Last month, Elon Musk, the tech billionaire who founded SpaceX, said on Twitter that he planned to launch a Tesla electric car into Mars orbit in 2018. While the announcement was initially met with skepticism, Musk has backed up his claim by posting a photo of the Tesla Roadster inside the carbon fiber composite fairing of a SpaceX Falcon Heavy rocket.

“Test flights of new rockets usually contain mass simulators in the form of concrete or steel blocks. That seemed extremely boring,” Musk wrote in a Dec. 22 Instagram post. “Of course, anything boring is terrible, especially companies, so we decided to send something unusual, something that made us feel.”

The Falcon Heavy is a variant of the Falcon 9 rocket, which last year completed a successful launch from the original NASA liftoff pad that first sent astronauts to the moon. For both rockets, the use of composites extends beyond just the payload. The interstage, which connects the upper and lower stages of the rockets, is a composite structure with an aluminum honeycomb core and carbon fiber face sheets.

SpaceX says the launch vehicle, the first of its kind for SpaceX, is the most powerful rocket in the world today. Only the Saturn V moon rocket, last flown in 1973, delivered more payload to orbit. With the ability to lift into orbit over 54 metric tons (119,000 lb)–a mass equivalent to a 737 jetliner loaded with passengers, crew, luggage and fuel–Falcon Heavy can lift more than twice the payload of the next closest operational vehicle, the Delta IV Heavy, at one-third the cost.

If successful, the Roadster will be the first ever to fly free through the vacuum of space. The launch is expected before the end of January.