Scientists and engineers are working on machines to do the most difficult jobs in space. Here we present some of the impressive space robots that may soon rewrite our understanding of much of our solar system.

Since 1995 astronomers have discovered some 550 confirmed planets orbiting other stars. NASA's Kepler space telescope is in the process of uncovering thousands more, including ones similar to Earth in size and temperature. Before long, people will be clamoring to know what they look like. The only way to find out is to go there. But reaching even the nearest star system, Alpha Centauri, within a human lifetime would require a spacecraft capable of cruising at 10,000 miles a second. Voyager 1, the fastest-moving spacecraft, is moving at one-tenth of 1 percent of that speed.

Although NASA canceled its Breakthrough Propulsion Physics project in 2002, engineers are still pushing the limits of speed and range. The New Horizons probe has the most distant target of any space mission ever attempted: everyone's favorite dwarf planet, Pluto, which it will reach in July 2015. Around the same time, scientists will begin testing a prototype of the Variable Specific Impulse Magnetoplasma Rocket, or VASIMR, which expels searing hot plasma to produce thrust, at the International Space Station. VASIMR will not reach the stars, but it may allow future probes to leave the solar system in years rather than decades. True star travel will probably require technologies like antimatter or nuclear fusion rockets, which are currently not much more than dreams.