Engineering Test

NASA Launch Vehicle Hydro-Dynamic Suspension System (HDS)

Michael Sachs, System Engineer, NASA Marshall Space Flight Center

So, what is an HDS? Well it is one of the underpinning technologies of IVGVT. Critical to establishing flight readiness for all NASA SLS. Provided sufficient confidence to permit humans to be aboard the Maiden flight of the Space Shuttle. So why did I include a picture of the ISS here.Of course it looks cool, But actually ISS mission control is at MSFC and every ISS component and Shuttle payload undergoes structural and environmental testing at MSFC.1

History of the HDS and IVGVT HDS Refurbishment and Design HDS Control Room HMIs HDS System Architecture IEEE1588 PTP (GPS, UTC, TAI, DST) cRIO SCADA Reference DesignAgendaSo, what is an HDS? Critical to establishing flight readiness for all NASA SLS. ISS component and Shuttle payload undergoes structural and environmental testing at MSFC.2

7,200,000 lb Lifting cap. 6 Axis DOF to simulate Free-Free boundary flight conditions. Strategically placed electro-dynamic shakers simulate thrust oscillation and acoustic shock.

What is a Hydrodynamic Suspension System (HDS)?Integral part of IVGVT allowing meas. of vehicle modal characteristicsVerification of FEM, improve GN&C stability, identify resonance anomalies

Most launch and space vehicles, as well as aircraft, undergo a low-energy vibration test to measure the modal characteristics of the vehicle. This modal testing or ground vibration testing (GVT) usually captures the natural frequencies, mode shapes, and damping of the vehicles structure. This data is then used to correlate dynamic finite element models (FEMs) to produce test-verified dynamic FEMs for use by disciplines such as aeroelasticity, structural loads and dynamics, and guidance, navigation and control (GN&C) to analyze, and estimate vehicle responses to expected flight, and ground loads and environments. Analyses employing the test-verified FEMs are used to support the design certification review (DCR) process, ensuring that the vehicle is structurally sound and safe to fly. Current analyses show the fundamental frequencies of a fully fueled, launch-ready Ares I launch vehicle to be in the 1 to 10 Hertz (Hz) range, giving the Ares I the lowest primary bending frequency of any human-rated launch vehicle that NASA has ever flown. Therefore, understanding the flex properties of this vehicle is especially important. By measuring the response to a known excitation at the precise location of the flight control sensors a significant amount of uncertainty can be removed from the sensed data processed by GN&C algorithms allowing improved flight control system performance. Furthermore, the IVGVT data can help fine-tune models used to optimize the performance of thrust oscillation mitigation and POGO suppression devices. Without test-calibrated IVGVT models, the model uncertainty factors (MUF) used in verification loads analysis are not updated and remain the more conservative values employed during earlier phases of the design. This can translate into flight envelope reduction and launch/payload restrictions. If model uncertainties are too large, GN&C stability requirements either cannot be met or make the design of the GN&C system more challenging. Model inaccuracies in the bending dynamics of the vehicle could create an unstable control system design, which in turn could result in loss of the mission. A GVT also supports GN&C analysis by reducing uncertainty in the flex model. 3

Saturn V in the Test Stand, circa 1966

Prior to the HDS, IVGVT was accomplished by suspending the vehiclewith cables. Prohibitive due to weight limitations and cable resonance.Two people pushing on the nose cone orthe fins on the first stage, could deflect the vehicle as much as two inches. The suspension system required to simulate free flight was a particular challenge. Suspending the vehicle by cables would not work, as the cables resonate at frequencies similar to that of the vehicle which might have complicated or invalidated test results. NASA developed a state-of-the-art suspension system to simulate the free-free boundary conditions of flight. The hydrodynamic support system or HDS consists of oil bearings and vertical gas springs for lateral and roll stability (Figure 2). Oil under pressure was pumped between flat contacting surfaces to provide a near-frictionless support. This system transmits the heavy vehicle load directly to the ground, enabling the support mass to be relatively small.9 The HDS units were so effective that the entire six- million-pound vehicle could be excited in its low frequency suspension modes by two people pushing the fins on the first stage, deflecting the vehicle as much as two inches.1 4

Original HDS testing, circa 1965Martin Marietta Engineers

I wonder what a day around hydraulic oil doesto a white shirt and tie?NASA engineers circa 1965. 5

Refurbished HDS Cylinder and PistonHydrodynamic Suspension System

One year to refurbish 4 HDS, replacement cost > $1,000,0006

Unique Design: Nearly 100% inefficient but 100% effective! Why? Continuous Hydraulic flow through and across bearing surfaces.HDS Piston and CylinderHydraulic Lift with N2 Gas Spring

HPUSVU

Each HDS = 1.5 million lbs of lift capacity upon a tuned gas spring with calculated N2 volume stiffness, natural freq. < 1/10 fundamental mode of vehicle (.6 Hz), Damping ~ 24 lb sec/in. Float Sunk Issues, detection, recovery procedure, Bearing contact sensing transient and static, float height measurement using delta p. Discuss upper and lower ring bearings and pressure monitoring/calibration. Mechanical safety features, Float seal prevent N2 blowby, Oil flow control prevent Estop setdown < 90s

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Hydraulic Pump Unit and Sump Valve StandHydrodynamic Suspension System

Interface to wide variety of analog and digital controls and sensorsMotor Controls (4), Discrete Valves (24), Proportional Valves (10), Pressure (20), Temp (9), Flow (3), Discrete Inputs (45), RTD (3), Discrete Outputs (14)8

Design Goals:Extensible Architecture supporting Distributed RT control

2. Workbook based Configuration (GXML based)

3.Instrumentation Management Toolsa. Tag Properties: Scaling, Filtering, ZOFS, Initial Value, DB%b. Target Imagingc. HMI bindings

I remember when I first came to NASA, (What was it like to be there) even with much experience under my belt, the realization of the scale and criticality of the system that I was deisigning was giving me heart palptitations. (Our new National SLS was irreperably damaged due to software flaws in HDS control system). the But being able to work with such experienced and high caliber engineers particularly my good friende BB an expert in hydraulic systems provided great assurance that we had covered all faiolure modes. I had the luxury to be able to study several possible architectures ranging from PXI to cRIO. The utility of the cRIO with rugged design wide range of IO, scan engine / NSV technology, and supporting toools such as the DSC, Citadel DB, DSM were most compeling. 9

Design Goals:24/7 Historical Data Logging (up to 20Hz)

RT Target sync to GPS, timestamped +/- 1ms

6. Diagnosticsa. Multi-Tiered Alarmb. RT process Monitorc. Syslog, DSM

7. Safety/Reliability features (FMEA driven)a. Watchdog based ESTOP->Parkb. Pump Dropout detectionc. N2 pressure interlocksd. Bearing Contact monitor

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HDS Instrumentation ManagerOne stop shopping for all your HDS configuration needs

Overview of HDS networked devices, cRIO, HMI, PXI-668211

HPU HMI, Primary Operation Screen

Pump Startup Sequencing, Tank Heater/Level, HE Temp Reg. +/- .2F, Filter Life MonitorHeat Exchanger with PID + Heat Load Balance Model (FF) + Adaptive SI (Recursive ARX)+/- .2F over wide range of operating conditions.12

HDS HPU, Manual Pump ControlsTouchpanel aware data entry, Tag ZOFS, Tag Stats Display

HDS HPU, Manual Pump ControlsTouch Panel Numeric Data Keypad, activated by 2s touch on any control

HDS HPU, Manual Pump ControlsHMI tag stats display, right click on any control or indicator

SVU HMI, Operate Screen

Individual and syncd HDS control, N2 Autocharge, DPH (Dynamic Piston Height Control)dPH/dt, DPH Mean, HDS state, Bearing Contact Monitor (transient and persistent)

HDS Software ArchitectureMVC (Model View Controller)

Model SVE/PSP interface supports NSV bindings, events, static/dynamic NSV accessIf you have the model or State of the system hosted in the SVE then you have created the heart of the MVC architecture. The PSP (Publish Subscribe Protocol) is the underlying technology in the SVE and provides an API to manage SV libraries, SVE transactions, SV bindings, SV events, etc. With the PSP, multiple client apps or Views can subscribe to collections of data tags in the system.17

ModuleIOVScan EngineNSVcRIOPCNSVCitadelcRIO 1588 TimeSyncIOV Timestamp by Module in Scan EngineIOV -> NSV binding preserves timestamp+/- 100us RT system time, +/- 1ms data timestampDataTimestamp

PXI-6682GPSIEEE 1588 EthernetTimeSync1588 PTP Master1588 PTP SlaveTAI (1588) = GPS+19sUTC = TAI-34sGPS Publishes GPS time with UTC offset18

HDS Instrumentation ManagerWorkbook Configuration, Compile to GXML -> Target

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DSM Historical Trend Capability

Manual Shake Test, Natural HDS damping characteristic20

DSM Historical Trend Capability

New water chiller cycling disturbances

cRIO SCADA Reference Design

Features:

XLS/GXML Configuration ManagerOn-the-fly cRIO config. deploymentPer channel SR, Filter, Scaling,DB, ZOFSHMI->cRIO Messaging (async and sync)Built-in TP ControlsHMI Tag Management a. Creates NSV binding b. Creates embedded HMI Tag Desc. c. ZOFS apply/remove at tagCritical timing verificationSyslog (UDP)CVT API

Can be obtained at www.viScience.com22

viScience.com

PLEASE USE THIS AS YOUR LAST SLIDE IN YOUR NIWeek PRESENTATION24