Following Orbital ATK successful test-firing of an Orion launch abort system (LAS) abort motor at their Promontory facility in Utah on June 15, two more qualification tests will be required before the vital crew safety element is officially ready to fly with crewed Space Launch System (SLS) missions, beginning with Exploration Mission -2 (EM-2) mission in the early 2020s.
The solid propellant rocket motor is designed to quickly pull the Orion spacecraft’s crew module (CM) away from its launch vehicle in an emergency, either on the launch pad or during the early part of launch.
The June 15 quick, five-second ground firing, called Qualification Motor-1 (QM-1), tested changes to the motor’s reduced thrust profile and used a special test configuration to collect additional acoustic data.
The abort motor was fired in the T-93 test facility at Promontory, with the test occurring on-time at 1 pm Mountain Daylight Time on June 15.
Abort motors are configured in a vertical, upside-down orientation for ground tests at Promontory. As the designation indicates, QM-1 was the first qualification test of the abort motor using a design that is largely expected to be the one used for crewed Orion flights beginning with the Exploration Mission-2 (EM-2) flight planned for early in the next decade on the Space Launch System (SLS) launch vehicle.
One of the primary objectives of the test was to qualify the new thrust profile. The thrust profile was changed from earlier motors by changing the grain design, reducing the thrust from 500,000 to 400,000 pounds.
“Originally, the motor was 500,000 pounds of thrust and it produced [a maximum of] sixteen g’s,” Dr. Roger McNamara, Director of the Orion Launch Abort System for Lockheed Martin, explained, “so when it pulls off with a fully loaded crew module with crew [on-board], it accelerated [at] 16gs.
“It puts a lot of stress not only on the crew, but it puts it on the vehicle itself. When we moved away from the Ares rocket and now we’ve gone to SLS, SLS does not achieve the same type of velocities as quickly. So that allowed us to go take a look at that.
“Now this motor will [produce] 400,000 pounds of thrust, so it reduces the loads down to probably around 12 or 13 gs and that will be easier on the crew but [also] on the crew module, the weld joints, all the avionics, and everything that is inside the crew module, it doesn’t put as much stress on them, so we don’t have to test them [to] as high [requirements].
“So it helps us out with all the qualification of all the components and the overall system.
“There’s a couple of big deals out of this. Yes, we brought the g’s down, but we have a lot of components out there that we’re trying to validate and to qualify.
“That’s all the avionics, right down to the chips, the components inside — they’ve all got to be able to handle the abort loads. So by going from sixteen down to thirteen, we’re also reducing a lot of the cost out of the system because we’re not driving failure [requirements] and then building to something that we don’t need to design and build to.”
As with full-scale SLS booster test-firings, the abort motor is being tested at edges of its required operating temperature range. This test conditioned the motor to the upper end of the range.
“To qualify the motor under high temperature limits, the mean bulk temperature of the propellant is supposed to be a hundred degrees [Fahrenheit] or higher,” Steve Sara, Orbital ATK’s Launch Abort Motor Program Director said prior to the test.
In contrast to the large boosters, conditioning the abort motor takes much less time.
“The thermal conditioning for this motor isn’t like a large motor where you have a big mass [and] it takes probably weeks to get under condition,” Sara explained. “This motor needed four days.”
Similar to the large SLS boosters, the abort motor itself is started by a smaller, internal solid motor, an igniter. Within the LAS, the abort motor itself is upside-down, with the igniter firing from bottom to top. The exit gasses are directed through a turn-flow manifold to four nozzles at the top of the abort motor.
“The purpose of this is to allow the gasses to come from the motor up through the center and then make a turn and go the opposite way, so it becomes a tractor motor, pulling the vehicle away,” Sara explained.
Other test objectives included verifying the performance of the joints where the motor attaches to the turn-flow manifold and where the four nozzles attach to the manifold.
Configuration and preparations:
Manufacturing and assembly of the abort motors is done at Orbital ATK’s Propulsion Systems Utah facilities.
The composite case of the motor is manufactured in their Refurbishment/Aerospace Structures facility in Clearfield, Utah, facility. The nozzles and other smaller components are manufactured at the Promontory facility. Final assembly of all the components is done at the Headquarters/Bacchus facility in Magna, Utah.
The fully assembled motor arrived at the T-93 facility in April to begin the final part of the test campaign.
“As far as the test itself, we get all things ready ahead of time that we can in terms of tools, materials, and instrumentation and then we get [the motor] to the test area,” Sara said. “Actually, [it was] a little bit late because of weather delays. It was supposed to arrive at the test facility and be in the test stand on the first of April, but had a delay of almost two weeks.”
Another significant objective of the QM-1 test was to better characterize the acoustics that firing the abort motor produces on Orion.
The configuration at the T-93 facility for this test included a more elaborate set up to collect acoustic data than the previous full-scale test conducted there in 2008, which had a single near-field plume acoustic (NFPA) array positioned on the perimeter of the motor.
“When we did this back in 2008 we had one of these arrays, that had acoustic gauges on it to gather information,” Sara explained. “It was felt since that time from the entire community that there was a desire to have more information on acoustics.”
In addition to a second NFPA array around the motor, a heat-shield array with additional acoustic sensors was hung over it.
“It’s called the heat shield array — it’s essentially the same distance [from the abort motor] as the heat shield for the crew module. What’s also unique about it is we usually don’t hang things over or near our motor when we go fire. So it was an interesting challenge to figure out how we’re going to do this. It was desired not to build a structure because the structure would be in the way of acoustics reflection.”
Dr. McNamara said that the additional acoustic data collected from this test should allow refining of loads analysis.
“The acoustics translates into loads. Originally from the ST-1 firing that we did out here, the acoustic levels were higher than we thought and so we had to go back and come up with the ogives on the outside of the LAS,” he explained.
“And those ogives require a hatch on them and then the components inside with all the higher [acoustic] levels cause the qualification of all the other components on the crew module and the service module all to be tested and qualified at a higher level. The acoustics information we get back [and the] reduced thrust here, we’ll be able to apply that to the loads and drop the loads down across the vehicle, across the spacecraft.”
The abort motor is one of three primary solid rocket motors in the overall Orion LAS; together with the crew module, the LAS elements make up a launch abort vehicle.
If activated in an abort, the abort motor pulls the full abort vehicle away from the launch vehicle while the attitude control motor assists with controlling the initial separation. The abort motor.
The ACM then reorients the vehicle for separation events and for the crew module parachute deployment sequence. The LAS is then separated from the crew module with the jettison motor.
Other elements of the LAS include a fairing assembly that covers the crew module and a Motor Adaptor Truss Assembly (MATA) that structurally connects the LAS with the CM.
The LAS can be used for aborts while the spacecraft is still on the pad and during launch up to altitudes of 300,000 feet. During a nominal SLS crew launch, the jettison motor will fire to separate the LAS from the CM and the rest of the launch vehicle about three and a half minutes after liftoff.
Development of the LAS began during Orion’s days within the Constellation program of the past decade. The QM-1 test is the third full-scale test-firing of an abort motor.
The first was the ST-1 static test that was conducted in the same T-93 test facility in November, 2008. The second was as a part of the PA-1 pad abort test in New Mexico at the White Sands Missile Range in May, 2010.
“We kept the attitude control motor the same. So working down the stack, attitude control motor is on top — we kept that the same,” Dr. McNamara noted about some of the changes to the LAS since Constellation.
“Then [with] the jettison motors, we have made some changes to it after we did demonstration motor firings and after we did Pad Abort-1. We did a remix on the propellant to stabilize it a little bit more, and then on this abort motor is where we really backed down on the thrust on it.”
He also noted that the MATA design changed from composite to metallic, which will reduce its mass and increase its strength.
Data reviews and modal testing:
Sara said that the initial data “quick look” would be available just a couple of hours after the test was conducted.
“We have a lot of data lines that we’re going to be analyzing and reviewing,” he said. “We can do some of it immediately — we’re going to have a test review later this afternoon to review much of that data and that’s mostly ballistic data for the performance of the motor, thrust and time and that kind of thing.
“But there’s a lot of data that we’re going to analyze, the strain gauges and so forth.”
In a press release posted after the quick look review, Orbital ATK noted “more analysis will be performed in the coming weeks, but all initial test results appear to be nominal.” The Orbital ATK press release also noted that the quick look confirmed that the motor reached 400,000 pounds of thrust in the expected one eighth of a second.
Rather than immediately begin disassembly of the motor, Sara said it will stay in the stand for modal testing first.
“It will have to sit in that stand for a couple of weeks. The reason for that is we’re going to do what we call a modal survey where we ping the motor and get vibration back to get the frequency of the motor and also multiple frequencies of the motor to get that kind of information,” he explained.
“So we can’t really take anything apart until we do that test. Once that’s done, then we take it apart, take all the parts apart, look at the joints. We also cut up some of the pieces as well, to look how they performed against what we expected them to do.”
Future test sequence:
Two additional qualification tests of the abort motor are planned at Promontory to verify that the design is ready to fly on Orion with a crew on-board EM-2.
“So this motor test is QM-1. We have QM-2 and QM-3 that we need to test,” Dr. McNamara added. “We’ll do all three qualification motor firings before EM-2, when we put crew on [Orion]. If we were going to have to put crew on EM-1, we were going to have to accelerate those firings.
“QM-2 and QM-3 should be an exact duplicate of this motor, so we feel we’ve got everything into this that we plan on doing to it and then almost like you’re in production we’ll do two [further tests] and then we’ll say it’s repeatable from QM-1 to QM-2 to QM-3.”
In parallel with the abort motor tests, the attitude control and jettison motors are also going through their qualification tests.
“As far as the attitude control motor, we’ve got some other tests going on there but same thing — QM-1, QM-2, and QM-3 with those,” Dr. McNamara explained. “And then on the jettison motor, same thing — three qualification motor firings there.”
The goal is to have the final design of all the LAS elements in place for the Ascent Abort-2 (AA-2) integrated LAS test, which will launch the full launch abort vehicle on top of a modified Peacekeeper missile up to simulated maximum dynamic pressure conditions where an abort sequence will be triggered.
Although it was decided not to put crew on the EM-1 flight, the feasibility assessment showed that the AA-2 test date could still be accelerated.
Dr. McNamara said it could be moved up into the second quarter of 2019 from the current December, 2019, target.
“We’re on track to accelerate that, we’re working out all of the schedules, the funding, the personnel, where everything is located and can we actually get there,” he said.
“We’re detailing that out right now.”
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