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Transcript of Prof Michael D. Smith School of Physical Sciences (pictures and some text reproduced from NASA...
Prof Michael D. SmithSchool of Physical Sciences
(pictures and some text reproduced from NASA sources)
The Challenger Disaster
• Build-up to the 1986 mission.
• Analysis of the Space Shuttle break-up.
• Presidential Commission Report.
• Conclusions.
Lecture outline
• Further details.
Columbia historyMilestones – OV102
July 26, 1972 Contract Award
Nov. 21, 1975 Start structural assembly of crew module
June 14, 1976 Start structural assembly of aft-fuselage
March 16, 1977 Wings arrive at Palmdale from Grumman
Sept. 30, 1977 Start of Final Assembly
Feb. 10, 1978 Completed final assembly
Feb. 14, 1978 Rollout from Palmdale
April 12 1981 Launch
Jan 16, 2003 28th and Last Flight
Construction Milestones - OV-099 (Space shuttle Challenger)
Jan. 1, 1979 Contract Award
Jan. 28, 1979 Start structural assembly of crew module
June 14, 1976 Start structural assembly of aft-fuselage
March 16, 1977 Wings arrive at Palmdale from Grumman
Nov. 3, 1980 Start of Final Assembly
Oct. 21, 1981 Completed final assembly
June 30, 1982 Rollout from Palmdale
July 1, 1982 Overland transport from Palmdale to Edwards
July 5, 1982 Delivery to Kennedy Space Center
Dec. 19, 1982 Flight Readiness Firing
April 4, 1983 First Flight (STS-6)
January 28, 1986 10th and Last Flight
Challenger history.
• Challenger launched on her maiden voyage, STS-6, on April 4, 1983.
Challenger firsts.
• That mission saw the first spacewalk of the Space Shuttle program,
as well as the deployment of the first satellite in the
Tracking and Data Relay System constellation.
• The orbiter launched the first American woman, Sally Ride,
into space on mission STS-7
and was the first to carry two U.S. female astronauts
on mission STS 41-G.
Challenger against a backdrop of blue water and white clouds
taken from a camera aboard the Shuttle Pallet Satellite during mission STS-7.
Challenger history.
• This would be the busiest year ever for NASA.
• Halley's comet would be observed.
• The Hubble telescope lofted.
• 25th shuttle flight.
• The first average American in space.
Background to the mission.
National Aereonautics and Space Administration
1986
Shuttle Mission was plagued by problems from onset.
weather conditions
technical problems
Shuttle Mission STS-51L: problems
Shuttle Mission STS-51L: delays
Challenger was originally scheduled for July, 1985, but by the time the crew was assigned in January, 1985, launch had been postponed to late November to accommodate changes in payloads.
The launch was subsequently delayed further and finally rescheduled for late January, 1986.
Liftoff was initially scheduled January 22, 1986. Launch delays
It slipped to Jan 23
then Jan. 24,
reset for Jan. 25,
rescheduled for Jan. 27,
but delayed another 24 hours.
The Challenger finally lifted off
at 11:38:00 a.m. EST, 28th Jan.
Shuttle Mission STS-51L
Launch delays
The first delay of the Challenger mission was due to a weather front
expected to move into the area, bringing rain and cold temperatures.
Vice President expected to be present for the launch and NASA officials
postponed the launch early.
The Vice President was a key spokesperson the space program,
NASA coveted his good will.
Shuttle Mission STS-51L
Launch delays
The second launch delay was caused by a defective microswitch in the
hatch locking mechanism and problems in removing the hatch handle.
Once these problems had been sorted out, winds had become too high.
The weather front had started moving again, and appeared to be
bringing record-setting low temperatures to the Florida area.
Shuttle Mission STS-51L
Challenger was scheduled to carry some cargo
Mission details
• Tracking Data Relay Satellite-2 (TDRS-2)
• Shuttle-Pointed Tool for Astronomy (SPARTAN-203)
Halley's Comet Experiment Deployable
free-flying module designed to observe Halleys comet
using two ultraviolet spectrometers and two cameras.
Back row from left to right: Mission Specialist, Ellison S. Onizuka, Teacher in
Space Participant Sharon Christa McAuliffe, Payload Specialist, Greg Jarvis
and Mission Specialist, Judy Resnik.
In the front row from left to right: Pilot Mike Smith, Commander, Dick Scobee
and Mission Specialist, Ron McNair.
The Crew
Mission Highlights (Planned)
On Flight Day 1:• Arrive in orbit.
• Check the readiness of the TDRS-B satellite.
• Deploy the satellite
and its Inertial Upper Stage (IUS) booster.
On Flight Day 2:
• The Comet Halley Active Monitoring Program
CHAMP) experiment scheduled to begin.
• ”Teacher in space" (TISP) video taping.
• Firing of the orbital maneuvering engines (OMS)
at 152-mile altitude from which the
Spartan would be deployed.
Mission Highlights (Planned)
On Flight Day 3:• Pre-deployment preparations on the Spartan.• Deployment using remote manipulator system
(RMS) robot arm.
• Separate from Spartan by 90 miles.
On Flight Day 4:
• Continue fluid dynamics experiments
(started on day 2 and day 3). • Challenger begin to close in on Spartan• Live telecasts by Christa McAuliffe.
Mission Highlights (Planned) On Flight Day 5 Rendezvous with Spartan
Use the robot arm to capture the satellite..
On Flight Day 6
Re-entry preparations, including flight control checks, test firing of maneuvering jetsCrew news conferences also scheduled
On Flight Day 7Prepare for deorbit and re-entry Scheduled to land at the Kennedy Space Center 144 hours and 34 minutes after launch.
Basic shuttle design
External Tank
Left Solid Rocket Booster
Right Solid Rocket Booster
Orbiter
• The primary component:
A reusable, winged craft containing the crew and payload
that actually travels into space and returns to land on
a runway.
1. Orbiter• Length 37.2m• Height 17.25m• Mass 68.5tonnes • Payload:32,000kg• Crew: 7 max
• The External Tank carries liquid oxygen and liquid
hydrogen in two separate compartments. This is the fuel
that is fed to the three orbital engines.
2. External Tank
The ET is jettisoned at an altitude of 111,400m (365,000ft),
and burns-up over the Indian Ocean.
External Fuel TankExternal Fuel Tank• Mass: 30 tonnes, empty.• Lift off mass 762 tonnes.• The skeleton of the shuttle vehicle
assembly.• The tank holds: 550,000L LOX 1,500,000L LH2
• Only part of the shuttle system to be thrown away.
• Without the SRBs, the shuttle cannot produce
enough thrust to overcome the earth's gravitational pull.
3. Solid rocket boosters
• An SRB is attached to each side of the external fuel tank.
• Each booster is 149 feet long (45m) and
12 feet (3.6m) in diameter.
• Before ignition, each booster weighs 2 million pounds
(900 tonnes, 150 elephants).
80% of the total vehicle mass, 83% of total thrust
Solid rocket boosters
• SRBs, in general, produce much more thrust per weight
than their liquid fuel counterparts.
Solid rocket booster
• The drawback is that, once the solid rocket fuel has
been ignited, it cannot be turned off or even controlled.
• Morton Thiokol was awarded the contract to design and
build the SRBs in 1974.
• Thiokol's design is a scaled-up version of a Titan missile,
which had been used successfully for years.
• NASA accepted the design in 1976.
• After the SRBs have lifted the Shuttle to an altitude
of about 150,000 ft (45,760 m), the SRBs are jettisoned
using small explosive charges.
Solid rocket booster
• The SRBs then deploy parachutes
• and fall into the ocean.
• they are recovered by tugs.
O-rings
Pressurised Joint deflection on Solid Rocket Booster
Pressurised joint(exaggerated)
Unpressurised joint
Inte
rio
r
Inte
rio
r
Ext
erio
r
Ext
erio
r
Each SRB joint is sealed by two O-rings: the bottom ring known as
the primary O-ring, and the top known as the secondary O-ring.
Solid rocket booster
Putty: To provide a barrier
between the rubber O-rings and
the combustion gasses,
a heat-resistant putty is applied
to the inner section of the joint.
The purpose of the O-rings is to prevent hot combustion gasses from
escaping from the inside of the motor.
The Titan booster had only one O-ring.
The second ring was added as a measure of safety.
Except for the increased scale of the rocket's diameter,
this was the only major difference between the
shuttle booster and the Titan booster.
Solid rocket booster
O-Rings
Typical Space Shuttle mission profile
Temperature on day of the launch
The air temperature had dropped to -8°C (18°F) the night before
and 36°F (2°C) on the morning of the launch.
No previous flight had been attempted below 11°C (51°F ), and
the manufacturer, Morton Thiokol, had insufficient data on how
the boosters would perform at lower temperatures.
Although Thiokol engineers were concerned about launching under these conditions and recommended a delay, many felt that the boosters should be able to operate safely even at that low of a temperature.
Wind blowing over the ET and impinging on the aft field joint of the right SRB
Wind
Super-cooledair descending
Aft FieldJoint O-ring
LowerAttachment Strut
Cold conditions pre-launch
Cold conditions pre-launch
It is common procedure for ground personnel to use infrared
cameras to measure the thickness of the ice that forms on the
ET prior to launch. By chance, the Ice Team happened to point
a camera at the aft field joint of the right SRB and recorded a
temperature of only 8°F (-13°C), much colder than the air
temperature and far below the design tolerances of the O-rings.
Had this wind been blowing in almost any other direction and
not impinged on the aft field joint, it is likely that the O-rings
would have been considerably warmer and the disaster may
not have occurred.
Cold conditions pre-launch
An additional factor was that the information collected by the Ice Team was never passed on to decision makers, primarily because it was not the Ice Team's responsibility to report anything other than the ice thickness on the ET.
Had the aft field joint temperature been provided to engineers at NASA and Morton Thiokol, the launch almost surely would've been aborted and the loss of Challenger avoided.
Countdown and launch
The Challenger was counted-down and lifted-off
at 11:38:00 a.m. EST, 28th Jan.
O-ring blow-by from the right SRB
0.678 sec
O-ring blow-by from the right SRB
Eight more distinctive puffs of increasingly blacker smoke were
recorded between .836 and 2.500 seconds.
The black color and dense composition of the smoke puffs
suggest that the grease, joint insulation and rubber O-rings in
the joint seal were being burned and eroded by the hot propellant
gases.
WarningWarning• Roger Boisjoly, a Thiokol
engineer had gone on record the night before the launch.
• In a teleconference with NASA he stated:
• “If we launch tomorrow we will kill those seven astronauts”
• He was ignored.
No further smoke was observed since the joint apparently
sealed itself. This new seal was probably due to a combination of
two factors:
First, the O-rings were heated by the hot burning fuel
which would've increased their temperature and resiliency.
Second, the solid rocket propellant contains particles of aluminum
oxide that melt when heated, and probably sealed the gap.
O-ring blow-by from the right SRB
At approximately 37 seconds, Challenger encountered the first of
several high-altitude wind shear conditions, which lasted until
about 64 seconds. The wind shear created forces on the vehicle
with relatively large fluctuations.
Wind-shear
At 56 seconds after launch, right around the time of max q ……..
Challenger passed through the worst wind shear in the history of
the Shuttle program.
The wind loads on the vehicle caused the booster to flex and
dislodged the aluminum oxide plug
that had sealed the damaged O-rings.
Wind-shear at max dynamic pressure q
Variation in air density (), velocity (V), altitude (h), and dynamic pressure (q)
during a Space Shuttle launch.
58.788 s
58.788 s
Still photograph of the 51-L launch from a different angle shows an
unusual plume in the lower part of the right hand SRB (027).
The flame continued to grow and became caught up in the
aerodynamic flowfield of the accelerating Shuttle. Had this flame
been pointed in nearly any other direction, the Shuttle probably
could have continued flying safely until booster separation.
The mission would however been aborted and the Challenger
would have emergency-landed at an abort site.
ET damage by SRB
THE SRB however pointed towards the ET and eventually caused
damage resulting in a leak of the hydrogen fuel.
ET damage by SRB
66.764 s
At 70 seconds, a circumferential leak of hydrogen appeared about
a third of the way up from the bottom of the ET indicating that the
hydrogen inner-tank had failed and the ET was disintegrating.
ET damage by SRB
73.124 s
Failure of the liquid oxygen tank in the ET
The bright luminous glow at the top is attributed to the rupture
of the liquid oxygen tank just above the SRB/ET attachment.
Challenger is completely engulfed in an incandescent flow of
escaping liquid propellant.
76 s
Structural breakup of the Shuttle
The two SRBs crossed paths and continued operating
until 110 seconds after launch,
when they were destroyed using onboard self-destruct explosives.
Structural breakup of the Orbiter
The nose of the Orbiter separates
from the crew cabin.
The reddish-brown
cloud that can be seen emerging from
the cloud is the hypergolic
nitrogen tetroxide
fuel used in the reaction control system
(RCS).
Structural breakup of the Shuttle
76 seconds into the flight, the Shuttle was travelling Mach 1.92
(equating to a speed over 1,250 mph or 2,040 km/h), at an
altitude of 46,000 ft (14,035 m).
The continuing rotation of the right SRB pushed the Shuttle
off course such that its nose was no longer pointed in the same
direction as it was flying.
Structural breakup of the Shuttle
The stresses these loads created were too great for the Shuttle
to bear, and it quickly broke up into several large pieces.
76.795 s
The Challenger's left wing, main engines (still burning residual
propellant) and the forward fuselage (crew cabin).
78 s
Structural breakup of the Orbiter
Challenger crew compartment following the break-up
Fate of the Crew
The momentum of the crew cabin, carried it to an altitude of
about 19,525 m (64,000 ft) before it began a free-fall into
the ocean.
While it is not conclusively known what happened to
the crew during this period, it is believed that they probably
survived the initial breakup of the Challenger since the loads
experienced were only greater than 4 g's for a very brief period.
Fate of the Crew
The cabin did lose electrical power and oxygen as it separated
from the rest of the vehicle. If the cabin was depressurized
during this period, it is likely that the crew was knocked
unconscious due to lack of oxygen.
However, the astronauts were equipped with
Personal Egress Air Packs (PEAPs)
containing an emergency air supply.
Of the four PEAPs recovered, three had been activated and
partially used indicating that at least some of the crew survived
long enough to turn them on.
Fate of the Crew
Nevertheless, these PEAPs were not designed for high-altitude
use and would not have prevented the astronauts from
passing out had the cabin depressurized. Whether they were
conscious throughout the 2 minutes 40 seconds descent or not,
the cabin impacted the
surface of the ocean at 200 mph (320 km/h), creating a force of
about 200 g's that would have killed any survivors instantly.
Presidential Commission
The mandate of the Commission was to:
1. Review the circumstances surrounding the accident to establish the probable cause or causes of the accident; and
2. Develop recommendations for corrective or other action based upon the Commission's findings and determinations.
“... the loss of the Space Shuttle Challenger was caused
by a failure in the joint between the two lower segments
of the right Solid Rocket Motor. The specific failure was
the destruction of the seals that are intended to prevent
hot gases from leaking through the joint during the
propellant burn of the rocket motor. The evidence
assembled by the Commission indicates that no other
element of the Space Shuttle system contributed
to this failure.”
CONCLUSION: joint failure
“Cause of Challenger accident was:
failure of the pressure seal in the aft field joint of the
right Solid Rocket Booster.
Failure due to a faulty design unacceptably sensitive
to a number of factors.
CONCLUSION: design failure
These factors were the effects of:
temperature,
physical dimensions,
the character of materials,
the effects of reusability,
processing
and the reaction of the joint to dynamic loading.”
(Source: The Presidential Commission on the SSCA Report, 1986 p.40, p.70)
CONCLUSION
Credit: Time Life Pictures/Getty Images
For a successful technology,reality must take precedence over public relations, for nature cannot be fooled.
Richard Feynman
“If a reasonable launch schedule is to be maintained, engineering
often cannot be done fast enough to keep up with the expectations
of originally conservative certification criteria designed to
guarantee a very safe vehicle.
In these situations, subtly, and often with apparently logical
arguments, the criteria are altered so that flights may still be
certified in time.
They therefore fly in a relatively unsafe condition, with a chance of
failure of the order of a percent (it is difficult to be more accurate).”
Richard Feynman: altered criteria
“Official management, on the other hand, claims to believe the
probability of failure is a thousand times less. One reason for this
may be an attempt to assure the government of NASA perfection
and success in order to ensure the supply of funds. The other
may be that they sincerely believed it to be true, demonstrating
an almost incredible lack of communication between themselves
and their working engineers.”
Richard Feynman:communication
Launch delays
NASA wanted to check with all of its contractors to determine if there would be any problems with launching in the cold temperatures. Alan McDonald, director of the SRB Project at Morton-Thiokol, was convinced that there were cold-weather problems with the SRBs and contacted two of the engineers working on the project, Robert Ebeling and Roger Boisjoly.
Further details
O-ring problems
Thiokol knew there was a problem with the boosters as early as 1977, and had initiated a redesign effort in 1985. NASA Level I management had been briefed on the problem on August 19, 1985. Almost half of the shuttle flights had experienced O-ring erosion in the booster field joints. Ebeling and Boisjoly had complained to Thiokol that management was not supporting the redesign task force.
Further details
Organizations/People Involved
Marshall Space Flight Center - in charge of booster rocket development Larry Mulloy - challenged the engineers' decision not to launch Morton Thiokol - Contracted by NASA to build the solid rocket booster Alan McDonald - Director of the Solid Rocket Motors project Bob Lund - Engineering Vice President Robert Ebeling - Engineer who worked under McDonald Roger Boisjoly - Engineer who worked under McDonald Joe Kilminster - Engineer in a management position Jerald Mason - Senior executive who encouraged Lund to reassess his decision not to launch.
Further details
Pressure to launchNASA managers were anxious to launch the Challenger for several reasons,
including economic considerations, political pressures, and scheduling backlogs.
• Unforeseen competition from the European Space Agency put NASA in a
position in which it would have to fly the shuttle dependably on a very ambitious
schedule to prove the Space Transportation System's cost effectiveness and
potential for commercialization.
• This prompted NASA to schedule a record number of missions in 1986 to
make a case for its budget requests.
Further details
Pressure to launch• The shuttle mission just prior to the Challenger had been delayed a record
number of times due to inclement weather and mechanical factors.
• NASA wanted to launch the Challenger without any delays so the launch pad
could be refurbished in time for the next mission, which would be carrying a
probe that would examine Halley's Comet. If launched on time, this probe
would have collected data a few days before a similar Russian probe
would be launched.
• There was probably also pressure to launch Challenger so that it could be in
space when President Reagan gave his State of the Union address.
Reagan's main topic was to be education, and he was expected to mention
the shuttle and the first teacher in space, Christa McAuliffe.
Further details
Key Dates
1974 - Morton-Thiokol awarded contract to build solid rocket boosters. 1976 - NASA accepts Morton-Thiokol's booster design. 1977 - Morton-Thiokol discovers joint rotation problem.November 1981 - O-ring erosion discovered after second shuttle flight.January 24, 1985 - shuttle flight that exhibited the worst O-ring blowby.July 1985 - Thiokol orders new steel billets for new field joint design.August 19, 1985 - NASA Level I management briefed on booster problem.January 27, 1986 - night teleconference to discuss effects of cold temperature on booster performance. January 28, 1986 - Challenger explodes 72 seconds after liftoff.
Further details
1. redesign of the SRB O-ring joint seals2. addition of a crew escape system3. greater restrictions on conditions in which the Shuttle can be launched
These measures proved effective until 2003 when the Columbia was lost
It is interesting to note that one of the key factors in the Challenger disaster was: the worst wind shear ever experienced by a Shuttle, and Columbia happened to experience the second worst wind shear in history a factor that played a key role in its eventual loss as well.
Improvements