- Introduction
The Apollo missions were a series of space flights planned and implemented in the 1960’s and early 1970’s by the National Aeronautics and Space Administration (NASA) to achieve circumlunar flight and ultimately a moon landing. The vehicles used to achieve these goals comprised a Saturn V rocket as the launch vehicle, carrying atop the initially-combined Apollo Command and Service Module (CSM) and the Lunar Module (LM).
- The Obstacles
The first and important obstacle was obtaining the necessary funding for the program. NASA’s budget estimate was originally circa $20 billion needed from government funding. At the outset sufficient funding was achieved to commence the program, though more had to be prised from government coffers as time and the program progressed. The second hurdle to overcome was the need for huge numbers of personnel. NASA’s civil service staff grew from10,000 in 1960 to 36,000 by 1966. In addition, numbers of contract employees including researchers and technicians grew tenfold from 36,500 in 1960 to over 367,000 by 1965.
Existing NASA facilities also had to be expanded dramatically, plus new facilities were established. The design of the Apollo spacecraft itself and of the launch platform for the lunar module, the Manned Spacecraft Center was created near Houston, Texas. It was here that Mission Control was set up and it also became the base for NASA’s astronauts. On the Atlantic coast of Florida, the Cape Canaveral’s Launch Operations Center was expanded. All Apollo launches were made from Launch Complex 34 there. Nearby was the 36-storey Vehicle Assembly Building where the Saturn rockets and Apollo modules were assembled. There was a new facility established in Mississippi, the Mississippi Test Facility. Altogether, this expansion cost over $2 billion, of which the greater part was spent by 1966.
On the purely technical side of things the precise method actually getting to the moon had be hammered out within NASA; basically deciding one of the three possible methods. It was essential to make this decision at an early stage because the method chosen would have an effect on the spacecraft design. The three options were:
- A Direct Ascent: A straightforward direct flight to the moon, landing a large lunar vehicle, then returning a part of that to Earth. In the event this method was ruled out because the huge Nova rocket generating over 40 million pounds thrust needed for the launch proved to be too complex and costly;
- Earth Orbit Rendezvous: Using this method, modules for the trip to the moon would be launched into Earth orbit, assembled in space, and then sent to the moon after refuelling. Although this method had merits in respect of including setting up of a space station, it was also rejected, mainly due to the complexities of rendezvousing and safely refuelling in space;
- Lunar Orbit Rendezvous: This was the method adopted. The entire spacecraft was launched on a 7.5 million pounds thrust Saturn V rocket, heading off to a lunar orbit, then sending a small, detachable lunar lander down to the moon’s surface.
Despite the perceived risks of the rendezvous being in lunar orbit (where an error could mean the crew would be unable to return home) and the fact that the finer course corrections and other maneuvers had to be implemented when the spacecraft was already heading for circumlunar orbit, this was the method chosen.
Another obstacle to overcome to achieve a safe and successful lunar landing was a lack of detailed knowledge of the moon, especially its topography, the nature of its surface, whether there were any harmful radiations, etc. To counter that significant problem, NASA implemented a series of satellite programs to map the moon’s surface, to measure radiation, eventually gaining enough information to give the green light for a future lunar landing.
- The Saturn V Rocket and Launch
Developed from earlier Saturn versions under the guidance of the renowned rocket scientist Werner von Braun, the Saturn V was a 3-stage rocket standing 102 meters tall, and 10.1 metres in diameter. At liftoff it weighed circa 3,038,500 kg – about the same as twelve Boeing 747 passenger jets. By itself the fully-fuelled Saturn V first stage alone weighed more than one of the more recently-used Space Shuttles complete with its solid rocket boosters and the huge external fuel tank. Each Saturn V cost around $135 million.
Capable of lifting a payload of 47,000 kg towards the moon, its 42.1 meters long first stage comprised five massive F-1 engines developing a combined total of 7.5 million pounds of thrust. The power of all that thrust at liftoff was sufficient to create seismic shock waves that were felt for miles. Of the five engines, the outer four could be moved to provide control of pitch, roll and yaw, while the fifth and centrally-mounted engine was fixed in position. The engines were mounted onto X-configured beams fitted to the base of the thrust structure which supported a 130,000 liter cylindrical fuel tank made of welded aluminium and filled with a refined kerosene called RP-1. Above this tank was mounted a 1,204,000 liter liquid oxygen tank, also manufactured from welded aluminum. Five 17-inch diameter “tunnels” carried the liquid oxygen feed lines straight through the fuel tank. The top of the liquid oxygen tank was fitted with a skirt that attached it to the rocket’s second stage.
At launch the five engines were ignited in a 1-2-2 sequence – center engine first, then opposing pairs of the outer engines at 300 millisecond intervals. When the engines had reached full thrust (about 7 seconds), four launch pad hold down arms released to allow the Saturn V to lift away. Beginning with lifting in a slightly off vertical direction to clear the launch tower, the rocket then executed a pitch and roll maneuver. At 69 seconds after launch (T+69) the Saturn V accelerated through maximum dynamic pressure. At 135.5 seconds after launch, first the center F-1 engine shut down, followed moments later by the other four.
Then – 0.6 seconds after engine shutdown – eight solid fuel rockets fired to discard the engine fairings tops. At an altitude of 38.8 miles and a speed of 6,000 mph, first stage separation occurred. The first stage then continued up to a maximum of 69 miles before dropping into the Atlantic Ocean about 350 miles away from the launch site.
The second stage (S-2) also had five engines, burning a fuel mixture of liquid oxygen and liquid hydrogen. This stage of the Saturn V had proved tricky in development by North American Aviation and had caused problems in meeting the Apollo mission launch schedule.
The five Rocketdyne engines between them generated around 527,000 kg of thrust for up to 6 minutes 30 seconds. As with the first stage engines, the outer four could be moved to provide control, while the fifth and centrally-mounted engine was fixed in position. Empty, the second stage weighed only 39,000 kg, but carried almost 452,000 kg of propellant. Totalling 24.8 metres in length, the aluminium S-2 housed a liquid oxygen tank surmounted by a liquid hydrogen tank, insulated by a spray-on foam insulation.
After the first stage had separated, separation rockets fired up from it to increase separation while eight small rockets on an interstage section were fired to thrust the S-2 further ahead. Then, a few seconds later, the S-2 engines were ignited, followed thirty seconds after first stage separation by the interstage section falling away.
The third stage (S-4B) was an enlarged version of the earlier Saturn IB model and had proved comparatively trouble free. It was powered by one Rocketdyne engine producing up to 104.3 metric tons of thrust and burning a mixture of liquid oxygen and liquid hydrogen from S-4B’s tanks, which contained around 87 metric tons of liquid oxygen (LOX) and 18 metric tons of liquid hydrogen (LH2). The liquid hydrogen tank had internal insulation fitted.
S-4B also had two auxiliary propulsion units used for roll control when in powered flight and for attitude control in coasting phases. These burned nitrogen tetroxide oxidizer and monomethyl hydrazine. Each unit had two roll/yaw engines, a pitch control engine, and a rearward facing ullage engine used for settling the propellants during the orbital part of the flight. (During separation of the second & third stages, two other high thrust solid rocket ullage motors with a 4-second burn capability were used to settle the propellants). There were also two solid fuel ullage rockets, used to settle the liquid fuels prior to main engine restart.
During the Apollo mission, the first S-4B engine burn lasted about 2.5 minutes to position the spacecraft in a temporary, low Earth orbit. Then, after coasting for two orbits (about 90 minutes), the main engine was reignited and run for almost six minutes for trans-lunar injection. Finally, after separating from the CSM and LM, S-4B used its ullage rocket motors to maneuver clear, then vented the LH2 tank and dumped the LOX tank, using its ullage motors for a final burn to send S-4B into either a solar orbit or a lunar impact course (There are several S-4B’s orbiting the sun today).
Cold helium was used to pressurize the propellant tanks. That was stored in tanks within the hydrogen tank and on the exterior of the thrust skirt. When the spacecraft was coasting, pressure in the liquid oxygen tank was allowed to drop. (The liquid hydrogen tank was self-pressurizing). Prior to main engine restart the helium was expanded using a LOX/LH2 burner to pressurize the fuel tanks.
- The Apollo Spacecraft
Designed by NASA to sustain the astronauts for a period of at least two weeks, the 3-person, teardrop shaped command module was fitted with two hatches – a side hatch used for crew entry/exit at both the start and finish of the mission and one in the nose for access to the lunar lander via a docking collar that connected the two. It was connected to the service module which contained oxygen, fuel, maneuvering rockets, fuel cells, plus other life support systems that would be jettisoned before re-entry on the return journey. The combined unit was called the Command/Service Module (CSM). The service module also carried the retro rockets used to slow the spacecraft before re-entry and a launch escape system that was jettisoned once the spacecraft had reached orbit. Beneath the CSM, the Lunar Module (LM) was stowed with its legs folded, inside the Spacecraft-to-LM Adapter (SLA). Once the spacecraft was headed for the moon the SLA opened and the CSM separated from it, the CSM then turned around, docked with the LM and extracted it from the Saturn V third stage (S-4B). Then docking hatches were opened and the LM Pilot (one of the three astronauts on board), entered the LM to test its systems.
- The Lunar Module
The Lunar Module (LM) was probably the most challenging component of the Apollo mission equipment to design. It was started a year late and was always running late and over budget. The tricky part was how to design two separate components of the spacecraft – one to descend to the lunar surface and the other to return up to the command module that would remain in orbit around the moon. The engines on each of these two parts had to function faultlessly for the astronauts to return home. As well as solving problems of maneuverability, guidance and spacecraft control, design of the landing gear structure was also critical. That had to be strong and shock resistant yet as light as possible. Eventually, Grumman Aerospace designed and constructed the LM, which looked ungainly but would function as required and could be piloted by two astronauts in a standing position. Once the spacecraft was in a lunar parking orbit, the mission commander and the LM pilot would enter the LM, configure it for landing and separate it from the CSM, now orbiting independently.
Once ready for the landing phase, the descent engine was pointed forward and a 30-second burn slowed the LM to reduce its speed and lower its orbit. Then the descent engine was fired up again until the LM’s forward and vertical velocities approached zero. Until the very last moments these procedures were computer-controlled, using a combination of throttle and attitude thrusters, then the pilot exercised manual control to touchdown.
- The Re-entry Procedure
Following jettison of the LM, the propulsion systems in the Service Module were fired up to insert the spacecraft carrying the three astronauts into a transearth injection (TEI) that would send Apollo back towards Earth on a course that terminated with the Command Module making a controlled descent into the Pacific. Before re-entry the astronauts had to re-install the launch couch in position, then just prior to re-entry they jettisoned the Service Module, then used the CM’s thrusters to adjust the orientation of the vehicle so that its base with massive heat shield faced forwards and towards the surface of the Earth.
As the CM penetrated further into the atmosphere, the friction caused the heat shield temperature to increase to 5,000 degrees Fahrenheit as the forward velocity was reduced. Whilst still protecting the CM’s interior and the astronauts from the intense heat, the heat shield was (intentionally) ablated; i.e. melted and partially eroded, as it diverted the heat away from the astronauts travelling inside. Then, to further arrest the speed of descent, three large parachutes were deployed before splashdown in the ocean.
- Splashdown and Recovery
On splashdown, should the module land inverted, air compressors and balloons stowed in the top could be activated to turn it the right way up. Once safely floating on the surface of the sea, the CM’s ventilation system was triggered to bring fresh air into the capsule, and the astronauts activated a VHF recovery beacon and radio to guide recovery personnel (helicopters and ships) to them, prior to being transferred out of the module.
- Apollo 11 Moon Landing Mission
The actual lunar landing mission, the primary goal of the entire Apollo program, began with the launch of Apollo 11 on 16 July 1969. On 20 July at 4:18pm EST, the LM was landed on the moon’s surface by Neil Armstrong and Edwin (Buzz) Aldrin. Meanwhile astronaut Michael Collins in the command module orbited overhead. Then came the moment when Armstrong descended from the LM and made his now famous statement: “one small step for man – one giant leap for mankind”. Aldrin joined Armstrong and the two planted an American flag, set up various experiments and gathered samples of moon rock and soil.
They took off in the ascent part of the LM the next day, successfully docked with the orbiting command module, then fired the rockets to return to Earth, splashing down on 24th July in the Pacific Ocean. This was the first of a total of six lunar landing missions, each successive one spending longer on the moon’s surface, and three of them using a lunar rover vehicle to explore the area near to the landing site and to procure further samples.
References
Apollo Lunar Module. (March 2012). Retrieved from http://en.wikipedia.org/wiki/Apollo_Lunar_Module
Apollo Program. (Updated April, 2012). Retrieved from http://en.wikipedia.org/wiki/Apollo_program
How the Apollo Spacecraft Worked. Apollo’s Re-entry. Strickland, Jonathan. Retrieved from http://science.howstuffworks.com/apollo-spacecraft7.htm
Project Apollo: A Retrospective Analysis. (Updated October, 2004). Retrieved from http://www.hq.nasa.gov/office/pao/History/Apollomon/Apollo.html
The Lunar Module Descent Stage. Duncan, John. (March, 1998). Retrieved from http://www.apollosaturn.com/Lmnr/descent.htm
Space Launch Report Saturn Vehicle History.(Updated December, 2010). Retrieved from http://www.spacelaunchreport.com/satstg5.html
