During his years at Colgate, Holbrow frequently joined other academic institutions temporarily as a visiting professor and researcher, including Stony Brook University, Massachusetts Institute of Technology, Cornell University, Brookhaven National Laboratory, SRI International, Stanford University, the University of Wisconsin-Madison, University of Vienna, and the GSI Helmholtz Centre for Heavy Ion Research. He spent a sabbatical year in 1969-70 at the Stanford Linear Accelerator, and another at the California Institute of Technology in 1975-76, working in the Kellogg Radiation Laboratory. During the summer of 1975, Holbrow was a NASA -ASEE Summer Faculty Fellow at Stanford University and Ames Research Center, where he participated in a NASA project to develop colonies in space, culminating in the report Space Settlements: A Design Study, and featured in an article by Isaac Asimov in the July, 1976, issue of National Geographic.