I am grateful to the following for assistance with research, suggestions and comments:
Jardine Barrington-Cook and his colleagues of the Space Division, Logica U.K. Ltd., who developed the guidance software for the Huygens Titan landing probe.
Mitchell Clapp of Pioneer Rockerplanes, author of the Black Horse spaceplane proposal.
Martyn Fogg, author of Terraforming: Engineering Planetary Environments, the standard text on the subject.
Dr. J. F. Zarnecki of the Space Sciences Unit, Kent University, U.K., who developed the surface science package for the Huygens probe.
And to the following for reading versions of the manuscript:
Simon Bradshaw
Eric Brown
Kent Joosten of the Solar System Exploration Division, Johnson Space Center, NASA.