Houston, we’ve had a problem

Young Astronomers Blog, Volume 28, Number 8.

Something happened on April 13, 1970 – fifty years ago this month.  A spacecraft was heading for a landing on the Moon.  If successful, it would be humankind’s third landing on another object in space.  Part way to the Moon, there was a problem.

Apollo oxygen tank 10024X-TA0009 was initially installed in the service module designated for Apollo 10.  It was removed for maintenance and then damaged.  It was repaired, tested and installed as the #2 oxygen tank in the Apollo 13 service module.  Prior to the launch of Apollo 13, the oxygen tanks were emptied and refilled.  Tank #1 emptied as planned, but tank #2 wouldn’t empty.  It was decided to boil off the remaining oxygen and then refill the tank.  This process damaged the internal heating elements of the tank.  Evidently, the allowable voltage for the tank heaters was raised in 1965, but the switches on the heaters weren’t modified for the change. The switches probably welded shut and some insulation was damaged.

In August 1969, NASA officials announced the crew for Apollo 13.  It was Jim Lovell, who had been to the Moon on Apollo 8, Fred Haise and Ken Mattingly.  A few days prior to the launch, backup Charlie Duke exposed the crew to the measles.  Lovell and Haise were immune, Mattingly was not.  It was decided to replace Mattingly with backup Jack Swigert.

Apollo 13 launched on April 11, 1970.  During the liftoff, one of the Saturn SII-B engines shut down early requiring the remaining engines and the SIV-B engine to burn longer than planned.  The three astronauts thought they had experienced their “glitch” for the mission.

Around 56 hours into the mission and over halfway to the Moon, the crew held a TV broadcast which wasn’t carried by any of the networks.  Evidently going to the Moon was getting a bit boring.  Shortly after concluding the program, the crew was asked to “stir” the oxygen tanks.  The tanks were kept cold and the oxygen was in a slushy form which had to be remixed from time to time.  Just after 9 pm on April 13, 1970, Swigert hit the switch and there was a bang along with a shaking of the command module.  The number 2 oxygen tank blew up damaging the number 1 tank.  Swigert reported, “Houston, we’ve had a problem here.”

Jim Lovell repeated, “Houston, we’ve had a problem” and reported a “main B bus undervolt.”  They also noticed that two of their three fuel cells, which powered the command module, had failed, oxygen tank two was empty and oxygen tank one was depleting quickly.  A few minutes later, Lovell looked out the window and saw a gas venting into space.  This turned out to be oxygen from the number 1 tank.

With the oxygen level going down, and an hour and half after the bang, Mission Control suggested using the lunar module (LM) as a lifeboat.  By that time, it was clear, the command module would be out of oxygen and its third fuel cell would fail.  Lovell and Haise moved over to the lunar module (LM) and began to power it up.  Swigert, with 15 minutes of power left, began to power down the command module to make sure there was enough battery power to land.

Navigation was an issue.  Normally they used a telescope as a sextant to find their position in space based on the position of selected stars.  The problem was they were traveling in a swarm of particles from the explosion that obscured their view.  So, the command module alignment had to be correctly transferred to the LM before the command module was shut down.

The spacecraft was speeding toward the moon.  It wasn’t practical to stop and turn around.  The easiest option was to continue, swing around the moon, and head back toward the Earth.  NASA was afraid to use the service module engine, so they fired the LM engine to adjust the trajectory and put the spacecraft on a “free-return” path.  The LM engine was fired again later to speed up the spacecraft and reduce the time required to reach the Earth.

It would still take around 3 ½ days to return to Earth.  The Lunar Module had plenty of oxygen for three astronauts.  Water was going to be the problem.  Although the astronauts cut down on their water intake and managed to stretch their supply until landing, they became quite dehydrated during the return trip.

The other problem was carbon dioxide, which was removed from the air using lithium hydroxide canisters.  There were enough canisters between the command module and lunar module, but the canisters in the lunar module were round and the canisters in the command module were square.  Around a day and a half after the explosion, the atmosphere in the LM was getting saturated with CO₂.  Fortunately, Mission Control came up with a way to fit square canisters into round holes using the square canisters, plastic bags, cardboard, hoses, and duct tape.

During the return, the spacecraft was coming in at too shallow of an angle, so they performed a 3^rd burn.  Because the LM’s computer had been turned off, the three astronauts performed a manual burn using the Sun and Earth to maintain their position in space.

As they traveled back to the Earth, the LM became damp and cold.  They had turned off all unnecessary systems including heat.  Making things worse, Mission Control was concerned that dumping their urine bags into space would impact their trajectory, so they had to store them in the cabin.

Finally, as Apollo 13 approached the Earth, the command module had to be powered up.  There was only a finite amount of power available.  Mission Control managed to find a sequence that worked.  But before the power up, the astronauts noticed that the inside of the command module was covered with condensation.  They were concerned that a spark could cause problems as power was brought online.  Fortunately, after the Apollo 1 fire, all the electrical connections were properly insulated, and the command module came back to life.

A few hours before landing, they jettisoned the service module and noticed one whole side had been blown away.  Then they shed the lunar module and began reentry.

As Apollo spacecraft reenter the atmosphere, there is a communication blackout for a few minutes.  Finally, a message was received, and a few minutes later Apollo 13 landed safely in the Pacific Ocean on April 17, 1970.

Selected Sources and Further Reading

“Apollo 13.” NASA Webpage. (accessed March 7, 2020).  https://www.nasa.gov/mission_pages/apollo/apollo-13

“Apollo 13.” NASA Mission Overview. (accessed March 7, 2020). https://www.nasa.gov/mission_pages/apollo/missions/apollo13.html

“Apollo 13.” NASA Science, Solar System Exploration. (accessed March 20, 2020). https://solarsystem.nasa.gov/missions/apollo-13/in-depth/

“The Flight of Apollo 13.” Excerpt from W. David Compton, Where No Man Has Gone Before: A History of Apollo Lunar Exploration Missions (Washington, D.C.: NASA SP-4214, 1989), pp. 386-93. https://www.hq.nasa.gov/office/pao/History/apollo/apo13hist.html

James A. Lovell. “Houston, We’ve Had a Problem.” Chapter 13 from Apollo Expeditions to the Moon. NASA History. (accessed March 7, 2020).  https://www.hq.nasa.gov/office/pao/History/SP-350/ch-13-1.html

Dr. David R. Williams. “The Apollo 13 Accident.” NSSDC/GSFC/NASA. (accessed March 7, 2020). https://nssdc.gsfc.nasa.gov/planetary/lunar/ap13acc.html

“Apollo 13 Audio Highlights.” NASA. https://images.nasa.gov/details-Apollo13Highlights

Jim Lovell and Jeffrey Kluger. Lost Moon: The Perilous Voyage of Apollo 13. Houghton Mifflin Co., Boston, 1994.

Andrew Chaikin. A Man on the Moon: The Voyages of the Apollo Astronauts. Viking, New York, 1994,  pages 285-336.

Charles Murray and Catherine Bly Cox. Apollo: The Race to the Moon. Simon and Schuster, New York, 1989, pages 387-446.

Alan Shepard and Deke Slayton. Moonshot: The Inside Story of America’s Race to the Moon. Turner Books, New York, 1994, pages 259-274.

Technical Reading

“Apollo 13 Mission Report.” Manned Spacecraft Center, NASA. September 1970. https://www.hq.nasa.gov/alsj/a13/A13_MissionReport.pdf

“Report of Apollo 13 Review Board.” NASA. June 15, 1970. https://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_13_review_board.txt & https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19700076776.pdf

“Apollo 13 ‘Houston, we’ve got a problem’.” EP-76 NASA. Pdf version by Jerry Woodfill of the Johnson Space Center. https://nssdc.gsfc.nasa.gov/planetary/lunar/apollo13.pdf

David Woods, Johannes Kemppanen, Alexander Turhanov and Lennox J. Waugh. “The Apollo 13 Flight Journal.” Apollo Flight Journal, NASA. March 1, 2020.  https://history.nasa.gov/afj/ap13fj/index.html