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!”
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.
“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:
Note: To celebrate the 40th anniversary of the Apollo 13 mission, for 13 days, Universe Today will feature “13 Things That Saved Apollo 13,” discussing different turning points of the mission with NASA engineer Jerry Woodfill.
After Flight Director Gene Kranz and his team in Mission Control had ascertained the true peril the Apollo 13 crew faced following the explosion of an oxygen tank in the Command and Service Module, they next faced a big decision. What was the best way to get the astronauts back to Earth? Do they get them home as fast as possible, or as safely as possible? The final decision they made likely saved Apollo 13.
“Immediately after the explosion, some recommended a faster return using the powerful service propulsion system (SPS), the engine designed for the retro burn into lunar orbit and the subsequent firing to propel the crew homeward to Earth,” said NASA Engineer Jerry Woodfill.
Using these engines to execute a direct abort burn would allow the crew to turn the spacecraft around, come around the front side of the Moon and be back to Earth within a day and a half. This was the quickest option, but it meant using the SPS, which were very near the area that had exploded on the CSM. No one knew if the engine had been damaged, too.
The risk of using using the lunar module’s descent engine was an unknown. If it failed or blew, or if the burn wasn’t executed perfectly, the crew could impact the Moon.
The other option was to go completely around the Moon on a so called free-return trajectory, which would take between four to five days to get back to Earth. But would the crew have enough consumables to survive that long?
This flight plan, too, called for an engine burn to set the spacecraft on the correct path back to Earth. But should they use the SPS engine, which was designed for this maneuver but could be damaged, or use the use the descent engine on the Lunar Module, which had never been designed for this type of use?
In his book, “Failure is Not an Option,” Kranz said it was purely a gut feeling that made him choose to take the long way – to go around the Moon and use the descent engine on the lunar lander rather than the CSM.
“Later, Gene Kranz shared he felt a foreboding about using that engine,” said Woodfill. “Nevertheless, even the use of the lander’s descent engine had some risk. The system was not expected to be fired more than once on a lunar mission. It was designed for descent from lunar orbit to landing. To use it for both Apollo 13’s mid-course correction burn (to return to the free-return trajectory) and a subsequent firing to accelerate the journey home amounted to a second firing.”
With the first burn of the LM engines working as hoped, the crew swung around the far side of the Moon (some records indicate Apollo 13 traveled the farthest distance from the far side of the Moon, making them the crew that traveled the farthest away from Earth), Mission Control considered a second burn.
Without the second burn the ship’s trajectory likely would have successfully returned the crew to Earth approximately 153 hours after launch. This provided less than an hour of consumables to spare, a margin too close for comfort.
After a much discussion and calculating, the engineers in the Mission Evaluation Room (MER) and Mission Control determined the LM’s engines could handle the required burn. So, the descent engine was fired sufficiently to boost their speed up another 860 feet per second, cutting the flight time to 143 hours – which provided a better margin for survival.
But what if the SPS engines had been fired? We will never know for sure, but Woodfill said the final photo taken of the damaged command ship after jettison from the reentry capsule appeared to show a slight deformation of the SPS engine nozzle. He believes the SPS panel adjacent to the exploding O2 tank severed the four horns from the mast of the hi-gain communication antenna system. Likely, the shrapnel from the devastating impact with those four dishes ricocheted into the SPS engine bell compromising its use. A hole in the engine’s thrust nozzle would have been catastrophic.
“The fiery bazooka-like blast of the explosion might have cracked the heat shield and damaged critical parts of that engine,” said Woodfill. “The engine’s systems were adjacent to the tunnel-like chimney located in the center of the service module. If the nozzle was deformed, surely, there would have been a potentially fatal consequence of its firing, akin to the loss of the Challenger resulting from the failed solid rocket (SRB) engine.”
Woodfill said that likely, the use of the SPS would have triggered the caution and warning combustion chamber high temperature alarm. “And its use might have made Apollo 13 a fiery meteor-like streak of light never to reach Earth,” he said. “Though a successful firing would have landed the crew days earlier in the Indian Ocean, the peril was too great.”
Tomorrow, Part 5: Unexplained Shutdown of the Saturn V engine
Other articles from the “13 Things That Saved Apollo 13” series: