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Project Apollo - Mission Planning

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Project Apollo: The Beginnings | Mission Planning | Landing Site Selection | Earthbound Support Systems
Astronaut Selection and Training | The Saturn V | The Saturn 1B | The Apollo Spacecraft
Guidance and Navigation | Command and Service Modules | The Lunar Module
Assembling and Launching | Pathfinders | The Early Missions | Apollo 11, The First Landing
The Intermediate Missions | Apollo 15 Exploration | Apollo 16 Exploration | Apollo 17 Exploration
Skylab and Apollo-Soyuz | Conclusion

In the 1950s, the popular notion of a rocket trip to the moon was of a single streamlined craft blasting off from the Earth, journeying to the moon in a direct line of ascent and landing tail-first on a cone of fire. Then, after a suitable period of exploration, the rocket would take off and return to Earth landing tail-first at the spaceport from which it had started. The reality would be somewhat different....

Direct Ascent

The problems inherent in the so-called direct ascent method centred around the enormous power required to accelerate the craft's own weight and that of the fuel necessary for a round trip. It requires four pounds of fuel to carry one pound of payload into Earth orbit. The fuel needed at lift off required a strong structure to support its weigh, which in turn requires more fuel and more or larger engines in an escalating spiral. Any spacecraft built strongly enough to support both its own weight and that of the fuel requirements for a direct ascent, lunar landing and return soon became impractical even if it could actually be built.

One Direct Ascent project did exist on paper. Named 'Nova', it was proposed as a three-stage rocket weighing 5,300 tons when fully fuelled, that launched a 90-foot-high third stage that would land on the moon and return to Earth. It was eventually dropped as its impracticalities became obvious. Designers balked at the thought of attempting to land a fully fuelled rocket, the size of an Atlas Inter Continental Ballistic Missile and weighing 75 tons vertically onto the lunar surface.

Earth Orbit Rendezvous (EOR)

Another concept, Earth Orbit Rendezvous (EOR), used a number of launches to ferry the component parts of a spacecraft and fuel into Earth orbit and assemble it there. After assembly the rocket would be fuelled and fired towards the moon. This concept was thought to be the most practical method of establishing a presence in space as it could use boosters and engines which were already under construction that were far smaller than those that would be required for a direct ascent.

EOR was a long-term concept envisioned to provide a means of establishing manned Earth orbiting stations and colonies on the moon, as a first step towards the manned exploration of the solar system. However, in 1962 the practicalities of a rendezvous between two craft, or even whether anyone could live in a space environment and carry out the effective work necessary to assemble a rocket in orbit were all unknown quantities. Handling and transferring volatile cryogenic fuels between craft in a weightless environment was another unknown, and potentially dangerous hazard.

Lunar Orbit Rendezvous (LOR)

Another concept, Lunar Orbit Rendezvous (LOR), came under consideration in 1960 when engineer John Houbolt at the Langley Centre promoted the method that he believed gave the best approach to achieve a manned lunar landing. This involved placing a spacecraft in orbit around the moon and using a separate module to effect the landing from the command ship which would remain in orbit. The biggest advantages of LOR was that the Lunar Excursion Module (LEM), which would be used only once and then discarded as it became redundant, allowed considerable weight savings and would be possible with only one launch vehicle from Earth. Initially this method was received unfavourably as it was thought to be too hazardous to carry out the docking manoeuvres that would be necessary in lunar orbit, which could leave astronauts stranded a 250,000 miles from home if anything went seriously wrong.

Brainerd Holmes, associate administrator for manned spaceflight, had recruited Joseph F Shea as a deputy director to the Office of Manned Spaceflight and assigned him to resolve the mode issue. In January 1962 Convair Astronautics was awarded a contract to carry out a feasibility study of LOR and Grumman Aviation also undertook a privately funded study which they submitted in June 1962 thereby establishing their understanding of the LOR mode problems.

The method to be used dictated the design of the craft for the landing attempt and unless a decision was taken little progress could be made with hardware design. Houbolt's team continued to lobby for the LOR concept showing that it would be the most effective method of achieving the Kennedy's deadline while others still advocated EOR.

With different NASA centres pushing different solutions the decision on which method to adopt was stalled until a meeting at the Marshall Space Flight Centre on 7 June 1962. A letter from Houbolt to NASA Associate Administrator Dr Robert Seamans precipitated the meeting in November 1961, by-passing the formal channels. The meeting was called to resolve the differences and resulted in accepting LOR as the best method of achieving a manned landing before the end of the decade. Subsequently, further objections were raised by Jerome Weisener, the president's scientific advisor but by the end of 1962 LOR was accepted as the most expeditious method of achieving the deadline.

Lunar Orbit Rendezvous required placing a two-part spacecraft into orbit around the moon. The spacecraft would consist of a command ship from which a separate lander would descend to the lunar surface leaving the command ship in orbit. The lander, or Lunar Excursion Module (LEM), was itself a composite of descent and ascent stages. It would use its descent stage engine to effect a landing and on completion of the lunar excursion by the two-man crew, return them in the upper ascent stage back to the command ship leaving the descent stage on the lunar surface. Return of the ascent stage would be accomplished using its own separate ascent engine and the expended descent stage as a take off platform. After docking with the command ship, the Command Service Module (CSM), the crew would transfer with their samples to the CSM, and discard the ascent stage.

The whole LOR technique hinged upon the ability to bring together and dock the LEM and the CSM from different orbits. They would have to be able to change the height and plane of their orbits and dock with one another while in lunar orbit. To carry out these manoeuvres would require bringing the two craft into the same orbital flight path, one behind the other

To gain experience with these techniques while the Apollo spacecraft progressed through its design stage the USA's space program would continue with an extended Mercury program. This program would also test the feasibility of the rendezvous and docking techniques and to try to answer some of the other unknowns inherent in working in space. The extended Mercury program would use spacecraft similar to the Mercury design, enlarged to carry two men and a power system that would provide the ability to effect changes in orbit and altitude. The project was to be named Gemini reflecting the spacecraft's two-man capability.

Nominal Apollo Mission Profile

The typical lunar mission scenario required the launch of the Apollo spacecraft by a three-stage launch vehicle into Earth orbit. The Apollo spacecraft remained attached to the third stage in Earth orbit while a final check was run on its systems to verify that it remained 'go'. Once those checks were completed satisfactorily the command to restart the third stage's engine to increase the craft's velocity and place it on a course that would intersect with the moon's orbit.

Immediately after the rocket burn the Command and Service Module (CSM) would separate from the third stage, turn 180 degrees and return to dock with the Lunar Module (LEM) which was housed in the top of the third stage. Once docked, the CSM would separate and withdraw the LEM from the third stage and the third stage would be discarded. During the remainder of the outbound journey mid-course corrections would be completed with burns of the CSM's reaction control thrusters.

Approaching its target the spacecraft was aimed for a point just 60 to 80 miles in front of the moon. If left unchecked the speed gained from the moon's gravitational pull would cause the spacecraft to slingshot around the moon and return in the direction of the Earth. In order to remain in orbit around the moon the spacecraft would be required to fire its main engine against its line of flight to slow its velocity and allow the moon's gravity to capture the spacecraft in an elliptical orbit. A second manoeuvre, firing the engine retrograde at the lowest point of the orbit (pericynthion), reduced velocity further and created a circular orbit about 60 miles above the lunar surface.

After a further checkout of both the CSM and LEM, the CM pilot would undock and separate the CM from the LEM. At a point in the orbit on the lunar far side, the LEM would fire its descent engine retrograde, to slow the craft and place it in an orbit with its pericynthion of 50,000 feet altitude, 15 degrees up range of the landing site. After a further revolution and updating of the guidance computer the craft could commit to a landing. At pericynthion the LEM would be rolled into a windows-up attitude and fire the engine at full thrust and continue to brake the spacecraft and descend along a pre-determined approach path which took it to 'High Gate'. This point in the descent trajectory was at about 7000 feet altitude and five miles from the landing site, where its attitude was pitched upwards to bring the craft's windows forward and allow the crew to observe the landing site area. Descending at an increasingly vertical angle the lander passed through 'Low Gate' at about 500 feet at which point the commander can take over full manual control to land the craft on a suitable spot.

The mission continued with Extra Vehicular Activities (EVA) during which the LEM crew exited the spacecraft to the lunar surface, photographed and collected samples from the surface. Further activities included environmental experiments and setting out remote experiment packages of various kinds. On completion of the EVAs the spacecraft was readied for return to orbit and at a point when the CSM passed overhead, the crew would fire the ascent stage engine and using the lower descent stage as a launch platform, lift off from the surface. A series of manoeuvres were performed to match the orbits of the two spacecraft which docked together and allowed the LEM crew to transfer to the CSM with their samples and equipment. Once completed the LEM was jettisoned and under remote control de-orbited to crash into the lunar surface.

Return to Earth was accomplished by firing the engines from behind the moon to accelerate the spacecraft into a trajectory that would meet up with the Earth's upper atmosphere. Mid-course corrections carried out en route placed the spacecraft in an Earth re-entry corridor with a tolerance of accuracy of only one degree either side. At about four hours prior to re-entry the command module with the crew separated from the service module and orientated their craft so that its base-end heat shield was forward, ready to guard the crew from the intense heat generated from friction with the Earth's atmosphere during re-entry.

Re-entry speeds of around 25,000 mph into a tightly defined re-entry corridor were expected, but friction and a programmed switchback flight path would then slow the craft to a point at which drogue parachutes were deployed at about 24,000 feet to stabilise and slow the craft to 175 mph. At an altitude of about 10,000 feet, three main descent parachutes were deployed to lower the craft to a splashdown in the sea. Recovery of the crew from the floating spacecraft was by helicopter from an aircraft carrier recovery vessel. Spacecraft, crew and samples were then all returned to quarantine to safeguard against contamination.

All Up Testing

In October 1963, George E Mueller took over as associate administrator and as head of the Office of Manned Space Flight at NASA Headquarters and began to inject a sense of urgency into the Apollo program. He realised that NASA's conservative approach to the individual testing of the major components of the Saturn booster and the Apollo spacecraft with separate launches would consume time that the program could not spare. Within a month of taking office and mindful of the need to meet the end of decade deadline, he took a critical decision to introduce the concept of 'all up testing' to speed up the development of the Saturn V and the Apollo spacecraft. This involved launching fully assembled Saturn V rockets and spacecraft together instead of testing individual components on separate flights. Mueller's decision took months off the overall development time and removed the requirement for several Saturn 1B test launches.

Mueller also appointed USAF Major Gen Samuel C Phillips as deputy director for the Apollo program. Phillips who had previously been responsible for development of the Minuteman ICBM program was to oversee the integration of all aspects of management of the Apollo program. This included the procurement of the myriad of components and systems that would be required from over 500 subcontractors and to manage their development and quality testing. Meanwhile, Owen Maynard of the Apollo Spacecraft Program Office planned an incremental flight test program to develop the Apollo hardware from initial unmanned tests through to the eventual manned landing. They were classified with identifying type letters A through to G, they were:

  • Unmanned tests of the Command and Service Module (First Saturn V launch, Apollo 4 and the second Saturn V test Apollo 6)

  • Unmanned test of the Lunar Module (Apollo 5)

  • Manned Earth orbital tests of Command and Service Module (Apollo 1, became Apollo 7)

  • Manned Earth orbital tests of the Command and Service Module with Lunar Module (Apollo 9)

  • High altitude Earth orbit tests of Lunar Module. 1 (Redesignated C Prime, and became Apollo 8)

  • Lunar orbital tests of Command and Service and Lunar Module with simulated landing. (Apollo 10)

  • Lunar landing (Apollo 11)

In 1968 three other type missions were added to the list:

  • Walking lunar landings with two EVAs (Apollo 12, 13 14 and 15).

  • Manned lunar orbital science missions 2

  • Long lunar stay with three EVAs using transportation (Apollo 15, 16 and 17 with the Lunar Rover)

1None were flown as LM was not ready.2None were flown.

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