On a day when cities across the country were scrambling to submit their bids to become the home to Amazon’s second headquarters, Jeffrey P. Bezos had something else on his mind: rocket engines and wind farms.

In a tweet Tuesday afternoon, Bezos’s Blue Origin space company said that its first “hotfire” test of its BE-4 engine was a success. That’s a significant milestone for the company as it works to develop a massive new rocket it calls New Glenn, and sell the engine to the United Launch Alliance, the joint venture of Lockheed Martin and Boeing. (Bezos owns The Washington Post.)

Earlier in the day, Bezos tweeted out a video of himself in a hard-hat christening Amazon's latest energy-generating wind farm.

Rocket engines are extremely difficult to design and build — so difficult that ULA for years relied on engines built in Russia for its Atlas V rocket. But as tensions between the United States and Russia grew in recent years, many in Congress began to pressure ULA to find an American-made engine.

ULA had indicated it was leaning toward the BE-4. But it also said that it would keep Aerojet Rocketdyne’s AR1 as a backup. Now that Blue Origin has had a successful test fire, it would appear it has solidified its edge.

Or maybe not.

After the test firing, ULA issued a statement congratulating Blue Origin, calling it “a tremendous accomplishment.” But it didn't commit to the BE-4 and said that it “continues to work with both of our potential engine suppliers Blue Origin and Aerojet Rocketdyne to develop a new engine for our Vulcan Centaur rocket. While we are looking to make a down select to one engine provider, it is an on-going procurement and down selection and we are not commenting at this time.”

Bezos loves rocket engines. He grew up reading about them. He admired Wernher von Braun, the father of the Saturn V rocket that took the Apollo astronauts to the moon. He loves rocket engines so much that he even commissioned a three-week trip in 2013 to recover the Saturn V’s F-1 engines from the bottom of the Atlantic Ocean, some of which went on display at the Seattle Museum of Flight earlier this year.

Sometime in the next couple of years, Blue Origin plans to take paying tourists on trips to suborbital space on a smaller rocket called New Shepard that uses a smaller engine, the BE-3. But now, his company has built a very powerful engine, one capable of 550,000 pounds of thrust at sea level for its New Glenn rocket. With seven BE-4 engines, New Glenn is capable of carrying much more mass, farther into space, helping Bezos achieve his goal of “millions of people living and working in space.”

But his motto for Blue Origin is also “step by step, ferociously.”

The test-firing of a powerful, new American-made engine was an important step.