After a hiatus of nearly 20 years, NASA is once again actively examining manned Mars missions. As part of this activity, a very recent engineering study has shown that providing artificial gravity for the crew of a long-duration Mars mission might be accomplished with a primary vehicle mass penalty of about 20% or less. This finding is important because it carries the promise of removing one more potential barrier to the long term human habitation of space. Before committing to the inclusion of artificial gravity on a Mars mission, however, a Variable Gravity Research Facility (VGRF) in low Earth orbit would be necessary in order to build confidence in the technology of large, flexible, rotating systems and to fill in the gaps in the scientific understanding of the response of humans to rotating, partial gravity environments. This paper discusses both the Mars mission vehicle study results and other drivers for the VGRF design. Conceptual mission and system hardware descriptions of a VGRF satisfying these constraints are also presented.