Lunar Module Attitude Controller AssemblyLunar Module Attitude Controller AssemblyDigital Input ProcessingDigital Input Processing

José PortilloJosé Portillojportillo34@hotmail.comjportillo34@hotmail.com

Two types of Input:

– PROPORTIONAL• Make use of the LM Guidance Computer Counter Interfaces and

Transformer based Interface circuit.• Used for Rate Command Augmentation Mode.

– DISCRETE• Make use of the LM Guidance Computer discrete Interface Channel

bits.• Used for Pulse Mode.• Used for Man-in-the-Guidance-Loop capabilities.

Lunar Module Attitude Controller AssemblyLunar Module Attitude Controller AssemblyDigital Input ProcessingDigital Input Processing

Proportional Input ProcessingProportional Input Processing

• 1958: NACA technical paper describing “Systems that Command Velocity” as

feedback control concept. Simulator investigation of Command Reaction Controls - Holleman, Euclid C.; Stillwell,

Wendell H. - NACA RM H58D22 - April 14, 1958.

• 1959: Development of a Self-Adaptive flight control system for 1960: the X-15

research vehicle.

• 1963: Development of an Analog Rate Command Augmentation/Attitude-Hold

1964: control system for the Gemini Spacecraft.

• 1964: AIAA conference paper describing a Rate Command and Acceleration

Comand systems implemented in the Langley Research Center Gemini-

Agena Docking Simulators. Full-Scale Gemini-Agena Docking using Fixed and Moving base Simulators - Hatch, Howard G.;

Riley, D. R.; Cobb, J. - AIAA paper 64-334 - June-July 1964.

• 1964: Apollo lunar program: decision to implement a “Digital Autopilot” for the

Lunar Module Primary Guidance System.

Manual Rate Command Augmentation SystemsManual Rate Command Augmentation SystemsA brief chronologyA brief chronology

• 1966: NASA LRC technical paper describing a Rate Command and

Acceleration Command electronic control system for control of the

Lunar Landing Research Vehicle. Flight Tests of a Manned Rocket-Powered Vehicle Utilizing the Langley Lunar Landing

Research Facility - O’Bryan, Thomas C. - Presented at AIAA Guidance and Control Specialists

Conference - Siattle, Washington - August 1966.

• 1966: NASA technical paper describing a Rate Command Augmentation

system (fly-by-wire bang-bang) implemented in the DFRC lunar Landing

Research simulation vehicle. Operational experience with the Electronic Flight control Systems of a lunar-Landing

Research vehicle - Jarvis, Calvin R. - NASA TN D-3689 - July 5, 1966.

• 1966: Grumman Aircraft developed a Lunar Module Simulator for development

and testing purposes. An Analog processing for the Hand Controller was

implemented. Lunar Module Hover and Landing, Separation and Docking Simulation - Greene S.; Russo, J. -

Presented at AIAA Flight Test, Simulation and Support Conference - Cocoa Beach, Florida -

February 6-8, 1967.

Manual Rate Command Augmentation SystemsManual Rate Command Augmentation SystemsA brief chronologyA brief chronology

• 1968: Development of a Rate Command Augmentation system embedded into

the LGC Digital Autopilot.

• 1969: First flight test of the Lunar Module Digital Autopilot, including its manual

Rate Command Augmentation/Attitude-Hold capability. Apollo 9 Mission in earth orbit.

• 1969: First Lunar Landing operation for the Lunar Module Digital Autopilot. Apollo 11 Mission. It includes an more complete Manual Rate Command Augmentation System.

Manual Rate Command Augmentation SystemsManual Rate Command Augmentation SystemsA brief chronologyA brief chronology

• Embedded into the Digital Autopilot Software.

• Shows all the advantages of Digital Control System implementations over Analog Control System implementations: input data processing follows conditional paths, switching points (if ... then), and storage for past iterations to be used during present Command Control computations.

Apollo Lunar Module Digital Manual Rate Command Apollo Lunar Module Digital Manual Rate Command Augmentation SystemAugmentation System

Proportional CommandsProportional Commands

ExternalExternalControlControlParametersParameters

• Two Control Laws were employed for Manual Rate Command Augmentation:

– DIRECT RATE• Used each time the “Commanded Rate change” exceeds a Breakout

Level.• Computes Jet-on time based only in Rate Error information: do it fast!• To damp vehicle Rates below a “Target” Dead Band (before return

control to the Attitude Hold Autopilot).• Used on a per-Axis base.

– PSEUDO-AUTOMATIC• Used while there is no Manual input. To Hold an Attitude.• Computes Jet-on time based upon Rate and Attitude Error information.• Uses a Phase-Plane logic to exercise Control.• It can achieve very small Commanded Rates.• Used on a per-Axis base to prevent Attitude drift about uncommanded

Axes.

Apollo Lunar Module Digital Manual Rate Command Apollo Lunar Module Digital Manual Rate Command Augmentation SystemAugmentation System

Apollo Lunar Module Digital Manual Rate Command Apollo Lunar Module Digital Manual Rate Command Augmentation SystemAugmentation System

Control Law SelectionControl Law Selection

MCR

CommandedRate Exceeds

Breakout Level?

no

yes

BreakoutLevel Switch

RHCCTR Counter

PSEUDO-AUTOControl Law

DIRECT RATEControl Law

Dead Band Switch

Digital Autopilot Control Parameters:• Constant Values in Rope Memory• Entered in-flight by crew• Flags set ON/OFF by previous iterations

ControlFlowFlags

Discrete Input ProcessingDiscrete Input Processing

• A LM Guidance Computer Common 28 Volt. DC excitation source is applied to the Attitude Controller Assembly Plus and Minus Switches, and returning through the LM Guidance Computer input Channel.

• Provides a way to input low Rate Commands as well as Man-inthe-Guidance-Loop capabilities.

Apollo Lunar Module Digital Manual Minimum ImpulseApollo Lunar Module Digital Manual Minimum Impulseand LPD Redesignator and LPD Redesignator

Discrete CommandsDiscrete Commands

ExternalExternalControlControlParametersParameters

• Two Discrete Inputs:

– MINIMUM IMPULSE• Enables the crew to perform economical low Rate maneuvers.• Embedded into the Digital Autopilot Software.• LM Guidance Computer Channel 31 includes the Input bits.

– LPD REDESIGNATOR• Enables the crew to enter into the Lunar Landing Automatic Guidance

Loop.• Embedded into the Landing Approach Phase Guidance Software (the

so called “Manual Steering Section”).• LM Guidance Computer Channel 31 includes the Input bits.• LPD Redesignation Input Commands are processed by an Interrupt.

Apollo Lunar Module Digital Manual Minimum ImpulseApollo Lunar Module Digital Manual Minimum Impulseand LPD Redesignator and LPD Redesignator

“A” Circuit

“D” CircuitMinimum Impulse& Discrete LPD

DiscreteInbit (Channel 31)

RHCCTR Counter

“Start Gating” bit

10 cps

Out-Of-Detent Inbit (Channel 31)

10 cps

Digital Autopilot

CA L No MASK -AZBIT CCS A -AZ CS AZEACH ADS AZINCR1 CA L MASK +AZBIT CCS A +AZ CA AZEACH ADS AZINCR1 CA L MASK -ELBIT CCS A -EL CS ELEACH ADS ELINCR1 CA L MASK +ELBIT CCS A +EL CA ELEACH ADS ELINCR1 TCF RESETRPT

DETENTCK EXTEND READ CHAN31 TS CH31TEMP MASK BIT15 EXTEND BZF RHCMOVED CAF OURRCBIT MASK DAPBOOLS EXTEND BZF PURGENCY

RHCMOVED CS RCSFLAGS MASK BIT9 ADS RCSFLAGS CA OURRCBIT MASK DAPBOOLS EXTEND BZF JUSTOUT - 1RATERROR CA CDUX TS CDUXD

Lunar Module ACA Digital Input Processing

Interrupt 10 (Redesignator Trap)

HI

LO(proportional)

Fixed-Address Instruction  4050 DXCH ARUPT 4051 CA RUPT10BB 4052 XCH BBANK 4053 TCF PITFALL

1. Handling Qualities for Pilot Control of Apollo Lunar-Landing Spacecraft – Cheatham, D. C., Hackler, C. T. - Journal of Spacecraft and Rockets, Vol. 3, No. 5, May 1966, pp. 632-638.

2. MIT's Role in Project Apollo - Volume III – Computer Subsystem – Hall, Eldon C. - August 1972.

3. Manual Attitude Control of the Lunar Module – Stengel, Robert F. – AIAA paper 69-892 – August 1969.

4. Apollo Experience Report - Crew Station Integration - Volume III – Spacecraft Hand Controller Development - Wittler, rank E. – Lyndon B. Johnson Space Center, Huston Texas 77058 - March 1975.

5. A Manual Retargeted Automatic Landing System for the Lunar Module - Klumpp, Allan R. – Journal of Spacecraft and Rockets - Volume 5 - Number 2 -February 1968 - pp 129-138.

6. Lunar Module Digital Autopilot - Widnall, William S. - Journal of Spacecraft - Vol. 8, No. 1 - January 1971.

ReferencesReferences

QuestionsQuestions

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