Minor delay drowned out by successful, bright and loud test of five segment QM-2 booster
PROMONTORY, Utah — On Tuesday, June 28, 2016, Orbital ATK and NASA successfully completed the second of two qualification tests (QM-2) for the five-segment solid rocket booster (SRB) that is planned for use on NASA’s Space Launch System (SLS). Much as in actual flights into the black of space, things didn’t go as planned.
At approximately 7:30 a.m. MDT (13:30 GMT), NASA announced that a computer anomaly, which was tracked down to a data link software issue on the hard drive, resulted in the malfunctioning part needing to be swapped out before the test could take place.
Charlie Precourt, Orbital ATK’s vice president and general manager of propulsion systems, provided SpaceFlight Insider with the following details about the problem and the operation of the system:
“We have a number of computer systems in line with the motor, some of them command the motor, some of them take data, this one is called a sequencer; it is responsible for the starting up and the right timing of the startup of a number of pieces of equipment. That had been run perfectly during all of the dry runs and then when we booted it up for the dry run this morning; of course, we got a failure to link in its communication so we had to change out the hard drive with another version of the software and to make sure that we could proceed with the test,” Precourt said.
Despite this delay, this cold-soak static fire test was, by all appearances, successful and completes the qualification series for the upgraded booster. The next time one of these boosters fires, it will be as part of a pair that will be used on the maiden flight of the SLS on Exploration Mission 1 (EM-1), currently slated for the latter half of 2018.
Approximately five seconds after the “FIRE!” command was given, the roar of the booster pierced the Utah desert air where media and dignitaries were gathered for the test. For slightly more than two minutes, the motor belched flame and smoke as the solid propellant was consumed, mimicking the thrust profile of an actual launch.
Since active throttling isn’t possible with a booster of this design, engineers use a passive method achieved by casting the propellant in a manner so that the surface area of the rubbery mixture changes at a predictable rate over the duration of the burn. This changing surface area impacts the resultant thrust from the booster. Casting and curing the propellant takes approximately one week. Attendees could hear the changing thrust levels from the booster as it varied in timbre and tone related to the variation of the booster’s output.
At the conclusion of the burn, a CO2 quenching tool was used to extinguish any latent fire in the booster casing, allowing the hours-long cool down period to begin so that personnel could enter the test area to secure the site after the conclusion of the test. Water was also sprayed on the aft segments of the booster to further promote cooling. The intensity of the heat from the booster’s flame was such that sand in the area was melted to form what test personnel call “booster glass”.
Watching the test were several officials with NASA who noted that, while they had completed yet another milestone successfully with the help of their partners in industry, they still had a way to go on the road to EM-1.
“We will probably take a pause – for about 48 hours,” said Alex Priskos, NASA’s boosters manager. His comments caused the room of officials and media to burst out in knowing laughter. “If that,” Precourt added with a chuckle, “this was a big deal today, the design certification review coming up in August for us, is a big, big deal and at the same time, we’re building production hardware […] I get visions, I feel that next fall is only a week away – at least that’s what it mentally feels like to me.”
The QM-1 test, conducted in March of last year (2015) saw that booster kept in a hot environment (90 °F / 32.22 °C) to test the booster’s performance at the upper-temperature limit. Today’s test was designed to test the performance at the lower operational temperature limit (40 °F / 4.44 °C). The booster had been kept in a chilled environment for more than a month in an effort to uniformly cool the casing and propellant. All things being equal, solid propellant burns more slowly at colder temperatures, and now booster engineers will have the data they need to validate pre-test models.
During the course of the one hundred twenty-six second burn, roughly 600 gigabytes of data was recorded. This data should allow engineers to confirm the booster performs as designed, and it will be integrated into flight simulation software to further refine the vehicle’s avionics. Though initially in the domain of the Orbital ATK engineers, the test data will soon be sent to NASA’s booster team at Marshall Space Flight Center in Huntsville, Alabama.
While superficially similar to the booster used throughout the Shuttle program, the ones developed to be used for SLS are essentially a new design. Beyond being lengthened by an additional segment, the 177-foot (54-meter) long motor also sports a slightly different fuel mixture, upgraded flight software and hardware, a larger nozzle, removal of recovery hardware, and an all-new insulating liner.
Fully loaded with propellant – polybutadiene acrylonitrile (PBAN) – each booster weighs 1.6 million pounds (725,747 kilograms) and is capable of producing 3.6 million pound-force (16,000 kN) of thrust. The propellant for the SLS-designed boosters has been modified slightly from that used during the Shuttle Program in order to meet performance needs particular to SLS, but it is still composed of the same constituent materials. With a combined output of 7.2 million pound-force (32,000 kN), the twin boosters will provide more than 75 percent of SLS’ total thrust at liftoff, and burn approximately six tons of propellant every second.
Keeping such a powerful rocket in-place is the job of a lot of concrete and steel. The forward thrust block is a large structure comprising more than 13 million pounds (5.9 million kilograms) of concrete designed to keep the booster in its static firing position. Per Orbital ATK: “The test stand is made up of a system of load cells and flexures to measure motor thrust and side loads. In the very unlikely event that a flexure failed, the test stand would maintain control of the motor by transferring thrust loads to the test stand overload system. In addition to the overload system, there is a third redundancy of a forward restraint which is an I-beam structure around the front of the motor.”
Removing the booster recovery hardware – something which had been an integral component of the boosters throughout the Shuttle program – is a significant departure from NASA’s hardware recovery efforts of years past. However, opting to design the boosters to be disposable makes them both lighter and more cost-effective to operate, as well as reducing failure points.
According to NASA, eliminating the recovery system reduces the weight of the vehicle by 10,000 pounds (4,536 kilograms) per booster, correlating to a 2,000-pound (907-kilogram) increase in payload capability. Additionally, the agency has saved millions of dollars in infrastructure and personnel costs by not needing to maintain a standing recovery fleet in support of flight hardware with a projected low launch cadence.
Further differentiating itself from the Shuttle-era booster is the all-new insulating liner. No longer allowed to use an asbestos-derived insulation, NASA was forced to utilize something more environmentally friendly. The new material has superior insulating characteristics while maintaining a low weight requirement. However, the development of this new liner wasn’t without its issues.
Early iterations of the new liner showed an adverse reaction with the propellant mixture. Thorough inspection of the propellant at its interface with the insulation indicated that unexpected – and unwanted – voids had formed. After nearly a year of redesigns and testing, a suitable insulator was developed and booster validation could move forward. As there was adequate time available in the development timeline – and since other SLS qualification milestones could be achieved independently of the booster’s development – this did not delay SLS’ overall schedule.
Unlike other major components of the launch vehicle, the booster’s 12-foot (3.66-meter) diameter segments are not so large as to prevent being shipped by rail. The individual booster segments will be shipped to NASA’s Kennedy Space Center in Florida, where they will be assembled. Once stacked and mated to the SLS core stage, the entire weight of the launch vehicle and payload will be fully supported by the two boosters and their attachment points on both the forward and aft booster segments.
“I’m truly blessed to get to see this at a top level and then, occasionally, when I can’t stand Washington anymore, I get to go some remote location where something cool is going to happen; I get to pretend I’m an engineer for a brief period of time and then get motivated and go back and do my day job in D.C.,” said NASA’s Associate Administrator for Human Exploration and Operations Directorate Bill Gerstenmaier. “You got to see something really special today.”
Denoting the changing demographic that NASA has witnessed since the close of the Apollo Program, when asked by a member of the media if a 49-year-old could expect to see a man on Mars [in his lifetime] Gerstenmaier confirmed that he would – with a slight change to the question.
“Yes. The answer is yes – and I would say ‘man’ may be the wrong word – you will see a human being […] we’re still on track to have the ability to put humans in the vicinity of Mars, maybe a kind of fly around mission, without a Mars lander roughly in the 2030s,” Gerstenmaier stated to applause.
Video Courtesy of NASA.gov Video
Curt Godwin has been a fan of space exploration for as long as he can remember, keeping his eyes to the skies from an early age. Initially majoring in Nuclear Engineering, Curt later decided that computers would be a more interesting - and safer - career field. He's worked in education technology for more than 20 years, and has been published in industry and peer journals, and is a respected authority on wireless network engineering. Throughout this period of his life, he maintained his love for all things space and has written about his experiences at a variety of NASA events, both on his personal blog and as a freelance media representative.