Presentation Title

Precision Asteroid Astrometry

Faculty Mentor

Paul McCudden

Start Date

18-11-2017 2:00 PM

End Date

18-11-2017 2:15 PM

Location

9-279

Session

Physical Sciences 1

Type of Presentation

Oral Talk

Subject Area

physical_mathematical_sciences

Abstract

Among the methods used to guide spacecraft, Optical Navigation (OpNav) remains an effective option. OpNav makes use of star fields and small body ephemerides to precisely locate spacecraft. To facilitate accurate OpNav, the small body ephemerides must be constantly updated; asteroid orbits accumulate errors yearly of a few milliarcseconds. Through extended exposures, taken with strategic offsets, a least-squares solution can be found that determines updated ephemeris data. This data can also be used by occultation astronomers to gain further information about the small bodies, including their size and shape.

Using the 24-inch telescope at the Caltech Table Mountain Observatory (TMO), we capture two or more 180 second exposures of each target. These images, combined with a file for the predicted background star field and two reference files, are then processed through a series of scripts and programs. Starting with a prediction file and two to five exposures of the asteroid, the data is processed. This original data is about 32MB per observation. Once the data are reduced to only Right Ascension and Declination for each target, the data are ready for delivery. This consists of text only, and for each target takes about 80 bytes; this resulting data reduction is about five orders of magnitude. This method produces observed positions that are refined by about 12 milliarcseconds, a refinement that is accomplished almost nowhere else. The occultation observations that are facilitated by the ephemerides being refined also produce results that are not possible in any other way from ground-based observations.

Summary of research results to be presented

After data delivery, the data are reviewed by the MPC. The MPC publishes the results to their website, and these data are then used by occultation observers to image the occultation using the refined ephemerides for a more accurate prediction of the asteroid’s location. Similarly, the data may be used for optical navigation, considering the updated information about the objects’ orbits. Given an opportunistic occultation, these data can facilitate high resolution occultation observations. Particularly when there are many observers, the resulting observations produce a combination of occultation lines.

The line formed by the star, while the star field is in relative motion, is broken by the occultation. Observations from different locations produce unique lines, and when put together they can form a silhouette of the asteroid, revealing size and shape information in a way that can only be improved upon by direct observation from a passing spacecraft. This effect can be seen best when there are many observers. The results of this type of observation are clearly visible, as the higher the number of observations, the higher the resolution of the resulting silhouette. For OpNav, the same program used during the prediction stage would be used by the spacecraft to determine its location based on the relative locations of asteroids, and other bodies, against the known star field.

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Nov 18th, 2:00 PM Nov 18th, 2:15 PM

Precision Asteroid Astrometry

9-279

Among the methods used to guide spacecraft, Optical Navigation (OpNav) remains an effective option. OpNav makes use of star fields and small body ephemerides to precisely locate spacecraft. To facilitate accurate OpNav, the small body ephemerides must be constantly updated; asteroid orbits accumulate errors yearly of a few milliarcseconds. Through extended exposures, taken with strategic offsets, a least-squares solution can be found that determines updated ephemeris data. This data can also be used by occultation astronomers to gain further information about the small bodies, including their size and shape.

Using the 24-inch telescope at the Caltech Table Mountain Observatory (TMO), we capture two or more 180 second exposures of each target. These images, combined with a file for the predicted background star field and two reference files, are then processed through a series of scripts and programs. Starting with a prediction file and two to five exposures of the asteroid, the data is processed. This original data is about 32MB per observation. Once the data are reduced to only Right Ascension and Declination for each target, the data are ready for delivery. This consists of text only, and for each target takes about 80 bytes; this resulting data reduction is about five orders of magnitude. This method produces observed positions that are refined by about 12 milliarcseconds, a refinement that is accomplished almost nowhere else. The occultation observations that are facilitated by the ephemerides being refined also produce results that are not possible in any other way from ground-based observations.