The Challenger Disaster
Prof Michael D. Smith
School of Physical Sciences
(pictures and some text reproduced from NASA sources)
Lecture outline
•
Build-up to the 1986 mission.
•
Analysis of the Space Shuttle break-up.
•
Presidential Commission Report.
•
Conclusions.
•
Further details.
Columbia history
Milestones – 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
Challenger history.
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 firsts.
• Challenger launched on her maiden voyage, STS-6, on April 4, 1983.
• 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 history.
Challenger against a backdrop of blue water and white clouds
taken from a camera aboard the Shuttle Pallet Satellite during mission STS-7.
Background to the mission.
1986
National Aereonautics and Space Administration
• 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.
Shuttle Mission STS-51L: problems
Shuttle Mission was plagued by problems from onset.
weather conditions
technical 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.
Shuttle Mission STS-51L
Launch delays
Liftoff was initially scheduled January 22, 1986.
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.
Mission details
Challenger was scheduled to carry some cargo
• 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.
The Crew
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.
Mission Highlights (Planned)
• Arrive in orbit.
On Flight Day 1:
• Check the readiness of the TDRS-B satellite.
• Deploy the satellite
and its Inertial Upper Stage (IUS) booster.
• The Comet Halley Active Monitoring Program
CHAMP) experiment scheduled to begin.
On Flight Day 2:
• ”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.
• Continue fluid dynamics experiments
On Flight Day 4:
(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 jets
Crew news conferences also scheduled
On Flight Day 7
Prepare for deorbit and re-entry
Scheduled to land at the Kennedy Space Center
144 hours and 34 minutes after launch.
External Tank
Basic shuttle design
Right Solid
Rocket Booster
Left Solid
Rocket Booster
Orbiter
1. Orbiter
• The primary component:
•
•
•
•
•
Length 37.2m
Height 17.25m
Mass 68.5tonnes
Payload:32,000kg
Crew: 7 max
A reusable, winged craft containing the crew and payload
that actually travels into space and returns to land on
a runway.
2. External Tank
• 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.
The ET is jettisoned at an altitude of 111,400m (365,000ft),
and burns-up over the Indian Ocean.
External 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.
3. Solid rocket boosters
• Without the SRBs, the shuttle cannot produce
enough thrust to overcome the earth's gravitational pull.
• 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
Solid rocket booster
• SRBs, in general, produce much more thrust per weight
than their liquid fuel counterparts.
• 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.
Solid rocket booster
• 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.
• The SRBs then deploy parachutes
• and fall into the ocean.
• they are recovered by tugs.
O-rings
Pressurised joint
(exaggerated)
Exterior
Interior
Exterior
Interior
Pressurised Joint deflection on Solid Rocket Booster
Unpressurised joint
Solid rocket booster
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.
The purpose of the O-rings is to prevent hot combustion gasses from
escaping from the inside of the motor.
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.
Solid rocket booster
O-Rings
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.
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-cooled
air descending
Aft Field
Joint O-ring
Lower
Attachment
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.
Warning
• 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.
O-ring blow-by from the right SRB
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.
Wind-shear
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 max dynamic pressure q
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.
Variation in air density (r), 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).
ET damage by SRB
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.
66.764 s
ET damage by SRB
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.
Failure of the liquid oxygen tank in the ET
73.124 s
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.
Structural breakup of the Shuttle
76 s
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
78 s
The Challenger's left wing, main engines (still burning residual
propellant) and the forward fuselage (crew cabin).
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.
CONCLUSION: joint failure
“... 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: design 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
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)
Richard Feynman
For a successful technology,
reality must take precedence over public relations,
for nature cannot be fooled.
Credit: Time Life Pictures/Getty Images
Richard Feynman: altered criteria
“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:communication
“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.”
Further details
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 launch
NASA 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.
Improvements
1. redesign of the SRB O-ring joint seals
2. addition of a crew escape system
3. 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.