The facility Hazardous Gas Detection System (HGDS) at Kennedy Space Center (KSC) is a mass spectrometer based gas analyzer. Two instruments make up the HGDS, which is installed in a prime/backup arrangement, with the option of using both analyzers on the same sample line, or on two different lines simultaneously. It is used for monitoring the Shuttle during fuel loading, countdown, and drainback, if necessary. The use of complex instruments, operated over many shifts, has caused problems in tracking the status of the ground support equipment (GSE) and the vehicle. A requirement for overall system reliability has been a major force in the development of Shuttle GSE, and is the ultimate driver in the choice to pursue artificial intelligence (AI) techniques for Shuttle and Advanced Launch System (ALS) mass spectrometer systems. Shuttle applications of AI are detailed

Adams, F. W.

English

NASA Technical Reports Server

I 91-25 069
AI'MASS SPECTROMETERS
FOR SPACE SHUTTLE HEALTH MONITORING
F. W. Adams
NASA
Mail Code DL-ESS-24
Kennedy Space Center, Florida
BACKGROUND
Modem rocket development in the United States formally began in 1914 with Dr. Robert Goddard's
patents on the concept of utilizing liquid nitrous oxide for the oxidizer and gasoline for fuel in self-contained,
change of momentum based, main propulsion systems (1). His first flight, with hardware using gasoline and
liquid oxygen, did not occur until 1926, some 12 years later. German acquisition of the concept prior to
World War 11 led to Dr. von Braun's development of the V-2, powered by liquid oxygen and alcohol. Post
war U.S. development of the Redstone, Jupiter, Atlas, Apollo, Shuttle, and ultimately, Advanced Launch
System (ALS) are the historical background for this presentation.
Development of the concept of using liquid hydrogen for fuel began in 1960 with the beginning of the
Apollo program. Fuels used prior to this were hydrocarbons (alcohol, kerosene, jet fuel), or solids. There is
approximately a 700:1 volume reduction achieved by converting gaseous hydrogen at room temperature to
liquid at cryogenic temperatures. The increase in specific impulse f o r hydrogen/oxygen over
hydrocarbon/oxygen fuels is approximately 1.5:1. (2) The choice of hydrogen for fuel imposed greatly increased
hardware requirements for being able to identify and evaluate leaks.
Shuttle is the first system where liquid hydrogen was used in the liftoff stage of the propulsion system. It
is boosted by detachable solid rocket motors to help attain orbit. The launch countdown formally begins 3
days prior to liftoff, and the loading of cryogenic hydrogen and oxygen begins about 11 hours prior to liftoff.
During launch countdown, ground support systems are prepared for use by verifying that they are functional
and capable of holding a calibration. They are then carefully maintained "powered up", and watched for
problems as the count continues.
INTRODUCTION
Mass spectrometers were first used in a ground support role in 1964 for Saturn I launch vehicle testing,
for identifying hydrogen leakage in the main propulsion system of the S-IV second stage, during cryogenic
operation (3). Early instruments for Saturn centered around a magnetic sector type analyzer. Shuttle
instrumentation is based on quadrupole and magnetic sector type mass spectrometers. Other types of
hydrogen detectors, while capable of locating and quantifying hydrogen leaks at low levels, are not usable
above approximately 10% hydrogen concentration, and are unable to differentiate oxygen leaks from air
intrusion, which the mass spectrometer can do. A recent patent, #4,953,976 based on Raman scattering, is the
nearest technology to the mass spectrometer, for use in this type of service.
Mass spectrometers can be made to be sensitive to helium, the purge gas used in liquid hydrogen systems.
Helium is also used as the trace gas (for safety reasons, during testing, when hydrogen is not present) as an
aid in flagging and locating leaks. The general utility of the ruggedized mass spectrometer as a process
instrument, as opposed to a laboratory curiosity, has led to its' increased use in facility ground support
equipment to enhance the visibility of flight hardware with respect to liquid hydrogen and oxygen leakage.
Facility mass spectrometers were not installed for the classical liquid oxygen / hydrocarbon main
propulsion system ground support equipment (GSE). In these systems, mass spectrometers existed in the
form of drag-on helium leak detectors, using helium as a trace gas. They were not used to sense fuel leaks
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https://ntrs.nasa.gov/search.jsp?R=19910013756 2020-03-19T17:38:52+00:00Z
directly.Permanent,facilityanalyzers,wereinstalledforShuttlebecauseit ispoweredbyliquidhydrogen,
whichproducesleaksin realtime,thatcannotbedetectedbyuseof classicalheliumleakdetectors.
MASSSPECTROMETERINSTALLATIONSAT KSC
The facility Hazardous Gas Detection System (HGDS) at Kennedy Space Center, Florida (KSC), is a
mass spectrometer based gas analyzer (4). Two instruments make up the HGDS, which is installed in a
prime/backup arrangement, with the option of using both analyzers on the same sample line, or on two
different lines simultaneously. It is used for monitoring Shuttle during fuel loading, countdown, and
drainback, if necessary. The system is located in the mobile launch platform, underneath the vehicle, and
must sustain the shock and vibration of launch. It must be operational during main engine firing for flight
readiness firings (FRF), and after main engine firing, for launch, in order to perform during de-tanking, if
launch is aborted.
HGDS is controlled and monitored, during countdown, from the Launch Control Center approximately
four miles away. It was HGDS that discovered the hydrogen leaks in STS-6 Flight Readiness Firing (FRF),
and STS-35 and STS-38 launch attempts, while monitoring the aft compartment of the orbiter.
Four compartments on the flight vehicle are monitored for their fraction of hydrogen, helium, nitrogen,
oxygen, and argon. These are the External Tank/Inter-tank area, Payload Bay, Mid-body and Aft
compartment. One sample is drawn from the hydrogen tail service mast (TSM). The presence of anything
but nitrogen indicates main propulsion system, payload, fuel cell, or ground support hardware system leakage
respectively. Launch Commit Criteria (LCC's), are determined prior to tanking, for the amount of each gas
that will be allowed without taking action in some form.
Samples from the various compartments are pulled down dedicated stainless steel lines by small
diaphragm type pumps. A sample switching arrangement, utilizing remotely controlled valves, is used to direct
the sample to the analyzer. In order to reduce the time required for the sample from a particular area to
reach the analyzer, a system of differential-flow / pressure-reduction stages are used. Disruption of flow in the
sample delivery system can cause the analyzer to report data on a non-representative sample, and thereby give
a distorted picture of the status of the vehicle.
Additional mass spectrometers have been added, as facility hardware, to monitor the 17 inch hydrogen
orbiter/ET disconnect for flight readiness firings, special tanking tests, and launch. Plans are in process to
add mass spectrometer capability to monitor the hydrogen fill and drain lines on the ground side, to more
quickly determine the state of purge before and after fueling operations. A miniature, ruggedized flight
version of the facility mass spectrometers is in the prototype stage at this time, and may some day be flight
hardware. Mass spectrometers have flown in space aboard satellites and planetary probes since the beginning
of the program.
THE NEED FOR ARTIFICIAL INTELLIGENCE (AI)
The use of complex instruments, operated over many shifts, by different people, in a flexible operational
environment, has caused problems in tracking status of GSE and the vehicle. A requirement for overall
system reliability has been a major force in the development of Shuttle GSE, and is the ultimate driver in the
choice to pursue AI techniques for Shuttle and AI_,S mass spectrometer systems. The need for certainty that
the numbers displayed on the operators' console are truly representative of the variables that are being
measured, is critical.
SHUTI'LE APPLICATIONS OF Ai
There are five areas that have been identified, where AI techniques, can help solve KSC's problems for
Shuttle. First is the pre-launch system validation. It takes about two weeks to validate HGDS for launch.
This involves a complete check of critical system voltages, gain and offset adjustments in critical stages,
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verificationof theamountof consumables(calibrationgases),redundantcircuitrychecks(f'llamentsin the
ionizer,vacuumgages,etc.),andverificationofnormaloperation,bothlocally,andfromtheremotecontrol
stationsin thefiringrooms.Manypartsofthisoperationcanbeautomated.Useof anAdvisorherewould
beto guidepersonnelthroughtheinstrumentcheckoutprocedures.
Second,is thereductionof displaycomplexity,asseenbytheoperatorsandusers,duringoperations.This
isaseriousproblemwhenmorethanonemasspectrometerdisplaymustbeviewedsimultaneously.Often
twoinstrumentsareusedto lookat thesamesampletoverifythat thedataisconsistent.An ideal display
driver would indicate only the gas concentrations on the sample lines and would have the mass spectrometer
function completely transparent to the operator. An Advisor here would provide visibility of background
functions when problems occur, as a console operator aid. Near real time operation here is a firm
requirement. Figure 1 shows the current display for the HGDS console for Shuttle. Figure 2 shows the actual
variables (function designators) displayed, and where they appear on the screen.
Third, is the requirement to verify that samples from the vehicle are within the allowed limits, LCC'S,
which normally vary, depending on the state of loading. During countdown, console operators are constantly
looking at the data for clues that there might be something wrong with the it. The sample seen by the
analyzer must be representative of the environment around the hardware being evaluated for leaks. There
must be no unknown system hardware failures which might distort the readings seen by the operators. An
Advisor here would comment on the certainty of the data, including cross correlation between other
instruments that might be looking at the same gas stream. Historical data from earlier launches could be
referred to if deemed significant. Near real time performance is required at this phase.
LCC's are sometimes real-time variables, depending on the situation, and must be constantly observed in
this light. LCC's for hydrogen, oxygen, and helium concentration, apply to ground and flight hardware during
cryo loading sequences up to liftoff, or drainback and boiloff, if launch is not possible. The vehicle data is
monitored by many knowledgeable persons at different locations on KSC and at other NASA centers (JSC,
MSFC), and it is important, for this reason, that this data be representative and reliable. System oversight by
knowledgeable instrument operators is necessary because data users will not normally be aware of abnormal
system operation.
The fourth requirement is that real time troubleshooting of one of these systems (not to mention three or
four), is a major undertaking, particularly when being performed simultaneously with launch support. KSC
Design Engineering personnel, in coordination with operations, are developing techniques and special test
sequences that will improve the console operators' ability to perform advanced troubleshooting during
countdown, to verify whether a problem is in the vehicle or the analyzer, and evaluate the impact on the
launch operation. As a side note, the first thing the data users question is not their system, but the integrity
of data that indicates hardware problems. The advisor here would suggest testing routines that could be run
real time while the system is still gathering data in support of the launch countdown.
The fifth and last application of AI is a tool for training new operators and upgrading skills of those
familiar with the instruments. One serious problem with complex hardware is the limited number of people
who understand specific instruments. During high pressure situations, where testing of a vehicle on one pad is
being worked simultaneously with either testing or launching on another, skilled personnel are in short supply.
Often the skills required for launch and testing are different, and less skilled people can be effectively used in
testing situations. Allowing less skilled personnel to operate the system quickly can be a tremendous benefit
to operations, provided everyone knows their limits and responsibilities. Here the advisor would track
progress and advise operators where they need additional training to become proficient.
CONCLUSION
It should be emphasized here that a specific instrument or capability will be installed for Shuttle only
because the launch system cannot reliably function without it. AI would not normally be applied to a hazard
warning system at KSC if it did not offer a significant advantage over manual methods of tracking problems
394
and reducing data in real time.
The burden of operating multiple mass spectrometers has increased greatly with each new system
installation. The proper response to the situation is not to bring in more people, as there are only limited
facilities in the firing rooms (console screen space, personnel access, etc.). ALS GSE will be deployed with
similar motivation.
Shuttle has been used as a testbed for conceptual aspects of mass spectrometer application development
for ALS. One reason that teams at KSC were ready to support special testing, when the latest group of leaks
was discovered on Shuttle, was that personnel were looking at advanced applications of mass spectrometer
systems in preparation for a demonstration of hardware for ALS.
In support of Shuttle and development for ALS GSE, it is important to keep the target in mind when
designing a system of this magnitude. One is constantly being distracted by peripheral operations and special
test support that are going on in parallel with system development. Often, new concepts are identified in
these situations, and it is tempting to try to incorporate everything learned into new GSE.
Real system requirements must be kept isolated and not changed during system development. Experience
with Shuttle has indicated that certain failure modes are more likely to occur than others. Equipment design
must be based on knowledge of the hardware (what it is, how it is used, how it has failed in the past), and
what kinds of surprises were seen when previous systems were installed. The ability to zero in on
requirements, up front, is the key to achieving high and successful launch rates, in present and future systems.
BIBLIOGRAPHY
, Robert Goddard, Pioneer of Space Research, Dacapo Series of Space, Dacapo Press, Inc., Subsidiary
of Plenum Publishing Corp., 1963.
,
3.
°
Starr, Start, Personal conversation, 10/02/90.
Helms, W. R., History, Design and Performance of the Space Shuttle Hazardous Gas Detection
System, Space Shuttle Technical Conference, NASA Conference Publication 2342, Part 1, 1983.
Helms, W. R. & Raby, B. A. A prototype Gas Detection System for NASA's Space Shuttle. 26th
Annual Conference on Mass Spectrometry and Allied Topics, 1983.
395
APPENDIX A: SOFTWARE USED IN SYSTEM DEVELOPMENT
GOLDWORKS: (GOLDHILL COMPUTERS, INC., EXPERT SYSTEM INTEGRATED
DEVELOPMENT ENVIRONMENT.)
LISP DEVELOPMENT ENVIRONMENT FOR GENERAL PROTOTYPING AND
PRELIMINARY MODELING
CXPERT: SOFTWARE PLUS, LTD, CROFTON, MD.
EXPERT SYSTEM DEVELOPMENT ENVIRONMENT COMPATIBLE WITH THE GOAL OF
ROMMING THE EXPERT SYSTEM VIA DOS OR UNIX. RULES, DATA BASE, INFERENCE
ENGINE.
OS-9: MICROWARE CORP., DES MOINES, IOWA
ROMMABLE OPERATING SYSTEM AND DEVELOPMENT ENVIRONMENT
ZORTECH C + + : ZORTECH CORP., WOBURN, MASS
AUXILIARY DEVELOPMENT, COMMUNICATION AND GRAPHICS INTERFACE, CXPERT
SUPPORT, ETC.
SALIENT HARDWARE FEATURES
ROMMED OPERATING SYSTEM AND APPLICATIONS FOR OPERATION IN A HIGH
SHOCK AND VIBRATION ENVIRONMENT.
396
APPENDIX B: HARDWARE USED
COMPAQ 386/LISP AND GRAPHICS TERMINAL
68030/TARGET EMBEDDED PROCESSOR TO BE USED IN THE LAUNCH ENVIRONMENT
(FORCE/VME, GESPAC)
GMX / 68020 GMX CORP., CHICAGO, IL
MGA-1200 MASS SPECTROMETER, PERKIN ELMER CORPORATION
397
11
11
1879186
1879187
APPENDIX C:
FIRST EVIDENCE OF RUSSIAN INTEREST IN ROCKETRY 1881
TSIOLKOVSKY, INVESTIGATION OF SPACE BY MEANS OF ROCKETS
02653
03503
GODDARD'S PATENTS RELATIVE TO ROCKET PROPULSION DEVELOPMENT
1903
MULTI STAGE ROCKET 07/07/1914
BREECH BLOCK TO INJECT SUCCESSIVE CHARGES, COMBUSTION CHAMBER,
NITROUS OXIDE, ETC 07/14/1914
GODDARD, A METHOD OF REACHING EXTREME ALTITUDES 1919
GODDARD AWARE THAT GERMANY WAS INTERESTED IN ROCKETRY
ALSO 1923
OBERTH FIRST PUBLISHED 1924
IGNITION OF LIQUID FUEL, CURTAIN COOLING 09/27/1934
GYROSCOPIC STEERING 09/27/1934
398
APPENO_/_ SOFIWARE UgED IN SYSTEM DEVELOPMENT
(GOLOHILL COMPUTERS, INC., EXPERT SYSTEM
hNTEGRATED DEVELOPMENT ENVIFK_NMENT.)
LISP DEVELOPMENT ENVIRONMENT FOR GENERAL PROTOTYPING
AND PRELIMINARY MOOEUNG
CXPERT: _ARE PLUS, LTD, P._, MD.
EXPERT SYSTEM DEVELOPMENT ENVIRONMENT COMPATIBLE WITH
THE GOAL OF ROMMING THE EXPERT SYSTEM VIA DOS OR UNIX.
RULES, DATA BASE, INFERENCE ENGINE.
OS-9: MICROWARE CORP., DES MOINES, IOWA
RCNMABLE OPERATING SYSTEM AND DEVELOPMENT
ENVI_ENT
ZORTECH C-_: _ CORP.,_, MASS
AUXILIARY DEVELOPMENT, COMMUNICATION AND GRAPHICS
INTERFACE, CXPERT SUPPORT, ETC.
SALIENT HARDWARE FEATURES
ROMMED OPERATING SYSTEM AND APPLICATIONS FOR OPERATION
IN A HIGH SHOCK AND VIBRATION ENVIRONMENT.
APPENDIX B: _ARE USED
COMPAQ 386/I.ISP AND GRAPHICS TERMINAL
68030/TARGET EMBEDDED PROCESSOR TO BE USED IN THE LAUNCH
ENVIRONMENT (FORC_/ME, GESPAC)
GMX / 68020 GMX CORP., CHICAGO, ¢
MGA*1200 MASS SPECTROMETER, PERKIN ELMER CORPORAT_
APPENDIX C:
DEVBJOPMB_
1102653
1103503
1879186
1879_87
GOOOAROS" PATENTS RELATIVE TO ROCKET
RRST EVIDENCE OF RLI6SlAN
INTEREST IN ROCKETRY
TSIOLKOVSKY, INVESTIGATION OF
SPACE BY MEANS OF RC_
MULl1 STAGE ROCKET
BREECH BLOCK TO INJECT
SUCCESSNE CHARGES,
COUlBJSTION _
NITROUS OXIDE, ETC
GOODARD, A ME11-tOD OF _
EXTREME ALTITUDES
GOODARD AWARE THAT
WAS INTERESTED |N ROCKE'fT:IY ALSO
OBERTH RRST PUBUSHED
IGNITION OF LK_JID FUEL
CURT/_N COOUNG
GyROSCO_ STEER_G
1881
1903
07/0711914
0711411914
1919
1923
1924
09127/1934
0912711934
399


AI mass spectrometers for space shuttle health monitoring

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