WASHINGTON — Elon Musk, the founder and chief executive of Space Exploration Technologies (SpaceX), tamped down expectations ahead of a long-awaited June 4 launch attempt of the company’s Falcon 9 rocket, which is cleared to proceed now that Cape Canaveral range officials have signed off on a key safety certification for the rocket.

During a June 3 prelaunch teleconference with reporters, Musk said the U.S. Air Force had given its final approval of the Falcon 9 flight termination system (FTS), which uses explosives to destroy the rocket in the event that it veers off course during launch.

“It’s a pretty intense testing process for the flight termination system. Obviously they want to make sure it works even under extreme circumstances,” Musk said. “There were some elements of it that we underestimated, some elements that our suppliers underestimated completing the development of the FTS system.”

If the weather cooperates, SpaceX will attempt to launch the Falcon 9 from Cape Canaveral Air Force Station, Fla., between 11 a.m. and 3 p.m. EDT. The launch range forecasts a 40 percent chance of a weather-related delay. SpaceX has an identical four-hour window reserved for June 5. Musk likened the odds of a successful first launch to surviving a game of Russian roulette.

“I think my personal assessment of the likelihood of success is probably 70 to 80 percent,” he said. “However … that is less than the probability of success in Russian roulette.”

Musk said his biggest concern is the rocket’s second-stage performance.

“If I were to say, like, what the scariest moment is, stage separation and second-stage start [are] probably what I worry about the most of anything,” he said.

Even if the launch is not a complete success, Musk said SpaceX intends to push ahead with its first NASA Commercial Orbital Transportation Services (COTS) demonstration flight, currently slated for July.

The COTS demo calls for launching Dragon on a five-hour flight meant to prove the reusable capsule can complete multiple orbits, transmit telemetry, receive commands, maneuver, re-enter the atmosphere and make a safe water landing and recovery.