Abort mode one-alpha

The first 42 seconds of the flight up to a height of about three kilometres was flown in abort mode one-alpha. This meant that in an abort, the escape tower above the command module would fire its large solid-fuelled motor to quickly pull the CM up and away from the service module and the rest of the stack below. The LHT included a small sideways-firing rocket motor at the Lop, called the pitch control motor, whose function was to steer the CM eastward out over the ocean to ensure that it would not subsequently descend into the conflagration caused by the destruction of its launch vehicle. Safely clear, the CM would dump its manoeuvring fuel (nasty, toxic, highly corrosive stuff that would otherwise present a danger to the recovery forces), jettison the complete escape system both Lower and boost protective cover – followed by the forward heatshield in order to deploy its parachutes and make a normal landing in the ocean.

At the centre of the decision to abort was the commander. From the launch pad to orbit, he closely monitored various lights and displays on the panel that supplied him with whatever information was relevant to making that decision. All the equipment that fed these displays, and which sensed whether an emergency was imminent, was called the emergency detection system (EDS). It was decided that he would not react to a single cue. lest it be spurious; but if two cues from the EDS called for an abort, this was sufficient indication for him to twist the T-handle in his left hand counterclockwise to activate the appropriate sequence to abandon the malfunctioning launch vehicle. There was also a set of conditions that could initiate an automatic abort. The idea of ending a half-billion-dollar mission at the behest of a few’ bits of hardware necessitated detection systems that were triple-redundant and which were required to ‘vote’ electronically for an abort. The automatic portion of the EDS was switched off once the rocket was out of the densest part of the atmosphere. Once aerodynamic forces were left behind, situations could not develop so rapidly.

The EDS was responsible for lighting a cluster of indicators that showed whether each engine was running at full thrust, whether the rocket was veering Loo fast and whether the Saturn’s guidance system really knew which way was up. In the latter case, from Apollo 11 onwards, if the commander saw that the Saturn was incapable of guiding itself, he had the option of twisting the T-handle clockwise to pass control of the entire rocket to the spacecraft’s computer, and if that was also failing then he could manually guide it to orbit. Another prominent light informed him when launch control in Florida, or the range safety officer, also in Florida, or mission control in Houston, believed an abort was advised. A gauge that normally showed the state of the spacecraft’s main engine for the rest of the mission was pressed into service by the EDS to show the rocket’s angle-of-attack; that is. whether it was moving cleanly through the air with no tendency to slip sideways – a condition that could impose such aerodynamic stress as to cause the break-up of the vehicle’s structure.