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Disaster on the Dark Side of the Moon

THE ASTRONAUTS OF APOLLO 13 WERE 320,000 KM (200,000 MILES) FROM EARTH WHEN AN EXPLOSION CRIPPLED THEIR SPACECRAFT. FORCED INTO THE LUNAR MODULE TO CONSERVE POWER AND OXYGEN, THEY BATTLED PROBLEM AFTER PROBLEM FOR NEARLY FOUR DAYS AS THEY SWUNG ROUND THE MOON AND RETURNED HOME.

DATE: 1970 SITUATION: SPACE DISASTER CONDITION OF CONFINEMENT: LOSING OXYGEN IN LUNAR MODULE DURATION OF CONFINEMENT: 3½ DAYS MEANS OF ESCAPE: IMPROVISED REPAIRS, METICULOUS PLANNING NO. OF ESCAPEES: 3 DANGERS: OXYGEN STARVATION, EXPLOSION, FREEZING TO DEATH EQUIPMENT: A DAMAGED SPACECRAFT

The Apollo 13 prime crew onboard USS Iwo Jima following splashdown. From left to right: Lunar Module pilot, Fred W. Haise, Command Module pilot, John L. ‘Jack’ Swigert Jr and Commander, James A. Lovell.

The mission

Apollo 13 was launched on 11 April 1970. It was to become the third manned spacecraft to land on the Moon, with a mission to explore formations near the 80 km (50 mile) wide Fra Mauro crater. The flight was commanded by James A. Lovell with John L. ‘Jack’ Swigert as Command Module pilot and Fred W. Haise as Lunar Module pilot.

There was a small problem on takeoff when an engine shut down two minutes early during the second stage boost. But four other engines burned longer to compensate, and the craft reached orbit successfully.

Then, on 14 April 1970, nearly sixty hours into the mission, the astronauts were 321,860 km (199,995 miles) from Earth when they heard a loud bang.

The explosion

At first the crew thought a meteoroid had hit them. As well as the noise of an explosion, the electrics were going haywire and the attitude control thrusters had fired.

In fact, a short circuit had ignited some insulation in the Number 2 oxygen tank of the Service Module. The Service Module provided life support, power and other systems to the Command Module, which held the astronauts as they travelled to and from lunar orbit. The Lunar Module was a separate, though connected, craft that would be used to ferry the men to the lunar surface and back.

The fire caused a surge in pressure that ruptured the tank, flooding the fuel cell bay with gaseous oxygen. This surge blew the bolts holding on the outer panel, which tore off free and spun into space, damaging a communications antenna. Contact with Earth was lost for 1.8 seconds, until the system automatically switched to another antenna.

The shock also ruptured a line from the Number 1 oxygen tank. Two hours later all of the Service Module’s oxygen supply had leaked into the void.

As the Command Module’s fuel cells used oxygen with hydrogen to generate electricity, it could now only run on battery power. The crew had no option but to shut down the Command Module completely and move into the Lunar Module. They would then use this as a ‘lifeboat’ for the journey back to Earth before rejoining the Command Module for re-entry.

As for the mission, the Service Module was so badly damaged that a safe return from a lunar landing was impossible. These men would not be landing on the Moon.

320,000 km from home

The Flight Director immediately aborted the mission. Now he just had to get the men home. The quickest way would be a Direct Abort trajectory, using the Service Module engine to essentially reverse the craft. But it was too late: the craft was already within the Moon’s gravitational sphere of influence making it harder to ‘reverse’. The engine could also have been damaged in the explosion and restarting might cause an even worse disaster.

So Mission Control opted for a ‘free return’, essentially using the Moon’s gravity to hitch a ride and slingshot them back towards Earth.

First, Apollo 13 needed to be realigned; it had left its initial free return trajectory earlier in the mission as it lined up for its planned lunar landing. Using a small burn of the Lunar Module’s descent propulsion system, the crew got the spacecraft back on track for its return journey.

Now they started their nerve-shredding journey round the dark side of the Moon. It was a trip that would demand incredible ingenuity under extreme pressure from the crew, flight controllers, and ground crew if the men were to make it back alive.

More problems

The Lunar Module ‘lifeboat’ only had enough battery power to sustain two people for two days, not three people for the four days it would take the men to return to Earth.

The life support and communication systems had to be powered down to the lowest levels possible. Everything that wasn’t essential was turned off. The drama was being shown on TV but no more live broadcasts were made. Power levels were dropped so low that even voice communications were difficult.

Removing carbon dioxide from the air was another serious problem. Lithium hydroxide normally did the job but there wasn’t enough of it. The only additional supply they had was in the Command Module, and its canisters were cube-shaped whereas the Lunar Module’s sockets were cylindrical. It looked like the men would suffocate before they made it back.

In one of the most inspired brainstorming sessions of all time, engineers on the ground got out all the kit that the crew would have available. They then improvised a ‘mailbox’ that would join the two incompatible connections and draw the air through.

The air was becoming more poisonous with every breath as the astronauts followed the meticulous radio instructions to build the Heath Robinson repair. Amazingly, it worked. They would have enough clean air.

But they weren’t out of the woods yet.

They needed to re-enter the atmosphere in the Command Module, but it had been totally shut down to preserve its power. Would it start up again? Its systems hadn’t been designed to do this.

Again, engineers and crew on the ground had to think on their feet if their friends were to live. They invented an entirely new protocol that would power the ship back up with the limited power supply and time available without blowing the system. They also feared that condensation in the unpowered and freezing cold Command Module might damage electrical systems when it was reactivated.

It booted up first time.

Back to Earth with a splash

With Apollo 13 nearing Earth, the crew jettisoned the Service Module and photographed the damage for later analysis. Then they jettisoned the redundant Lunar Module, leaving them sitting tight in the Command Module Odyssey as they plunged into the atmosphere.

The enormous heat of re-entry ionized the air around the capsule causing a total communications blackout. For four and a half minutes the world held its breath. Were the men all right? Had the heat shield been damaged in the explosion? Was the craft now disintegrating in the upper atmosphere?

There must have been a few whoops of joy in Mission Control when the radio finally sparked back into life. Odyssey splashed down in the Pacific Ocean southeast of American Samoa and just 6.5 km (4 miles) from the recovery ship, USS Iwo Jima. The crew were generally in good shape. And they were home.