Orbit of One Wayward Galileo Satellite Raised

December 1, 2014  - By

The orbit of one of the two Galileo satellites launched into incorrect orbits on August 22 is being adjusted. Tracking data supplied by the North American Aerospace Defense Command (NORAD) and the U.S. Joint Space Operations Center (JSpOC) has confirmed the change.

Also, the first navigation signal from Galileo 5 has been received.

The satellites were supposed to go into circular orbits with an inclination to the equator of 56 degrees and with a semi-major axis of about 29,600 km. They ended up in eccentric orbits with semi-major axes more than 3,300 km shorter and with an inclination of about 49.7 degrees.

Instead of an orbital height of 23,222 km above the surface of the Earth, they were moving between apogee heights of about 25,900 km and perigee heights of about 13,800 km, perilously close to the most dangerous regions of the Van Allen radiation belts.

The European Space Agency announced on November 10 that the orbit of one of the two wayward satellites, Galileo 5, would have its perigee raised to 17,339 km through a series of 15 orbital maneuvers. This orbital adjustment would put the satellite into a safer orbit and potentially make it useable for positioning and navigation. If the operation is successful, Galileo 6 will follow suit.

These maneuvers likely started on or shortly after November 8. After the maneuvers began, NORAD/JSpOC temporarily “lost” the satellite as often happens when satellites undergo unpredicted Delta-V operations. NORAD/JSpOC recovered the satellite after about 18 days and issued new orbital elements for the satellite on November 25.

The new elements show that (so far) the perigee of Galileo 5 has been raised from about 13,820 km to 17,230 km with a corresponding change in the orbital eccentricity from about 0.23053 to 0.15619. The apogee height is virtually the same as that immediately after launch. Also, the inclination is not and will not be materially changed.

An animation, produced using the NORAD/JSpOC orbital element sets and the XEphem software, compares Galileo 5’s old and new orbits:

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About the Author: Richard B. Langley

Richard B. Langley is a professor in the Department of Geodesy and Geomatics Engineering at the University of New Brunswick (UNB) in Fredericton, Canada, where he has been teaching and conducting research since 1981. He has a B.Sc. in applied physics from the University of Waterloo and a Ph.D. in experimental space science from York University, Toronto. He spent two years at MIT as a postdoctoral fellow, researching geodetic applications of lunar laser ranging and VLBI. For work in VLBI, he shared two NASA Group Achievement Awards. Professor Langley has worked extensively with the Global Positioning System. He has been active in the development of GPS error models since the early 1980s and is a co-author of the venerable “Guide to GPS Positioning” and a columnist and contributing editor of GPS World magazine. His research team is currently working on a number of GPS-related projects, including the study of atmospheric effects on wide-area augmentation systems, the adaptation of techniques for spaceborne GPS, and the development of GPS-based systems for machine control and deformation monitoring. Professor Langley is a collaborator in UNB’s Canadian High Arctic Ionospheric Network project and is the principal investigator for the GPS instrument on the Canadian CASSIOPE research satellite now in orbit. Professor Langley is a fellow of The Institute of Navigation (ION), the Royal Institute of Navigation, and the International Association of Geodesy. He shared the ION 2003 Burka Award with Don Kim and received the ION’s Johannes Kepler Award in 2007.