New model-independent constraints on possible modifications of Newtonian gravity over solar-system distance scales are presented and their implications discussed. The constraints arise from the analysis of various planetary astrometric data sets. The results of the model-independent analysis are then applied to set limits on a variation in the 1/r 2 behavior of gravity, on possible Yukawa-type interactions with ranges of the order of planetary distance scales, and on a deviation from Newtonian gravity of the type discussed by Milgrom. PACS numbers: 04.80,+z, 04.90.+e, 96.35.Tf We present here the results of an analysis of highprecision solar-system data in which we test for an apparent variation of the effective value of /IQ=GMQ with distance, where G is the Newtonian constant of gravity and M© is the mass of the Sun. We also present new limits on an anomalous precession of the perihelia of Mercury and Mars, obtained by studying how closely the orbits of these planets complied with the predictions of general relativity. Both of these results are then interpreted in terms of constraints on a deviation of the law of gravity from Newton's 1/r 2 behavior, on possible Yukawa-type intermediate-range interactions, and on a modification of nonrelativistic gravitation of the type suggested by Milgrom.One of the consequences of a variation of /*© with distance is a modification of Kepler's third law:where T p is the period and a p is the physically measured semimajor axis of the orbit of planet p. Given a set of values for a p and T p > Eq. (l) can be used to determine jio(r). However, the period of a planet has historically been determined much more accurately than has the semimajor axis. For this reason the standard method of analysis of solar-system astrometric data 1 has been to define //© to have a particular (constant) value, jUo(r)=/io(tf®) = K: 2 , where K is Gauss's constant (0.017 20209895 AU 3/2 /day, where AU denotes the astronomical unit), and to derive a "semimajor axis parameter" viaThis procedure gives the semimajor axis relative to a standard orbit at 1 AU, and this is all that can be determined with period data alone. However, for several planets there are also range data available-either planetary radar or spacecraft tracking to a planetary orbiter, lander, or flyby. In these cases it is possible to measure a p directly (and to thereby determine the size of the AU in kilometers). If ju© is a function of distance, then the scale of the semimajor axes will be different for each planet, and we can combine Eqs. (1) and (2) to yield sU + ifr)-^o (flp) 1/3 (3)Thus, the signature for a variation of JIQ with distance is a disparity r\ p in the conversion from AU's to kilometers appropriate to each planet. We note that Eq. (3) assumes no particular functional form for p©(r), except that ji©(r) varies such that r\ p may be treated as a constant over the orbit of planet p.In addition to the prediction of a variation of p® from planet to planet, the various modifications of Newtonian gravity that have been sugg...

Integer ambiguity fixing is routinely applied to double-differenced GPS phase measurements to achieve precise positioning. Double-differencing is interesting because it removes most of the common errors between the different signal paths. However, if common errors can be estimated it becomes attractive to fix integer ambiguities on undifferenced measurements. Phase measurements then become pseudorange-like measurements with a noise level of a few millimeters.This paper introduces a new method for fixing dual-frequency GPS ambiguities on undifferenced phase measurements either locally or globally. The clocks for the GPS constellation obtained during this process can be used for precise point positioning of ground based receivers and for precise orbit determination of low Earth orbiting satellites. The resulting positioning precision is comparable to that of standard differential positioning without the need for a reference station. Ambiguity-fixed satellite orbits for the GRACE and Jason satellites are more precise than the most precise solution available today.

On the NASA 2020 rover mission to Jezero crater, the remote determination of the texture, mineralogy and chemistry of rocks is essential to quickly and thoroughly characterize an area and to optimize the selection of samples for return to Earth. As part of the Perseverance payload, SuperCam is a suite of five techniques that provide critical and complementary observations via Laser-Induced Breakdown Spectroscopy (LIBS), Time-Resolved Raman and Luminescence (TRR/L), visible and near-infrared spectroscopy (VISIR), high-resolution color imaging (RMI), and acoustic recording (MIC). SuperCam operates at remote distances, primarily 2–7 m, while providing data at sub-mm to mm scales. We report on SuperCam’s science objectives in the context of the Mars 2020 mission goals and ways the different techniques can address these questions. The instrument is made up of three separate subsystems: the Mast Unit is designed and built in France; the Body Unit is provided by the United States; the calibration target holder is contributed by Spain, and the targets themselves by the entire science team. This publication focuses on the design, development, and tests of the Mast Unit; companion papers describe the other units. The goal of this work is to provide an understanding of the technical choices made, the constraints that were imposed, and ultimately the validated performance of the flight model as it leaves Earth, and it will serve as the foundation for Mars operations and future processing of the data.

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To achieve maximum benefit from the altimetric data collected by the French‐American TOPEX/POSEIDON spacecraft, radial orbit accuracy of 10 cm or better is required. This unprecedented requirement led the French Space Agency Centre National d'Etudes Spatiales (CNES) to develop a new high‐accuracy tracking system, Doppler orbitography and radiopositioning integrated by satellite (DORIS), and a new precision orbit production facility, the Service d'Orbitographie DORIS. A global effort produced new models and new orbit determination strategies. The result of these efforts has been assessed after 1 year of operation. The original goal has clearly been met, and the TOPEX/POSEIDON orbits produced by NASA and CNES agree to better than the 5 cm RMS level in the radial direction. At this level of accuracy, traditional techniques cannot correctly describe the actual orbit error, and some new procedures are proposed.