The main engine burn (MEB) of the Space Shuttle deposits ~2¿1012 joules of explosive energy and ~3¿105 kg of exhaust in almost horizontal flight at 105--110 km altitude during the period 300--550 s into the ascent. This extremely robust perturbation provides a potential active-excitation source for a variety of geophysical processes, including (1) the effects of aurora-like localized heating on the generation of gravity waves in the thermosphere, (2) the ducting mechanisms for long-period infrasound in the upper atmosphere, (3) dynamo effects associated with transient charge separation, (4) interactions with ambient midlatitude current systems at E-layer heights, and (5) effects in the Earth-ionosphere waveguide of transient electron-density perturbations in the D-region. The sine qua non of such an agenda is to gain a quantitative understanding of the near-field behavior of the MEB exhaust-plume's quasi-cylindrical expansion, which generates a blast wave propagating away from the explosion. We report on observed electron-density signatures of this blast wave as manifested on lines-of-sight (LSOs) from a very-long-baseline interferometer (VLBI) illuminated by 137-MHz beacon signals from the MARECS-B satellite. We also compare the observations to a preliminary three-dimensional neutral-air acoustic model coupled to the ionospheric electron density. ¿ American Geophysical Union 1994