NASA Office of Logic Design

NASA Office of Logic Design

A scientific study of the problems of digital engineering for space flight systems,
with a view to their practical solution.


SP-287 What Made Apollo a Success?
 

8. FLEXIBLE YET DISCIPLINED MISSION PLANNING

By C. C. Kraft, Jr., J. P. Mayer, C. R. Huss, and R. P. Parten
Manned Spacecraft Center

[69] Apollo mission planning extended over a period of approximately 8 years and encompassed many technical disciplines. It progressed from the early design-reference lunar mission in 1962 through the detailed operational planning of specific missions which began in 1964. A pattern of mission-planning procedures. techniques, and management processes evolved that brought order to the many (and sometimes diverse) elements of the mission-planning team. This report examines the Apollo mission planning process, the important considerations that influenced the mission planners, and the evolution of the Apollo development flight schedule. The report concludes with a brief description of the more important panels, meetings, and working groups that helped to coordinate the mission-planning activities.

The planning and design of a mission, like the development of spacecraft hardware, proceeds from previously specified objectives and becomes constrained by system characteristics and operational considerations. Fundamentally, the process consists of a series of iterative cycles (fig. 8-1) in which a design is defined to increasingly finer levels of detail as the program progresses and as the flight hardware and operational considerations become better known. Initially, mission design has the purpose of transforming broad objectives into a standard profile and sequence of events against which the space-vehicle systems can be designed. Usually, incompatibilities arise immediately between system design and mission design, and these necessitate trade-off studies to arrive at a compromise. Later, as hardware design solidifies, the emphasis of mission design becomes more operationally oriented, as the mission planners attempt to constrain their design to the operating capabilities of the space vehicles, ground-support facilities, and flight software. The final planning phase, which occurs during the year before a launch, involves development of the detailed procedures, techniques, and mission rules which are used by the flight crew and ground control team for both nominal and contingency missions. 


Figure 8-1. Iterative mission-planning process.

Figure 8-1. Iterative mission-planning process.

[70] MAJOR CONSIDERATIONS

The considerations important to Apollo mission planners depended somewhat on the type of mission: manned or unmanned, development or operational. For manned missions, the prime consideration was crew safety, whereas unmanned missions stressed mission success. For development missions, the prime consideration was to maximize the number of test objectives that could be met successfully, as opposed to operational missions, in which the number of final mission objectives was maximized.

The need for early decisions made the Apollo mission planners the driving force in stating the requirements for collecting and documenting all constraints. This need existed particularly during the development phase of the program. After the constraints were obtained, the development of mission techniques that would achieve the required test or mission objectives within them was necessary. This development proved to be an iterative process which involved constraints, techniques, and objectives It usually was carried to the time of final mission rules and flight plans. The iteration process and the consideration of possible failures or contingency situations entailed much alternate mission and contingency mission planning. This type of planning activity reached a peak during the manned development missions.

Because of involvement early in the planning stage of a mission, the mission planners have been able to affect materially the development of both onboard and ground software In many cases, the software had to be tailored to a specific mission, although every effort was made to use the final program software wherever possible.

The software development schedule and costs can (and did) influence the design of some missions. In the early days of Apollo, separate programs were being developed for the unmanned Saturn IB and Saturn V test missions, because of distinct differences in the test requirements for the missions. Later, it became apparent that the development of several different spacecraft- and ground-software programs was not feasible, considering the schedule and costs for delivering the lunar-landing-mission program. Because of this, the Saturn V mission test objectives were reexamined and were modified to accept the software used for the Saturn IB missions.

 

OPERATIONAL PLANNING CYCLE

Usually, the Apollo operational planning cycle began between 36 and 18 months before a launch, depending on the extent of mission complexity. Because several organizations within NASA and throughout industry were participating in the analysis and design of the Apollo development and lunar missions, a need was identified for coordinating the efforts of all mission-planning elements.

In late 1964, an Apollo Mission Trajectory Documentation Plan was prepared, which defined the principal documents and information flow in the areas of mission planning and trajectory analysis. This plan became a major vehicle for coordinating the more significant mission-planning milestones throughout the Apollo Program.

[71] The operational mission design was divided into three separate phases: mission definition, mission design, and flight preparation. Schedules for the beginning and termination of each phase were established specifically to dovetail with the major hardware development, airborne- and ground-software development, and crew-training milestones.

Although each phase sometimes specified as many as 20 major milestones (documents), the nucleus of the plan involved only four basic milestones for each phase: a mission requirements document, an operational data book, a trajectory plan, and of course a flight plan. The remainder of the milestones concerned abort and contingency planning, dispersion analyses, consumables analyses, and other special requirements. such as range-safety plans, orbital-debris studies. onboard-data-file information, and crew-simulator data.

Early in the Apollo Program, considerable difficulty was experienced in the exchange, standardization, and dissemination of critical data required both by and from the mission planners. In view of the interdependency of most mission-planning milestone documents. the need for coordination and tight control in disseminating these data became acute. As a result, the Apollo Spacecraft Program Office in conjunction with the hardware contractors and operational elements exercised strict controls and procedures in governing mission-planning data. As a part of this program, most organizations appointed key personnel on a full-time basis to support the data-management network. In retrospect, this action must be regarded as vital in consolidating and strengthening the Apollo mission-planning process.

The next step in the Apollo operational planning cycle involves what came to be known as mission techniques, which were developed in the form of logic flows that detail each decision point, threshold value, and ground rule for each phase of both nominal and contingency missions. Section 7 discusses mission techniques in some detail.

In Apollo, as any other complex space mission, it is virtually impossible to develop premission plans for every contingency that could arise during flight. Although specific plans are developed for all abort potentialities that involve crew safety. most alternate missions are developed on a class basis by using the alternate test and mission objectives. However, the real-time mission planner is given a powerful assortment of mission-planning computer programs that enhance his ability to manage any contingency. By the proper use of these on-line computer programs, alternate mission plans can be developed in real time and can thereby augment the premission planning activities.

 

DEVELOPMENT FLIGHT SCHEDULE

To understand the complexity of the task of mission planning for the Apollo Program, the evolvement of the development flight schedule may be reviewed. From the beginning of the Apollo Program, it was recognized that the flight tests for verifying hardware design, hardware performance, and operational techniques would be extensive. At the same time, it was recognized that the cost and scheduling of such flights must be controlled and limited to keep development costs for the program at a minimum.

[72] Test requirements for the major hardware elements (launch-escape system, command module aerodynamics, spacecraft structural verification, thermal-protection system, separation systems, communications systems, propulsive systems, landing systems, etc. ) were recognized early as tests that could be made by unmanned flight vehicles. This realization resulted in the series of Little Joe II test flights (launched at the NASA White Sands Test Facility) and in three Saturn IB and two Saturn V test flights (launched at the NASA John F. Kennedy Space Center), which can be noted in table 8-1.


TABLE 8-1. APOLLO SPACECRAFT FLIGHT HISTORY

 

Mission

Spacecraft

Description

Launch date

Launch site

.

PA-1

BP-6

First pad abort

Nov. 7. 1963

White Sands Missile Range, N. Mex.

AS-001

BP-12

Transonic abort

May 13, 1964

White Sands Missile Range, N. Mex.

AS-101

BP-13

Nominal launch and exit environment

May 28. 1964

Kennedy Space Center, Fla.

AS-102

BP-15

Nominal launch and exit environment

Sept. 18. 1964

Kennedy Space Center, Fla.

AS-002

BP-23

Maximum dynamic pressure abort

Dec 8. 1964

White Sands Missile Range, N. Mex.

AS-103

BP-16

Micrometeoroid experiment

Feb. 16, 1965

Kennedy Space Center, Fla.

A-003

BP-22

Low-altitude abort (planned high-allotted abort)

May 19. 1965

White Sands Missile Range, N. Mex.

AS-104

BP-26

Micrometeoroid experiment and service module reaction control system launch environment

May 25, 1965

Kennedy Space Center, Fla.

PA-2

BP-23A

Second pad abort

June 29, 1965

White Sands Missile Range, N Mex

AS-105

BP-9A

Micrometeoroid experiment and service module reaction control system launch environment

July 30, 1965

Kennedy Space Center, Fla

A-004

SC-002

Power-on tumbling boundary abort

Jan 20, 1966

White Sands Missile Range, N. Mex

AS-201

SC-009

Supercircular entry with high heat rate

Feb. 26, 1966

Kennedy Space Center, Fla.

AS-202

SC-011

Supercircular entry with high heat load

Aug. 25, 1966

Kennedy Space Center, Fla.

Apollo 4

SC-017 LTA-10R

Supercircular entry at lunar return velocity

Nov. 9, 1967

Kennedy Space Center, Fla.

Apollo 5

LM-1

First lunar module flight

Jan. 22. 1968

Kennedy Space Center, Fla.

Apollo 6

SC-020

Verification of closed-loop emergency detection system

April 4, 1968

Kennedy Space Center, Fla.

Apollo 7

CSM 101

First manned flight; earth orbital

Oct.11, 1968

Kennedy Space Center, Fla.

Apollo 8

CSM 103

First manned lunar orbital flight. First manned Saturn V launch

Dec. 21, 1968

Kennedy Space Center, Fla.

Apollo 9

CSM 104 LM-3

First manned lunar module flight; earth orbit rendezvous; extravehicular activity

March 3, 1969

Kennedy Space Center, Fla.

Apollo 10

CSM 106 LM-4

First lunar orbit rendezvous: low pass over lunar surface

May 18, 1969

Kennedy Space Center, Fla.

Apollo 11

CSM 107 LM-5

First lunar landing

July 16, 1969

Kennedy Space Center, Fla.

Apollo 12

CSM 108 LM-6

Second lunar landing

Nov. 14, 1969

Kennedy Space Center, Fla.


[73] The Little Joe II flights were unmanned ballistic flights strictly for command and service module (CSM) hardware development, mainly of the launch-abort escape system, separation systems, spacecraft aerodynamics and structural integrity, and landing systems. The Saturn IB series extended these tests to more extreme conditions (higher entry speeds, higher heating conditions, longer flight times). Also, the Saturn IB flights began testing the propulsion and guidance and control systems, on both the CSM and the landing module. The Saturn V flights completed the unmanned test program, which exercised the CSM at very near the conditions expected for a lunar mission, the major variance being less flight time. By their nature, these missions required that many special hardware and software elements be developed which were not applicable to the manned program. However, they did aid considerably in the development of ground operational techniques, mission rules, spacecraft checkout, and launch preparation.

Many systems, because of their complexity and numerous modes of operation (electrical power, environmental, computer, communications) could be tested only on manned missions. The number of missions being planned was quite large in the early days of the program, not because of the spacecraft test requirements, but because of the uncertainty of success of the development program, both from the spacecraft and launch-vehicle standpoint. In late 1963, there were eight Saturn IB and eight Saturn V development missions scheduled and in the planning stages, and approximately six to eight more backup missions in the planning stages.

During the period from late 1967 to early 1968, a major redefinition of the development flight program reduced to a minimum the number of development flights leading to the landing mission. After the first two Saturn IB flights, the program had been reduced to two Saturn IB and seven Saturn V development missions, and only two Saturn IB backup missions were being planned. This reduction reflected successes with Little Joe II, the two Saturn IB missions, and Saturn development tests, as well as increased confidence in the system performance and reliability bases on flight and ground tests. In mid-1968, after the successful unmanned Saturn V missions, a partially successful unmanned lunar module mission, and a successful manned CSM mission, the development flight test program was reduced to three Saturn V missions with complete spacecraft: a low-earth-orbit mission (D), a high-ellipse earth-orbit mission (E), and a lunar-orbit mission (F).

Because of the high confidence in the CSM, which was established by the early missions, and because of the requirement of additional checkout and testing of the first manned lunar module, it was decided to fly a CSM alone on a lunar-orbit mission (C). This mission provided an early evaluation of lunar navigation techniques and operational procedures, and added immeasurably to the progress and to the eventual success of the program. It was also decided at this time to eliminate the high-ellipse earth-orbit mission (E) in favor of doing tests in the actual lunar environment. Of course, these extremely complicated E missions completed the necessary testing and development of hardware, software and operating techniques, ground checkout and launch preparation, and development of mission rules and overall operational capability, except for the actual lunar landing. This phase of the mission could be tested only through the use of the lunar landing training vehicle and by the actual lunar landing.

 

[74] MISSION-PLANNING COORDINATION

Because the development of the Apollo mission plans involved close cooperation of three widely separated NASA centers, intercenter panels were organized to coordinate all activities in which an interface occurred between the launch vehicle and the spacecraft. For example. early in the program both the launch vehicle and the spacecraft had development objectives which had to be met with as few flights as possible. The development of missions which supported adequately the mission objectives of both launch vehicles and spacecraft took considerable planning effort among the centers.

At the NASA Manned Spacecraft Center (MSC), a series of flight operations plans meetings was conducted to develop the basic mission plan after the issuance of requirements. These meetings brought together the various experts in spacecraft systems, trajectory analysis, and guidance and control and the flight controllers, crew, and flight plan developers from contractors and MSC organizations. (See fig. 8-2. ) The chief importance of these meetings was to set constraints on the mission.


Figure 8-2. Apollo mission design instrumentation.

Figure 8-2. Apollo mission design instrumentation.

Mission techniques meetings took over where the flight operations meetings left off. The flight operations meetings led to a definition of the basic mission and the mission constraints. The detailed operational procedures for flying the mission were developed in the mission techniques meetings. The basic mission-planning documents which these working groups influenced were the operational trajectory, the flight plan and procedures, and the mission rules.

As changes to hardware must be controlled, so must changes to mission plans. Mission plan changes were controlled by three basic control boards. The Apollo Spacecraft Configuration Control Board (directed by the Manager of the Apollo Spacecraft Program) exerted control over all changes that affected mission objectives, hardware, trajectories, and propellant requirements. The Software Configuration Control Board (directed by the Director of Flight Operations) controlled all changes to the onboard and ground computing programs. The Crew Procedures Configuration Control Board (directed by the Director of Flight Crew Operations) controlled changes to the mission flight plan and all operational crew procedures. The Data and Requirements Control Panel controlled operational data affecting the mission flight plan.

 

[75] CONCLUDING REMARKS

In planning the Apollo missions, much emphasis was placed on the demand for flexibility in the development program and responsiveness to changing needs. The dynamic conditions present in Apollo strongly influenced the mission planners in providing comprehensive alternate mission capability and flexibility in the ground and airborne flight software. Probably of more importance, however, was the capacity of the mission-planning team to react to major program readjustments, as evidenced typically by the Apollo 8 success. The effectiveness of this team, by using the process described here, is measured by the Apollo record.


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