Fri. Apr 21, 2000

 
SPACE.com Exclusive: If Rescue Failed, Apollo 13 Would Have Crashed Into Earth

By Andrew Chaikin
Executive Editor,
Space and Science
posted: 02:14 pm ET
12 April 2000
    

 

After all that's been said about Apollo 13, it might seem there's nothing new to tell. But now, 30 years after NASA's heroic rescue of the three Apollo 13 astronauts, details have surfaced that give the story a new twist.

Newly analyzed data suggest that the astronauts on the nearly fatal mission would not have been entombed in space, had efforts to steer the craft back on course failed. In fact, the capsule eventually would have passed quite close to Earth, and later collided with it, at least bringing the astronauts' bodies back to their home planet.

Chuck Deiterich, who served as lead retrofire officer during the mission, aided in the new analysis, supplying the "what-if" data for a simulation that now shows the crippled spacecraft would have missed Earth by 2,600 miles (4,184 kilometers), not the 40,000 miles (64,372 kilometers) reported for decades.

"I'm very confident that that's the right number," Deiterich told SPACE.com.

Simulation shows alternative

After the explosion of an oxygen tank crippled the Apollo 13 command and service modules 200,000 miles (321,860 kilometers) from Earth, mission commander Jim Lovell knew he and his crew might not make it back. Even worse, Lovell feared, Apollo 13 would end up circling in space forever, as a silent tomb, or in Lovell's words, "a monument to the U.S. space program."

Now, a computer simulation created by two companies, Analytical Graphics Incorporated of Philadelphia and Colorado-based Space Exploration Engineering, shows what would have happened to Apollo 13 had the astronauts failed to get back on the proper course for a safe return to Earth.

 

If the Apollo 13 astronauts had not been able to get onto the free-return path to Earth, they would have followed the orbits shown. After launch from Earth and outbound voyage (green), Apollo 13 loops around the moon (red) and heads back toward Earth. The craft passes 2,645 miles from Earth, then continues on a long ellipse (white) that reaches past the moon's orbit (yellow). Another orbit (blue) brings Apollo 13 within 29,500 miles of the moon, whose gravity bends the spacecraft's path onto a direct course for Earth.

The simulation is one of several created for SPACE.com (AGI is a vendor that supplies this site with visual animations), and the discovery of the new trajectory came up during the project to create animations for SPACE.com's special report on Apollo 13.

The new simulation starts with the path that Apollo 13 was on before the accident on April 13, 1970. On the day of the explosion, the astronauts were following a course called a hybrid trajectory. Unlike the so-called free-return trajectory followed by most of the earlier moon missions, the hybrid path did not guarantee the astronauts a "free ride" back to Earth in the event of an abort.

In the first hours after the explosion -- after determining that the command/service module engine would not work, or could not be fired safely -- Mission Control devised a plan for the astronauts to fire the engine of their lunar lander to steer back home. Lovell and his crew worked feverishly to get back onto the free-return trajectory, and they succeeded. But what if they hadn't achieved this critical step?

40,000 miles?

Many published accounts of the Apollo 13 mission, including this writer's, have stated that Apollo 13 would have missed the Earth by an enormous margin, on the order of 40,000 miles, and circled indefinitely.

The origin of that figure is unknown. Neither flight controller Deiterich nor Apollo 13 flight director Gene Kranz could trace the origin of the 40,000-mile estimate, but it shows up in Henry S.F. Cooper's book, Thirteen: The Flight that Failed, published in 1973.

The new computer simulation suggests a very different scenario. If the astronauts could not alter their path after the explosion, Apollo 13 would have looped around the moon and then, its path bent by lunar gravity, would have headed homeward.

On April 18, 1970, the spacecraft would have flown past Earth, missing it by a distance of 2,645 miles.

Initially, the analysts were taken aback by their findings. "We were puzzled how our results could be so different from what's been written about the mission," said Bob Hall, AGI's director of Technical Services. Then, after speaking with Apollo 13 veterans, Hall and his colleagues resolved the discrepancy.

Third time would bring them home

In making their calculations, AGI received special assistance from Deiterich. Before, during and after the flight, Deiterich was instrumental in analyzing the spacecraft's trajectory. He is perhaps the only existing source of detailed information on this subject, and he supplied AGI with the data for the simulation.

Because the astronauts would not have survived much, if at all, beyond a first Earth flyby, Deiterich never calculated what would have happened next. But the AGI results reveal the craft's ultimate fate -- and that is where the biggest surprise turns up.

Apollo 13, after flying past Earth in AGI's simulation, travels back out into deep space, tracing a vast ellipse that stretches beyond the orbit of the moon. On April 27 Apollo 13 reaches its maximum distance from Earth, at 355,949 miles (572,829 kilometers). By this time, the astronauts have surely perished. (Their oxygen reserves at the time of the accident were enough to keep them alive for eight to 10 days; food and water were in much shorter supply.)

On May 6, the craft makes another Earth flyby, this time passing 1,563 miles (2,515 kilometers) from the planet and heads moonward once more. Sometime around May 9, Apollo 13's path is altered when it passes within 30,000 miles (48,279 kilometers) of the moon. On May 13, after reaching the far point of its orbit again, Apollo 13 heads Earthward one last time.

This time, the spacecraft is on a collision course. On May 20, 1970, some five weeks after the explosion, the spacecraft plunges into Earth's atmosphere at a steep angle over the eastern Atlantic Ocean. The steepness of the reentry would have meant that the spacecraft, carrying the bodies of the astronauts, would have been destroyed by crushing deceleration forces and searing heat.



 
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