This document summarizes early engineering work from 1984-1985 to design connections between pressurized crew modules for a Space Station. It describes initial concepts using flexible metal bellows and actuators to allow movement between modules under atmospheric pressure, but these designs risked modules being forced apart by air pressure. Later concepts evolved to a simpler rigid connection, assembled slowly, to minimize these risks. Visual explanations like comparing the pressure forces to a swaying concrete cube helped convey the problem and influence the redesign towards today's safer module joints.

1. The Need for Visual Thinking
Lockheed submitted Space
Station Phase A Proposal 1984
• Included work package
2, structures
Project included engineering to
connect pressurized crew
modules
Rapid design needed, to check
feasibility
384 ft
5 connected pressurized crew modules
(each was the size of a school bus)
Little was decided about the Inter-module joint—
— how do we make this happen?
Entire Space Station was just a sketch in 1985

2. Evaluating Module Joint with Sketch Designs
(“Napkin Drawings”)
Late Phase A, Dec 84 to Apr 85
Project:
Rough-estimate design difficulty
of connecting two crew modules
for Space Station
Required
• Rigid joints module-to-frame
• Module-module joints 6 DOF
(fully free to “breathe”)
• 1 atm pressure (14.7 psi)
• 50 inch clear passageway
Work performed by John Nurre
(Lockheed) for NASA GSFC
My assignment: module
connections
Dec 1984

3. Early Study of Clocking Alignment
Alignment “petals” based
on Apollo-Soyuz
heritage, and NASA JSC
Desires
• Gradually align ports (and
lock mechanisms) as
interfaces approach
Cable Concept gradually
abandoned
• Remote docking desired
• Actuators for 6 DOF
motion could
accommodate
Dec 1984

4. Evolving Overall Design
Jan 1985
Metal Bellows to
allow flexibility with
reliable air seal
Motorized actuators (with
sophisticated software) resist 1-atm
pressure while allowing flexibility
Note actuators and
clamps are within
the bellows
• Allows crew
member servicing

5. Mar
Maturing Design transferred into CAD Layout
Bearing allows rotary
motion
• Accommodation of
bellows, that will
allow no torsion
Note
actuators, clamp
motors (etc) are now
external
• Minimize inflation
force at 14.7 psi

6. Realizing a Very Large Problem
• As a manned facility:
• Large pass-through hatches
• Atmospheric pressure (14.7 psi)
– For controlled flight:
• want independent modules
• modules attached to structure separately
• “perfect” module-module flexibility
– Issue: pressure inflation of flexible joint
• Air will force “independent” modules apart

7. Describing a Problem, Visually
• “Engineer’s Waltz”
– 40,000-pound air load (60 inch pass-thru at 14.7 psi)
– Connection is automatic: no manual connection or checks
– Joint must bob and swing with perfect freedom
– Astronauts (and NASA) must trust this joint, perfectly
• Question: would YOU stand under a swaying 6’9” concrete cube?
• The problem (and arguments like this) began to change the system
design
Apr 1985

8. Today’s Space Station Module Joint Evolved from Early Studies
Rigid joint (no bellows)
• Far less complexity
and cost
Smaller alignment features
• Assemble slowly and
carefully
Door and clamp ring have
same diameter
• Minimize pressure effects
NASA reshaped requirements, allowing modern design