Even the nicer drones you can buy typically last for just minutes in the air, which isn't much help if you're delivering packages or shooting movies. Horizon Unmanned Systems (HUS) thinks it has a solution, however: hydrogen power. Its recently unveiled Hycopter drone runs on a lightweight hydrogen fuel cell that should deliver up to 4 hours of flight time unloaded, and 2.5 hours when it's carrying 2.2 pounds of cargo. That still may not sound like much, but it makes long-distance flights practical -- it's the difference between flying across the city and staying within the neighborhood. HUS won't even fly the Hycopter's prototype until later this year, but patience could well pay off if you're tired of piloting robotic aircraft in half-hour bursts.