Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “astrometric”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Development of a radio-astrometric catalog by means of very long baseline interferometry observations

The Jet Propulsion Laboratory has been developing a radio-astrometric catalogue for use in the application of radio interferometry to interplanetary navigation and geodesy. The catalogue consists of approximately 100 compact extragalactic radio sources whose relative positions have formal uncertainties of the order of 0.01 arcsec. The sources cover nearly all of the celestial sphere above -40 deg declination. By using the optical counterparts of many of these radio sources, this radio reference frame has been tied to the FK4 optical system with a global accuracy of approximately 0.1 arcsec. This paper describes the status of this work.

Fanselow, J. L.↗
NASA NTRS1982

Astrometric observations and the motion of comet Halley

Beginning with studies related to the 1835 appearance of comet Halley, it became apparent that comets may undergo substantial nongravitational perturbations due to the rocket-like effect of an outgassing cometary nucleus. Marsden (1968, 1969) modeled these nongravitational effects with a semiempirical term in the cometary equations of motion. The most successful orbital solution was consistent with an outgassing water ice nucleus in direct rotation. For the conduction and coordination of accurate astrometric observations of comet Halley, an Astrometry Network is being established within the International Halley Watch program. Attention is given to the support of the Halley flight projects provided by the Astrometry Network, and the support of ground based observers by this network.

Yeomans, D. K.↗
NASA NTRS1984

The parallax and astrometric orbit of Mu Cassiopeiae

A total of 371 photographic plates were made of the binary Mu Cassiopeia (Mu Cas) region with a 76 cm refractor. An astrometric orbit of nearly 22.09 yr was calculated, accompanied by an eccentricity of close to 0.58 and a semimajor axis close to 0.19 arcsec. The absolute magnitude was approximately 5.83 and the radial velocity 164 km/sec.

Russell, J. L.↗
NASA NTRS1984

Astrometric applications of the Mt. Stromlo PDS 1010A

Problems in photographic astrometry to which the Mt. Stromlo (VA) microdensitometer is applied are described. It is used for measuring southern parallax region plates to determine photographic positions of the brighter satellites of the outer planets. Tests of the overall astrometric accuracy and stability of the machine, as well as results, show micron-level pecularities, but overall a quite satisfactory level of performance for the system.

Ianna, P. A.↗
NASA NTRS1984

Astrometric plates obtained at the primary focus of large aperture reflectors

Coma, astigmatism, and great differences in stellar magnitudes between photographed object and reference stars constitute the main sources of errors in measuring positional plates. These three sources of error can easily be eliminated by the method used at the Klet Observatory for obtaining precise observations of faint objects. The astrometric plates are taken by the method of two diaphragms. The first diaphragm, with a small central aperture; is located in front of the photographic plate. The second diaphragm is situated in front of the mirror. By a very short (of the order of tens of seconds) exposure a sufficient number of reference stars can be obtained throughout the entire plate. The stars are very well defined to the very edge of the plate and are easy to measure. Moreover, this method makes it possible to use plates of larger dimensions than usual so that it is always possible to find the necessary reference stars.

Markos, A.↗
NASA NTRS1984

Astrometric needs for the ISEE-3/ICE mission to Comet Giocobini-Zinner

The Third International Sun-Earth Explorer satellite (ISEE-3) was rechristened Internation Cometary Explorer (ICE) when the spacecraft left the Earth-Moon system after a close Lunar flyby on 1983 December 22. On 1985 September 11, ICE will pass through the inner parts of the tail of Comet Giacobini-Zinner to obtain the first in-situ measurements of any comet. Since the spacecraft has no cameras, its trajectory will be determined only from radio tracking. Astrometric updates of Comet Giacobini-Zinner will be critical for the final targeting of the spacecraft to achieve a successful encounter. ICE's flyby of Comet Giacobini-Zinner will provide valuable experience for the astrometry needed to target other spacecraft to encounter Hally's Comet six months later.

Dunham, D. W.↗
NASA NTRS1986

Astrometric Telescope Facility - Status report

The advent of the Space Station Program has provided an unexpected opportunity for the Astrometric Telescope Facility (ATF) study program by providing a potential long-duration on-orbit serviceable platform. It required a concept change for ATF from a free-flyer observatory to a Space-Station-based Observatory. The program was sent in this new direction at the start of fiscal year 1985, and program plans including study schedules and science and technical requirements are being revised and defined. The facility is designed to be versatile and capable of fulfilling the primary goal of planet detection, and to be highly useful for other astrophysics observations. Basically the ATF observing program is a long-duration plan requiring repetitive observations of single stars over a one to two decade period. These repetitive observations are needed to provide data necessary to conclusively determine the existence (or nonexistence) of planets of the Uranus and Neptune class in extrasolar planetary systems.

Nishioka, K.↗
NASA NTRS1987

Astrometric Telescope Facility preliminary systems definition study. Volume 1: Executive summary

The Astrometric Telescope Facility (ATF) is a spaceborne observatory proposed for use on the Space Station (SS) as an Initial Operating Capability (IOC) payload. The primary objective of the ATF will be the search for extrasolar planetary systems and a detailed investigation of any discovered systems. In addition, it will have the capability of conducting other astrophysics investigations; e.g., measuring precise distances and motions of stars within our galaxy. The purposes of the study were to: (1) define mission and system requirements; (2) define a strawman system concept for the facility at the Prephase A level; (3) define the need for additional trade studies or technology development; and (4) estimate program cost for the strawman concept. It has been assumed for the study that the ATF will be a SS payload, will use a SS-provided Coarse Pointing System (CPS), will meet SS constraints, and will make maximum use of existing flight qualified designs or designs to be qualified by the SS program for general SS use.

Sobeck, Charlie↗
NASA NTRS1986

POINTS - A small astrometric interferometer in space

The 'precision optical interferometry in space' instrument, or 'POINTS', is an astrometric interferometer design concept which as currently configured possesses a pair of 2-m baselines and four 25-cm telescopes. Fully assembled with its support spacecraft, POINTS would take up one-third of the Space Shuttle cargo bay. For a pair of tenth-magnitude stars about 90 deg apart, POINTS would yield a separation that was uncertain by 5 microarcsecs after 10-min observation. Both instrument design and mission aspects are discussed.

Reasenberg, R. D.↗
NASA NTRS1987

An astrometric facility for planetary detection on the Space Station

The preliminary system definition study for an Astrometric Telescope Facility (ATF) designed for the Space Station IOC is discussed, and a strawman system is designed which is found to meet the requirements for extrasolar planetary systems search and study. The strawman facility design, with a prime-focus 1.25-m aperture telescope and an f ratio of 13, was selected to minimize random and systematic errors. A basic operations approach is identified, including the approach to launch, initial on-orbit assembly and checkout, normal operations, and the response to anomolous conditions or failures. The preliminary system is designed to be fail-safe and single-fault tolerant. Mission analysis indicates that the basic viewing required for planetary detection can be accomplished in about 2/3 of the total viewing time.

Nishioka, Kenji↗
NASA NTRS1988

Astrometric results of 1978-1985 Deep Space Network radio interferometry - The JPL 1987-1 extragalactic source catalog

An astrometric radio reference frame has been determined from intercontinental dual-frequency radio interferometric measurements. These measurements were carried out on a regular basis during 1978-1985 between NASA's Deep Space Network stations in California, Spain, and Australia. Analysis of 6800 pairs of delay and delay-rate observations made during 51 sessions produced estimates of 1300 parameters. The most significant of these are geophysical quantities and positions of extragalactic sources. The source catalog resulting from this analysis includes 106 sources fairly uniformly distributed over the celestial sphere, north of -45 deg declination. Almost all of the resulting source positions have formal uncertainties between 0.5 and 3 milliarcseconds (mas), with rms values of 2 mas in both angular coordinates. Internal consistency checks, as well as comparisons with independently determined source catalogs of comparable quality, indicate that relative source coordinates determined by VLBI contain systematic errors at the level of 1 to 2 mas.

Sovers, O. J.↗
NASA NTRS1988

Phobos and Deimos astrometric observations from Viking

This article describes the reduced astrometric observations of Phobos and Deimos derived from Viking Orbiter 1 and 2 imaging data. This data set spans four years from 1976 to 1980, contains 275 sets of spacecraft-centered, right ascension and declination observations, and has a limiting accuracy of a few km (1 sigma). The details of observation formulation and use for ephemeris improvement are given.

Duxbury, T. C.↗
NASA NTRS1988

Astrometric observations of asteroids and small bodies

Comets and asteroids are observed with the Palomar 1.5 m telescope using a charge coupled device (CCD) array. The goal is observations of astrometric quality (the reduction to position is separately funded) and the priorities are comets plus minor planets which are planet crossers, have high inclinations, or otherwise have unusual orbits. The stress is on recoveries of comets and asteroids seen at previous oppositions and follow up on newly discovered objects. Surveys and new discoveries are not being attempted. The modest amount of available dark time is used for faint objects, while brighter objects can be followed in the more plentiful light time. Since asteroids are usually discovered near perihelion when bright, the next several opportunities for recovery are normallly fainter. Thus recoveries and follow up with big telescopes complement surveys by smaller instruments. During the past year two periodic comets were recovered. They were P/Jackson-Neujmin (1987t) and P/Longmore (1987c1). Both were shared recoveries. A follow up observation of the newly-discovered comet Rudenko (1987u) appeared on an IAU card as did the newly discovered Comet Maury-Phinney (1988c). A magnitude 14.4 outburst of comet Schwassmann-Wachmann 1 was recorded at the end of May and was reported on an IAU card.

Williams, James G.↗
NASA NTRS1988

Space Station Astrometric Telescope tracking for the detection of planetary systems

The paper presents a comprehensive star observation and tracking strategy, which uses a computer simulation of the Space Station orbital mechanics, system constraints, and Astrometric Telescope Facility (ATF) tracking maneuvers over a long observational period. This approach may be used to obtain data which may assist in the preliminary systems definition of the ATF. Results are given for an analysis which uses a restricted target set in order to demonstrate the disproportionate effect of the galactic-photon-rate index on the observation times for each star.

Mascy, Alfred C.↗
NASA NTRS1989

Space Station utilization for the Astrometric Telescope Facility

It is shown how it is possible for the Astrometric Telescope Facility (ATF) to utilize the Space Station Freedom as an attached payload by complying with changes in the Station concept and schedule. The ability of the station to accommodate ATF's firm requirements is also addressed. The main factors that led the ATF to utilize the Space Station Freedom are the Station's relative orbital stability and longevity, the availability of maintenance and repair services, and the provision of utilities.

Nishioka, Kenji↗
NASA NTRS1988

A tethered astrometric telescope facility

A comparison is made between a tethered platform and a kinematically attached payload. Tethered platforms are capable of achieving a high level of passive vibration attenuation while reducing exposure to induced contamination to near-background levels. The Astrometric Telescope Facility, a payload being considered for operation from the Space Station, is described in detail.

Lemke, L. G.↗
NASA NTRS1989

Phobos and Deimos astrometric observations from Mariner 9

This article describes the reduced astrometric observations of Phobos and Deimos derived from Mariner 9 imaging data. This data set spans 11 months from 1971 and 1972, contains 82 sets of spacecraft-centered right ascension and declination observations, and has an accuracy of 3 to 10 km (1-sigma) in orbital position. The details of the observation formulation and its use for ephemeris improvement are given.

Duxbury, T. C.↗