13 Things That Saved Apollo 13, Part 1: Timing


Note: To celebrate the 40th anniversary of the Apollo 13 mission, for the next 13 days, Universe Today will feature “13 Things That Saved Apollo 13,” discussing different turning points of the mission with NASA engineer Jerry Woodfill. Click here for our preview article.

Oxygen Tank two in the Apollo 13 Service Module exploded at Mission Elapsed Time (MET) 55 hours and 55 minutes, 321,860 kilometers (199,990 miles) away from Earth. If the tank was going to rupture and the crew was going to survive the ordeal, the explosion couldn’t have happened at a better time. “Not everyone agrees with all the things I’ve come up with in my research,” said NASA engineer Jerry Woodfill who has studied the Apollo 13 mission in intricate detail, “but pretty much everyone agrees on this, including Jim Lovell. The timing of when the explosion happened was key. Much earlier or later in the mission would have prevented a successful rescue.”

If the explosion happened earlier (and assuming it would have occurred after Apollo 13 left Earth orbit), the distance and time to get back to Earth would have been so great that there wouldn’t have been sufficient power, water and oxygen for the crew to survive. Had it happened much later, perhaps after astronauts Jim Lovell and Fred Haise had already descended to the lunar surface, there would not have been the opportunity to use the lunar lander as a lifeboat.

But looking at why the explosion happened when it did shows how fortuitous the timing ended up to be.

The control panel of the Apollo 13 capsule. The module is on display at the Kansas Cosmosphere and Space Center in Hutchinson, KS. Photo courtesy Kansas Cosmosphere and Space Center.

The explosion occurred when Jack Swigert flipped a switch to conduct a “stir” of the O2 tank. The Teflon insulation on the wires to the stirrer motor in O2 tank 2 had unknowingly been damaged because the manufacturer failed to update the heater design for 65 volt operation, and the tank overheated during a pre-flight test, melting the insulation. The damaged wires shorted out and the insulation ignited. The resulting fire rapidly increased pressure beyond its nominal 1,000 psi (7 MPa) limit and either the tank or the tank dome failed.

The O2 tanks were stirred in order to get an accurate reading on the gauging systems, as the cryogenic oxygen tends to solidify in the tanks, and stirring allows for a more accurate reading on the quantity of O2 remaining in the tank.

But this was not the first time the crew had been ordered to stir the tank. It was the fifth time during the mission. And most interestingly, the tanks normally were stirred approximately once every 24 hours. So, why was it stirred that often?

In what Woodfill said was a problem unrelated to what caused the explosion, the quantity sensor or gauge was not working correctly on O2 tank 2. The EECOM (Electrical Environmental and Consumables) flight controller in Houston discovered that the quantity sensor was not reading accurately, and because of that Mission Control asked the astronauts to perform additional actuations of the stirrer to try and troubleshoot why the sensor wasn’t working correctly.

So, it took five actuations until the short circuit and the resulting fire and explosion occurred. If the gauge had been working correctly and the normal stirring of the tank had been done, that would have put the time of the fifth stirring after Lovell and Haise had departed for the lunar surface, and the rescue scenario that ultimately was carried out couldn’t have happened.

“Check the arithmetic,” said Woodfill. “Five actuations at 24 hour periods amounts to a MET of 120 hours. The lunar lander would have departed for the Moon at 103.5 hours into the mission. At 120 hours into the mission, the crew of Lovell and Haise would have been awakened from their sleep period, having completed their first moon walk eight hours before. They would receive an urgent call from Jack Swigert and/or Mission Control that something was amiss with the mother ship orbiting the Moon.”

Apollo 13 crew: Jim Lovell, Jack Swigert and Fred Haise. Credit: NASA

Who knows what would have happened to the crew? The fuel cells required the liquid oxygen tanks. This meant no production of electrical power, water and oxygen. The attached lunar lander had to be available. Likely, the two ships couldn’t even have docked back together. And what if the accident had happened behind the Moon without mission control’s help? Alone in the Command module, Swigert would have had difficulty analyzing the problem. Without a fueled lunar lander descent stage attached, lacking its consumables and engines as well as the needed battery power, water and oxygen, the crippled Command Module could not have returned to Earth with live astronaut(s). Not only would Lovell and Haise have perished but Swigert’s fate would have been the same. Even if the damaged Service Module’s engine had worked, no fuel cells meant the ship would die. The situation that the Apollo 13 crew actually faced was dire, but the alternative scenario would certainly have been fatal.

Woodfill contends that the quantity sensor malfunction assured the lunar lander would be present and fully fueled at the time of the disaster. It was an extremely fortuitous event. Had it not occurred, the timing of the explosion would have been far different and the crew would have perished.

Additional Articles from the “13 Things That Saved Apollo 13” series that have now been posted:


Part 2: The Hatch That Wouldn’t Close

Part 3: Charlie Duke’s Measles

Part 4: Using the LM for Propulsion

Part 5: Unexplained Shutdown of the Saturn V Center Engine

Part 6: Navigating by Earth’s Terminator

Part 7: The Apollo 1 Fire

Part 8: The Command Module Wasn’t Severed

Part 9: Position of the Tanks

Part 10: Duct Tape

Part 11: A Hollywood Movie

Part 12: Lunar Orbit Rendezvous

Part 13: The Mission Operations Team


Your Questions about Apollo 13 Answered by Jerry Woodfill (Part 1)

More Reader Questions about Apollo 13 Answered by Jerry Woodfill (part 2)

Final Round of Apollo 13 Questions Answered by Jerry Woodfill (part 3)

Never Before Published Images of Apollo 13’s Recovery

Listen to an interview of Jerry Woodfill on the 365 Days of Astronomy podcast.

Latest LRO Image Solves Apollo 14 Mystery

During the second EVA of the Apollo 14 mission on the moon, astronauts Alan Shepard and Edgar Mitchell had a goal of hiking to the rim of nearby Cone Crater in the Fra Maura highlands. But the steep terrain made the going difficult, elevating the astronauts’ heart rates. Additionally, without landmarks it was difficult to judge distances and the rolling terrain was filled with similar-looking ridges, so Shepard and Mitchell couldn’t really tell if they were close to the rim or not. Realizing time and available oxygen were getting short, Mission Control told the astronauts to head back to the Lunar Module, and although disappointed, the astronauts agreed. But how close did they actually come to the crater? No one knew for sure, until now.

One of the latest images from the Lunar Reconnaissance Orbiter shows new details of the Apollo 14 landing site. If you look closely at the image above, visible are the tracks from the astronauts steps and their three-wheeled MET cart, and you can clearly follow the trail of the astronauts on their “radial traverse.” Click the image for larger version if you’re having trouble seeing the tracks. Their tracks stop just 30 meters short of the rim, near a dark spot just to the lower left of the crater, which might be Saddle Rock, shown in the image below. Shepard and Mitchell never realized just how close they really were.

This photograph shows Saddle Rock, the largest boulder seen on this mission. Named for its shape, Saddle Rock is 4.5 meters across
This photograph shows Saddle Rock, the largest boulder seen on this mission. Named for its shape, Saddle Rock is 4.5 meters across

On the LROC (Lunar Reconnaissance Orbiter Camera) website, Samuel Lawrence notes that more and different detail is visible on this image as opposed to the initial images released prior to the Apollo 11 anniversary in July because the lighting is different. “This time the Sun is 24 degrees higher above the horizon providing a clearer view with fewer shadows. Albedo contrasts are greater, and more clearly show soil disturbances from landing, astronaut surface operations, and blast off.”
The MET cart from Apollo 14. Credit: NASA
The MET cart from Apollo 14. Credit: NASA

Lawrence notes how the term “radial traverse” does not quite do the crew of Apollo 14 justice. “Their journey sounds like a stroll in the park, however the reality is quite the contrary. The hike up Cone crater was quite challenging. For the first time, astronauts traveled out of the sight of their lunar module while hiking uphill over 1400 meters with only a poor map, dragging the tool cart (MET), and wearing their bulky spacesuits. It was an amazing feat that the two astronauts made it to the top of Cone ridge and acquired all their samples. They ended up about 30 meters shy of peering into Cone crater itself, surely a disappointment at the time, but absolutely no reflection on the success of the traverse and the scientific results gleaned after the mission.”

Here’s an annotated video of the Apollo 14 landing site. North is up, image width is approximately 1.6 km

Source: LROC

Gigapan the Apollo Landing Sites

If you haven’t had enough Apollo yet, this is like a firehose of image goodness. Gigapan and NASA Ames have collaborated to make huge, zoomable, panable images from two of the Apollo missions to the Moon. Apollo 16 and 17 are the only missions where the astronauts took panoramic images, so these are the only landing sites available in Gigapan. And if you really want to blow your socks off, look at these images in Google Moon. Click your icon for Google Earth (you DO have it downloaded already, don’t you?? If not go to Google Earth and download it,) choose Moon under the little Saturn-like icon on top, zoom in and find the flags for the Apollo 16 and 17 landing sites. Then look for the “camera” icons and click on one, and then choose the option to “fly” into the images. I’m still gasping from doing this with Apollo 17! Once you recover from flying in, you can then pan around and feel like you are walking alongside Gene Cernan and Harrison Schmitt on the Moon. It really is amazing!

Here’s the Gigapan image site. Enjoy!

Forgotten Apollo Data Could Solve Moon Dust Problem

Old, forgotten data from three Apollo moon missions could help overcome one of the biggest environmental hurdles facing future lunar colonists. Pervasive moon dust can clog equipment, scratch helmet visors –or worse, get inside astronaut lungs and cause serious health problems. But 173 data tapes hold information that could be essential in overcoming the problems the dust causes. The only trouble is that the tapes are archived on “ancient” 1960’s technology and no one could find the right equipment to playback the tapes. However, the Australian Computer Museum has an old IBM729 Mark 5 tape drive that should do the trick, IF the machine can be restored to operable condition again…

The IBM729 Mark 5 tape recorder is about as big as a household refrigerator. It recorded data from Apollo 11, 12 and 14 missions that carried “dust detectors.” Information from the detectors was beamed back to earth and recorded onto tapes. Copies of the tapes were supposedly sent to NASA, but the tapes were lost or misplaced before they could be archived in NASA’s holdings. But the original data tapes have sat in Perth, Australia for almost 40 years.

Physicist Brian O’Brien invented the detectors. He wrote a couple of papers on the information in the 1970’s, but no one was very interested in moon dust back then. However now, scientists realize this information could help make future missions to the moon more feasible.

Apollo astronaut Gene Cernan covered with moon dust.  Credit: NASA
Apollo astronaut Gene Cernan covered with moon dust. Credit: NASA

“These were the only active measurements of moon dust made during the Apollo missions, and no one thought it was important,” said O’Brien. “But it’s now realised that dust, to quote Harrison Schmitt, who was the last astronaut to leave the moon, is the number one environmental problem on the moon.”

O’Brien quit his work on lunar dust when he left the University of Sydney. Two years ago, someone at NASA remembered the data had been taken, but couldn’t find the duplicate tapes.

O’Brien says there is no indication as to when exactly the tapes were lost, but he guesses that it was “way, way back.” When O’Brien learned of the tape loss, he was contacted by Guy Holmes from a data recovery company who offered to try and extract the information on the old, original tapes. But Holmes realized he needed some old equipment to do the job, and came across the right IBM tape drive at the Australian Computer Museum.

The archaic-looking recorder is in need of refurbishing, however. Holmes jokes that a 1970s Toyota Corolla fan belt could be used to get the recorder up and running.

“The drives are extremely rare, we don’t know of any others that are still operating,” he said.

“It’s going to have to be a custom job to get it working again. It’s certainly not simple, there’s a lot of circuitry in there, it’s old, it’s not as clean as it should be and there’s a lot of work to do.”

Holmes is hopeful of getting the tape recorder working again in January, and then he says it should only take a week to extract information that has been locked away since the early 1970s.

Source: Australia’s ABC News