Apple has hired three engineers who previously worked at NASA’s Jet Propulsion Laboratory and an engineer who worked on the space agency's autonomous vehicle for exploration on Jupiter's moon. The engineers reportedly will work on the company's self-driving venture, said the Wall Street Journal, which obtained documents related to the company's autonmous vehicle plan.

The NASA engineers, who will test Apple's self-driving car software, have previously worked on detection of 3D objects and motion planning algorithms.

Read: Are Self-Driving Cars Safe? One In Four Cars On U.S. Roads In 2035 Will Be Self-Driven, Study Says

One of the engineers Apple hired had previously worked with German company Bosch during the firm’s efforts to make a self-driving car and making autonomous wheelchairs travel more smoothly. Robert Bosch recently was added to Apple’s list of suppliers last month.

Less than two weeks ago Apple was given the green light for testing self-driving cars in California, according to the state’s Department of Motor Vehicles’ webpage.

A Business Insider report Friday revealed details about Apple’s Project Titan from the company’s California DMV self-driving car application. The documents include a walkthrough of the Development Platform Specific Training and details about an autonomous-vehicle system called the Apple Automated System. An Apple official revealed in the documents the "development platform uses hardware and software to monitor surrounding objects and events."

The full application was uploaded by AppleInsider. The documents include a copy of the testing process Apple used to certify six drivers who will pilot three modified 2015 Lexus RX450h SUVs.

Read: Apple Self-Driving Car Program To Be Tested In California

Last week, it was reported Apple was moving away from its self-driving car plans and focusing on developing apps instead. The report said the fact that only three vehicles are involved in the tests suggests the company is focusing on its CarPlay connectivity and infotainment platform, rather than autonomous technology.

Meanwhile, a March report said Apple was quietly operating a research lab in Switzerland and had hired computer visions and robotics researchers, possibly for Project Titan.

Other tech companies, such as Uber, Amazon and Google, are also working on autonomous cars. On Monday, The Wall Street Journal reported Amazon has created a 12-person team focused on driverless-vehicle technology to improve shipping operations.