The U. S. Navy NOVA Drag-Free Navigation Satellites

As an operational follow-on to DISCOS and the other satellites of the TRANSIT Improvement Program, the U. S. Navy launched three single-axis drag-free satellites, NOVA I on May 25, 1981, NOVA III on October 12, 1984, and NOVA II on June 16, 1988. See NOVA I, II, and III.

The NOVA satellites were essentially the same design as TIP III. They consisted of three units connected by a long boom for gravity-gradient stabilization. The Drag-Free system was single axis using a cylindrically shaped proof mass which slid along a wire in the direction parallel to the orbit velocity vector.

In the end the single-axis Drag-Free satellite worked, and the time that the Ephemeris could be predicted was increased from 12 hours to two weeks. It took three launches, however, to finally get the single-axis system to work correctly. The engineers who developed it said that although in the beginning they thought that a single-axis system would be simpler; in retrospect, it would have been much easier and cheaper to stick with the three-axis system of the original DISCOS/TRIAD I.