POINTS Abstracts


Contents

Astron. J. (Nov 1988)
ESA Targets for Space-based Interferometry (Beaulieu, Fr, Oct 1992)
SAO report (1993)
NASA, Relativistic Gravitational Experiments in Space (1989)
IAU, Leningrad, USSR (1989)
Relativity in celestial mechanics and astrometry, Leningrad, USSR (1985)
SPIE Spaceborne Interferometry (1993): SPIE Large Optics Technology (1985)

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Index
Title:             Microarcsecond optical astrometry - An instrument and
                   its astrophysical applications
Authors:           Reasenberg, R.D.; Babcock, R.W.; Chandler, J.F.; Gorenstein,
		   M.V.; Huchra, J.P.; Pearlman, M.R.; Shapiro, I.I.; Taylor,
		   R.S.; Bender, P.; Buffington, A.; Carney, B.; Hughes, J.A.;
		   Johnston, K.J.; Jones, B.F.; Matson, L.E.
Affiliation:       AE(Harvard-Smithsonian Center for Astrophysics,
                   Cambridge, MA)
Journal:           Astronomical Journal (ISSN 0004-6256), vol. 96, Nov.
                   1988, p. 1731-1745. Research supported by the
                   Smithsonian Institution and NASA.
Publication Date:  11/1988
Category:          Astronomy
NASA/STI Keywords: ASTROMETRY, INTERFEROMETRY, SKY SURVEYS (ASTRONOMY),
                   CEPHEID VARIABLES, ERROR ANALYSIS, GALACTIC CLUSTERS,
                   GALACTIC STRUCTURE, MAGELLANIC CLOUDS, STELLAR MASS
Bibliographic Code:1988AJ.....96.1731R

Abstract

The applications of a proposed space-based optical astrometric interferometer with a large optical bandwidth are discussed. Such an instrument would make possible an improved deflection test of general relativity, a precise and direct calibration of the Cepheid distance scale, and the determinations of stellar masses. The nominal 5-microarcsec uncertainty in the measurement of the angular separation of two stars about 90 deg apart in the sky and the projected measurement rate of 60 star pairs per day would support a range of astrophysical studies during a nominal mission life of 10 years. Means of controlling the instrument's systematic error are considered.
Index
Title:             Space-based astrometric optical interferometry with
                   POINTS
Authors:           Reasenberg, R. D.; Babcock, R. W.; Phillips, J. D.;
                   Noecker, M. C.
Affiliation:       Smithsonian Astrophysical Observatory, Cambridge, MA.
Journal:           In ESA, Targets for Space-Based Interferometry p 59-69
                   (SEE N93-31750 12-89)
Publication Date:  12/1992
Category:          Astronomy
NASA/STI Keywords: ASTROMETRY, ASTRONOMICAL INTERFEROMETRY,
                   INTERFEROMETERS, OPTICAL MEASUREMENT,
                   SPACEBORNE ASTRONOMY, SPACECRAFT DESIGN, ACCURACY,
                   APERTURES, ASTROPHYSICS, INSTRUMENT ERRORS,
                   POINTING CONTROL SYSTEMS, SPACE MISSIONS,
                   SYSTEMS ENGINEERING
Bibliographic Code:1992tsbi.rept...59R

Abstract

POINTS, a dual space-based astrometric optical interferometer with nominal baseline length of 2 meters and measurement accuracy of 5 microarcseconds, which could be a powerful new multidisciplinary research tool is introduced. The instrument, including the laser gauges which are a central aspect of the instrument, are described. The design of the spacecraft, and the mission operations, including the bias determination and correction, are discussed. As a candidate for the Astrometric Interferometry Mission (AIM) mission, POINTS could open new areas of astrophysical research and change the nature of the questions being asked in some old areas. As a candidate for the TOPS-1 (Towards Other Planetary Systems) mission, it could be used to perform a definitive search for extra solar planetary systems, either finding and characterizing a large number of them or showing that they are far less numerous than now believed. POINTS, which is small, agile, and mechanically simple, would be the first of a new class of powerful instruments in space and would prove the technology for the larger members of that class to follow.
Index
Title:             Precision optical interferometry in space
Authors:           Reasenberg, Robert D.
Affiliation:       Smithsonian Astrophysical Observatory, Cambridge, MA.
Journal:           Final Report, 6 Feb. 1989 - 31 Jan. 1993 Smithsonian
                   Astrophysical Observatory, Cambridge, MA. 
Publication Date:  07/1993
Category:          Astronomy
NASA/STI Keywords: A STARS, ASTROMETRY, INTERFEROMETERS, INTERFEROMETRY,
                   OPTICAL MEASURING INSTRUMENTS, SPECTRA, ASTROPHYSICS,
                   PLANETARY SYSTEMS, SOLAR SYSTEM
Bibliographic Code:1993N93-29163.....R

Abstract

POINTS, an astrometric Optical interferometer with a nominal measurement accuracy of 5 microarcseconds for the angle between a pair of stars separated by about 90 deg, is presently under consideration by two divisions of NASA-OSSA. It will be a powerful new multi-disciplinary tool for astronomical research. If chosen as the TOPS-1 (Toward Other Planetary Systems) instrument by the Solar-System Exploration Division, it will perform a definitive search for extra-solar planetary systems, either finding and characterizing a large number of them or showing that they are far less numerous than now believed. If chosen as the AIM (Astrometric Interferometry Mission) by the Astrophysics Division, POINTS will open new areas of astrophysical research and change the nature of the questions being asked in some old areas. In either case. it will be the first of a new class of powerful instruments in space and will prove the technology for the larger members of that class to follow. Based on a preliminary indication of the observational needs of the two missions, we find that a single POINTS mission will meet the science objectives of both TOPS-1 and AIM. The instrument detects dispersed fringe (channel led spectrum) and therefore can tolerate large pointing errors.
Index
Title:             Optical interferometers for tests of relativistic
                   gravity in space
Authors:           Reasenberg, R. D.
Affiliation:       Smithsonian Astrophysical Observatory, Cambridge, MA.
Journal:           In NASA, Relativistic Gravitational Experiments in
                   Space p 155-162 (SEE N90-19940 12-90)
Publication Date:  08/1989
Category:          Astrophysics
NASA/STI Keywords: ASTROMETRY, LASER INTERFEROMETRY, RELATIVITY,
                   SPACEBORNE EXPERIMENTS, ASTROPHYSICS,
                   GRAVITATION THEORY, QUASARS, STELLAR MAGNITUDE,
                   STELLAR PARALLAX, TIME DEPENDENCE
Bibliographic Code:1989rges.rept..155R

Abstract

A space-based astrometric interferometer with a large optical bandwidth is considered. POINTS (Precision Optical INTerferometry in Space) would measure the angular separation of two stars separated by about 90 deg on the sky with a nominal measurement error of 5 microarcseconds (uas). For a pair of mag 10 stars, the observation would require about 10 minutes. It is estimated that the instrument would measure daily the separation of two stars for each of about 60 pairs of stars; a random sequence of such measurements, if suitably redundant, contains the closure information necessary to detect and correct time dependent measurement biases to well below the nominal measurement accuracy. The 90 deg target separation permits absolute parallax measurements in all directions. A redundant observing schedule for 300 stars and 5 quasars would provide extra redundancy to compensate for the quasars' higher magnitude. If a nominal 30-day observation sequence were repeated 4 times per year for 10 years, stellar parameter uncertainties would be obtained of: 0.6 uas, position; 0.4 uas/y, proper motion; and 0.4 uas, parallax. This set of well-observed stars and quasars would form a rigid frame and the stars would serve as reference objects for measurements of all additional targets, as well as being targets of direct scientific interest. The instrument global data analysis since objectives are considered including a relativity test and technology.
Index
Title:             POINTS - A global reference frame opportunity
Authors:           Chandler, J. F.; Reasenberg, R. D.
Affiliation:       AB(Smithsonian Astrophysical Observatory, Cambridge,
                   MA)
Journal:           IN: Inertial coordinate system on the sky; Proceedings
                   of the 141st Symposium of the IAU, Leningrad, USSR,
                   Oct. 17-21, 1989 (A91-54762 23-89). Dordrecht,
                   Netherlands, Kluwer Academic Publishers, 1990, p.
                   217-227; Discussion, p. 228. Research supported by
                   Smithsonian Institution.
Publication Date:  00/1990
Category:          Astronomy
NASA/STI Keywords: ASTROMETRY, CELESTIAL REFERENCE SYSTEMS,
                   INTERFEROMETERS, SATELLITE-BORNE INSTRUMENTS,
                   ANGULAR RESOLUTION, DESIGN ANALYSIS,
                   SPACEBORNE ASTRONOMY
Bibliographic Code:1990icss.symp..217C

Abstract

POINTS is a space-based optical astrometric interferometer capable of measuring the angular separation of two stars about 90 degrees apart with 5-microarcsec nominal accuracy . During the intended ten-year mission, a repeated survey of a few hundred targets over the whole sky, including a few bright quasars, establish a 'rigid' reference grid with 0.5 microarcsec position uncertainties. At that level, the grid is free of regional biases and tied to the extra-Galactic frame that is the present best candidate for an inertial frame. POINTS will also determine parallaxes and annual proper motions at about the same level. Further, the planetary ephemeris frame is tied through stellar aberration to the grid at about 300 microarcsec. Additional targets of interest, to a limiting magnitude of greater than 20, are observed relative to the grid, yielding determinations with uncertainties depending on the observing schedule. Measurement at the microarcsec/year level of the apparent relative velocities of quasars that are widely separated on the sky severely test the assumption of cosmological quasar distances and may also constrain models of the early universe.
Index
Title:             Prospects for observations of relativistic effects in
                   the solar system
Authors:           Reasenberg, R. D.; Shapiro, I. I.
Affiliation:       AB(Harvard-Smithsonian Center for Astrophysics,
                   Cambridge, MA)
Journal:           IN: Relativity in celestial mechanics and astrometry:
                   High precision dynamical theories and observational
                   verifications; Proceedings of the Symposium,
                   Leningrad, USSR, May 28-31, 1985 (A87-24502 09-90).
                   Dordrecht, D. Reidel Publishing Co., 1986, p.
                   383-390; Discussion, p. 391. Research supported by
                   the Smithsonian Institution.
Publication Date:  00/1986
Category:          Astronomy
NASA/STI Keywords: ASTROMETRY, RELATIVISTIC EFFECTS, SOLAR GRAVITATION,
                   SOLAR SYSTEM, SPACEBORNE ASTRONOMY, INSTRUMENT ERRORS,
                   LIGHT TRANSMISSION
Bibliographic Code:1986rcma.......383R

Abstract

In this paper the authors concentrate on an experiment that promises a dramatic improvement in a classical test of general relativity - the deflection of light by solar gravity. The goal is to measure the post-post-Newtonian contribution of nearly 11 microarcseconds to this deflection. The proposed technique is based on use of an astrometric optical interferometer, POINTS, which could be operated from the bay of the Space Shuttle, mounted on the proposed Space Station, or supported by an independent spacecraft. POINTS should be able to measure the separation of stars about 90 deg apart with an uncertainty of only a few microarcseconds.
Index
        TITLE:  POINTS: the first small step
      AUTHORS:  Reasenberg, R.D.; Babcock, R.W.; Noecker, M.C.; Phillips, J.D.
  CORP SOURCE:  Harvard-Smithsonian Center for Astrophys., Smithsonian
                Astrophys. Obs., Cambridge, MA, USA
       SOURCE:  Proc. SPIE - Int. Soc. Opt. Eng. (USA), Proceedings of the
                SPIE - The International Society for Optical Engineering,
                vol.1947, p. 12-29
   CONF TITLE:  Spaceborne Interferometry
CONF LOCATION:  Orlando, FL, USA; 15-16 April 1993

ABSTRACT

POINTS, an astrometric optical interferometer with a nominal measurement accuracy of 5 microarcseconds for the angle between a pair of stars separated by about 90 deg, is presently under consideration. If chosen as the TOPS-1 (Toward Other Planetary Systems) instrument, it will perform a definitive search for extra-solar planetary systems. If chosen as the AIM (Astrometric Interferometry Mission), POINTS will open new areas of astrophysical research and change the nature of the questions being asked in some old areas. Based on a preliminary indication of the observational needs of the two missions, a single POINTS mission is found to meet the science objectives of both TOPS-1 and AIM (13 Refs.)
Index
        TITLE:  Fringe tracking filters for space-based interferometers
      AUTHORS:  Padilla, C.E.; Chun, H.M.; Matson, L.; Reasenberg, R.D.
  CORP SOURCE:  Moldyn Inc., Cambridge, MA, USA
       SOURCE:  Proc. SPIE - Int. Soc. Opt. Eng. (USA), Proceedings of the
                SPIE - The International Society for Optical Engineering,
                vol.1947, p. 30-43
   CONF TITLE:  Spaceborne Interferometry
CONF LOCATION:  Orlando, FL, USA; 15-16 April 1993

ABSTRACT

The purpose of the authors' research is to explore, from the point of view of nonlinear filtering, the feasibility of microarcsecond astrometry using space-based optical interferometers in typical disturbance environments. Two nonlinear estimators are developed to enable high precision estimates of the optical path difference (OPD) between the two starlight paths in a spaceborne optical interferometer. Focal plane fringe data measurements by either CCD (charge coupled device) or photon counting (PC) cells are processed by an Extended Kalman Filter (EKF)-based algorithm to yield the OPD estimate. Whereas the filter based on CCD cell measurements results in a straightforward implementation of an EKF, the filter utilizing PC cells requires some innovations before yielding to the EKF framework. Instead of using the photon arrival events as measurements, the filter measurements are taken to be the interarrival time between photons. The excellent results obtained with the PC filter are backed by intuition based on linear analysis results. Simulation studies show that as the CCD readout time is decreased, the performance of the CCD filter approaches that of the PC filter. The POINTS instrument concept is used as a test baseline (24 Refs.)
Index
        TITLE:  Internal laser metrology for POINTS
      AUTHORS:  Noecker, M.C.; Phillips, J.D.; Babcock, R.W.; Reasenberg, R.D.
  CORP SOURCE:  Harvard-Smithsonian Center for Astrophys., Smithsonian
                Astrophys. Obs., Cambridge, MA, USA
       SOURCE:  Proc. SPIE - Int. Soc. Opt. Eng. (USA), Proceedings of the
                SPIE - The International Society for Optical Engineering,
                vol.1947, p. 174-87
   CONF TITLE:  Spaceborne Interferometry
CONF LOCATION:  Orlando, FL, USA; 15-16 April 1993

ABSTRACT

The authors present the designs for laser distance gauges to be used in the POINTS instrument, and preliminary performance data. For the target 5 micro-arcsecond astrometric accuracy, one must hold or monitor some critical internal dimensions of the POINTS instrument with 2 picometer (pm, 10/sup -12/m) accuracy for a few hours. The POINTS architecture makes good use of these gauges, minimizing the number and range of dimensions that must change during operation, and maximizing the similarity of the starlight and metrology measured paths. Gauge designs have been developed for both optical-path differencing (Michelson) and point-to-point measurements (Fabry-Perot). The Michelson fringes have been measured in a differential (comparison) test. A second design for the point-to-point measurements incorporates cornercube retro-reflectors in a resonant cavity. The authors discuss the new problems anticipated in this design, including the problem of maintaining laser alignment in these point-to-point gauges over the +or-3 degree range of instrument articulation (14 Refs.)
Index
        TITLE:  Optic-misalignment tolerances for the POINTS interferometers
      AUTHORS:  Noecker, M.C.; Murison, M.A.; Reasenberg, R.D.
  CORP SOURCE:  Smithsonian Astrophys. Obs., Cambridge, MA, USA
       SOURCE:  Proc. SPIE - Int. Soc. Opt. Eng. (USA), Proceedings of the
                SPIE - The International Society for Optical Engineering,
                vol.1947, p. 218-31
   CONF TITLE:  Spaceborne Interferometry
CONF LOCATION:  Orlando, FL, USA; 15-16 April 1993

ABSTRACT

The authors present the results of two parallel studies of the sensitivity of astrometric measurements to misalignment of each of the major optical assemblies in the POINTS instrument. Tilt and displacement of the optics lead to tilt, displacement and defocussing of the starlight and metrology beams, giving rise to systematic errors. In one method, they derive analytic expressions for the lowest order dependence of the error on the misalignment, and evaluate them in the present interferometer design. In the second method, they use a commercial numerical ray tracing program to calculate the overall optical path travelled through the misaligned starlight and metrology paths: from those results, software determines the dependence of the residual error on the original misalignment. These sensitivities are compared to the analytic results for mutual verification. The impact these results have had on the design of the instrument is also discussed (4 Refs.)
Index
        TITLE:  Newcomb, a POINTS precursor mission with scientific capacity
      AUTHORS:  Reasenberg, R.D.; Babcock, R.W.; Phillips, J.D.; Johnson,
                K.J.; Simon, R.S.
  CORP SOURCE:  Harvard Smithsonian Center for Astrophys., Smithsonian
                Astrophys. Obs., Cambridge, MA, USA
       SOURCE:  Proc. SPIE - Int. Soc. Opt. Eng. (USA), Proceedings of the
                SPIE - The International Society for Optical Engineering,
                vol.1947, p. 273-81
   CONF TITLE:  Spaceborne Interferometry
CONF LOCATION:  Orlando, FL, USA; 15-16 April 1993

ABSTRACT

Newcomb is a design concept for an astrometric optical interferometer with nominal single-measurement accuracy of 100 microseconds of arc (uas). The instrument is a highly simplified variant of POINTS. It has three (or four) interferometers stacked one above the other. All three (four) optical axes lie on a great circle, which is also the nominal direction of astrometric sensitivity. The second and third axes are separated from the first by fixed 'observation angles' of 40.91 and 60.51 deg. The fourth axis would be at either 70.77 or 78.60 deg from the first. Each interferometer detects a dispersed fringe (channeled spectrum), which falls on a CCD detector array nominally 8k elements long and a small number of elements wide. With a nominal length of 30 cm and optical passband from 0.9 to 0.3 microns, the Nyquist limit is reached by a star +or-21 arcmin from the optical axis (8 Refs.)
Index
        TITLE:  POINTS: a small astrometric interferometer in space
       AUTHOR:  Reasenberg, R.D.
  CORP SOURCE:  Smithsonian Astrophys. Obs., Cambridge, MA, USA
       SOURCE:  Proc. SPIE - Int. Soc. Opt. Eng. (USA), Proceedings of the
                SPIE - The International Society for Optical Engineering,
                vol.571, p. 245-51
   CONF TITLE:  Large Optics Technology
CONF LOCATION:  San Diego, CA, USA; 19-21 Aug. 1985

ABSTRACT

POINTS (Precision Optical INTerferometry in Space) is a design concept for an astrometric interferometer originally conceived as a means of performing the light deflection experiment of general relativity to second order. The present 'strawman' version, which has a pair of 2 m baselines and four 25 cm telescopes, would fit fully assembled with a support spacecraft in one-third of the Shuttle bay. For a pair of tenth-magnitude stars about 90 degrees apart, POINTS would yield the separation uncertain by 5 uas after a 10-minute observation. The author considers both the design of the instrument and aspects of a mission (6 Refs.)