13 MORE Things That Saved Apollo 13, part 9: Avoiding Gimbal Lock

The Display & Keyboard (DSKY) mounted in the Main Display Console of the Apollo 13 spacecraft, Odyssey. Note the gimbal lock display in the second row. Credit: NASA/The Apollo Flight Journal

It was an unlikely case, having an Apollo command ship disabled thousands of miles from Earth. But during the Apollo 9 mission, the crew had actually conducted a test of firing the Lunar Module’s engines while it was docked to the Command Module. It turned out to be fortuitous to have considered such a situation, but Apollo 9 didn’t have to perform the type of maneuvering under the myriad of conditions Apollo 13 faced.

Steering was among the crucial threats for Jim Lovell and his crew. Without the command ship’s thrusters to steer, only the lander’s were available, and flying the crippled Apollo 13 spacecraft stack and keeping it on the right trajectory was a huge challenge.

During a normal mission, the ship’s computers allowed for much of the navigation, but the Apollo 13 crew had to fly “by hand.” The Command Module was shut down, and the LM’s limited battery power required the shutting down most of its systems, so even backup propulsion and navigation functions were unavailable. Lovell had to struggle to bring the unwieldy two-vehicle craft under control.

Apollo 13 commander Lovell with a model Lunar module. Image credit: NASA
Apollo 13 commander Lovell with a model Lunar module. Image credit: NASA
The lander’s steering was fashioned to handle only its mass and center of mass location. Now it had to steer the entire assemblage, which included the dead mass of the Command and Service Module as well as the lander. Then there was oxygen venting from the damaged tanks in the SM. This all contributed to putting the stack through contortions of pitch, roll, and yaw.

In his seminal book, “A Man on the Moon,” author Andrew Chaikin succinctly captured the scene:

Even now, oxygen spewed from Odyssey’s side like blood from a harpooned whale. The escaping gas acted like a small rocket, fighting Lovell’s efforts to stabilize the joined craft – which the astronauts called “the stack” – with Aquarius’s thrusters. Lovell soon found that trying to control the stack from the lander was strange and awkward, like steering a loaded wheelbarrow down the street with a long broom handle. When he nudged the hand controller the joined craft wobbled unpredictably. It was, Lovell would say later, like learning to fly all over again. And he had to learn fast, because if he let the spacecraft drift uncontrolled, there was a danger that one of Aquarius’s gyros would be immobilized – a condition called gimbal lock that would ruin the alignment of the navigation platform. With no way of sighting in the stars, there would be no hope of realigning it….

“I can’t take that doggone roll out, “Lovell said. Throughout the next 2 hours Lovell wrestled with his unwieldy craft, as the time for the free-return maneuver approached. He wondered if Aquarius would be able to point them toward home, and whether it would last long enough to get them there. Lovell and his crew had become the first astronauts to face the very real possibility of dying in space.

From “A Man on the Moon,” chapter 7, “The Crown of an Astronaut’s Career”
by Andrew Chaikin
Used by permission

One of the items discussed in the original “13 Things That Saved Apollo 13” was how well suited rookie Apollo crewman Jack Swigert was to the Apollo 13 mission, as he was said to have basically ‘wrote the book’ on Command Module malfunctions. Likewise, says NASA engineer Jerry Woodfill, was Commander Jim Lovell’s ability as Apollo 13’s helmsman.

“Tales are often shared about Lovell’s skills as a naval aviator,” said Woodfill, “making aircraft carrier deck landings in the dark with a malfunctioning display, or in storm-tossed seas.”

Being able to judge aircraft descent rates and attitude with respect to a wave-tossed carrier deck was a challenge. Woodfill said this ideally trained Lovell for avoiding gimbal-lock on Apollo 13.

An annotated image of the Apollo Flight Director Attitude Indicator, commonly called the navigation 8-ball. Via Kerbal Space Program.
An annotated image of the Apollo Flight Director Attitude Indicator, commonly called the navigation 8-ball. Via Kerbal Space Program.

“Gimbal-lock meant the guidance system could no longer trust its computer,” explained Woodfill. “The guidance system’s orthogonal gyroscopes (gyros) judged the degree of pitch, roll, and yaw. Gimbal-lock exceeded the system’s ability to gauge position. Such an instance could be compared to an automobile’s tires slipping on an icy road. Steering becomes almost useless in such an event.”

Historian and journalist Amy Shira Teitel recently posted this video in regards to gimbal lock and Apollo 13:

Then, later came a second dire “steering” challenge to Lovell and his crew. Apollo ships required a rotating maneuver about their longest axis known as Passive Thermal Control (PTC), nicknamed the rotisserie, to protect one part of the spacecraft from continually being baked by the Sun. Normally, this was done by the CM’s computer, and the LM’s computer didn’t have the software to perform this operation. Lovell had to maneuver the unwieldy ship by hand nearly every hour to perform the “slow motion barbeque spin” as Chaikin called it. Without the CM’s orientation control thrusters and having the center of gravity extremely off-center with respect to the lander’s control system, it made the situation problematical.

“Lovell seemed to have the ability to quickly adapt to difficult situations,” said Woodfill, “and the knack of quickly coming up with solutions to problems.”

But that’s part of the makeup of being a test pilot and what distinguished the men who were chosen to be astronauts in the Apollo program.

“As great a pilot as Jim Lovell was, I think any of the Apollo commanders could have handled that situation from a piloting point of view,” Chaikin told Universe Today via phone. “One benefit that Lovell brought to the situation was his calm, composed personality—a real asset during that entire ordeal.”

As Chaikin quoted original Apollo 13 crew member Ken Mattingly in “A Man on the Moon,” if Apollo 13 had to happen to any spacecraft commander, there wasn’t anyone who could have handled it better than Jim Lovell.

Nancy Atkinson with Jim Lovell in 2010 at the Abraham Lincoln Presidential Museum.
Nancy Atkinson with Jim Lovell in 2010 at the Abraham Lincoln Presidential Museum.

Here’s an additional, more technical description of gimbal lock:

Previous articles in this series:


Part 1: The Failed Oxygen Quantity Sensor

Part 2: Simultaneous Presence of Kranz and Lunney at the Onset of the Rescue

Part 3: Detuning the Saturn V’s 3rd Stage Radio

Part 4: Early Entry into the Lander

Part 5: The CO2 Partial Pressure Sensor

Part 6: The Mysterious Longer-Than-Expected Communications Blackout

Part 7: Isolating the Surge Tank

Part 8: The Indestructible S-Band/Hi-Gain Antenna

Find all the original “13 Things That Saved Apollo 13″ (published in 2010) at this link.

Apollo 13 images via NASA. Montage by Judy Schmidt.
Apollo 13 images via NASA. Montage by Judy Schmidt.

When Typhoid (Briefly) Struck Apollo 16

Charles Duke in a light-hearted moment during Apollo 16. Credit: NASA

Astronaut pranks are, well, just a part of the job. Often they poke at a sore spot in the astronaut’s history, and Charles Duke found himself the subject of a particularly painful one in the 1970s.

Duke was in the final moments of preparations before climbing into the Apollo 16 spacecraft, which was exploring the Moon in this week in 1972. It was a serious moment as Duke and his crew were about to rocket off to the moon. Then Duke got a surprise, courtesy of backup commander Fred Haise, as Duke recalled in an interview with NASA in 1999.

We were up climbing into the command module on the launch pad, and [launch pad leader] Guenter Wendt and the team were up there. And so John gets in, and I’m the next in on the right side. And as I start to climb in, I reach in and I look over and taped to the back of my seat was a big thing, “Typhoid Mary suit—seat.” So, we had a … laugh over that. Yeah, Fred would never let me forget that.

Typhoid Mary referred to Mary Mallon, a cook who was put under quarantine for the latter half of her life in the 1900s — against her stringent objections. She was accused of passing along typhoid to several families for which she did cooking, even though she didn’t show any symptoms herself. At the time, typhoid had no cure. Her curious story has been the subject of a PBS show and numerous books.

The joke on Duke hearkened back to the ill-fated Apollo 13 two years before, when Duke’s son caught the German measles. Duke fell ill and unwittingly exposed several astronauts during his contagion period — including the upcoming Apollo 13 prime crew of Jim Lovell, Fred Haise and Ken Mattingly.

Of the three crew members, Mattingly had not been exposed to the German measles. This led to Mattingly being yanked from the mission days before launch. Adding to the drama, Apollo 13 suffered an explosion in space that crippled the spacecraft and, without the extraordinary efforts of the astronauts and Mission Control, could have killed the crew.

Anyway, Apollo 13 came back safely, and in 1972 lessons had been learned from the mission. Haise, to his credit, wasn’t afraid to poke a little fun at the early havoc Duke’s illness wreaked on his crew.

What are your favorite astronaut pranks?

Ken Mattingly Explains How the Apollo 13 Movie Differed From Real Life

The original Apollo 13 crew, from left to right: Jim Lovell, Thomas "Ken" Mattingly, Fred Haise. Credit: NASA

Many astronauts seem to like the Apollo 13 movie, but being technically minded folk they also enjoy pointing out what actually happened during that so-called “successful failure” that landed safely on this day in 1970.

Thomas “Ken” Mattingly was supposed to be on that crew, but was yanked at the last minute because he was exposed to the German measles. The movie shows him wallowing on the couch with a can of beer before hearing of an oxygen tank explosion on board. He then spends most of the movie stuck in a simulator, helping to save the three men on board the spacecraft.

Real life wasn’t quite the same as the movie portrayed, the real Mattingly said in a 2001 interview with NASA.

For one thing, Mattingly had no assigned role in the rescue as he was a backup crew member. He ended up working in a lot of teams rather than a single project or two. There also were some technical differences between the movie and real life. Some examples:

The “lifeboat” procedures: In the movie, mission controllers huddle in a side room and try to figure out how to stretch the resources of the lunar module — designed to carry only two men for a couple of days — into a four-day lifeboat to support three men. While this is somewhat true, NASA already had a preliminary lifeboat procedure simulated, Mattingly pointed out. The movie made it appear as though, he said, “we invented a lot of stuff”.

Somewhere in an earlier sim [simulation], there had been an occasion to do what they call LM lifeboat, which meant you had to get the crew out of the command module and into the lunar module, and they stayed there. I vaguely remember—when you have a really exciting sim, why, generally everybody knows about it. I vaguely remember that they had come up with a thing that contaminated the atmosphere in the command module, and they had to vent it, and they put the crew into the—there’s some reason that instead of staying in their suits in the command module, they put them in the lunar module while they did this.

Apollo 13's original crew of Jim Lovell, Ken Mattingly and Fred Haise with an unidentified person. Credit: NASA
Apollo 13’s original crew of Jim Lovell, Ken Mattingly and Fred Haise with an unidentified person. Credit: NASA

The carbon dioxide filter: In the movie, as the crew faces a deadly buildup of carbon dioxide, a team in mission control builds a new system on the spot that adapts an originally incompatible filter. “Well, the real world is better than that,” Mattingly explained, saying there was a simulation for the Apollo 8 mission where a cabin fan was jammed due to a loose screw.

The solution that they came up with was that they could make a way to use the vacuum cleaner in the command module with some plastic bags cut up and taped to the lithium hydroxide cartridges and blow through it with a vacuum cleaner. So, having discovered it, they said, “Okay, it’s time for beer.” Well, on 13, someone says, “You remember what we did on that sim? Who did that?” So in nothing short, Joe [Joseph P.] Kerwin showed up, and we talked about “How did you build that bag and what did you do?” … Of course it worked like a gem.

Simulating the startup: In the movie, Mattingly spends hours in a simulator putting together the procedures for starting up the cold, dead command module in time to bring the astronauts safely back to Earth. While that is a good way of conveying the mission’s aim to the public, the simulation runs (done by other astronauts, Mattingly said) were more of a verification of already written procedures.

We said, “Let’s get somebody cold to go run the procedures.” So I think it was [Thomas P.] Stafford, [Joe H.] Engle — I don’t know who was the third person, might have been [Stuart A.] Roosa. But anyhow, they went to the simulator there at JSC [Johnson Space Center], and we handed them these big written procedures and said, “Here. We’re going to call these out to you, and we want you to go through, just like Jack will. We’ll read it up to you. See if there are nomenclatures that we have made confusing or whatever. Just wring it out. See if there’s anything in the process that doesn’t work.”

For more on what Mattingly thinks of the Apollo 13 movie, check out the entire transcript of his interview on NASA’s website. We’re sure there are other technical details the movie simplified or got wrong, so feel free to share your thoughts in the comments.