Maximizing total and specific power from space nuclear reactor (SNR) systems requires alloys that approach ultimate material capabilities. This requirement dictates improvement of the maximal metal tungsten (W) through its combination with other very effective refractory additives. Perhaps the best known addition is rhenium (Re) which improves W creep strength, recrystallization resistance and ductility. More ductile ultralloys command attention because W brittleness poses problems in both fabrication and service. However a “composition for good workability” is W,27Re, and perhaps its most practical processing procedure is sintering. Furthermore a promising SNR application for such ultralloys is very-high-temperature thermionic energy conversion. Therefore determinations of thermionic and thermal emissive characteristics for sintered W,27Re at temperatures near and above 2000 K in hard vacuum enable both scientific and pragmatic progress. Such research results comprise the data and interpretive presentations in this paper. These findings emphasize the fallacy of characterizing ultralloys similar to W,27Re with single-valued thermophysicochemical properties—such as the work function. They further stress the necessity for investigations of this type to determine and demonstrate effective prototypic ultralloy compositions and processing methods.