The solid rocket booster that will propel NASA’s skyscraper-size, 300-plus-foot-tall Space Launch System (SLS) rocket and its Orion spacecraft in the coming years marked off a significant development milestone in March 2015, unleashing its fury on a barren mountainside at Orbital ATK’s test stand in Promontory, Utah, for the Qualification Motor-1 test fire (QM-1). The 154-foot-long booster, the largest of its kind in the world, ignited to verify its performance at 90 degrees, the highest end of the booster’s accepted propellant temperature range and the temperature the SLS can expect to encounter at its Florida launch site on Kennedy Space Center (KSC) Launch Complex 39B.
Detailed inspections of the now disassembled booster took place over the course of 2015, with all the data collected confirming the QM-1 test as a resounding success. More than 500 instrumentation channels were used to help evaluate over 100 defined test objectives, and now work is underway at the test stand preparing the second booster for another test fire, Qualification Motor-2 (QM-2), which is scheduled to take place June 28, 2016.
A cold-temperature test, at a target of 40 degrees Fahrenheit, the low end of the propellant temperature range, is planned for QM-2 before the hardware testing to support qualification of the boosters for flight will be complete, at which point Orbital ATK will be ready to proceed toward the first flight of the SLS, an uncrewed mission to validate the entire integrated system, currently scheduled to fly on the Exploration Mission-1 (EM-1) in late 2018 (at the earliest and likely to slip further).
“We are making significant progress in preparation for the second qualification test,” said Bruce Tiller, deputy manager of the SLS Boosters Office at NASA’s Marshall Space Flight Center in Huntsville, Ala. Marshall manages the SLS Program for the agency. “The completion of these qualification tests is crucial in getting the boosters certified for the first two flights of SLS and staying the course for the journey to Mars.”
Last September engineers successfully tested the booster thrust vector control and avionics systems during an off-motor hot-fire test to simulate the test cycle that will be used in the QM-2 test fire this summer, which will closely resemble flight conditions. The thrust vector control and avionics system successfully provided the required command and control of the motor nozzle position during the QM-1 test fire, and the same is expected of QM-2.
The thrust vector control system steers the rocket nozzle based on commands passed through the booster avionics system made up of hardware, software, and operating systems that will communicate with the SLS avionics system and ground operations. The avionics also will control booster operations, like motor firing and separation motor ignition.
Small voids were previously discovered prior to QM-1 between the propellant and outer casing of the booster’s aft segment, which demanded a lengthy investigation and trouble-shooting effort by Orbital ATK and NASA to determine root cause(s) and corrective actions before they could move forward with booster testing for QM-1 (which had been significantly delayed due to the issue). The problem which significantly delayed QM-1, however, doesn’t appear to be an issue with the QM-2 booster.
“Finding no defects in the segment insulation we’ve inspected is a huge accomplishment for our teams, and something that hasn’t been done on past NASA programs,” says Tiller. “That’s a testament to the work we’ve put in on refining our manufacturing processes and materials.”
With QM-1 there have been four fully developed, five-segment SRBs fired up on Orbital ATK’s Promontory, Utah, T-97 test stand since 2009, with the most recent prior to QM-1 having been conducted in 2011, and all performed fine. The first three tests, known as the Development Motor test series (DM-1, DM-2, and DM-3), helped engineers measure the new SRB’s performance at low temperature, verify design requirements of new materials in the motor joints, and gather performance data about upgrades made to the booster since the space shuttle program.
The five-segment SLS boosters will burn for the same amount of time as the old shuttle boosters—two minutes—but they will provide 20 percent more power, while also providing more than 75 percent of the thrust needed for the rocket to escape the Earth’s gravity.
“Ground tests are very important – we strongly believe in testing before flight to ensure lessons-learned occur on the ground and not during a mission,” said Charlie Precourt, Vice President and General Manager of Orbital ATK’s Propulsion Systems Division and four-time space shuttle astronaut. “With each test we have learned things that enable us to modify the configuration to best meet the needs for the upcoming first flight.”
The first of 10 flight segments for the boosters that will be employed on that first SLS flight, EM-1, was recently cast as well. A couple weeks ago workers filled the insulated metal case of a booster aft segment with propellant and let it solidify, or “cure,” for several days.
The five-segment solid rocket booster has been in development for years, having been initially designed to launch NASA’s Ares rockets for the agency’s cancelled Constellation program. The booster is similar to the four-segment SRBs that helped launch NASA’s now retired space shuttle fleet, but it’s larger and incorporates several upgrades and improvements.
Orbital ATK also received a $47 million contract from the U.S. Air Force earlier this year for development of something similar: “a solid rocket propulsion system prototype to support the EELV program for national security space missions.” The rocket, if it ever manifests into reality, would use VAB high-bay 2 at KSC and launch off pad 39B—the same pad as SLS.
Although the boosters themselves will provide 75 percent of the power needed to break Earth’s hold, the SLS will still employ four engines of its own—former (upgraded) liquid-fueled space shuttle RS-25 engines—which are currently at NASA’s Stennis Space Center in Mississippi undergoing their own series of tests.
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