"Ignition!"

Orbiting Earth aboard the command module Odyssey, Jim Lovell, Jack Swigert and Fred Haise felt a mild jolt and the onset of acceleration. Their once-weightless bodies sank into their couches. Lovell radioed Houston that the engine of the S 4-B booster, third stage of the giant Saturn 5 moon rocket, had begun firing to accelerate Apollo 13 out of Earth orbit and on a course for the moon.

For only the fifth time in history, human beings were leaving their home planet to visit another world. Remarkably, to Lovell, there was a familiarity about it all: He had been to the moon before, as a crewman on the historic Apollo 8 mission in December 1968.

Lovell was not a superstitious man, but he had to admit that quite a few "13"s had cropped up in his life. It began when NASA gave him command of the third lunar landing mission -- Apollo 13. Then there was the time of liftoff, which was set for 1:13 p.m. Houston time -- or, in military time, 13:13.

This wasn't someone's idea of a joke; the launch window was dictated by the lighting conditions Lovell would need for his landing attempt, some four days later. None of this bothered Lovell; in fact, he'd been told that in Italy, 13 is considered a lucky number. Besides, everything was going well with preparations for Apollo 13.

That is, until the week before launch, when one of the Apollo 13 backup astronauts, Charlie Duke, came down with German measles. Lovell and his rookie crew, Ken Mattingly and Fred Haise, had also been exposed. From blood tests, the NASA doctors concluded that Lovell and Haise were probably immune, but not Mattingly. He could already be harboring the illness, and the doctors feared he could come down with symptoms during the mission.

Lovell argued strenuously to keep Mattingly on his crew. Even if Mattingly got sick, Lovell pointed out, it would be during the relatively low-stress trip back to Earth, when Lovell and Haise could cover for him. But Lovell's pleas were to no avail. With only days to go before launch, NASA decided to replace Mattingly with his backup, rookie Jack Swigert.

For Lovell, the immediate concern was whether Swigert could mesh with Haise and himself. With Mattingly, they had developed a close working relationship and the verbal shorthand that goes along with it. In the heat of an emergency rendezvous above the far side of the moon, for example, would they be able to communicate with Swigert as well?

After two days of intensive sessions in the Apollo mission simulators at Cape Kennedy, Lovell was convinced this "shotgun marriage" would work. His only sorrow -- one shared by Haise -- was having to leave Ken Mattingly behind as Apollo 13 headed for the moon.

Apollo 13 got off to an uneventful start, if going to the moon can be called uneventful. In the first hours of the moon-ward voyage, Swigert separated Odyssey from the S 4-B booster and steered the command ship to turn and dock with the lunar module Aquarius, still attached to the spent rocket. Once the two craft were firmly linked, the men extracted the lander from its berth in the Saturn's third stage and pulled away. If all went according to plan, they would not need to activate Aquarius until the mission's fifth day, as Lovell and Haise were getting ready to land on the moon.

"American citizens out of the country get a 60-day extension on filing... I assume this applies to you."

For now, Lovell and his crew settled into the so-called translunar coast, which would last a bit less than three days. They removed their spacesuits and changed into lightweight coveralls. Within the command module, they got used to the freedom of movement afforded by weightlessness. And they began to turn Apollo 13 in a slow rotation to even out the sun's fierce heat on the joined craft.

Through Odyssey's windows, the astronauts could see the Earth dwindling in the sunlit blackness. It was a view only a handful of human beings had so far experienced. From that Earth came news of more mundane things: Baseball scores. News that schoolteachers in Minneapolis had gone on strike. And an unpleasant preoccupation of millions of Americans that came around every April. In Mission Control, capcom Joe Kerwin asked, "Have you guys completed your income tax?"

For Jack Swigert, the question brought a sudden pang of apprehension. From space came the words, "How do I apply for an extension?

"Things happened real fast down there," Swigert continued, "and I do need an extension."

Kerwin tried to control his laughter, but Swigert wasn't laughing. "I didn't get mine filed," he told Kerwin. "I'm really serious."

"You're breaking up the room down here," said Kerwin, as the controllers seated around the room joined his laughter.

"I may be spending time in a another quarantine besides the one they were planning for me," Swigert said, referring to the post-mission period of medical confinement.

Ken Mattingly (left), pulled from the Apollo 13 crew at the last minute, follows the progress of Apollo 13 in mission control. At right is astronaut Joe Kerwin, serving as capcom.

But just then, Flight Director Glynn Lunney offered words of reassurance: "American citizens out of the country get a 60-day extension on filing," Lunney radioed, and added wryly, "I assume this applies to you."

So it was that the extraordinary business of flying history's third lunar landing attempt got underway. For Jim Lovell, there was no reason to suspect that there was anything unlucky about Apollo 13. Already, on three space missions, he had gone farther and faster than anyone, with 572 hours in space and 7 million miles (11.3 million kilometers) under his belt. Only much later, looking back on it, would Lovell say it was only a matter of time before the law of averages caught up with him.