SpaceX's giant Mars vehicle has a crewed moon mission on its docket. 

A "private passenger" has signed up for a trip around the moon aboard SpaceX's BFR rocket-spaceship combo, company representatives announced via Twitter this evening (Sept. 13). SpaceX founder and CEO Elon Musk will fill in the details Monday (Sept. 17), during a webcast that begins at 9 p.m. EDT (0100 GMT on Sept. 18). You can watch the SpaceX moon shot webcast live here, courtesy of SpaceX.

Musk may already have given us a clue about the private space explorer's identity. Somebody on Twitter asked Musk if he was the passenger, and the billionaire entrepreneur responded by tweeting an emoji of the Japanese flag. [The BFR: SpaceX's Giant Spaceship for Mars in Images]

Even without the mystery of whom, exactly, SpaceX has signed for the "BFR Lunar Mission" (as SpaceX dubbed it), it sounds like it will be an epic trip. 

"Only 24 humans have been to the Moon in history," SpaceX wrote in a subsequent Twitter post. "No one has visited since the last Apollo mission in 1972." NASA's last Apollo lunar mission was Apollo 17, which sent astronauts Gene Cernan, Harrison Schmitt and Ron Evans to the moon in December 1972. Cernan and Schmitt landed on the moon while Evans remained in orbit. 

SpaceX announced in February 2017 that two people had signed up for a weeklong trek around the moon, which the company aimed to launch before the end of 2018. That mission was to use SpaceX's Dragon crew capsule and Falcon Heavy rocket. Had SpaceX followed through with that plan, it could have returned humans to the moon near the 50th anniversary of NASA's historic Apollo 8 mission around the moon in December 1968.

But this June, The Wall Street Journal reported that the flight had slipped into 2019 at the earliest. SpaceX representatives told the WSJ that such a mission remained in the company's plans, but they didn't lay out a timeline or other details. Presumably, we will get a timeline on Monday and perhaps learn if the passenger flying on the BFR trip is one of the folks who signed up for the original Dragon-Falcon Heavy flight.

The BFR — which is short for "Big Falcon Rocket" (or the "Big F------ Rocket") — is still under development. It will consist of the most powerful rocket ever built and a spaceship capable of carrying 100 or so passengers at a time to and from Mars, Musk has said. Both of these elements will be reusable. 

The BFR's main job will be to help enable Red Planet settlement — that's the chief reason that Musk founded SpaceX back in 2002, after all — but it will also perform a variety of other tasks.

Indeed, Musk has said that SpaceX plans to phase out all of its rockets and spacecraft, letting the BFR take over everything eventually. The company envisions the BFR performing satellite launches, cleaning up space junk, carrying folks on superfast "point-to-point" trips here on Earth — and, of course, helping our species spread out into the solar system, to the moon, Mars and beyond.  

Follow Mike Wall on Twitter @michaeldwall and Google+. Follow us @SpacedotcomFacebook orGoogle+. Originally published on Space.com.