September 20, 2019

NASA kicks off SLS engine testing in Mississippi


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The RS-25 engine fires up for a 500-second test Jan. 9 at NASA's Stennis Space Center near Bay St. Louis, Mississippi. Credit: NASA
The RS-25 engine fires up for a 500-second test Jan. 9 at NASA’s Stennis Space Center near Bay St. Louis, Mississippi. Credit: NASA

A powerful space shuttle-era rocket engine ignited for more than eight minutes on a test stand in Mississippi last week, kicking off hotfire testing for NASA’s Space Launch System mega-rocket after contamination and computer woes kept the engine silent several months longer than planned.

The engine fired Friday on the A-1 test stand at NASA’s Stennis Space Center in southern Mississippi, consuming a mixture of super-cold liquid hydrogen and liquid oxygen propellants for 500 seconds.

NASA plans to use four of the engines on each flight of the Space Launch System, which the space agency is developing to send astronauts on missions into deep space aboard Orion crew capsules.

Three of the engines were used on each space shuttle launch. When fitted with upgrades for SLS flights, the engines are called RS-25s.

The SLS will be boosted into space with the four hydrogen-fueled core stage engines, twin solid rocket boosters enlarged from the shuttle’s strap-on motors, and an upper stage derived from the Delta 4 rocket’s second stage. The rocket will generate 8.4 million pounds of thrust at liftoff and haul up to 70 metric tons — more than 154,000 pounds — into low Earth orbit.

The SLS will be the most powerful rocket ever built when it flies.

The first SLS test flight is scheduled for 2018, when it will send an Orion spaceship around the moon without a crew. The first human mission aboard the Space Launch System and Orion spacecraft is set for 2021.

The RS-25 engine is a modified version of the liquid-fueled main engines that powered space shuttles into orbit. NASA kept parts for 16 functional engines after the space shuttle’s retirement in 2011.

Unlike when the engines flew on the space shuttle, the RS-25 engines will be expendable on SLS missions. The agency has enough inventory to cover four SLS flights before it has to use newly-built RS-25 engines.

The engines were built by Aerojet Rocketdyne, which is managing upgrades of the shuttle-era engines with a new computer controller to replace a unit originally manufactured in the 1980s.

The engines assigned to fly on the Space Launch System will operate at higher thrust — 512,000 pounds of vacuum thrust instead of 491,000 pounds on shuttle launches — at a 109 percent throttle setting.

“We’ve made modifications to the RS-25 to meet SLS specifications and will analyze and test a variety of conditions during the hot fire series,” said Steve Wofford, manager of the SLS liquid engines office at NASA’s Marshall Space Flight Center in Huntsville, Ala. “The engines for SLS will encounter colder liquid oxygen temperatures than shuttle; greater inlet pressure due to the taller core stage liquid oxygen tank and higher vehicle acceleration; and more nozzle heating due to the four-engine configuration and their position in-plane with the SLS booster exhaust nozzles.”

The 500-second engine test Friday was the first time a shuttle-era main engine had fired since the last space shuttle launch in July 2011, and the first ground firing since shuttle testing ended in 2009.

The primary change to the shuttle-era engines is a new controller, a computer avionics box that is similar to units developed for the J-2X upper stage engine, which has designed for an upgrade to the Space Launch System in the 2020s, but has been shelved in favor of a grouping of smaller RL10 engines.

The controller also has similarities to a computer already used on the RS-68 engine, a disposable hydrogen-fueled powerplant built by Aerojet Rocketdyne.

“We can save money (by having) a common supplier building these parts for multiple engines,” said Gary Benton, NASA’s RS-25 rocket engine test project manager at Stennis.

Supplied by Honeywell in partnership with Aerojet Rocketdyne, the controller is the brain of the engine, serving as the intermediary between the rocket’s flight computer and the engine’s myriad parts.

“It’s actually telling the engine valves what position to be in, how fast to open or close,” Benton said. “It’s looking at sensors on the engine and determining what it needs to do. It’s controlling everything on the engine — purges, valve positions, all that kind of stuff.”

Friday’s test “demonstrated the ability of the engine’s new computer to control the engine — from fuel-mixture ratios to power levels and performance,” Aerojet Rocketdyne said in a statement.

A close-up of the RS-25 engine in the A-1 test stand. Credit: NASA TV/Spaceflight Now
A close-up of the RS-25 engine in the A-1 test stand. Credit: NASA TV/Spaceflight Now

“The RS-25 is the most efficient engine of its type in the world,” Wofford said. “It’s got a remarkable history of success and a great experience base that make it a great choice for NASA’s next era of exploration.”

The engine fired Friday — Engine No. 0525 — will never fly. It is a holdover from the space shuttle program, which used it for checkouts of new components before they were introduced for real launches.

The engine has a similar purpose for the Space Launch System.

Technicians installed the engine into the A-1 test stand in July 2014, aiming to start engine firings by August or September.

Officials said the delay was caused by contamination discovered in a liquid oxygen inlet line on the test stand, requiring the plumbing to be removed, cleaned and inspected. There were also delays in the delivery of the RS-25 engine controller from Honeywell, according to Todd May, NASA’s SLS program manager.

Eight tests of Engine No. 525 are planned over the next few months, totaling about 3,500 seconds, according to NASA. Another development engine will be placed in the A-1 test stand for another series of 10 firings before flight-worthy engines begin testing.

The SLS engine testing at Stennis will culminate in a full-up hot fire of four RS-25 engines on the rocket’s core stage before its shipment to Kennedy Space Center in Florida for launch preparations.

Follow Stephen Clark on Twitter: @StephenClark1.


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