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A Quick Primer On Rocket Engine Technology – in Just 20 Quick Slides Once upon a time, America built, powered, and launched its own rockets. Photo: Wikimedia Commons.
This here is Russia’s RD-180 rocket engine -- the one that all the fuss is about. Fueled by a mixture of liquid oxygen (LOX) and kerosene, the RD-180 generates 860,000 pounds of thrust at sea level, enough to lift the Pentagon's biggest military satellites into orbit. Of course, that's just what Russia is objecting to. Photo: Wikimedia Commons.
Note, though, that the RD-180 is just an engine. It's not the "rocket" itself. What RD-180 is used for, is to power the first stage of liftoff for this bad boy, Lockheed Martin's Atlas V launch vehicle. Photo: Wikimedia Commons.
But you can't just switch out an RD-180 and swap in some other engine – or engines adding up to the same amount of thrust – on an Atlas V. The engine and the rocket must be designed to work together, or the whole system won’t work right. That's why, even though two of these RS-25 "Space Shuttle" engines generate a combined thrust nearly equal to the RD-180's, they can't do the same job of powering the Atlas V. Photo: Wikimedia Commons.
That adds time to our list of problems. Take away the RD-180, and you may end up having to design a new rocket engine and an entirely new rocket ship to go with it. What you really want is a new rocket engine as nearly equal as possible to the RD-180 in size, power, and performance, so that it can replace the RD-180 on the Atlas V. Photo: Wikimedia Commons.
And that's just for starters. On most space missions, you want your rocket to carry multiple engines, each servicing a separate "stage" of the launch. Each should burn its fuel as quickly as possible, then be jettisoned, to shed weight so that the next stage doesn't have to carry it. Photo: Wikimedia Commons.
As a general rule, most space launches these days operate in two or three stages. For an added boost, "booster" rockets, solid-fueled, are strapped on. They burn their fuel first, are dumped quickest, and are sometimes referred to as "stage zero". Photo: Wikimedia Commons.
Speaking of solid fuel, there are two main types of fuel used in rockets -- solid and liquid. As a general rule, solid fuels are easier to transport and use. They're built into the rocket engine, which therefore doesn't have to be "fueled" before launch. Photo: Wikimedia Commons.
Trivia: Used to be, a solid fuel rocket engine would be lit, burn itself entirely out, and then get dumped. But some modern solid fuel rocket engines can be throttled down, much like liquid-fueled rocket engines. “The more you know...”
The RD-180 burns liquid fuel -- LOX and kerosene. Another liquid fuel common in large rocket engines is liquid Hydrogen (LH2). GenCorp's RS-68 rocket engine, which powers Boeing's Delta IV, uses LOX and LH2 propellants. Liquid-fueled engines tend to give better performance, and burn fuel more efficiently. As a rule, it takes less weight in liquid fuel to do an amount of work equal to what a solid-fueled rocket engine could accomplish. . Photo: Wikimedia Commons.
At present, the U.S. has no equivalent to Russia's RD-180 and its 860,000 pounds of thrust. Even GenCorp's RS-68 generates only 663,000 pounds of force at sea level. (Although the improved RS-68A ramps that to 705,000 pounds). Also, the RS-68’s different propellants mean it can’t directly replace the RD-180. Photo: Wikimedia Commons.
And that, in a nutshell, is why America needs to design a replacement for the RD-180. We simply don't make a big, LOX/kerosene engine capable of replacing the RD-180. Rocketdyne's RS-27A and SpaceX's Merlin1C use LOX and kerosene for fuel, but you’d need several of these engines to generate the kind of thrust that a single RD-180 can generate.
If we want to continue using the Atlas V as the go-to space launch system for Pentagon satellites, well, we can... IF Russia agrees to keep selling us the engines, and IF we’re willing to accept the risk that they’ll decide to stop selling them again sometime in the future.
Otherwise, we simply have to design an “RD-180-like” replacement of our own. Preferably one with similar thrust characteristics... similar in weight, too... and ideally, using LOX and kerosene for fuel.
Longer term, the solution may be to move away from Atlas V and the RD-180 altogether. And in fact, we’re working on that.
NASA recently hired GenCorp and Dynetics, Inc. to work up new designs for LOX/kerosene rocket engines. GenCorp is working on a new engine that would be slightly smaller than the RD-180, capable of 550,000 pounds of thrust, but similar enough that it may represent a possible RD-180 replacement down the road.
Dynetics is rejiggering the old F-1 engine that originally took America to the moon -- the largest rocket engine that America has ever flown. Dynetics aims to modernize the F-1, producing an “F-1B” that is both easier to produce and more affordable. Photo: Wikimedia Commons.
SpaceX’s Falcon 9 rocket, powered by nine Merlin 1C engines, generates more thrust than the Atlas V and its RD-180. SpaceX's new Falcon Heavy will be even bigger, mating a Falcon 9 core with two boosters – each powered by 9 more Merlin 1C's. That'll be 2.25 million pounds of thrust, enough to lift 53 tons of payload into orbit -- about half as powerful as NASA's new Space Launch System. Photo: Wikimedia Commons.
And according to NASA’s own former head of propulsion and power... Maybe even enough to get America back to the Moon.
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