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?
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
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
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
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.