SpaceX billionaire Elon Musk clapped back to Boeing CEO Dennis Muilenburg's claim that Boeing will be the first space company to get to Mars.

"Do it," Musk tweeted Thursday in response to a story about the assertion.

Do it

Muilenburg was asked by The Street, "Who arrives to Mars first, SpaceX or Boeing?"

"Boeing," Muilenburg responded. A video of the interview was posted on The Street Thursday.

"We are working jointly with NASA and our industry team right now. We are building that first rocket space launch system. It's about 38 stories tall, the first article is being built right now. About 9.2 million pounds of thrust on that rocket, the biggest rocket ever," says Muilenburg.

"If you want to put that in car terms, that's about the equivalent thrust of 207,000 Corvettes and we are going to begin test flights starting next year."

Musk has also said SpaceX will start test flights for its rocket going to Mars in 2019.

In a question and answer session at South by Southwest in Austin March, Musk said, "we are building the first Mars, or interplanetary ship, and I think we'll be able to do short trips, flights by first half of next year."