Recovering the rotational light curve of Phoebe
We present rotational light-curve data for Saturn's satellite Phoebe taken over the observing period prior to the Cassini mission's encounter with that moon.
planetsasteroids satellite Phoebe↗
Engineering topics
Owen, W. M., Jr.
Publications and source records attributed to Owen, W. M., Jr..
NEAR Shoemaker's low altitude operations at EROS
This paper discusses the design, execution, and results of NEAR's low altitude operations at Eros.
NEAR EROS asteroid landing small bodies navigation↗
A global solution for the gravity field shape rotation and ephemeris of Eros
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gravity field rotation epemeris eros x-band NEAR↗
Comet 19P/Borrelly orbit determination for the DS1 flyby
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comet orbit determination Borrelly↗
The overlapping plate method for asteroid astrometry
The overlapping plate method, first introduced in the early 1960s by Henrich Eichhorn, was originally intended to provide better star catalogs through improved data reduction techniques.
astrometry asteroids↗
The overlapping plate method for asteroid astronomy
The overlapping plate method, first introduced in the early 1960s by Henrich Eichhorn, was originally intended to provide better star catalogs through improved data reduction techniques.
astrometry asteroids data reduction techniques↗
The NEAR Spacecraft's Flyby of Asteroid 253 Mathilde
The Terminal navigation of the NEAR spacecraft during its close flyby of asteroid 253 Mathilde involved coordinated efforts first to determine the heliocentric orbits of the spacecraft and Mathilde and then to determine the relative trajectory of the spacecraft with respect to Mathilde.
Asteroid 253 Mathilde↗
Navigation for the new millennium: Autonomous navigation for Deep Space 1
The autonomous optical navigation system technology for the Deep Space 1 (DS1) mission is reported on. The DS1 navigation system will be the first to use autonomous navigation in deep space. The systems tasks are to: perform interplanetary cruise orbit determination using images of distant asteroids; control and maintain the orbit of the spacecraft with an ion propulsion system and conventional thrusters, and perform late knowledge updates of target position during close flybys in order to facilitate high quality data return from asteroid MaAuliffe and comet West-Kohoutek-Ikemura. To accomplish these tasks, the following functions are required: picture planning; image processing; dynamical modeling and integration; planetary ephemeris and star catalog handling; orbit determination; data filtering and estimation; maneuver estimation, and spacecraft ephemeris updating. These systems and functions are described and preliminary performance data are presented.
Reidel, J. E.↗
The overlapping plates method applied to CCD observations of 243 Ida
The overlapping plates method has been applied to crossing-point Charge Coupled Device (CCD) observations of minor planet 243 Ida to produce absolute position measurements precise to better than 0.1 sec and differential position measurements precise to better than 0.06 sec. Although these observations numbered only 17 out of the 520 that produced the final ground-based Ida ephemeris for the Galileo spacecraft flyby, their inclusion decreased Ida's downtrack error from 78 to 60 km and its out-of-plane error from 58 to 44 km.
Owen, W. M., Jr.↗
The Plate Overlap Technique Applied to CCD Observations of 243 Ida
The plate overlap technique has been applied to crossing-point CCD observations of minor planet 243 Ida to produce position measurements accurate to better than 0.
Plate Overlap Ida ephemeris Galileo↗
Telescope pointing for GOPEX
In order for photons emitted by the GOPEX lasers to be detected by Galileo's camera, the telescopes at Table Mountain Observatory and Starfire Optical Range had to be pointed in the right direction within a tolerance less than the beam divergence. At both sites nearby stars were used as pointing references. The technical challenge was to ensure that the transmission direction and the star positions were specified in exactly the same coordinate system; given this assurance, neither the uncertainty in the star catalog positions nor the difficulty in offset pointing was expected to exceed the pointing error budget. The correctness of the pointing scheme was verified by the success of GOPEX.
Owen, W. M., Jr.↗
Masses and densities of Pluto and Charon
We have analyzed HST Wide Field Camera CCD images of Pluto, Charon, and a background star to observe Pluto's barycentric motion and to determine the individual masses and bulk densities of Pluto and Charon. The most fundamental new result was an accurate solution for a previously undetermined parameter, the Charon/Pluto mass ratio q; the new solution is q = 0.0837 +/- 0.0147. Significant accuracy improvements by almost a factor of two were obtained for Charon's orbital semimajor axis, a = 19,405 +/- 86 km and the Pluto system mass of 1.401 +/- 0.019 x 10 exp 8 inverse solar masses. The Pluto and Charon masses were (13.10 +/- 0.24) x 10 exp 24 g and (1.10 +/- 0.18) x 10 exp 24 g, respectively. Computed densities depend strongly on the assumed radius values. The density of Pluto is 2.13 +/- 0.04 g/cu cm and that of Charon is 1.30 +/- 0.23 g/cu cm.
Null, G. W.↗
Targeting an asteroid - The Galileo spacecraft's encounter with 951 Gaspra
On 1991 October 29, the Galileo spacecraft provided the first in situ observations of an asteroid. To a significant degree, the successful encounter with asteroid 951 Gaspra was made possible by the high accuracy of the ground-based Gaspra ephemeris and the refinement to this initial ephemeris provided by the use of optical navigation images taken on board the spacecraft itself. The success of these celestial navigation efforts was dramatically demonstrated when Gaspra appeared in the central frame of the large mosaic of CCD images-less than one asteroid diameter from Gaspra's expected location in the camera's field of view. The corrections to Gaspra's ground-based ephemeris, based upon the optical on-board navigation images, were less than 80 km. The ground-based observation program that went into this ephemeris development is discussed and the accuracy of the ephemeris is used to validate the assumptions that went into the error analysis studies.
Yeomans, D. K.↗
Systems analysis for ground-based optical navigation
Deep-space telecommunications systems will eventually operate at visible or near-infrared regions to provide increased information return from interplanetary spacecraft. This would require an onboard laser transponder in place of (or in addition to) the usual microwave transponder, as well as a network of ground-based and/or space-based optical observing stations. This article examines the expected navigation systems to meet these requirements. Special emphasis is given to optical astrometric (angular) measurements of stars, solar system target bodies, and (when available) laser-bearing spacecraft, since these observations can potentially provide the locations of both spacecraft and target bodies. The role of astrometry in the navigation system and the development options for astrometric observing systems are also discussed.
Null, G. W.↗
Deep-space navigation applications of improved ground-based optical astrometry
Improvements in ground-based optical astrometry will eventually be required for navigation of interplanetary spacecraft when these spacecraft communicate at optical wavelengths. Although such spacecraft may be some years off, preliminary versions of the astrometric technology can also be used to obtain navigational improvements for the Galileo and Cassini missions. This article describes a technology-development and observational program to accomplish this, including a cooperative effort with U.S. Naval Observatory Flagstaff Station. For Galileo, Earth-based astrometry of Jupiter's Galilean satellites may improve their ephemeris accuracy by a factor of 3 to 6. This would reduce the requirements for onboard optical navigation pictures, so that more of the data transmission capability (currently limited by high-gain antenna deployment problems) can be used for science data. Also, observations of European Space Agency (ESA) Hipparcos stars with asteroid 243 Ida may provide significantly improved navigation accuracy for a planned August 1993 Galileo spacecraft encounter.
Null, G. W.↗
Geometric distortion analysis of a wide-field astrograph
Ground-based optical navigation seeks to determine the angular position of a star, Solar System body, or laser-emitting spacecraft relative to objects with well-known coordinates. Measurement accuracies of 25 nrad would make optical techniques competitive with current radio metric technology. This article examines a proposed design for a wide-field astrograph and concludes that the deviation of an image centroid from the ideal projection can be modeled to the desired accuracy provided that the field of view does not exceed 5 deg on a side.
Owen, W. M., Jr.↗