Sandia National Lab assists NASA with several shuttle projects (Forwarded)

Sandia National Laboratories

Sandia media contact:
Michael Padilla, (505) 284-5325

FOR IMMEDIATE RELEASE: August 17, 2005

Sandia assists NASA with several shuttle projects

Sandia-created sensor finds loose gap filler on Discovery

ALBUQUERQUE, N.M. -- Several Sandia National Laboratories projects were
instrumental in helping NASA with its Space Shuttle Discovery's
return-to-flight mission (STS-114).

Projects ranged from creating an orbiter inspection sensor to analyzing
sensors placed on the orbiter's wing-leading edges to providing peer
review reports. Sandia also studied the vibrations caused during the
rollout of the space vehicle, and developed an ultrasonic nondestructive
inspection method.

Sandia was instrumental in analyzing the cause of the accident that
destroyed the Columbia during reentry in Feb. 1, 2003. A Labs-wide team
effort helped confirm that the accident was caused by foam from the
external tank that impacted the wing leading edge on takeoff.

The following is a summary of Sandia projects contributing to STS-114:

Orbiter inspection sensor

Sandia provided the primary Thermal Protection System (TPS) inspection
sensor to NASA for the mission.

Sandia engineers Bob Habbit and Bob Nellums led a collaborative effort
of nearly 120 Sandia employees in creating the sensor.

Using 3-D imaging, the sensor inspects the orbiter for critical damage
during the mission and alerts astronauts if further investigations are
needed to repair the damage. The crew used the orbiter's robotic arm to
scan the front edge of both wings for damage as little as a 0.020-inch
crack.

The Sandia-patented 3-D technology uses a modulated laser illuminator
coupled with a modulated receiver to image and spatially locate each
point in the scene. The intensity data was used to detect damage and the
geometric data to assess the damage criticality.

The sensor data was relayed back to Mission Control at Johnson Space
Center -- Houston. A team of more than 20 Sandia employees working in
the Mission Control Center during the mission processed and reviewed the
data. The processed data was provided to the NASA Mission Management
Team. The Mission Management Team used the Sandia data and other data to
determine if it was safe for the orbiter to re-enter.

The Sandia-created sensor discovered loose gap fillers on Discovery. The
short strips of dangling material required an unprecedented repair by
spacewalking astronauts. The material posed danger for overheating on
reentry.

Gap fillers are thin fabric stiffened with a ceramic material and used
to plug gaps between the shuttle's tiles. One piece was sticking out 1.1
inches between thermal tiles. The other was at an angle from six-tenths
to nine-tenths of an inch. One of the gap fillers kept the tiles from
vibrating against each other during liftoff and had no purpose for
re-entry. The other was designed to prevent repeated overheating of a
gap between two tiles.

Habbit says once it was discovered that there was something visible,
NASA took action to use the Laser Dynamic Range Imager (LDRI) to
characterize the protruding gap filler. The geometric data collected by
the LDRI allowed NASA to model the effects of the protruding gap filler.
The modeling indicated potentially catastrophic results if the pieces
were left in place. Astronaut Stephen Robinson added a significant
milestone to the history books when he removed the protruding gap
fillers during the extravehicular activity (EVA).

Habbit says the sensor provided hours of data including raw video of the
scans. Once the data was processed it was given to NASA to clear
Discovery for reentry.

"We had the smallest but most capable sensor on the orbiter," Bob says.
"The LDRI was able to take enhanced 2- and 3-D images of the orbiter."

The sensor began scanning the orbiter on day two of the flight, after
the robotic arm was deployed. The sensor completed wing leading edge and
nose cap scans, and focused on inspection of tile, gap filler, and the
port wing.

Bob said the team took the Sandia ethos with them to Houston. "We worry
about everything and plan for the worst," he said. "This helped us out a
lot."

NASA has requested the Sandia-developed sensor be on the next space
shuttle mission, tentatively planned for September [NOTE: No earlier
than March 2006 - A.Y.], with space shuttle Atlantis.

Peer reviews

Members of Sandia's Aerosciences and Compressible Fluid Mechanics
Department contributed two peer reviews on NASA's development of
computational tools that are being used to support rapid damage
assessments should anything occur during future flights.

Sandia aerospace engineer Basil Hassan serves as an external member of
NASA's Engineering and Safety Center's (NESC) Flight Sciences "Super
Problem Resolution Team" (SPRT). NESC was formed shortly after the
Columbia accident to oversee any safety issues that might arise in any
of NASA's flight programs.

Hassan and two staff members, David Kuntz and Jeffrey Payne,
participated in several peer reviews as NASA prepared for
return-to-flight. They were also part of a larger group of Sandia
management and staff who were active in the post-accident investigation.

Two recent reviews focused on Debris Transport Review and Boundary Layer
Transition Review.

The Debris Transport Review focused on NASA's development of tools to
model external tank foam or ice buildup that may come off during ascent
and potentially hit the orbiter. While several efforts have been under
way to minimize foam and ice release from the external tank, NASA wants
to predict if the released debris will impact the orbiter in critical
areas. NASA has used these tools to redesign parts of the external tank
so that catastrophes like the Columbia accident will not re-occur.

The Boundary Layer Transition Review focused on reentry. During the
reentry trajectory the airflow around the orbiter will transition from
laminar to turbulent flow. When the flow becomes turbulent, the heat
transfer to the vehicle can increase two to four times above the laminar
heating. While the thermal protection system (TPS) is designed to absorb
the heating rates generated by turbulent flow, damage to the TPS could
cause the flow to become turbulent at a higher altitude. The result of
this damage could mean higher localized heating rates on the TPS, and
ultimately higher than normal integrated heating on the orbiter during
reentry.

"Sandia's participation on these two reviews teams is one part of a
larger effort of the Labs supporting a variety of return-to-flight
activities," Hassan says.

The team also reviewed NASA's rapid damage assessment tools to help the
agency ensure that the codes were being applied appropriately and that
the relevant assumptions in the codes were not being violated. In
general, these tools make use of data from computer codes that model the
fundamental physics, wind tunnel test data, and data from previous
shuttle flights. Should it be found in orbit that damage occurred during
the ascent stage, NASA engineers will use these tools to decide whether
the orbiter can safely return or if some in-orbit repair is needed.

Shuttle rollout

Moving the shuttle from the Vehicle Assembly Building at Kennedy Space
Center in Florida to the launch normally takes five to six hours at 0.9
mph. As the equipment ages, emphasis is being given to understanding how
the rollout may fatigue the orbiter.

To help understand the fatigue caused by vibrations during the Discovery
rollout, NASA contacted Sandia to assist with a series of tests.

Sandia helped NASA design the test and instrumentation to measure the
dynamic vibration environment of the rollout. Sandia also provided
additional support to NASA by computing the input forces that the
crawler applies to the MLP, which are being used by Boeing and NASA to
compute the fatigue life for critical shuttle components.

Sandia engineer Tom Carne assisted with a series of tests beginning in
November 2003 to develop the data necessary to understand the
environment and the response of the space shuttle vehicle during rollout.

The analyses showed that modifying the speed of the crawler would reduce
the fatigue stresses of the critical shuttle components. Merely reducing
the speed from 0.9 mph to 0.8 mph would significantly reduce the
vibrations in the shuttle by shifting the engagement frequency of the
crawler treads. The shuttle's vibration response can be much reduced
when the driving frequencies are shifted away from its own resonant
natural frequencies.

Sensor tests

David Crawford and Kenneth Gwinn analyzed tests conducted on sensors
that were placed on the leading edge of the orbiter's wings.

The project focused on validating forcing functions for NASA's Impact
Penetration Sensing system (IPSS) Wing Model. The model was developed at
Boeing to predict the accelerometer data collected during ascent and
micrometeoroid/orbiting debris (MMOD) impacts on shuttle wing and spar
leading-edge materials.

The sensors developed by NASA were significant to the return-to-flight
effort. The addition of the sensors to the leading edge was in response
to one of the prime objectives identified by the Columbia Accident
Investigation Board.

Crawford and Gwinn evaluated test data and were comparing it with
structural models of the shuttle and assessing what the signal levels
mean. Tasks included defining the forcing functions for foam, pieces of
ice (from takeoff), ablator particles, and micrometeorites. Full-scale
tests of foam, ice, ablator, metal particle, and MMOD impacts were
performed at Southwest Research Institute in San Antonio, Texas. Tests
on fiberglass and RCC (reinforced carbon composite) wing panels were
conducted at the White Sands Test Facility.

Inspection hardware

NASA funded a Sandia team to develop an ultrasonic nondestructive
inspection method (hardware, techniques, and standards) that led to a
scientifically rigorous pre-flight shuttle certification process. The
team investigated and proposed ways to improve nondestructive inspection
methods for certifying the flightworthiness of orbiter wing leading edges.

The team, led by Dennis Roach and Phil Walkington, initially evaluated
and refined their inspection methods and hardware using carbon-composite
samples with known defects created by the Sandia team. Later, as part of
the selection process, a NASA engineer hand-carried orbiter wing samples
to all the labs involved in the project and asked that each lab try to
find defects known only to NASA scientists.

The team developed the revised inspection and certification protocols,
and the ultrasonic scanning system was integrated into NASA's Shuttle
Orbiter Processing Facility at Kennedy Space Center to monitor the
health of the shuttle after each orbiter flight.

Sandia produced an in-situ ultrasonic inspection method while NASA
Langley developed the eddy current and thermographic techniques. These
groups were the primary players on the NASA In-Situ NDI Team. The NASA
In-Situ NDI Team consisted of members from all of the NASA facilities
and was assembled to guide NASA as it moves to increased use of advanced
nondestructive testing techniques to closely monitor the health of the
space shuttle.

In 10 months the Sandia team developed and assembled customized hardware
to produce an ultrasonic scanner system that can meet the shuttle wing
inspection requirements. Optimum combinations of custom ultrasonic
probes and data analysis were merged with the inspection procedures
needed to properly survey the heat shield panels. System features were
introduced to minimize the potential for human factors errors in
identifying and locating the flaws. A validation process, including
blind inspections monitored by NASA officials, demonstrated the ability
of these inspection systems to meet the accuracy, sensitivity, and
reliability requirements.

Sandia is a multiprogram laboratory operated by Sandia Corporation, a
Lockheed Martin company, for the U.S. Department of Energy's National
Nuclear Security Administration. Sandia has major R&D responsibilities
in national security, energy and environmental technologies, and
economic competitiveness.

IMAGE CAPTIONS:

[Image 1:
http://www.sandia.gov/news-center/ne...th-scanner.jpg
(644KB)]
Sandia's orbiter inspection sensor, attached to the space shuttle
Discovery's robotic arm, characterized loose gap fillers. (NASA photograph)

[Image 2:
http://www.sandia.gov/news-center/ne...RI-payload.jpg
(644KB)]
Sandia's orbitor inspection sensor was attached to Discovery's robotic
arm. (NASA photograph)