Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/STATION/STFJUL92.NWS

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STATION BREAK -- July 1992


FOR FREEDOM:  SKYLAB 4 CREW REUNITED UNDERWATER

        Boeing Defense & Space Group engineers in Huntsville,
Alabama, are enlisting the aid of space veterans from America's first
space station, Skylab, in designing and building America's next space
station -- Freedom.
        Skylab 4 astronauts Jerry Carr, Ed Gibson and Bill Pogue were
suited up again, this time for underwater tests to evaluate components
designed for use inside the station and to practice daily intravehicular
activity (IVA) tasks, such as moving payloads from one module to
another.  They were joined by space shuttle veterans Robert Springer,
who now works for Boeing's space station program, and Wubbo
Ockels, representing the European Space Agency.
        The six-week test was being carried out at NASA's Marshall
Space Flight Center in the Neutral Buoyancy Simulator.  The building's
1.32 million-gallon tank simulates the weightlessness of outer space.
        Astronauts and test subjects from Boeing, NASA, the National
Space Development Agency of Japan, and the European Space Agency
donned diving gear and practiced moving space station hardware
around a full-size mockup of the orbiting laboratory.
        "This test will evaluate some of the internal components we
and our international partners have designed to work when the space
station is on orbit," said Livingston Holder, international programs
manager for Boeing work on the station.
        The astronauts will be working specifically with the
international standard payload rack, a design agreed upon by the
program's international partners as one that meets common needs and
can "plug in" to almost any rack location in the station's three
laboratories.  The rack is space station's basic modular unit, a closet-
sized composite structure that houses experiments, station subsystems
or storage space.
        "Boeing, NASA and our international partners are using
Skylab and Space Shuttle operational experience to design and build
the orbiting laboratory," Holder said.  "Because of their spaceflight
experience, this is the perfect cast of consultants."
        The Skylab 4 crew spent 84 days together in space between
Nov. 16, 1973 and Feb. 8, 1974.
        "Aboard Skylab, we moved a lot of large, 'heavy'
experiments," said Carr, working on the tests as a subcontractor to
Boeing. "We're familiar with how things move in space.
        "We will be comparing our spaceflight experience with the
tasks performed in the simulator and advising the test conductors on the
similarity of operations," Carr said.
        Boeing Defense & Space Group is designing and building the
space station laboratory, living and supply modules, plus connecting
node structures and selected on-board systems for NASA.  Hardware
for the orbiting lab is being built right now by Boeing and its nationwide
subcontractor team, with the first components of the station scheduled
for launch in less than four years.
        The station will be ready for visiting astronauts to tend
experiments by the end of 1996.


SPACE STATION VERIFICATION:  THE 3-D PUZZLE COMES TOGETHER

        As if one of the world's largest engineering projects -- involving
13 countries and an array of time zones and languages -- isn't
complicated enough, imagine building a spacecraft in orbit over four
years, knowing that the first piece must work with the last.  There lies
one of the greatest space station challenges ? the challenge of
verification.
        This is the first time NASA will launch a spacecraft packaged
in pieces.  Space Station Freedom will never be completely assembled
on the ground as a unit, making verification imperative.  Verification is
the all-encompassing term used to describe the complicated
coordination and checkout of hardware and software that will be built at
various locations around the world.
        This incremental approach of building Freedom is necessary
because of the station's size and weight.  It will take about 18 Space
Shuttle flights to lift the elements into space and then assemble them
using extra-vehicular activity and robots.  Since this has never been
attempted before, this incremental approach requires coupling classic
design and verification principles with some futuristic planning to create
a finished product in space.
        Typically, flight articles designed in the classic sense begin at a
"breadboard" or "brassboard" phase, where designs aim only to fulfill a
function.  Breadboard models answer the question, "Does it work?"  At
the next phase, engineering models (or prototypes) are designed
which integrate function, form and fit.  Form is the article's shape, and
fit is the article's ability to fit into an assigned space.  From there, flight
hardware-like models are built to simulate the article's function.  These
models are true to form and fit and are built with the actual materials
intended for the actual station.
        At this point, the qualification model is tested for its ability to
perform in the launch and the space environment.  It is pushed to the
limits of both environmental and functional capabilities, and every
possible scenario is created to challenge the qualification model.  If the
model survives the qualification test, the design is approved for flight.
In past missions, a flight unit was fully assembled and tested on the
ground before launch.  This marks the critical difference between Space
Station Freedom and any other spacecraft ever built.
        For Space Station Freedom, the Integrated Systems
Preliminary Design Review, held in November of 1990, initiated the
process of creating bread-and-brassboard designs and engineering
models for the station.  Designs for the first six elements, which
comprise the man-tended configuration, next will be reviewed at the
critical design review, scheduled for the spring of 1993.
Simultaneously, the next five elements, comprising a portion of the
permanently manned configuration, will undergo preliminary design
review.  Qualification models will then be built by the program's
contractors and tested.  At design certification reviews, scheduled
throughout 1995, the results of the qualification tests will be reviewed to
certify the design of the man-tended phase.  The permanent occupation
design certification process will be done incrementally as each
subsequent piece is qualified throughout Freedom's construction.
        Flight acceptance tests for each element will be conducted
prior to the delivery of each element to Kennedy Space Center for
launch preparation.  Flight acceptance tests will verify the
manufacturing and assembly of each element.  This is less demanding
than the qualification tests, intended only to stress the design.
        This complex arrangement of designs and tests, however,
cannot be applied to Space Station Freedom in the classical sense.
Since Freedom is being designed by an international team, built on
Earth piece by piece and assembled in space over four years, a tailored
approach is needed.  To date, no other space system has required a
verification system adaptable to these dynamics.  NASA will achieve
the intent of the classical process and deliver a station to space which
has been tested incrementally to guarantee the success of the whole.
While the design facilitates verification at the element level (elements
such as truss segments, nodes and pressurized modules can be tested
prior to launch), the success of the integrated system will be determined
by verification between 1995 and 1999.
        While the space station will never be completely assembled on
the ground, it is essential that the first six sections fit and function
together on the ground before launch.  To accomplish this and hold the
launch schedule, a detailed plan was developed to ensure that all
connections will be tested in their flight configuration on the ground.
As experience is gained, those connections will be tested while mated to
qualification hardware or specially designed test equipment.
        What can't be tested, however, is the difference between the
Earth and space environments.  Knowing how two elements merge and
interact on the ground differs from the near zero-G environment where
this facility will function.  No simulator on Earth can give life-like zero-
G conditions.
        Early in the development process, technical phenomena,
needing zero-G verification, were identified and flight tests aboard the
Space Shuttle were developed.  For these tests, prototype versions of
the space station equipment are simulated in a flight environment
aboard a Shuttle.  This testing verifies the design features and
operations protocol that will ultimately fly on Freedom.  For example, a
process particularly sensitive to the absence of gravity is the separation
of liquid and gas phases of a fluid.  This is critical in the pumps and heat
transfer devices primarily found in the thermal control system and in
the environmental control and life support system of the space station.
        Verifying the integrated systems (such as the data
management systems, electrical power systems, thermal control
systems, audio/visual systems, etc.) as they span the entire 18-step
space station assembly ? and verifying their functions at each step along
the way ? presents a major challenge.  This problem is being tackled by
distributed system architects.  These architects are responsible for the
verification of each of the systems previously mentioned.  Because
these systems are provided by more than one developer, the distributed
system architect must use a variety of tools to accomplish this
verification.  System test beds -- laboratories in which the function of a
major portion of the system is replicated -- have been created, but are
limited by what's contained in the end-to-end systems.  The distributed
system architect must determine how much of the end-to-end system
must be included in the test bed, how much can be accomplished by
interface verification and what must be done at other sites to provide
the comprehensive verification program required for each system.
        This only completes half of the functional verification process.
The other half consists of verifying the system-to-system interactions,
such as how the data management system interacts with the thermal
control system.  Where these interactions are physical, they will be
treated as part of the element verification process or as part of the
demonstration of flight-to-flight connections.  Where these interactions
are functional (electronic or driven by software), they will be verified in
the Central Avionics Facility or the Central Software Facility.  These
facilities are being developed at the Johnson Space Center.
        Prototypes of the electronic processors, their connecting data
bases and the sensors and effectors they interact with will be arranged
in an electronic replication of the flight configuration and will be tested
using flight software.
        Once the flight elements are delivered to the launch site at the
Kennedy Space Center in Florida, they will undergo four to six months
of additional testing.  Kennedy is responsible for conducting
independent tests to demonstrate the interface integrity and the
functionality of each delivered element.  The first two launches of the
space station comprises the first active configuration of the vehicle, so
they will be assembled and tested at Kennedy Space Center before
launch.


AMES RESEARCHERS STUDY 'GRAVITY' OF BED REST

        Scientists at NASA's Ames Research Center are investigating
the importance of gravity to life on Earth.  They also are studying if
intermittent exposure to gravity may, as a last resort, help keep future
space explorers healthy.
        Volunteers in a recently completed study were confined to bed
24 hours a day in the head-down position used to induce the physical
changes associated with exposure to the microgravity of space.  Results
of the study indicated that these volunteers could avoid the changes
simply by standing quietly for 15 minutes each hour over a 16-hour
period.  Standing two hours a day (15 minutes each hour over an eight-
hour period), or walking at 3 mph, were almost as effective, according
to Dr. Joan Vernikos, the study's principal investigator and acting chief
of Ames' Life Science Division.
        "The question we must answer is both practical and basic:
How much gravity, how often and for how long?" Vernikos said.  "We
must know whether humans need gravity 24 hours a day to remain
healthy."
        "If intermittent gravity, which can be provided by an on-board
centrifuge, is sufficient, we may not need a permanently rotating
spacecraft to produce a constant gravity force," she said.
        The practical implications of this may be significant, as a
rotating spacecraft presents serious design, financial and operational
challenges.  On a basic level, Vernikos said, this and future studies can
help explain gravity's role in the development of life on Earth and
human physiology.
        In a series of five 6-day experiments conducted over 8 months
with the same male volunteers, the team of investigators compared the
effects of gravity's head-to-toe "pull" with and without activity.  All the
volunteers spent four days in bed, with a six-degree head-down tilt.
They remained in bed throughout one of the tests.  In others they
remained in bed except for either standing quietly by the bed or walking
at 3 mph for two or four hours a day in 15-minute segments.
        Vernikos said the results showed the four-day head-down bed
rest model to be an excellent simulation of many of the early physical
responses to the microgravity of space.  Changes found in astronauts in
space -- including reduced blood volume, fluid and sodium loss,
decreased aerobic performance and a tendency to faint upon standing
after return to Earth -- also were seen in the bed rest volunteers.  She
said changes begin within hours after the volunteers go "head-down"
and continue to develop through the next several days.
        Vernikos said this study is only the beginning.  She and her
collaborators plan to conduct similar tests using the large centrifuge at
Ames.  By having healthy volunteers exercise on a treadmill on the
centrifuge, Ames investigators "hope to determine whether exercising
under increased gravitational forces will decrease the amount of time
required to maintain health and fitness," she said.
        By spinning at various speeds, the centrifuge produces forces
that exceed the normal gravity force on Earth.  Some scientists believe
that exercise at such increased gravitational forces may further reduce
the daily minimum exposure time needed to prevent the effects of
simulated and actual microgravity.


NASA STUDIES TEAM PERFORMANCE IN 30-DAY UNDERSEA MISSION

        The Florida Keys may not seem as distant as the Moon, but
for three men during a 30-day period, it might as well have been.
        During "La Chalupa 30," sponsored by the Marine Resources
Development Foundation (MRDF) of Key Largo, Florida, three men
conducted investigations in an underwater habitat without any direct
outside human contact for 30 days, giving the Behavior and
Performance Laboratory at NASA's Johnson Space Center, Houston,
the opportunity to study team performance as part of its continuing
investigation to identify pertinent psychological issues for long duration
space flight.
        Two of the aquanauts surfaced in early June, and one decided
to extend his stay.  NASA will be working with the three aquanauts to
learn how they coped with their isolation.
        At present, NASA employs passive studies to develop its
knowledge base on long-term team performance and human behavior,
such as talking to crew members of existing remote facilities, including
polar expeditions.  Those studies, however, have progressed to the
point at which researchers are ready to test improved behavioral
collection methods, said Dr. Al Holland, Head of the Behavior and
Performance Laboratory.
        "The mission will serve as an environment that is analogous to
future extended space missions on the Shuttle or Space Station
Freedom," Holland said.  "This project is primarily a testbed for field
data collection methods and procedures."
        The information collected will assist investigators in
conducting further studies in field environments which are of longer
duration and possibly in more remote areas."
        The three aquanauts lived and worked in the undersea
laboratory with regular excursions into the lagoon to perform the in-the-
water portion of their marine research projects ? an analog to
extravehicular activity during space flight.  They were in contact with
surface crews via voice and video links, but no direct contact occurred
during the test.
        The behavioral investigations addressed three primary areas
pertinent to extended missions in confined environments:  individual
health and well-being, work, team maintenance and data collection
methods.
        Tests looking at individual health and well-being include
studies of sleep, cognitive functioning and stress, while those focusing
on team maintenance will collect individuals' perceptions on the state of
the team's functioning, communication, leadership and social climate.
Perceptions of work organization also were collected and investigations
of methodology will help investigators evaluate the different ways of
collecting behavioral information from people in remote environments.
        MRDF is providing the 3,300-cubic-foot underwater habitat,
originally named La Chalupa.  Formerly a research station operating off
the coast of Puerto Rico, the facility has been used as a commercial
undersea lodge since 1986.


48TH SHUTTLE MISSION TO BE LONGEST, FOCUS ON WEIGHTLESSNESS

        The longest flight ever for a Space Shuttle and around-the-
clock investigations of the effects of weightlessness on plants, humans
and materials will highlight the next Shuttle Columbia mission, STS-50.
        Much of the data collected on this flight will be useful to Space
Station Freedom planners, and one of the mission specialists aboard
this flight is on the Space Station Freedom experiments planning group.
        The crew will perform several ongoing medical investigations
during the flight, research that aims at counteracting the effects of
prolonged exposure to weightlessness on the human physique.
        The crew also will be testing a stabilized ergometer bicycle.
The stabilizers, designed by Lockheed, are necessary to provide 'quiet'
exercise equipment so vibrations do not interfere with ongoing
microgravity experiments.
        The 48th flight of a Space Shuttle and the 12th flight of
Columbia, carrying the U.S. Microgravity Laboratory-1 (USML-1), is
planned for launch June 25.  Details of the mission will be highlighted
in the August edition of Station Break.
        The mission is scheduled to last 12 days, 20 hours and 28
minutes, with landing planned at Edwards Air Force Base, Calif.
        USML-1 includes 31 experiments ranging from manufacturing
crystals for possible semiconductor use to the behavior of weightless
fluids.  In addition, STS-50 will carry the Investigations into a Polymer
Membrane Processing experiment, an experiment in manufacturing
polymers, used as filters in many terrestrial industries, and the Space
Shuttle Amateur Radio Experiment-II, an experiment that allows crew
members to contact ham radio operators worldwide and conduct
question-and-answer sessions with various schools.
        Columbia is currently the only Shuttle capable of a 13-day
flight and will carry the necessary additional hydrogen and oxygen
supplies on a pallet in the cargo bay.  New systems for removing carbon
dioxide from the crew cabin, for containing waste and for increased
stowage of food and crew equipment also have been added.


AUTOMATED MODEL-BASED DIAGNOSIS KEEPS AN EYE ON ECLSS

        On orbit in Space Station Freedom, a component in the
Carbon Dioxide Removal Assembly (CDRA) fails.  The temperature in
one of the assembly's desiccant beds, which remove moisture from the
air, starts rising, causing a decrease in the assembly's efficiency.  A
temperature sensor triggers an alarm.  Operation switches to a backup
CDRA, and normal operation returns.  On the ground, mission
controllers want to know what caused the problem.  Which CDRA
component has failed?  Ground-based computers immediately run
diagnostic programs, which run quickly, but suggest nearly a dozen
possible explanations.  The mission controllers narrow the field down to
two suspects, both of which lie upstream of the desiccant bed.  How do
they determine which one it is?
        When equipment fails, it usually has some set of symptoms.
The symptoms of the actual problem may be similar to those of other
possible failures.  Initially, an engineer will consider all possible causes
of the failure.  Each possibility can cover dozens of individual
components.  Some of these causes are rejected on fairly simple criteria.
For instance, there may be no connection between a particular suspect
and some of the sensors which triggered an alarm.  Or the engineer may
reason that, if a particular component had failed, other sensors also
should have triggered alarms.   If they didn't, the component must not
have failed.  These are associative methods.  They associate a failure
with a characteristic pattern of alarms.  They can be used to rapidly
eliminate many incorrect hypotheses.  But they may leave too many
remaining possibilities.
        The mission controllers then decide to consult a new tool on
the computer, one that performs automated model-based diagnosis.
The tool runs a computer simulation of both possible failures. Either
could lead to an over-temperature in the desiccant bed, but each one
has a distinct time profile; some have slight but distinctive effects on
other sensors.  The simulations are compared to the log of the sensor
data.  The computer performs a differential diagnosis; that is, it selects
one explanation as more sound, when several are fairly plausible.  The
simulation of the actual fault matches the logs closely, the other
possible fault does not.  The mission controllers then identify the failed
component and issue a maintenance action for the crew to fix it.
        Such automated model-based diagnosis has been used for
some time in building diagnostic programs for digital electronics.
NASA has led the way in research and development which adapts this
approach to continuous systems, such as those involving fluid and heat
flows.  This technology is being applied to Space Station Freedom in a
project called the Environmental Control and Life Support System --
Advanced Automation Project (ECLSS AAP).  The work is led by
Marshall Space Flight Center's Information & Electronic Systems
Laboratory.  As reported in the May issue, the same technical approach
is being applied by researchers at the Johnson Space Center to the
Space Station's Thermal Control System.
        The project has developed a diagnostic model of the ECLSS
Carbon Dioxide Removal Assembly.  Current work focuses on
connecting this model to actual CDRA equipment in the ECLSS
system testbed at Marshall.  When in place, the project will help
diagnose equipment failures in the testbed, as well as give engineers a
useful, real-time view of the testbed data.  Lessons learned will guide
the deployment of automated model-based diagnosis into the ground
support environment for Space Station Freedom.
        Automated model-based diagnosis draws on recent
developments in process control.  Sensor information is compared to
the output of a model, shown below.  Discrepancies from the
comparison guide the search for suspect faults.  The model is used to
test the hypotheses by sifting through alternative explanations using
both numerical reasoning (e.g., solving equations to determine the value
of a continuous variable such as temperature) and symbolic reasoning
(using logic that does not require numerical calculation, e.g., if there is
no flow, then the valve must be closed).
        The Advanced Automation Project will provide faster and
more reliable diagnosis of ECLSS equipment failures and performance
trends.  In the near term, this will speed testing and ease interpretation
of testbed equipment data.  When the Space Station is in orbit, it will
reduce the demand for crew monitoring of systems and it will improve
the efforts of mission controllers monitoring the health and safety of
Space Station Freedom's environment.
        For information contact:  Amy Cardno, Code EB-42, NASA,
Marshall Space Flight Center, AL  35812 [phone] or Mark
Gersh, Code MT, Space Station Engineering, NASA, Washington, DC
20546 [phone].


INTELLIGENT ASSISTANCE IN SENSOR PLACEMENT

        As the complexity of spacecraft increases, more and more
sensors are required to properly monitor the condition and performance
of the spacecraft's systems.  As system complexities increase, the
number of potential faults within a system and the interactions among
systems increase rapidly.  Ensuring that a necessary and sufficient
number and type of sensors are appropriately located within the
spacecraft's systems becomes an increasingly difficult and costly job.
        One solution is to simply add more sensors at every
conceivable location that may contribute to monitoring and control of
the spacecraft.  However, this approach is not acceptable for a space
system, particularly one as large and complicated as Space Station
Freedom.  Because of the expense of launching payloads into orbit,
tight constraints are placed on weight and volume.  This in turn, places
limitations on the final power, databus, computing, telemetry, and other
spacecraft resources.  Each additional sensor places more demands on
these resources, and Space Station Freedom has only a finite amount of
resources.  The designers of Freedom must be able to identify the
minimum number of sensors, placed to gather the most effective data
necessary for the safe and efficient operation of Space Station Freedom.
        Researchers in the Jet Propulsion Laboratory's Advanced
Information Systems Section are developing software to provide
intelligent assistance to engineers for evaluating sensor placements.
This technology is being applied to Space Station Freedom in a project
called Environmental Control and Life Support System ?Predictive
Monitoring (ECLSS PM).  This project focuses on automatic evaluation
of proposed sensor placements by using a model of the target system to
evaluate how well the set of sensors meet monitoring and diagnosis
requirements.  This approach can also be used to recommend
placement of a set of sensors.
        The overall sensor placement approach uses artificial
intelligence techniques based on model-based reasoning and machine
learning.  A functional model of the target system is used to identify
monitoring situations of interest and to determine the consequences of
faults.  Machine learning techniques are then used to automatically
analyze data to form rules for monitoring and diagnosis.  A rule might
be of the form, "If Sensor 1 reads over 50 and Sensor 3 reads between
4.5 and 4.75 then conclude that Fault 5 has occurred."  Once a
candidate set of rules has been selected, optimization techniques are
used to select a subset of the rules (and hence sensors) for system
monitoring and diagnosis.
        These techniques are currently being applied to the water-
related functions of the Environmental Control and Life Support
System (ECLSS) of Space Station Freedom.  The principal focus has
been the Potable Water Processor subsystem, which provides water
sterilization and filtration capability on board Space Station Freedom.
Current testing of this approach is based upon preliminary fault models
derived from discussions with ECLSS Test Engineers at the Marshall
Space Flight Center.  Future extensions of this work include coverage
of additional water-related subsystems and development of sensor and
process noise models to better understand how well a sensor may
diagnose a specific fault.
        As system complexity increases, it becomes more difficult to
ensure adequate sensing within resource constraints.  The ECLSS
Predictive Monitoring task will enable design of more easily monitored
and diagnosable systems for Space Station Freedom while reducing the
number of required sensors and their associated costs.  Reducing the
number of sensors makes more resources available for other uses.  The
intelligent selection and location of sensors will increase the efficiency
of operations by reducing the demands on ground-based personnel
while improving fault detection, isolation and recovery capabilities.


MAINTAINING SPACE STATION FREEDOM'S ENVIRONMENTAL SYSTEMS

        Have you ever wondered how NASA's engineers and scientists
can diagnose and correct the problems of Earth-orbiting and planetary
spacecraft from the ground?  Well, it may seem like magic to some, but
it requires state-of-the-art engineering and a lot of hard work.
        Spacecraft are designed and built with many different types of
sensors incorporated into the various subsystems and science
instruments in order to monitor the condition and performance of the
spacecraft.  Sensors are the eyes and ears of engineers on the ground.
While most spacecraft telemetry consists of science data, a good
portion of it is data from the various sensors monitoring the spacecraft's
condition.
        Space Station Freedom will be the largest, most complex, and
most sophisticated spacecraft ever to be placed in orbit.  It will have
thousands of sensors monitoring the performance of its various
systems.  A large portion of its operating cost will be associated with
the hours of labor required to keep it operating safely and efficiently.
        The Marshall Space Flight Center and the Jet Propulsion
Laboratory (JPL) are conducting research to improve the engineer's
ability to perform faults detection, isolation, and recovery (FDIR) for
the station's Environmental Control and Life Support System.


LEARN ABOUT RESEARCH OPPORTUNITIES ON SPACE STATION FREEDOM

Attend the Space Station Utilization Conference August 3-6, 1992, Von
Braun Civic Center, Huntsville, Alabama.  For information call (800)
448-4031.