After more than four years developing its BE-4 engine, private spaceflight company Blue Origin is one step closer to liftoff, the company revealed on Monday.

Blue Origin owner Jeff Bezos, who is also the chief executive officer of online giant Amazon, shared two pictures of the newly-completed BE-4 engine via Twitter. The pictures show the first “fully assembled” rocket, Bezos wrote, and two more are close to completion.

With construction well underway, the company plans to move swiftly on to testing the rocket for flight, a process Blue Origin hopes to complete by the end of 2017, according to its website.

1st BE-4 engine fully assembled. 2nd and 3rd following close behind. #GradatimFerociter pic.twitter.com/duE4Tnzvkx — Jeff Bezos (@JeffBezos) March 6, 2017

Here’s one more shot of BE-4 in its transport cradle. pic.twitter.com/T2HdZ3UtQZ — Jeff Bezos (@JeffBezos) March 6, 2017

If all goes well, this timeline will allow the company to have a rocket ready to launch by 2019. That’s an important date, since US law mandates that the government stop using Russian-built engines by 2019, and substantial business will likely flow to whatever company is ready to fill the void.

"The American-made BE-4 liquid rocket engine provides the fastest path to production and the lowest cost engine to power the nation’s access to space,” Blue Origin said in a statement.

Blue Origin and its chief competitor, SpaceX – founded by Tesla billionaire Elon Musk – are pushing forward to a future of commercial spaceflight. Both companies aim to use reusable rockets, a technologically challenging approach that has the potential to cut the costs of space travel. Blue Origin has already tested that approach with its New Shepard rocket, which can take off and fly back to Earth if it travels vertically.

The next step is the New Glenn rocket, named for John Glenn, the first American to orbit Earth. The New Glenn is intended to be powerful and fast enough to take heavy payloads of cargo, as well as passengers, into orbit.

With power in mind, Blue Origin has been working to produce the BE-4 engine, fueled by liquid natural gas, that Bezos showed off on Monday. When completed, the New Glenn will use seven BE-4 engines.

And these engines may power more than just Blue Origin’s rockets. Following the Russian invasion of Ukraine in 2014, Congress passed legislation requiring the government to phase out use of the Russian-made RD-180 rocket engine to launch military satellites by 2019, a deadline that is fast approaching.

The United Launch Corporation, a joint venture between Lockheed Martin and Boeing that has been the military’s primary launch provider over the past decade, currently uses the RD-180 to launch probes and resupply the International Space Station. The company has therefore been on the lookout for an alternative, and ultimately decided to build its own Vulcan rocket powered by the BE-4.

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“BE4 is the primary path to replace the Atlas’ Russian RD180. Looking good,” ULA chief executive Tory Bruno tweeted on Monday.

BE4 is the primary path to replace the Atlas' Russian RD180. Looking good https://t.co/FHN4pZHqGC — Tory Bruno (@torybruno) March 6, 2017

This report contains material from Reuters.