No suitable technology currently exists to ensure that drones will “sense and avoid” other aircraft, Gerald Dillingham of the Government Accountability Office recently told lawmakers, adding that the Federal Aviation Administration lacks sufficient dedicated frequency spectrum to operate unmanned aircraft systems in domestic airspace.

Additionally, non-encrypted GPS navigation signals leave drones vulnerable to jamming and spoofing, according to Dillingham, GAO’s director for physical infrastructure issues, who testified Friday at a hearing held by the Oversight Subcommittee of the House Committee on Science, Space, and Technology.

Last Thursday, FAA kicked off a process to set up six test sites to conduct drone research and development toward a goal of widespread use of UAS by law enforcement agencies, universities and other organizations in domestic airspace by 2015. Rep. Ted Poe, R-Texas, estimated that, by 2030, “30,000 drones will be cruising American skies.”