This wealth of documentation on ACTS has made the job of preparing this issue of the Online Journal a much more difficult task than I anticipated when I accepted the assignment, since I now realize that the selection of material will, of necessity, include only a small portion of the research conducted and the material published. I hope that my choices will not alienate the many collaborators contributing to the success of this complex program whose work could not be included.

The aim is to provide an overview of the program, its history, its technology, its experimental results, and its contributions to Space/Earth communication, for example, as in the study of propagation phenomena and development of fade compensation techniques. Emphasis will be on the results of experiments conducted in a multitude of applications areas, to show prospective users how the satellite could serve their particular needs. At the same time, the issue will provide an overview for policy makers, journalists, managers, financial analysts, students and others with an interest in development of advanced communication technologies.
 
This show the user approach was chosen by the members of the NASA ACTS Experiment Office, with whom I collaborated in publicizing ACTS to the many prospective experimenters, and proved very effective in gaining acceptance for the satellite. It proved very successful in demonstrating digital satellite voice telephony at the AIAA show in San Diego in 1994, where NASA set up telephone lines, connected to a T1 VSAT outside the exhibit area. Attendees were able to make calls anywhere in the US using the satellite connection into terrestrial lines via NASA Glenn. I remember quite vividly the skepticism of satellite experts whom I personally escorted to the phones and their surprised reaction at the clear voice quality free of the infamous GEO satellite echo!

In the area of propagation (having to do with electromagnetic signals traveling through space and their behavior in Earth's atmosphere), ACTS has made a lasting contribution by providing not only the stable beacons on the spacecraft, but also the receiving stations deployed in different rain zones that collected uniform data over a five year period. The published results have been used to optimize commercial Ka Band system designs.

Much of the source material, including the ACTS program overview and ACTS history and technology, has been excerpted from the book The Advanced Communications Technology Satellite by Richard Gedney, Ron Schertler and Frank Gargione, available from Scitech Publishing, Inc. The papers on the experimental results were taken from the NASA Glenn ACTS website http://acts.grc.nasa.gov which also contains other documents that are available for further study.

Finally, I would like to thank Dr. Richard T. Gedney, the ACTS Project Manager during the ACTS development, launch and initial operations period; Robert A. Bauer, the current ACTS Project Manager; Richard Krawczyk, the current ACTS Operations Manager, and Dr. Roberto Acosta, all from the NASA Glenn Research Center for their assistance and suggestions in assembling the material contained in this issue.