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Ground controllers will then begin navigating the craft into closer and closer orbits of the sun by properly trimming the sail. Then they can put the ship—moving at a top speed of 198,000 kilometers (124,000 miles) an hour—on a course to intercept Halley's comet in March 1986. Jettisoning the sail, and "flying station" just two kilometers above the comet's head, the ship will take TV pictures and readings to determine the visitor's composition and origin. Says J.P.L.'s Murray: "We don't have a clue about comets. The space sailer could help provide some."
It might also effectively open up the rest of the solar system to manned spaceflights that cannot be considered now because of tremendous costs. J.P.L.'s Louis Friedman thinks that a flotilla of sunjammers could embark on a manned Mars mission by the end of the century, and foresees a day when fleets of huge kites shuttle through space—as the East Indiamen plied the oceans three centuries ago—making regular stops at Mercury, Venus, Mars or the asteroids.
Should plans for the space sailer hit a snag, earthlings could still get their first closeup view of Halley's comet in 1986. Another group at J.P.L. is working on the design of a spaceship that would be propelled by an ion engine; a small, continuous amount of thrust would be provided by the engine's ejecting ions produced when a beam of electrons (generated by electric current from solar cells) is sent through vaporized mercury. Such a low-thrust ion engine could, like the sunjammer's sail, maneuver a ship to a rendezvous with the comet. NASA is scheduled to decide next August which craft, if either, will make the mission. Until it decides, there will be fierce but friendly competition at J.P.L., where employees last week identified their allegiance by wearing buttons reading either TRUCKING WITH ION DRIVE or I'M A SOLAR SAILOR.