The world's most advanced ionospheric research facility has in its lifetime faced allegations of being a 'military death beam', a weapon of weather control and even a top-secret mind-control project. Now, the US government's High Frequency Active Auroral Research Program (HAARP) is threatened with closure. HAARP, near Gakona, Alaska, comprises radio transmitters and antennas that are used to heat up the ionosphere - the uppermost region of the atmosphere - creating a laboratory in the sky for scientists.The facility has been used to produce an artificial aurora and to study how charged particles behave in the ionosphere, at a total cost of more than $250 million to build and operate. To justify HAARP's price, the Pentagon had to dream up exotic military applications, sparking conspiracy theories. The practical challenge for HAARP has been to balance its role as a Pentagon-operated site for developing military applications with its function as a basic science facility. Supporters have long tried to come up with potential military uses, such as testing deep-sea communications for submarines, detecting underground military bunkers and cleaning up satellite-disabling electrons in the event of a high-altitude nuclear detonation. Research into that last application had been supported by the US Defense Advanced Research Projects Agency (DARPA), but its chief says that the agency is now abandoning its work at HAARP. The final DARPA-sponsored experiment, called Basic Research on Ionospheric Characteristics and Effects (BRIOCHE), is scheduled to end in mid-June.