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.”
“Things had gone real well up to at that point of 55 hours, 54 minutes and 53 seconds (mission elapsed time),” said Apollo 13 astronaut Fred Haise as he recounted the evening of April 13, 1970, the night the Apollo 13’s command module’s oxygen tank exploded, crippling the spacecraft and endangering the three astronauts on board.
“Mission Control had asked for a cryo-stir in the oxygen tank …and Jack threw the switches,” Haise continued. “There was a very loud bang that echoed through the metal hull, and I could hear and see metal popping in the tunnel [between the command module and the lunar lander]… There was a lot of confusion initially because the array of warning lights that were on didn’t resemble anything we have ever thought would represent a credible failure. It wasn’t like anything we were exposed to in the simulations.”
What followed was a four-day ordeal as Haise, Jim Lovell and Jack Swigert struggled to get back to Earth, as thousands of people back on Earth worked around the clock to ensure the astronauts’ safe return.
In 2010, Universe Today also commemorated the Apollo 13 anniversary with a series of articles titled “13 Things That Saved Apollo 13.” We looked at 13 different items and events that helped turn the failure into success, overcoming the odds to get the crew back home. We interviewed NASA engineer Jerry Woodfill, who helped design the alarm and warning light system for the Apollo program, which Haise described above.
Now, five years later on the 45th anniversary of Apollo 13, Woodfill returns with “13 MORE Things That Saved Apollo 13.” Over the next few weeks, we’ll look at 13 additional things that helped bring the crew home safely.
Woodfill has worked for NASA for almost 50 years as an engineer, and is one of 27 people still remaining at Johnson Space Center who were also there for the Apollo program. In the early days of Apollo, Woodfill was the project engineer for the spacecraft switches, gauges, and display and control panels, including the command ship’s warning system.
On that night in April 1970 when the oxygen tank in Apollo 13’s command module exploded, 27-year-old Woodfill sat at his console in the Mission Evaluation Room (MER) at Johnson Space Center, monitoring the caution and warning system.
“It was 9:08 pm, and I looked at the console because it flickered a few times and then I saw a master alarm come on,” Woodfill said. “Initially I thought something was wrong with the alarm system or the instrumentation, but then I heard Jack Swigert in my headset: “Houston, we’ve had a problem,” and then a few moments later, Jim Lovell said the same thing.”
Listen to the audio of communications between the crew and Mission Control at the time of the explosion:
Located in an auxiliary building, the MER housed the engineers who were experts in the spacecrafts’ systems. Should an inexplicable glitch occur, the MER team could be consulted. And when alarms starting ringing, the MER team WAS consulted.
The ebullient and endearing Woodfill brings a wealth of knowledge — as well as his love for public outreach for NASA — to everything he does. But also, for the past 45 years he has studied the Apollo 13 mission in intricate detail, examining all the various facets of the rescue by going through flight transcripts, debriefs, and other documents, plus he’s talked to many other people who worked during the mission. Fascinated by the turn of events and individuals involved who turned failure into success, Woodfill has come up with 13 MORE things that saved Apollo 13, in addition to the original 13 he shared with us in 2010.
Woodfill tends to downplay both his role in Apollo 13 and the significance of the MER.
“In the MER, I was never involved or central to the main events which rescued Apollo 13,” Woodfill told Universe Today. “Our group was available for mission support. We weren’t flight controllers, but we were experts. For other missions that were routine we didn’t play that big of a role, but for the Apollo 13 mission, we did play a role.”
But Apollo Flight Director Gene Kranz, also speaking at the 2010 event at the Smithsonian Air and Space Museum, has never forgotten the important role the MER team played.
“The thing that was almost miraculous here [for the rescue], was I think to a great extent, the young controllers, particularly the systems guys who basically invented the discipline of what we now call systems engineering,” Kranz said. “The way these guys all learned their business, … got to know the designs, the people and the spacecraft … and they had to translate all that into useful materials that they could use on console in real time.”
Join Universe Today in celebrating the 45th anniversary of Apollo 13 with Woodfill’s insights as we discuss each of the 13 additional turning points in the mission. And here’s a look back at the original “13 Things That Saved Apollo 13:
45 years ago on July 20, 1969, NASA astronaut and Apollo 11 Commander Neil Armstrong became the first human being to set foot on another celestial body when he stepped off the Apollo 11 Lunar Module Eagle and onto our Moon’s utterly alien surface.
On that first moonwalk, Armstrong was accompanied by fellow NASA astronaut Buzz Aldrin on a two and a half hour excursion that lasted into the early morning hours of July 21. They came in peace representing all mankind.
Today’s ceremony was broadcast on NASA TV and brought together numerous dignitaries including Armstrong’s surviving crewmates Buzz Aldrin and Command Module pilot Mike Collins, Apollo 13 Commander Jim Lovell who was also Apollo 11’s backup commander, NASA Administrator Charlie Bolden, Kennedy Space Center Director Bob Cabana, and Armstrong’s family members including his sons Rick and Mark Armstrong who all spoke movingly at the dedication.
They were joined via a live feed from space by two NASA astronauts currently serving aboard the International Space Station (ISS) – Expedition 40 crew member Rick Wiseman and Commander Steve Swanson.
The backdrop for the ceremony was the Orion crew capsule, NASA’s next generation human rated spaceflight vehicle which is currently being assembled in the facility and is set to launch on its maiden unmanned test flight in December 2014. Orion will eventually carry US astronauts on journey’s to deep space destinations to the Moon, Asteroids and Mars.
Many of Armstrong’s colleagues and other officials working on Orion and NASA’s human spaceflight missions also attended.
The high bay of what is now officially the ‘Neil Armstrong Operations and Checkout Building’ was built in 1964 and previously was known as the Manned Spacecraft Operations Building.
It has a storied history in human spaceflight. It was used to process the Gemini spacecraft including Armstrong’s Gemini 8 capsule. Later it was used during the Apollo program to process and test the command, service and lunar modules including the Apollo 11 crew vehicles that were launched atop the Saturn V moon rocket. During the shuttle era it housed the crew quarters for astronauts KSC training and for preparations in the final days leading to launch.
“45 years ago, NASA’s journey to land the first human on the Moon began right here,” NASA Administrator Charlie Bolden said at the ceremony. “It is altogether fitting that today we rename this facility the Neil Armstrong Operations and Checkout Building. Throughout his life he served his country as an astronaut, an aerospace engineer, a naval aviator, a test pilot and a university professor, and he constantly challenged all of us to expand the boundaries of the possible.”
“He along with his crewmates, Buzz Aldrin and Michael Collins, are a bridge from NASA’s historic journey to the moon 45 years ago to our path to Mars today.”
The Apollo 11 trio blasted off atop a 363 foot-tall Saturn V rocket from Launch Complex 39A on their bold, quarter of a million mile moon mission from the Kennedy Space Center , Florida on July 16, 1969 to fulfill the lunar landing quest set by President John F. Kennedy early in the decade.
Armstrong and Aldrin safely touched down at the Sea of Tranquility on the lunar surface on July 20, 1969 at 4:18 p.m EDT as hundreds of millions across the globe watched in awe.
“Houston, Tranquility Base here. The Eagle has landed !,” Armstrong called out and emotional applause erupted at Mission Control – “You got a bunch of guys about to turn blue.”
Armstrong’s immortal first words:
“That’s one small step for [a] man, one giant leap for mankind.”
During their 2 ½ hours moonwalk Armstrong and Aldrin unveiled a plaque on the side of the lunar module. Armstrong read the words;
“Here men from the planet Earth first set foot upon the moon. July 1969 A.D. We came in peace for all mankind.”
Here is NASA’s restored video of the Apollo 11 EVA on July 20, 1969:
Video Caption: Original Mission Video as aired in July 1969 depicting the Apollo 11 astronauts conducting several tasks during extravehicular activity (EVA) operations on the surface of the moon. The EVA lasted approximately 2.5 hours with all scientific activities being completed satisfactorily. The Apollo 11 EVA began at 10:39:33 p.m. EDT on July 20, 1969 when Astronaut Neil Armstrong emerged from the spacecraft first. While descending, he released the Modularized Equipment Stowage Assembly on the Lunar Module’s descent stage.
Armstrong passed away at age 82 on August 25, 2012 due to complications from heart bypass surgery. Read my prior tribute articles: here and here
Michael Collins concluded the ceremony with this tribute:
“He would not have sought this honor, that was not his style. But I think he would be proud to have his name so closely associated with the heart and the soul of the space business.”
“On Neil’s behalf, thank you for what you do every day.”
Stay tuned here for Ken’s Earth & Planetary science and human spaceflight news.
Forty-five years ago yesterday, the Sea of Tranquility saw a brief flurry of activity when Neil Armstrong and Buzz Aldrin dared to disturb the ancient lunar dust. Now the site has lain quiet, untouched, for almost half a century. Are any traces of the astronauts still visible?
The answer is yes! Look at the picture above of the site taken in 2012, two years ago. Because erosion is a very gradual process on the moon — it generally takes millions of years for meteors and the sun’s activity to weather features away — the footprints of the Apollo 11 crew have a semi-immortality. That’s also true of the other five crews that made it to the moon’s surface.
In honor of the big anniversary, here are a few of NASA’s Lunar Reconnaissance Orbiter’s pictures of the landing sites of Apollo 11, Apollo 12, Apollo 14, Apollo 15, Apollo 16 and Apollo 17. (Apollo 13 was slated to land on the moon, but that was called off after an explosion in its service module.)
Editor’s note:We posted this yesterday only to find that the original video we used had been pulled. Now, we’ve reposted the article with a new and improved version of the video, thanks to Spacecraft Films.
To the moon! The goal people most remember from the Apollo program was setting foot on the surface of our closest neighbor. To get there required a heck of a lot of firepower, bundled in the Saturn V rocket. The video above gives you the unique treat of watching each rocket launch at the same time.
Some notes on the rockets you see:
Apollos 4 and 6 were uncrewed test flights.
Apollo 9 was an Earth-orbit flight to (principally) test the lunar module.
Apollo 8 and 10 were both flights around the moon (with no lunar landing).
Apollos 11, 12, 14, 15, 16 and 17 safely made it to the moon’s surface and back.
Skylab’s launch was also uncrewed; the Saturn V was used in this case to send a space station into Earth’s orbit that was used by three crews in the 1970s.
You don’t see Apollo 7 pictured here because it did not use the Saturn V rocket; it instead used the Saturn IB. It was an Earth-orbiting flight and the first successful manned one of the Apollo program. (Apollo 1 was the first scheduled crew, but the three men died in a launch pad fire.)