Amazon CEO Jeff Bezos on Tuesday morning sent his very first tweet, which announced the successful launch and landing of a New Shepard rocket built by Bezos’s space company, Blue Origin.

Elon Musk, the CEO of private space company SpaceX (which is also testing reusable, vertical-landing rockets), congratulated Bezos and his team, but had a few corrections.

The ability to land rockets after a space launch is an important goal for private space companies, because reusing rockets (rather than letting them fall into the ocean, as NASA and other space operations do) could save millions of dollars in lost equipment.

Read more about Blue Origin’s successful rocket test here, and find out what happened when SpaceX’s rocket crash-landed on an ocean barge.