Space-borne protective energy systems, like the deflector shields on the fictional starship U.S.S. Voyager, are on the drawing board of real-world scientists. These "cold plasmas" -- analogs to the sophisticated defensive grids envisioned by Star Trek's creators -- are ambient-temperature, ionized gases related to those found deep within the sun?s core. Such plasmas are capable of shielding satellites and other spacecraft; or making them invisible to radars; or both. Nor will they fry electronics or melt metal.