It was 11:39 am (EST) on January 28, 1986 when the Space Shuttle Challenger took off to face its tenth mission, which only after 73 seconds of flight was also the last.
The mission was the STS-51-L, 25th of the NASA Space Shuttle Program, the take-off from Launch Complex 39 (Launch Pad 39A) of the Kennedy Space Center was particularly awaited by the public, as aboard the Challenger, for the Teacher in Space project, the first teacher trained for a space flight was found.
The crew consisted of seven members: Mission Commander Dick Scobee; Pilot Michael John Smith; mission specialists Judith Resnik, Ellison Onizuka, Ronald McNair and the two cargo specialists Gregory Jarvis and Christa McAuliffe, the latter being the selected teacher who was to deliver the first science lesson from Space.
Even before the departure of the Space Shuttle, NASA engineers had encountered many complications, in fact, the day scheduled for the launch was initially set for January 22 but following the delay of the previous mission, the STS-61-C , and the adverse weather conditions continued to be postponed from day to day.
Precisely because of this constant postponement, however, it was decided to proceed with the launch on January 28, despite the weather conditions not yet entirely optimal.
After a long wait, the take-off procedures could finally be started. The Shuttle was essentially composed of three subsets: the Orbiter Vehicle (OV), in which the astronauts resided, which has three separate propulsion systems, a main propulsion system consisting of three cryogenic rocket engines (SSME), a system orbital maneuvering (OMS) and attitude control motors (RCS); two Solid Rocket Boosters (SRB) and the External Tank (ET) which basically had the task of powering the three main engines of the Orbiter.The operations before and during take-off seemed to be proceeding well, as per protocol, at the six seconds before launch, the three main engines of the Orbiter (SSME) started up first, which went from 100% performance to 104% instantly in which the Shuttle left the launch pad, followed by the ignition of solid fuel rockets (SRB). The Shuttle was secured to the ramp through blocks that are intended to keep it firmly and were removed by explosive charges, once detached from the ramp, the Challenger was officially in flight and five seconds from the start of the launch was declared by the Data Processing Systems Engineer “Liftoff confirmed”.
During this part of the take-off the SSMEs had to slow down to prevent the aerodynamic forces in the lower atmosphere from damaging or even tearing the Shuttle, after almost thirty-six seconds from launch the performance of the cryogenic rockets had decreased up to 65% to reach the speed limit.
The onset of the problems occurred once Mach 1 was exceeded, after about fifty seconds, when the nacelle was almost in the vicinity of the max q point, that is the point of maximum aerodynamic pressure on the vehicle (about 34 KPa). in these moments that the Shuttle had to face the most violent wind cut in the history of space flight. These violent gusts of wind brought to light complications that had occurred during take off, complications which, however, were unfortunately discovered only after the disaster.
From the analysis of the launch videos it was noticed that almost from instant zero there is an emission of dark gray smoke near the coupling point of the right solid propellant rocket to the external tank, a trail of smoke visible for the next four seconds; the leak was caused by the strong pressure, this had destroyed the weld present between two sections of the right SRB, although it was an important leak, the structure was built in such a way as to be able to deal with it thanks to the presence of O-rings, mechanical seals in rubber, the primary O-ring should have intervened, in fact, sealing the hole present but due to the excessive frost this had practically lost all its elastic properties, but, thanks to the principle of redundancy, which in the aerospace field is basis of the safety of each vehicle,
The gusts of wind encountered by the Shuttle subjected it to a transverse force causing strong fluctuations that split the layer of oxide present in the gash, the internal pressure of the right SRB, at that point, began to decrease due to the leak in the junction.
At the spot where smoke had previously been spotted a well-defined plume of fire began to form which quickly moved to the outer tank changing shape, this was a clear sign that there was a leak in the liquid hydrogen tank in the portion. lower than ET, as a consequence also the pressure of the external liquid hydrogen tank begins to drop rapidly, indicating a considerable leak.
The Space Shuttle flight control system attempted to act to counteract the forces caused by the fire, shifted the thrust vector of the left rocket to counter the yaw resulting from the flaw in the right rocket resulting in a reduction in the thrust force of the right rocket. ‘last and the main engine nozzle rotated under the control of the computer to compensate for the thrust imbalance produced by the rocket; despite this, the consequences of the flare-up of the flames are now too many to be countered and in fact right at the junction between the right SRB and the external tank, where there was the gash, the detachment took place, everything happened in a fraction of a thousandth of a second , the aft dome of the liquid hydrogen tank burst,
This was the instant in which all the structures gave way, almost simultaneously, in fact, following the disintegration of the external tank, the Challenger (which was traveling at Mach 1.92 at 14,000 meters above sea level) was completely engulfed in flames and veered from the correct order, breaking into a thousand pieces.
The two SRBs, on the other hand, broke apart and continued to travel independently as they were structures capable of withstanding greater aerodynamic loads.
Investigators are not sure when the death of the crew occurred, they tried in every way to reconstruct the facts by analyzing the parameters of altitude, speed and pressure in order to understand if they could be tolerated by the human body, but they could not find many answers , the conclusion came on July 28, 1986, when Admiral Righard H. Truly published a report by biomedical specialist Joseph P. Kerwin, who following further investigation finally stated that the cause of death of the Challenger astronauts could not be determined. with certainty as the forces to which the crew had been subjected during the rupture of the Orbiter were not sufficient to cause death or serious injuries,However, it is possible that the crew lost consciousness in the seconds following the breakdown of the Orbiter due to the loss of pressure in flight of the cabin in which it resided, unfortunately the sudden impact that this had on the surface of the ocean canceled the evidence of the damage that occurred in the seconds after the explosion.
Following this accident, it was wondered if the crew could have survived with the use of ejection seats, present in previous missions, but it was found that in any case not all the crew members would be able to escape from the cockpit, as this depended on their position; after the loss of the Challenger a new emergency rescue system was nevertheless designed but which, given the particular conditions in which the Shuttle found itself, would not have been able to guarantee an escape route for the astronauts.
Everything that has been described, for those who at that moment had their eyes turned towards the sky, for the relatives of the victims, for the proud pupils of their teacher, lasted only an instant at their sight, that seventy-third second that will not be never forgotten.