Near-Ultraviolet Spectroscopy of the Stardust Sample Return Capsule Reentry

The320–460nmwavelength emission of the Stardust SampleReturnCapsule’s reentry inEarth’s atmospherewas observed remotely with an intensified slitless spectrograph, which recorded spectra at a video rate of 29:97 frames=s. The spectral response remained constant during the full range of recovery, with only motion blurring from imperfect guiding contributing to small variations in detection response. The data are well suited for evaluating the temporal variation of the intensity of the various light-emitting components. A line of zinc identifies the period when a layer of ZnO pigment containing thermal protection paint was ablated. Ca emission was more intense during (and just following) the ablation of this zinc, but present throughout flight. Shock emission from nitrogen is no longer detected shortly after peak heating. The data are dominated by strongmolecular band emission from the radical CN. The CN band intensity is thought to be proportional to the carbon ablation rate from the heat shield. Corrected for distance, the CN band intensity peaked early in flight, before peak heating, followed by an exponential decrease through peak heating.