The country that invented the Walkman may be back on track to burnish its image as a technological pioneer. Right now, more than 4.7 million miles from Earth, is a revolutionary spacecraft that could be the future of interstellar travel. Japan's space program, JAXA, confirmed on June 10 they had successfully unfurled the world's first solar sail — a spacecraft that uses the velocity of sunlight to propel it. Then, just three days later, Japan announced what could be an even more impressive accomplishment: a spacecraft that left Earth seven years ago had returned home. Before brilliantly burning up over...