Two mid-span supports required to avoid booster sag for QM-1

by Chris Bergin

ATK will use two “mid-span” supports on their upcoming static test of their five segment Solid Rocket Booster (SRB). The large pieces of hardware will help mitigate “sagging” in the motor, as it is tested in the horizontal position. The test – known as Qualification Motor -1 (QM-1) – has been slightly delayed to later in the year, partly due to a problem with one of the segments.

ATK Five Segment Testing:

Since increasing the length from a four segment Reusable Solid Rocket Motor (RSRM) used by the Space Shuttle – to 154 foot long five segment booster that will ride with the Space Launch System (SLS) – a mid-span support was deemed necessary to decrease the sag in the test motor as it finds itself firing in the “usual” horizontal position.

The tests – originally for the Ares 1 first stage – have been realigned ahead of their use on the SLS, which will debut at the end of 2017 as the Block 1 configuration.

This initial capability Heavy Lift Launch Vehicle (HLV) will consist of a core stage using four Pratt and Whitney Rocketdyne (PWD) RS-25Ds – formerly used by the Shuttle Program – two ATK five segment Solid Rocket Boosters (SRBs) and an Interim Cryogenic Propulsion Stage (ICPS), highly likely to be a Delta Cryogenic Second Stage (DCSS).

Three static fire tests have already taken place on the five segment boosters, all with a single span located in the middle of the booster.

Screenshot from the DM-3 L2 VideoThe most recent test – DM-3 – took place 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 previous test – DM-2 in 2010 – was carried out with 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.

DM-3 live on Fox NewsThe 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.

ATK are already deep into preparations for the first qualification firing of the five segment booster, with QM-1.

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 source information noting SLS managers have the option to launch up to 10 missions using the current five segment booster design.

QM Mid Span Supports:

QM-1 – and the follow on QM-2 – will both be fired at ATK Propulsion Systems base in Promontory, Utah. However, there will be a visual difference from previous firings, with the debut of two mid-span supports to further decrease motor sag to more closely simulate a vertical flight motor.

SAE and their Major ToolAfter ATK determined the need for a second mid-span support, they contracted with the same vendors that fabricated the first mid-span.

The three major vendors for mid-span support include Major Tool and Machine from Indiana, Force Measurement Systems (FMS) of California, and Specialized Analysis Engineering (SAE) of Utah.

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.

A single mid--span on DM-3The engineers at FMS manufactured the structure load cells and flexures used to support the sling, while the SAE team designed and built the control system for the support.

SAE are currently in the process of wiring and programming the control system – just as they did with the first mid-span support used for the DM static test motors.

The system uses a custom programmable logic controller to control the electric motors and also receive load cell data.

“These suppliers have a long-standing history with ATK and have once again proven their worth as deserving partners. We appreciate their ability to perform as required,” noted Fred Brasfield, vice president, Next-generation Booster.

“These vendors have supplied the components and structures needed to help obtain necessary data from our test motors.”

QM-1 Delay:

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.

QM-1 SegmentCasting operations continued without issue, with the Center/Forward segment casting operations beginning in August of 2012.

SLS L2 Update Section did, however, note a few issues that had to be worked during the development schedule, one relating to the replacement of the ultrasonic sensor instrumentation in the QM-1 nozzle, and another involving the new over/under speed protection (GTx) feature of the Electrical Ground Support Equipment (EGSE).

“A continuity failure of one sensor following nozzle assembly initiated an investigation revealing out of spec connector assemblies to several sensors. The decision has been made to re-terminate all 20 ultrasonic sensor connectors and re-assemble the Nozzle,” noted the updates.

“The second issue – specific to the GTx – relates to flight acceptance testing. The early development of the GTx allows multiple hot-fire exposures prior to deployment to KSC and buys down significant flight schedule risk. Initial testing of the GTx revealed an unacceptable sensitivity to noise, which will required modification.

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The GTx design was then verified during a hot-fire dry-run known as the Flight Control Test -2 (FCT-2), which took place earlier this year.

This key avionics and controls test included a “hot fire” of the fully integrated heritage TVC (Thrust Vector Control), the new SLS booster avionics subsystem and new EGSE.

FCT-2The test – of which an impressive video was made available – showed the TVC’s systems purring into life during the FCT-2 countdown, prior to the actual firing of the SRM Ignition Initiators at T-0, simulating an actual lift-off. This was followed by the TVC systems gimballing the nozzle (not in place) on the hot fire aft skirt.

“The FCT-2 test marked a definite milestone for ATK and NASA’s SLS program,” added Mr Brasfield. “Working with Marshall, we have designed and developed a modern system and common interface that allows for multiple uses of the same equipment at all necessary locations for both qualification and operational phases of the program, greatly reducing complexity and costs.”

QM-1 had already slipped from its initial schedule of conducting the static test in May by the time of the FCT-2 success, with the latest estimate showing the firing of the QM-1 will be no sooner than November.

Slide from the expansive presentation collection known as the ATK/RSRM "Bible", L2The slip to the end of the year is in part related to an issue with the aft segment of the QM-1, 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 – which found no voids in the actual propellant – NASA decided to ask ATK to scrap the segment and cast a replacement.

The delay holds no impact on the schedule for the second static test – QM-2 – or the schedule towards the EM-1 flight in 2017, due more than a year of margin.

(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.)

(L2 is – as it has been for the past several years – providing full exclusive SLS and Exploration Planning coverage. To join L2, click here:

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