19 minute read
Apollo's Amazing Spacecraft
The Apollo program’s rockets and spacecraft have earned a lasting place in human history.
BY CRAIG COVAULT Photos courtesy of NASA
WELL BEFORE PRESIDENT JOHN F. KENNEDY CALLED FOR A MANNED LUNAR LANDING, KEY APOLLO HARDWARE ELEMENTS, ESPECIALLY THE ENGINES FOR THE SATURN V MOON ROCKET, HAD ALREADY BEEN PUT IN DEVELOPMENT BY THE EISENHOWER ADMINISTRATION.
This work was fueled by the leadership of German rocket pioneer Wernher von Braun. Concepts for the Apollo command and lunar modules were also being laid out at companies like Grumman and North American Aviation years before the Kennedy speech.
These largely unheralded conceptual efforts were closeted in many companies that would later bid on the nearly $25 billion of Apollo contracts during the 1960s.
Von Braun’s heavy rocket design work during the Eisenhower administration was centered at the Army Ballistic Missile Agency in Huntsville, Alabama. By 1959, it was shifted to NASA and renamed the Marshall Space Flight Center, with von Braun as director. But it was the Defense Advanced Research Projects Agency, not NASA, that funded initial Saturn rocket work pioneered there.
These efforts laid the technological foundation for the first machines that would carry humans from Earth to another body in space.
Soviet rocket pioneer Sergei Korolev had started to develop the massive N-1 rocket, equal to a Saturn V, but he envisioned it as a manned Mars vehicle that would possibly do only circumlunar missions that would not even land on the Moon.
The Soviet government did not change N-1 plans to put the USSR into a race to land on the Moon until 1964.
All four unmanned flight tests of the N-1 between 1969-1972 failed, indicating the Soviets never really had a chance to win the Moon race.
Kennedy was not acting out of hubris, but rather homework when he made his challenge. He knew that key hardware elements, like the 1.5-million-pound-thrust F-1 engine – a power plant that could propel the United States to the Moon – was, by 1960, already being built and tested.
The Saturn I (SA-4) flight lifts off from Kennedy Space Center Launch Complex 34 on March 28, 1963. This was the fourth launch of Saturn launch vehicles developed at the Marshall Space Flight Center (MSFC) under the direction of Dr. Wernher von Braun.
NASA had been formed in 1958 as a civilian agency, and needed a mission to go somewhere using something larger than converted ballistic missiles. The early development of the F-1 engine, powered by liquid oxygen and kerosene, was seen as one of the steps necessary to get ready for whatever was to come in the civilian space program.
The Moon was high on the list, but so also was a large Earth-orbiting space station.
To carry three men to the Moon and back, the United States would need to develop a launcher that could place about 260,000 pounds in Earth orbit. This would be an assemblage of propellant and hardware for a 500,000-mile, seven-day round trip with as many as three days on the lunar surface.
A decision on how to fly a mission to the Moon would be critical to how the Apollo spacecraft, the machines of Apollo, would be built. NASA had to choose among:
• Direct ascent. In this concept, pictured in many science fiction depictions, the vehicle would launch directly to the Moon. It would not stop in Earth or lunar orbit to reconfigure what had been launched from Earth. It would take off and fly to the surface of the Moon and back as mostly a single entity.
• Earth orbit rendezvous (EOR). An Apollo mission using this concept would require two launches: the first to Earth orbit carrying a lunar module for the Moon and propellant for the round trip, and a second launch to fly up the crew that would then climb into the large vehicle that would fire off to the Moon. Von Braun favored this concept because it would also involve a small space station as a refueling point and docking location for both rockets. But EOR was too complex to succeed by 1969.
• Lunar orbit rendezvous (LOR). In this mode, all of the elements would be launched at once, but be reconfigured en route and again on the lunar surface as part of the sequence of events to return to Earth. Originally considered a “dark horse” concept, the LOR plan had been proposed in 1923 by German rocket visionary Herman Oberth. NASA Langley Research Center engineers in Hampton, Virginia, began re-looking at the concept in 1959 under the leadership of John C. Houbolt, and it was adopted by the Apollo program in 1962.
The selection of the LOR mode affected the function, shape, cost, and engineering appearance of every component of the Apollo program. It was the single most sweeping engineering decision of the entire project.
The Apollo command and service module (CSM) with the threeman crew would be launched atop a Saturn V. The Saturn V would also carry a two-stage lunar module (LM) tucked under the CSM in a fairing atop the rocket. All of that would be put into Earth orbit for a short checkout, then fired to the Moon using the upper stage of the Saturn V.
The ascent stage of the lunar module Eagle approaches the command service module Columbia in lunar orbit after departing the Moon. The lunar module consisted of two stages; the descent stage was used for the lunar landing phase of the mission, and then served as the “launch pad” for the upper, or ascent, stage of the LM, which would launch back into lunar orbit to dock with the command service module.
Shortly after the upper stage firing, the CSM would undock from the nose of the stage and perform a 180-degree turn to face the LM still nested in the upper stage of the Saturn. The CSM pilot on the crew would then pilot the module to dock with the top of the LM. Then, using its thrusters, the CSM would back away, pulling the LM out of the upper stage of the Saturn V.
A close-up view of the 363-foot-tall Apollo 11 space vehicle as it is launched from Pad A, Launch Complex 39, Kennedy Space Center, at 9:37 a.m. on July 16, 1969.
All of this would take place with the upper stage of the Saturn and CSM flying in formation at approximately 25,000 mph with the Earth as a gigantic blue backdrop.
But it was an ever-shrinking backdrop, as the CSM, with the LM now on its nose, headed to the Moon. Some of the Saturn V upper stages were fired again to forever orbit the sun, but others were allowed to hit the Moon to see how the lunar interior would react as sensed by seismometers left on the Moon by Apollo 11 and subsequent missions.
The Apollo 7/Saturn IB space vehicle is launched from the Kennedy Space Center’s Launch Complex 34 at 11:03 a.m. on Oct. 11, 1968.
After a three-day transit, the CSM’s large rocket engine would be fired to place it and the LM in lunar orbit. The following day, the commander and lunar module pilot would undock the LM and descend to the Moon, leaving the CSM pilot in lunar orbit.
Once surface operations were completed, the descent stage would form the launch pad for the LM’s ascent stage.
The LM, with its two pilots standing up (since it had no seats to save weight), would fire itself off the Moon to dock with the command ship in orbit, then return to Earth.
It sounded the most complicated of all the concepts. But, in fact, it broke the lunar mission down into bite-size elements that could be distributed to different contractors for development, assembly, and checkout, and then operated with specific individual mission roles.
Another benefit was that with LOR, in the event of any lifethreatening emergency the process could be interrupted at virtually any point, except the liftoff from the Moon, for a mission abort to return a crew safely home to Earth.
In addition, LOR allowed the complex management principles needed by Apollo, especially multiple tests and redundant design, to be divided up into more efficient tasks.
A cutaway illustration of the Saturn V launch vehicle with callouts of the major components. The Saturn V was the largest and most powerful launch vehicle developed in the United States. It was designed to perform Earth orbital missions through the use of the first two stages, while all three stages were used for lunar expeditions.
All of the decisions that led to this flight hardware and operational concept were still undetermined in the late 1950s when the rocket hardware was being sized.
In fact, the Saturn rocket designs predated by two to three years how the spacecraft would actually look and operate. But the von Braun team knew they could resize the Saturn to suit the other mission hardware, and that is what they did.
The Saturn Vs that went to the Moon all had five first stage F-1s. Had EOR been selected, smaller Saturn versions with just two to three first stage F-1s would have been developed instead. Von Braun had already done major design work on the smaller vehicle – as well as an even bigger “Nova” launcher with 10 F-1s.
Engine “clustering” was also a key engineering detail. The von Braun team knew well before Kennedy’s mandate that to propel the U.S. space program, it needed experience on how to develop large clustered engine boosters powered by liquid oxygen and kerosene.
Until then, most launchers were simply intercontinental ballistic missiles (ICBMs) that required only one to three small first-stage engines.
Further, the program needed to flight-test a high-energy upper stage powered by liquid hydrogen and liquid oxygen, because ICBMs did not need such powerful second and third stages to launch nuclear warheads or the small satellites of the day.
By clustering engines, tons of weight were saved while gaining tons of lift-off thrust. This was done by using common propellant tankage and lines. Some wags noted that if the concept were unsuccessful, it would be forever known as “cluster’s last stand.”
The first engine selected for clustering was the Rocketdyne H-1, a 200,000-pound-thrust engine that had been used in the much smaller Thor- Delta rocket. By clustering eight of them together, the rocket could generate 1.2 million pounds of lift-off thrust and put heavy payloads into low-Earth orbit.
It also created the first rocket ever developed specifically as a space booster, not as a weapons launcher. Ten Saturn Is were launched from Cape Canaveral between 1961-65. The age of big rockets had arrived.
Another key part of the Apollo family was developed from scratch. This was the Rocketdyne J-2 oxygen/hydrogen engine with 200,000 pounds of thrust. It would form the basis of upper stages used on both the future Saturn IB and then the Saturn V.
The introduction of liquid hydrogen was a key development because of its highenergy capability. But it was also a serious challenge. The cryogenic hydrogen was high risk and had to be kept at nearly -400 degrees Fahrenheit while the cryogenic oxygen was also dangerous, at nearly -300 degrees Fahrenheit.
Out of this engine design came the second stage of the Saturn V, the North American Aviation S-II, equipped with five J-2s, and the McDonnell Douglas S-IVB upper stage, with just one J-2 engine.
When added to a Saturn I, the new oxygen/hydrogen S-IVB stage converted it into a more powerful launcher called the Saturn IB. There were nine successful launches of IBs, proving the cluster concept.
Together Saturn I and IB launched the first unmanned flight tests of the LM and CSM into Earth orbit, and then in October 1968, the first manned test of the CSM. Three other IBs launched crews to the Skylab space station in 1973-74 and the final Apollo mission – the joint Apollo-Soyuz Test Project mission in 1975.
The three stages of the Saturn V, with the Apollo spacecraft on top, formed a 363-foot-tall vehicle. The first of only two unmanned flight tests was in 1967.
Designed and developed by Rocketdye under the direction of the Marshall Space Flight Center, the F-1 engine measured 19 feet tall by 12.5 feet at the nozzle exit, and each engine produced a 1,500,000-pound thrust using liquid oxygen and kerosene as the propellant. A cluster of five F-1 engines was mounted on the Saturn V S-IC (first) stage and burned 15 tons of liquid oxygen and kerosene each second to produce 7,500,000 pounds of thrust.
Unlike the Saturn Is and IBs, the Saturn Vs were not launched from Cape Canaveral, but rather the new Kennedy Space Center (KSC) built on Merritt Island, Florida, several miles north of the Cape.
KSC’s 550-foot-tall Vehicle Assembly Building (VAB) was designed as a gigantic processing facility to hoist Moon rocket stages onto a platform for transport to Launch Complex 39 three miles away. The Boeing-built S-1C first stage alone would be loaded with about 4.4 million pounds of liquid oxygen and kerosene.
Fueled on the launch pad, a Saturn V and its payload weighed about 7 million pounds, while the five F-1s in the first stage had 7.5 million pounds of thrust.
That was only 500,000 pounds of “up.” But it was enough to slowly get the monster rolling to more than 6,000 mph, where the first stage would burn out. The second and third stages, pushing a much lighter vehicle, would accelerate the rocket to 17,500 mph to achieve Earth orbit.
Just above the third stage was the IBM electronics unit – a ring of humble boxes dwarfed in capability by today’s laptop computers. The ring contained the basic guidance system components: a gyro platform, accelerometers, a digital computer, and control electronics. The instrument unit’s stable gyroscopic system was based on the one used in the German V-2 rocket developed by von Braun in World War II. The Bendix Corporation produced the Saturn V gyro platform, while IBM designed and built the unit’s digital computer.
The Saturn V’s 72-pound IBM computer consumed 137 watts of power and had four memory modules, giving a total capacity of 16,384 words.
By today’s standards, the processor was slow, with a 2.048 MHz clock cycle versus a fraction of a nanosecond on a current computer. The Saturn V’s computer memory was only 32,768 28- bit words. But it was good enough 50 years ago to get your 3,500- ton rocket into Earth orbit, then on to the Moon.
The CSM and LM space vehicles carried by the Saturn Vs were the “Chariots of Apollo,” as NASA’s history of the program calls them. Between 1969-72, they carried 27 crewmen to the Moon – and 12 of them all the way to the lunar surface and back.
The LM Spider, still attached to the Saturn V third (S-IVB) stage, is photographed from the CSM Gumdrop on the first day of the Apollo 9 Earth orbital mission. This picture was taken following CSM/LM-S-IVB separation and prior to LM extraction from the S-IVB. The Spacecraft Lunar Module Adapter (SLA) panels have already been jettisoned. Inside the command module were astronauts James A. McDivitt, commander; David R. Scott, command module pilot; and Russell L. Schweickart, lunar module pilot.
No Saturn rocket or lunar module ever suffered a complete failure. They often had significant malfunctions – but never a missionending failure.
Unfortunately this was not the case for the CSM.
But the CSM also had a very tough role to fulfill. It was mankind’s first spaceship capable of carrying three humans on a round trip to orbit another body in space. That achievement alone – its first manned trip to the Moon as Apollo 8 in December 1968 – is viewed by many astronauts, historians, and program officials as even more awesome, if not historic, than Apollo 11, the first lunar landing.
Tragically, astronauts Gus Grissom, Roger Chaffee, and Ed White would die in a 1967 launch pad fire in the first CSM to make Apollo 8 and then the launch of six safe lunar landing missions possible.
According to space historian Mark Wade, in his Apollo research in Encyclopedia Astronautica (Astronautix.com) the CSM, much like the Saturn V, was under contract (to North American) before the Apollo LOR decision had been made.
Originally, two Apollo CSM design blocks were to be produced: one a Block 1 series of spacecraft for solo Earth-orbit missions, and Block II configured with all the added components for a lunar mission. Only Block IIs were ever flown.
The design called for two major components: the cone-shaped manned “command module” with an Earth re-entry heat shield, sitting atop an unmanned cylindrical “service module.” The service module was unpressurized and carried all of the electrical, propellant, rocket engine, and other systems, including attitude control thrusters.
The Apollo 17 CSM America, piloted by astronaut Ron Evans, orbits 70 miles above the Moon, where it was imaged by astronauts Gene Cernan and Harrison Schmitt as they returned from the lunar surface in December 1972. This was the ninth and last CSM to reach the Moon, but through 1975 four more were launched into Earth orbit for the Skylab and Apollo-Soyuz Test Project mission. The Scientific Instrument Module (SIM) has been revealed at the top of the service module.
In total, the CSM measured 36 feet tall and 12.7 feet wide, with a launch mass of 66,863 pounds. Of this, 41,000 pounds was propellant for the spacecraft’s Aerojet engine, which would fire to insert the vehicle into lunar orbit, then fire again to send it back to Earth. The command module was a truncated cone measuring 10 feet, 7 inches tall and having a diameter of 12 feet, 10 inches across the base.
As on the Mercury and Gemini spacecraft, the honeycomb ablative heat shield was designed to carry off heat by gradually ablating – wearing away – during re-entry. But a major difference was that spacecraft re-entering from Earth orbit were “only” traveling 17,500 mph, compared with 25,000 mph returning from the Moon.
The Apollo heat shield was not a perfect concave shape; it was instead lenticular. This was done so that by changing spacecraft roll during re-entry, different lift vectors could be achieved for a safer, more precise descent.
The spacecraft was first dipped into the atmosphere to bleed off initial speed and heating, then eased out slightly to cool off before diving back in to complete each descent. Astronaut Tom Stafford, who commanded Apollo 10 to the Moon, said approaching Earth at 25,000 mph “was like having giant vivid blue pie thrown toward you.”
But after the launch pad fire, the CSM had to be redesigned before ever flying. To save weight, it had been designed to operate using only pure oxygen and with a hatch that opened inward. Its interior also had significant flammable materials. All of these deficiencies and its electrical system had to be redesigned.
The Apollo crew that was lost had been dissatisfied with the ground tests of the spacecraft. No one could bring this first Apollo crew back, but the spacecraft redesign saved the program.
One of the marvels of the CSM was the ability of its flight computer to navigate the spacecraft to the Moon and back using updates from ground control punched in by the astronauts. The Apollo Guidance Computer was designed by MIT and built by Raytheon. It was the first aerospace computer to use integrated circuits – with more than 4,000 in the unit. But it had only 2,000 words of random access memory and 36,000 words of core memory.
The Apollo lunar modules used to descend to the Moon carried the exact same computer as that in the CSM, plus two others for landing abort and redundancy purposes.
The LM today remains a marvel of aerospace engineering. It was developed by Grumman in Bethpage, Long Island, New York – the home to a long line of Navy fighters so robust that Grumman was nicknamed “the Iron Works.”
At the time, Grumman seemed a long shot to be involved in a unique space program vehicle development. But superb engineering talent and its position on the team that lost the CSM competition to North American worked in Grumman’s favor to win the LM contract.
Grumman was one of a few companies that had actually been studying manned Moon landing concepts since the late 1950s. When Apollo happened, Grumman and key managers there, especially Joe Gavin and Tom Kelly, were ready to lead the company in a whole new direction.
Among the major factors that impressed NASA was that Grumman – on its own – had arrived at a conclusion that the LOR technique should be used involving a two-stage LM.
The descent stage would use the first throttleable rocket engine ever flown, giving the commander helicopter-like control to balance thrust to hover over a landing position. And the ascent stage would use a simple rocket engine to shoot the vehicle off the surface with high reliability.
Grumman built 14 LMs for ground test and spaceflight, of which nine flew in space, and of those nine, six landed on the Moon. One of the nine, LM-7, saved the lives of the Apollo 13 crew when an oxygen tank exploded in their CSM. The Apollo 13 LM oxygen sustained the crew while its computers made calculations, and the descent engine was used for rocket firings to keep the vehicle on course for an Earth return.
“Simplicity was the byword for LM designers,” wrote Kelly in his book Moon Lander.
Astronaut James B. Irwin, Apollo 15 lunar module pilot, salutes the flag during an EVA at the Hadley-Apennine landing site. The lunar module (LM) Falcon is in the center. On the right is the Lunar Roving Vehicle (LRV). While the LM and LRV are rightly celebrated, the astronauts’ spacesuits were themselves spacecraft of a sort, with life support and protection from heat and cold a part of their design.
In a scholarly assessment of the LM by the Australian Broadcasting Corporation (ABC), its science writers found major examples of that simplicity: “The lunar module descent engine was arguably the most technologically advanced piece of equipment on the Apollo-Saturn vehicle.”
Grumman sub-contracted Rocketdyne to develop the descent engine. Rocketdyne proposed a helium injection throttle mechanism where the inert gas was introduced into the propellant lines. This had the advantage of keeping propellant flow constant.
“A constant propellant flow simplified the design of the injector,” a critical high-risk area on other rocket engines, according to the ABC.
The notion of a manned spacecraft with a wide throttle range – 10 to 100 percent – was so novel that NASA directed Grumman to run a parallel descent engine development program and choose which engine was better.
It was thought at the time that one design would outperform the other. Space Technology Laboratories (STL) was selected to develop an alternative descent engine. STL proposed a pressurefed system that used mechanically linked flow control valves and a variable geometry injector.
Both Rocketdyne and STL had considerable success developing the LM descent engine. Finally, Grumman awarded the contract to Rocketdyne, only to have NASA reverse the decision. This meant that STL’s engines would power all the Apollo landings. Simplicity was especially true of the super-critical ascent engine. The Bell Aerosystems engine was all pressure-fed by helium gas to avoid the use of complex pumps and plumbing. Its nozzle was simply ablatively cooled. “Minimizing the amount of plumbing, components, and joints was also a virtue because it reduced the chance of leakage, which, due to the small margins on the amount of propellant required to achieve lunar orbit from the Moon’s surface, could be disastrous,” wrote Kelly in Moon Lander.
Aerodynamics was not a part of the LM challenge, since the LM would only function in the vacuum of space. The placement of propellant tanks for center-of-gravity purposes with no aerodynamic coverings gave the LM its odd angular shape.
It was built so lightweight that the shock and ascent engine blowback of liftoff from the lunar surface harmlessly tore all the LMs’ outer skin panels.
At times in its development, the LM program was months behind schedule and thousands of pounds overweight. The first test LM delivered to KSC had many defects, including pressurization leaks. But Grumman assessed all the problems and ended up with total mission success across the program.
The LM was a big spacecraft, standing 23 feet tall and spanning 31 feet across its four landing legs. Weight was at such a premium that Grumman initially proposed astronaut crews use a rope to descend from the cockpit to the surface instead of adding the weight of a ladder – something the astronauts vetoed immediately. To save weight, Grumman also proposed that seats be removed so the pilots would fly standing up, looking straight down through special triangular windows at the approaching surface. The astronauts liked that idea.
By the last three flights in the program – Apollo 15, 16, and 17 – the Saturn V lift capability had increased to the point of allowing the LM weight to grow about a ton heavier, to 36,000 pounds. This especially allowed J-Mission LMs to carry the Boeing lunar rover electric car that allowed crews to travel 3 to 4 miles from their LMs.
The lunar module descent profile designed by the NASA Manned Spacecraft Center, along with Grumman and other contractors, was as complex as anything in the Apollo program. It involved precision targeting and precision flying – where time was the enemy. Initially, the LMs were to fly with enough propellant for 120 seconds of hover time for the pilots to look for a safe smooth spot before touchdown, but to save weight, the hover time was reduced to 60 seconds.
That nearly resulted in an Apollo 11 landing abort. Auto-guidance was taking the lunar module Eagle into a boulder field when Neil Armstrong took manual control and, with Buzz Aldrin calling out critical parameters, maneuvered until he dodged the boulders, as well as a large crater. Armstrong eventually landed with only about 25 seconds of fuel left before an abort would have been necessary.
The LM powered descent profile began at only about 50,000 feet of altitude, with the lunar module flying backward in order to fire its descent engine thrust forward to negate lunar orbit velocity. At this phase, the pilots were on their stomachs relative to the lunar surface, which they could see passing below.
At 35,000 feet, however, the LM was rolled onto its back, putting the astronauts on their backs looking out at space, but aiming the LM’s landing radar so it could begin to “see” the surface for final computer calculations. The data was needed for when the LM computer was to command and carry out the LM pitch over at 10,000 feet or lower.
At this point, the LM pitched forward – in effect taking the astronauts from a position on their backs relative to the surface to standing upright in the LM cockpit.
It was at this point that the descent engine began to counter the Moon’s one-sixth gravity pulling the LM down. The mission commander, standing at the left window, then took manual control to find a safe spot to continue the descent, throttling the engine to change the descent rate.
After landing, the crews “camped” on the Moon in the LM, where they could take off their spacesuits and sleep on the floor or in hammocks.
On departure day, the ascent engine was fired at the same moment explosive wire joints separated the ascent stage from the descent stage. The LM would then fly into lunar orbit for rendezvous and docking with the CSM, and then return to Earth.
