The Hindenburg and Challenger Disasters

The LZ-129 Hindenburg and her sister-ship LZ-130 "Graf Zeppelin II" were the two largest aircrafts ever built. The Hindenburg was named after the President of Germany, Paul von Hindenburg. It was a brand new all-aluminum design: 245 m long, 41 m in diameter, containing 211 890 m3 of gas in 16 bags or cells, with a

Blimp That Caught Fire
Fig. 2.6 On May 6, 1937, at 19:25 the German zeppelin Hindenburg caught fire and was utterly destroyed within a minute while attempting to dock with its mooring mast at Lakehurst Naval Air Station in New

Jersey. Of the 97 people on board, 13 passengers and 22 crew members were killed. One member ofthe ground crew also died, bringing the death toll to 36.

useful lift of 112 000 kg, powered by four 820 kW engines giving it a maximum speed of 135km/h. It could carry 72 passengers (50 transatlantic) and had a crew of 61. For aerodynamic reasons the passenger quarters were contained within the body rather than in gondolas. It was skinned in cotton, doped with iron oxide and cellulose acetate butyrate impregnated with aluminum powder. Constructed by Luftschiffbau Zeppelin in 1935 at a cost of £500 000, it made its first flight in March 1936 and completed a record double crossing in five days, 19 h, 51 min in July.

The Hindenburg was intended to be filled with helium but a United States military embargo on helium forced the Germans to use highly flammable hydrogen as the lift gas. Knowing of the risks with the hydrogen gas, the engineers used various safety measures to keep the hydrogen from causing any fire when it leaked, and they also treated the airship's coating to prevent electric sparks that could cause fires.

The disaster [28] is remembered because of extraordinary newsreel coverage (Fig. 2.6), photographs, and Herbert Morrison's recorded radio eyewitness report from the landing field. Morrison's words were not broadcast until the next day. Parts of his report were later dubbed onto the newsreel footage (giving an incorrect impression to some modern eyes accustomed to live television that the words and film had always been together). Morrison's broadcast remains one of the most famous in history - his plaintive words "oh the humanity" resonate with the memory of the disaster.

Herbert Morrison's famous words should be understood in the context of the broadcast, in which he had repeatedly referred to the large team of people on the field, engaged in landing the airship, as a "mass of humanity". He used the phrase when it became clear that the burning wreckage was going to fall onto the ground, and that the people underneath would probably not have time to escape it. It is not clear from the recording whether his actual words were "Oh, the humanity" or "all the humanity".

There had been a series of other airship accidents (none of them Zeppelins) prior to the Hindenburg fire, most due to bad weather. However, Zeppelins had accumulated an impressive safety record. For instance, the Graf Zeppelin had flown safely for more than 1.6 million km (1 million miles) including making the first complete circumnavigation of the globe. The Zeppelin company was very proud of the fact that no passenger had ever been injured on one of their airships.

But the Hindenburg accident changed all that. Public faith in airships was completely shattered by the spectacular movie footage and impassioned live voice recording from the scene. Because of this vivid publicity, Zeppelin transport came to an end, marking the end of the giant, passenger-carrying rigid airships.

Questions and controversy surround the accident to this day. There are two major points of contention: (i) How the fire started and (ii) Why the fire spread so quickly.

At the time, sabotage was commonly put forward as the cause of the fire, in particular by Hugo Eckener, former head of the Zeppelin company and the "old man" of the German airships. The Zeppelin airships were widely seen as symbols of German and Nazi power and, as such, they would have made tempting targets for opponents of the Nazis. However, no firm evidence supporting this theory was produced at the formal hearings on the matter.

Although the evidence is by no means conclusive, a reasonably strong case can be made for an alternative theory that the fire was started by a spark caused by static buildup. Proponents of the "static spark" theory point to the following: The airship's skin was not constructed in a way that allowed its charge to be evenly distributed and the skin was separated from the aluminum frame by nonconductive ramie cords. The ship passed through a moist weather front. The mooring lines were wet and therefore conductive. As the ship moved through the moist air the skin became charged. When the wet mooring lines connected to the aluminum frame touched the ground they grounded the aluminum frame. The grounding of the frame caused an electrical discharge to jump from the skin to the grounded frame. Witnesses reported seeing a glow consistent with a St. Elmo's fire.

The controversy around the rapid spread of the flames centers around whether blame lies primarily with the use of hydrogen gas for lift or the flammable coating used on the outside of the envelope fabric.

Proponents of the "flammable fabric" theory [29] contend that the extremely flammable iron oxide and aluminum impregnated cellulose acetate butyrate coating could have caught fire from atmospheric static, resulting in a leak through which flammable hydrogen gas could escape. After the disaster the Zeppelin company's engineers determined that this skin material, used only on the Hindenburg, was indeed more flammable than the skin used on previous crafts. Cellulose acetate butyrate is of course flammable but iron oxide increases the flammability of aluminum powder. In fact iron oxide and aluminum can be used as components of solid rocket fuel or thermite.

Hydrogen burns invisibly (emitting light in the UV range) so the visible flames (see Fig. 2.6) of the fire could not have been caused by the hydrogen gas. Moreover, motion picture films show downward burning whereas hydrogen, being less dense than air, burns upward. Some speculate that the German government placed the blame on flammable hydrogen in order to cast the US helium embargo in a bad light.

Also, the naturally odorless hydrogen gas in the Hindenburg was "odorized" with garlic so that any leaks could be detected, but nobody reported any smell of garlic during the flight or at the landing prior to the disaster.

It is also pointed out that none of those who died were burned by hydrogen. Of the 36 victims, 33 died because they jumped or fell out of the airship, two died of burns from the fabric and diesel fuel, and Allen Hagaman of the ground crew was killed when one of the motors fell on him.

Opponents [30] of the "flammable fabric" theory contend that it is a recently developed analysis focused primarily on deflecting public concern about the safety of hydrogen. These opponents contend that the "flammable fabric" theory fails to account for many important facts of the case.

The space shuttle was developed by NASA between 1972 and 1979. The first launch was April 12th 1981.The total weight of the space shuttle at launch is 2055 ton and the thrust at launch is 32 600 kN allowing the space shuttle to reach orbits of 185 to 965 km. The empty orbiter has a weight of 68 ton and is manufactured by Rockwell. The orbiter itself contains 15 ton of fuel and is equipped with 3 fuel cells of 2-12 kW electric power. The total weight at launch of the orbiter is 126 ton.

The three main engines, from Rocketdyne, of the space shuttle operate with liquid hydrogen and liquid oxygen as fuel and develop a thrust of 1750 kN at launch for about 10 s. The fuel is stored in the external tank from Martin Marietta. The external tank contains 616 ton liquid oxygen (19911) and 102 ton liquid hydrogen (14 5001) and has a total weight of756 tons and an empty weight of 35 ton. The solid rocket boosters (SRB) from Thiokol each contain 503 ton of fuel (16% atomized aluminum powder as fuel, 69.83% ammonium perchlorate as oxidizer, 0.17% iron-powder as catalyst, 12 % polybutadiene acrylic acid acrylonite as binder, 2 % epoxy curing agent) and the total weight (tank + fuel) is 590ton. Each SRB develops a thrust of 13 800 kN and operates for about 120 s.

January 28, 1986, 11:38:00 a.m. EST the first shuttle lift-off was scheduled from Pad B. Launch set for 3:43 p.m. EST, Jan. 22, slipped to Jan. 23, then Jan. 24, due to delays in mission 61-C. Launch reset for Jan. 25 because of bad weather at transoceanic abort landing (TAL) site in Dakar, Senegal. To utilize Casablanca (not equipped for night landings) as an alternate TAL site, T-zero moved to morning lift-off time. Launch postponed a day when launch processing unable to meet new morning lift-off time. Prediction of unacceptable weather at KSC led to launch rescheduled for 9:37 a.m. EST, Jan. 27. Launch delayed again by 24h when the ground servicing equipment hatch closing fixture could not be removed from the orbiter hatch. Fixture sawed off and attaching bolt drilled out before close-out completed. During delay, cross winds exceeded return-to-launch-site limits at KSC's Shuttle Landing Facility. Launch Jan. 28 delayed 2 h when hardware interface

Rocket Lift Off Explosion

Fig. 2.7 On January 28, 1986, at 11:38 AM Eastern Standard Time, Challenger space shuttle left Pad 39B at Kennedy space center in Florida for Mission 51-L, the tenth flight of Orbiter Challenger. Seventy three seconds later the space shuttle was com pletely destroyed due to an explosion of the hydrogen tank and all 7 crew members (6 astronauts, 1 civilian) were killed. The solid rocket boosters can be seen speeding away from the gulf of smoke caused by the exploding Challenger.

Fig. 2.7 On January 28, 1986, at 11:38 AM Eastern Standard Time, Challenger space shuttle left Pad 39B at Kennedy space center in Florida for Mission 51-L, the tenth flight of Orbiter Challenger. Seventy three seconds later the space shuttle was com pletely destroyed due to an explosion of the hydrogen tank and all 7 crew members (6 astronauts, 1 civilian) were killed. The solid rocket boosters can be seen speeding away from the gulf of smoke caused by the exploding Challenger.

module in launch processing system, which monitors fire detection system, failed during liquid hydrogen tanking procedures.

The solid rocket boosters (SRB) were ignited, and the thundering noise started. Figure 2.7 shows lift-off and the resulting disaster. Just after lift-off at 0.678 s into the flight, photographic data show a strong puff of gray smoke was spurting from the vicinity of the aft field joint on the right SRB. Computer graphic analysis of film from pad cameras indicated the initial smoke came from the 270 to 310-degree sector of the circumference of the aft field joint of the right SRB. This area of the solid booster faces the external tank. The vaporized material streaming from the joint indicated there was not complete sealing action within the joint.

Eight more distinctive puffs of increasingly blacker smoke were recorded between 0.836 and 2.500 s. The smoke appeared to puff upwards from the joint. While each smoke puff was being left behind by the upward flight of the Shuttle, the next fresh puff could be seen near the level of the joint. The multiple smoke puffs in this sequence occurred at about four times per second, approximating the frequency of the structural load dynamics and resultant joint flexing. As the Shuttle increased its upward velocity, it flew past the emerging and expanding smoke puffs. The last smoke was seen above the field joint at 2.733 s.

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.

At approximately 37 s, Challenger encountered the first of several high-altitude wind shear conditions, which lasted until about 64 s. The wind shear created forces on the vehicle with relatively large fluctuations. These were immediately sensed and countered by the guidance, navigation and control system. The steering system (thrust vector control) of the SRB responded to all commands and wind shear effects. The wind shear caused the steering system to be more active than on any previous flight.

Both the Shuttle main engines and the solid rockets operated at reduced thrust approaching and passing through the area of maximum dynamic pressure of 720 pounds per square foot. Main engines had been throttled up to 104% thrust and the SRBs were increasing their thrust when the first flickering flame appeared on the right SRB in the area of the aft field joint. This first very small flame was detected on image enhanced film at 58.788 s into the flight. It appeared to originate at about 305 degrees around the booster circumference at or near the aft field joint.

One film frame later from the same camera, the flame was visible without image enhancement. It grew into a continuous, well-defined plume at 59.262 s. At about the same time (60 s), telemetry showed a pressure differential between the chamber pressures in the right and left boosters. The right booster chamber pressure was lower, confirming the growing leak in the area of the field joint.

As the flame plume increased in size, it was deflected rearward by the aerodynamic slipstream and circumferentially by the protruding structure of the upper ring attaching the booster to the external tank. These deflections directed the flame plume onto the surface of the external tank. This sequence of flame spreading is confirmed by analysis ofthe recovered wreckage. The growing flame also impinged on the strut attaching the SRB to the external tank.

The first visual indication that the swirling flame from the right SRB breached the external tank was at 64.660 s when there was an abrupt change in the shape and color ofthe plume. This indicated that it was mixing with leaking hydrogen from the external tank. Telemetered changes in the hydrogen tank pressurization confirmed the leak. Within 45 ms of the breach of the external tank, a bright sustained glow developed on the black-tiled underside of the Challenger between it and the external tank.

Beginning at about 72 s, a series of events occurred extremely rapidly that terminated the flight. Telemetered data indicate a wide variety of flight system actions that support the visual evidence of the photos as the Shuttle struggled futilely against the forces that were destroying it.

At about 72.20 s the lower strut linking the SRB and the external tank was severed or pulled away from the weakened hydrogen tank permitting the right SRB to rotate around the upper attachment strut. This rotation is indicated by divergent yaw and pitch rates between the left and right SRBs.

At 73.124 s, a circumferential white vapor pattern was observed blooming from the side ofthe external tank bottom dome. This was the beginning ofthe structural failure ofthe hydrogen tank that culminated in the entire aft dome dropping away. This released massive amounts of liquid hydrogen from the tank and created a sudden forward thrust of about 2.8 million pounds, pushing the hydrogen tank upward into the intertank structure. At about the same time, the rotating right SRB impacted the intertank structure and the lower part of the liquid oxygen tank. These structures failed at 73.137 s, as evidenced by the white vapors appearing in the intertank region.

Within milliseconds there was massive, almost explosive, burning of the hydrogen streaming from the failed tank bottom and liquid oxygen breach in the area of the intertank.

At this point in its trajectory, while traveling at a Mach number of 1.92 at an altitude of 46 000 feet, the Challenger was totally enveloped in the explosive burn. The Challenger's reaction control system ruptured and a hypergolic burn of its propellants occurred as it exited the oxygen-hydrogen flames. The reddish brown colors of the hypergolic fuel burn are visible on the edge of the main fireball. The Orbiter, under severe aerodynamic loads, broke into several large sections which emerged from the fireball. Separate sections that can be identified on film include the main engine/tail section with the engines still burning, one wing of the Orbiter, and the forward fuselage trailing a mass of umbilical lines pulled loose from the payload bay.

The explosion 73 s after lift-off claimed crew and vehicle. The cause of the explosion was determined to be an O-ring failure in the right SRB. Cold weather was a contributing factor. The temperature at ground level at Pad 39B was 36 °F, that was 15 °F colder than any other previous launch by NASA. The last recorded transmission from Challenger was at 73.62 s after launch, when it truly fell apart.

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Responses

  • kristian
    How is the challenger space ship and the hindenburg different?
    8 years ago
  • riku
    How to post a comment on The Hindenburg Airship and The NAZI REGIME?
    8 years ago
  • Monika
    Why 16% atomized aluminum powder (fuel) is used in solid rocket boosters?
    8 years ago
  • elias
    Why hydrogen was used in the challenger?
    6 years ago
  • michelle
    What was the circumference of the hindenburg?
    4 years ago

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