Scientific Method / Science & Exploration

Saturn V “moon rocket” engine firing again after 40 years, sort of

NASA pulls giant engine parts from museums, remakes 'em, and lights 'em up.

NASA continues to push forward with the design of its new heavy lift rocket, the Space Launch System. With the cancellation of the Constellation Program, SLS is NASA's planned heavy launch vehicle at the moment. While commercial entities continue to tackle the problem of moving payloads and crews to low Earth orbit, SLS is intended to replace the Space Shuttle as a heavy lift platform for shifting large cargoes into low Earth orbit and points beyond.

If SLS is ever to actually fly, it will require a tremendously powerful set of engines to get it off the ground. Perennial launch contract winner ATK is sure to get in on the action, supplying solid rocket boosters to the launch stack. But a powerful liquid-fueled engine is required as well. There are many candidates and design options, but NASA is actually turning its gaze a bit toward the past for inspiration.

The largest and most powerful rocket to successfully lift off was the Saturn V, which flew men and equipment to the Moon as part of Project Apollo in the 1960s and 1970s. The rocket's first stage had a lot of lifting to do, so it boasted the largest and most powerful liquid-fueled rocket engines to ever fly: the Rocketdyne F-1. Producing 1,500,000 pounds of thrust at sea level and consuming one ton of refined kerosene (RP-1) and two tons of liquid oxygen per second, the Saturn was propelled skyward on five of these monstrous engines.

Enlarge / Modern engineers in 1960s engineer dress cluster around an F-1. The Russian RD-170 produced more power but isn't really a single engine.

The F-1 is a gas-generator cycle rocket engine, burning a bit of fuel outside the combustion chamber to power the pumps of the engine. Earlier today, NASA test fired an F-1 engine's gas generator segment at the Marshall Space Flight Center in Alabama. This is the second F-1 gas generator firing this year; an earlier test took place on January 10.

The process for test-firing a 40+ year-old rocket engine, even if it's just the gas generator segment, is complicated: no current launch vehicles use the engine, so it wasn't a matter of simply grabbing one from a warehouse somewhere. Engineers removed components from an F-1 engine in storage at MSFC, as well as from another in "pristine" condition at the Smithsonian National Air and Space Museum in Washington, and then laser-scanned them using a structured light 3D scanner. Once this had been done, new gas generator parts were fabricated from the scans.

The gas generator itself was no slouch, producing about 31,000 pounds of thrust when lit. In the full-up engine, this thrust was used to drive a turbine that produced about 55,000 bhp, which in turn drove the turbopumps that kept the thirsty engine fed with the three tons per second of RP-1 and LOx.

Enlarge / Test firing the remanufactured F-1 gas generator.

A redesigned version of the F-1 engine itself almost certainly won't be used for SLS, but there's still a huge amount of value in studying the old engine's design. "This effort provided NASA with an affordable way to explore an engine design in the early development phase of the SLS program," said Chris Crumbly, manager of the SLS Advanced Development Office.

The Space Shuttle Main Engines are far more efficient beasts than the venerable F-1—in addition to being reusable, they're staged combustion engines, reclaiming and combusting their exhaust gasses. However, these engines are also tremendously complex compared to the F-1 design, and they are too expensive to use in single-use applications like SLS. The F-1 is a proven design, and by measuring exactly how it worked, it can be improved upon.

"Modern instrumentation, testing and analysis improvements learned over 40 years, and digital scanning and imagery techniques are allowing us to obtain baseline data on performance and combustion stability," noted Nick Case, an engineer working at Marshall's Propulsion Systems Department. He even indicated the modern-day test stand instrumentation was gathering data not collected when the engine was originally being checked out in the 1960s.

NASA will continue testing on reconstructed F-1 components to gain more insight into the giant engine's functional parameters. The testing will ultimately culminate in combined test of a reconstructed F-1 "powerpack" that will include the gas generator and turbopump.

Listing image by NASA

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