This article highlights that three approaches for the Apollo mission were considered and investigated early in the program: direct ascent, Earth orbit rendezvous, and lunar orbit rendezvous. Direct ascent would entail a direct shot from Earth to the moon, requiring an enormous rocket assembly, named the Nova rocket that required 15 first stage engines and would dwarf the Saturn V eventually selected as the launch vehicle. It also required a massive lunar landing vehicle to return the astronauts from the moon directly to Earth. At liftoff, the first stage burned 15 tons of fuel a second, requiring approximately 50,000 horsepower to power the fuel pumps to feed the engines. The Apollo 13 movie followed the actual flight with a fair degree of accuracy, recognizing that it had to compress four days of real-life tension into a two-hour motion picture. The film dramatized the explosion of the oxygen tank by showing the astronauts being thrown about in the cabin. In reality, the astronauts only heard a bang and then the warning alarm for low electrical bus voltage.
President Kennedy made a historic speech on may 25, 1961, that turned a dream into and engineering challenge on which the prestige of the United states would rest. IT contained these 31 words: "I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the moon and returning him safely to the Earth."
NASA already had been working for years on the requirements for a manned mission to the moon.
Apollo 11 fulfilled the goal on time, on July 20, 1969, when astronauts Neil Armstrong and Buzz Aldrin landed on the moon's Sea of Tranquility and made the historic statement "Houston, Tranquility base here, the Eagle has landed."
The program for a manned mission to the moon was named Apollo, after the Greek god of light who was twin brother of Artemis, the goddess of the moon.
Three approaches for the Apollo mission were considered and investigated early in the program: direct ascent, Earth orbit rendezvous, and lunar orbit rendezvous.
Direct ascent would entail a direct shot from Earth to the moon, requiring an enormous rocket assembly, named the Nova rocket, that required 15 first stage engines and would dwarf the Saturn V eventually selected as the launch vehicle. It also required a massive lunar landing vehicle to return the astronauts from the moon directly to Earth.
The second approach, Earth orbit rendezvous, required the design and fabrication of an Earth orbiting space station where launch vehicles would bring up supplies to assemble the vehicle that would then go to the moon. While this approach was practical and provided longer-term benefits, it became clear that it could not be accomplished within the decade.
The third approach, lunar orbit rendezvous, was proposed after the first two and became the best practical approach to meet all the requirements. The approach and its challenges can be described in a single long sentence: Take off from Earth, which is rotating approximately 1,000 mph, orbit Earth at 18,000 mph, accelerate to 25,000 mph to break out of Earth’s orbit toward the moon 250,000 miles away and traveling 2,000 mph relative to Earth, go into lunar orbit, send a manned spacecraft to land on the moon to explore and leave scientific instruments before returning to lunar orbit, rendezvous with the rest of the spacecraft, and then blast out of lunar orbit back to Earth.
Three major elements were required for the mission. The first was a colossal three- stage launch vehicle, the Saturn V The second was a command and service module in which three astronauts would travel to the moon and return to Earth. The third element was a lunar landing vehicle, which would take two astronauts down to the moon’s surface and bring them back up, to rendezvous with the command module for the return to Earth.
The Saturn V was the largest launch vehicle ever built by the United States. It stood 363 feet tall, six stories taller than the Statue of Liberty and one-third the height of the Empire State building. The Saturn V consisted of three stages, upon which the service and command modules, along with the lunar module, rested. The first stage of the Saturn V was the key to Apollo’s success, essentially consisting of a giant tank of kerosene and liquid oxygen connected to five F-l rocket engines capable of generating a total of 7.5 million pounds of thrust.
Fifteen Tons of Fuel a Second
At liftoff, the first stage burned 15 tons of fuel a second, requiring approximately 50,000 horsepower to power the fuel pumps to feed the engines. The first stage was 33 feet in diameter and 150 feet long, with a tank capacity of 200,000 gallons of kerosene and 330,000 gallons of liquid oxygen at a temperature of-297°F.
The second stage contained five T-2 rocket engines with a combined thrust of one million pounds. The fuel for the second stage consisted of liquid hydrogen at —423°F and liquid oxygen.
The hydrogen fuel gave this stage a 40 percent increase in thrust compared to kerosene. So, why not use liquid hydrogen in the first stage as well? The answer is insulation. Maintaining liquid hydrogen at -423°F is a monumental insulation task, and the first-stage tanks would have required so much more insulation that the size increase would have resulted in serious design problems.
The third stage, like the second, used a single T-2 engine with 200,000 pounds of thrust using liquid hydrogen and oxygen.
The command module was the main vehicle the astronauts would use for the trip. Its general shape was that of a slightly flattened cone, with a base diameter of 13 feet. It was 11 feet tall and weighed about six tons. The interior space for the astronauts was ap-proximately that of a typical telephone booth, luxury accommodations compared to the even smaller volume of the previous Mercury and Gemini capsules.
The service module carried the fuel cells for electric power, oxygen for the environmental system, and a 20,500-pound- thrust engine. The service module was attached to the base of the cone, behind the command module, was 13 feet in diameter and 24 feet long. Fully loaded, it weighed 26 tons. It would be left behind when the command module re-entered the atmosphere.
The rocket engines and thrusters used on the command and service modules, and on the lunar module used the hypergolic fuel monomethyl hydrazine and nitrogen tetroxide, which will ignite spontaneously upon mixing. Another advantage is that these engines did not require liquid oxygen.
The lunar module basically consisted of two main halves: the ascent and descent stages. It was designed to accommodate two astronauts, had seats, and only a limited quantity of fuel. It was intended only to operate in the vacu-1 urn of space and support itself under lunar gravity (one-sixth that ' of Earth).
The Lunar Module
How does an engineeir get assigned to a project that is destined to make histry? As usual, you must be in the right place at the right time his is not as easy as it sounds, since most engineers have to earn a living where the work may not be in the history-making class. I was not involved in drafting the original Grumman aircraft proposal to NASA for the lunar module. In November 1962, I was busy with flight development of the Navy A-6 carrier-based aircraft at Grumman’s Calverton Airfield, some 50 miles east of the main Grumman plant in Bethpage, N.Y.
Upon returning from the airfield late one evening, I went back to my desk for some papers and noticed a copy of the lunar module proposal. Tired and not up to reading it, I just paged through it quickly until I noticed an organization chart. Something on the chart caught my eye; my name was on it.
It was too late to find out what was going on, so I inquired the next morning. I was told to go home, pack a bag, and get down to Houston to negotiate the NASA letter of intent and contract to build Apollo’s lunar module. At the time, Grumman was a small aircraft company not as formally structured as its larger counterparts.
As expected, the proposal price increased dramatically by the time we finished the negotiations and included all the testing and support items in the contract. The original lunar module proposal was priced at $387 million. After negotiations, the price climbed to approximately $1 million. By the early 1970s, toward .e end of the program, the total cost vas closer to $2 billion, approximately a tenth of the total Apollo program cost.
The first problem in any large project is to get a fast start, Management and customer pressures re practically nonexistent at the start of a project, but become almost undatable toward the end, when delivery is due and costs are in dispute. The overall design and systems approach for the lunar module was rapidly arrived at: an ungainly. looking two-stage vehicle, capable of transporting two astronauts to the t noon’s surface, where the bottom half of the vehicle would remain, after serving as the launch platform for the upper half, which would return the astronauts to the orbiting command module.
Grumman management gave me a “hunting license” to hand-pick the engineers who would be destined to supervise the many disciplines required to design and build the lunar module. They in turn were required to staff their disciplines.
This is the second large project problem. You must assemble a large number of engineers without introducing confusion and duplication of effort. Each engineer must know what is expected and how he or she fits into the overall project.
While the number of engineers and technicians was increasing rapidly, fundamental and critical design decisions had to be made. For the lunar module the first design consideration was reliability. Severe weight constraints would limit the backup and redundant systems so that each piece of equipment had to be made as reliable as possible. This consideration forced the project to use discrete components instead of integrated circuits, which were available, although there was simply not enough experience to determine their reliability during the early 1960s.
Soldering was also a problem, since all circuits had to be conformal coated to prevent moisture damage during the final rocket assembly at Cape Kennedy. Expansion and contraction of the conformal plastic coating relative to the solder cause cracks and open circuits. It was decided to weld as many electrical connections as possible as well as all liquid and gas tubing connections.
All parts were selected based on reliability. Every part or shipment of material had serial or lot numbers. If defects were found during testing, the whole lot was declared suspect and either replaced or cleared by additional tests.
There could be no backup or redundancy for the engines. If there was trouble with the descent to the moon, it would be possible to abort and return to the command module. On the lunar surface, failure of the ascent engine would mean the end for two astronauts.
Anxiety over the ascent engine was so acute that Grumman added a subcontractor in mid-design. The prototype from Bell Aerosystem Co., the original subcontractor, failed a key test. Known as the bomb test, it checked on a source of combustion instability great enough to have exploded some early Titan rockets. The bomb test injected a pressure pulse into the combustion chamber while it was operating. If the pulse disappeared after a certain number of engine cycles, the pressure spikes that might cause the engine to explode would be avoided.
The Bell engine never malfunctioned, but the threatening pulse remained. An alternate design competition was held, and North American’s Rocketdyne division won the contract for an alternate fuel injector with Bell continuing as the contractor for the rest of the rocket engine.
Anyone who has worked on state-of-the-art military aircraft or missiles knows that weight always increases. Apollo was no exception. NASA instituted a super weight improvement program, known as SWIP. The contractors were offered a substantial financial incentive for each pound of weight removed from the spacecraft. Since NASA covered the engineering and material, there was good reason to change design or material and make some profit. Most stainless steel was changed to titanium, and aluminum was changed to magnesium or beryllium.
Even with the careful selection of parts and materials, there were many problems that required attention. The actuator for the gimbal of the descent engine had a hangup when subjected to thermal vacuum testing and required much troubleshooting to correct. Stainless steel tanks turned to a gold color when annealed, driving the materials engineers crazy.
Moon Dust: How Deep
There was much debate on how much dust was on the moon. Predictions ranged from a few inches to more than 10 feet. “Pie plate” pads 37 inches in diameter were placed on the ends of the landing gear so that the lunar module could sink in up to the descent stage and still allow the ascent stage to launch successfully, even if the moon’s surface were covered with 10 feet or more of dust. Four-foot descent engine cutoff probes were attached to the pads to indicate contact with the surface because the astronauts might not be able to see the surface if there was dust flare-up.
Sneak electronic and fluid circuits were also a constant concern. Throwing a switch or valve under the many combinations of open and close could lead to an unexpected and unwanted response. We were very fortunate in having an electrical engineer who could look at circuits all day long without falling asleep.
One day he came to my office in a very agitated state. It took some time to - calm him down and understand what he was saying. He finally was able to blurt out his discovery of a sneak circuit that would immediately fire the ascent engine when the arming switch was turned on before staging. This would blow up the lunar module on the surface of the moon.
The backup engineering teams at both Houston and Bethpage solved a number of other, less severe lunar module flight problems. On one mission the abort switch started making contacts randomly. The engineers surmised that a solder ball had come loose and might cut the mission short if it hit the proper contacts. A software fix was devised, allowing the switch inputs to be ignored. The astronauts keyed in the data manually on the lunar module and finished just a few minutes before the vehicle passed behind the moon, cutting off communication.
There were comic moments also. The lunar module's water levels dropped more than expected, and it took several missions to discover why. One of the astronauts casually commented that the lunar vehicle's water tasted better. The command module's water was purified with chlorine; the LM's with iodine, making it taste like a little scotch had been added.
On one mission, the lunar module left in lunar orbit after the astronauts returned to the command module failed to respond to a computer command to deorbit into the moon. A seismic transducer left by the astronauts was to measure the LM's impact to help determine the structure of moon rock. Later it was learned that one of the astronauts had unscrewed the hand controller as a souvenir, deactivating the circuitry.
The First Landing
Much has been written about the most famous mission, when Neil Armstrong and Buzz Aldrin became the first humans to set foot on the moon.
During descent, two occurrences caused quite a tense time. The first was a series of computer alarms, indicating the landing computer was being overloaded with in-coming data that it could not process. It was later found that the docking radar was not turned off, so the computer was attempting to find the command module at the same time it was calculating descent rates and curves. The computer functioned perfectly, ignoring the docking radar information and concentrating on the landing program. It signaled this by flashing the codes “1201” and “1202.” The codes were recognized by an astute member of Mission Control, averting an unnecessary abort of the mission.
As the module neared the lunar surface, Armstrong realized that the programmed landing profile would put the vehicle in the middle of a large boulder field. He took over manual control to find a suitably smooth landing area, where the lunar module touched down with approximately 15 seconds of fuel remaining; hence Houston’s remark: “Copy you down Eagle; you have a bunch of guys here about to turn blue.”
The Apollo 13 mission demonstrated the full effectiveness of Mission Control and contractor support teams. Mission Control at Houston had just finished telling the Apollo 13 crew that everything was looking good and that they were “bored to tears down here,” when Jack Swigart first uttered the famous words, “Houston we’ve had a problem here.” James Lovell then repeated the statement to Houston.
Later investigation revealed that one of the two oxygen tanks in the service module had suffered damage during testing before launch, and that an electrical failure caused the tank to explode and damage the second tank. These tanks were used by the fuel cells, to generate the needed electrical power and water for cooling. Upon their loss, the command module lost all power and oxygen.
It was now up to the lunar module to take over as a lifeboat for Apollo 13. There were no standard procedures for this multiple failure. The lunar module descent engine would now have to substitute for the service module engine, and the lunar module’s oxygen, water, and power, designed to last two men for two days, had to be conserved to last three men almost four days.
Things became very cold and damp when as much power as possible was turned off. Water was limited. Carbon dioxide began to build up in the spacecraft; the lithium hydroxide canisters of the command module did not fit the lunar module because they were the wrong shape, square instead of round. This misfit was solved by the Mission Control staff on Earth, and instructions were transmitted to the crew for making modifications using tape, plastic bags, and cardboard—“just like building a model air-plane,” as one of the astronauts put it. The crew was at least temporarily safe, if very uncomfortable.
The lunar module’s descent engine made the 35-second burn to get a free-return trajectory, the slingshot around the moon, and then another longer burn of five minutes to hasten the return to Earth. A final, very short trajectory correction was all that was necessary to put the module down within a half-mile of the recovery aircraft carrier. Power was so limited and critical that the crew had to maintain attachment with the lunar module until the start of re-entry.
The Apollo 13 movie followed the actual flight with a fair degree of accuracy, recognizing that it had to compress four days of real-life tension into a two- hour motion picture. The film dramatized the explosion of the oxygen tank by showing the astronauts being thrown about in the cabin. In reality, the astronauts only heard a bang and then the warning alarm for low electrical bus voltage. The confirmation of a crippling explosion was the loss of electrical power and “snowflakes” floating outside the module’s window.
Oxygen was not the problem that the Apollo 13 movie made it out to be. The main problem was running out of electrical power or cooling water for the electronics. The cooling- water loop was a total-loss system; water circulated through once and then vented into space. If the water ran out, the electronics would overheat and fail, making re-entry control and stability impossible. On landing, there was little more than an hour of water remaining compared with about 10 hours of oxygen.
NASA eventually spent approximately $24.5 billion on the Apollo program of 16 unmanned missions and 12 manned missions. A total of 12 men walked on the moon, the first on July 20, 1969 (Apollo 11) and the last on Dec. 11, 1972 (Apollo 17).
The final words spoken on the moon’s surface were: “As we leave the moon and Taurus-Littrow, we leave as we came, and God willing, as we shall return, with peace and hope for all mankind. As I take these last steps from the surface for some time to come, I’d just like to record that America’s challenge of today has forged man’s destiny of tomorrow.”
It may be interesting to note that, as a fraction of the United States gross national product, the cost of the Apollo program was roughly equivalent to the amount spent by Queen Isabella on Christopher Columbus’s voyage to the New World.
In 1961, President Kennedy united the nation behind a heroic mission to land a man on the moon. The story of the Apollo program was not just about the astronauts who made the voyages. At its peak, the Apollo program included almost 400,000 people across the nation with focused dedication to make those landings on the moon a reality.
The landing on the moon was the work of a generation of American men and women who came of age during the Great Depression and World War II. They built Apollo and the modern technology of America. This generation was united not only by the common purpose of Apollo, but also by the common values of duty, service, patriotism, honor, courage, love of family, and above all, responsibility to oneself.
There is a story that on the night of july 20, 1969, a small bouquet of flowers was placed on John F. Kennedy’s grave in Arlington with a card on which was written “Mr. President, the Eagle has landed.” It would be nice to think that it really happened.