The Mammoth Book of Space Exploration and Disasters

Easier, but no less elegant, was the procedure for jettisoning the LEM. Before a lunar module was released on a normal mission, the astronauts would close the hatch in both the lander itself and the command module, sealing off the tunnel from the cockpits of either ship. The commander would then open a vent in the tunnel, bleeding its atmosphere into space and lowering its pressure to a near vacuum. This would allow the twin vehicles to separate without an eruption of air blowing them uncontrollably apart.

During the flight of Apollo 10 last spring, the controllers had experimented with the idea of leaving the tunnel partially pressurized, so that when the clamps that held the vehicles together were released, the LEM would pop free of the mother ship, but in a slower, more controlled way than it would if the passageway between the two spacecraft was fully pressurized. This method, the controllers figured, would come in handy if a service module ever lost its thrusters. Now, a year later, a service module had done just that and the flight dynamics officers were glad they had the maneuver tucked away in the contingency flight-plan books. Yesterday, the procedure had been explained to Jack Lousma, and the Capcom had proudly relayed it up to Lovell.

“When we jettison the LEM,” he had reported, “we’re going to do it like we did in Apollo 10 – just let the beauty go.”

Lovell had radioed back a far more sceptical “OK.”

Finally Odyssey’s guidance system would have to be realigned for reentry. Normally this angle was checked visually against the arc of the horizon. But Odyssey would arrive on the night time side when the planet was only visible as a dim mass.

But Chuck Deiterich, the Gold Team RETRO, had an idea. “Fellows,” he said to the other flight dynamics men in the staff support room, “tomorrow around lunchtime we’re going to have a problem – specifically, we’re going to be trying to check our attitude against a horizon that isn’t there.”

He turned to the blackboard and drew a large downward arc representing the edge of the Earth. “Now while the Earth will be invisible, the stars will always be there” – he tapped a few chalk dots onto the board above his horizon – “but as fast as the ship will be moving, there might not be time to determine which ones we’re looking at.” He eliminated his stars with a sweep of his eraser.

“Of course, what we’ll also have out there,” Deiterich said, “will be the moon.” He drew a neat little moon above his ragged Earth. “As the spacecraft arcs around the planet and gets closer and closer to the atmosphere, the moon will appear to set.” Deiterich drew another moon below his first one, then another and another and another, each moving closer to the chalk horizon, until the last one vanished partially behind it.

“At some point,” he said, “the moon will set behind the Earth and disappear. It will disappear at the same time whether it’s daytime below or nighttime, whether we can see the horizon or can’t see it.” The RETRO touched the corner of his eraser to the blackboard and carefully erased only the long arc that represented the horizon, leaving all his moons behind. He pointed to the one moon that was half obscured by the horizon that was no longer there.

“If we know the exact second the moon is supposed to disappear, and if our command module pilot tells us it indeed disappears, then gentlemen, our entry attitude is on the mark.”

The temperature in the LEM was so low that the astronauts’ breath fogged the windows, cold making sleep almost impossible.

Deke Slayton was chief astronaut and was deeply concerned about the crew. He had been monitoring Apollo’s power consumption and was confident there was enough power left to power up the LEM. He called the flight director on duty, Milt Windler, to ask if the LEM could be brought back on line early if enough power had been saved. This was confirmed.

Windler called Jack Knight at the TELMU console, who in turn contacted his backroom. Knight’s assistants put him on hold, conducted some quick-and-dirty amp projections, and came back with the good word: the crew was free to switch on their ship.

“Jack, they’re go for power-up,” the backroom called to the TELMU.

“Flight, he can power up if he wants,” the TELMU called to Windler.