Elon Musk’s Mars-bound rocket is making big progress. On Tuesday, the SpaceX CEO revealed on Twitter that the Raptor engine, which will be used to power the “BFR” rocket that could take humans to Mars as soon as 2024, is making “good progress,” with Musk “really proud of this design & SpaceX propulsion team” and praising the engine as “something special.”

The engine, first announced in 2009, took center stage at the International Astronautical Congress in Adelaide, Australia, back in September 2017. A staggering 31 Raptors will power the BFR — an abbreviation that stands for “big” and “rocket” — to produce liftoff thrust of 5,400 tons to lift the total vehicle mass of 4,400 tons. At the conference, Musk said the company has run over 1,200 seconds of firing across 42 main engine tests, with the longest test lasting 100 seconds. Test engines operated at 200 atmospheres of pressure, with the final version expected to work at 250 to 300. It seems these tests have progressed even further.

The engine packs a far bigger punch than the Merlin engines behind the company’s current Falcon 9 rockets. At the conference, Musk explained that the sea-level Raptor engines will produce a thrust of 1,700 kilonewtons with a specific impulse of 330 seconds at sea level, rising to 356 seconds in vacuum, and an exit diameter of 1.3 meters. The thrust of the vacuum engines will total 1,900 kilonewtons,, with a a specific impulse of 375 seconds and an an exit diameter of 2.4 meters.

Musk has big plans for these engines. The first BFR missions are scheduled for 2022, when two rockets will send the first unmanned cargo to Mars. This will be followed by four BFRs, two unmanned and two manned, which will place the first humans on Mars and establish a refueling system to get back home.

It’s unclear when SpaceX will next reveal updates for the Raptor engine. SpaceX has not announced whether it’s attending this year’s International Astronautical Congress, scheduled for October 1-5 in Bremen, Germany, but Musk’s appearance at the past two shows has fans excited for the possibility of another update at the event.

Apollo 11 astronaut Buzz Aldrin’s dream to “get your ass to Mars” may finally come true.