The Challenger Disaster
Posted by Nishant on October 13th, 2018
What went wrong?
Challenger was the name of one of NASA’s space shuttle. The purpose of the shuttle was to make multiple trips and launch satellites into space.
Challenger was one of NASA's greatest triumphs. It was the second shuttle to reach space, in April 1983. It successfully completed nine milestone missions.
But Challenger was also NASA's darkest tragedy. On its 10th launch, on Jan. 28, 1986, the shuttle was torn apart, its parts blew into flames and fell off into the water, killing all of its crew members. And all this happened just 73 seconds after its flight. The accident changed the space program forever.
What exactly happened?
Challenger was on its 10th mission in space, with the aim of deploying Tracking and Data Relay Satellites and observe Halley’s Comet. Challenger was at the time the most-flown orbiter in NASA’s fleet, setting numerous records and leaving behind a legacy of education, inspiration, and safety.
The mission experienced trouble at the outset, as the launch was postponed for several days. On the night before the final launch day, central Florida was swept by a severe cold wave that deposited thick ice on the launch pad.
Some engineers warned higher officials regarding this and that this might be a problem, but the warning went unheeded.
All appeared to be normal on the morning of the launch, when hundreds on the ground, including the families of astronauts on board, witnessed an explosion just 73 seconds after liftoff, at an altitude of 14,000 meters (46,000 feet). Millions more watched the wrenching tragedy unfold on live television.
Why? Let us understand basic composition of any space shuttle - any Space Shuttle consists of three major components: the Orbiter which houses the crew; a large External Tank that holds fuel for the main engines; and two Solid Rocket Boosters which provide most of the Shuttle's lift during the first two minutes of flight. All of the components are reused except for the external fuel tank, which burns up in the atmosphere after each launch.
This happened because the space shuttle's external fuel tank collapsed, releasing all its liquid hydrogen and liquid oxygen propellants. As the chemicals mixed, they ignited to create a giant fireball thousands of feet in the air.
Note at this point the shuttle itself was intact - and all crew members were safe and sound.
But due to the explosion in the fuel tank, the shuttle became unstable and was trying very hard to stay on its path, because it sensed something very irregular was happening underneath it.
But finally it broke off the tank and—moving so fast but without its boosters and tank—it couldn't tolerate the aerodynamic forces.
The tail and the main engine section broke off. Both of the wings broke off. Big chunks of the shuttle fell out of the sky, and they further broke up when they hit the water with enough force to crush everything inside the cabin.
Debris rained into the Atlantic Ocean for more than an hour after the explosion; searches revealed no sign of the crew.
The tragedy and its aftermath received extensive media coverage and prompted NASA to temporarily suspend all shuttle missions.
And the question that NASA had to answer was - what went wrong?
Shortly after the disaster, President Ronald Reagan appointed a special commission to determine what went wrong with Challenger and to develop future corrective measures. Headed by former secretary of state William Rogers, the commission included former astronaut Neil Armstrong and famous scientist - Richard Feynman.
It was a cold morning on the day of Challenger’s launch - temperatures dipped below freezing.And some parts making the shuttle - the O-rings in particular, were unsafe to use at such temperatures.
To make things worse - NASA had no prior experience of launching a shuttle in temperatures as cold as on the morning of Jan 28, 1986. The coldest temperature of the previous launch was 20 degrees warmer.
Their investigation revealed that the O-ring seal on Challenger’s solid rocket booster, had become brittle in the cold temperatures, and failed at doing its function - seal the joints so tightly they would prevent violently hot gases from escaping as spears of flame. Flames then broke out of the booster and damaged the external fuel tank, causing the spacecraft to explode and disintegrate.
Let us now see what these O-rings were - and what made them “brittle”.
Any space shuttle consists of what is known as solid-fuel rocket boosters (SRBs). They are large solid propellant motors used to provide thrust in spacecraft launches during the initial launch.
In the booster rocket skin, there were grooves where structures called o-rings, made of rubber, were supposed to fit in. Note that two o-rings - primary and secondary were added to add double protection from leaking. Just in case first o-ring couldn’t do its work, the second would be sufficient.
Inside this booster rocket skin, a structure called tang was put in to avoid the fuel to leak.
Important note - the o-rings do not initially seal the structure - their purpose is to start the work when an initial gas leak is observed - by expanding. When the initial bit of gas hits the first primary o ring, that pressure pushes the o-ring into the little space between the flange and the tang. And this makes the seal.
Thus the o-ring has to move dynamically at the time of ignition to be able to make the seal. And the requirement for it to move quickly - is where temperature comes in. At lower temperature, the o-rings lose flexibility - failing to expand and prevent the leak.
Famously, scientist Richard Feynman, a member of the commission, demonstrated the O-ring flaw to the public using a simple glass of ice water.
The O-rings were never tested in extreme cold in the first place. Some Thiokol and NASA engineers did raise the problem on the morning of the launch, which went unheard.
The commission also found that Morton Thiokol, the company that designed the solid rocket boosters, had ignored warnings about potential issues. NASA managers were aware of these design problems but also failed to take action.
But the pressing question is - why was the Challenger launched that day, in spite of many engineers raising a concern against it? Almost everyone knew that the o-rings are not designed to work at low temperatures, so why did they go ahead with it anyway!?
challenger had already received a lot of funding which it blew on celebrity coverage and attracting media on the project rather than actually improving the shuttle.. in addition, a project of America's air force was shut down and its funding was also given to challenger, as it was attracting media. So when challenger's launch was getting delayed, people got restless and NASA has no explanation in return and had also stopped receiving any more funds.
As Richard Feynman correctly puts, the Challenger disaster was a man-made disaster that didn’t have to happen. The thinking of NASA’s and Thiokol’s officers that “nothing happened so nothing will happen” took the lives of 7 crew members.
But along came many learnings as well - after the accident, all shuttles were grounded until 1988. The problem with o-rings was fixed - an additional heating pad was fit into the system, to make sure that they remain warm enough to function properly, no matter how cold it gets outside.
They also changed many policies and management structure, to ensure that a warning against a launch will never again go unheard.
Traveling to space is one of the hardest and dangerous things humans have ever done - and space companies have been trying to do it right. But the sad truth is that we can learn and minimize risk - but we may not ever be able to do without it.
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