Category How to Find the Apollo Landing Sites

Apollo 12

Date: 14-24 November 1969

Crew: Commander – Pete Conrad

CM Pilot – Dick Gordon LM Pilot – Alan Bean

Command Module: Yankee Clipper Lunar Module: Intrepid

Accomplishments: Pinpoint landing within 535 feet of Surveyor 3, two extended Moonwalks, setup and initiated Geophysical Station and Lunar Nuclear Power Station.

J. L. Chen, How to Find the Apollo Landing Sites,

The Patrick Moore Practical Astronomy Series, DOI 10.1007/978-3-319-06456-7_4, © Springer International Publishing Switzerland 2014

Early in Apollo program planning, NASA defined a sequence of missions:

• “A” missions were unmanned tests of the launch vehicles and the Command Module

• “B” missions were unmanned tests of the LM

• “C” missions (Apollo 7) were manned, Earth orbital tests of the Command Module

• “D” missions (Apollo 9) were LM/CSM tests in Earth orbit

• “E” missions (none were flown) were tests in high Earth orbit

• “F” missions (Apollo 10) were lunar orbit tests

• The “G” mission was the Apollo 11 landing.

• “H” missions (Apollo 12, 13, and 14) would be subsequent flights to other land­ing sites using the basic equipment

• “I” missions (none flown) would be lunar orbit-only science flights

• “J” missions would be the longer visits that LM design changes would make possible. Equipped with Lunar Roving Vehicles (LRV), the J-mission crews would be able to extend their range on the lunar surface and visit a variety of geologic features some distance away from the landing site, collect greater quantities of rock and soil samples, utilize a greater number of tools carried on the Rover, and LRV would serve as a mobile experiment platform. In general, the J-missions promised a significant increase in productivity. However, before the J-missions could be attempted, NASA had to demonstrate that crews could achieve pinpoint landings, work a full-day in the stiff suits and, if necessary, walk several kilometers back to the LM from a disabled Rover.

Apollo 12 represented the first of the H missions. The Apollo 12 mission was presented with a couple of challenges not faced by Apollo 11, one known prior to launch and one occurring during launch.

The particular challenge for the Apollo 12 mission was the achievement of a pinpoint landing. One of the significant discoveries prior to the Apollo landings was the existence of mass concentrations, or mascons, on the Moon. The lunar mascons were discovered by scientists at the NASA Jet Propulsion Laboratory (JPL) in 1968 from analyzing the orbital and navigational data from the NASA’s Lunar Orbiter spacecraft. The analysis established a correlation between very large positive gravity anomalies and depressed circular basins on the moon. Many of the Apollo experiments on the lunar surface tried to collect data to explain the gravity variations.

NASA had to establish a special team of scientists and engineers to explain why the Lunar Orbiter spacecraft being used to test the accuracy of the Apollo naviga­tion system were experiencing errors. The mission specification required an accu­racy of 200 meters, whereas the test results predicted a navigational position of 2,000 meters, ten times the allowed specification error. This meant that the pre­dicted landing areas were 100 times as large for reasons of safety, and posed a challenge to precise lunar landings. The principle cause for these lunar orbital errors was due to the strong gravitational perturbations of the mascons. NASA was able to compensate for the existence of the mascons in the Apollo navigation soft­ware, and this compensation was first applied to Apollo 12. The Apollo 12 landing was within 163 meters of the target, the Surveyor 3 spacecraft.

During the launch of Apollo 12, the spacecraft and Saturn V were twice struck by lightning, causing a momentary power crisis aboard Yankee Clipper that almost aborted the mission. Apollo 12 launched on schedule from Kennedy Space Center, during a rainstorm. 36.5 seconds after lift-off, friction from the vehicle passing through the rainstorm triggered lightning through the launch vehicle, through the Saturn’s ionized plume, and down to the ground. The protective circuits of the fuel cells in the Service Module (SM) took all three fuel cells offline because the lightning caused a surge that falsely indicated overloads. The cascading effect of the lightning strike also disabled much of the Command/Service Module (CSM) instrumentation. A second strike at 52 seconds after launch knocked out the attitude control. The telemetry stream at Mission Control was totally disrupted. However, the vehicle con­tinued to fly correctly; the strikes had not affected the Saturn V Instrument Unit.

The loss of all three fuel cells put the CSM entirely on batteries. Apollo 12 power systems were unable to maintain normal 28 V DC bus voltages into the heavy 75 amp launch loads. One of the AC inverters dropped offline. As a result, these power supply under volt conditions lit nearly every warning light on the con­trol panel and caused much of the instrumentation to malfunction.

Legendary NASA “steely-eyed missile man” John Aaron was the EECOM at Mission Control for the launch. Aaron remembered a similar telemetry failure pat­tern from an earlier test when a power supply malfunctioned in the CSM Signal Conditioning Equipment (SCE). The SCE converts raw signals from instrumenta­tion to standard voltages for the spacecraft instrument displays and telemetry encoders.

Aaron made a call to the Apollo 12 crew, “Try SCE to aux.” This switched the SCE to a backup power supply. The switch was fairly obscure and neither the Launch Flight Director Gerry Griffin, CAPCOM Gerry Carr, nor Commander Conrad immediately recognized it. Lunar Module Pilot ( and future Apollo artist) Alan Bean, flying in the right seat as the CSM systems engineer, remembered the SCE switch from a training incident a year earlier when the same failure had been simulated. Aaron’s and Bean’s quick recall saved the mission and prevented an abort. Bean put the fuel cells back on line, and with telemetry restored, the launch continued successfully. Once in earth orbit, the crew and Mission Control reviewed all systems and declared all systems go prior to trans-lunar injection. The lightning strikes had caused no serious permanent damage and the crew, with the onboard power systems restored, were able to continue the mission.

The key to sighting the Apollo 12 landing site is first recognizing the great Copernicus crater. Copernicus is one of the most easily identifiable features on the Moon, located south of Mare Imbrium, or the Sea of Rains. Through a small tele­scope, one can make out the layered nature of Copernicus, and outward “rays” of light and dark material splashed by the impact of an object that created the crater eons ago. South of Copernicus and past a smaller crater known as Reinhold, is the small Ocean of Storms and the site of Apollo 12. NASA’s conservative approach to landing site selection resulted in another rather featureless landing zone that can be appreciated, but the actual site is difficult to pinpoint for the backyard observer. Apollo 12 landed near the Surveyor 3, near the edge of a small crater. However, the Surveyor 3 and the crater are beyond the resolution of most backyard telescopes.

As with Apollo 11, conservative safety considerations dominated the criteria for landing site selection for Apollo 12. The Ocean of Storms site was chosen because it had few craters and boulders, with less than 2° slope in the approach path and landing site. The site had no large hills, high cliffs, or deep craters that could reflect erroneous altitude radar returns to the lunar module landing radar. As with the Apollo 11 landing site, the Ocean of Storms presented a fairly featureless target area. NASA still wanted the least expenditure of spacecraft propellants, with crew and mission safety in mind.

These criteria dictated landing in a mare region near the equator. Mare regions in Ocean of Storms were given high priority because telescopic study suggested that these areas are younger and of a slightly different composition than the Apollo 11 landing site.

Since Apollo 11 overshot its planned target by 4 miles, the goal of Apollo 12 was to demonstrate a precision landing capability. Precise landings capability was vital to set the stage for more complex missions. Therefore, a landing near where Surveyor 3 landed was planned. This provided both a clear marker for determining the accuracy of the landing, and an opportunity to return parts of the Surveyor 3 that had failed to function 2 1/2 years earlier. Of scientific interest was sampling ejecta from the crater Copernicus, in an effort to establish the crater’s age. And, this land­ing site allowed the CM Yankee Clipper good orbital imaging of the Fra Mauro site that was the target of the ill-fated Apollo 13 mission, and was eventually achieved by the Apollo 14 mission.

Fig. 4.6 LRO view of Apollo 12 Landing site in 2009. Photo courtesy of NASA and Arizona State University

As previously mentioned, the difficulty of attempting such a precision landing was complicated by the existence of mass concentrations, or mascons, on the Moon. These mascons caused variations in local gravity on the Moon, variations that easily affected the navigation landing computer onboard the LM, as well as the lunar orbiting CM. These mascon regions were first discovered in 1968, and proved to be a problem for both the American Lunar Orbiter missions, and the Russian Luna missions. NASA’s Lunar Orbiter spacecraft was used to test the Apollo navi­gation algorithms, and produced errors ten times the specification requirement because of the lunar mascons. Instead of specification error of 200 meters, an error of 2,000 meters would result. An error of almost 1-1/4 mile was intolerable.

NASA had to develop a method to compensate for the mascon error, without actually knowing what a mascon was. The answer was using the Doppler effect to map and compensate for the mascon gravity variations. The Doppler shift of an orbiting LM, although variable, would be predictable. By comparing the predicted Doppler shift against actual Doppler shifts, it could be determined if the LM was off course and how far off course. The trick was how to input the correction infor­mation into the LM guidance computer, recognizing the state-of-the-art of the 1960s. The Apollo CM and LM computers were highly primitive by today’s stan­dards. It’s hard to believe that the computer technology of the 1960s limited the LM memory to 2,056 bytes (that’s right, kilobytes, not megabytes, not gigabytes). The technological slight-of-hand was used to fool the computer into thinking the land­ing site had moved instead of the LM being off-course! The result of this software finesse was the Apollo 12 landed within 163 m of the planned target, and an easy lunar stroll to the Surveyor 3 spacecraft.

Once on the Moon, a major task for the crew of Apollo 12 was the collection of lunar soil and rock samples. A major find of Apollo 12 was the discovery of the first KREEP samples. Unique to the Moon’s geology in the highlands, and not found on Earth, KREEP is a moon rock containing potassium (chemical symbol K), rare-earth elements (REE), and phosphorus (chemical symbol P). Containing potassium, phosphorus oxides, rubidium, and lanthanum, KREEP is made up of normally incompatible elements, and was first found in the Apollo 12 samples in agglutinate glasses and polymict breccias.

KREEP and other anorthosite samples represent part of the evidence for the formation of the Moon. The leading theory for the Moon’s formation is that it was formed from the remains of an ancient impact between the Earth and a Mars-sized proto-planetary body about 4.5 billion years ago. This collision threw a large amount of material into orbit around the Earth that eventually became the Moon.

A large amount of energy was generated by this collision. Scientists have deduced that a large portion of the Moon would have liquified, initially creating a magma covered Moon. As the magma crystalized, minerals precipitated and sank to the bottom to form the lunar mantle.

As the Moon solidified, low density anorthosite material began to crystallize and float towards the surface, forming a solid crust. Elements that are usually incompat­ible then progressively concentrate into the magma. The magma that formed, sand­wiched between the crust and mantle, was rich in KREEP. The evidence for these processes came from the presence of the rocks rich in KREEP, and the highly anorthositic composition of the crust of the lunar highlands from samples from later Apollo missions.

The Apollo Lunar Surface Experiments Package, or ALSEP, aboard Apollo 12 and deployed by Astronauts Conrad and Bean at the Ocean of Storms was made up of a more extensive set of experiments than the EASEP of Apollo 11:

• The Passive Seismic Experiment (PSE) detected lunar seismic activities and provided information about the internal structure of the Moon. The Passive Seismic Experiment studied the propagation of seismic waves through the Moon and provided data about the Moon’s internal structure. The Apollo 11 seismometer returned data for just 3 weeks but provided a useful first look at lunar seismology. More advanced seismometers were deployed at the Apollo 12, 14, 15, and 16 landing sites and transmitted data to Earth until September 1977.

Each of the PSE’s measured all three components of ground displacement (up-down, north-south, and east-west). In 2011, based on 30 year old data from these four PSE sites, a new analysis confirmed the layering of the Moon’s core. This analysis, using a technique borrowed from one originally developed to analyze Earth’s earthquakes, concludes that the Moon’s core has a solid inner core surrounded by a molten outer core. Additionally, the analysis suggested that the iron-rich lunar inner core contains less than 6 % of the light elements of the Periodic Table. Most useful for this study utilized data from more than 6,000 deep moonquakes occurring about 435 miles below the Moon’s surface.

• The Lunar Surface Magnetometer (LSM) measured the strength of the Moon’s magnetic field. The magnetic field data included field strengths both from the Moon’s intrinsic magnetic field mixed with external magnetic fields of the Earth and Sun. These external fields varied in strength with time as the Moon moved through Earth’s magnetosphere as it orbited the Earth. By making measurements over several months, these time-varying fields were be separated from the Moon’s steady, intrinsic magnetic field. LSM experiments were part the ALSEP included in the Apollo 12, 15, and 16 missions.

• The Cold Cathode Gauge (CCG) measured the atmospheric pressure of the lunar atmosphere. On Apollo 12, the CCG instrumentation was a part of the Supra Ion Detector Experiment (SIDE). Unfortunately, the CCG failed after 14 hours. The strong magnetic field of the CCG caused interference with the SIDE, which resulted the experiment was packaged as a standalone implementation in later missions.

• The Suprathermal Ion Detector Experiment (SIDE) studied the lunar ionosphere, by measuring the various properties of positive ions in the Lunar environment, collecting data on the plasma interaction between solar wind and the Moon, and measuring the electrical potential of the Lunar surface.

• The Solar Wind Spectrometer (SWS), in addition to the SWCE, was identical to that included in the Apollo 11 EASEP, measured the composition of the solar wind. This experiment, unlike the SWCE, continually sampled the solar wind to measure the effects of the Earth’s magnetic field on the constitution of the solar wind. The results of this experiment showed that most of the Moon’s orbit, which is outside the Earth’s magnetic field, a proton density of 10-20 protons per cubic centimeter was detected. However, no protons were detected during the 5 days in which the Moon is in the tail of the Earth’s magnetic field. Clearly, the SWS demonstrated the shielding effect of the Earth’s magnetic field from the solar wind.

• The Lunar Dust Detector (LDD) studied the effects of lunar dust on the opera­tion of the experiment package.

Pete Conrad Jr., Apollo 12 Commander, examined the unmanned Surveyor III spacecraft during the second moon walk as seen in Fig. 4.10. The “Intrepid” landed on the Moon’s Ocean of Storms less than 600 feet from Surveyor 3. The television camera and several other components were taken from Surveyor 3 and brought back to earth for scientific analysis. Surveyor 3 soft-landed on the Moon on 19 April, 1967.

Surveyor 3 was unintentionally the first spacecraft to liftoff from the Moon’s surface. In fact, it did this twice. Due to a problem with the Surveyor 3 landing radar, which did not shut off the vernier engines, kept them firing throughout the first touchdown, and continued until a second touchdown. The Lunar Module Intrepid landed 600 feet from Surveyor 3, as planned. Surveyor 3’s TV and telemetry systems were found to have been damaged by its unplanned landings and liftoffs.

Another element of Apollo 12 is the Radioactive Thermoelectric Generator. Astronaut Alan Bean can be seen in Fig. 4.12 unloading the nuclear fuel element for the RTG in the foreground. Bean is attempting to remove the fuel element from the cask using the Fuel Transfer Tool (FTT). On Apollo 12, the fuel element stuck in the cask because of thermal expansion (Bean could feel the heat through his suit). Conrad pounded the side of the cask with a hammer while Bean successfully worked it loose. He then inserted it into the RTG and discarded the FTT.

From a public relations point-of-view, the only part of the mission that had gone really wrong was the failure of the color TV camera. The public had great expecta­tions for a spectacular television broadcast from the Moon. The Apollo 11 televi­sion camera produced low resolution, grainy, black-and-white video. This was the first color TV camera to be used on the Moon. Unfortunately, the development of the camera had experienced delays, and the contractor Westinghouse delivered the camera to NASA just days before the launch. As a workaround, Alan Bean trained with a mockup of the camera, which did not highlight the design limitations of the equipment. Initially, the TV camera was operational, but 42 minutes into telecasting the first EVA, astronaut Bean accidentally pointed the camera at the Sun while preparing to mount it on the tripod. The Sun’s extreme brightness burned out the vidicon imaging tube, rendering the camera inoperable. When the camera was returned to Earth, it was shipped to Westinghouse for post-mission analysis. Westinghouse engineers were able to get an image on the section of the tube that wasn’t damaged. Procedures for future Apollo missions were re-written in order to prevent such damage, including the addition of a lens cap to protect the tube when the camera was repositioned. Fortunately, the loss of the TV camera was not crucial from a technical point of view, and did not impact the success of the mission. However, the loss of television coverage of the Apollo 12 mission disappointed millions of viewers in the United States and the world.

In the early Apollo lunar missions, the Saturn V S-IVB third stage that propelled the CSM/LM towards the Moon during the trans-lunar injection phase was lost in space and allowed to enter a heliocentric orbit following separation. Apollo 13, 14, 15, 16, and 17 used the spent S-IVB stage as an opportunity to perform seismic studies and were deliberately crashed into the Moon. The third stage impact pro­vided seismic data to the ALSEP seismometers.

The Apollo 12 Saturn third stage did not impact the Moon, but was supposed to be sent into heliocentric orbit, and was considered lost. Then on September 3, 2002, an amateur astronomer named Bill Yeung discovered what was then considered an asteroid, and officially given the designation of J002E3. At the time of its discovery, J002E3 was in a highly elliptical orbit around Earth. University of Arizona astrono­mers found that the object’s spectrum was consistent with titanium dioxide paint, the type of paint used on the Saturn V launch vehicles. An analysis of the orbit has identified the Apollo 12 third stage as the likely candidate for J002E3. The Apollo 12 S-IVB did not achieve a true heliocentric orbit, having not achieving escape velocity for the Earth-Moon system. After flying past the Moon on November 18, 1969, J002E3 attained a semi-stable orbit in which the third stage entered a highly elliptical orbit around the Earth-Moon system, then flung into deep space by the combined gravity forces of Earth and the Moon, and then re-captured by the Earth – Moon system at a later date. Following its discovery, J002E3 left Earth orbit in 2003, and is expected to return in either 2032, or the mid-2040s, depending on the orbital model used.

The mystery of the mascons has finally been solved. In May, 2013, NASA released the findings of the Gravity Recovery and Interior Laboratory (GRAIL) mission to the Moon. GRAIL consisted of two lunar orbiting probes, GRAIL A and GRAIL B, launched in September 2011, orbiting in near circular orbits at an alti­tude of 55 miles. The distance between the two GRAIL probes, nicknamed Ebb and Flow, were precisely measured as they passed over gravity variations caused by mountains, craters and mascons until the data collection ended in December of 2012. NASA reported that the GRAIL data confirmed the lunar mascons were generated by large asteroids and comets impacting the young Moon when it had a thin crust and dense molten mantle. The impact created a circular ripple effect of material that cooled beneath the visible surface of the Moon consisting of rings of dense and lighter lunar material.

On September 12, 1962, President John F. Kennedy spoke at Rice University and spoke these immortal words that launched the United States on its quest to the Moon:

We choose to go to the moon. We choose to go to the moon in this decade and do the other things, not because they are easy, but because they are hard, because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one which we intend to win, and the others, too.

In an era of international and geo-political competition, President Kennedy launched the United States into its decade long quest that culminated in the Apollo landings that are the subject of this book.

Now over 40 years after those historic manned Apollo landings, a number of other countries including Japan and China, are taking aim at our satellite neighbor. During the writing of this book, China soft landed a robotic rover onto the Moon.

Meanwhile, the United States and NASA, with a number of fits and false starts, inches its way towards a manned mission to the other legendary celestial objective, Mars. Robotic Mars rovers such as Curiosity, Opportunity, and Spirit have landed and explored Mars, and have expanded our knowledge of our red planet neighbor.

The Moon and the planet Mars dominate the imaginations of mankind. Literature of all cultures, both poetry and prose, are filled with the romance, the science, and the adventure of traveling to the Moon and Mars. Well-known authors, such as H. G. Wells, Edgar Rice Burroughs, Ray Bradbury, and Isaac Asimov, have penned books about the Moon and Mars.

To each generation, the Moon and Mars represents a challenge, impacting its technology, medical sciences, society, and culture.

A look at the challenges that the Apollo program faced, and the comparison that a Mars effort will have to overcome, is in order.

Courtesy of NASA

Sunday, July 20, 1969. 4:10 pm EDT.

For readers of a certain age, this is a date and time that can never be forgotten. A moment in time in which everyone remembers where they were, and what they were doing. And unlike other dates that live in infamy, such as December 7 or 9/11,
this is a moment of history that brings awe, inspiration, and pride. For this was the day that Neil Armstrong and Buzz Aldrin landed the LM Eagle on the Moon.

Decades later, generations of people look to the Moon, and know that mankind has been there. But many have no idea where the landings occurred. The Moon has been visited by both robotic and human visitors, with landing sites scattered across its surface. It is the goal of this book to enlighten the reader, and show where to look upon the Moon for mankind’s landing sites.

As a child of the Sixties, I grew up entranced by the burgeoning Space Age. I received as a Christmas present my first telescope at the age of eleven, and my first target was to view the Moon. It was thrilling. I grew up to become a professional engineer, spending most of my career in the field of aviation. But my love for tele­scopes and astronomy never waned. Since my retirement, I have devoted a great deal of time supporting local Washington D. C. telescope stores and giving lectures on telescopes and astronomy equipment to astronomy clubs in Maryland and northern Virginia. And for those of sharp memories and a stack of old astronomy magazines in their basements, you’ll find an article written by yours truly in the November, 1989 issue of Astronomy magazine on the subject of building a Dobsonian telescope.

Now that I am retired from my professional engineering life, I’ve found that I can spend more time viewing the skies through my telescopes. (Yes, that is plural. I’m afraid I’m slightly on the lunatic fringe of the hobby, pun intended.) Photos from NASA’s Lunar Reconnaissance Orbiter, showing the Apollo landing sites from an altitude of 50 miles, inspired me to search for the lander locations using my telescopes. And, with a subtle nudge from my older son Adam is the inspiration for this book.

The intent of this book is twofold: to serve as a visual guide, stepping the reader through a process for locating and viewing the Apollo landing sites, and an appreciation of what was accomplished there. The reader should look elsewhere for a more historical accounting of the Apollo Program, as there are many fabulous books on the subject written by former Apollo astronauts, Apollo flight controllers, engineers, and other well-known authors. There is a conscious informality that I’ve used in referring to the astronauts and their missions and equipment. This book serves as an observational guide, allowing the casual and serious observer a chance to locate the Apollo landing sites visually (with or without visual aid), and appreci­ate the historic experiments and equipment left behind. A review of the scientific results is included, and interestingly enough new knowledge is being added about the Moon from Apollo data to this day!

Also included are photos from the lunar probes leading up to Apollo. The long – forgotten Ranger series and the Surveyor series of lunar probes provided valuable information to NASA, both in terms of science and in terms of engineering require­ments and techniques needed to getting to the Moon.

Maybe someday in the future, Mankind can reach out to the Moon again. And provide a reason for a Volume 2 to this book.

Gore, VA January 25, 2014

Dates: 11-17 April, 1970

Crew: Commander Jim Lovell CM Pilot Jack Swigert LM Pilot Fred Haise

Command Module: Odyssey Lunar Module: Aquarius

Accomplishments: Successful return to Earth after an on-board explosion.

J. L. Chen, How to Find the Apollo Landing Sites,

The Patrick Moore Practical Astronomy Series, DOI 10.1007/978-3-319-06456-7_5, © Springer International Publishing Switzerland 2014

The inclusion of the Apollo 13 mission in a book about Apollo landings on the Moon may seem odd, since obviously the Apollo 13 failed in its mission to land on the Moon. Apollo 13 is one of the most famous and best remembered manned spaceflights in history, exceeded only by the history making Apollo 11 mission. However, the story of Apollo 13 does include its Saturn S-IVB third stage being targeted to impact the Moon and providing seismic data for the Apollo 12 ALSEP seismometer. Thus, the historic Apollo 13 mission’s inclusion.

Books have been written, a long-forgotten made-for-television movie aired, and a very successful theatrical movie have been produced about this ill-fated mission. Apollo 13 is often described as NASA’s finest moment as the agency successfully returned the astronauts safely home. It is a testament to the many NASA engineers and scientists who brought Lovell, Haise and Swigert to a safe landing.

The genesis of the mission failure was the Oxygen Tank No. 2. The oxygen tank was originally to fly as part of the Apollo 10 mission. The Apollo 10 mission, with the crew of Tom Stafford, John Young, and Gene Cernan, was a planned dry run and prelude to the actual landing on the Moon mission, with all procedures and maneu­vers rehearsed with the exception of an actual landing.

During pre-flight testing, Oxygen Tank No. 2 caused a major problem in the Apollo 10 service module. It was removed from the Apollo 10 service module for further testing, inspection, and repair. During the removal, the oxygen tank was dropped and damaged. After repair work was performed, the oxygen tank was then installed onto the Apollo 13 service module, whereupon it failed again during test­ing. Again, NASA performed some adjustments and deemed the oxygen tank flight worthy. Apparently, the continual maintenance actions performed and the acciden­tal damage resulted in the teflon insulation of the wires to the cyro stir fans becom­ing frayed.

Oxygen Tank No. 2 was part of a redundant fuel cell system for the CSM that provided power to the CSM system, with the by-product of drinkable water. The redundant fuel cell system was designed with separate units each having a cryo­genic hydrogen and cryogenic oxygen tank, separate power buses, and separate indicator and control systems. The hydrogen and oxygen liquid gases tended to settle into layers of different temperatures and densities as the Apollo spacecraft was exposed to the heat of the Sun on one side, and the cold of the unlit side. Since the hydrogen and oxygen tanks were chilled down to their liquid states, it was nec­essary to perform a “cryo stir” in each of the tanks to maintain a constant internal tank temperature and pressure, and enable sensors to produce consistent readings for the crew and Mission Control telemetry. By flipping on the cryo stir switch, the CM pilot would activate two small fans within each hydrogen and oxygen tank to mix the tanks contents, hence the term cryo stir.

The night of the Apollo 13 explosion, Mission Control was receiving signals from one of the hydrogen tanks that necessitated an extra cryo stir. When Swigert received the order from CapCom Jack Lousma, he flipped the switch for the cryo stir, which caused a spark across the frayed fan wire in Oxygen Tank No. 2, igniting the pure liquid oxygen, and causing the explosion in the service module. The cause of the explosion was not the extra cryo stir. The explosion would have occurred the next day during a scheduled cryo stir. Disaster was inevitable.

As a side note, the actual quote from this historic mission was “Okay, Houston, we’ve had a problem.”, spoken by Jack Sweigert. After CapCom Jack Lousma called back “This is Houston. Say Again, please,” Jim Lovell responded “Houston, we’ve had a problem We’ve had a Main B Bus under volt.” The public’s collective memory has misquoted the line, much of it cemented as a result of the Hollywood movie Apollo 13, replaced the “had” with “have”, changing it to “Houston, we have a problem.” with Tom Hank’s Jim Lowell speaking the line, thus changing the line from past-tense to present-tense. The director of Apollo 13, Ron Howard, changed the line in the movie script in order to create a dramatic effect, but as a result has perpetuated the misquote.

The impact of the explosion is well documented in books and movies. The loss of the lunar landing, loss of power, the power up issues, the carbon dioxide issue and the jury-rigged oxygen scrubbers (Fig. 5.6a, b), and the computer-less course correc­tions are all well known. One issue caused by the explosion that is often missed by the public is the loss of drinking water. The fuel cell system, when properly operat­ing, provided both power and water to the spacecraft and the crew. The water could be used to both cool the electrical systems and for drinking by the crew. The Apollo spacecraft therefore did not have to carry huge stores of water to make the flight. The destruction of the fuel cell system caused by the Oxygen Tank No. 2 explosion deprived Lovell, Haise and Swigert of drinking water. Normal water intake for the crew was 75 ounces per person. From the moment of the explosion to splashdown, the Apollo 13 astronauts were limited to 6 ounces of water per day! All three astro­nauts returned extremely dehydrated, and the kidney infection that Fred Haise suf­fered during the latter part of the mission was a result of the water shortage.

While the primary mission of Apollo 13 was landing on the Moon, it was forever blasted away by the Oxygen Tank No. 2 explosion. However, one scientifically significant objective was achieved. The Saturn V rocket that rocketed Apollo 13 towards the Moon consisted of a 3-stage launching system. While the first and second stage of the launch vehicle dropped back to Earth after launch, the third stage, known as the Saturn-IVB (or alternatively S-IVB) was used to propel the docked Apollo Command Module and Lunar Module from Earth orbit into a lunar trajectory. The spent S-IVB third stage separated from the Command Module, and was sent on a trajectory to impact the moon north of Mare Cognitum. From the tracking of the radio signals of the rocket, the impact locations on the moon and the impact times were fairly well known, with the impact site confirmed with photos from the 2009 LRO mission.

Seismogram of the Apollo 13 S-IVB impact recorded at the Apollo 12 seismic station in digital units (DU). The three traces designate the signal of the 3 orthogo­nal components of the ground motion at long wavelengths. The arrows mark the arrival times of the p (primary) and the slower s (secondary) seismic waves. Image modified from: Ewing et al. (1971), Seismology of the moon and implications on internal structure, origin and evolution, in: De Jaeger (Eds.): Highlights of Astronomy, IAU, pp. 155-172)

At the time of the Apollo 13 mission, only the seismometer at Apollo 12 was available, which had been deployed 5 months earlier. The S-IVB impact occurred on April 14, 1970, at a distance of 135 km from that seismic station at longitude 332.11°, latitude -2.56°, elevation 1166 m. The later Apollo missions all took advantage of their third stages by impacting them on the Moon. With an expanding network of seismometers with each subsequent mission, impacting the known size and weight of the S-IVB third stage served as a calibration tool for all the ALSEP seismometers. The impacts by the S-IVB stages represented unique calibration signals for the Apollo seismic station network, which operated on the lunar surface from 1969 to 1977. Since the rocket impacts occurred at known times and places, the seismic wave velocities, in particular those within the upper lunar crust, could be measured directly.

In 2010, a company called Analytical Graphics, Inc. (AGI) used Satellite Tool Kit (STK) software to perform an analysis of the Apollo 13 mission with the some­what fatalistic assumption that the course corrections failed and NASA was unable to get the Apollo astronauts home safely. The previously accepted thought was the Apollo spacecraft would miss the Earth, the astronauts would die and the CM would drift through space. The AGI analysis revealed a much different outcome. The command module would have missed the Earth by 2,500 miles and entered into an elongated orbit that would have apogee of 350,000 miles. Upon returning Earthwards, Apollo 13 would have passed within 30,000 miles of the Moon, close enough to perturb its orbital path and send the CM towards the Earth and its atmo­sphere. The STK software then predicted a re-entry on May 20, 1970, 5 weeks after Oxygen Tank No. 2 exploded. Unfortunately, the simulation predicted a steep

re-entry path, with the CM burning up in the atmosphere. This simulated scenario did not take into account the limited expendables on board Apollo 13, such as water, food, and oxygen. Either way, in the case of a failed course correction, the fate of the astronauts was fatal. The results of the AGI analysis was confirmed by Apollo 13 flight controller Chuck Dietrich using historic Apollo 13 flight data. Thank goodness Apollo 13 had a happy ending!

As the CM Odyssey splashdown safely in the Pacific Ocean, some pieces of the LM Aquarius survived re-entry. NASA’s projected trajectory data indicated that pieces of Aquarius landed in the open sea between Samoa and New Zealand. Although the mission was not a complete success, a lunar flyby mission was accomplished, with three planned experiments completed: lightning phenomena, Earth photography, and the S-IVB lunar impact.

After the safe return of Apollo 13, Grumman Aerospace Corporation, the designers and builders of the LM sent a spoof invoice A441066 to North American Rockwell, the designers and builders of the CSM, for towing Apollo 13 around the moon and home to Earth. The bill was submitted by Sam Greenberg, a pilot for Grumman Aerospace, and was written by workers at Grumman’s Flight Control Integration Lab in 1970. Greenberg was apparently fired for it, but was reinstated 2 hours later as Lou Evans, president of Grumman signed the invoice and sent it to Rockwell. It included towing at $4.00 first mile, $1.00 each additional mile, battery charge, oxygen and addition guest at $8.00/night. Water and baggage handling was free. With a 20 % commercial discount and 2 % cash discount (net 30 days), the total bill came to $312,421.24. Rockwell responded in a press conference that they still had not received payment for shipping four of Grumman’s LMs to the Moon!

The development of the Saturn-V rocket was key to the success of the Apollo pro­gram. The accomplishments of Werhner Von Braun and his team of German and American engineers are undeniable. The liquid rocket technology that began with the early efforts of Robert Goddard in the 1920s, the wartime development of the A-4 and V-2 missiles of World War 2 Germany under Von Braun’s leadership, the continuing development of ballistic missiles through the Cold War years of the 1950s and 1960s, led to the crowning achievement of the Saturn-V.

Current rocket propulsion technology does have its limitations. Using current rocket technology for Moon travel has been demonstrably practical. However, lon­ger trips into space beyond the Moon and within the Solar System demonstrates the limitations of current technology. Just to travel within the confines of the Solar System demands a staggering amount of fuel and rocket power for direct trips to adjacent planets. Deep space probes, such as Cassini, Galileo, and New Horizons, takes years of planning and reliance on planetary gravity assists to achieve the goals of the designed missions. Any manned mission to Mars and return to Earth becomes a multi-year effort, with considerable scientific, technological, logistical, and human health risks involved. Any attempt to travel to Mars with current rocket technology becomes an extraordinary expensive proposition.

Truth be known, a new propulsion technology is needed. If years of space travel can be cut to months, or even days, an attempt at Mars becomes more than a pipe dream. Unmanned probes, such as the Mars Orbiter, and the aforementioned Mars rovers are laying the groundwork, just as Ranger and Surveyor did for the Apollo program. Current propulsion technology works for remote probes, robotic landers, and rovers. But the exposure to the harsh realities of space renders a manned Mars mission a very risky business.

Like the chemical liquid fueled launch vehicles that NASA and the rest of the world relies on now, alternative space drive systems have been in slow development for over a century. Propulsion systems utilizing ion/plasma reaction engines have been proposed, with several designs undergoing some form of development.

The most promising of these alternative drive systems is the Variable Specific Impulse Magnetoplasma Rocket, or VASIMR. VASIMR uses radio waves to ionize and heat argon gas, and subjects the ionized argon to magnetic fields in order to accelerate the resulting plasma which provides thrust to a space vehicle. This plasma rocket technology was first introduced in 1977 by Franklin Chang Diaz, a Costa Rican scientist and astronaut.

A VASIMR driven spacecraft will allow for a mission to Mars with a travel period of just 39 days, almost 6 times faster than current rocket technology. The VASIMR driven spacecraft can develop speeds estimated at 35 miles a second, and will conceivably cover the distance between Earth and Mars in a more timely manner.

NASA rates new systems on a scale of one to ten based on its readiness to be deployed. The VASIMR system is currently rated by NASA as a six, which means that testing in space is the next step. NASA is testing a 200-kW VASIMR engine on the International Space Station in 2015. The engine is envisioned to provide periodic boosts to the ISS, which gradually drops in altitude due to atmospheric drag. ISS boosts are currently provided by spacecraft with conventional rocket thrusters, that consume about 7.5 tons of fuel per year. By cutting fuel use down to 0.3 ton per year, a huge cost saving can be realized in ISS operations. A success for VASIMR on the ISS will lead to a possible Mars application, with a nuclear reactor approximately equivalent to those carried aboard nuclear submarines. A reactor capable of generating 10-12 MW of power is required. Dr. Franklin Chang Diaz stated in a paper called The VASIMR Rocket which appeared in the November 2000 issue of Scientific American, that a 10-12 MW nuclear reactor is required for a 39 day journey from Earth to Mars. In addition, on September 29, 2009 Dr. Franklin Chang Diaz stated the following. “In fact, with the power close to what a nuclear submarine generates, you could use VASIMR to fly humans to Mars in 39 days.”