The Apollo Spacecraft - A Chronology.

Appendix 8

Block II vs. Block I Apollo Spacecraft;

Hardware, Changes, Tests

[From "Manned Space Flight Report: Block II Spacecraft" in House Committee on Science and Astronautics, Subcommittee on NASA Oversight, Investigation into Apollo 204 Accident: Hearings, 90th Cong., 1st sess, 3, no. 4, May 10, 1967, 223-35.]

Subsystems and Units Unchanged for Block II CSM

  • Launch escape system
  • Command module reaction control system
  • Service module reaction control system engine cluster
  • Fuel cell power plants and entry batteries
  • Cryogenic oxygen and hydrogen storage system
  • Sequential events control system
  • Emergency detection system
  • Spacecraft LM adapter
  • Atmosphere supply system
  • Primary equipment cooling loop
  • Waste management system
  • Crew couches
  • C-band radar transponder
  • Ordnance devices
  • Parachutes and recovery aids

New Subsystems and Units in Block II CSM

Docking system
Docking tunnel and probe

Umbilical and pressurization

Rendezvous radar transponder

Sequence controllers
LM docking and separation events
S-band antennas
Flush omnidirectional

High gain

Subsystems and Units Changed in Block II CSM


Command module
Docking provisions, mechanism, and hatch

Extravehicular capability

CM/SM mechanical connection

Scientific airlock available

Service module
Propellant tanks

Empty bay

Internal rearrangement

Structural redesign

Radiator areas

RCS mounting panels


Service module propulsion system
Mixture ratio

Thrust chamber

Gimbal actuator

Service module reaction control
Propellant capacity

Monomethylhydrazine fuel

Crew support:

Environmental control system
Redundant cooling loop

Radiator design and area

Apollo suit

Extravehicular capability

Displays and controls
Panel structure

Electroluminescent lighting

Entry monitor system

Power and communication:

Electrical power system
Radiator area

Distribution bus added

Cable harnessing

Pyrotechnic initiator

Wire deadfacing at separation

Unified S-band
Primary mode for all communications


Simultaneous data and tape dump or TV

Electrical redundancy

Voice VHF
Redundant and duplex

Guidance and control:

Guidance and navigation
Digital autopilot

Computer repackaged

Electronics repackaged

Navigation base support

Stabilization and control system
Revised interface

Electronics repackaged

Redundant attitude display

Atmospheric entry and touchdown:

Redistributed ablative thickness

Truncated apex

Umbilical location

Flush antennas

Earth-landing system
Steel parachute risers

Parachute attach points


Crew Safety Systems

  • Launch escape system
  • Emergency detection system
  • Sequential events control system
  • Earth-landing system
  • Environmental control system
  • Reaction control system
  • Electrical power system
  • Command module heatshield
  • Structure system

Mission Success Systems

  • Spacecraft adapter
  • Waste management system
  • Guidance and control system
  • Stabilization and control system
  • Communications system
  • Displays and controls
  • Service propulsion system

Subsystems with Internal Redundancy

(Subsystem)(Major function)
CM reaction control systemAttitude control

Lift vector control

SM reaction controlAttitude control

S-IVB/CSM separation

CM/SM separation

Communications systemNavigation data

Voice, telemetry, and tracking


Electrical power systemElectrical power
Environmental control systemEquipment cooling

Cabin environmental control

Sequential events control systemSeparation signals

Earth-landing functions

Emergency detection systemLaunch vehicle malfunction
Earth-landing systemAtmospheric descent

Uprighting at impact

Backup System Capabilities for Earth-Orbital Flight

SubsystemMajor FunctionBackup
Service propulsion systemDeorbitSM-RCS; CM-RCS
Command module reaction control systemAttitude controlSM-RCS spinup before separation for ballistic reentry
Guidance and control systemAttitude, translation, and lift vector control

Control of SPS burns

Stabilization and control system
Stabilization and control systemBackup attitude, translation, and SPS controlManual

Flight Safety Systems Changed in Block II

  1. Earth-landing system
  2. Service module reaction control system
  3. Electrical power system
  4. Environmental control system
  5. Command module heatshield
  6. Structural system
  7. Service propulsion system

Environmental Control System Changes for Block II before AS-204 Accident

  1. New radiator design:
    • Increased size.
    • Selective stagnation control.
    • Secondary loop tubes.
  2. Secondary coolant loop:
    • Additional pump.
    • Redundant cold plate passages.
  3. Repackage environmental control unit (ECU):
    • Coolant pumps relocated external to ECU, repackaged, and capacity increased.
    • Coolant reservoir located external to ECU.
    • Redesigned suit heat exchanger.
  4. LM pressurization capability.
  5. Relocate postlanding ventilation valves.
  6. Redesign steam duct.
  7. Add rendezvous radar cold plates in SM.

Proposed ECS Changes for Block II after AS-204 Accident

  • Add armor plating to exposed solder joints.
  • Change soldered-aluminum oxygen lines to stainless steel.
  • Rapid cabin repressurization.
  • Improve accessibility of selected ECS controls.
  • Shields for plumbing lines.
  • Optional use of air in cabin during launch.
  • Emergency breathing masks.
  • Add quick disconnects to environmental control unit.
  • Replace selected materials.

Block I - Major Ground Test Programs

Test ArticleTestPurpose
CM BP-6AParachute drop-testing of boilerplate CMFlight-qualify earth recovery system by series of aircraft drop tests
SM-001SPS propulsion ground testDemonstrate SPS performance (oxidizer-to-fuel ratio = 2), 2nd SPS-structure compatibility
SLAStatic structural test of spacecraft-LM adapterTest SLA static structural load capability (ultimate)
CSM 004Static and thermal structural ground testCM static structural load test (ultimate)

CSM static structural load test (ultimate)

CM thermal structural load test (reentry design)

CSM 007Varied spacecraft testingCM and SM acoustic vibration environment test

CM water-landing impact drop test

Postlanding systems operational/crew compatibility tests (uprighting, postlanding ECS, postlanding communications)

CSM 008Thermal vacuum test of complete systems spacecraftDemonstration of structural, integrated subsystems and crew compatibility under thermal vacuum environment

White Sands Missile Range Flight Tests

Test ArticleTestPurpose
BP-6Boilerplate - LES pad abort flight testDemonstrate launch escape system's pad abort performance
BP-12Boilerplate - LES transonic abort flight testDemonstrate launch escape system's transonic abort performance
BP-23Boilerplate - LES high-dynamic-pressure abort flight test Demonstrate launch escape system's maximum-dynamic-pressure-region abort performance
BP-23ABoilerplate - LES pad abort flight test Demonstrate launch escape system's pad abort performance with Canard, BPC, and major sequencing changes
CSM 002Spacecraft structure - SM boost environment and LES tumbling abort flightDetermine actual spacecraft SM's dynamic structural response to boost dynamic loads

Demonstrate launch escape system's tumbling abort performance and plume-impingement-load capability of CSM

Block II - Major Ground-Test Programs

Test ArticleTestPurpose
BP-6BParachute drop-testing of boilerplate CMFlight-qualify earth recovery system by series of aircraft drop tests
F-2AFixture for SPS testingEvaluate performance effects on SPS engine of fuel and oxidizer mixture's ratio change from 2.0 to 1.6
180 degree SM segmentAcoustic test article (SM) testingQuality SM structure and systems to launch and boost vibration environment
CM 28-1Static and dynamic structural testingEvaluate water impact on CM structure

Docket CM/LM interface static structural tests

CMS 2S-2Static structural testingStatic-test CM and SM structures (ultimate)
CMS 2TV-1Complete systems spacecraft thermal vacuum testingDemonstrate structural, integrated subsystems, crew compatibility, and life support in thermal vacuum environment

Block II - Revisions of and Additions to Major Ground-Test Programs

Test ArticleTestPurpose
2TV-1Complete spacecraft thermal vacuumQualify fire related changes
004A, 007AUnified hatch qualificationFunctionally qualify acoustic testing, postlanding testing
CSMAcoustic vibrationDemonstrate functional and structural integrity of stacked CSM-SLA
MaterialMaterials evaluationContinue evaluation of non- or low-flammable material
BoilerplateCommand module fire testEvaluate fire propagation in flight-configuration CM interior
EMU articlesExtravehicular mobility unit qualificationQualify Block II unit with materials change
ECU articlesEnvironmental control unit qualificationQualify Block II unit with all required modifications