Another serious design for advanced spacecraft, this time a Solar Sail. This works by using a huge flimsy sail to catch sunlight, and the gentle pressure pushed the craft forwards Thrust is very low, but requires no fuel. I've taken some liberties with the realism to get things nicely lit and reflected! It's not a new concept - J.D. Bernal wrote in 1929, "A form of space sailing might be developed which used the repulsive effect of the sun's rays instead of wind. A space vessel spreading its large, metallic wings, acres in extent, to the full, might be blown to the limit of Neptune's orbit. Then, to increase its speed, it would tack, close-hauled, down the gravitational field, spreading full sail again as it rushed past the sun."