1. K. S. Noll, Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA.
2. R. E. Johnson, University of Virginia, Nuclear Engineering and Engineering Physics, Charlottesville, VA 22901, USA.
3. A. L. Lane, Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, USA.
4. D. L. Domingue, Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX 77058, USA.
5. H. A. Weaver, Johns Hopkins University, Department of Physics and Astronomy, Baltimore, MD 21218, USA.