Up, up the Long, Delirious, Burning Blue

STS-51-F launched on this date in '85.  Most folks probably don't remember the mission, so let's turn to Dark Star: A New History of the Space Shuttle:

The launch hiccup—the failure of a heat sensor that resulted in the premature automatic shutdown of one of the three Space Shuttle Main Engines (SSMEs)—was a peculiar form of emergency: serious enough to warrant special contingency measures but relatively tame in impact. In the event that one SSME failed, the shuttle would still reach Earth orbit, but lower than planned. “ 

‘Abort to orbit,’ it was called at the time,” the Post noted of the incident. In a space program that had, until that point, been relatively free of well-publicized in-flight mishaps, the failure was both a troubling warning and a metaphor for the Space Transportation System (STS). Although giving the appearance of an operational infrastructure (deploying satellites and conducting scientific work), the space shuttles’ flights from 1981 to 1986 were marred by a series of worrisome problems. 

The problem that struck STS-51F came as little surprise to those who designed and operated the shuttle: the three main engines mounted at the rear of the orbiters operated under unprecedented pressure, using one of the most energetic propellant combinations available: liquid hydrogen and liquid oxygen, each chilled to hundreds of degrees below zero. Unlike previous engines using this combination of propellants, the SSMEs were intended to be reusable for up to 100 flights, a level of performance never expected from a propulsion system devised to work for only a few minutes. 

The National Aeronautics and Space Administration (NASA) had hoped that the engines would require little maintenance between flights, but as problems mounted, the engines required almost complete disassembly and recertification before each flight, an expensive process representative of the tremendous risks that NASA sought to control. On July 29, 1985, though, Challenger dodged a bullet: it had not failed, but neither had it quite succeeded. Procedures intended to compensate for problems had worked, but the abort had left the orbiter where nobody wished it to be. 

Abort to Orbit (ATO) was one of several contingencies scripted by NASA in the event that the shuttle suffered a serious malfunction on launch. Astronauts, to the extent possible, trained for these aborts and carried printed procedure books in the cockpit to perform the often-complex steps required for each. Each abort mode was keyed to a failure of the shuttle’s propulsion system at various points in the flight, from a relatively late, partial failure (ATO) to more crippling early failures of the main engines or solid rocket boosters (SRBs). 

A more profound propulsion system problem (or inflight emergency) required an Abort Once Around (AOA), in which the shuttle, having limped into too low an altitude to sustain multiple revolutions around the Earth, would reenter the atmosphere and land after a single ninety-minute circumnavigation. A more disabled shuttle unable to enter orbit could, alternatively, coast on a suborbital trajectory to Transoceanic Abort Landing (TAL) on a predesignated airstrip several thousand miles east of the launch site in Florida. 

More extreme and most difficult to execute would have been a Return to Launch Site (RTLS) abort, which would have been the earliest option available to the crew. The crew would jettison the shuttle’s boosters after they burned out and fire the SSMEs to try to loop the shuttle in a return trajectory that would place it on a path to land on the runway at NASA’s Kennedy Space Center (KSC). Astronauts regarded this abort mode as impossible to execute: NASA had considered attempting it during an early shuttle test flight, but astronauts refused, finding the abort more dangerous to fly than an orbital mission. 

Just presaging what would come:

The space shuttle was, simply, only half-complete: safety systems intended for the craft were shed during its tortuous development...

The peculiar dangers that the Challenger and Columbia astronauts experienced were not a feature of spaceflight generally. Rather, they were caused by specific flaws manufactured into a vehicle by engineers who knew about better alternatives and hoped the vehicles would never fly long enough to be undermined by the compromises they had made. 

The Thrust-Assisted Orbiter Shuttle (TAOS) configuration that NASA selected in 1972 lacked robust propulsion technologies, redundancies, and safety systems that would protect a crew in the event of trouble; that is what had made it cheap and why it was chosen over safer vehicles that would have cost twice as much and employed liquid-fueled boosters, escape pods, and configurations that generally offered lower risk. While NASA publicly insisted that the shuttle was safe, even the engineers and analysts who developed the TAOS configuration believed that the shuttle would be redesigned to improve its safety. 

Challenger’s loss appeared to stem principally from the fact that these upgrades came too late; indeed, most never came at all. A second fatal accident involving the orbiter Columbia in 2003 similarly failed to derail the space shuttle program, despite new evidence that the shuttle was even more fragile than the public believed. 

It's well-known that I still love the beautiful, compromised machine, but it was a fucking deathtrap all the same.  One hopes we learned those lessons written in blood as we continue to reach for the stars.

Selah.