to radar scattering coefficients and associated supporting parameters. A description is given of the instrument receiver and related processing used by the scatterometer to measure signal power backscattered from the earth's surface. The applicable radar equation used for determining scattering coefficient is derived. Sample results of SASS data processed through current algorithm development facility (ADF) scattering coefficient algorithms are presented which include scattering coefficient values for both water and land surfaces. Scattering coefficient signatures for these two surface types are seen to have distinctly different characteristics. Scattering coefficient measurements of the Amazon rain forest indicate the usefulness of this type of data as a stable calibration reference target.

The determination of the Mars-centered ephemerides of the Viking Orbiters and positions of the Landers from two way Doppler and range data is described. An overview of mission satellite orbit determination functions and methods is given. Topics covered include: postmaneuver orbit convergence, local orbit knowledge accuracies, the effects of interplanetary media, use of constrained solutions, and solving through trim burns. Procedure and results relevant to the determination of the planet gravity field are included. Results relative to sensing Mars' gravity field during the extended mission are presented along with a discussion of the Phobos Flyby Experiment conducted during February 1977.

Differential altimetry is concerned with the employment of differenced satellite altimeter measurements at orbit ground trace intersections. The employment of this procedure makes it possible to eliminate two of the major error sources found in direct altimetry. Previous applications have not included the appropriate dynamic constraints required to account for correlations due to satellite orbit motion. A description is given of an investigation in which these correlations are included. The methodology produced is consistent with the dynamic environment. The regional or local limitations of previous approaches are overcome by extending the technique to the global scale. Attention is given to the description of the data type, the geometric topography height, altimeter errors, discretization errors, an approximate orbit determination problem, and a comparison of differenced altimeter measurements for retrograde and prograde orbits.

During the summer of 1976, the two Viking spacecraft, each consisting of an orbiter-lander combination, were inserted into orbit about Mars. The paper describes the experiences of the Viking Satellite Orbit Determination Team in determining Mars centered ephemerides of the orbiters and positions of the landers from the two-way Doppler and range data, and synthesizes the different phases of the navigation plan which involves pre-flight modeling and error analysis for all Viking navigation functions from launch through landing. The problem of initial orbit convergence is solved by using DPODP's (Double Precision Orbit Determination Program) square-root batch data filter, and gravity models for both Viking I and Viking II were produced from the combination of short arc estimates. The importance of synchronous Viking orbits (with the rotational period of Mars) is stressed and future extended missions of the spacecraft are outlined.

Weighted least squares nonlinear estimation problem, presenting partial step algorithm for convergence region enlargement

A historic account of the activities of the Satellite OD Group during the MM'71 mission is given along with an assessment of the accuracy of the determined orbit of the Mariner 9 spacecraft. Preflight study results are reviewed, and the major error sources described. Tracking and data fitting strategy actually used in the real time operations is itemized, and Deep Space Network data available for orbit fitting during the mission and the auxiliary information used by the navigation team are described. A detailed orbit fitting history of the first four revolutions of the satellite orbit of Mariner 9 is presented, with emphasis on the convergence problems and the delivered solution for the first orbit trim maneuver. Also included are a solution accuracy summary, the history of the spacecraft orbit osculating elements, the results of verifying the radio solutions with TV imaging data, and a summary of the normal points generated for the relativity experiment.