Orbital ATK’s Qualification Motor -1 (QM-1) test has conducted a key firing on Wednesday, on the path towards the debut launch of the Space Launch System (SLS). The five segment solid rocket booster came to life at the Promontory test site in Utah, concluding a long path to its big day, involving a major investigation – and subsequent solution – after the discovery of voids in one of its segments.
Three static fire tests have already taken place on the five segment boosters, as the motors transitioned from the Space Shuttle Program, through to the since-defunct Constellation Program (CxP) for the Ares rocket, before finding a new role with SLS.
The most recent test – DM-3 – took place back in 2011 and was the last in a series of development motors to be tested. It was also the 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 DM-2, in 2010, sported a total of 53 design objectives, measured through more than 760 instruments. For that test, the motor was cooled to 40 degrees F – a “cold motor” test – in order to measure solid rocket motor performance at low temperature, as well as to verify design requirements of new materials in the motor joints.
The DM-3 incorporated several performance-based improvements to the designs of the first two development motors.
Additionally, the core of DM-3 was heated to 90 degrees Fahrenheit for this full-duration firing to verify the motor’s performance at high temperatures.
The success of DM-3 paved the way for the testing to move into the Qualification stage, the final test series that would graduate the giant motors towards their role in aiding SLS launch through first stage flight.
Preparations for the upcoming QM-1 test began with the first casting operation of the Forward Segment back in July 16, 2012 at ATK’s Promontory facility.
Casting operations continued without issue, with the Center/Forward segment casting operations beginning in August of 2012.
However, in early 2013, the QM-1 test was slipped, due to issues found during the inspection of the aft segment, which was found to have about a two foot-wide area where propellant had debonded from the inside of the segment wall.
After some analysis, NASA decided to ask ATK to scrap the segment and cast a replacement.
Unfortunately, the replacement segment was seen to suffer from the same problem – believed to be caused by processing and design changes in the motor’s insulation and liner material that had replaced the previous use of crysotile – the most common mineral form of asbestos.
Following the x-ray discovery of the voids within the propellant of the two aft QM-1 motor segments, ATK placed segment processing on hold until an investigation could determine primary/root cause(s) and corrective actions.
With confirmation of a Propellant/Liner/Insulation (PLI) unbond and propellant void, ATK began a “deep dive assessment in support of Knowledge Point Share” meetings with NASA to determine the path forward.
At an initial meeting with engineers from the Marshall Space Flight Center, the investigation team prioritized the dissection of the QM-1B segment, the one that showed signs of an unbond, as the first site for a PLI sample extraction and detailed examination.
The investigation resulted in an impressive evaluation path, utilizing Process Simulation Article-1 (PSA-1) and then Evaluation Article-1 (EA-1), feeding into new processing techniques that finally resulted in a segment being cast that was the “cleanest we’ve ever seen” – according to SLS manager Todd May.
Ultimately, this allowed for the QM-1 test to press ahead, with a date being set – a date that is still well within the critical path for SLS’ debut launch.
The test involved the QM-1 booster being fired for its full duration of around two minutes, while it is put through its paces, such as the steering of its nozzle via the Thrust Vector Control (TVC) system, as would be utilized during a real launch.
Once the firing was complete, a remote controlled arm swung into place to extinguish the remaining flames around the nozzle – with 31 tons of CO2 – to protect the inner workings of the motor for post-firing investigation and data gathering.
This data will be feed into the QM-2 firing, which is set to be conducted in less than a year’s time.
QM-1 – as will the follow on QM-2 – sported a slight difference in support structures when compared to previous firings, with the debut of two mid-span supports to further decrease motor sag to more closely simulate a vertical flight motor.
The mid-span structures include two uprights bolted to the floor and a structure that spans the width of the static test motor and supports the weight taken up by the slings during build-up and testing.
The system uses a custom programmable logic controller to control the electric motors and also receive load cell data.
It is expected that the five segment solid motor will be used on all SLS flights until at least the middle of the 2020s, with previous source information noting SLS managers have the option to launch up to 10 missions using the current five segment booster design, prior to moving to the Advanced Boosters – which are also highly likely to be Orbital ATK solids.
(Images: Via ATK and L2 content from L2’s SLS specific L2 sections, which includes, presentations, videos, graphics and internal – interactive with actual SLS engineers – updates on the SLS and HLV, available on no other site.)
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