Musk's Tesla Roadster parked outside SpaceX in 2010
In March 2017, SpaceX's founder, Elon Musk, said that because the launch of the new Falcon Heavy vehicle was risky, it would carry the "silliest thing we can imagine". In June 2017, one of his Twitter followers suggested that the silly thing be a Tesla Model S, to which Musk replied "Suggestions welcome!". In December 2017 he announced that the payload would be his personal "midnight cherry Tesla Roadster". Later that month, photos of the car prior to payload encapsulation were released.
One of the test flight objectives was to demonstrate that the new rocket could carry a payload as far as the orbit of Mars. NASA had declined SpaceX's offer to carry a scientific payload.
Following the successful launch, the Roadster became the first standard roadworthy vehicle sent into space,  though several special-purpose lunar and Mars rovers had previously been launched.
Roadster as payload
The Roadster is permanently attached to the upper stage of the Falcon Heavy rocket.
The car was permanently mounted on the rocket in an inclined position above the payload adapter. Tubular structures were added to mount front and side cameras.
Positioned in the driver's seat is "Starman", a full-scale human mannequin clad in a SpaceX pressure spacesuit. It was placed with the right hand on the steering wheel and the left elbow resting on the open window sill. The mannequin was named after the David Bowie song "Starman" and the car's sound system was set before launch to continuously loop the Bowie song "Space Oddity".
There is a copy of Douglas Adams' novel The Hitchhiker's Guide to the Galaxy in the glovebox, along with references to the book in the form of a towel and a sign on the dashboard that reads "DON'T PANIC!". A Hot Wheels miniature Roadster with a miniature Starman is mounted on the dashboard. A plaque bearing the names of the employees who worked on the project is placed underneath the car, and a message on the vehicle's circuit board reads "Made on Earth by humans". The car also carries a copy of Isaac Asimov's Foundation trilogy on a 5D optical disc, a proof of concept for high-density long-lasting data storage, donated to Musk by the Arch Mission Foundation.