A 154-foot-long (47-meter) solid rocket booster will be ignited for two minutes Tuesday at a remote test site in Utah, wrapping up a series of five ground firings to prove the motor’s readiness for flight on NASA’s Space Launch System.
Sitting horizontally at a test cell at Orbital ATK’s rocket propulsion manufacturing facility in Promontory, Utah, the solid rocket motor will fire at 11:05 a.m. EDT (1505 GMT) for slightly more than two minutes.
Burning 5.5 tons of powdered aluminum fuel, oxidizer and binding agents per second, the rocket motor is a test unit of a booster that will help power the Space Launch System off the ground.
The SLS is NASA’s heavy-lift launcher under development to hoist astronauts aboard the Orion crew capsule on missions into deep space, first to the vicinity of the moon and eventually to Mars. The first test flight of the new rocket, without astronauts on-board, is scheduled for late 2018 from launch pad 39B at the Kennedy Space Center in Florida.
A mission with astronauts inside the Orion spacecraft will launch on the second SLS flight as soon as 2021.
Two of the boosters will provide more than 75 percent of the rocket’s total thrust in the first two minutes of flight. Four hydrogen-fueled RS-25 engines — upgraded units that flew on space shuttle missions — will power the 27.6-foot-wide (8.4-meter) SLS core stage.
Tuesday’s booster firing in Utah is the fifth in a series of ground tests conducted on the rocket motor, which is an extension of the strap-on boosters flown on the space shuttle. The shuttle’s boosters had four segments, while the SLS strap-on motors comprise five sections with pre-packed propellants inside metal casings.
With a successful test Tuesday, engineers should declare the booster design fully qualified for flight.
NASA plans to reuse some existing, previously-flown shuttle booster components for SLS launches.
The test firings of the five-segment booster began in September 2009 under the auspices of the now-defunct Constellation moon program. Answering a call from Congress for a new heavy-lift rocket — the Space Launch System — NASA kept the five-segment motor development alive, transferring its management from Constellation’s canceled Ares 1 rocket to the new SLS.
The booster’s second test in August 2010 had more than 50 objectives, and a third ground firing in September 2011 was the last of the motor’s three developmental tests, informing engineering design decisions.
NASA and booster-builder Orbital ATK conducted the first qualification motor test, or QM-1, in March 2015. Tuesday’s firing, called QM-2, is the second and final qualification test.
“You may ask what do we think we’re going to learn from this motor,” said Kent Rominger, a retired space shuttle commander and Orbital ATK’s vice president of strategy and business development for the company’s propulsion division. “Ideally, we don’t learn too much because on the fifth time we’re hoping to really understand with a fine-tuned pencil how this motor performs.”
The booster has been inside a refrigerated building since early May to chill its propellant to 40 degrees Fahrenheit (4 degrees Celsius). The “cold” test will allow engineers to analyze how the rocket motor fires at the low end of its operating temperature range.
Last year’s qualification firing was a “hot” test, with the booster’s propellant heated to 93 degrees Fahrenheit (34 degrees Celsius).
“Temperature matters,” Rominger said Monday. “What (this) allows us to do is to measure the thrust and understand how the motor performs at different temperatures.”
Rominger said engineers predict the booster will generate about 3.3 million pounds of thrust at cold temperatures, down from the 3.6 million pounds of thrust produced during the hot test last year.
Tuesday’s ground firing has 82 qualification test objectives to be measured through more than 530 instrumentation channels, according to Orbital ATK.
Some objectives include collecting data on several motor upgrades, including new insulation and liner, and a redesigned nozzle, the company said. Engineers will also study the dynamic response of the booster separation motors, which will drive the strap-on motors away from the SLS core stage about two minutes after liftoff.
Other changes from the shuttle-era booster include the removal of asbestos from the motor’s insulation to comply with environmental regulations, a change in the location of attach fittings where the motor will connect to the SLS core stage, and the removal of the rocket’s parachutes used for recovery after space shuttle launches.
Upgraded command and control avionics will also be tested on Tuesday’s firing.
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