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.


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.


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.


• 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.


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.


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


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.


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


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.


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).


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.


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

Prof Michael D. Smith School of Physical Sciences (pictures and some text reproduced from NASA...

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