How hot was Apollo 13 on reentry?

Reader Scott Davis of Clovis, California is curious about one of the most memorable moon missions, Apollo 13. The third manned mission to the moon was aborted on April 13, 1970, two days after launch, when an oxygen tank exploded, crippling the service module, to which the command module was attached.

The crew—commander James Lovell, command module pilot Jack Swigert, and lunar module pilot Fred Haise—was forced to power down systems in the command module to conserve batteries. They used the lunar module as a “life boat,” looped around the moon, and jettisoned the service and lunar modules en route home.  Protected by the heat shield on the command module, they splashed down safely on April 17.

 “We all know that the exterior of the Apollo capsule was subjected to intense heat during reentry,” Davis writes. “In the movie Apollo 13, we know many of the instruments were frozen due to the [electrical] shutdown, and the ice melted during reentry. My question is, how much of the heat did the astronauts actually feel? How much did the interior of their capsule heat up during this time?”

For the answers, we turned to Lovell, now a restaurateur in Lake Forest, Illinois. “The movie depicts the command module very cold because we turned off most of the electrical systems to save power,” Lovell writes in an email. “The spacecraft cabin temperature on a normal mission is controlled by using heat produced by electrical systems, with the excess heat dissipating by radiation into space. With the electrical systems turned off, the temperature approached about 34 degrees Fahrenheit prior to entering the atmosphere.

“The instruments did not actually ‘freeze.’ They were inoperable with the system turned off. They came to life when we powered up the command module just prior to reentry. The temperature inside the command module did not rise during reentry. In fact, it was still cold when we landed in the ocean.”

So, in one of NASA’s most nail-biting missions ever, the astronauts not only kept their cool in space, they stayed like that all the way to splashdown.