Apollo 13’s Battery Charge Miracle


Jerry Woodfill, Former Apollo 13 Warning System Engineer



Only two of the Bible’s sixty-six books feature women as the main character:  Ruth and Esther.  Ruth’s story is only four pages in most Bibles, Esther’s only nine.  Remarkably, Esther’s book never mentions God.  Yet, no sequence of  circumstances is more obviously the hand of God’s  providence than Esther’s experience.  Likewise, few Apollo 13 accounts acknowledge God or prayer contributing to the rescue.  Nevertheless, a succession of “fortuitous” happenings is inexplicable. To understand the rescue, God must be included in the outcome.  Indeed, God’s providential care for Esther and her Jewish brethren is a template for Apollo 13’s rescue.  Though twenty-five centuries apart,  correlation of Apollo 13 and Esther’s story  makes this point.


 God promised Esther the same kind of oversight given Apollo 13 three centuries earlier.  He made the Prophet Isaiah His spokesman,  “Before you call, I will answer, and while you are yet speaking I will hear.” (Isaiah 65:24).  It became an everlasting two part pledge to the faithful:  the first part has Him ordering our ways and directing our paths as an overseer.  That’s His definition of  Providence.  But the second part is every bit as important. It is answered prayer for those “who are yet speaking.”  Esther and Apollo 13 are products of this spiritual duality, Providence and Prayer.                                                         

To begin, let’s compare Esther and Apollo 13 as historic accounts.  Admittedly,  they are unlikely ecclesiastical “bedfellows.”  Nevertheless, their examination confirms that principle cited by the Apostle Paul, that both Scripture and  Jesus, the Lord, are “the same yesterday, today, and forever.”                                                                                                


A brief paraphrase of Esther has four principle characters: Esther, her Uncle Mordecai, King Xerxes. and the Villain Haman,  Incidentally, Esther’s name in its native tongue means, star, just as Apollo 13 journeyed among the stars. Neither Ester nor Apollo 13 appeared exceptional among their kind.  Esther, though a beautiful Jewish maiden, hoped to be picked as the King’s Queen.  Likewise, Apollo 13  was not especially notable among ten potential moon landing missions.                                                        


Yet, both Esther and Apollo 13 were uniquely selected, singled out for God’s plans and purposes, in Esther’s case for the salvation of the Jewish people, for Apollo 13  as a demonstration of his providence and answered prayer.   Each fulfilled the words of Isaiah, providentially and prayerfully.                                                              


Both began with adversity.  The King’s Queen refused his request and is banished from her throne and executed.  This led to a Persian queen beauty contest, akin to American Idol competition.  Likewise, Apollo 13 began with the adverse explosion of its life sustaining power and oxygen system.  The contest which ensued was one of survival, not unlike Esther’s contest for the lives of the Jewish people.  Whether it be  three astronauts or three million  Hebrew men, women, and children, God fulfills his promises.  But first, read the paraphrase below from the Book of Esther  to examine the correlation of events: 


Chapter 1 - The account begins with a lavish banquet thrown by King Xerxes of Persia, a potentate of  great wealth and power.  Because Queen Vashti refuses to attend, the king has her executed.

Chapter 2 - The king launches  a  search of the realm for a new queen. A particularly fair Jewish maiden named Esther, whose devout uncle is Mordecai,  is brought by  the king's officers to the palace.  There, she participates in an extended  beauty pageant to replace the former  queen.  Xerxes chooses Esther as his queen.  Per her uncle’s command, she does not disclose her Jewish lineage.  Then, Mordecai hears of a plot to assassinate the king. As a result of Mordecai warning the king, the conspirators are killed, and Mordecai’s heroic deed is recorded in the king's chronicles.  

Chapter 3 -  After the king appoints the self-serving  Haman as  his viceroy,  all citizens  are ordered to bow before the pompous opportunist.  However, Mordecai refuses.  Such incites Haman’s  wrath not only on Mordecai but also Mordecai’s people,  the Jews. Through the casting of lots,  Haman decides that the 13th day of the month of Adar shall be the appropriate  time to exterminate  Mordecai and his people. Citing the disloyal act of Mordecai’s failure to bow, Haman receives  the king's permission to murder all Jews.   In the realm. He edicts that this be done in all 127 provinces of Xerxes’s kingdom..

Chapter 4 – Predictably, earnest mourning prevails among the Jewish people. Mordecai sees in Esther  one who might   intercede in behalf of her people.  Despite knowing that the former Queen met her death by disobeying the King, Esther risks her life by agreeing to go  before the king without being summoned.

Chapter 5 – Only after fasting  three days, does Esther approach the king.  As a result God favors her such that the king is not angered by her forthrightness.  In fact, she is able to invite both King Xerxes and Haman to a feast.  This is to be a subtle  trap planned to snare the wicked Haman. At the banquet, Esther invites the king and his viceroy Haman to yet another banquet.  It is to be held the following day. In the interim, Haman is building the gallows on which he plans to hang Mordecai.

Chapter 6 – But that very  night the king has insomnia.  He can not sleep.  As a result,  he asks  that his book of chronicles be read to him. During the reading, the king is reminded how Mordecai had saved him from assassination.  “But I have never rewarded Mordecai for this heroic act,” thinks the king.  Haman has been in the outer courtyard of the palace planning to ask the king's permission to hang Mordecai.  However, when he is brought before the king, the kings first asks,  “Haman, what should be done for a man whom the king wants to honor?”  Of course, the pompous Haman, thinks it is he the king wishes to honor.  For that reason, Haman suggests a lavish award which includes having the honoree dressed in royal garments and paraded around the city on the finest of the   king's steeds.  Then, to Haman’s surprised dismay, King Xerxes  commands the heinous  plotter, Haman,  honor Mordecai with the celebration Haman had suggested for himself. 

Chapter 7 – Next comes the second banquet at which Esther tells  the king of  Haman’s  plot to destroy  her people.  King Xerxes is so angered that  he orders  Haman hanged on the very gallows which he had built to  execute Esther’s uncle Mordecai.

Chapter 8 – Mordecai is made the new viceroy, replacing Haman.  Additionally, Esther entreats the king  to  cancel  Haman's decree to kill  the Jews. The king not only grants Esther’s wish but gives  permission  for the Jews to defend themselves and annihilate their enemies on the same day Haman called for their destruction.  Great rejoicing sounds throughout the city by and  for its Jewish people.

Chapter 9 -  It is on the 13th day of Adar when the Jewish people not only defeat  their adversaries but also  hang the ten sons of Haman. Then, the Jewish brethren  of the city  are given yet another day to destroy their enemies. It is Esther’s Uncle Mordecai who records these historic events which  establish the festival of Purim.

Chapter 10 – Mordecai is honored  by  his Jewish  people.

How the events in the book of Esther relate to Apollo 13’s rescue are a parable of joyful victory over adversity.  Such was the characterization of the month of Adar by the Jews as a result of the rescue from Haman’s gallows.  Adar became, on God’s calendar,  the  time to set aside grief and mourning for happiness and joy…so it was for Jim Lovell and crew, though their joy came a month later as recorded on man’s Gregorian calendar..  Obviously, the number 13 relates to Apollo 13 when the circumstantial technical adversaries began to be defeated on April 13th of the year 1970. 

These verses relate to the rescue of both the Jewish people and Apollo 13…

In…the month of Adar, on its thirteenth day ... on the day that the enemies of the Jews were expected to prevail over them, it was turned about: the Jews prevailed over their adversaries. - Esther 9:1


The Jewish month of Adar is characterized by joy because it is the month of transforming dread into joy. Adar was the month that Haman selected for grief and mourning, specifically on the 13th day, but for the past 2,400 years it has, instead, been a time of Jewish rejoicing and celebration. In 1991, when Saddam Hussein tried to rain missiles down on Israel, he was defeated on Purim day, the thirteenth day. Adar contains the power to succeed against an opposing force, both on a national level and on an individual level.  Likewise, it not only was Apollo 13’s day of potential doom but the day of the onset of the rescue.  With regard to the threat of the depleted batteries, it directly relates to Purim.                                                                                                                                 


Apollo 13’s Haman gallows are analogous to the depleted command module’s batteries, over-used to keep the ship alive until the guidance platform numbers could be transferred from the mother ship’s computers to the lander’s.   Those gallows were erected around ten p.m. Houston time on Apollo 13’s  thirteen day of the month.                             


But, like the God sent King’s insomnia, the lander’s power manager is awakened from slumber by the voice of Mission Control via a phone call.   Told of the peril, the power manager recalls, like the King, an obscure document prepared long ago as a means of charging those batteries.                                                                                                    


As with King Xerxes, the manager’s recollection promises to save Lovell and crew just as remembrance of Mordecai’s good deed might be the Jewish people’s salvation.   Likely, both divine interventions came at like-periods in the night, at the onset of  sleep,  both on the 13th day of the month, the Apollo 13 Purim.   For Apollo 13, the recollection was the detailed recording of the charging procedure.  The written text was never found in the power manager’s files.   But the manager had fully transcribed the step-by-step plan from memory by midnight. Thus, as Scripture had promised for Esther and the Jews,  likewise for Lovell as crew:  Apollo 13 had gained potential relief on the fourteenth:


Esther 9:17

And they gained relief on the fourteen - - Esther 9:17


Yet, the fullness of the miracle required the taking down of the depleted battery “gallows.”  This would be the miracle of the recharge.   But how was it accomplished?


The answer requires a brief primer on rudimentary battery technology as well as Apollo’s spacecraft power systems.   Perhaps, the best example for discussion is the common car battery, its function, design, and charging approach.  Consider the sketch below for what is to follow:

Figure 1.


The three tiered diagram above has the Apollo 13  lander and command ship compared to the modest sized yellow vehicle on the left and more massive purplish auto on the right, each with their respective batteries.  Sandwiched between the Apollo vehicles and automobiles is a representation of the battery systems in each.  The lander’s batteries held considerably more charge (electrical capacity or power) than the depleted emergency  reentry batteries of  command module entry capsule. For that reason, they are depicted as the HEAVY DUTY battery.   In that sense the massive power source resides in the lander identified with the yellow economy car.                                                                


Because the Apollo command module’s main power source, its fuel cells, was rendered useless by the Oxygen tank 2 explosion, those modest entry batteries (three in number with total amp hour capacity of ?????) were called upon to keep the ship’s systems alive while the crew powered up the lander as a rescue vessel.                                          


Continuing the space/auto analogy would have the Cadillac’s generator failing during a  night crossing of  a desert highway.   With the yellow  Volks-wagon in tow,   soon electricity drained by the lights would deplete the Cadillac battery. The road would no longer be illuminated.  However, the towed vehicle has a working generator and fully charged battery.  Before the Cadillac’s lights fully deplete its battery, a work-around is enacted,  The cars are interchanged such that the Volkswagon tows the Cadillac. The Cadillac’s engine and electrical power system are inactive during the tow.                                 

Obviously, the night journey can continue as long as the Volkswagon’s generator is turning, charging its battery.  All depends on having adequate gasoline available to the vehicle’s engine.   Once daylight comes, and the desert is crossed, the pair of vehicles can move onto the highway shoulder.  There, a jumper charge from the Volkswagon replenished power into the depleted Cadillac battery.   With the Caddy’s battery charged, the large sedan makes the final leg into a nearby town.  Since no lights are needed in daylight, the charged battery need only  start the Cadillac engine.  This would be akin to reentry of Apollo 13’s capsule under entry battery power.                                                                          

It is the charging procedure which has made the final leg of the Cadillac’s trip possible.   While such a process would seem rudimentary, the nature of the physics involved is instructive.   The figures below help  explain the battery charge. By  comparing the flow of electricity to water current,  understanding is enhanced.


Figure 2.


The above Figure 2.  likens the flow of water to electric current.  The measure of current is in amps. or coulombs per second moving within the circuit wire. (A coulomb is the measure of current moved by one volt of electromagnetic force through a resistance of one ohm.) To move water some kind of pump is needed to pressurize the pipe.  


The extent or magnitude of the pressure force which moves the electrical current is measured in volts.  Just as water will only flow from higher pressure to lower pressure through a pipe, electric current will only flow through a wire from a higher voltage device or battery to one of lower voltage.                                                                                          

As the Apollo emergency batteries were depleted, the electrical pressure or voltage they possessed dropped as well.  This meant that placing a higher voltage device, i.e., a fully charged battery in parallel with their positive and negative terminals would recharge them.                                                                                                                  


Figure 3. below continues the water to electricity analogy, showing that a switch or, in the case of the Apollo 13 charging, a circuit breaker, does the same job as a valve enabling and disabling current flow.  

Figure 3.


For Apollo 13’s charging of the command module’s batteries, the pump was the lander’s batteries, the load or  resistance was the entry battery system.   Continuing the comparison in the sketch below demonstrates the importance of attaching like polarity terminals of the lander and entry capsule’s batteries.    Such a connection is deemed a “parallel” hookup for charging.   Alternatively, connecting unlike terminals, i.e., plus to minus, and minus to plus, known as a “series” hook-up, will not charge the weaker battery but simply add it pressure  or voltage to the pump’s circuit.  Such a series connection increases the overall voltage or pressure whether fluid or electrical.                               


This leads to examining the makeup of the lander’s battery system.  As with the command ship, more than one battery comprised the power systems for both the ascent stage and the descent stage.  Of course, the descent stage needed far more electrical capacity than the ascent by virtue of the systems powered and duration of use.  For that reason the lander’s ascent stage had but two batteries, each providing 296 amp-hours capacity,  while the descent stage had four batteries, each providing 400 amp-hours capacity for operating the lander’s electrical systems during descent and lunar operations until  ascent stage liftoff when the ascent batteries were employed.                                                 

The concept of amp hours is a good one for describing the rescue scenario.  With regard to the water analogy, it is likened to how long a pump is able to supply a given water flow for filling a reservoir with an adequate pressure (voltage) to keep the water (amps or current) flowing.  Of course, even though current may continue to flow, it may become a trickle unable to push a paddle wheel or power an electrical device requiring a minimum voltage for operation.  For Apollo 13’s command module, the range of operating voltage designed into electrical devices was approximately 26.5 to 32 voltage DC.  Below 26.5 volts, an alarm would trigger warning the crew that corrective action must be taken.  The lander had similar specifications.                                                            


Providentially, the Apollo Operations Handbook has the lander’s batteries at a nominal voltage of 30.0, a full two volts above the operating voltages for Apollo entry capsule electrical systems.  It seemed from the beginning, God had foreseen making those LM batteries ideal for charging those in the entry vehicle.  There would be a natural plus two volts pressure available to flow an electrical charge through “jumpers” between the two vehicles.  


However, the extent of God’s “keeping and care” is seen by the post flight comment:  The Lunar Module batteries performed above the specified requirements when emergency power was needed during Apollo 13 after the loss of command and service module fuel cell power.  However, post-flight analysis revealed that an unexplained current spike occurred during trans-earth coast.  The charging by the batteries created a short circuit, igniting the mixture of hydrogen and oxygen normally produced by a silver-zinc battery.  The discharged mixture was ignited, thus causing the “thump and snowflakes”  experienced by the crew.   This mode could not be reproduced and the battery continued to operate satisfactorily throughout the mission.  A number of significant design changes were made to preclude the possibility of any future explosions.  The spike was associated with the occurrence of  “thump and snowflakes” reported by the crew.  The postulated cause was venting of potassium hydroxide by one of the descent batteries


(The previous comments were reported in the Apollo Experience Report subsequent to the last Apollo mission. Incidentally, this author wrote the lunar lander caution and warning section of that Apollo Experience Report which included a discussion of the battery/electrical power alarm design.)


Remarkably, the above italized commentary shows yet another instance of God’s keeping and care subsequent to Apollo 13’s Purim.  Imagine an exploded battery operating nominally for the duration of the mission.  The mystery event could not even be reproduced in later Earth simulated tests.  This is, indeed, a case of God doing wonders “above and beyond” man’s expectations.                                                                                          

It is true that the power manager was singled out for a specific commendation regarding the miracle battery charge.  The honor was bestowed in a later awards ceremony at the space center.  Likewise, the above account is offered as a special commendation to God the Father. His  Purim, the 13th of Adar, kept that scarlet thread alive, a thread which lead to the birth of His Son, in human form, centuries later.  


Jerry Woodfill

Former Apollo 13 Warning System Engineer

Houston, Texas

(April 13, 1970 – Purim Day for Apollo 13)

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