So what does SpaceX CEO Elon Musk think of Boeing CEO Dennis Muilenburg’s claim that the first people to set foot on Mars will arrive on a Boeing rocket? “Do it,” Musk tweeted, in one of many two-word comebacks that might have come to mind.

The latest round of media jousting started when CNBC’s Jim Cramer brought up Mars during an interview with Muilenburg. “Who’s going to get a man on Mars first, you or Elon Musk?” Cramer asked.

In response, Muilenburg touted the Space Launch System, the heavy-lift rocket that Boeing is helping NASA build for deep-space missions.

“We’re going to take a first test flight in 2019, and we’re going to do a slingshot mission around the moon,” he said. “Eventually, we’re going to go to Mars, and I firmly believe the first person that sets foot on Mars will get there on a Boeing rocket.”

Muilenburg said pretty much the same thing last year during an industry conference in Chicago, but since then, Musk has laid out a vision that calls for sending settlers to Mars on SpaceX’s yet-to-be-built monster spaceship starting in the 2020s.

If Musk and NASA stick to their current schedules, the first bootprints on the Martian surface would be left by folks arriving on a SpaceX rocket as much as a decade before the Space Launch System sends a spaceship there.

Is Musk’s response a dare? A space-race smackdown? Maybe. But the billionaire has always said his main goal in life is to help make humanity a multiplanet species by facilitating cities on Mars. Taken in that light, the “Do It” tweet may well be Musk’s way of saying that he’s glad for anyone else to be taking the move to Mars as seriously as he is.

That’s how John Gardi, an engineer and SpaceX fan who anticipated Musk’s hyperloop design in 2013, chooses to see the exchange. “You win either way, @elonmusk!” Gardi said in his tweeted response. “You can only lose if NOBODY goes to Mars!”

Meanwhile, Boeing and SpaceX are enmeshed in a shorter-term rivalry, to finish work on the space taxis that they’re building to transport NASA astronauts to and from the International Space Station.

The current schedules call for SpaceX to conduct a crewed demonstration flight with its Dragon capsule next August, while Boeing plans the first crewed flight of its Starliner space taxi in November 2018. But those schedules have been shifting to the right for years, so it’s too early to call the race.

The first to deliver astronauts to the space station will win a U.S. flag that was left aboard the outpost in 2011 by the last space shuttle crew. May the best team win? I prefer to look at it the way Gardi does: In this space race, may all teams win.