NAUTILUS EDUCATION | BETA PRODUCT momentum and push- ’ es on whatever surface v7 it strikes. The force is he f' feeble, but becomes wae bey noticeable if you have = \ / me hg - a large enough surface, —— <i * % ; - —= i T a low mass, and a lot i a — > of time. Sunlight can Pas oy 3 xy & f. —_ ‘ accelerate a large sheet ; od me = 2» \ ] | ee of lightweight material, eek \ i? = r such as Kapton, to an - ut & ~ ‘ impressive speed. To <a i & ~~ reach the velocity need- / . ed to escape the solar [ . system, the craft would aa > y, \ first swoop toward i f . the sun, as close as it ~~ & x dared—ainside the orbit ri: %y = of Mercury—to fill its { sails with lusty sunlight. Such sail craft could a negatively charged grid draws the atoms toward the conceivably make the back of the ship. They overshoot the grid and stream crossing to Alpha Centauri in a thousand years. Sails off into space at speeds 10 times faster than chemical are limited in speed by how close they can get to the rocket exhaust (and 100 times faster than a bullet). sun, which, in turn, is limited by the sail material’s For a post-Voyager probe, ion engines would fire for 15 durability. Gregory Matloff, a City University of New years or so and hurl the craft to several times the Voy- York professor and longtime interstellar travel propo- agers’ speed, so that it could reach a couple of hundred nent, says the most promising potential material is gra- AU before the people who built it died. phene—ultrathin layers of carbon graphite. Star flight enthusiasts are also pondering ion drives A laser or microwave beam could provide an even for a truly interstellar mission, aiming for Alpha Cen- more muscular push. In the mid-1980s, the doyen of tauri, the nearest star system some 300,000 AU away. interstellar travel, Robert Forward, suggested piggy- Icarus Interstellar, a nonprofit foundation with a mis- backing on an idea popular at the time: solar-power sion to achieve interstellar travel by the end of the cen