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.
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.
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.
“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.
Here’s an additional, more technical description of gimbal lock:
The explosion of a liquid oxygen tank in Apollo 13’s Service Module violently propelled debris and a 13-foot (4 meter) outer panel of the SM out into space.
Later, the crew saw the damage when they jettisoned the SM prior to reentering Earth’s atmosphere. Commander Jim Lovell described the scene:
“There’s one whole side of the spacecraft missing!” Lovell radioed to Mission Control. “Right by the high-gain antenna, the whole panel is blown out, almost from the base to the engine.”
The panel was likely blasted outward and rearward, toward the deep space S-Band radio antenna. The antenna was attached to the outer edge of the module’s rear base via a meter-long strut, and was used for both telemetry and voice communications.
NASA engineer Jerry Woodfill feels this hi-gain antenna was surely struck by the panel and/or schrapnel ejected by the oxygen tank explosion.
“That deep space radio communication was maintained during and after the explosion was almost miraculous,” Woodfill said. “Such a blow should have destroyed that hi-gain antenna. Those of us who watched the telemetry display monitors saw only a momentary flickering of the telemetry, but after a few flickers we continued to receive data.”
Woodfill said it was as though a boxer had taken a devastating punch and continued to stand unfazed.
This video of the severely damaged Apollo 13 service module was taken by the crew after it was jettisoned.
If instead, the antenna had been destroyed, the loss of data would have resulted in an impaired ability to analyze the situation and communicate with the crew.
The moments following the explosion are seared into Woodfill’s memory. On the night of April 13, 1970, 27-year-old Woodfill sat at his console in the Mission Evaluation Room (MER) in Building 45 at Johnson Space Center — next door to Mission Control in Building 30 — monitoring the caution and warning system.
“Because I was watching the command ship’s telemetry on a monitor at the moment of the explosion, both the words heard in my headset, “Houston, we’ve had a problem” and the scene I saw of the video monitor have not been forgotten” Woodfill said. “Seconds before I heard the audio of Jack Swigert’s call, I watched the video screen flicker several times.
To this day, Woodfill said he cannot understand how it continued to function following the explosion.
“As an engineer, I have studied the basics of simple machines,” he said. “The concept of the lever arm dictates that when an explosive blow strikes a structure atop an arm, the arm must bend back about its attachment to the supporting structure. In this case, that structure was the command ship’s supply module, the Service Module. Later photos by the crew (below) showed the antenna intact and the conical reflector dishes present with their center probes intact. In my mind, the entire assembly simply should have been severed altogether.”
The Unified S-band (USB) system was a tracking and communication system that combined television, telemetry, command, tracking and ranging into a single system. The high-gain antenna consisted of an 11-inch-diagonal wide-beam horn flanked by an array of four 31-inch-diameter parabolic reflectors. Its multifunctional system simplified operations, and its construction saved on weight.
And obviously, it was very durable.
Woodfill reiterated how important it was that the antenna survived the explosion.
“Later on it wasn’t needed, as the crew used the Lunar Module communication system,” said Woodfill, “but having that initial continuous communication was one of the things that was very important.”
And later those in Mission Control and the MER were be able to go back and look at the data that had been transmitted to Earth during that very crucial period of the mission, to help understand what had actually occurred.
“It was critical to have that data in those first moments of the explosion to analyze what had happened,” Woodfill said. “Uninterrupted communication was essential to investigating the status of the vehicle. While it may be true that the backup omni-antenna might have provided temporary communication, based on my analysis, the omni-antenna would not have served as ably during the time of greatest initial peril. In fact, to configure its use with the NASA world-wide tracking network would have caused an unfortunate delay.”
Here are some zoomed-in photos taken by the crew of Apollo 13 after the explosion of the S-Band/hi-gain antenna, and Woodfill has noted the parts of the antenna. They show the explosion failed to sever the hi-gain antenna mast and the conical dish receivers as well as the rectangular antenna, and the center probes of the conical dishes appear intact. Considering the force of the explosion, this is remarkable.
Join Universe Today in celebrating the 45th anniversary of Apollo 13 with insights from NASA engineer Jerry Woodfill as we discuss various turning points in the mission.
Within minutes of the accident during the Apollo 13 mission, it became clear that Oxygen Tank 2 in the Service Module had failed. Then Mission Control radioed up procedures and several attempts were made to try to save the remaining oxygen in Tank 1. But the pressure readings continued to fall, and it soon became obvious that Tank 1 was going to fail as well. At that point, both the crew and those in Houston realized the extreme seriousness of the situation.
No oxygen meant the fuel cells would be inoperative, and the fuel cells produced electrical power, water and oxygen – three things vital to the lives of the crew and the life of the spacecraft.
For power in the Command Module, all that was left were the batteries, but they were to be the sole source of power available for reentry. Besides the ambient air in the CM, the only oxygen remaining was contained in a so called ‘surge tank’ and three reserve one pound O2 tanks. These, too, were also mainly reserved for reentry, but they were automatically tapped in emergencies if there any oxygen fluctuations in the system.
In Chris Kraft’s autobiography Flight: My Life in Mission Control, the former flight director and former director of Johnson Space Center cited Gene Kranz’ decision to immediately isolate or seal off the surge tank as being one of the things that made rescuing the crew possible.
Why was it so essential to assure that the spare oxygen surge tank in the CM was protected?
“With the luxury of nearly a half century to review each decision made during those April days in 1970,” said NASA engineer Jerry Woodfill, “we can look back and see that those in Mission Control indeed made the right decisions, but at the time, many of those decisions had to be made without knowing the full extent of the problem. But more importantly, they had the presence of mind to look beyond their immediate problem and see the big picture of how to save Apollo 13.”
Shortly after the accident, electrical output readings for fuel cells 1 and 3 were at zero. Fuel cell 2 was still working, but without oxygen from the main tanks, it began to pull oxygen from the reserve surge tank. The 3.7 lb capacity tank was called a ‘surge tank’ because one of its functions was to absorb pressure fluctuations in the oxygen system. Due to the depletion of the two main oxygen tanks, the remaining fuel cell 2 began to automatically pull from the surge tank’s small supply of oxygen.
However, the surge tank also served as the reserve tank of oxygen that the crew would use to breathe during reentry to Earth after the Service Module (with -– during a normal mission — its two large full and functioning oxygen tanks) had been jettisoned. But with those tanks damaged and empty, the remaining fuel cell was starting to draw on the surge tank’s small supply in order to keep power flowing.
Kranz’ decision to isolate the tank was important, but of course, he didn’t make that decision alone. In an article in IEEE Spectrum, the EECOM (Electrical Environmental and Consumables) officer for Apollo 13 Sy Liebergot, recalled the moment he realized the Service Module was running out of power and oxygen — permanently. He, too, didn’t make that realization alone.
As writer Stephen Cass explained in IEEE Spectrum, “Each flight controller in mission control was connected via so-called voice loops–pre-established audio-conferencing channels–to a number of supporting specialists in back rooms who watched over one subsystem or another and who sat at similar consoles to those in mission control.” (This includes the Mission Evaluation Room where Jerry Woodfill monitored the Caution and Warning System.)
Liebergot was in communications with a team down the hall from Mission Control in Building 30, consisting of Dick Brown, a power-systems specialist, and George Bliss and Larry Sheaks, both life support specialists. When they confirmed the surge tank was being tapped, they realized they had to revise their priorities, from stabilizing Odyssey to preserving the command module’s re-entry reserves so that the crew could eventually return to Earth.
Liebergot said his call to isolate the surge tank initially took Kranz off guard, as it was exactly opposite of what was needed to keep the last fuel cell operating.
But Liebergot and his team were looking ahead. “We want to save the surge tank which we will need for entry,” writer Cass quoted Liebergot, and Kranz almost immediately understood. “Okay, I’m with you. I’m with you,” said Kranz resignedly, and he ordered the crew to isolate the surge tank.
“Because Gene was Flight Director at the time of the determination,” explained Woodfill, “his decisions result from inputs from a team of experts. He, like all the lead flight directors, is, ultimately, responsible for determining and weighing inputs from the chief system controllers who likewise receive instructions and information from a support team. To this end, ‘Flight’ is responsible for the final decision which is passed to the CapCom who, in turn, instructs the astronaut crew to act. Based on the process, often, an unknown expert might have been the original source of the instruction.”
This demonstrates how it was a team effort to save Apollo 13, and decisions that may have initially seemed incomprehensible ended up being the right ones.
“Loss of either Command Module capability — entry battery power or oxygen — threatened to be a fatal situation during the capsule’s entry return to Earth,” said Woodfill. Fortunately, as stated in one of our articles the first series of “13 Things,” a ‘jumper-charge technique dealt with the recharging the reentry batteries in the CM.
But while the LM had ample oxygen – in the form of oxygen tanks for repressurization after moon walks, tanks in the lander’s descent and ascent stages, and in the Portable Life Support System (PLSS) in the spacesuits that would have been used during moonwalks — apparently, there was no such similar way to replace oxygen in the CM from the lander’s oxygen stores.
Woodfill noted that had the surge tank been expended by the failed service module O2 tanks, there likely could have been a backup reentry plan of the crew wearing their launch suits and some type of jury-rigged system of using the oxygen from the PLSS system’s oxygen.
“A ‘shirt-sleeve’ entry would not have been the case,” said Woodfill. “This could have entailed a process similar to three scuba divers breathing from a pair of aqua lungs following the failure of one of the three.”
Woodfill noted one interesting fact. “Both Mission Control and the crew of Apollo 13 were so certain of the availability of surge tank oxygen that everyone agreed reentry would be space-suit-less.”
Join Universe Today in celebrating the 45th anniversary of Apollo 13 with insights from NASA engineer Jerry Woodfill as we discuss various turning points in the mission.
The final scenes of the movie Apollo 13 depict the spacecraft’s dramatic reentry into Earth’s atmosphere. As the seconds count beyond the time radio blackout should have lifted, the Capcom calls for Apollo 13’s crew to answer, but there is no response.
Everyone’s thoughts run through the possibilities: Had the heat shield been compromised by shrapnel from the exploded oxygen tank? Had the previously finicky hatch failed at this critical time? Had the parachutes turned to blocks of ice? Had the Inertial Measurement Unit (IMU) gyros failed, having inadequate time to warm-up causing the capsule to skip off the atmosphere, or incinerate with the crew in a fiery death plunge to Earth?
Of course, the crew finally did answer, but confirmation that Lovell, Haise and Swigert had survived reentry came nearly a minute and a half later than expected.
Some might feel director Ron Howard may have over-sensationalized the re-entry scenes for dramatic effect. But in listening to the actual radio communications between Mission Control and the ARIA 4 aircraft that was searching for a signal from the Apollo 13 crew, the real drama is just as palpable – if not more — than in the movie.
For virtually every reentry from Mercury through Apollo 12, the time of radio blackout was predictable, almost to the second. So why did Apollo 13’s radio blackout period extend for 87 seconds longer than expected, longer than any other flight?
During the Apollo era, the radio blackout was a normal part of reentry. It was caused by ionized air surrounding the command module during its superheated reentry through the atmosphere, which interfered with radio waves. The radio blackout period for the space shuttle program ended in 1988 when NASA launched the Tracking and Data Relay Satellite System (TDRS), which allowed nearly constant communication between the spacecraft and Mission Control.
It is difficult to find official NASA documentation about the extended radio blackout time for Apollo 13. In the mission’s Accident Review Board Report, there’s no mention of this anomaly. The only discussion of any communication problem comes in a section about reentry preparations, after the Service Module was jettisoned. There was a half-hour period of very poor communications with the Command Module due to the spacecraft being in a poor attitude with the Lunar Module still attached. Some of the reentry preparations were unnecessarily prolonged by the poor communications, but was more of a nuisance than an additional hazard to the crew, the report said.
In numerous interviews that I’ve done and listened to in preparation for this series of articles, when those involved with the Apollo 13 mission are asked about why the blackout period was longer than normal, the answer normally comes as a hedged response, with the crew or a flight director indicating they don’t know exactly why it happened. It seems analysis of this has defied a reasonable and irrefutable scientific explanation.
Jim Lovell gave the most detailed response – which is the one most often given as a likely explanation — suggesting it perhaps had to do with a shallowing reentry angle problem, with a strange space-like breeze that seemed to be blowing the spacecraft off-course with respect to entry.
“I think the reason why it was longer was the fact we were coming in shallower than we had planned,” Lovell said at the 2010 event. “Normally we come in from a Moon landing and have to hit the atmosphere inside a very narrow pie-shaped wedge and I think we were continually being pushed off that wedge. The reason was, we found out about 2-3 months after from analysis, was the lander’s venting of cooling vapor. The way we cool the electronic systems in LM was to pass water through a heat exchanger, and that water evaporates into space. That evaporation — which would be insignificant during a normal lunar landing mission — was going on for the 4 days we were using the LM as a lifeboat, acting as a small force, forcing us off the initial trajectory.”
Coming in on a shallower trajectory would result in a longer period in the upper atmosphere where there was less deceleration of the spacecraft. In turn, the reduced pace of deceleration lengthened the time that the heat of reentry produced the ionized gasses that would block communications.
But NASA engineer Jerry Woodfill offers additional insight into the communication delays. He recently spoke with Jerry Bostick, the Flight Dynamics Officer (FIDO) for Apollo 13, who told him, “Many believe the added time resulted from the communication signal skipping, like a stone, over layers of the upper atmosphere because of the shallow entry angle.”
“Bostick likened the radio signals to a stone skipping on a pond, and finally, the signal found a location to sink Earthward,” Woodfill said.
However, this explanation too, leaves questions. Woodfill said he has studied the “signal skipping” phenomenon, and has found information to both support and refute the concept by virtue of when such an occurrence could be expected.
“The consensus was it is a night time phenomena,” Woodfill said. “Apollo 13 entered in daylight in the Pacific and in Houston. Nevertheless, the question to this day demonstrates just how near Apollo 13 came to disaster. If the radio signal almost skipped off the Earth’s atmosphere, one wonders, just how very close was Apollo 13’s capsule and crew near to a fatal skipping into the oblivion of space as well.”
Another “angle” on Apollo 13’s reentry was how it very nearly escaped another potential disaster: landing in a typhoon.
“A tropical storm is a retro’s (retrofire officer) worst nightmare,” said Woodfill. “Knowing how unpredictable the movement and intensity of such storms are makes selecting a landing site difficult. No NASA reentry had ever landed in a tropical storm, and Apollo 13 might be the first. Among NASA scientists are meteorologists, and by their best science, they predicted that Tropical Storm Helen would move into the designated Apollo 13 landing site the day of reentry and splashdown.”
If Apollo 13 had splashed down amidst the storm, the capsule may have drifted and been lost at sea. To conserve the entry battery power, the beacon light recovery system had been deactivated. The crew would have been invisible to those looking for the capsule bobbing up and down in the Pacific Ocean. They eventually would have had to blow the hatch, and the Apollo 13 capsule likely would have sunk, similar to Gus Grissom’s Liberty Bell during the Mercury program. But the crew of Apollo 13 might not have been as fortunate as Grissom who had helicopter rescuers overhead quickly pulling him to safety.
However, the decision was made to ignore the weather forecasts, which ended up being fortuitous because Helen ultimately changed course. But then there was the uncertainty of the entry location due to the ‘shallowing’ the spacecraft was experiencing.
“Once more, the retro made the decision to ignore that shallowing at reentry in the same fashion as he had ignored the weathermen’s ominous prediction,” said Woodfill. “In both instances, the retro was correct. He rightly predicted that the drift would not be a problem in the final stages of reentry after the lander was jettisoned. Again, this was altogether fortuitous in that no one knew the lander’s cooling system was the source of the drift. Earlier, however, the retro had compensated for the shallowing drift by bringing Apollo 13 into the correct entry corridor angle via first having the crew fire the lander’s descent engine and later the lander’s thrusters.”
As it turned out those mysterious extra seconds caused by coming in at a shallow angle were also fortuitous.
While the added time of communications blackout was nail-biting, the more shallow and longer angle “added to the downrange path of Apollo 13, dropping the capsule in calm water so near the waiting aircraft carrier Iwo Jima that the accuracy was among the finest of the program,” Woodfill said.
Revisiting the length of the communications blackout, there are some discrepancies in various sources about the length of the extra time Apollo 13’s blackout time lasted. Some websites lists 25-30 seconds, others a minute. Again, I was unable to find an ‘official’ NASA statement on the subject and the transcript of the technical air to ground voice communications does not include time stamps for the beginning and end of blackout. Additionally, two of the definitive books about Apollo 13 – Lost Moon by Jim Lovell and Jeffrey Kluger, and A Man on the Moon by Andrew Chaikin – don’t give exact numbers on the timing of the blackout.
“Per my mission log it started at 142:39 and ended at 142:45— a total of six minutes,” Kranz told journalist Joe Pappalardo in 2007. “Blackout was 1:27 longer than predicted … Toughest minute and a half we ever had.”
87 seconds also is confirmed by a transmission recorded on one of the ARIA, the Apollo/Advanced Range Instrumentation Aircraft, which provided tracking and telemetry information for the Apollo missions, especially at launch and reentry, when the Manned Spaceflight Network tracking could not.
Space Historian Colin Mackellar from the Honeysuckle Creek website told Universe Today that until it was recently published on the Honeysuckle Creek website, the recording had not been heard by anyone other than Dunn’s family. Mackellar explained that it contains simultaneous audio of the NASA Public Affairs commentary, audio of the Flight Director’s loop, the ARIA transmissions and a portion of the Australian Broadcast Commission radio coverage.
Again, you can hear the palpable tension in the recording, which you can listen to at this link. At 7:21 in the audio, as communications blackout nears the predicted end, one of the ARIA communicators asks ARIA 4 if they can see the spacecraft. Negative is the reply.
At 7:55 you can hear Kranz asking if there is any acquisition of signal yet. Again at 8:43, Kranz asks, “Contact yet?” The answer is negative. Finally, at 8:53 in the audio, ARIA 4 reports AOS (acquisition of signal), which is relayed to Kranz. You can hear his relieved exhalation as he replies, “Rog (roger).”
Then comes Kranz saying, “Capcom, why don’t you try giving them a call.”
It required no great imagination to know that back in the US, and in fact all around the world, folks were glued to their TV sets in anticipation, and that Walter Cronkite was holding forth with Wally Schirra on CBS, and at the Houston Space Center breathing had ceased.
But we were there, ground zero, with front row seats and we would be the first to know and the first ones to tell the rest of the world if the Apollo 13 crew had survived…
On all the aircraft and all the airwaves there was complete silence as well as we all listened intently for any signal from Apollo 13.
ARIA 2 had no report of contact; ARIA 3 also had no report.
Then I observed a signal and Jack Homan, the voice radio operator advised me we had contact.
From Apollo 13 came the reply “OK, Joe……” relayed again from our radios to Houston and the rest of the world. Not much, but even such a terse reply was enough to let the world know the spacecraft and its crew had survived. In an age before satellite TV, teleconferencing, and the Internet, it was easy for us in the clouds at 30,000 feet above the splashdown zone to visualize breathing resuming in Houston and around the world.
Dunn concluded, “Now, exactly why would Ron Howard leave such a dramatic moment out of his film? There’s a real mystery!”
The Apollo 13 accident crippled the spacecraft, taking out the two main oxygen tanks in the Service Module. While the lack of oxygen caused a lack of power from the fuel cells in the Command Module, having enough oxygen to breathe in the lander rescue craft really wasn’t an issue for the crew. But having too much carbon dioxide (CO2) quickly did become a problem.
The Lunar Module, which was being used as a lifeboat for the crew, had lithium hydroxide canisters to remove the CO2 for two men for two days, but on board were three men trying to survive in the LM lifeboat for four days. After a day and a half in the LM, CO2 levels began to threaten the astronauts’ lives, ringing alarms. The CO2 came from the astronauts’ own exhalations.
NASA engineer Jerry Woodfill helped design and monitor the Apollo caution and warning systems. One of the systems which the lander’s warning system monitored was environmental control.
Like carbon monoxide, carbon dioxide can be a ‘silent killer’ – it can’t be detected by the human senses, and it can overcome a person quickly. Early on in their work in assessing the warning system for the environmental control system, Woodfill and his co-workers realized the importance of a CO2 sensor.
“The presence of that potentially lethal gas can only be detected by one thing – an instrumentation transducer,” Woodfill told Universe Today. “I had an unsettling thought, ‘If it doesn’t work, no one would be aware that the crew is suffocating on their own breath.’”
The sensor’s job was simply to convert the content of carbon dioxide into an electrical voltage, a signal transmitted to all, both the ground controllers, and the cabin gauge.
“My system had two categories of alarms, one, a yellow light for caution when the astronaut could invoke a backup plan to avoid a catastrophic event, and the other, an amber warning indication of imminent life-threatening failure,” Woodfill explained. “Because onboard CO2 content rises slowly, the alarm system simply served to advise and caution the crew to change filters. We’d set the threshold or “trip-level” of the alarm system electronics to do so.”
And soon after the explosion of Apollo 13’s oxygen tank, the assessment of life-support systems determined the system for removing carbon dioxide (CO2) in the lunar module was not doing so. Systems in both the Command and Lunar Modules used canisters filled with lithium hydroxide to absorb CO2. Unfortunately the plentiful canisters in the crippled Command Module could not be used in the LM, which had been designed for two men for two days, but on board were three men trying to survive in the LM lifeboat for four days: the CM had square canisters while the LM had round ones.
As was detailed so well by Jim Lovell in his book “Lost Moon,” and subsequently portrayed in detail in the movie “Apollo 13,” a group of engineers led by Ed Smylie, who developed and tested life support systems for NASA, constructed a duct-taped-jury-rigged CO2 filter, using only what was aboard the spacecraft to convert the plentiful square filters to work in the round LM system. (You can read the details of the system and its development in our previous “13 Things” series.)
Needless to say, the story had a happy ending. The Apollo 13 accident review board reported that Mission Control gave the crew further instructions for attaching additional cartridges when needed, and the carbon dioxide partial pressure remained below 2mm Hg for the remainder of the Earth-return trip.
But the story of Jerry Woodfill and the CO2 sensor can also serve as an inspiration to anyone who feels disappointed in their career, especially in STEM (science, technology, engineering and math) fields, feeling that perhaps what you are doing doesn’t really matter.
“I think almost everyone who came to NASA wanted to be an astronaut or a flight director, and I always felt my career was diminished by the fact that I wasn’t a flight controller or astronaut or even a guidance and navigation engineer,” Woodfill said. “I was what was called an instrumentation engineer. Others had said this is the kind of job that was superfluous.”
Woodfill worked on the spacecraft metal panels which housed the switches and gauges. “Likely, a mechanical engineer might not find such a job exciting,” he said, “and to think, I had once studied field theory, quantum electronics and other heady disciplines as a Rice electrical engineering candidate.”
Later, to add to the discouragement was a conversation with another engineer. “His comment was, ‘No one wants to be an instrumentation engineer,” Woodfill recalled, “thinking it is a dead-end assignment, best avoided if one wants to be promoted. It seemed that instrumentation was looked upon as a sort of ‘menial servant’ whose lowly job was servicing end users such as radar, communications, electrical power even guidance computers. In fact, the users could just as readily incorporate instrumentation in their devices. Then, there would be no need for an autonomous group of instrumentation guys.”
But after some changes in management and workforce, Woodfill became the lead Command Module Caution and Warning Project Engineer, as well as the Lunar Lander Caution and Warning lead – a job he thought no one else really wanted.
But he took on the job with gusto.
“I visited with a dozen or more managers of items which the warning system monitored for failure,” Woodfill said. He convened a NASA-Grumman team to consider how best to warn of CO2 and other threats. “We needed to determine at what threshold level should the warning system ring an alarm. All the components must work, starting with the CO2 sensor. The signal must pass from there through the transmitting electronics, wiring, ultimately reaching my warning system “brain” known as the Caution and Warning Electronics Assembly (CWEA).”
And so, just hours after the explosion on Apollo 13, the Mission Engineering Manager summoned Woodfill to his office.
“He wanted to discuss my warning system ringing carbon dioxide alarms,” Woodfill said. “I explained the story, placing before him the calibration curves of the CO2 Partial Pressure Transducer, showing him what this instrumentation device is telling us about the threat to the crew.”
Now, what Woodfill had once had deemed trivial was altogether essential for saving the lives of an Apollo 13 astronaut crew. Yes, instrumentation was just as important as any advanced system aboard the command ship or the lunar lander.
“And, I thought, without it, likely, no one would have known the crew was in grave danger,” said Woodfill, “let alone how to save them. Instrumentation engineering wasn’t a bad career choice after all!”
This is an example of the team effort that saved Apollo 13: that the person who was working on the transducer years prior was just as significant as the person who came up with the ingenious duct tape solution.
And it was one of the additional things that saved Apollo 13.
To celebrate the 45th anniversary of the Apollo 13 mission, Universe Today is featuring “13 MORE Things That Saved Apollo 13,” discussing different turning points of the mission with NASA engineer Jerry Woodfill.
During the first two days of the Apollo 13 mission, it was looking like this was going to be the smoothest flight of the program. As Capcom Joe Kerwin commented at 46:43 Mission Elapsed Time (MET), “The spacecraft is in real good shape as far as we are concerned. We’re bored to tears down here.”
Everything was going well, and in fact the crew was ahead of the timeline. Commander Jim Lovell and Lunar Module Pilot Fred Haise had entered the Aquarius Lunar Module 3 hours earlier than the flight plan had scheduled, wanting to check out the pressure in the helium tank – which had given some erroneous readings in ground tests before the launch. Everything checked out OK.
Opening up Aquarius early may have been one more thing that saved Apollo 13, says NASA engineer Jerry Woodfill.
“The first time the hatches between both vehicles are opened is a time consuming process,” Woodfill told Universe Today. “It’s as though a bank teller is requested to provide a customer access to a safety deposit box behind two locked vault doors.”
The removable hatch in the Odyssey Command Module had to be tied down and stowed before entering the tunnel for access to the second door, the lander’s entry hatch. Time was required for pressure equalization process so that the tunnel, command ship and lander were at one uniform pressure.
Often, there was a putrid, burnt insulation odor when the hatch to the LM was first opened, as previous crews described, so normally time was allowed for the smell to dissipate. All of these tasks were dealt with by about 55 hours MET, much earlier than originally planned. For some reason, the LM Pilot even brought the lander’s activation check list back into the command ship for study, though activation was scheduled hours away.
“Perhaps, this would be Fred Haise’s bedtime book to read preparing himself for sleep,” Woodfill said.
But first, the crew provided a 49-minute TV broadcast showing how easily they moved about in weightlessness in the cramped spacecraft.
Then, it happened. Nine minutes later, at 55:54:56 MET, came the explosion of the oxygen tank in the Service Module. Despite ground and crew efforts to understand the problem, confusion reigned.
13 minutes after the explosion, Lovell looked out one of Odyssey’s windows and reported, “We are venting something out into space,” and quickly the crew and ground controllers knew they were losing oxygen. Without oxygen, the fuel cells that provided all the power to the CM would die. Tank 2, of course, was gone with the explosion and the plumbing on Tank 1 was severed, so the oxygen was bleeding off from that tank, as well.
At one hour, 29 seconds after the explosion, the new Capcom Jack Lousma said after instructions from Flight Director Glynn Lunney, “[The oxygen] is slowly going to zero, and we are starting to think about the LM lifeboat.” From space, astronaut Jack Swigert replied, “That’s what we have been thinking about too.”
At that point, only fifteen minutes of power remained in the Command Module.
“Fifteen minutes more and the entire assemblage might have been a corpse with no radio, no guidance, no oxygen flowing into the cabin to keep Lovell, Haise and Swigert alive,” said Woodfill. “Certainly, it was fortuitous circumstances that led to opening the LM early. Simply consider how much time it would have taken to remove both hatches, stabilize and inspect the tunnel and lander interior. Add to this the time required to power up the lander’s life support systems. As it was, they had an open pathway into a safe haven, a lifeboat, called the lunar lander, crucial to survival.”
If the LM had not been opened, the crew would have likely run out of time before the Command Module’s batteries died, which would have created several problems.
As we discussed five years ago in one of the original “13 Things” articles, all the guidance parameters which would help direct the ailing ship back to Earth were in Odyssey’s computers, and needed to be transferred over to Aquarius. Without power from the fuel cells, they kept the Odyssey alive by using the reentry batteries as an emergency measure. These batteries were designed to be used during reentry when the crew returned to Earth, and were good for limited number of hours during the time the crew would jettison the Service Module and reenter with only the tiny Command Module capsule.
“Those batteries were not ever supposed to be used until they got ready to reenter the Earth’s atmosphere,” said Woodfill. “If those batteries had been depleted, that would have been one of the worst things that could have happened. The crew worked as quickly as they could to transfer the guidance parameters, but any extra time or problem, and we could have been without those batteries. Those batteries were the only way the crew could have survived reentry. This is my take on it, but the time saved by not having to open up the Lunar Module helped those emergency batteries have just enough power in them so they could recharge them and reenter.”
By 58:40 MET, the guidance information from the Command Module computer had been transferred to the LM guidance system, the LM was fully activated and the Command and Service Module systems were turned off.
Mission Control and the crew had successfully managed the first of many “seat of the pant” procedures they would need to do in order to bring the crew of Apollo 13 back home.
To celebrate the 45th anniversary of the Apollo 13 mission, Universe Today is featuring “13 MORE Things That Saved Apollo 13,” discussing different turning points of the mission with NASA engineer Jerry Woodfill.
Very quickly after the explosion of Oxygen Tank 2 in Apollo 13’s service module, it became apparent the Odyssey command module was dying. The fuel cells that created power for the Command Module were not working without the oxygen. But over in the Aquarius lunar lander, all the systems were working perfectly. It didn’t take long for Mission Control and the crew to realize the Lunar Module could be used as a lifeboat.
The crew quickly powered up the LM and transferred computer information from Odyssey to Aquarius. But as soon as they brought the LM communications system on line another problem developed.
The Apollo 13 crew couldn’t hear Mission Control.
The crew radioed they were getting lots of background static, and at times, they reported communications from the ground were “unreadable.”
Additionally, the Manned Space Flight Network (MSFN) tracking stations around the world were having trouble “hearing” the Apollo 13 spacecraft’s radio broadcasting the tracking data.
“Without reliable knowledge of where the vehicle was or was going might result in disaster,” said NASA engineer Jerry Woodfill.
What was going on?
The dilemma was that two radio systems were using the same frequency. One was the transmitter from the LM’s S-band antenna. The other was the broadcast from the spent third stage of the Saturn V, known as the S-IVB.
As part of a science experiment, NASA had planned for crashing Apollo 13’s S-IVB into the Moon’s surface. The Apollo 12 mission had left a seismometer on the Moon, and an impact could produce seismic waves that could be registered for hours on these seismometers. This would help scientist to better understand the structure of the Moon’s deep interior.
In Apollo 13’s nominal flight plan, the lander’s communications system would only be turned on once the crew began preparing for the lunar landing. This would have occurred well after the S-IVB had crashed into the Moon. But after the explosion, the flight plan changed dramatically.
But with both the Saturn IVB and the LM’s transmitters on the same frequency, it was like having two radio stations on the same spot on the dial. Communications systems on both ends were having trouble locking onto the correct signal, and instead were getting static or no signal at all.
The Manned Space Flight Network (MSFN) for the Apollo missions had three 85 foot (26 meter) antennas equally spaced around the world at Goldstone, California, Honeysuckle Creek, Australia and Fresnedillas (near Madrid), Spain.
According to historian Hamish Lindsay at Honeysuckle Creek, there was initial confusion. The technicians at the tracking sites immediately knew what the problem was and how they could fix it, but Mission Control wanted them to try something else.
“The Flight Controllers at Houston wanted us to move the signal from the Lunar Module across to the other side of the Saturn IVB signal to allow for expected doppler changes,” Hamish quoted Bill Wood at the Goldstone Tracking Station. ”Tom Jonas, our receiver-exciter engineer, yelled at me, ‘that’s not going to work! We will end up locking both spacecraft to one up-link and wipe out the telemetry and voice contact with the crew.’”
At that point, without the correct action, Houston lost telemetry with the Saturn IVB and voice contact with the spacecraft crew.
But luckily, the big 64 meter Mars antenna at Goldstone was already being switched over to help with the Apollo emergency and “their narrower beam width managed to discriminate between the two signals and the telemetry and voice links were restored,” said Wood.
That stabilized the communications. But then it was soon time to switch to the tracking station at Honeysuckle Creek.
There, Honeysuckle Creek Deputy Director Mike Dinn and John Mitchell, Honeysuckle Shift Supervisor were ready. Both had foreseen a potential problem with the two overlapping frequency systems and before the mission had discussed it with technicians at Goddard Spaceflight Center about what they should do if there was a communication problem of this sort.
When Dinn had been looking for emergency procedures, Mitchell had proposed the theory of getting the LM to switch off and then back on again. Although nothing had been written down, when the emergency arose, Dinn knew what they had to do.
“I advised Houston that the only way out of this mess was to ask the astronauts in the LM to turn off its signal so we could lock on to the Saturn IVB, then turn the LM back on and pull it away from the Saturn signal,” said Dinn.
It took an hour for Mission Control in Houston to agree to the procedure.
“They came back in an hour and told us to go ahead,” said Mitchell, “and Houston transmitted the instructions up to the astronauts ‘in the blind’ hoping the astronauts could hear, as we couldn’t hear them at that moment. The downlink from the spacecraft suddenly disappeared, so we knew they got the message. When we could see the Saturn IV downlink go way out to the prescribed frequency, we put the second uplink on, acquired the LM, put the sidebands on, locked up and tuned away from the Saturn IVB. Then everything worked fine.”
Dinn said they were able to “pull” the frequencies apart by tuning the station transmitters appropriately.
This action, said Jerry Woodfill, was just one more thing that saved Apollo 13.
“The booster stage’s radio was de-turned sufficiently from the frequency of the LM S-Band so that the NASA Earth Stations recognized the signal required to monitor Apollo 13’s orbit at lunar distances,” explained Woodfill. “This was altogether essential for navigating and monitoring the crucial mid-course correction burn which restored the free-return trajectory as well as the set-up of the subsequent PC+2 burn to speed the trip home needed to conserve water, oxygen and water stores to sustain the crew.”
As for the S-IVB science experiment, the 3rd stage crashed successfully on the Moon, providing some of the first data for understanding the Moon’s interior.
Later, on hearing that the stage had hit the Moon, Apollo 13 Commander Jim Lovell said, “Well, at least one thing worked on this mission!”
(Actually, in spite of the Apollo 13 accident, a total of four science experiments were successfully conducted on Apollo 13.)
In early 2010, NASA’s Lunar Reconnaissance Orbiter spacecraft imaged the crater left by the Apollo 13 S-IVB impact.
Thanks to space historian Colin Mackellar from the Honeysuckle Creek website, along with technician Hamish Lindsay and his excellent account of the Honeysuckle Creek Tracking station and their role in the Apollo 13 mission.
To celebrate the 45th anniversary of the Apollo 13 mission, Universe Today is featuring “13 MORE Things That Saved Apollo 13,” discussing different turning points of the mission with NASA engineer Jerry Woodfill.
Understandably, it was chaotic in both Mission Control and in the spacecraft immediately after the oxygen tank exploded in Apollo 13’s Service Module on April 13, 1970.
No one knew what had happened.
“The Apollo 13 failure had occurred so suddenly, so completely with little warning, and affected so many spacecraft systems, that I was overwhelmed,” wrote Sy Liebergot in his book, Apollo EECOM: Journey of a Lifetime. “As I looked at my data and listened to the voice report, nothing seemed to make sense.”
But somehow, within 53 minutes of the explosion, the ship was stabilized and an emergency plan began to evolve.
“Of all of the things that rank at the top of how we got the crew home,” said astronaut Ken Mattingly, who was sidelined from the mission because he might have the measles, “was sound management and leadership.”
By chance, at the time of the explosion, two Flight Directors — Gene Kranz and Glynn Lunney — were present in Mission Control. NASA engineer Jerry Woodfill feels having these two experienced veterans together at the helm at that critical moment was one of the things that helped save the Apollo 13 crew.
“The scenario resulted from the timing,” Woodfill told Universe Today, “with the explosion occurring at 9:08 PM, and Kranz as Flight Director, but with Lunney present to assume the “hand-off” around 10:00 PM. That assured that the expertise of years of flight control leadership was conferring and assessing the situation. The presence of these colleagues, simultaneously, had to be one of the additional thirteen things that saved Apollo 13. With Lunney looking on, the transition was as seamless as a co-pilot taking the helm from a pilot of a 747 passenger jet.”
Woodfill made an additional comparison: “Having the two Flight Directors on hand at that critical moment is like having Michael Jordan and Magic Johnson on a six-man basketball squad and the referee ignoring any fouls their team might make.”
“Gene was on the team before me and he had had a long day in terms of hours. …And shortly before his shift was scheduled to end is when the “Houston, we’ve got a problem” report came in. And at first, it was not terribly clear how bad this problem was. And one of the lessons that we had learned was, “Don’t go solving something that you don’t know exists.” You’ve got to be sure … So, it was generally a go slow, let’s not jump to a conclusion, and get going down the wrong path…. We had a number of situations to deal with.”
The “not jumping to conclusions” was equally expressed by Kranz when he told his team, “Let’s solve the problem, but let’s not make it any worse by guessing.”
The presence of Kranz and Lunney, simultaneously, is especially obvious reading Gene Kranz’s book, Failure Is Not an Option.
“Kranz captures the wealth of “brain power” present at the moment of the explosion,” said Woodfill. “Besides both Kranz and Lunney, their entire teams overlapped. Yes, there were two squads on the floor competing with the dire opponents who threatened the crew’s survival.”
The crew’s survival was foremost in the minds of the Flight Directors. “We will never surrender, we will never give up a crew,” Kranz said later.
Perhaps, the most obvious evidence of how fortuitous the presence of both Kranz and Lunney was, Kranz recorded on page 316-317 of his book. The pair refuses to accept the more popular but potentially fatal decision (a direct abort) to speed the crew’s return to Earth using the damaged command ship’s engine. The direct abort would have been to jettison the lander and fire the compromised command ship’s engine to potentially quicken the return to Earth by 50 hours.
Mattingly recalled those early minutes in Mission Control after the explosion.
“The philosophy was ‘never get in the way of success,’” said Mattingly, speaking at a 2010 event at the Smithsonian Air and Space Museum. “We had choices, we debated about turning immediately around and coming home or going around the moon. In listening to all of those discussions, we never closed the door about any option of getting home. We didn’t know yet how we were going to get there, but you always make sure you don’t take a step that would jeopardize it.”
And so, with the help of their teams, the two Flight Directors quickly ran through all the options, the pros and cons, and – again – within 53 minutes after the accident they made the decision to have the crew continue their trajectory around the Moon.
Later, when Jim Lovell commented on viewing the damaged Service Module when it was jettisoned before the crew re-entered Earth’s atmosphere — “There’s one whole side of that spacecraft missing. Right by the high gain antenna, the whole panel is blown out, almost from the base to the engine,” — it was indeed an ominous look at what might have ensued using it for a quick return to Earth.
By the end of the Lunney team’s shift about ten hours after the explosion, Mission Control had put the vehicle back on an Earth return trajectory, the inertial guidance platform had been transferred to the Lunar Module, and the Lunar Module was stable and powered up for the burn planned the would occur after the crew went around the Moon. “We had a plan for what that maneuver would be, and we had a consumable profile that really left us with reasonable margins at the end,” Lunney said.
“We had many problems here – we had a variety of survival problems, we had electrical management, water management, and we had to figure out how to navigate because the stars were occluded by the debris cloud surrounding the spacecraft. Basically we had to turn a two day spacecraft into a four and a half day spacecraft with an extra crewmember to get the crew back home. We were literally working outside the design and test boundaries of the spacecraft so we had to invent everything as we went along.”
A look at the transcripts of the conversations between Flight Controllers, Flight Directors and support engineers in the Mission Evaluation Room reveals the methodical working of the problems by the various teams. Additionally, you can see how seamlessly the teams worked together, and when one shift handed off to another, everything was communicated.
“The other thing I would say about it is, and we talked about Flight Directors and teams, equally important was the fact that, during those flights, we had this Operations team that you have seen in the Control Center in the back rooms around it and we sort of had our own way of doing things in our own team, and we were fully prepared to decide whatever had to be decided. But in addition to that, we had the engineering design teams that would follow the flight along and look at various problems that occurred and put their own disposition on them. …That was part of this network of support. People had their certain jobs to do. They knew what it was. They knew how they fit in. And they were anticipating and off doing it.”
Without the leadership of the Flight Directors, keeping the teams focused and on-task, the outcome of the Apollo 13 mission may have been much different.
“It is the experience of these two, Kranz and Lunney, working together which likely saved the crew from what might have been certain death,” said Woodfill.
In our original series 5 years ago on the “13 Things That Saved Apollo 13,” the first item we discussed was the timing of the explosion. As NASA engineer Jerry Woodfill told us, 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.
An explosion earlier in the mission (assuming it would have occurred after Apollo 13 left Earth orbit) would have meant 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. An explosion later, perhaps after astronauts Jim Lovell and Fred Haise had already descended to the lunar surface, and all three crew members wouldn’t have been able to use the lunar lander as a lifeboat. Additionally, the two spacecraft likely couldn’t have docked back together, and without the descent stage’s consumables left on the Moon (batteries, oxygen, etc.) that would have been a fruitless endeavor.
Now, for our first article in our subsequent series “13 MORE Things That Saved Apollo 13,” we’re going to revisit that timing, but look more in detail as to WHY the explosion happened when it did, and how it affected the rescue of the crew. The answer lies with the failure of a pressure sensor in Oxygen Tank 2, an issue unrelated to the uninsulated wires in the tank that caused the explosion.
Most who are familiar with the story of Apollo 13 are acquainted with the cause of the explosion, later determined by an accident investigation committee led by Edgar Cortright, Director of the Langley Research Center.
The tank had been dropped five years before the flight of Apollo 13, and no one realized the vent tube on the oxygen tank was jarred out of alignment. After a Count Down Demonstration Test (CDDT) conducted on March 16, 1970 when all systems were tested while the Apollo 13 spacecraft sat atop the Saturn V rocket on the launch-pad, the cold liquid oxygen would not empty out of Oxygen Tank 2 through that flawed vent pipe.
The normal approach was to use gaseous oxygen to push the liquid oxygen out of the tank through the vent pipe. Since that wasn’t working, technicians decided the easiest and quickest way to empty the liquid oxygen would be to boil it off using the heaters in the tank.
“In each oxygen tank were heaters and a paddle wheel fan,” Woodfill explained. “The heater and fan (stirrer) device encouraged a portion of the cold liquid 02 to turn into a higher pressure 02 gas and flow into the fuel cells. A fan also known as the cryo-stirrer was powered each time the heater was powered. The fan served to stir the liquid 02 to assure it was uniformly consistent in density.”
To protect the heater from being overly hot, a switch-like device called a relay turned off heater power anytime the temperature exceeded 80 degrees F. Also, there was a temperature gauge which technicians on the ground could monitor if temperature exceeded 80 degree F.
The original Apollo spacecraft worked on 28 volts of electricity, but after the 1967 fire on the Launchpad for Apollo 1, the Apollo spacecraft’s electrical systems had been modified to handle 65 volts from the external ground test equipment. Unfortunately Beech, the tank’s manufacturer failed to change out this tank, and the heater safety switch was still set for 28 volt operation.
“When the heater was powered up to vent the tank, the higher voltage “fused” the relay contacts so that the switch could not turn off power when the temperature of the tank exceeded 80 degrees F (27 C),” said Woodfill.
Additionally, the temperature gauge on the ground test panel only went to 88 degrees F (29.5 C), so no one was aware of this excessive heat.
“As a result,” said Woodfill, “the heater and the wires which powered it reached estimated temperatures of around 1000 degrees F. (538°C), hot enough to melt the Teflon insulation on the heater wires and leave portions of them bare. Bare wires meant the potential for a short-circuit and an explosion since these wires were immersed in the liquid oxygen.”
Because the tank had been dropped, and because its heater design had not been updated for 65 volt operation, the tank was a virtual bomb, Woodfill said. Anytime power was applied to those heaters to stir the tank’s liquid oxygen, an explosion was possible.
At 55:54:53 Mission Elapsed Time (MET), the crew was asked to conduct a stir of the oxygen tanks. It was then that the damaged wires in Oxygen Tank 2 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.
But back to the quantity sensor on Oxygen Tank 2. For a reason yet to be understood, during the early part of the Apollo 13 flight, the sensor failed. Prior to launch, that Tank 2 quantity sensor was being monitored by the onboard telemetry system, and it apparently worked perfectly.
“The failure of that probe in space is, perhaps, the most important reason Apollo 13’s crew lived,” said Woodfill.
Here’s the explanation of why Woodfill makes that claim.
Woodfill’s research of Apollo 13 indicated that standard operating procedure (SOP) had Mission Control request a stirring of the cryos approximately every 24 hours. For the Apollo 13 mission, the first stir came about 24 hours into the mission (23:20:23 MET). Ordinarily, the next cryo stir would not be called for until 24 hours later. The heater-cryo stir procedure was done to assure accuracy of the quantity gauge and proper operation of the system through the elimination of O2 stratification. The sensor read more accurately because the stir made the liquid oxygen more uniform and less stratified. After the first stir, 87 % remaining oxygen quantity was indicated, a bit ahead of expectations. The next stir came about a day later, about 46:40 MET.
At the time of this second heater-cryo-stir, Oxygen Tank 2’s quantity sensor failed. Post mission analysis by the investigation committee indicated the failure was not related to the bare heater wires.
The loss of ability to monitor Oxygen Tank 2’s quantity caused mission control to radio to the crew: “(Because the quantity sensor failed,) we’re going to be requesting you stir the cryos every six hours to help gage how much 02 is in tank 2.”
However, Mission Control chose to perform some analysis of the situation in Tank 2 by calling for another stir, not at 53 hours MET but at 47:54:50 MET and still another at 51:07:41 . Because the other oxygen tank, Tank 1, indicated a low pressure, both tanks were stirred at 55:53.
“Count the number of stirs since launch,” Woodfill said. “1. at 23:20:23, 2. at 46:40, 3. at 47:54:50, 4. at 51:07:44 and 5. at 55:53. There were five applications of current to those bare heater wires. The last three occurred over a period of only 8 hours rather than 72 hours. Had it not been for the non-threatening failure of Tank 2’s quantity probe and the low pressure in O2 Tank 1, this would not have been the case.”
Woodfill explained that anyone who has analyzed hardware failures understands that the more frequent and shorter the period between operations of a flawed component hastens ultimate failure. NASA performs stress testing on hundreds of electrical systems using this approach. More frequent power-ups at shorter intervals encourages flawed systems to fail sooner.
The short circuit in Oxygen Tank 2 after the fifth heater-cryo-stir resulted in the explosion of Apollo 13’s Oxygen Tank 2. Had the normal sequence of stirs been performed at 24 hour intervals, and the failure came after the fifth stirring, the explosion would have occurred after the lunar module, the life boat, was no longer available.
“I contend that the quantity sensor malfunction was fortuitous and assured the lander would be present and fully fueled at the time of the disaster,” Woodfill said.
5 heater actuations at 24 hours periods amounts to a MET of 120 hours.
“The lunar lander would have departed for the Moon at 103.5 hours into the mission,” Woodfill said. “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.”
Furthermore, Woodfill surmised, analysis of Swigert’s ship’s problems would likely be clouded by the absence of his two crewmates on the lunar surface. Added problems for Mission Control would have been the interruption of communications each time the command ship went behind the Moon, interrupting the telemetry so crucial to analyzing the failure. When it became evident, the cryogenic system would no longer produce oxygen, water, and electrical power, those command module emergency batteries would have been activated. Likely, Mission Control would have ordered an abort of the lunar lander earlier, but, of course, that would have been futile. Had the tiny lander’s ascent stage rendezvoused and docked with the depleted CM, all the life supporting descent stage consumables would remain on the Moon.
“The nightmare would have the Apollo 13 crew saying their last farewells to their families and friends,” said Woodfill. “One can only speculate how the end might have come.”
And there likely would not have been Apollo 14, 15, 16 and 17 — at least not for a very long time.
Another aspect of the timing of the explosion that Woodfill has considered is, why didn’t the tank explode on the Launchpad?
Following the March 16 CDDT, no additional “power-up” or tests were planned. However, it is not uncommon for pre-launch re-verification to be performed.
“One such re-check might easily have been these heater circuits since they had been used in a non-standard way to empty the oxygen from the cryo tanks after the Countdown Demonstration Test (CDDT) weeks earlier,” Woodfill said. “Such re-do’s often occur for myriad reasons. For Apollo 13, despite the compromised system, none occurred until the craft was safely on its way to the Moon.”
However, such a routine re-test involving cryo stirring would have unknowingly jeopardized the launch vehicle, support persons, or astronaut crew.
Or, if the quantity sensor had failed on the ground, likely the same kind of trouble shooting that was done by Mission Control and the Apollo 13 crew, would have been performed by the KSC ground team.
Had the sensor failed at that time, a series of heater actuations/stirrings would have been executed to trouble-shoot the device.
“Of course, the result would have been the same kind of explosion nearly 55 hours 55 minutes after launch,” Woodfill said. “On the ground, the Apollo 13 explosion could have taken the lives of Lovell and crew if trouble-shooting had been done while the crew awaited launch.”
If the trouble-shooting had been done earlier, with several heater actuations/stirrings during the days before the launch, Woodfill said, “a terrible loss of life would have ensued with, potentially, scores of dedicated Kennedy Space Center aerospace workers bravely attempting to fix the problem. And the towering thirty-six story Saturn 5 would have collapsed earthward in a ball of fire reminiscent of that December 1957 demise of America’s Vanguard rocket.”
“Yes, the fact that the Oxygen Tank 2 quantity sensor did not fail on the launch pad, but failed early in the flight was one of the additional things that saved Apollo 13.”