SpaceX is building the world’s most powerful rocket, but Elon Musk has suggested it could become even more powerful. The CEO wrote on Twitter Wednesday that the BFR designed for Mars and other planet-hopping trips could increase its engine count from 31 to 42 — perhaps a subtle reference to The Hitchhiker’s Guide to the Galaxy.

The BFR was announced last September as part of a planned series of missions to Mars, with two unmanned rockets launching in 2022 and two manned rockets launching alongside two unmanned rockets in 2024. SpaceX announced this week that it’s also planning to send Japanese billionaire Yusaku Maezawa with six to eight artists on a four to five day trip around the Moon in 2023. Musk unveiled an updated design of the BFR that takes inspiration from Tintin with three large fins, and internally can carry 100 tons to low-Earth orbit. While last year’s design used a mix of vacuum and sea-level engines, the new design uses sea-level across the board for simplicity.

See more: Elon Musk Reveals How SpaceX Mars-Bound Raptor Engine Tests Are Going

The Raptor engines are critical to SpaceX’s Mars plans. They’re powered by liquid oxygen and methane, rather than the liquid oxygen and rocket propellant used in the Falcon family’s Merlin engines. This means the first humans can set up a propellant plant on Mars to refuel the BFR and return home. While the BFR was first rated or carrying 150 tons at the International Astronautical Congress last year, this figure has been revised to 100 tons. Each rocket provides around 200 tons of thrust, and the whole design is capable of 5,400 tons, but adding extra engines could make the rocket even more powerful.

Musk has a habit for making science fiction references in his work. He’s confirmed that the first ship to visit Mars will be dubbed Heart of Gold, a reference to the ship in The Hitchhiker’s Guide to the Galaxy. The idea of using 42 engines could also be a subtle hint to the “answer to life, the universe and everything” referenced in the novel. Musk’s work also makes reference to the Culture series of novels and the movie Spaceballs.

SpaceX has a tough schedule ahead. Next step is completing BFR hop tests of a few hundred kilometers at the Boca Chica facility in Texas, expected to take place next year.

It could lay the groundwork for transforming humanity into a multi-planet civilization.

Photos via Elon Musk/Twitter