We investigate the potential of the upcoming LOBSTER space observatory (due circa 2009) to detect soft X-ray flashes from shock breakout in supernovae, primarily from Type II events. LOBSTER should discover many SN breakout flashes, and will constrain the radii of their progenitor stars far more tightly than can be accomplished with optical observations of the SN light curve. We anticipate the appearance of blue supergiant explosions (SN 1987A analogs), allowing for the first time a snapshot of stellar evolution at the point of core collapse. We consider also how the mass, explosion energy, and absorbing column can be constrained from X-ray observables alone and with the assistance of optically-determined distances. These conclusions are drawn using known scaling relations to extrapolate, from previous numerical calculations, the LOBSTER response to explosions with a broad range of parameters.