ATK’s test facility in Promontory, Utah is now officially looking forward to the next full-scale test of a five-segment solid rocket motor – set to take place at 9:30 am local time on March 11, 2015. The realigned date was set following a lengthy investigation – and resolution path – into problems found in the aft segment of the Qualification Motor -1 (QM-1).
Solid Rocket Boosters (SRBs) – as they are best known – provide numerous launch vehicles with the extra push for the ride uphill during first stage flight.
Solid motors come in various shapes and sizes, some of which even provide the role of an upper stage. However, by far the best known solids were the ones that provided the Space Shuttle fleet with the majority of their power during the first two minutes of flight.
By the time the Space Shuttle Program (SSP) was coming to a conclusion, the large solids already had a future. A five segment version of the booster was set to provide the first stage to the Ares 1 launch vehicle.
When Ares fell by the wayside during the cancellation of the Constellation Program (CxP), the boosters refused to go quietly into the night, earning a new place in NASA’s future.
This time they would return to their traditional configuration of being placed on either side of a big orange tank – paired on the Space Launch System (SLS).
The addition of an extra segment to the booster was never going to be as simple as it sounds. Numerous evaluations were required, including a test series involving static fires – which also would allow for additional technologies to be implemented in improving the motor.
Testing of the five segment motors proceeded without issue during the Development Motor (DM) test program. In total, three static firings were conducted.
By the time ATK fired the DM-3 motor, it became most heavily instrumented solid rocket motor in NASA history, with a total of 37 test objectives measured through more than 970 instruments.
(Image taken from the amazing 220mb super slow-mo DM-3 Five Seg Motor Ground Test Video – available in L2 – LINK)
The 2011 test successfully completed the DM test series, with the motor set to move into QM (Qualification Motor) testing that would ready the booster for its role with the Space Launch System (SLS).
Preparations for the static fire of the QM-1 booster began to take place at ATK Propulsion Systems base in Promontory, Utah – where segments started to arrive for build up in 2013. The first segment of the QM-1 motor was cast in August, 2012.
However, the test was delayed by an investigation into the discovery of voids in the bondline between the propellant and the case insulation – seen during inspections of the aft segment of the QM-1 booster.
The evaluations into the problem began in the summer of 2013.
“That thing has dragged on longer than I would have liked (it) to,” noted Todd May, SLS Program Manager, during an interview with NASASpaceflight.com this month.
During the early stages of the investigation, engineers thought the problem was related to a streamlined production process.
“One of the reasons (the investigation) has taken so long is we thought we had it nailed (at the first attempt),” Mr. May added. “We had done a lot of value-stream mapping to reduce the (processing) flow of the motors through the factory – and we had reduced 56 percent of all the steps in processing.
“We undid all (the reduced steps) and re-poured (the motor segment), but we got exactly the same problem, so we realized that wasn’t the problem – we had to rethink it all again.”
With two aft segments now displaying the same issue, the investigation was expanded to determine what was causing the propellant to de-bond from the casing wall and form voids.
Quickly, evidence began to mount that the issues were related to use of a new material in the insulation lining between the propellant and the motor casing wall.
“(During) the Shuttle program, our insulation had asbestos and when we moved into the Ares program one of the things we did was to change the insulation formulation to make it environmentally-friendly,” added Mr. May.
“The old insulation had some voids in the main body of the material, but not along the borders between the propellant and the insulation. (In) the new insulation, we got some voids in the bondline between the insulation and the propellant.
“The concern you have there is, if you burn up to the point where you get that void, you could unzip and burn up the backside – if the combustion goes inside of that void and pressurizes it – which is not a good thing.”
The solution involved the casting of additional test segment hardware, as part of an impressive evaluation into the issue.
“We finally figured out that we were getting some off-gassing,” added Mr. May. “We use this stuff called Chemlok between the insulation and the casing, and we found that if we lay all but the last couple of layers of insulation, and then a layer of Chemlok, and then put the last layer on, that Chemlok actually (mitigates) out-gassing up through to the barrier to the propellant.”
“Not only that, but (in) the micro-cores we were seeing, it actually wicks down in those holes and heals all those micro-cores.
“So we finally were able to pour a new segment with this new process – it’s the cleanest we’ve ever seen, it looks great and we think we’ve nailed the problem. It’s passed inspection at this point, we’ve done a full inspection.”
This breakthrough has allowed for NASA and ATK to set a date to static fire the QM-1 motor in March of next year.
“So at this point we can say with pretty good confidence that we’re going to test in the March timeframe. We’ve been shooting for March 26th, we’re actually looking at accelerating that a week to deconflict with some other meetings (and now advanced to March 11 – confirmed by ATK), so that’s how confident we are at this point.
“So we think that problem is behind us at this point.”
Notably, a static fire in March, much-delayed from the original schedule, was always noted as not being a lead item on SLS’ schedule, even based on the December, 2017 target for the readiness of SLS.
The debut mission has slipped into 2018, but that is based mainly on Orion’s readiness for EM-1.
“We’re on the order of twenty to thirty weeks of schedule slack to the 2017 readiness date with the boosters, so schedule is not as big an issue there – and the way we’re managing the contractor is (different),” Mr. May added.
“In other words, the cost is not driven by schedule, it’s driven by holding them (the contractor) down to a certain head count and so they just spread the work out within that timeframe.”
ATK has also continued with work on several other elements for the SLS boosters, including the next generation advanced boosters that will come online in the mid to late 2020s.
The QM-1 booster is expected to be the parent configuration for SLS launches until at least 2025.
(Images: Via ATK, NASA and L2 content from L2’s SLS specific L2 section, which includes the SRS “Bibles” – numerous non-restricted presentations all in one place. SLS Render by L2 artist Nathan Koga)
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