13 Things That Saved Apollo 13, Part 12: Lunar Orbit Rendezvous

[/caption]

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.

Going to the Moon was big. It was a giant stride in doing what had once been thought impossible. Initially many scientists and engineers had big plans for huge rockets akin to the ships imagined in science fiction: one piece vehicles that took off from Earth, landed intact bottom down on the Moon and had the ability to launch again from the lunar surface. But other rocket engineers had different ideas, and this caused some big arguments. The method of going to the Moon that eventually won out used — in part — a little lunar lander. This decision ended up being instrumental in saving the crew of Apollo 13. And that was big.

The three different Apollo flight modes. Credit: NASA

There were three different methods to choose from in reaching the Moon. One, called the Direct Ascent Mode, would have used the big Flash Gordon-like enormous rocket – which was known as a Nova class rocket –to fly straight to the Moon, land and return. Second, the Earth Orbital Rendezvous technique called for two not-quite-as big Saturn V boosters to launch and rendezvous in Earth orbit. In this mode, one rocket would carry a single Apollo vehicle and its crew, and the other, more fuel, which would be transferred to Apollo in Earth orbit, and then the spacecraft would head off to the Moon. The third option was Lunar Orbit Rendezvous which used only one three-stage Saturn V booster, and split the Apollo vehicle into two separate vehicles – a combined Command and Service Module (CSM), and a Lunar Module (LM).

Those familiar with NASA history know that Lunar Orbit Rendezvous was the final choice.

But this mode wasn’t an obvious choice, said NASA engineer Jerry Woodfill.

“At first, Werner Von Braun wanted to use the Nova class rocket Direct Ascent approach, and so did President Kennedy’s science advisor, ” Woodfill said. “But a group at Langley Research Center led by Dr. John Houbolt came up with the Lunar Orbit Rendezvous design. And most everyone ignored them at first.”

NASA engineer John C. Houbolt describes the Lunar Orbit Rendezvous concept at the chalkboard in July 1962. Image Credit: NASA

But Houbolt insisted the one-rocket system was not feasible. In a NASA interview Houbolt said, “It can not be done. I said you must include rendezvous in your thinking — to simplify, to manage your energy much better.”

Houbolt said it turned into a two-and-a-half year fight to convince people, but he and his team had the facts and figures to back up their claims.

Woodfill said one of his colleagues, former NASA engineer Bob Lacy was part of the discussions on which plan to use. “He said it was unbelievable,” Woodfill recalled. “They were debating in a meeting room at Langley about the best way to go to the Moon. One side was for sending a single vehicle requiring a huge booster to get it there. The other group wanted a two spaceship method. No one seemed agreeable to the other side’s approach. Tempers were starting to flare. To ease the situation someone said, ‘Let’s flip a coin to settle the score.’ Can you believe that?”

No one flipped a coin, but the story demonstrates the intensity of the debate.

In the race to get to the Moon, the Soviet Union had embraced the Nova rocket concept. “The Soviets pressed forward with the direct assent approach to use a Nova class booster,” said Woodfill. “Designated N-1, it clustered 30 engines on its first stage. The design achieved a Herculean thrust of 10-12 millions pounds. Additionally, this uncomplicated direct ascent launch would be less complex was thought to take less time to accomplish. Designing, building, testing and launching two separate spaceships might not win the race to the Moon.”

Woodfill said the Nova rocket may have proved to be the best choice except for the failure of just one of those 30 engines at launch. “This would unbalance the entire assemblage,” Woodfill said.

And twice in 1969 – one occurring just weeks before the scheduled launch of Apollo 11 — the Soviet N-1 booster exploded at liftoff. The huge rocket proved to be too complicated, while the Lunar Orbit Rendezvous method had a simple elegance that was also more economical.

A diagram of the lunar-orbit rendezvous used on Apollo by John Houbolt. Credit: NASA

In November 1961, Houbolt boldly wrote a letter to NASA associate administrator Robert C. Seamans, “Do we want to go to the Moon or not?” he wrote. “Why is Nova, with its ponderous size simply just accepted, and why is a much less grandiose scheme involving rendezvous ostracized or put on the defensive? I fully realize that contacting you in this manner is somewhat unorthodox,” Houbolt admitted, “but the issues at stake are crucial enough to us all that an unusual course is warranted.”

The bold move paid off, and Seamans saw to it that NASA took a closer look at Houbolt’s design, and surprisingly, it soon became the favored approach – after a little debate..

Houbolt’s design separated the spacecraft into two specialized vehicles. This allowed the spacecraft to take advantage of the Moon’s low gravity. The lunar lander could be made quite small and lightweight, reducing bulk, fuel, and thrust requirements.

The Lunar Module Aquarius, after it was jettisoned from the CSM. Farewell Aquarius, we thank you, the crew radioed. Credit: NASA

When the oxygen tank in Apollo 13’s Service Module exploded, the Lunar Module “Aquarius” played an unexpected role in saving the lives of the three astronauts, serving as a lifeboat to return the astronauts safely back to Earth. Additionally, its descent stage engine was used for propulsion, and its batteries supplied power for the trip home while recharging the Command Module’s batteries critical for re-entry. And with ingenuity of Mission Control the LM’s life support system – which was originally designed to support two astronauts for 45 hours, — was stretched to support three astronauts for 90 hours.

Imagine, Woodfill said, if Apollo 13 had been a single vehicle employing the Direct Ascent approach. “After the explosion and subsequent loss of the fuel cells, only those entry batteries would have been available to sustain life. Their life, even if all systems except life support, were turned off would be less than 24 hours. And Lovell, Swigert and Haise along with Apollo 13 would return to Earth on that “free-return-trajectory” being cremated in the fiery heat of reentry. But for the clever Lunar Orbit Rendezvous approach, Apollo 13 would have been a casket. Instead, its lunar lander became a wonderful lifeboat” Woodfill said.

Next: Part 13: Houston

Earlier articles from the “13 Things That Saved Apollo 13” series:

Introduction

Part 1: Timing

Part 2: The Hatch That Wouldn’t Close

Part 3: Charlie Duke’s Measles

Part 4: Using the LM for Propulsion

Part 5: Unexplained Shutdown of the Saturn V Center Engine

Part 6: Navigating by Earth’s Terminator

Part 7: The Apollo 1 Fire

Part 8: The Command Module Wasn’t Severed

Part 9: Position of the Tanks

Part 10: Duct Tape

Part 11: A Hollywood Movie

Part 12: Lunar Orbit Rendezvous

Part 13: The Mission Operations Team

Also:

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

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

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

Never Before Published Images of Apollo 13’s Recovery

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

13 Things That Saved Apollo 13, Part 11: A Hollywood Movie

[/caption]

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.

A Hollywood movie depicts three astronauts who survive an accident in space, but their lives hang in the balance as the people in Mission Control at NASA work night and day to figure out a way to bring the spacefarers home safely.

You probably think I’m describing the 1995 movie, “Apollo 13” by producer Ron Howard, but actually this is a recap of a 1969 movie called “Marooned.

“The correlation between ‘Marooned’ and actual events threatening Apollo 13 is really uncanny,” said NASA engineer Jerry Woodfill. “People may not agree, but in my mind this movie was actually a catalyst to the rescue of Apollo 13.”

“Marooned” starred Gregory Peck as a Gene Kranz-like flight director, David Janssen as head of the astronaut office (who looked strikingly like the real Chief Astronaut Deke Slayton), with Richard Crenna, James Franciscus, and Gene Hackman as the astronauts. Like the movie “Apollo 13,” “Marooned” dealt with three astronauts stranded in space, but was an adaptation of a 1964 novel of the same name by author Martin Caidin, and not a real-life portrayal. The novel told the story of a single astronaut in a Mercury-like capsule, but the movie was adapted to reflect the current-day Apollo program.

Poster for the movie Marooned. Credit: Wikipedia

“Marooned” won an Oscar award for Best Special Visual Effects, but when the movie “Apollo 13” received an Academy Award for Best Screen Adaptation, Caidin joked that he should have received the award for scripting the movie in his novel a quarter century before.

Woodfill recounted how back in early 1970, he heard about the movie “Marooned” and that the flight directors at NASA were invited to a special screening of the film, and later, the Apollo 13 crew came to a special release and public viewing of the movie.

But most of the people who worked in Mission Control and the Mission Evaluation Room couldn’t afford to go see the movie. The viewing was at a plush theater on Richmond Avenue in Houston in January of 1970.

“Those days I worked as a young civil servant, and “Marooned” was playing at the theater on Richmond Avenue in Houston, which was $3.50 a ticket, which was out of reach for most of us,” said Woodfill. “But working for NASA we had to be clever about keeping costs down taking our wives out. We called this low-cost date, “NASA Night Out,” where we could go to a neighborhood theater for $1.25, plus get a two-for-one coupon if you took your wife to dinner at the Monterey House, and afterwards, you could get a free cup of coffee if you filled up at a local gas station. We had to be innovative in those days!”

“Marooned” made it to the $1.25-a-seat theater by the week of Apollo 13’s rescue, and several NASA employees went to see it, including Woodfill’s colleague and electrical engineer Art Campos, who is now deceased.

Jerry Woodfill and Art Campos (among others) in the MER. Image courtesy Jerry Woodfill.

“Art was a wonderful electrical engineer, a graduate of the University of Texas in Austin,” Woodfill recalled, “As an engineer hailing from a Hispanic family, he often encouraged those in his culture to pursue technical fields. Art was also my mentor with regard to the electrical power system for the lunar lander. I often consulted him about caution and warning issues with regard to his lunar module electrical power system. He served as its system manager.”

Campos went to see “Marooned” the evening of April 13, 1970, and later told Woodfill he was thinking about the movie as he returned home and went to sleep, and wondered about a problem faced by the astronaut actors regarding the emergency batteries, which had been depleted.

“In the movie, charging the batteries was the instruction to fix the problem,” said Woodfill, “and Art said he wondered, ‘What if we faced such dire problems?’ and other ‘what-ifs.’”

Just a couple of hours later, Campos was awakened by a phone call informing him that the Apollo 13 spacecraft had suffered an accident, and that he needed to come in immediately to work on a way to get power to the emergency batteries in the Command Module, required for reentry.

“The crew had to use the emergency batteries in the Command Module to have time to transfer the guidance parameters to the Lunar Module computer,” said Woodfill, “and there may not have been enough power in them for when the crew returned to Earth. As Art was driving to Building 45 at the Manned Spacecraft Center, where the Mission Evaluation Room (MER) was housed, he recalled the movie, where they said ‘charge the batteries’ and then remembered a procedure he devised about a year earlier, a way to charge depleted emergency batteries by using a jumper charge between the two vehicles, because the lunar lander batteries are huge and would have ample power.”

Engineers in Mission Control during Apollo 13. Credit: NASA

Woodfill said Campos starting writing out the procedure while he and others in the MER rolled out drawings and schematics for the electrical systems on the two vehicles showing all the connectors and harness wiring. They finally found a small wire running between the two vehicles. It had been designed into the vehicles years ago to heat some components in the lander during the coast phase to the Moon until the lander is powered up.”

“They found the wire, but they didn’t know if the procedure would work,” said Woodfill, who sat next to the electrical engineers in the MER working this problem,” because there is a trickle charge and you have to set switches and the circuit breakers just the right way. They tried it out in the simulators, because there was a concern that current would flow the wrong way.”

And in fact, Woodfill said, in the simulators, it didn’t work. The computer in the simulator refused to allow the procedure, but nevertheless, there was no other alternative. So, they tried it in space and it actually worked to re-charge the batteries in the Command Module.

“I really think “Marooned” was the catalyst for Art remembering this wire,” said Woodfill, although we’ll never know for sure.

Video clip from NASA footage. Art Campos is among the engineers shown in the MER.

Woodfill also listed several other similarities between “Marooned” and the real-life drama of Apollo 13:

• The use of simulators is almost identical to that which Apollo 13’s ground team used in the course of the rescue.
• Gregory Peck’s character announces, “Every resource of NASA and our industrial contractors is being used to the fullest extent,” similar to what was done during the real Apollo 13 drama.
• Press conferences in the movie were similar to those conducted by Chris Kraft for the Apollo 13 media coverage.
• The “Marooned” crew wrongly thinks they may have suffered a meteor strike as did the crew of Apollo 13.
• A hurricane threatens the rescue as was the case with Apollo 13. Even the weathermen wrongly predict its course as did the Apollo 13 meteorologists.
• Commanders of both “Marooned” and Apollo 13 are named Jim.
• The threat of consumables running out is dealt with in the same fashion as Apollo 13 with severe conservation measures being utilized.
• The medics in “Marooned” express concern for the crew’s sleep deprivation as did Apollo 13’s doctors.
• The “Marooned” crew is told to shut down fuel cells 2 and 3, using only fuel cell 1. This is what the Apollo 13 flight controllers experienced as a result of the oxygen tank explosion, two fuel cells shut down with only one sustaining power, until it, too, was lost.

But perhaps, said Woodfill, the most notable of “Maroon’s” correlations with the Apollo 13 rescue had to do with those reentry batteries discussed above, and this earlier article in the “13 Things That Saved Apollo 13” series. The batteries were used during the time the ground team was confused about the source of Apollo 13’s explosion. This severely depleted them, and without enough power to the Command Module, reentry could be fatal. These batteries normally were to be used only during the mission’s final hours to power the reentry capsule.

NASA Engineer John Aaron during a Gemini mission. Source: Wikipedia

Woodfill said that Apollo EECOM John Aaron commented recently at an Apollo 13 anniversary event at Johnson Space Center that he has reflected on how he allocated power from the those batteries to various system managers. He had refused a request for 2 amps from a DOD official wanting power for to light a rescue beacon to locate the crew capsule in the ocean.

Aaron commented, “Thankfully, the splashdown was in sight of the carrier and no beacon was needed to find Lovell and crew.“ But, he granted, “What if the landing had not been so accurate?” And Woodfill, likewise wonders, “What if Apollo 13 had landed in the storm-tossed seas of tropical storm Helen?”

Indeed, Campos’ contribution was huge, and Woodfill believes the procedure to recharge the batteries saved Apollo 13.

Next: Part 12: The Lunar Orbit Rendezvous Plan

Earlier articles from the “13 Things That Saved Apollo 13” series:

Introduction

Part 1: Timing

Part 2: The Hatch That Wouldn’t Close

Part 3: Charlie Duke’s Measles

Part 4: Using the LM for Propulsion

Part 5: Unexplained Shutdown of the Saturn V Center Engine

Part 6: Navigating by Earth’s Terminator

Part 7: The Apollo 1 Fire

Part 8: The Command Module Wasn’t Severed

Part 9: Position of the Tanks

Part 10: Duct Tape

Part 11: A Hollywood Movie

Part 12: Lunar Orbit Rendezvous

Part 13: The Mission Operations Team

Also:

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

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

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

Never Before Published Images of Apollo 13’s Recovery

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

13 Things That Saved Apollo 13, Part 10: Duct Tape

[/caption]
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.

It’s the handy man’s secret weapon, and has become a must-have item for astronauts, too. While duct tape alone didn’t save the Apollo 13 crew, it certainly would have been difficult for them to have survived without it. Even though the accident which crippled the ship took out the two main oxygen tanks in the Service Module, having enough oxygen really wasn’t an issue for the crew. A big problem was having too much carbon dioxide (CO2), which came from the astronauts’ own exhalations.

The Lunar Module 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. However, with a little ingenuity and duct tape, the Apollo Mission Operations Team was able to fit “a square peg in a round hole.”

The Mission Evaluation Room for Apollo. Image courtesy Jerry Woodfill.

“Any of us in the Mission Evaluation Room (MER) might be called upon to assist in an Apollo 13 ‘solution,’” said Jerry Woodfill, who helped design and monitor the Apollo caution and warning systems. The MER was where the spacecraft systems engineers were stationed during a mission, and should a problem arise on any Apollo mission, the “MER-men” were called on for expert advice.

“Should an inexplicable glitch in an alarm occur, I might be consulted,” Woodfill said, “and I was – when the carbon dioxide levels began to threaten the astronauts’ lives, ringing alarms. However, to this day, I am proud that the Command Module’s alarm system was the first warning alerting Mission Control and Lovell’s crew to the life-threatening problem.”

The MER engineering team was led by Don Arabian. “His loud, challenging voice could carry the entire length of the Mission Evaluation Room,” Woodfill said. “Despite his fierce personality, he was a brilliant engineer. No forensic engineer working with any attorney had a greater ability of assessing a spacecraft mission anomaly than Don Arabian.”

Additionally, Woodfill said, Arabian was wholly unorthodox in his management approach. “He feared no man above or below his pay grade. He was honest almost to the point of embarrassment. He would not ‘sugar coat’ any situation Apollo 13 was dealing with as far as the press was concerned.”

Woodfill recalled how Arabian commanded the MER team from the “throne-like” center seat of a long table perpendicular to tables of engineers. “He was, perhaps 20 feet from my station as the Caution and Warning Apollo 13 Engineer. Don never intimidated me, though I had felt nervous about many of my superiors. Don had that same quality of leadership Gene Kranz possessed. He was fair with lower level workers and respected their knowledge.”

For that reason, Woodfill said he felt privileged rather than frightened when summoned to Arabian’s private office to discuss the threat to the lives of the Apollo 13 crew, the build-up of CO2 in the spacecraft.

Woodfill had worked with the environmental system engineers to establish an alarm level based on the percentage of CO2 in the cabin atmosphere. The idea was to use the warning system as an alert for changing the filters.

With the CO2 alarms ringing on Apollo 13, Woodfill met with Arabian. “As I recall there were three calibration curves, one for three different cabin pressures,” Woodfill said. “Arabian began to throw questions at me across his desk: ‘Is the alarm accurate…is the transducer working correctly…what about the calibration?'”

Woodfill had the information on the calibration curves with him, and together, he and Arabian carefully studied it based on the known cabin pressure, the voltage output from the CO2 transducer and the voltage level at which my warning electronics initiated the alarm.

“Yes, the warning system was telling the right story,” Woodfill said.

Jack Swigert works on the CO2 canister during the Apollo 13 mission. Credit: NASA

But there was a problem with the CO2 “scrubbers,” the lithium hydroxide canisters. The cabin air was fed continuously through environmental control equipment, and the lithium hydroxide reacted with the carbon dioxide and trapped it.

“There were but two round lithium hydroxide canisters in the LM, able to provide filtering for two men for two days,” said Woodfill. “With the trip back to Earth at least four days in length, and three men on board, the carbon dioxide content of the cabin air would rise to poisonous levels, and the crew would expire without a solution.”

Each canister had a life of approximately 24 hours with two men on board. Since there were now three men, that life would be somewhat shortened. The round filters were housed in two separate barrels in the lander. One barrel was plumbed into the cabin’s environmental control system, and the other barrel simply stowed the second cartridge. When the first filter was consumed, the crew simply interchanged the filters in the barrels.

“While there were plenty of filters in the Command Module, these were square and wouldn’t fit in the LM barrel,” Woodfill said. “Without some kind of unusual miracle of making a square peg fit into a round hole the crew would not survive.”

The fix for the lithium hydroxide canister is discussed at NASA Mission Control prior to having the astronauts implement the procedure in space. Credit: NASA

The experts in the MER had 24 hours to deal with the challenge and solve the problem. “My recollection of the threat,” said Woodfill, “besides the earlier meeting with Don Arabian, was Don’s voice bellowing from his throne in the mission evaluation room that Tuesday, ‘I need those guys to come up with an answer on the CO2 thing and do it fast!’ He was referring to the ‘tiger team’ led by Ed Smylie, the crew systems manager working the problem.”

Using only the type of equipment and tools the crew had on board –including plastic bags, cardboard, suit hoses, and duct tape — Smylie and his team conceived a configuration that just might work.

“The concept seemed to evolve as all looked on,” Woodfill said. “It was to attach a suit hose into a port which blew air through the hose into an astronaut’s space suit. If the space suit was eliminated and, instead, the output of the hose somehow attached to the square filter, perhaps, the crew could be saved. This, in effect, would bypass the barrel. The air blown through the filter by the suit fan would have no carbon dioxide as it reentered the cabin atmosphere.”

The biggest challenge was attaching the hose into a funnel-like device having a small round inlet hole for the suit hose and a much larger square outlet attached and surrounding the square filter. But the funnel would most likely leak. Added to that difficulty was the hose and plastic bags tended to collapse restricting the air flow through the filter.

“Then the thought came, ‘Use cardboard log book covers to support the plastic,” said Woodfill. “It worked! But more importantly, they had to figure out how the funnel could be fashioned to prevent leaking. Of course…the solution to every conceivable knotty problem has got to be duct tape! And so it was.”

Screen shot from Apollo 13 footage showing Jim Lovell with duct tape.

Woodfill said that duct tape had been stowed on board every mission since early in the Gemini days.

The contraption that Smylie and his team came up with was checked out in the simulators, which worked, and then the team quickly radioed instructions to the crew, carefully leading them through about an hour’s worth of steps.

At a mission debrief, Jack Swigert noted, “At this point in time I think the partial pressure of CO2 was reading about 15 millimeters. We constructed two of these things and I think within an hour was down to 2 tenths.”
Woodfill watched his systems from the MER. “I saw the alarm light go out and it stayed out the rest of the mission.”

As Jim Lovell wrote in his book “Lost Moon, “The contraption wasn’t very handsome, but it worked.”

And it saved Apollo 13.

Next: Part 11: A Hollywood Movie

Earlier articles from the “13 Things That Saved Apollo 13” series:

Introduction

Part 1: Timing

Part 2: The Hatch That Wouldn’t Close

Part 3: Charlie Duke’s Measles

Part 4: Using the LM for Propulsion

Part 5: Unexplained Shutdown of the Saturn V Center Engine

Part 6: Navigating by Earth’s Terminator

Part 7: The Apollo 1 Fire

Part 8: The Command Module Wasn’t Severed

Part 9: Position of the Tanks

Part 10: Duct Tape

Part 11: A Hollywood Movie

Part 12: Lunar Orbit Rendezvous

Part 13: The Mission Operations Team

Also:

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

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

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

Never Before Published Images of Apollo 13’s Recovery

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

13 Things That Saved Apollo 13, Part 9: Position of the Tanks

[/caption]

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.

The saga of the Apollo 13 accident actually began years prior to the launch of the mission. As Jim Lovell wrote in his book, “Lost Moon” the accident was “an accumulation of human errors and technical anomalies that doomed Apollo 13.” But had coincidences been just a little different Apollo 13 could have been an accident from which there was no rescue. NASA engineer Jerry Woodfill believes where Tank Two was positioned in the Service Module led to a successful rescue. “I contend that the crew would have died if the flawed O2 Tank Two had not been on the outer perimeter of the Service Module,” Woodfill said. “The position of that tank had much to do with the extent of the explosion’s damage. Had Tank One been damaged, no rescue would have been possible.”

Graphic showing the Apollo Service module interior. Credit: NASA

The oxygen tanks were specially insulated spherical tanks which held a “slush” of liquid oxygen with a fill line and heater running down the center. Tank Two used for Apollo 13 had originally been installed in Apollo 10, but was removed for modification. In what was considered a minor mishap, O2 Tank Two was accidently dropped and damaged. The two tanks were on a “shelf” in the Service Module and held in place by two bolts. During removal, inadvertently, only one bolt on the shelf was removed, the side that contained Tank Two. When the lifting fixture picked up the shelf, Tank One stayed in place while Tank Two accelerated upward, striking the fuel cell shelf overhead. It only moved about 5 cm (2 inches) but the jolt displaced a loosely fitted fill tube in Tank Two. This tank was replaced with another for Apollo 10, and the exterior was inspected. Since the interior wasn’t inspected, no one knew about the fill tube damage, and the shelf with the damaged Tank Two was installed in the Apollo 13 Service Module (SM-109) November 22, 1968.

Unfortunately there was another problem with the tank, that were it not for the fill tube damage, may not have been an issue. The oxygen tanks had originally been designed to run off the 28 volt DC power of the Command and Service modules. However, in 1965 the tanks were ordered to be refitted to also run off the 65 volt DC ground power at Kennedy Space Center. All components were upgraded to accept 65 volts except the heater thermostatic switches, which were overlooked. These switches were designed to open and turn off the heater when the tank temperature reached 26 degrees C (80 degrees F — Normal temperatures in the tank were -74 C to -174 C (-300 to -100 F.)

During pre-flight testing, Tank Two would not empty correctly, possibly due to the damaged fill line. The heaters in the tanks were normally used for very short periods to heat the interior slightly, increasing the pressure to keep the oxygen flowing. It was decided to use the heater to “boil off” the excess oxygen, requiring 8 hours of 65 volt DC power. This probably damaged the thermostatically controlled switches on the heater, designed for only 28 volts.

Schematic of the oxygen tank. Credit: NASA

The Apollo 13 review board came to the conclusion that the switches welded shut, allowing the temperature within the tank to rise to over 538 degrees C (1000 degrees F). The gauges measuring the temperature inside the tank were designed to measure only to 80 F, so the extreme heating was not noticed. The high temperature emptied the tank, but also resulted in serious damage to the Teflon insulation on the electrical wires to the power fans within the tank.

When the tanks were put into the Apollo 13 spacecraft, the damaged Tank Two was placed in the exterior position.

“Because the spark which ignited the oxygen in Tank Two was located at the top of the tank,” said Woodfill, the tank acted like a cork on a Thermos bottle. Since it was on the outside perimeter, it simply blew out into space along with the 13 foot panel covering the side of the service module. The oxygen tank shelf served to isolate the explosion from the hydrogen tanks below. But had the inboard oxygen Tank One 1 exploded, likely, this would not have been the case.”

Should the flawed tank have been the inner tank, Woodfill said, its explosive force would have taken with it the sister O2 tank amplifying the force of the explosion, just as using two sticks of dynamite instead of one, the destruction would be a magnitude greater.

Image of the damaged Apollo 13 Service Module, taken by the crew. Credit: NASA

“The added explosive force would have fractured the O2 tank shelf involving the fragile hydrogen tanks below,” Woodfill explained. “The volatile hydrogen gas now having a wealth of oxygen from the overhead tanks would surely have destroyed the entire spacecraft assemblage. Of course, the crew would have immediately perished as well. There would have been no clues, no telemetry data trace to explain what had happened.”

“Oxygen Tank One was given the inboard location adjacent to the flawed tank,” Woodfill continued. “Consider the likelihood of that placement. It is one chance in two. The odds for Apollo 13’s survival were fifty percent, a flip of the coin.”

Next: Part 10: Duct Tape

Other articles from the “13 Things That Saved Apollo 13” series:

Introduction

Part 1: Timing

Part 2: The Hatch That Wouldn’t Close

Part 3: Charlie Duke’s Measles

Part 4: Using the LM for Propulsion

Part 5: Unexplained Shutdown of the Saturn V Center Engine

Part 6: Navigating by Earth’s Terminator

Part 7: The Apollo 1 Fire

Part 8: The Command Module Wasn’t Severed

Part 8: The Command Module Wasn’t Severed

Part 9: Position of the Tanks

Part 10: Duct Tape

Part 11: A Hollywood Movie

Part 12: Lunar Orbit Rendezvous

Part 13: The Mission Operations Team

Also:

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

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

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

Never Before Published Images of Apollo 13’s Recovery

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

13 Things That Saved Apollo 13, Part 8: The Command Module Wasn’t Severed

[/caption]

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.

When the Apollo 13 crew jettisoned the crippled Service Module as they approached Earth, they saw the extent of the damage from the explosion of an oxygen tank. “There’s one whole side of that spacecraft missing!” Jim Lovell radioed to Mission Control, his voice reflecting his incredulousness at seeing the damage of a 13-ft panel blown off the spacecraft. However, the situation could have been more dire. The heat shield on the Command Module could have been damaged. What’s more, NASA engineer Jerry Woodfill said that instead of the panel blowing out, the explosion could have — and maybe should have –severed the Command Module from the Service Module.

Graphic of the CSM. Credit: NASA

Photos taken by the Apollo 13 crew after the service module was jettisoned in preparation for the command module’s reentry via the heat shield revealed that not only was the panel missing from the side of the spacecraft — blown into the vastness of space by the exploding pressure of the detonating oxygen – there was also damage to the Hi Gain Antenna, at the right of the vehicle drawing above, indicating the panel had catapulted into space, striking the antenna. What the images couldn’t show, and what the Apollo 13 crew couldn’t see was if there was any damage to the Command Module’s heat shield.

“The structural design of the interior of the Service Module is that it has a long open tunnel-like volume in the center of the module, about 30 inches by 13 feet,” said Woodfill. “The tunnel is much like a chimney such that gases, liquids, or particles could readily move through it toward the main engine bell at the right and the heat shield at the left. The tunnel is not sealed so that the explosive force of the burning oxygen from the exploded O2 tank 2 could escape into and around the tunnel in the direction of both the heat shield and main engine.”

Woodfill said concern was voiced in Mission Control that shrapnel from the exploding tank had entered the tunnel, and perhaps ultimately caused damage to both the heat shield and main engine. The main engine wasn’t the biggest issue, as the crew was able to use the lunar lander’s descent engine. (see our previous article , “Using the LM for Propulsion.”) But there was only one heat shield, and it had to work to enable the capsule and the crew to survive the fiery reentry through Earth’s atmosphere.

Thankfully, as it turned out ,the heat shield wasn’t damaged.

The recovery of the Apollo 13 Command Module. Credit: NASA

But almost miraculously, Woodfill said, the command module and service module remained connected following the explosion, while the internal pressure of the explosion rocketed the exterior panel into space.

“The attachment strength of the Service Module panel to the structure required a considerable internal pressure of 24 pounds per square inch for severing it from the service module,” Woodfill said. “A much lower pressure was required to separate the Command Module with its heat shield from the Service Module, only 10 pound per square inch. One can only speculate on why the panel blew and the crew capsule/service module attachment remained intact.”

Since there is no air pressure in space, Woodfill explained, the force which held the vehicles together was the strength of their mechanical attachments.

“Two pressures were at work,” he said. “Each attempted to overcome respective attachment forces: the force which attached the Service Module to the Command capsule and the force which attached the Service Module panel to the Service Module. Because the explosive pressure force of the oxygen was immediately applied in great strength to the panel, this overwhelming force would be expected to blast that panel apart from the vehicle, exceeding the 24 pound per square inch attachment strength. However, venting of residual explosive oxygen into the framework of the Service Module could well be expected to overcome the attachment strength between the two vehicles, separating them.”

Yet, it did not. Why?

Sequence photo from 16mm motion picture film of test at Langley Research Center which seeks to determine mechanism by which Apollo 13 panel was separated from Service Module. Credit: NASA. Click image for more information

“Apparently, the presence of ‘tankage’ and other structure acted to mitigate and dissipate the sudden pressure spike before it reached the interface between the vehicles,” Woodfill said. “However, if a shard from the exploded O2 tank 2 had punctured any of the adjacent tanks, likely a secondary explosion of any of them would have propagated both the explosion and build up of pressure. In that event, certainly, the vehicles would have experienced either a fatal separation or fatal damage to the heat shield.

A piece of shrapnel did fracture the plumbing between the oxygen tanks that allowed the oxygen to leak out of Tank 1, causing the complete loss of power in the Command Module, for without oxygen the fuel cells couldn’t work.

Some may say that having the Service Module attached to the Command Module wasn’t important – it was just dead weight anyway. However, other problems could have developed without the Service Module attached, according the Apollo 13 Failure Report. Having the heat shield exposed to low temperatures for a long period could have damaged it, and internal Command Module thermal problems could arise if the Service Module was jettisoned too early.

Additionally, flight control problems were anticipated if the Command Module wasn’t attached.
The immediate loss of the Service Module would have meant immediate loss of the residual power from the fuel cells while the crew and mission control wrestled to understand the problem. This would have required a much greater power drain on those emergency batteries to the extent that one wonders if the later “trickle-charge” from the lander’s batteries would have been sufficient for reentry.

The crew of Apollo 13, Jim Lovell, Jack Swigert and Fred Haise, during a post-flight debrief. Credit: NASA

Of course, since the Service Module was jettisoned before the crew re-entered (and the SM itself later burned up in the Earth’s atmosphere) no one could do any “forensic analysis” or an engineering “autopsy” on that part of the spacecraft.

“To me, it is amazing that, one, the heat shield wasn’t damaged from the explosion, and two, the connection that could withstand higher pressure ended up blowing, while the weaker connection stayed together,” said Woodfill.

But those were among the many things that saved Apollo 13.

Next: Part 9: Which tank was damaged

Earlier articles from the “13 Things That Saved Apollo 13” series:

Introduction

Part 1: Timing

Part 2: The Hatch That Wouldn’t Close

Part 3: Charlie Duke’s Measles

Part 4: Using the LM for Propulsion

Part 5: Unexplained Shutdown of the Saturn V Center Engine

Part 6: Navigating by Earth’s Terminator

Part 7: The Apollo 1 Fire

Part 8: The Command Module Wasn’t Severed

Part 9: Position of the Tanks

Part 10: Duct Tape

Part 11: A Hollywood Movie

Part 12: Lunar Orbit Rendezvous

Part 13: The Mission Operations Team

Also:

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

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

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

Never Before Published Images of Apollo 13’s Recovery

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

13 Things That Saved Apollo 13, Part 7: The Apollo 1 Fire

[/caption]
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.

“Far better is it to dare mighty things, to win glorious triumphs, even though checkered by failure than to rank with those poor spirits who neither enjoy much nor suffer much, because they live in a gray twilight that knows not victory nor defeat.” – Theodore Roosevelt

It’s hard to chronicle any of the Apollo flights without mentioning the Apollo 1 fire. And while many believe the Apollo program perhaps wouldn’t have succeeded without that disaster, the sacrifice made by Gus Grissom, Ed White and Roger Chaffee definitely saved the crew of Apollo 13.

“Among the early space missions, I’ve always believed that the greatest courage was needed by their first crews,” said Apollo engineer Jerry Woodfill. “Whether it was Al Shepard, the Apollo 1 crew, or shuttle astronauts John Young or Bob Crippen, the most likely danger would be the first time any new space craft was launched into space. Flaws in design or manufacture could very well be fatal during maiden missions.”

The crew of Apollo 1: Gus Grissom, Ed White and Roger Chaffee. Credit: NASA

On January 27, 1967, during a test on the launch pad with the crew on board, tragedy struck when a flash fire started in the command module. With the pure oxygen environment inside the capsule, the fire quickly proved fatal for the crew before they or workers at the launch pad could get the hatch open. Although the ignition source of the fire was never conclusively identified, the astronauts’ deaths were attributed to a wide range of design and construction flaws in the early Apollo Command Module. The manned phase of the project was delayed for twenty months while these problems were fixed.

“To suggest the dire event of losing three brave astronauts contributing to Apollo 13’s rescue seems almost ludicrous,” said Woodfill, “but the evidence is striking. What Grissom, White and Chaffee contributed to the rescue of Apollo 13 makes them even more heroic than they were when they gave their lives so that men could go to the moon.”

The irony of the whole situation involves the hatch. Following Gus Grissom’s near fatal drowning when his Mercury capsule sank, the Apollo hatch had been redesigned to avoid the kind of unexpected actuation thought to have caused Grissom’s “Liberty Bell 7” to sink.

Gus Grissom and the Liberty Bell 7. Credit: NASA

“Unfortunately, it led to a hatch impossible to open before the Apollo 1 crew expired,” said Woodfill. “Nevertheless, circumstances used Gus, Ed, and Roger’s sacrifice to save other crews in route to the Moon.”

NASA fire-proofed all future Apollo vehicles with non-flammable materials, used a pad atmosphere of a nitrogen/oxygen mix, and coated of all electrical connections to avoid short-circuits.

“Every switch contact and wire was coated with a moisture proofing substance called conformal coating,” said Woodfill. “Were it not for fire-proofing the Apollo command and service modules, Apollo 13, likely, could not have survived reentry. The cold, damp reentry module interior faced extreme condensation of water vapor from the astronauts’ breath. Droplets of water formed behind the display panels.”

Diagram of the Apollo Command Module control panel. Credit: NASA History Office. Click for larger version.

Woodfill said when Apollo 13’s switches were activated for reentry, the interior would surely have burst into flame, were it not for the fireproofing. Condensed water droplets might have short-circuited panel switches, circuit breakers, and connector wiring.

Woodfill said America might never have landed a man on the Moon without Apollo 1. If a fire had occurred on the way to the Moon, it might have ended the will to land men there. “Imagine the horror of the world at such an event,” said Woodfill, “hearing the crew’s painful cries from deep space, ‘We’ve got a fire in the spacecraft.’”

Apollo 1 and the fireproofing of future Apollo spacecraft prevented such an event.

A favorite quote of many managers of the Apollo program, Woodfill said, is from President Theodore Roosevelt, the one posted at the top of this article.

“In a sense, the Apollo One mission was altogether different from Challenger, Columbia, and Apollo 13,” said Woodfill. “No one had dared such a mighty thing as to man the first Apollo spacecraft into orbit. And it, in this case, was fraught with suffering, failure and defeat, rather than a glorious triumph and victory.”

But later, it allowed for great triumph with the success of the Apollo program, and a defying of the odds of the Apollo 13 crew’s survival.

Tomorrow, Part 8: What the Explosion Didn’t Do

Additional articles from the “13 Things That Saved Apollo 13” series:

Introduction

Part 1: Timing

Part 2: The Hatch That Wouldn’t Close

Part 3: Charlie Duke’s Measles

Part 4: Using the LM for Propulsion

Part 5: Unexplained Shutdown of the Saturn V Center Engine

Part 6: Navigating by Earth’s Terminator

Part 7: The Apollo 1 Fire

Part 8: The Command Module Wasn’t Severed

Part 9: Position of the Tanks

Part 10: Duct Tape

Part 11: A Hollywood Movie

Part 12: Lunar Orbit Rendezvous

Part 13: The Mission Operations Team

Also:

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

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

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

Never Before Published Images of Apollo 13’s Recovery

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

13 Things That Saved Apollo 13, Part 6: Navigating By Earth’s Terminator

[/caption]

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.

The rupture and explosion of Apollo 13’s oxygen tank crippled the spacecraft, endangering the lives of the crew and making a Moon landing not an option. But more problems arose as the perilous flight progressed. Keeping the spacecraft on the right trajectory was a huge challenge for Mission Control, and especially for the crew. Normally, the ship’s computers allowed for much of the navigation, but due to the loss of the Service Module as an electrical power source, even backup navigation and targeting functions were unavailable. The Lander’s limited battery power required the shutting down of its guidance computer. The astronauts also needed to use an on-board sextant to confirm their location by sighting-in the stars, similar to how ancient sailors navigated. “There are thirty-seven stars – and one is the sun,” said Apollo engineer Jerry Woodfill, “that provided an accurate way of aligning the spacecraft’s computer platform to allow the astronauts to steer their way through the heavens.”

But the explosion of the tank had enshrouded the Apollo 13 spacecraft with debris. Commander Jim Lovell and his crew couldn’t discern the stars from the particles that glimmered in the sunlight. “The situation was, without the ability to see the stars, you couldn’t navigate,” Woodfill said.

But NASA had a backup navigation plan, thanks to an insightful NASA contractor employee. This novel way of navigating had only been tried once before in space. And coincidentally, the astronaut who used it was Jim Lovell, during his previous flight — Apollo 8 — which orbited the Moon in December of 1968.

An employee of TRW – which was the contractor for many of the navigational systems and procedures for NASA — thought of an unusual backup navigation plan one day. “This fellow is a friend and neighbor of mine,” said Woodfill, “and by his account of the story to me, he said that a thought came to him one day about Apollo astronauts using stars to navigate. What if the stars couldn’t be seen? Now, that was highly unlikely, as there are no clouds, fog, or smoke to conceal stars from viewing by astronauts. But, nevertheless, the thought simply wouldn’t cease. Soon a follow-up idea came to mind. Why not use the Earth’s terminator?”

The nominal flight plan for a mission to the Moon. Credit: Apollo 13 report.

The terminator is the line which delineates between night and day on Earth; where the Sun is shining and where it is dark.

Woodfill’s friend figured out the geometry and wrote a computer program to validate the idea. He submitted the proposal to the navigation board, which approved the technique so that it was entered into the computers in the Mission Control Center.

Through unusual, and what could be called happenstance circumstances, Lovell experimented with the backup plan during Apollo 8.

Lovell served as navigator for the first manned mission to orbit the Moon. He made a star sighting in preparation for the return to Earth, and entered the coordinates into the Apollo spacecraft’s primitive computer using the “DSKY” (display and keyboard). Instead of pressing the ENTR (enter) key, he inadvertently pressed the adjacent CLR (clear) key erasing the entire navigational alignment.

“Lovell consulted with Mission Control whether to repeat the sextant star sighting,” Woodfill said, “and someone realized this would be an opportunity to test the backup ‘seat of the pants’ means of navigating using the Earth’s terminator. And it worked! But then everyone forgot about it, until…guess when?”

Apollo 13's view of the Moon. Credit: NASA

Initially, the Apollo 13 crew was able to use the Sun as a “marker” to help in guiding the spacecraft to confirm they were on the right path, and were able to fire the LM engines for course corrections using the transferred guidance platform from the Command Module.

But as Apollo 13 headed back to Earth, the Reentry (RETRO) and Guidance, Navigation and Control (GNC) officers looking at the trajectory analysis noticed the spacecraft was coming in too “shallow,” that is, Apollo 13 was headed to skip off the atmosphere and out into space forever. Something seemed to be “blowing” the spacecraft off course. Later, it was discovered that cooling vapor from the lander was responsible. Since no lander had been present for previous missions on a return trip from the Moon, such a mysterious “wind” had never been encountered prior to Earth re-entry.

Another burn was needed, but no help from the guidance system would be available, as powering the lander’s guidance system, its gyros, the computer, etc. would use too much electrical power.

Here’s where the backup navigation approach that Lovell experimented with on Apollo 8 came to the rescue.

“If a ‘dead-reckoning’ approach could be used, no electricity would be needed,” said Woodfill. “Simply point the vehicle correctly, start the engine and stop it based on Mission Control’s prescribed time for its operation.” Lovell eyed up the Earth’s terminator line and controlled the “yaw” of the spacecraft, Haise controlled the “pitch” and Swigert timed it with his accurate Omega Speedmaster watch.

Graphics from the Apollo 13 report on using Earth's terminator for navigation.

The Navigation report for Apollo 13 describes it this way:

“The cusps of the Earth terminator were placed on the Y axis of the COAS. The illuminated part of the Earth was placed at the top of the reticle. Pitch attitude was achieved by placing the Sun in the upper portion of the AOT (see below). This procedure aimed the LM +Z axis at the Earth and aligned the LM +X axis retrograde along the local horizontal. An AGS body axis alignment was performed, followed by transitioning the AGS to the automatic attitude hold mode. A maneuver to burn attitude was performed, followed by another body axis alignment.”

Navigation graphics from the Apollo 13 report.

Woodfill said he enjoyed Hollywood’s re-enactment of the procedure in the “Apollo 13” movie. Though the spacecraft gyrations about the heavens are wholly exaggerated, the scene where Tom Hanks, Bill Paxton, and Kevin Bacon set-up and execute the terminator burn is generally accurate.

Suffice to say, the procedure worked for Hollywood dramatics, but more importantly, it worked to save the lives of Lovell, Haise and Swigert.

Tomorrow, Part 6: Fire

Other articles from the “13 Things That Saved Apollo 13” series:

Introduction

Part 1: Timing

Part 2: The Hatch That Wouldn’t Close

Part 3: Charlie Duke’s Measles

Part 4: Using the LM for Propulsion

Part 5: Unexplained Shutdown of the Saturn V Center Engine

Part 6: Navigating by Earth’s Terminator

Part 7: The Apollo 1 Fire

Part 8: The Command Module Wasn’t Severed

Part 9: Position of the Tanks

Part 10: Duct Tape

Part 11: A Hollywood Movie

Part 12: Lunar Orbit Rendezvous

Part 13: The Mission Operations Team

Also:

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

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

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

Never Before Published Images of Apollo 13’s Recovery

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

13 Things That Saved Apollo 13, Part 5: Unexplained Shutdown of the Saturn V Center Engine

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.

While oxygen tank number two on the Apollo 13 spacecraft was an accident waiting to happen, another problem on the Saturn V rocket could have destroyed Apollo 13 before it reached Earth orbit. During the second-stage boost, the center – or inboard — engine shut down two minutes early. The shutdown wasn’t a problem, as the other four engines were able to compensate for the loss by operating for an extra four minutes. But why the engine shut down is a mystery that may have saved the mission.

“A catastrophic failure should have ensued,” said Apollo engineer Jerry Woodfill, “and would have, except for the unexplained behavior of the engine’s shutoff system. In fact, even the NASA Apollo 13 accident report fails to deal with the seriousness of the event.”

When the center engine shut down, it caused a few moments of uneasiness for Mission Control and the crew. Speaking after the flight, Commander Jim Lovell said that when NASA gave them the OK to carry on with the flight, “We all breathed a sigh of relief on the spacecraft. Hey, that was our crisis over with and we thought we’d have a smooth flight from then on.”

Woodfill said that the quick assessment in Mission Control was that a minor electrical signal failed to keep the engine operating so that it shut down prematurely. But that wasn’t the problem.
[/caption]
What happened was the Saturn V rocket experienced dangerous so-called “pogo” thrust oscillations, a problem NASA knew about. While a fix had been planned for Apollo 14, time did not permit its implementation on Apollo 13’s Saturn V.

“While a clerical error caused Apollo 13’s oxygen tank to explode,” said Woodfill, “because its heater design had not been updated for 65 volt operation, and the tank was a virtual bomb (see Part 1), similarly NASA’s failure to fix a known serious booster flaw should have destroyed Apollo 13.”

The Saturn V rocket had five J-2 engines, each producing 200,000 pounds of thrust, together creating the 1 million pounds of thrust needed for a mission to the Moon.

On previous Saturn flights, these pogo oscillations had occurred during launch. The phenomenon occurred as the fuel lines and structure of the rocket resonated at a common frequency. The resonance tended to amplify in force and potential destruction with each bounce of the “pogo” mechanism. So damaging was the phenomena on the unmanned Apollo 6 mission that an entire outer panel of the Saturn 5 ejected into space.

Launch of Apollo 6. Credit: NASA

“The oscillations are like a jack hammer and it was so dreadful on Apollo 6 that it tore off a panel on the booster, and threatened the mission,” said Woodfill. “Apollo 6’s orbit was supposed to be circular, but because of the pogo effect and failure of second stage engines, the orbit became an elongated orbit of about 60 by 180 miles.”

Woodfill said if Apollo 13 had ended up in that type of orbit, it would have been bad but not fatal. However, Apollo 13 was a much different situation than Apollo 6.

The Apollo 6 mission carried a mock lunar lander of more modest mass than the “full-up” lander which Apollo 13 carried to orbit. With the added mass for Apollo 13, the pogo forces were suddenly a magnitude greater in intensity. A mission report said that the engine experienced 68g vibrations at 16 hertz, flexing the thrust frame by 3 inches (76 mm).

Woodfill said that if the center engine had continued running a few more seconds, the oscillations may have destroyed the vehicle. “That engine was pounding horizontally up and down, a quarter foot, at the rate of 16 times a second,” he said. “The engine had become a two ton sledge hammer, a deadly pogo stick of destruction, putting enormous forces on the supporting structures.”

What shut the engine down?

“It is, to this day, not fully understood, but it had something to do with fooling the engine’s thrust chamber pressure sensor that pressure was too low,” said Woodfill. He has studied the mission report, but says the complete analysis of why the engine shut down isn’t included.

“Though the shutdown command came from a low thrust chamber pressure sensor assessment, actually, the engine was operating correctly,” he said. ” The sensor had nothing to do with the pogo phenomenon. For some inexplicable reason, it was like something sucked the pressure out of the chamber and a sensor turned the engine off. But no one knows exactly why.”

Woodfill said those who later examined the situation said it was altogether lucky that the sensor shut down the engine. “Something intervened, stopping the engine from pounding its way from the mount into the fragile fuel tanks. This would have destroyed the Apollo 13 launch vehicle.”

As it was, the engine shutdown likely saved the Apollo 13 mission.

Tomorrow, Part 6: Navigation

Other articles from the “13 Things That Saved Apollo 13” series:

Introduction

Part 1: Timing

Part 2: The Hatch That Wouldn’t Close

Part 3: Charlie Duke’s Measles

Part 4: Using the LM for Propulsion

Part 5: Unexplained Shutdown of the Saturn V Center Engine

Part 6: Navigating by Earth’s Terminator

Part 7: The Apollo 1 Fire

Part 8: The Command Module Wasn’t Severed

Part 9: Position of the Tanks

Part 10: Duct Tape

Part 11: A Hollywood Movie

Part 12: Lunar Orbit Rendezvous

Part 13: The Mission Operations Team

Also:

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

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

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

Never Before Published Images of Apollo 13’s Recovery

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

13 Things That Saved Apollo 13, Part 3: Charlie Duke’s Measles

[/caption]
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.

Just 72 hours before the scheduled launch of Apollo 13, Ken Mattingly was removed from the mission and replaced by Jack Swigert from the back-up crew as Command Module Pilot. Charlie Duke, also from the back-up crew caught the measles from one of his children, and exposed Mattingly — the only other member of either the prime or back-up crews who were not immune to the disease. If Mattingly were to come down with the measles, he might contract it while alone in the Command Module while Jim Lovell and Fred Haise were walking on the Moon.

“I think Charlie Duke’s measles contributed to the rescue,” said NASA engineer Jerry Woodfill, who has come up with “13 Things That Saved Apollo 13.” “This is one that probably everyone disagrees with me, but it seems like the astronauts on board were perfect to deal with what happened on the Apollo 13 mission.”

Woodfill says his conviction in no way denigrates the abilities of Ken Mattingly. “Ken was a wonderful crew member,” Woodfill said, “and he is a very detailed guy who helped with the rescue of Apollo 13 in a magnificent way. In the movie, Apollo 13, they capture the essence of how he is an ‘engineer’s engineer’.”

Astronaut Charlie Duke. Credit: NASA

Although, ironically Mattingly and Duke flew together later on the Apollo 16 mission, were it not for Charlie Duke’s measles, Woodfill said that Swigert’s special talents for an Apollo 13-type mission would not have been present.

Jack Swigert. Credit: NASA

First of all, his physique was better suited to the harsh conditions he experienced in the inoperable Command Module, where he was positioned for most of the flight. Woodfill said that likely, Swigert’s brawn as a former University of Colorado varsity football player better served him to withstand the cold conditions and endure the small amounts of water that the astronauts had to ration among themselves.

Water was one of the main consumables – even more than oxygen – of which the crew barely had enough.

“Mattingly and Haise had about the same build,” said Woodfill, “which was not as robust a build as Swigert and Lovell. Haise ended up with a urinary tract infection because of not getting enough water.”

But more importantly were Swigert’s familiarity with the Command Module and his “precise” personality.

Screenshot from Apollo footage of Jim Lovell and Jack Swigert. Credit: NASA

“Among the nearly thirty Apollo astronauts, Jack Swigert had the best knowledge of Command Module malfunction procedures,” said Woodfill. “Some have said that Jack had practically written the malfunction procedures for the Command Module. So, he was the most conversant astronaut for any malfunction that occurred in the CSM.”

Swigert had to quickly and accurately write down the procedure to transfer the guidance parameters from the CSM computers to the Lunar module computers. And the procedure for the reentry of the crew to Earth’s atmosphere had to be re-written, with Mission Control calling up to the crew with hundreds of changes to the original plan. “The team on the ground had to recreate a checklist and a procedural ‘cookbook’ that would normally take three months to create, and they had to do it in just days. Jack had to be accurate when he wrote down these procedures. And the communication system wasn’t always the best – it was sometimes garbled or couldn’t be heard very well. While all the astronauts had to have orderly minds, Jack Swigert was a man of extreme order.”

Woodfill said an account from Swigert’s sister bears out that fact. She at one time asked her brother Jack to put away cans of frozen orange juice and lemon juice in her freezer. When she looked in her freezer later, all the lemon juice cans were lined up in orderly fashion, with the orange juice cans neatly lined up in an adjacent row. Later, she asked her brother why he had neatly lined all the lemon cans in a row then a row of orange juice cans, and according to Woodfill, Swigert answered, “Because “L” comes before “O” in the alphabet.”

“The truth is, Swigert was gifted with a respect for extreme order and precision, and he was onboard for just that reason,” said Woodfill. “Every one of the steps in the rescue checklist had to be ‘in the right order’.”

Fred Haise, in 1966. Credit: NASA

And, equally important, said Woodfill, was the talent Haise brought to recording and rewriting operational procedures. “Fred had been a newspaper stringer for a small newspaper in Mississippi in his youth, taking notes and editing them for his local Mississippi paper’s stories. Utmost among reporters is accuracy in quoting sources. Those transmitted words from mission control had to be flawlessly transcribed if the crew was to survive, and Fred and Jack did an amazing job.

Remarkably, said Woodfill, each man’s talents specifically served the unique need. “Each man exhibited exceptional accuracy in adverse surroundings,” he said. “The lander was noisy, the audio sometimes fuzzy, movement unpredictable, temperatures cold, sleep scarce, and fatigue always present.”

Of course, those familiar with the Apollo 13 story know that Ken Mattingly never got the measles. But the role he played in getting the astronauts back home safely can’t be overestimated.

“Call it luck, call it circumstance,” said Woodfill, “but because of Charlie Duke’s measles the men on board Apollo 13 — and back on the ground — were perfect for the situation they encountered.”

Other articles from the “13 Things That Saved Apollo 13” series:

Introduction

Part 1: Timing

Part 2: The Hatch That Wouldn’t Close

Part 4: Using the LM for Propulsion

Part 5: Unexplained Shutdown of the Saturn V Center Engine

Part 6: Navigating by Earth’s Terminator

Part 7: The Apollo 1 Fire

Part 8: The Command Module Wasn’t Severed

Part 9: Position of the Tanks

Part 10: Duct Tape

Part 11: A Hollywood Movie

Part 12: Lunar Orbit Rendezvous

Part 13: The Mission Operations Team

Also:

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

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

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

Never Before Published Images of Apollo 13’s Recovery

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