Posted by schoen 5 hours ago
Some 2015 coverage of this mission:
https://www.americaspace.com/2015/07/25/going-to-spain-30-ye...
https://www.americaspace.com/2015/07/26/cola-and-solar-wars-...
Just two missions after Challenger, the orbiter experienced tile damage much like Columbia did 15 years later. It left an entire field of damage all the way down one side of the orbiter. They inspected under the orbiter using the canadarm as much as they could, and found some early indications of tile damage. Mission Control refused to use a high-resolution unencrypted camera to image under the orbiter due to the classified nature of the mission payload, instead using a lower resolution encrypted link, and dismissed the damage as video artifacts.
The crew wasn't happy at all at this assessment and seriously believed they were going to die on reentry. Mike Mullane believed he would see hot aluminum streak up the windshield like raindrops. Commander Hoot Gibson advised the crew there was no point in "dying all tensed up". Even if Mission Control had deemed this to be inevitable, it was not at all clear how quickly or even if NASA could process another orbiter and evacuate them in time.
The shuttle's wings have a combined elevator-aileron called an "elevon"; when both are in the same direction, they focus as an elevator (controlling pitch), and if they are in opposite directions, they function as an aileron (controlling roll). On reentry, Gibson kept his eyes glued to an elevon gauge to see if aerodynamic forces from a disintegrating airframe were forcing the onboard computer to roll the shuttle, creating a difference in degrees across the elevons. If they had deviated more than a few degrees, he planned on cussing out NASA before he and the rest of the crew died.
Fortunately, the shuttle made it back safely, but the damage was far worse than anyone anticipated. The foam strikes had spared the RCC leading edge panels that would eventually doom Columbia, however, nearly one half of the bottom of the shuttle had some degree of tile damage, and one had gone missing completely in a critical section. That section, by the grace of god, had a heavier plate welded to the airframe that was used as part of a communications antenna. One tile missing anywhere else, and the shuttle would have been destroyed.
As I understand it the energy management of an RTLS is tenuous because, ultimately, the orbiter is an unpowered glider (with a glide ratio similar to a brick). The limits of stress on the orbiter's airframe are a factor, too.
The orbiter's mass, energy (altitude), and downrange position all have to be in a reasonably tight envelope to make the landing without coming up short or overshooting (there's only so much energy you can bleed off doing S turns).
John Young[1] described an RTLS abort working thru "continuous miracles, interspersed with acts of God".
Somebody made a fun (if you like this kind of stuff) simulation of an RTLS abort[2] in Kerbal Space Program.
[0]: https://en.wikipedia.org/wiki/Space_Shuttle_abort_modes#Retu...
STS-51-F is the only exercised launch abort, and the Challenger was the orbital vehicle.
STS-51-L, which occurred the following year, is the famous Challenger disaster.
Originally, the numeral in the mission designation indicated the federal fiscal year of the mission and the launch site (51 being 1985 and launch site 1 (KSC, 2 would have been used for Vandenberg). The letter indicated the sequential launch index, so A=1m, B=2, etc.
This was originally done after STS-12. Superstition around Apollo 13 created the desire to avoid an STS-13. The numbering system returned to a strictly sequential schema after STS-51-L, with STS-26.
Incredible that human action during ascent (when everything is usually automated) potentially saved a crew. One of probably dozens of cases, is my guess.
STS still has the record for most astronauts killed. I don't believe we will surpass that grim record until Starship starts carrying humans.
They know it’s going to be tricky to make landings safe for crew. Nobody’s in a rush to fly people.