Four Days of Peril Between Earth and Moon

MAN'S fifth mission to the moon was going well, and from more than 200,000 miles out in space Commander Jim Lovell had just wound up a televised tour of the spacecraft. "This is the crew of Apollo 13 wishing everyone there a nice evening," he said. "We're just about ready to close out our inspection of Aquarius and get back for a pleasant evening in Odyssey." Minutes later, the almost idyllic journey of Astronauts Lovell, Fred Haise and John Swigert turned into a heart-pounding nightmare.

Interrupting a conversation between Swigert and a ground controller at the Manned Spacecraft Center in Houston, Lovell suddenly said in a laconic voice: "I believe we've had a problem here." It was the understatement of the space age. Apollo 13 had been rocked by "a pretty large bang" from Odyssey's service module, which houses the spacecraft's main engine as well as most of its life-giving power and environmental systems. Almost immediately, the command module's instruments recorded a surge of electrical current followed by an alarming drop. On Odyssey's instrument panels, red and yellow warning lights flashed on. In Houston, controllers snapped to attention as telemetered data from Apollo 13 began to confirm the magnitude of the problem.

In less than a minute, one of the service module's two spherical oxygen tanks was completely empty; nearly 320 Ibs. of supercold ( -297DEG F.) oxygen, a highly pressured mix of gas and liquid, had gushed out of the spacecraft, apparently through a rupture in its thin alloy skin. Looking out of his window, Lovell could see vapor streaming by. "We are venting something into space," he reported. "It's a gas of some sort." At the same time, the spacecraft began to pitch and roll in reaction to the violent expulsion of the gas.

Precious Cargo

There was more trouble to come. "One of the main electrical circuits is lifeless," Swigert radioed. "It's off. It's dead." The mysterious blast had also affected two of the service module's three fuel cells, which produce the bulk of the command module's vital electrical power. It quickly became obvious that a moon landing was now out of the question; mission rules forbid a lunar landing if even one fuel cell becomes inoperative. The loss of two requires the earliest possible return to earth. Even worse, the second oxygen tank was now also rapidly spilling its precious cargo. Unless the venting could be stopped, there would soon be insufficient oxygen aboard Odyssey. Oxygen was essential not only for breathing; it would also be needed to react with hydrogen to produce power in the remaining--and apparently undamaged--fuel cell.

Believing that the oxygen might be escaping through ruptures in the fuel cells, controllers ordered the oxygen supply valves to the two dying fuel cells closed. But the oxygen loss continued. Finally, in a desperate effort to conserve enough oxygen to sustain the astronauts on their way home, Flight Director Glynn Lunney directed the spacemen to close the valves to the third and apparently undamaged fuel cell. It was a crucial decision; once shut down, fuel cells cannot be reactivated except under precise temperature and pressure limits obtainable only before launch. Without the cells, Odyssey had no electrical power sources except for the command-module batteries, which had to be saved for the short but crucial period at the end of the mission between re-entry into the atmosphere and splashdown.

The gamble did not pay off. "It looks like Oxygen Tank 1 is just a hair over 200 Ibs. [less than one-fourth normal pressure]," Swigert reported. "We confirm that here," replied Houston. It was now apparent that the accident in Bay 4 of the service module (see diagram) had also started a leak from the second oxygen tank. Still showing no alarm, Swigert asked: "Does it look like it's still going down?" The reply from Houston was equally calm, but carried grave implications. "It's slowly going to zero," said Mission Control, "and we are starting to think about the lunar-module life-boat." "Yes," said Swigert, "that's what we're thinking about too."

In 91 minutes, ground controllers calculated, Odyssey would be completely dead and uninhabitable. Without the least indication of panic, the astronauts prepared to take shelter in Aquarius. The small, spindly craft had been designed primarily to land two men on the moon, sustain them there for two days or so, and then carry them back to an orbital rendezvous with the command module. Now, if all went well, it would serve as Apollo 13's lifeboat, taking over all the vital functions of the crippled mother ship until the astronauts again approached the earth.

Massive Failure

At the Manned Spacecraft Center, where many of the astronauts--including Donald ("Deke") Slayton, Edgar Mitchell and Alan Shepard--had hurriedly gathered, there was an air of tension and foreboding. The crippled Apollo 13 was about 207,000 miles from home and still speeding toward the moon. Under the best of circumstances, it would take days--not minutes or hours--for the astronauts to return to the safety of earth. Said Chris Kraft, the Manned Spacecraft Center's deputy director, in a candid briefing to newsmen: "This is as serious a situation as we've ever had in manned spaceflight."

As yet, no one really knew what had caused the spacecraft's massive failure. Some speculated that Apollo 13 might have suffered the fate of many science-fiction space voyagers: a collision with a meteor. But scientists at the Smithsonian Astrophysical Observatory calculated that the odds were a billion to one that Apollo had been hit by a meteor large enough to have caused such extensive damage. NASA officials were inclined toward a more mundane explanation. They suggested that there had been an explosion in the service module, caused either by a faulty valve or by a short circuit.

Aboard Apollo, the astronauts remained remarkably cool. Once Mission Control gave the order to begin the "lifeboat mode"--a procedure that had been rehearsed numerous times in ground simulators--Lovell and Haise drifted, like mariners abandoning ship, through the darkened tunnel connecting the command ship with the lunar lander.

While Lovell and Haise powered up the lunar lander, Swigert battened down Odyssey. Using the service module's last few gasps of oxygen and electrical power, he charged up Odyssey's small re-entry batteries, closed off its four back-up oxygen tanks, and transferred the precise alignment of the command module's "platform"--its complex of navigational gyroscopes and accelerometers--to a similar platform in the lunar lander. These last-minute maneuvers were vital to a successful return to earth. Apollo 13 could now be navigated from the lunar module, and the command module was assured of enough spare power for six hours of working life--more than enough time for the astronauts to re-enter the atmosphere and splash down in the ocean.

For the moment, the men seemed relatively safe. Swigert remained behind in the blacked-out command module, breathing oxygen from the lunar module through a ten-foot-long oxygen hose cannibalized from Haise's space suit. Lovell and Haise meanwhile stood guard over the lunar module's vital systems. Although Apollo 13 was still very much in trouble, there was one consolation: if the accident had to happen, it had occurred when the astronauts and Mission Control could do something about it. Had the service module become disabled later in the mission--during the lunar landing or afterward, when Aquarius had been discarded--the astronauts would have been doomed. The lunar module, lacking a heat shield to withstand the awesome temperatures of reentry, could not carry the crew back to the earth's surface. But its oxygen, electrical power and descent engine were vital to the safe return of Odyssey.

Aquarius responded well, but mission planners were still faced with a number of agonizing decisions. How could they best bring the distressed spacecraft home as quickly as possible but with a minimum of risk? A "deep-space abort"--turning the spacecraft around before it reached the moon and sending it back to earth--was obviously beyond the power of the lunar module's small descent engine. Odyssey's big propulsion engine, in the service module, was powerful enough to turn Apollo in midflight, but Houston was reluctant to try using it. Controllers were concerned that the engine might have been damaged by the accident. If it didn't work, Apollo's limited electrical power would be wasted in the firing attempt.

Unnecessary Risk

If the astronauts could use a small burn of the Aquarius descent engine to jog Apollo 13 back into a "free-return" trajectory, the combination of the spacecraft's velocity and lunar gravity would do the rest, slinging the ship around the moon and hurling it back on a direct course to the earth. Ironically, Apollo had been on a free-return trajectory, but its course was changed in preparation for the lunar landing.

Thus, five hours and 25 minutes after the service-module explosion, the lunar module's descent engine was fired. Had it not burned, Apollo 13 would have swung around the moon but missed the earth on the return trip by 2,951 miles and gone into a wide-ranging earth orbit, stranding the astronauts. But the lunar module engine performed reliably. With only a 30.7-second burn, it put Apollo 13 on a course that would carry it toward a splashdown in the Indian Ocean. Houston--and the world--breathed easier, but Mission Control knew that the burn was only a stopgap measure. The calculated splashdown area was not only far away from any U.S. recovery ships, but it would also take 74 hours to reach--perhaps longer than the LM's dwindling supply of water, oxygen and electricity would last.

There were additional alternatives, but the choice was not simple. If the astronauts could successfully fire the service module's powerful engine behind the moon, they would splash down in the Atlantic off the coast of Brazil in only 38 hours. Again Mission Control decided not to risk firing a possibly damaged engine. If, on the other hand, the 26-ton service module were jettisoned after rounding the moon, a long burn of the small Aquarius descent engine would impart about the same velocity to the lightened spacecraft, setting it down in the South Atlantic in less than 40 hours. But that strategy too carried unnecessary risks. It would so deplete the LM's fuel supply that later course corrections might not be possible. Also, loss of the service module would expose the command module's heat shield to possibly damaging ultraviolet radiation and temperature extremes, leaving the astronauts with insufficient protection for reentry.

Hurry-Home Burn

Next morning, having weighed the possibilities, the flight planners had a compromise answer. The Aquarius descent engine would fire just long enough to reduce the remaining flight time to 63 hours and drop the astronauts in the South Pacific about 600 miles southeast of Samoa. It was what engineers typically call a "trade-off"--not the fastest possible journey home, but one that would save fuel for later course corrections, not strain the remaining Aquarius oxygen, electricity and fuel supplies aboard, and set Odyssey down within easy range of the prime recovery ship Iwo Jima, already in the area.

Inside the darkened spacecraft, the astronauts struggled to make the best of their dangerous predicament. While two slept fitfully in the unpowered and chilly command module, the third remained on watch "downstairs" in the lunar module. Ground controllers had at least one bit of cheering news. To the delight of scientists, the Saturn third-stage S-4B rocket (which itself had been aimed toward the moon after giving Apollo its final boost) had hit the lunar surface exactly as planned. Its impact created a reverberation that registered for four hours on the Apollo 12 Ocean of Storms seismometer. "Well, at least something worked on this flight," sighed Lovell.

Apollo 13 itself reached the moon Tuesday night, but it never came closer than 158 miles. As it emerged from behind the far side, the astronauts prepared for the crucial "hurry-home" burn. But there was a hitch. So much debris was still floating outside the spacecraft's windows that a star sighting--to align Apollo properly for the burn--was impossible ("It looks like we're in the middle of the Milky Way," the astronauts had remarked earlier). But the spacemen neatly improvised by taking rougher fixes on the moon and the sun. Then they fired Aquarius' descent engine, increasing Apollo 13's speed by 600 m.p.h. The 4-minute, 24-second burn was so accurate that only two more small course corrections were subsequently needed.

For the first time in long hours, the tired men in Mission Control breathed easier. But the astronauts did not. Houston soon noticed that carbon dioxide exhaled by the astronauts was building up to a dangerous level in the lunar module's atmosphere; lithium hydroxide air purifiers in Aquarius, designed to absorb the potentially lethal gas for only relatively short periods of time, were becoming saturated. The deactivated command module was equipped with more purifiers, but their canisters were not interchangeable with the LM's. Mission Control instructed the astronauts to lead a second hose into the command module and connect it to the canisters. Leaving nothing to chance, the astronauts stuffed a sock in the connection to make sure it was snug.

High-Speed Train

With its normal heat-producing systems shut off to conserve electricity, the Odyssey's temperature dropped to nearly 40DEG. Had it continued to fall, the command module's chemical propellants might have thickened to the point where control thrusters would no longer have been able to perform the critical re-entry maneuvers.

Fortunately, only the astronauts felt frozen. On their last night in space, they donned two pairs of thermal underwear apiece to ward off the chill; Lovell even put on his bulky moonwalking shoes to keep his toes warm. Because they had slept only fitfully, Deke Slayton, NASA's director of flight-crew operations, suggested that each crew member take two Dexedrine pills to keep him alert for busy and fateful moments ahead. Said Lovell: "It's going to be an interesting day."

Picking up speed under the increasing pull of the earth's gravity, Apollo was now rapidly approaching its narrow re-entry slot. To make sure of a precise reentry, Lovell and Haise fired one more brief burst from Aquarius' thrusters. Swigert meanwhile took up his post in the command module pilot's seat. Looking out of the window, he commented: "That earth is whistling in like a high-speed train."

A few minutes later, Apollo 13 began its novel separation procedures. Again hitting the thrusters, Lovell forced Aquarius against the command and service modules. Almost simultaneously, Swigert fired several explosive bolts, detaching the service module from Odyssey. Lovell also fired the LM's thrusters again. The "push-pull" tactic shoved the service module away from Aquarius and Odyssey, enabling the astronauts to see the disabled module for the first time. It was an incredible sight. The module had lost an entire 15-foot-long panel covering Bay 4, and a tangle of wiring and debris trailed out of the gaping hole. Using still and movie cameras, the astronauts managed to photograph the damage; because the service module would burn up on reentry, the pictures would be important to scientists investigating the cause of the blast. "It's really a mess," Lovell told Mission Control. "Well, James," Houston answered, "if you can't take any better care of the spacecraft than that, we might not give you another."

Agonizing Adventure

About 30,000 miles from earth, the astronauts began preparing for their final separation maneuver. Climbing into Odyssey, they switched on its oxygen tanks and batteries and sealed the hatch shut. Then the crew exploded the small bolts connecting the command module with the LM. Propelled by the release of air in the connecting tunnel, the Aquarius drifted rapidly away, its lifeboat function reliably and amply fulfilled. "LM jettison," reported Apollo 13. "O.K.," replied Mission Control. "Farewell, Aquarius, and we thank you."

At 12:54 p.m., monitoring stations lost contact with Odyssey as it was enveloped by ionized gases formed by the heat of reentry. For three minutes and 38 seconds, the world anxiously waited to learn whether the astronauts had survived the final portion of their perilous voyage. Finally, the answer came. Responding to a call from one of the rescue planes, Apollo 13 replied: "O.K., Joe." A few seconds later, the descending spaceship hove into view of the TV cameras on the Iwo Jima's decks about four miles away. Under billowing white-and-orange main chutes, the spacecraft drifted slowly downward, headed for a splashdown just off target. At exactly 1:08 p.m., six days after its ill-starred journey began, Odyssey's wanderings had come to an end.

Forty-five minutes later, a helicopter ferried the three astronauts to the Iwo Jima. Smiling and remarkably steady on their feet, the astronauts were greeted by cheers from sailors and a fitting musical tribute from the Iwo Jima's band: Aquarius. Nine doctors on hand to meet the space travelers found them in surprisingly good health--except for Fred Haise's mild urinary-tract infection--after their exhausting and agonizing adventure.

In Houston, cheering and applauding flight controllers joyously lit up their customary cigars as a heartfelt message flashed on a big screen: WELCOME BACK. A few minutes later, NASA's Tom Paine arrived with greetings from President Nixon ("Wonderful team. A job well done"), who also smoked a splashdown cigar in Washington. An especially apt comment came from J. Leonard Swigert, the astronaut's father. Sipping champagne with reporters in his Denver home, the 67-year-old doctor said: "It was a wonderful beginning and a beautiful landing. But I wouldn't give you two hoots for the interim."

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