Starship Asterisk*

[i]Artists's conception of Saturn and its moons, seen from above its pole. [b]Credit: B. Kent, A. Angelich, NRAO/AUI/NSF[/b][/i]

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Scientists have used the National Science Foundation's Very Long Baseline Array (VLBA) radio-telescope system and NASA's Cassini spacecraft to measure the position of Saturn and its family of moons to within about a mile -- at a range of nearly a billion miles. This feat improves astronomers' knowledge of the dynamics of our Solar System and also benefits interplanetary spacecraft navigation and research on fundamental physics.

The researchers, from the National Radio Astronomy Observatory (NRAO) and NASA's Jet Propulsion Laboratory (JPL), used the continent-wide VLBA to pinpoint the position of Cassini as it orbited Saturn over the past decade by receiving the signal from the spacecraft's radio transmitter. Combined with information about Cassini's orbit from NASA's Deep Space Network, the VLBA observations allowed the scientists to make the most accurate determinations yet of the position of the center of mass, called the barycenter, of Saturn and its numerous moons. ...

The measurement, some 50-100 times more precise than those provided by ground-based optical telescopes, was possible because of the VLBA's great resolving power, or ability to discern fine detail. With its 10 dish antennas spread from Hawaii to the Virgin Islands, the VLBA operates as a single radio telescope with a virtual size nearly equal to the Earth's diameter.

The result is a greatly improved ephemeris -- a table of predicted positions -- for the Saturnian system. ...

• Astronomical Journal 149(1) 28 (2015 Jan) DOI: 10.1088/0004-6256/149/1/28
  arXiv.org > astro-ph > arXiv:1410.1067 > 04 Oct 2014

geckzilla wrote:All I want to say here is that I love the word ephemeris.