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We present results from a multiwavelength study of the blazar PKS 1954-388 atradio, UV, X-ray, and gamma-ray energies. A RadioAstron observation at 1.66 GHzin June 2012 resulted in the detection of interferometric fringes on baselinesof 6.2 Earth-diameters. This suggests a source frame brightness temperature ofgreater than 2x10^12 K, well in excess of both equipartition and inverseCompton limits and implying the existence of Doppler boosting in the core. An8.4 GHz TANAMI VLBI image, made less than a month after the RadioAstronobservations, is consistent with a previously reported superluminal motion fora jet component. Flux density monitoring with the Australia Telescope CompactArray confirms previous evidence for long-term variability that increases withobserving frequency. A search for more rapid variability revealed no evidencefor significant day-scale flux density variation. The ATCA light-curve revealsa strong radio flare beginning in late 2013 which peaks higher, and earlier, athigher frequencies. Comparison with the Fermi gamma-ray light-curve indicatesthis followed ~9 months after the start of a prolonged gamma-ray high-state --a radio lag comparable to that seen in other blazars. The multiwavelength dataare combined to derive a Spectral Energy Distribution, which is fitted by aone-zone synchrotron-self-Compton (SSC) model with the addition of externalCompton (EC) emission.

PKS 1954-388: RadioAstron Detection on 80,000 km Baselines and Multiwavelength Observations