You might not have realized, but Jeff Bezos has a rocket engine. Several, in fact. And on Wednesday, the Amazon chief executive (and Washington Post owner) unveiled the latest design — the Blue Engine 4, or what Bezos hopes will carry U.S. payloads into space in the near future.

The Blue Engine 4 — or BE4 — is named for Bezos's space exploration company, Blue Origin. The BE4 can produce 550,000 pounds of thrust and is propelled by a mix of liquefied natural gas and oxygen. The fuels are pressurized by a single turbopump before being burned, which scientists say may make it more efficient than using a two-prop system.

"It's time for a 21st-century booster engine," Bezos told reporters during an announcement at the National Press Club. "The engines built in the '50s, '60s, and '70s are remarkable pieces of hardware. But we have tools and capabilities — software simulations, computational horsepower — that the builders of those engines could only dream about."

Blue Origin announced a partnership with United Launch Alliance, a Boeing and Lockheed Martin joint venture that launches government military and civilian satellites and has a big rivalry with Elon Musk's commercial spaceflight company, SpaceX. The deal not only puts Blue Origin on the map but also means ULA will soon be able to stop buying the Russian-made RD-180 engines that have been the subject of so much political controversy.

So how does the BE4 stack up against other rocket engines? To answer that question, we have to talk a little bit about rocket technology.

"One of the problems with rocket engines is that there have been no big breakthroughs in the last 20 to 30 years," said Marshall Kaplan, a visiting professor of aerospace engineering at the University of Maryland. "The basic engine has not changed dramatically since the 1960s. What we're doing now is trying to make minor improvements -- a percent here, a percent there."

Experimenting with propellants is one of the key ways that manufacturers have tried to differentiate themselves, said Kaplan. Russia's engine uses liquid kerosene, as does SpaceX's, while Blue Origin's uses liquid natural gas. The latter provides a small boost to energy output — but even there the gains are slim. Technology has reached the point where decisions like these don't make a whole lot of difference.

The engines themselves do produce different amounts of thrust; the Russian RD-180 produces 860,000 pounds of thrust to the BE4's 550,000 pounds. A single Merlin engine built by SpaceX is designed to produce only 147,000 pounds of thrust, which is much lower, but a typical SpaceX craft will bundle multiple Merlin engines together for more lift. (The same will apply to the BE4, which Bezos said would be used in pairs to lift an Atlas V rocket to orbit.)

Some researchers believe they can find improvements in adapting another type of fuel that's more commonly found in upper-stage rockets. Instead of using liquid kerosene (like the Russian RD-180) or natural gas (like the BE4), scientists say, booster rockets could be fueled by liquefied hydrogen. Hydrogen has long been used in upper-stage engines where maximizing thrust is even more crucial. But — with some exceptions, like the space shuttle and the Delta IV rocket — we haven't figured out how to use hydrogen-oxygen mixes as cheaply or efficiently as other types of fuel, Kaplan said.

Where Musk and Bezos stand to benefit the most, however, is in being able to offer their engines for cheap. (Blue Origin did not release the cost of its engine.) Musk's engines, said Kaplan, are competitive in price with foreign alternatives because they operate outside of the traditional aerospace industry and have not faced the same level of government scrutiny while developing and testing their technology.

Bezos presumably has the same idea, although there are subtle differences in strategy. Blue Origin is considered to be behind SpaceX because it has spent much time perfecting its design. SpaceX, meanwhile, is already serving clients. On Tuesday, the company won a NASA contract (along with competitor Boeing) to operate flights to low-Earth orbit.

"This is a hobby for Bezos," said Kaplan, "whereas it's actually a business for Musk."

That Bezos's announcement came a day after NASA's commercial crew contract is no accident, however. It seems spaceflight is about to become much more than his hobby.