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Parker, J.

Publications and source records attributed to Parker, J..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2017

A Celestial Reference Frame Based on Kalman Filtering

In this study, we investigate a novel approach to the determination of celestial reference frames (CRF). Instead of a constant model for radio sources positions, we adopt a time series representation, which allows temporal variations of radio source coordinates to be taken into account. In particular, the added flexibility is beneficial for radio sources with extended structure. We compute our time series-based CRF solutions by Kalman filtering and smoothing radio source positions, which are initially obtained from single-session VLBI analysis. The temporal resolution of the estimated CRF coordinates is identical to that of the input data, i.e. usually 1-4 days. The magnitude of the coordinate variations is controlled by the amount of process noise applied in the filter, which is in turn derived from analyzing the Allan standard deviation of the corresponding radio source coordinate time series. Measures have been developed to reduce the impact of observation errors and datum effects on the noise model.

Soja, B.↗
NASA NTRS2010

The U.S. Rosetta Project at Its First Science Target: Asteroid (2867) Steins, 2008

On September 5, 2008, the International Rosetta Mission encountered its first formal science target of the mission, asteroid (2867) Steins. We report preliminary results from the U.S. experiments. NASA's contribution to the Rosetta mission consists of an ultraviolet (UV) spectrometer, a microwave spectrometer, a plasma instrument, and a portion of the electronics package for a mass spectrometer. The UV spectrometer (Alice) was used to obtain the first far-ultraviolet (FUV) spectrum of an asteroid. A ten-minute integration, surrounding the time of closest approach, averaging over a variety of geometries, showed very good signal from 850 Angstroms to 2000 Angstroms in the FUV. The microwave instrument (MIRO) obtained a high signal to noise measurement at both observing frequencies, enabling key thermal parameters to be derived. The plasma instrument (IES) obtained a brief measurement of the solar wind, and the Double Focusing Mass Spectrometer (DFMS) of the ROSINA instrument obtained a signal just at closest approach. Laboratory work with analogue materials was begun.

Alexander, C.↗
NASA NTRS2006

The U.S. Rosetta Project : eighteen months in flight

In this paper we will update the status of the instruments following the commissioning exercise, an exercise that was only partially complete when a report was prepared for the 2005 IEEE conference.We will present an overview of the 2005 Earth/Moon activities, and the Deep Impact set of observations. The paper will also provide an update of the role of NASA's Deep Space Network in supporting an ESA request for Delta Difference One-way Ranging to provide improved tracking and navigation capability in preparation for the Mars flyby in 2007.

Alexander, Claudia J.↗
NASA NTRS2000

Analysis and modeling of Southern California deformation

The large and rich quantity of data now becoming available through the Southern California Integrated GPS Network (SCIGN) makes possible a wide variety of research involving analysis and modeling.

geodesy earthquakes finite elements↗