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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.

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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS2008

Recent Results of the Guide-2 Telescope Testbed for the SIM-Lite Mission

The Space Interferometry Mission Planet QuestLite (SIM-Lite) is a new mission concept to perform microarcsecond narrow-angle astrometry to search approximately 50 nearby stars for Earth-like planets, and also to perform a global astrometry. The SIM-Lite consists of two Michelson interferometers and one telescope. The main six-meter baseline science interferometer observes a target star and a set of reference stars. The four-meter baseline interferometer (Guide-1) monitors the attitude of the instrument in the direction of a target star. A new Guide-2telescope (G2T) tracks a bright star to monitor the attitude of the instrument in the other two orthogonal directions. In the current mission concept, the G2T consists of a 30 cm siderostat and a 30 cm confocal telescope, similar to other four telescopes used in the science and Guide-1interferometers. A testbed has been built to demonstrate the G2T feasibility for SIM-Lite mission. Recent results show that field-independent, star-tracking capability of the system is less than 30 (mu)as after the SIM narrow angle analysis.

Guide-2 Telescope↗
NASA NTRS2000

Searching for Planets with the Space Interferometry Mission

The Space Interferometry Mission (SIM) will be the first space-based long baseline Michelson interferometer designed for precision astrometry. It will address a wide range of problems in stellar astrophysics and Galactic structure, delivering precision astrometry of stars down to 20 magnitude throughout the entire Galaxy. SIM uses a 10-m Michelson interferometer in Earth-trailing solar orbit to provide 4 microarcsecond (gas) precision astrometry. With a 5-year mission lifetime, SIM will be a powerful tool for discovering planets around nearby stars, through detection of the stellar reflex motion. The astrometric method complements the radial velocity technique which as already yielded many new planets, with an important benefit of directly measuring planetary masses. SIM will have a single-measurement precision of 1 microarcsecond in a frame defined by nearby reference stars, enabling searches for planets with masses as small as a few earth masses around the nearest stars. More massive planets will be detectable to much larger distances. In addition to precision astrometry SIM will also serve an important role as a technology precursor for future astrophysics missions using interferometers. Two technologies demonstrated will be high dynamic-range aperture synthesis imaging at 10-milliarcsec resolution in the optical, and fringe nulling to 10 (exp -4).

Unwin, Stephen↗
NASA NTRS2000

Searching for Extrasolar Planets with SIM

The Space Interferometry Mission (SIM) will be the first spacebased long base-line Michelson interferometer designed for precision astrometry. SIM will extend the reach of astrometry to cover the entire Galaxy, and will address a wide range of problems in Galactic structure and stellar astrophysics. It will also serve as a technology precursor for future astrophysics missions using interferometers. SIM will be a powerful tool for discovering planets around nearby stars, through detection of the reflex motion, and it will directly measure masses for the planets detected this way. It will have a single-measurement precision of 1 microarcsecond in a frame defined by nearby reference stars, enabling SIM to search for planets with masses as small as a few earth masses around the nearest star. More massive planets will be detectable to much larger distances.

Unwin, Stephen C.↗
NASA NTRS1995

VLBI Phase-Referenced Observations on Southern Hemisphere HIPPARCOS Radio Start

Presented are multiepoch Very Long Baseline Interferometry (VLBI) observations on Southern Hemisphere radio stars phase-referenced to background radio sources. The differential astrometry analysis results in high-precision determinations of proper motions and parallaxes. The astrophysical implications and astrometric consequences of these results are discussed.

Radio Emission Stars VLBI Radio Astronomy Astrophy↗
NASA NTRS2006

Results from the TOM3 testbed: thermal deformation of optics at the picometer Level

We have discussed the TOM3 testbed developed to assess the thermo-opto-mechanical stability of optical assembly such as SIM's siderostat and telescope in flight-like thermal conditions. Although limited by the metrology sensor noise, test results show that optical wavefront stability of SIM's optical assembly is compatible with single micro-arcsecond astrometry.

Space Interferometer Mission (SIM)↗
NASA NTRS2010

The Celestial Reference Frame at X/Ka-band (8.4/32 GHz)

A celestial reference frame at X/Kaband (8.4/32 GHz) has been constructed using fiftyone 24-hour sessions with the Deep Space Network. We report on observations which have detected 436 sources covering the full 24 hours of right ascension and declinations down to -45 deg. Comparison of this X/Ka-band frame to the S/X-band (2.3/8.4 GHz) ICRF2 shows wRMS agreement of 200 micro-arcsec ( mu as) in alpha cos delta and 290 mu as in delta. There is evidence for zonal errors at the 100 mu as level. Known errors include limited SNR, lack of phase calibration, troposphere mismodelling, and limited southern geometry. The motivations for extending the ICRF to frequencies above 8 GHz are to access more compact source morphology for improved frame stability, to provide calibrators for phase referencing, and to support spacecraft navigation at Ka-band.

interferometry↗
NASA NTRS2002

SIM science operations

This paper describes the science scheduling and operation of the Space Interferometry Mission (SIM) as a science instrument

SIM↗
DOE OSTI2022

Astrometric gravitational-wave detection via stellar interferometry

Here, we evaluate the potential for gravitational-wave (GW) detection in the frequency band from 10 nHz to 1 μ Hz using extremely high-precision astrometry of a small number of stars. In particular, we argue that nonmagnetic, photometrically stable, hot white dwarfs (WD) located at ~kpc distances may be optimal targets for this approach. Previous studies of astrometric GW detection have focused on the potential for less precise surveys of large numbers of stars; our work provides an alternative optimization approach to this problem. Interesting GW sources in this band are expected at characteristic strains around h c ~10 -17 × (μHz/ $f$ GW ). The astrometric angular precision required to see these sources is Δθ~h c after integrating for a time T~1/$f$GW. We show that jitter in the photometric center of WD of this type due to starspots is bounded to be small enough to permit this high-precision, small-N approach. We discuss possible noise arising from stellar reflex motion induced by orbiting objects and show how it can be mitigated. The only plausible technology able to achieve the requisite astrometric precision is a space-based stellar interferometer. Such a future mission with few-meter-scale collecting dishes and baselines of $\mathscr{O}$(100 km ) is sufficient to achieve the target precision. This collector size is broadly in line with the collectors proposed for some formation-flown, space-based astrometer or optical synthetic-aperture imaging-array concepts proposed for other science reasons. The proposed baseline is however somewhat larger than the km-scale baselines discussed for those concepts, but we see no fundamental technical obstacle to utilizing such baselines. A mission of this type thus also holds the promise of being one of the few ways to access interesting GW sources in this band.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Increasing Baselines and Precision of Optical Interferometers Using Two-Photon Interference

Observations using interferometers provide sensitivity to features of images on angular scales much smaller than any single telescope, on the order of Δθ ~ λ/b where b is the interferometric baseline. Present-day optical interferometers are essentially classical, interfering single photons with themselves. However, there is a new wave of interest in interferometry using multiple photons, whose mechanisms are inherently quantum mechanical, which offer the prospects of increased baselines and finer resolutions among other advantages. We will discuss recent ideas and results for quantum-assisted interferometry using the resource of entangled pairs, and specifically a two-photon amplitude technique aimed at improved precision in astrometry.

47 OTHER INSTRUMENTATION↗
NASA NTRS2004

White Light Modeling, Algorithm Development, and Validation on the Micro-arcsecond Metrology Testbed

The Space Interferometry Mission (SIM) scheduled for launch in early 2010, is an optical interferometer that will perform narrow angle and global wide angle astrometry with unprecedented accuracy, providing differential position accuracies of 1uas, and 4uas global accuracies in position, proper motion and parallax. The astrometric observations of the SIM instrument are performed via delay measurements provided by three Michelson-type, white light interferometers. Two 'guide' interferometers acquire fringes on bright guide stars in order to make highly precise measurements of variations in spacecraft attitude, while the third interferometer performs the science measurement. SIM derives its performance from a combination of precise fringe measurements of the interfered starlight (a few ten-thousandths of a wave) and very precise (tens of picometers) relative distance measurements made between a set of fiducials. The focus of the present paper is on the development and analysis of algorithms for accurate white light estimation, and on validating some of these algorithms on the MicroArcsecond Testbed.

metrology↗
NASA NTRS2004

White light modeling, algorithm development, and validation on the micro-arcsecond metrology testbed

The Space Interferometry Mission (SIM), scheduled for launch in early 2010, is an optical interferometer that will perform narrow angle and global wide angle astrometry with unprecedented accuracy, providing differential position accuracies of 1uas, and 4uas global accuracies in position, proper motion and parallax. SIM astrometric measurements are synthesized from pathlength delay measurements provided by three Michelson-type, white light interferometers. Two of the interferometers are used for making precise measurements of variations in the spacecraft attitude, while the third interferometer performs the science measurement. The ultimate performance of SIM relies on a combination of precise fringe measurements of the interfered starlight with picometer class relative distance measurements made between a set of fiducials that define the interferometer baseline vectors. The focus of the present paper is on the development and analysis of algorithms for accurate white light fringe estimation, and on the preliminary validation of these algorithms on the Micro-Arcsecond Testbed (MAM).

Shen, Janice TsaePyng↗
NASA NTRS1988

Astrometry in local reference frames for deep space navigation

Future deep space missions will benefit from submilliarcsecond angular navigation accuracy (less than 25 km projected distance at Neptune). Conventional Very Long Baseline Interferometry (VLBI) measurement strategies entail observations of a radio source (RS) and spacecraft pair. To increase the 3-5 milliarcsecond accuracies currently attainable, instrumental improvements could be coupled with either of two methods: (1) use improved calibration measurements with the single RS as the spacecraft reference, or (2) use a reference frame established by a local network of RSs near the spacecraft to reduce the contribution of sky-dependent error sources. The demanding baseline vector (earth orientation) and tropospheric calibrations needed to realize submilliarcsecond accuracy with the single-source strategy would not be necessary with the multisource strategy. The two strategies are compared via a sample covariance analysis. In this analysis, the single-source method yields 1.5 milliarcseconds for the navigation accuracy, while the multisource method yields 0.5 milliarcseconds.

Treuhaft, R. N.↗
NASA NTRS2002

High-precision early mission narrow angle sciene with the Space Interferometry Mission

We have developed a technique that allows SIM to measure relative stellar positions with an accuracy of 1 micro-arcsecond at any time during its 5-yr mission. Unlike SIM's standard narrow-angle approach, Gridless Narrow Angle Astrometry (GNAA) does not rely on the global reference frame of grid stars that reaches full accuracy after 5 years. GNAA is simply the application of traditional single-telescope narrow angle techniques to SIM's narrow angle optical path delay measurements. In GNAA, a set of reference stars and a target star are observed at several baseline orientations. A linearized model uses delay measurements to solve for star positions and baseline orientations. A conformal transformation maps observations at different epochs to a common reference frame. The technique works on short period signals (P=days to months), allowing it to be applied to many of the known extra-solar planets, intriguing radio/X- ray binaries, and other periodic sources. The technique's accuracy is limited in the long-term by false acceleration due to a combination of reference star and target star proper motion. The science capability 1 micro-arcsecond astrometric precision - is unique to SIM.

Space Interferometry Mission↗