yee@ames.arc.nasa.gov (Peter E. Yee) (09/08/88)
SHUTTLE STUDENT INVOLVEMENT PROGRAM
Utilizing a Semi-Permeable Membrane to Direct Crystal Growth
This is an experiment proposed by Richard S. Cavoli, formerly
of Marlboro Central High School, Marlboro, N.Y. Cavoli is now
enrolled at State University of New York, Buffalo School of
Medicine, Buffalo, N.Y.
The experiment will attempt to control crystal growth through
the use of a semi-permeable membrane. Lead iodide crystals will be
formed as a result of a double replacement reaction. Lead acetate
and potassium iodide will react to form insoluble lead iodide
crystals, potassium ions and acetate ions. As the ions travel
across a semi-permeable membrane, the lead and iodide ions will
collide, forming the lead iodide crystal.
Cavoli's hypothesis states that the shape of the semi-permeable
membrane and the concentrations of the two precursor compounds will
determine the growth rate and shape of the resultant crystal without
regard to other factors experienced in Earth-bound crystal growing
experiments.
Following return of the experiment aparatus to Cavoli, an
analysis will be performed on the crystal color, density, hardness,
morphology, refractive index and electrical and thermal
characteristics. Crystals of this type are useful in imaging
systems for detecting gamma and X-rays and could be used in
spacecraft sensors for astrophysical research purposes.
Cavoli's high school advisor is Annette M. Saturnelli of
Marlboro Central High School, and his college advisor and experiment
sponsor is Dr. Charles Scaife of Union College.
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Effects of Weightlessness on Grain Formation and Strength
in Metals
This experiment was proposed by Lloyd C. Bruce formerly of
Sumner High School, St. Louis. Bruce is now a senior at the
University of Missouri.
The experiment proposes to heat a titanium alloy metal filament
to near the melting point to observe the effect that weightlessness
has on crystal reorganization within the metal. It is expected that
heating in microgravity will produce larger crystal grains and
thereby, increase the inherent strength of the metal filament. The
experiment uses a battery supply, a timer and thermostat to heat a
titanium alloy filament to 1,000 degrees Celsius.
At a temperature of 882 degrees C, the titanium-aluminum alloy
crystal lattice network undergoes a metamorphosis from closely
packed hexagonal crystals to centered cubic crystals.
Following return of the experiment gear to Bruce, he will
compare the space-tested alloy sample with one heated on Earth to
analyze any changes in strength, size and shape of the crystal
grains and any change in the homogeneity of the alloy. If necessary
microscopic examination, stress testing and X-ray diffraction
analysis also will be used. Any changes between the two samples
could lead to variations on this experiment to be proposed for
future Shuttle flights. A positive test might lead to a new,
lightweight and stronger titanium-aluminum alloy or a new type of
industrial process.
Bruce's student advisor is Vaughan Morrill of Sumner High
School. His sponsor is McDonnell Douglas Corp., St. Louis, and his
experiment advisor is Dr. Diane Chong of McDonnell Douglas.
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OASIS INSTRUMENTATION
Special instrumentation to record the environment experienced
by Discovery during the STS-26 mission is aboard the orbiter mounted
in the payload bay.
The Orbiter Experiments Autonomous Supporting Instrumentation
System (OASIS) is designed to collect and record a variety of
environmental measurements during various in-flight phases of the
orbiter. The primary device is a large tape recorder which is
mounted on the aft, port side of the orbiter. The OASIS recorder
can be commanded from the ground to store information at a low,
medium or high data rate. After Discovery's mission is over, the
tapes will be removed for analysis.
The information will be used to study the effects on the
orbiter of temperature, pressure, vibration, sound, acceleration,
stress and strain. It also will be used to assist in the design of
future payloads and upper stages.
OASIS is about desk-top size, approximately 4 ft. long, 1 ft.
wide, 3 ft. deep and weighs 230 lbs. It was installed for flight in
the payload bay on April 18.
The OASIS data is collected from 101 sensors mounted on three
primary elements. The sensors are located along the sills on either
side of the payload bay, on the airborne support equipment of the
Inertial Upper Stage and on the tape recorder itself. These sensors
are connected to accelerometers, strain gauges, microphones,
pressure gauges and various thermal devices on the orbiter.
OASIS was exercised during the flight readiness firing of the
Space Shuttle Discovery in August and data was collected for
analysis.
On STS-26 launch day, the system will be turned on 9 minutes
before Discovery's liftoff to begin recording at high speed and
recover high fidelity data. Following the first burn of the orbital
maneuvering system, it will be switched to the low data rate. It
will be commanded again to high speed for subsequent Shuttle OMS
burns.
Different data rates are to be commanded from the ground to
OASIS at various times during the on-orbit operations. If tape
remains, the recorder will operate during descent.
NASA is flying OASIS aboard Discovery in support of the IUS
program office of the Air Force Space Division. The system was
developed by Lockheed Engineering and Management Services Co. under
a NASA contract. Development was sponsored by the Air Force Space
Division.
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STS-26 Cargo Configuration
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STS-26 PAYLOAD AND VEHICLE WEIGHTS
Pounds
Orbiter Empty 176, 019
IUS 32,618
TDRS-C 4,905
OASIS I 223
ADSF 266
ARC 168
ELRAD 3
IEF 66
IRCFE 9
IUS Support Equipment 176
MLE 15
PCG 97
PPE 2
PVTOS 184
SSIP (2) 42
Orbiter Including Cargo at SRB Ignition 253,693
Total Vehicle at SRB Ignition 4,521,762
Orbiter Landing Weight 194,800
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MAJOR ORBITER MODIFICATIONS
More than 100 mandatory modifications to the orbiter Discovery
were completed before returning to flight. Major modifications
include:
* Brake Improvements -- This included changes to eliminate
mechanical and thermally-induced brake damage, improve steering
margin and reduce the effects of tire damage or failure.
Modifications for first flight are the thicker stators, stiffened
main landing gear axles, tire pressure monitoring and anti-skid
avionics.
* 17-Inch Disconnect -- A positive hold-open latch design
feature for the main propulsion system disconnect valves between the
orbiter and the external tank (ET) was developed to ensure that the
valve remains open during powered flight until nominal ET separation
is initiated.
* Reaction Control System Engines -- The RCS engines provide
on-orbit attitude control and have been modified to turn off
automatically in the event any combustion instability were to cause
chamber wall burnthrough.
* Thermal Protection System -- The TPS was improved in areas on
the orbiter in the wing elevon cove region, nose landing gear door,
lower wing surface trailing edge and elevon leading edge.
* Auxiliary Power Unit -- An electrical interlock has been
added to the APU tank shutoff valves to preclude electrical failures
that could overheat the valves and cause decomposition of the fuel
(hydrazine).
* Orbital Maneuvering System -- To prevent development of leaks
as a result of improper manufacturing processes, bellows in critical
OMS propellant line valves have been replaced.
* Crew Escape System -- A pyrotechnically jettisoned side
hatch, crew parachutes and survival gear and a curved telescoping
pole to aid the crew in clearing the wing, have been added to give a
bail-out capability in the event of a problem where runway landing
is not possible. An egress slide has been added to facilitate rapid
post-landing egress from the vehicle under emergency conditions.
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SOLID ROCKET MOTOR REDESIGN
On June 13, 1986, the President directed NASA to implement the
recommendations of the Presidential Commission on the Space Shuttle
Challenger Accident. As part of satisfying those recommendations,
NASA developed a plan to provide a redesigned solid rocket motor
(SRM).
The primary objective of the redesign effort was to provide an
SRM that is safe to fly. A secondary objective was to minimize the
impact on the launch schedule by using existing hardware, to the
extent practical, without compromising safety.
A redesign team was established which included participation
from Marshall Space Flight Center; Morton Thiokol, NASA's prime
contractor for the SRM; other NASA centers; contractors and experts
from outside NASA.
All aspects of the existing SRM were assessed. Design changes
were deemed necessary in the field joint, case-to-nozzle joint,
nozzle, factory joint, local propellant grain contour, ignition
system and ground support equipment. Design criteria were
established for each component to ensure a safe design with an
adequate margin of safety.
Design
Field Joint -- The field joint metal parts, internal case
insulation and seals were redesigned and a weather protection system
was added.
In the STS 51-L design, the application of actuating pressure
to the upstream face of the o-ring was essential for proper joint
sealing performance because large sealing gaps were created by
pressure-induced deflections, compounded by significantly reduced o-
ring sealing performance at low temperature.
The major motor case change is the new tang capture feature
which provides a positive metal-to-metal interference fit around the
circumference of the tang and clevis ends of the mating segments.
The interference fit limits the deflection between the tang and
clevis o-ring sealing surfaces due to motor pressure and structural
loads. The joints are designed so the seals will not leak under
twice the expected structural deflection and rate.
External heaters with integral weather seals were incorporated
to maintain the joint and o-ring temperature at a minimum of 75
degrees F. The weather seal also prevents water intrusion into the
joint.
The new design, with the tang capture feature, the interference
fit and the use of custom shims between the outer surface of the
tang and inner surface of the outer clevis leg, controls the o-ring
sealing gap dimension.
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The sealing gap and the o-ring seals are designed so there is
always a positive compression (squeeze) on the o-rings. The minimum
and maximum squeeze requirements include the effects of temperature,
o-ring resiliency and compression set and pressure. The clevis o-
ring groove dimension has been increased so the o-ring never fills
more than 90 percent of the o-ring groove, enhancing pressure
actuation.
The new field joint design also includes a new o-ring in the
capture feature and an additional leak check port to assure that the
primary o-ring is positioned in the proper sealing direction at
ignition. This new or third o-ring also serves as a thermal barrier
should the sealed insulation be breached. Although not demanded by
the specification, it has proved to be an excellent hot gas seal.
The field joint internal case insulation was modified to be
sealed with a pressure actuated flap called a J-seal, rather than
with putty as in the STS 51-L configuration.
Longer field joint case mating pins, with a a reconfigured
retainer band, were added to improve the shear strength of the pins
and increase the margin of safety in the metal parts of the joint.
Case-to-Nozzle Joint -- The SRM case-to-nozzle joint, which
experienced several instances of o-ring erosion in flight, has been
redesigned to the same criteria imposed upon the case field joint.
Similar to the field joint, case-to-nozzle joint modifications
have been made in the metal parts, internal insulation and o-
rings. Radial bolts with "Stato-O-Seals" were added to minimize the
joint sealing gap opening.
The internal insulation was modified to be sealed adhesively
and a third o-ring included. The third o-ring serves as a dam or
wiper in front of the primary o-ring to prevent the polysulfide
adhesive from being extruded into the primary o-ring groove. It
also serves as a thermal barrier should the polysulfide adhesive be
breached. Like the third o-ring in the field joint, it has proven
to be an effective hot gas seal.
The polysulfide adhesive replaces the putty used in the 51-L
joint. Also, an additional leak check port was added to reduce the
amount of trapped air in the joint during the nozzle installation
process and aid in the leak check procedure.
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Nozzle -- The internal joints of the nozzle metal parts have
been redesigned to incorporate redundant and verifiable o-rings at
each joint. The nozzle steel fixed housing part has been redesigned
to permit incorporation of 100 radial bolts that attach the fixed
housing to the case aft dome.
Improved bonding techniques are used for the nozzle nose inlet,
cowl/boot and aft exit cone assemblies. The nose inlet assembly
metal part to ablative parts bondline distortion has been eliminated
by increasing the thickness of the aluminum nose inlet housing and
improving the bonding process. The tape wrap angle of the carbon
cloth fabric in the areas of the nose inlet and throat assembly
parts were changed to improve the ablative insulation erosion
tolerance.
Some of these ply angle changes were in progress prior to the
STS 51-L accident. The cowl and outer boot ring has additional
stuctural support with increased thickness and contour changes to
increase their margins of safety. Additionally, the outer boot ring
ply configuration was altered.
Factory Joint -- Minor modifications were made in the case
factory joints by increasing the insulation thickness and altering
the lay-up to increase the margin of safety on the internal in
sulation. Longer pins also were added, along with a reconfigured
retainer band and new weather seal to improve the factory joint
performance and increase the margin of safety. The o-ring and o-
ring groove size also were changed consistent with the field joint.
Propellant -- The motor propellant forward transition region
was recontoured to reduce the stress fields between the star and
cylindrical portions of the propellant grain.
Ignition System -- Several minor modifications were
incorporated into the ignition system. The aft end of the igniter
steel case, which contains the igniter nozzle insert, was thickened
to eliminate a localized weakness. The igniter internal case
insulation was tapered to improve the manufacturing process.
Ground Support Equipment -- The Ground Support Equipment (GSE)
has been redesigned to minimize the case distortion during handling
at the launch site; to improve the segment tang and clevis joint
measurement system for more accurate reading of case diameters to
facilitate stacking; to minimize the risk of o-ring damage during
joint mating; and to improve leak testing of the igniter, case and
nozzle field joints.
Other GSE modifications include transportation monitoring
equipment and lifting beam.
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Test Program
An extensive test program was conducted to certify the
redesigned motor for flight. Test activities included laboratory
and component tests, subscale tests, simulator tests and full scale
tests.
Laboratory and component tests were used to determine component
properties and characteristics. Subscale tests were used to
simulate gas dynamics and thermal conditions for components and
subsystem design. Simulator tests, consisting of motors using full
size flight type segments, were used to verify joint design under
full flight loads, pressure and temperature. Full scale tests were
used to verify analytical models; determine hardware assembly
characteristics; determine joint deflection characteristics;
determine joint performance under full duration, hot gas tests
including joint flaws and flight loads; and determine redesigned
hardware structural characteristics.
Five full scale, full duration motor static firing tests were
conducted prior to STS-26 to verify the redesigned solid rocket
motor performance. These included two development motor tests, two
qualification motor (QM) tests, and a production verification motor
test. Additionally, one post-STS-26 QM test is scheduled in late
December to certify the redesigned motor for cold weather operation.
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SPACE SHUTTLE MAIN ENGINE IMPROVEMENTS
The main engines for Space Shuttle flight STS-26 incorporate
numerous improvements over those on previous flights. Through an
extensive, ongoing engine test program, NASA has identified,
developed, certified and implemented dozens of modifications to the
Space Shuttle main engine.
In terms of hardware, areas of improvement include the
electronic engine controller, valve actuators, temperature sensors,
main combustion chamber and the turbopumps.
In the high pressure turbomachinery, improvements have focused
on the turbine blades and bearings to increase margin and
durability. The main combustion chamber has been strengthened by
nickel-plating a welded outlet manifold to give it extended life.
Margin improvements also have been made to the five hydraulic
actuators to preclude a loss in redundancy -- a situation which
occurred twice on the launch pad. To address several instances of
flight anomalies involving a temperature sensor in the critical
engine cutoff logic, the sensor has been redesigned and extensively
tested without problems.
Along with hardware improvements, several major reviews were
conducted on requirements and procedures. These reviews dealt with
topics such as possible failure modes and effects, and the
associated critical items list. Another review involved having a
launch/abort reassessment team examine all launch-commit criteria,
engine redlines and software logic. A design certification review
also was performed. In combination, these reviews have maximized
confidence for successful engine operation.
A related effort saw Marshall engineers, working with their
counterparts at the Kennedy Space Center, accomplish a comprehensive
launch operations and maintenance review. This ensured that engine
processing activities at the launch site are consistent with the
latest operational requirements.
In parallel with the various reviews, the most aggressive
ground testing program in the history of the main engine was
conducted. Its primary purposes were to certify the improvements
and demonstrate the engine's reliability and operating margin. It
was carried out at NASA's Stennis Space Center (formerly National
Space Technology Laboratories) in Mississippi and at Rocketdyne's
Santa Susana Field Laboratory in California.
The other vital area of ground testing activity was checkout
and acceptance of the three main engines for the STS-26 mission.
Those tests, also at Stennis, began in August 1987 and all three
STS-26 engines were delivered to Kennedy by January 1988.
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SPACEFLIGHT TRACKING AND DATA NETWORK
One of the key elements in the Space Shuttle mission is the
capability to track the spacecraft, communicate with the astronauts
and obtain the telemetry data that informs ground controllers of the
condition of the spacecraft and the crew.
The hub of this network is NASA's Goddard Space Flight Center,
Greenbelt, Md., where the Spaceflight Tracking and Data Network
(STDN) and the NASA Communications Network (NASCOM) are located.
The STDN is a complex NASA worldwide system that provides
realtime communications with the Space Shuttle orbiter and crew.
The network is operated by Goddard. Approximately 2,500 personnel
are required to operate the system.
The NASA-controlled network consists of 14 ground stations
equipped with 14-, 30- and 85-ft. S-band antenna systems and C-band
radar systems, augmented by numerous Department of Defense (DOD)
stations which provide C-band support and several DOD 60-ft. S-band
antenna systems. S-band systems carry telemetry radio frequency
transmissions. C-band stations conduct radar tracking.
In addition, there are several major computing interfaces
located at the Network Control Center and at the Flight Dynamics
Facility, both at Goddard; at Western Space and Missile Center
(WSMC), Vandenberg AFB, Calif.; at White Sands Missile Range, N.M.;
and at Eastern Space and Missile Center (ESMC), Cape Canaveral Air
Force Station, Fla. They provide realtime network computational
support for the generation of data necessary to point antennas at
the Shuttle.
The network has agreements with the governments of Australia,
(Canberra and Yarragadee); Spain (Madrid); Senegal (Dakar); Chile
(Santiago); United Kingdom (Ascension Island); and Bermuda to
provide NASA tracking station support to the National Space
Transportation System program.
Should the Mission Control Center in Houston be seriously
impaired for an extended period of time, the NASA Ground Terminal
(NGT) at White Sands becomes an emergency Mission Control Center,
manned by Johnson Space Center personnel, with the responsibility of
safely returning the orbiter to a landing site. During the
transition of the flight control team from Johnson to the White
Sands NASA Ground Terminal, Goddard would assume operational control
of the flight.
The Merritt Island, Fla., S-band station provides the
appropriate data to the Launch Control Center at Kennedy and the
Mission Control Center at Johnson during pre-launch testing and the
terminal countdown.
During the first minutes of launch and during the ascent phase,
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the Merritt Island and Ponce de Leon, Fla., S-band and Bermuda S-
band stations, as well as the C-band stations located at Bermuda;
Wallops Island, Va.; Antigua; Cape Canaveral; and Patrick Air Force
Base, Fla., provide appropriate tracking data, both high speed and
low speed, to the Kennedy and Johnson control centers.
During the orbital phase, all the S-band and some of the C-band
stations, which acquire the Space Shuttle at 3 degrees above the
horizon, support and provide appropriate tracking, telemetry, air-
ground and command support to the Mission Control Center at Johnson
through Goddard.
During the nominal entry and landing phase planned for Edwards
Air Force Base, Calif., the NASA/Goldstone and Dryden Flight
Research Facility, Calif., sites, and the S-band and C-band stations
at the WSMC and Edwards Air Force Base, Calif.,
provide highly-critical tracking, telemetry, command and air-ground
support to the orbiter and send appropriate data to the Johnson and
Kennedy control centers.
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NASA-CONTROLLED TRACKING STATIONS
Location Equipment
Ascension Island (ACN) (Atlantic Ocean) S-band, UHF A/G
Bermuda (BDA) (Atlantic Ocean) S- and C-band,
UHF A/G
Goldstone (GDS) (California) S-band, UHF
A/G, TV
Guam (GWM) (Pacific Ocean) S-band, UHF A/G
Hawaii (HAW) (Pacific Ocean) S-band, UHF
A/G, TV
Merritt Island (MIL) (Florida) S-band, UHF
A/G, TV
Santiago (AGO) (Chile) S-band
Ponce de Leon (PDL) (Florida) S-band
Madrid (RID) (Spain) S-band
Canberra (CAN) (Australia) S-band
Dakar (DKR) (Senegal, Africa) S-band, UHF A/G
Wallops (WFF) (Virginia) C-band
Yarragadee (YAR) (Australia) UHF A/G
Dryden (DFRF) (California) S-band, UHF
A/G, C-band
The Canberra, Goldstone and Madrid stations are part of the
Deep Space Network (DSN) and come under the management of NASA's Jet
Propulsion Laboratory, Pasadena, Calif.
Personnel: Tracking Stations; 1,100 (500+ are local residents)
Goddard Space Flight Center; 1,400
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