Liberalism

Giorgini, Giovanni

doi:10.1002/9781118541555.wbiepc091

Cited by 4 publications

(7 citation statements)

References 4 publications

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“…And from this data, to derive the magnitude and components of the anomalous acceleration acting upon the spacecraft, i. e., the acceleration that should be imparted upon the spacecraft to obtain an exact agreement among the predicted and the observed trajectories (By observed trajectories we mean the fittings to telemetry data incorporated in the Horizons database by the mission teams [17]. These trajectories take into account the information processing of the Doppler traking of each spacecraft [29]). We have found that such acceleration can be deduced from the numerical method and that its magnitude agrees with the expected estimate provided by some modified models of gravity [1,4] as given in Eq.…”

Section: Discussionmentioning

confidence: 99%

“…Another important issue is that the ephemeris for the spacecraft incorporated into Horizons are provided by the mission teams and they are fits to the telemetry data within the context of the specific orbital model [29]. In that sense, they can be seen as reflecting the real Doppler and ranging data.…”

Section: Development Of the Orbital Modelmentioning

confidence: 99%

“…To this aim we compare the predictions of our model with the ephemeris provided by the mission teams which incorporate the information of telemetry's monitoring to fit the trajectories [17,29].…”

Section: Introductionmentioning

confidence: 99%

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Anomalous accelerations in spacecraft flybys of the Earth

Acedo

2017

Astrophys Space Sci

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The flyby anomaly is a persistent riddle in astrodynamics. Orbital analysis in several flybys of the Earth since the Galileo spacecraft flyby of the Earth in 1990 have shown that the asymptotic post-encounter velocity exhibits a difference with the initial velocity that cannot be attributed to conventional effects. To elucidate its origin, we have developed an orbital program for analyzing the trajectory of the spacecraft in the vicinity of the perigee, including both the Sun and the Moon's tidal perturbations and the geopotential zonal, tesseral and sectorial harmonics provided by the EGM96 model. The magnitude and direction of the anomalous acceleration acting upon the spacecraft can be estimated from the orbital determination program by comparing with the trajectories fitted to telemetry data as provided by the mission teams. This acceleration amounts to a fraction of a mm/s 2 and decays very fast with altitude. The possibility of some new physics of gravity in the altitude range for spacecraft flybys is discussed.

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Section: Discussionmentioning

confidence: 99%

Section: Development Of the Orbital Modelmentioning

confidence: 99%

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Anomalous accelerations in spacecraft flybys of the Earth

Acedo

2017

Astrophys Space Sci

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“…Suggestion of the level of needed astrometric accuracy is from a simulation assuming a set of 4 astrometric measurements with ∼40 mas accuracy and taken over approximately 2 months for an NEA in a near Earth-like orbit (Giorgini 2013). It was found that 40 mas would be sufficient to predict the NEA position to ∼10 ′′ at the next apparition 3-4 years in the future.…”

Section: Astrometrymentioning

confidence: 99%

Finding Very Small Near-Earth Asteroids Using Synthetic Tracking

Shao

Nemati

Zhai

et al. 2014

ApJ

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We present an approach that significantly increases the sensitivity for finding and tracking small and fast nearEarth asteroids (NEAs). This approach relies on a combined use of a new generation of high-speed cameras which allow short, high frame-rate exposures of moving objects, effectively "freezing" their motion, and a computationally enhanced implementation of the "shift-and-add" data processing technique that helps to improve the signal-to-noise ratio (SNR) for detection of NEAs. The SNR of a single short exposure of a dim NEA is insufficient to detect it in one frame, but by computationally searching for an appropriate velocity vector, shifting successive frames relative to each other and then co-adding the shifted frames in post-processing, we synthetically create a long-exposure image as if the telescope were tracking the object. This approach, which we call "synthetic tracking," enhances the familiar shift-and-add technique with the ability to do a wide blind search, detect, and track dim and fast-moving NEAs in near real time. We discuss also how synthetic tracking improves the astrometry of fast-moving NEAs. We apply this technique to observations of two known asteroids conducted on the Palomar 200 inch telescope and demonstrate improved SNR and 10 fold improvement of astrometric precision over the traditional long-exposure approach. In the past 5 yr, about 150 NEAs with absolute magnitudes H = 28 (∼10 m in size) or fainter have been discovered. With an upgraded version of our camera and a field of view of (28 arcmin) 2 on the Palomar 200 inch telescope, synthetic tracking could allow detecting up to 180 such objects per night, including very small NEAs with sizes down to 7 m.

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“…Ideally we would have the GPU software running to detect the NEAs in near real time so that the second confirming observation could be made within the time frame (a few hours) later before the uncertainty in the location of the asteroid becomes larger than the FOV. Once confirmed we should spend significantly more than 30 sec to get astrometry approaching 50 mas so that three observations spaced a few days apart would let us derive an orbit where the object could be observed again at the next apparition (Giorgini 2013). Objects with H∼28-30 moving at 6 • /day are detectable only on medium to large telescopes with synthetic tracking cameras, and even then, only for a week or so before they are too faint to be detected.…”

Section: Discovery and Orbit Determination Of Neas With Synthetic Tramentioning

confidence: 99%

Detection of a Faint Fast-Moving Near-Earth Asteroid Using the Synthetic Tracking Technique

Zhai

Shao

Nemati

et al. 2014

ApJ

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We report a detection of a faint near-Earth asteroid (NEA), which was done using our synthetic tracking technique and the CHIMERA instrument on the Palomar 200-inch telescope. This asteroid, with apparent magnitude of 23, was moving at 5.97 degrees per day and was detected at a signal-to-noise ratio (SNR) of 15 using 30 sec of data taken at a 16.7 Hz frame rate. The detection was confirmed by a second observation one hour later at the same SNR. The asteroid moved 7 arcseconds in sky over the 30 sec of integration time because of its high proper motion. The synthetic tracking using 16.7 Hz frames avoided the trailing loss suffered by conventional techniques relying on 30-sec exposure, which would degrade the surface brightness of image on CCD to an approximate magnitude of 25. This detection was a result of our 12-hour blind search conducted on the Palomar 200-inch telescope over two nights on September 11 and 12, 2013 scanning twice over six 5.0 • ×0.043 • fields. The fact that we detected only one NEA, is consistent with Harris's estimation of the asteroid populationdistribution, which was used to predict the detection of 1-2 asteroids of absolute magnitude H=28-31 per night. The design of experiment, data analysis method, and algorithms for estimating astrometry are presented. We also demonstrate a milli-arcsecond astrometry using observations of two bright asteroids with the same system on Apr 3, 2013. Strategies of scheduling observations to detect small and fast-moving NEAs with the synthetic tracking technique are discussed.

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Liberalism

Cited by 4 publications

References 4 publications

Anomalous accelerations in spacecraft flybys of the Earth

Anomalous accelerations in spacecraft flybys of the Earth

Finding Very Small Near-Earth Asteroids Using Synthetic Tracking

Detection of a Faint Fast-Moving Near-Earth Asteroid Using the Synthetic Tracking Technique

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