There may be an indication of change in the spectral slopes at the highest energies, but the observational uncertainties preclude any definitive statement. Conversely, if new measurements in this region became available, significant constraints on present cosmic ray models would be obtained. At the highest energies, this requirement can only be fufilled with ground based air shower arrays which, however, are severely limited by their inability to determine the identity of primary particles on an event by event basis. At the same time, of course, the detector must conform to constraints of weight, size, power and consumables imposed by the limitations of balloons or spacecraft. However, spallation production in the residual atmosphere at balloon altitude leads to limitations in the measurements of rare secondary cosmic-ray components.
Space flight is especially important for such observations.
15 eV per particle. In this energy regiem, transition radiation detectors offer a distinct advantage. The TR effect is a purely electromagnetic effect and depends on the Lorentz factor. Thus, TRD's may be fully calibrated, both with respect to their Z-dependence, and with respect to fluctuations in response. Another final advantage of TR devices is the fact that they are very light in weight, so that detectors of very large area are feasible.