Private spaceflight company Blue Origin has finally assembled its first full-scale BE-4 rocket engine — the main engine the company plans to use to propel its future orbital rocket. It’s a major milestone for Blue Origin, which has been working on this crucial piece of hardware since 2011. This morning, CEO Jeff Bezos tweeted out two pictures of the finished engine, noting that two more fully assembled BE-4s will be ready soon.

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

Bezos tweeted out another view of the engine on its side in its “transport cradle.” He did not clarify where the BE-4 is headed, but the likeliest destination is Blue Origin’s test site in West Texas. That’s where the company has a number of rocket engine test stands, and where BE-4 testing has been done up until now. It’s also the place where Blue Origin has launched and landed its New Shepard rocket — the reusable vehicle aimed at taking tourists to and from the edge of space. Blue Origin did not respond to a request for comment.

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

Seven BE-4s will be used as the main engines for Blue Origin’s next big rocket — called the New Glenn. Like the New Shepard, the New Glenn will be a reusable vehicle, as the majority of the vehicle will be capable of landing after launch (similar to how SpaceX’s Falcon 9 vehicle lands after takeoff). But unlike the New Shepard, the New Glenn will have enough speed to take heavy payloads, and passengers, into orbit around Earth.

The New Glenn looks to be a monster rocket

The New Glenn looks to be a monster rocket. It will be 23 feet in diameter and range from 270 feet to 313 feet tall, so around one-third the height of 30 Rockefeller Plaza (Rockefeller Center's main skyscraper). That height range is due to the fact that there will be two versions of the rocket; one will have a single upper stage — the top portion of the vehicle that separates from the rest of the rocket during launch and propels a payload further into orbit. This second stage will be powered by just one BE-4 engine. Another version of the New Glenn will have two upper stages: the second stage will be powered by a BE-4 while the third stage on top will be powered by a BE-3, the smaller engine used in the New Shepard.

And if there was any doubt about the gargantuan size of New Glenn, Bezos compared his future rocket to the rockets of both SpaceX and ULA to hammer the point home.

The New Glenn doesn’t actually exist yet, though. It will be put together at Blue Origin’s manufacturing facility, which is currently being built at Cape Canaveral, Florida. Bezos says the New Glenn will make its first flight from the Florida coast before the end of this decade.

The United Launch Alliance also plans to use the BE-4 in a new rocket the company is building

But the New Glenn may not be the only rocket sporting the BE-4 engine in the future. The United Launch Alliance (ULA) also plans to use the BE-4 in a new rocket the company is building called the Vulcan. The Vulcan will be a successor to the Atlas V rocket, which has come under fire in recent years for using Russian-made RD-180 engines. After Russia invaded Ukraine in 2014, Congress passed a bill banning the use of Russian rocket engines to launch military satellites. Seeing how ULA has been the primary launch provider for the military over the past decade, the company had to make moves to get rid of the RD-180. As a result, ULA decided to build a completely new rocket that would use a new type of engine developed by Blue Origin.

The company hopes for the Vulcan to fly for the first time in 2019. The primary goal is for the Vulcan to use two BE-4 engines, but if for some reason that doesn’t work out, ULA has a backup plan of using a new type of engine being developed by Aerojet Rocketdyne, called the AR1. For now, ULA’s CEO Tory Bruno seems to pretty pleased with Blue Origin’s progress.