It's the Maneuvering Re-entry Research Vehicle. It was intended to be launched from the Shuttle to explore the hypersonic speed range between NHFRF ("X-24C") and orbital speed. It was to be used in several types of flight patterns, including low angle-of-attack re-entry, high cross-range, etc.
Thanks to you George and also to flateric (you know why ).
A concept for highly maneuverable research entry vehicles is presented. The vehicles could be transported into orbit within the payload bay of the Space Shuttle. Such research vehicles would bridge the technology gap between the National Hypersonic Flight Research Facility, advanced air-breathing aricraft and the Space Shuttle. Suggestions are given for evaluating the research utility of payload vehicles which have the potential of high versatility to investigate the technologies required for rapid recall from orbit and return to a precision Earth landing within minimum time. The ability to utilize aerodynamic means for performing a wide spectrum of operational modes is identified along with the relation to previous investigation. Experiments which are applicable to advanced high performance lifting entry and which could be incorporaded in this program are discussed.