Published: 2016-01-27 17:15:00
Updated: 2016-01-28 07:17:58
Posted January 27
Updated January 28
By Tony Rice
NASA pauses each year during the last week of January to remember the anniversaries of three tragedies in the manned spaceflight program. On Jan. 27, 1967, astronauts Gus Grissom, Ed White and Roger Chaffee were sitting atop the launch pad when a fire broke out in their Apollo capsule killing all three. On Feb. 1, 2003, just 16 minutes from touching down at the Kennedy Space Center, the Space Shuttle Columbia broke apart killing that crew of seven.
For many, the Space Shuttle Challenger disaster stands out in this day of remembrance. Apollo I was in pre-launch testing with only engineers and technicians focused on the event as it unfolded. Columbia was destroyed miles above the Texas-Louisiana border. Challenger is different though. Many in their 30s or 40s have stories of watching the launch in school to see the mission where teacher Christa McAuliffe would travel to space.
Thursday marks the 30th anniversary of the loss of the Space Shuttle Orbiter Challenger and all her crew, 73 seconds into flight of mission 51-L. While traveling at Mach 1.92 at 46k feet, Challenger was enveloped in flame coming from the right solid rocket motor. That flame was made up of liquid hydrogen from the ruptured external tank along with hypergolic propellants that instantly ignited when the reaction control system ruptured.
Contrary to popular belief, the orbiter did not explode. It broke into large sections under severe aerodynamic loads. Those sections emerged from the fireball before plummeting to the Atlantic ocean.
The “Report of the Presidential Commission on the Space Shuttle Challenger Accident” concluded that a seal intended to prevent hot gases from leaking through joints in the right Solid Rocket Booster (SRB) failed. Cameras on the launchpad captured the beginnings of the seal failure less than a second after liftoff. The disaster has since become a case study in engineering safety and ethics.
On the night before the launch, the temperature dropped to 18º F at Cape Canaveral, and ice had accumulated throughout the structures on the launchpad. The air temperature had risen to 36º by launch time, but this was still 15 degrees lower than the coldest previous launch. The o-ring which should have prevented those hot gasses from leaking failed because of those cold conditions.
You may be aware of the air temperature’s role in the disaster, but did you know it wasn’t the only contributing weather condition?
Beginning about 37 seconds after liftoff, the orbiter encountered the first of several high-altitude wind shear conditions lasting nearly 30 seconds. The incident report calls the fluctuations “large” and notes that the SRB leak may have been magnified or reinitiated by the amount of steering required to keep the vehicle on course through wind conditions, the most encountered during any launch to date.
Dr. Mark Salita, one of dozens of engineers interviewed by the Presidential Commission on the Space Shuttle Challenger Accident for input, agreed . He wrote in an American Institute of Aeronautics and Astronautics newsletter, "In the absence of the wind shear, the damaged, but plugged, O-rings probably would have survived the 120 seconds of booster operation without leaking, and the Challenger accident would not have happened."
We’ll never know if calmer conditions aloft would have saved the crew. but it does remind us why launch weather forecasts focus not just on conditions at the launchpad but throughout the vehicle’s path to orbit.