Apollo CSM GNC

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Apollo CSM Navigation, Guidance and Control

Navigation: determine current location
Guidance: determine target location and route
Control: carry out the journey

The Apollo Navigation, Guidance and Control system was a sophisticated and complex system. It has been developed based on a number of business requirements with regard to:

reliability;
redundancy;
human control on various levels of operation from auto pilot to direct manual control;
the NGC system in conjunction with the propulsion and reaction control systems must be configurable to suit various maneuvering modes of operation, like trajectory control, attitude control and docking maneuvering;
the NGC system must be self-contained; the crew must be able to perform NGC operations without any support from an Earth-based mission control center.
flexibility: the heart of the NGC system was formed by a computer; the mission control center must be able to uplink data into the computer remotely.

In this page is illustrated which NGC subsystems were involved in the various NGC control modes.

Content

Principles of operation
The hardware components of the CSM NGC System
Attitde & Translation Control Modes
1. Automatic Attitude & Translation Control in the Digital Autopilot Mode
2. Manual Attitude & Translation Control in the CMC Control Mode (ATT HOLD, AUTO or FREE)
3. Manual Attitude & Translation Control in the SCS Control Mode, Proportional Cmd Rate without Attitude Hold
4. Manual Attitude & Translation Control in the SCS Control Mode, Proportional Cmd Rate with Attitude Hold
5. Manual Attitude & Translation Control in the SCS Control Mode, Minimum Impulse Cmd
6. Manual Attitude & Translation Control in the SCS Control Mode, Acceleration Cmd
7. Manual Attitude & Translation Control in the SCS Control Mode, Direct Cmd
Thrust Vector Control Modes
1. Automatic Thrust Vector Control in the Digital Autopilot Mode
2. Automatic Thrust Vector Control in the SCS Autopilot Mode
3. Manual Thrust Vector Control in the CMC Control Mode (ATT HOLD, AUTO or FREE) (to be checked)
4. Manual Thrust Vector Control in the SCS Control Mode, Rate Cmd
5. Manual Thrust Vector Control in the SCS Control Mode, Acceleration Cmd
Title

1.Principles of operation

Based on ref.xxxx
Figure 1.1 Operation principle of a Navigation, Guidance and Control System for controlling a flight trajectory of a spacecraft In this diagram are shown the five major building blocks for a system that controls the flightpath of a spacecraft. Each block represents a task: Sensors The senses (eyes) of the system Navigation With the sensors, the navigation system determines the spacecraft's position, velocity, acceleration (also known as the state vector) and its spatial orientation, which is called the attitude. Guidance The Guidance system has a map of the environment with data about the celestial objects which can assert force on the spacecraft. In the case of the Apollo spacecraft these celestial objects are the Earth, The Moon and the Sun. If it is told the target state vector and it has received the navigational data it can calculate the required changes in velocity and acceleration to meet the target state vector. The calculation results are then translated into control commands. Control The control commands from "Guidance" are converted into control signals for the effectors (the propulsion systems and the small thrusters to control the attitude, the spatial orientation)

Based on ref.xxxx
Figure 1.2 Global block diagram of the Apollo CSM Navigation, Guidance & Control System In this diagram is shown how the principles of a NG&C system has been used in an Apollo CSM NG&C system. The PGNCS and the SCS each has its own sensor package. These packages are depicted in figure 3. The IMU of the PGNCS provides information about the spacecrafts' attitude and its location in space. The BMAGs of the SCS provides information about the spacecrafts' attitude only. When the crew wants to control the attitude manually by using the hand controllers, various control modes are available by which the thrusters of RCS are controlled. The SCS by itself provides all the avaialable control modes durng manual attitude control. As depicted in the diagram, user modes of control can be distinguished: Direct Control The command signals are direcly sent from the hand controllers (RHC and THC) to the thrusters of the Reaction Control System (RCS). The movemnts of the hand controllers result in the opening or closing of the propellant valves. This control mode is somewhat comparable with working in the ACCEL CMD MODE. SCS Control Mode The command signals from the hand controllers are interpreted by the SCS which results in command signals to the thrusters of the RCS and the SPS engine. These command signals are tailored by the SCS to obtain a specific type of control of the spacecaft's attitude and trajectory i accordance with the seelected mode of control: Acceleration Command Proportional Rate Command Attitide Hold Minimum Impulse CMC Control Mode In this mode the command signals from the hand controllers are interpreted by the CMC. But the user can also instruct the CMC to execute maneuvres by entering navigation data and or start navigation & control programs. The CMC is part of the PGNCS which contains data about the state vector and data about the planned trajectory. Submodes: FREE (Acceleration Command) ATTITIDE HOLD AUTO (ATT HOLD on specified target) CMC-SCS Redundancy It was possible to perform attitude and trajectory control without the CMC. Attitude control was fully supported by the SCS. But for trajectory control navigation data had to be acquired manually by using the sextant. Based on the navigation data and the target position in space, the thrust vector and the burn duration had to be determined and set. Since the spacecraft's attitude was known to the SCS, the crew could set the required gimbal position of the SPS engine by using the Gimbal Position Indicator (GPI). For the required burn duration, the support of Mission Control was needed. Computers were needed to calculate the required burn duration. Mission Control could also provide the required SPS gimbal angles. The position of the spacecraft in space could be measured by ground stations, and telemetry data from the SCS kept Mission Control informed about the spacecraft's attitude. So, in principle, Mission Control could provide all the data needed to enable the crew to control the trajectory by using the SCS only. However, it was important that the attitude data received by Mission Control be as accurate as possible. The BMAGs were the primary source for attitude data. Since the BMAGs were only measuring angular rates, a system was needed to transform these rates into attitude angles. That system was called the Gyro Display Coupler (GDC); it processed these rates into angles for pitch, yaw and roll. The BMAGs-GDC were sufficient to determine a course alignment of the spacecraft. However, for a precise alignment or a realignment of the BMAGs_GDC, there were manual procedures for realignment. There were two references which could be used: the IMU or the attitude data obtained with the sextant.
Notes Inertial gyro platforms and body-mounted gyro platforms The IMU was an inertial gyro platform, and the two BMAGs were body-mounted gyro platforms. The IMU was a much more complicated system than a BMAG. The IMU was inherently more accurate and required inherently less computation to obtain data on attitude, position and velocity. Inertial gyro platforms and body-mounted platforms can, in principle, both be used to determine attitude and location in space by measuring accelerations from which angular and lineair movements can be derived by using calculations. These calculations are basically mathematical integrations of acceleration measurement values over time to derive angular velocity, lineair velocities, pitch, yaw, roll angles and the position in space. However, in the Apollo spacecraft the body-mounted gyro platforms were only used to determine angular rates and pitch, yaw and roll angles. The Gyro Display Coupler (GDC), an electronic analogue system which processed the signals from the body-mounted gyro platforms, was only able to calculate the attitude.

2.The hardware components of the CSM NGC System

Based on diagrams and description from various handbooks and technical notes. (References still need to be mentioned.)

Figure 2.1
Detailed systems diagram of the Apollo CSM Navigation, Guidance and Control System

TOPICS TO BE ADDRESSED

Some remarks about the SCS control mode
The BMAG mode can be set for yaw, roll en pitch separately.
The SCS manual control modes ACCEL CMD, RATE CMD and MINIMUM IMPULSE can be set for yaw, roll en pitch separately.
In that case the RCS thrusters are controlled directly through the hand controllers. There is a separate switch panel to enable or disable each thruster of a quad, a total of 16 thrusters. It enabled the crew to select a thruster configuration.

Flight Director Attitude Indicator (FDAI)
There are 4 switches to determine what information is shown by the FDAI's.
Switch settings: (to be presented)

GNC contigency during the boost phase
When the triple redundant GNC systen of the Saturn V would fail, the GNC system of the Apollo spacecraft could take over. This was an eventuallity the astronauts were trained for. During ascent the GNC of the spacecraft was running a computer program to produce the data be able to feed the Saturn V control systems to control the rocket engines. The navigation and the guidance systems of the Saturn V would have been bypassed if the spacecraft's GNC would have taken over.

Navigation sources
The Command Module Computer (CMC) of the Apollo spacecraft can be considered has the heart of the GNC system.
In order for the CMC to know the position and attitude in space it relied on various information souces:

The Inertial Measurement Unit (IMU)
The Gyro Display Coupler (GDC)
Measurement data from the onboard sextant and scanning telescope
Navigation data entered by the crew via the DSKY
Navigation data provided by Mission Control which are based on radar measurements of ground based radar stations

Modes of operation

Alignment procedures for the IMU and the GDC

Trajectory control

Attitude control

Personal reminder 1
I need to check on the Apollo CSM PGNCS with regard to the ablity to take over the NGC of the Saturn launch vehicle.
It seems that the extent of this ability varied between the Apollo missions: from only controlling the S-IVB in a particular mission phase to the ability take over flight control over the entire launch vehicle in every mission phase during ascent.

Personal reminder 2
I need to check on the IMU whether the attitude data were part of the output or whether the CMC was needed to calculate the attitude based on the angular rates from the IMU.

The Apollo CSM Flight Director Attitude Indicator (FDAI)

FDAI display modes

	11	12	13
Mode	Switch positions			FDAI 1		FDAI 2
Mode	FDAI SEL	FDAI SRC	ATT SET	Attitude	Error	Attitude	Error
1	1	CMC	not relevant	IMU	CMC	FDAI 2 is OFF
2	1	ATT SET	IMU	IMU	Δ(IMU, ASCP)
3	1	ATT SET	GDC	GDC	Δ(GDC, ASCP)
4	1	GDC	not relevant	GDC	BMAG 1
5	2	CMC	not relevant	FDAI 1 is OFF		IMU	CMC
6	2	ATT SET	IMU			IMU	Δ(IMU, ASCP)
7	2	ATT SET	GDC			GDC	Δ(GDC, ASCP)
8	2	GDC	not relevant			GDC	BMAG 1
9	1/2	not relevant		IMU	CMC	GDC	BMAG 1

Figure 2.2
The Apollo CSM Flight Director Attitude Indicator (FDAI)

Text

Based on ref.xxxx
Figure 2.3 The Apollo CSM control panel and the systems in the lower equipment bay
Text BMAG: Body Mounted Attitude Gyro ECA: Elctronic Control Assembly EDA: Electronic Display Assembly GDC: Gyro Display Coupler RJEC: Reaction Jet & Engine Control TVSA: Thrust Vector Servo Amplifier

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Based on ref.xxxx
Figure 2.4 Text
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Apollo CSM control panels for operating the Primary Guidance, Navigation & Control System and the Stabilization & Control System

Apollo_CSM_PGNCS-SCS-ControlPanel

Credtit to NASA's Apollo Space Simulation Project

Figure 2.5
Apollo CSM control panels for operating the Primary Guidance, Navigation & Control System and the Stabilization & Control System

Eight groups of switches for selecting the NGC control modes.
In the picture above seven groups of switches are indicated which were used to select the various control modes for attitude & translation control and thrust vector control.

1
Switch group 1 (one switch) "SC CONT"
For selecting the NGC control mode of the Apollo spacecraft (SC) out of two possible modes:
CMC
SCS

2
Switch group 2 (one switch) "CMC MODE"
For selecting the control mode of the Command Module Computer (CMC) out of three possible modes:
AUTO
HOLD
FREE

3
Switch group 3 (three switches) "MANUAL ATTITUDE"
For selecting the control mode of manual attitude for the three rotation axes ROLL, PITCH and YAW. The control modes could be selected for each rotation axis seperately out of three possible modes:
ACCEL CMD
RATE CMD
MIN IMP

4
Switch group 4 (three switches) "BMAG MODE"
For selecting the signal outputs of the two body mounted gyros for the three rotation axes ROLL, PITCH and YAW. The signal outputs could be selected for each rotation axis seperately out of three possible modes:
RATE2
ATT1 & RATE2 CMD
RATE1

5
Switch group 5 (two switches) "SCS TVC"
For selecting the control modes of thrust vector control for the two rotation axes PITCH and YAW. The control modes could be selected for each rotation axis seperately out of three possible modes:
AUTO
RATE CMD
ACCEL CMD

6
Switch group 6 (two switches) "ROT CONTR PWR / NORMAL"
The rotation hand hand controllers were equipped with two groups of switches. The first group of switches were used for controlling the attitude manually in the normal control mode whereby the control signals from the hand controllers were sent to control electronics which controlled the RCS thrusters. The second group of switches were used to control the RCS thrusters directly.
Two power switches for the two rotation hand controllers for NORMAL operation. Each hand controller could be powered seprately. There were three power settings:
AC / DC
OFF
AC

7
Switch group 7 (two switches) "ROT CONTR PWR / DIRECT"
The rotation hand hand controllers were equipped with two groups of switches. The first group of switches were used for controlling the attitude manually in the normal control mode whereby the control signals from the handcontrollers were sent to control electronics which controlled the RCS thrusters. The second group of switches were used to control the RCS thrusters directly.
Two power switches for the two rotation hand controllers for DIRECT operation. Each hand controller could be powered seprately. There were three power settings for hand controller 1:
MNA / MNB
OFF
MNA
And three power settings for hand controller 2:
MNA / MNB
OFF
MNB

8
Switch group 8 (one switch) "TRANS CONTR"
The translation handcontroller was equipped with switches for controlling the translation movements in the X-, Y- and Z-direction manually. The signals from the translation hand controller were sent to the the control electronincs which controlled the RCS thrusters. Or the signals were sent to the logic circuitry which drove the valves of the RCS thrusters. There were three power settings for the translation hand controller:
OFF
PWR

Two groups of switches to select the control loop's response

9
Switch group 9 (one switch) "LIMIT CYCLE"
Text. There were two settings:
OFF
ON

10
Switch group 10 (two switches) "DEADBAND"
Two settings for the attitude deadband:
MAX
MIN
And two settings for the rate deadband:
HIGH
LOW

Credit to NASA

Figure 2.6

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Credit to NASA

Figure 2.7
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Figure 2.8
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3.Attitude & Translation Control Modes

Switch Settings for selecting the various Attitude & Translation Control Modes

			Attitude & Translation Control Modes
			AUTO	MANUAL CMC			MANUAL SCS
	Switch	Switch positions	DIGITAL AUTO-PILOT	CMC CONTROL AUTO	CMC CONTROL ATT HOLD	CMC CONTROL FREE	SCS CONTROL RATE CMD	SCS CONTROL ATT HOLD	SCS CONTROL MIN IMP	SCS CONTROL ACCEL CMD	SCS CONTROL DIRECT CMD
	Switch	Switch positions	Fig. 3.1	Fig. 3.2			Fig. 3.3	Fig. 3.4	Fig. 3.5	Fig. 3.6	Fig. 3.7
1	SC CONTROL	CMC	X	X	X	X
1	SC CONTROL	SCS					X	X	X	X	X
2	CMC MODE	AUTO	X	X			not relevant	not relevant	not relevant	not relevant	not relevant
		HOLD			X
		FREE				X
3	MANUAL ATTITUDE (YAW, PITCH, ROLL)	ACCEL CMD	not relevant	not relevant	not relevant	not relevant				X	not relevant
		RATE CMD					X	X
		MIN IMPULSE							X
4	BMAG MODE (YAW, PITCH, ROLL)	RATE 2	not relevant	not relevant	not relevant	not relevant	OR		not relevant	not relevant	not relevant
		ATT 1 / RATE 2						X
		RATE 1					OR
5	SCS TVC MODE	AUTO	not relevant
		RATE CMD
		ACCEL CMD
6	ROTATION CONTROL POWER NORMAL	OFF	X
6	ROTATION CONTROL POWER NORMAL	ON		X	X	X	X	X	X	X	X
7	ROTATION CONTROL POWER DIRECT	OFF	X	X	X	X	X	X	X	X
7	ROTATION CONTROL POWER DIRECT	ON									X
8	TRANSLATION CONTROL POWER	OFF	X
8	TRANSLATION CONTROL POWER	ON		X	X	X	X	X	X	X	X
	RHC BREAKOUT SWITCH	OFF	X
	RHC BREAKOUT SWITCH	ON		X	X	X	X	X	X	X	X
	RHC DIRECT SWITCH	OFF	X	X	X	X	X	X	X	X
	RHC DIRECT SWITCH	ON									X
	THC BREAKOUT SWITCH	OFF	X
	THC BREAKOUT SWITCH	ON		X	X	X	X	X	X	X	X
	THC DIRECT SWITCH	OFF	X	X	X	X	X	X	X	X
	THC DIRECT SWITCH	ON									X

MANUAL ATTITUDE and BMAG could each operate in three modes. For each rotational movement, YAW, PITCH and ROLL, these control modes could be selected separately.
For example, for YAW and PITCH MANUAL ATTITUDE control mode, ACCEL CMD could be selected and for ROLL, the control mode RATE CMD.

Figures 3.1 through 3.7 show the signal paths between the subsystems that were relevant in the various control modes.

"not relevant" means that the switch positions does not affect the concerned control mode.

Diagram based on xxxxxxx
Figure 3.1
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Figure 3.2
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Figure 3.3
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Figure 3.4
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Figure 3.5
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Figure 3.6
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Figure 3.7
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4.Thrust Vector Control Modes

Switch Settings for selecting the various Thrust Vector Control Modes

			Thrust Vector Control Modes
			AUTO		MANUAL CMC			MANUAL SCS
	Switch	Switch positions	TVC DIGITAL AUTO-PILOT	SCS AUTO TVC	CMC CONTROL AUTO	CMC CONTROL ATT HOLD	CMC CONTROL FREE	MTVC RATE CMD	MTVC ACCEL CMD
			Fig. 4.1	Fig. 4.2	Fig. 4.3 (to be checked)			Fig. 4.4	Fig. 4.5
1	SC CONTROL	CMC	X		X	X	X
		SCS		X				X	X
2	CMC MODE	AUTO	X	not relevant	X			not relevant	not relevant
		HOLD				X
		FREE					X
3	MANUAL ATTITUDE (YAW, PITCH, ROLL)	ACCEL CMD	not relevant
		RATE CMD
		MIN IMPULSE
4	BMAG MODE (YAW, PITCH, ROLL)	RATE 2	not relevant		not relevant	not relevant	not relevant		not relevant
		ATT 1 / RATE 2		X				X
		RATE 1
5	SCS TVC MODE	AUTO	not relevant	X	not relevant	not relevant	not relevant
		RATE CMD						X
		ACCEL CMD							X

"not relevant" means that the switch positions does not affect the concerned control mode.

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Figure 4.1
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Figure 4.2
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Figure 4.3 (to be checked)
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Figure 4.4
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Figure 4.5
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5.Title

Acronyms
ASCP Attitude Set Control Panel BMAG Body Mounted Attitude Gyro CDU Coupling Data Unit CMC Command Module Computer DSKY Display and Keyboard ECA Electronic Control Assembly EDA Electronic Display Assembly FDAI Flight Director Attitude Indicator FPI Fuel Pressure Indicator GDC Gyro Display Coupler GPI Gimbal Position Indicator IMU Inertial Measurement Unit MIC Minimum Impulse Controller MTVC Manual Thrust Vector Control	ORDEAL Orbital Rate Display - Earth And Lunar PIPA Pulse Integrating Pendulous Accelerometer PGNCS Primary Guidance Navigation & Control System RCS Reaction Control System RHC Rotation Hand Controller RJEC Reaction Jet & Engine Control SCS Stabilization and Control System SPS Service Propulsion System THC Translation Hand Controller TVC Thrust Vector Control TVSA Thrust Vector Servo Amplifier UPTLM Uplink Telemetry

Acronyms

ASCP Attitude Set Control Panel
BMAG Body Mounted Attitude Gyro
CDU Coupling Data Unit
CMC Command Module Computer
DSKY Display and Keyboard
ECA Electronic Control Assembly
EDA Electronic Display Assembly
FDAI Flight Director Attitude Indicator
FPI Fuel Pressure Indicator
GDC Gyro Display Coupler
GPI Gimbal Position Indicator
IMU Inertial Measurement Unit
MIC Minimum Impulse Controller
MTVC Manual Thrust Vector Control

ORDEAL Orbital Rate Display - Earth And Lunar
PIPA Pulse Integrating Pendulous Accelerometer
PGNCS Primary Guidance Navigation & Control System
RCS Reaction Control System
RHC Rotation Hand Controller
RJEC Reaction Jet & Engine Control
SCS Stabilization and Control System
SPS Service Propulsion System
THC Translation Hand Controller
TVC Thrust Vector Control
TVSA Thrust Vector Servo Amplifier
UPTLM Uplink Telemetry

References

Apollo Guidance, Navigation and Control (GNC) Hardware Overview
Slidedeck
by Micheal Interbartolo
NASA, Houston, Texas, 2009
Apollo Astronaut's Guidance and Navigation Course Notes
Prepared by MIT Instrumentation Laboratory
Sections:
1. Functional View of The Apollo Guidance & Navigation System (November 1962)
2. Gyro Principles (December 1962)
3. Stabilization (December 1962)
4. Electromagnetic Navigation (by Janusz Sciegienny, December 1962)
5. Midcourse Navigation and Guidance (by Dr. Richard H. Battin Jr. February 1963)
6. Re-entry Guidance (by Daniel J. Licky, March 1963)
7. Optics (by Robert J. Magee, February 1973)
Ref.
Ref.
Ref.

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