1986 Challenger Space Vehicle Accident (Research Paper Sample)

1986 Challenger Space Vehicle Accident
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1986 Challenger Space Vehicle Accident
Introduction
On the morning of January 28, 1986, the spaceplane “Challenger” exploded 73 seconds after liftoff, causing the deaths of all crewmembers and the total loss of the vehicle. No persons on the ground were injured, as the launch trajectory took the vehicle over the sea at the time of the explosion and the impact area of debris had been previously cleared of sea vessels as a routine safety precaution.
This event caused a nearly 3 years-long grounding of the Space Shuttle program while the investigation, redesign of some components, and new organizational policies were implemented at NASA.
Vehicle description
33718505969000The vehicle consisted of four main components: an orbiter spaceplane, housing the payload and crew, an external fuel tank for the orbiter’s engines, and two solid rocket boosters (SRB’s). (Figure 1).
33623251888490Figure 1- Vehicle Components (NASA, Public Domain)00Figure 1- Vehicle Components (NASA, Public Domain)The solid rocket boosters consisted of four segments that were stacked and contained propellant. Solid propellant rocket engines are not very efficient but they are very powerful CITATION Sut16 \l 11274 (Sutton, 2016), so they were used during the initial ascent phase when the vehicle was at its heaviest.
04570730Figure 2- Cross-section view of SRB joint (NASA, Public Domain)Figure 2- Cross-section view of SRB joint (NASA, Public Domain)left9525The segments used a tang and clevis joint for structural integrity and to transmit loads to the vehicle, and two rubber o-rings for sealing. As the propellant burned, hot gasses were prevented from escaping by these (Rogers et al, 1986), as shown in Figure 2.
Timeline of events
The mission STS 51 L was announced on January 27, 1985. The primary mission consisted of the deployment of a TDRS (Tracking and Data Relay Satellite) to be used to enable constant communication with future spacecraft. Secondary missions included research and flying a participant in the Teacher in Space project (Rogers et al, 1986).
The mission experienced several delays until the launch was finally set for January 28, 1986.
The prior evening was very cold, with temperatures expected to reach 18 degrees at night and rise to 26 degrees at launch time. This would constitute a record low launch temperature for the vehicle, and engineers at the manufacturer of the solid rocket boosters were concerned that a critical rubber sealing component may fail in these cold conditions. A conference call was set up between the engineers and NASA. Engineers argued that they did not have data on the rubber seals at these low temperatures and that they could not guarantee adequate sealing, recommending postponing the launch until the temperature had risen to 53 degrees.
However, the leadership of the company overrode the engineer’s concerns and stated that there was enough margin of error for a safe launch, thus ending the call with a recommendation to proceed with the launch CITATION McD09 \l 11274 (McDonald & Hansen, 2009).
Additionally, there were concerns expressed by the ground teams about the amounts of ice buildup on the launch tower and vehicle. Engineers at the spaceplane manufacturer (note that this was a different company from the makers of the solid rocket boosters) recommended not to proceed with the launch. The concern was that ice built up in the launch tower may shake free during launch and damage the orbiter’s delicate thermal protection tiles or be ingested by the engines.
Upon consultation with KSC staff, the ice danger was disregarded and the launch was set to go ahead.
46577258235950031242002206625Figure 3 - Smoke puff at liftoff (NASA, Public domain), highlighting done by the author.Figure 3 - Smoke puff at liftoff (NASA, Public domain), highlighting done by the author.312420013970Immediately after an otherwise nominal liftoff, a puff of gray smoke was seen escaping the right solid rocket booster near the external tank attachment ring. (Figure 3)
The smoke lasted for a few seconds and then disappeared.
As the flight progressed, the vehicle was gaining speed and so it was experiencing an artificial wind, much like any other object moving through an atmosphere. However, the vehicle was also climbing, and the reduced air density was acting in opposition to this effect. This wind stagnates against the vehicle and its relative momentum becomes pressure, which is known as dynamic pressure, or Q to aerodynamicists. During any 4305300137350500rocket launch, as the speed increases and air density decreases, there is a point of maximum Q, or “max Q” which is where the greatest 38290503267075Figure 4 - Plume on right aft SRB (NASA, Public Domain), highlighting by the author.Figure 4 - Plume on right aft SRB (NASA, Public Domain), highlighting by the author.right76200000aerodynamic stresses are placed on the vehicle.
Immediately before max Q, a plume started showing in the booster, and the booster telemetry system showed a decrease in inner pressure, which would be consistent with a hole in the motor casing, as shown in Figure 4.
A few seconds later, a pressure decrease was shown on the external fuel tank.
After that, the right-hand SRB separated from the vehicle while still under thrust from itself and the left SRB, causing the vehicle to yaw violently to the left.
The external fuel tank exploded, and the vehicle broke up due to aerodynamic forces.
The crew compartment was relatively intact at this point and continued on a ballistic upward trajectory.
Debris from the explosion and breakup, including the crew compartment fell to the ocean.
Investigation findings
Event Chain
The root cause of the event was the decision to launch against the recommendations of SRB engineers and orbiter engineers. While the ice is not known to have had any effect on the accident, a decision to postpone launch due to ice debris impact or ingestion concerns could still have saved the vehicle and crew.
Of note, there was an initial hypothesis that the TDRS satellite might have activated its engine while inside the payload bay, which was quickly dismissed as this engine was one of the first pieces of debris to be recovered CITATION Nav88 \l 11274 (Naval Sea Systems Command, 1988).
Immediately after SRB start, the forces applied to the cold rubber seals caused them to deform and crack, allowing hot gasses to flow past the O-rings and erode them. This caused the initial puffs of gray gas seen upon liftoff, as the O-ring and sealant grease burned CITATION New86 \l 11274 (New York Times, 1986).
One of the components of the solid rocket fuel is aluminum, and small pieces of molted aluminum temporarily plugged the gap and allowing the vehicle to fly for the first minute or so.
04506595Figure 5 - Recovered debris showing motor case hole with burn marks (NASA, Public Domain)Figure 5 - Recovered debris showing motor case hole with burn marks (NASA, Public Domain)left1264920As the aerodynamic loads on the vehicle increased and before max Q this temporary plug failed, allowing combustion gasses to streak past the O-rings and quickly erode a large hole in the SRB casing (Figure 5). This caused the loss of pressure seen in the SRB, and the fire also damaged the external fuel tank.
Eventually, the damage to the fuel tank caused it to explode and separate from the orbiter.
At this point, the entire vehicle broke up due to the aerodynamic forces and the explosion.
Contributing Factors
Contributing factors were the decision to launch in weather conditions that were outside the demonstrated envelope, the inability of solid rocket engines to be shut down after ignition, the design of the orbiter vehicle that did not include ejection seats or an alternate mechanism of escape, the culture at NASA that emphasized launch cadence (colloquially called go fever), and the design of the SRB’s themselves.
Lessons learned
After the accident, a presidential commission (The Rogers Commission, whose report is one of the main sources used in this paper) was established.
They investigated the disaster and produced a report which explained the causes of the accident and included a series of recommendations, which were mo