The solid rocket booster that will propel NASA’s skyscraper-size Space Launch System (SLS) rocket and its Orion spacecraft on deep space missions in the coming years took a huge step forward in its development on March 11, 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 colossal 154-foot-long (47-meter-long) booster, the largest of its kind in the world, ignited to verify its performance at the highest end of the booster has accepted propellant temperature range, 90 degrees. That’s the temperature the SLS can expect to encounter on a regular basis at its Florida launch site on Kennedy Space Center (KSC) Launch Complex 39B, and this week NASA and Orbital ATK released initial findings and data from the QM-1 test fire. Detailed inspections of the disassembled booster will take another several months.
«Having analyzed the data from QM-1 for a little more than a month, we can now confirm the test was a resounding success», said Charlie Precourt, Vice President and General Manager of Orbital ATK’s Propulsion Systems Division, and four-time space shuttle astronaut. «These test results, along with the many other milestones being achieved across the program, show SLS is on track to preserve our nation’s leadership in space exploration».
It took only a second for the booster to reach 3.6 million pounds of thrust (equivalent to 22 million horsepower/16,405 MW), burning through 5.5 tons of propellant per second, at 5,000 degrees Fahrenheit, for just over two minutes – exactly as it will when it launches the SLS. More than 500 instrumentation channels were used to help evaluate over 100 defined test objectives, and newly designed avionics hardware and equipment to control the motor helped provide improved test monitoring capability.
According to Mike Killian, AmericaSpace reporter, the test also demonstrated the booster’s ability to meet applicable ballistic performance requirements, such as thrust and pressure. Other objectives included data gathering on vital motor upgrades, such as the new internal motor insulation and liner and an improved nozzle design. «Current data show the nozzle and insulation performed as expected, and ballistics performance parameters met allowable requirements», noted Orbital ATK in their report. «Additionally, the thrust vector control and avionics system provided the required command and control of the motor nozzle position».
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 Solid Rocket Boosters (SRBs) that helped launch NASA’s now retired space shuttle fleet, but it is even larger and incorporates several upgrades and improvements. Now, after a lengthy investigation and trouble-shooting effort to determine root causes and corrective actions for the existence of small voids previously discovered prior to QM-1 between the propellant and outer casing of the booster’s aft segment, Orbital ATK is back on track with the booster’s development and already constructing the hardware for a second test fire in spring 2016 (QM-2).
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 then be ready to proceed toward the first flight of SLS, an uncrewed flight to validate the entire integrated system, currently scheduled to fly on the Exploration Mission-1 (EM-1) in late 2018.
With QM-1 there have now 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 gravitational pull of the Earth.
«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», added Precourt. «With each test we have learned things that enable us to modify the configuration to best meet the needs for the upcoming first flight».
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 preparing for their own series of tests, the first of which occurred earlier this year. A second RS-25 test fire is currently scheduled for May or June this year.
The SLS program also kicked off its Critical Design Review (CDR) this week at NASA’s Marshall Space Flight Center in Huntsville, Alabama, which demonstrates that the SLS design meets all system requirements with acceptable risk, and accomplishes that within cost and schedule constraints. The CDR proves that the rocket should continue with full-scale production, assembly, integration, and testing, and that the program is ready to begin the next major review covering design certification. The SLS CDR is expected to be completed by late July.