HOUSTON, April 15, 1970 (UPI) - The stricken Apollo 13 spaceship is slightly off course and its astronauts will miss the earth by 80 miles and soar off into a distant, fatal orbit if a steering correction is not made tonight or tomorrow, controllers reported today.
"If the descent engine does not burn, we cannot bring them back," said Thomas Weichel, one of the controllers.
The big engine, however, already has fired twice to head astronauts James A. Lovell, John L. Swigert and Fred W. Haise back toward earth after a near fatal explosion en route to the moon.
The prayers of millions went to the pilots for a safe splashdown at 1:04 p.m. Friday about 600 miles southeast of Pago Pago in the South Pacific.
But to successfully re-enter earth's atmosphere, the astronauts must fire the big engine on their lunar module briefly to put their ship into the narrow, imaginary corridor in space leading to safe splashdown.
"We're not yet in the re-entry corridor and we'll have to make this maneuver to get in," flight director Milton Windler said. Controller Weichel said the present path followed by Apollo 13 would miss the earth by 80 miles and carry the astronauts thousands of miles off in a great orbit around the earth.
The astronauts' meager supply of oxygen would be exhausted in a matter of a few days - long before they would approach earth again.
The engine needed for the course correction fired successfully last night to accelerate the astronauts' trip back to earth.
Windler said the course correction is scheduled for tonight, but might be delayed until tomorrow if weather in the primary landing zone deteriorated and made a change in the splashdown site desirable. He said the weather now appeared satisfactory.
During a loop of the moon and thrust at the earth last night, there were two rocket firings. In the second one, all three men got into the tiny lunar lander although it was designed to hold only two persons.
The supply of water, oxygen and electrical power was carefully rationed, but flight director Eugene Kranz said there was a more than adequate supply to get the astronauts home on Friday.
Emergency plans to bring down the astronauts in the Indian Ocean tomorrow instead of the Pacific Friday were scrapped because risks were considered too high.
The astronauts were well aware the splashdown will be preceded by a tougher-than-normal return into earth's atmosphere. The pilots must jettison their ruptured service module and the lunar module that saved their lives, and dive into the atmosphere blanket in the cone-shaped command module.
"We've got to be in good shape for entry day," Haise said. "That's going to be a busy one."
Ground controller Jack Lousma asked Haise "How would you like to spend a week on an aircraft carrier getting back?"
"If I could get on an aircraft carrier, I don't care how long it take, Jack," replied Haise, who was standing watch in the lunar module as Lovell and Swigert got a few hours of long-overdue sleep.
In contrast to the grim situation a day ago, there were a few jokes and wisecracks from Lovell, a Navy captain, and his rookie crewmen once the command ship Odyssey and the still-linked lunar lander Aquarius had swung around the back of the moon and the rocket engine successfully fired to accelerate their trip home.
But their mood was mostly businesslike. There also was evidence of their frustration at the way the $375 million mission developed.
The top stage of the Saturn rocket that pushed them toward the moon Saturday smashed into the moon as scheduled last night. Controllers told the pilots, "It's rocking the moon a little bit."
"Well, at least something worked on this flight," Lovell said with a bitter laugh.
The cause of the explosion that damaged the spacecraft Monday night was still a mystery. But flight director Lunney indicated he thought it probably resulted from a ruptured oxygen tank in the aft service section of the Odyssey.
Haise reported sighting what appeared to be some new venting of a gas from the service section early today. This, he said, produced "thousands of sparkles" that looked like stars. He also sighted outside a four-inch square piece of shiny metal, apparently broken off the service module.
One big concern is finding a way to get rid of carbon dioxide the astronauts are producing by breathing. Carbon dioxide is purged from the ship by treating it with lithium hydroxide, which is stored in cans. The astronauts, because of damage Monday night, are using a makeshift mechanism to conserve the supply.
If the lithium hydroxide can't be used, the astronauts may become dizzy. Officials here also are aware that another accident affecting electrical or oxygen supplies probably would doom the astronauts.