Mating modules in space

Joachim Feise (
Fri, 04 Dec 1998 17:12:50 -0800

By Jane Ellen Stevens

Who says engineers can't be romantic?

To link most of the International Space Station's modules, they designed a
mating mechanism made up of active and passive fasteners. By applying feminine
and masculine characteristics to these parts, us hopeless romantics have a
metaphor to help us understand how the space station

The Space Station partners gave one company, Boeing Space Systems, the job to
design, manufacture and test the active and passive parts (also known as "Common
Berthing Mechanisms" or CBMs). That's a good thing, since all the pieces need to
be speaking the same "international language." Most of the U.S. modules' parts
are Active, and those on most other countries' modules are Passive. (No comments
from the peanut gallery, please.)

The active model contains the moving and powered mechanisms (e.g., capture
latches), the passive model, the static mechanisms (e.g., capture fittings).

Now for the juicy stuff.

The active and passive parts don't just slam into each other. (Oh, no, no, no.)
go through an elaborate mechanical courtship before they join.

What happens at the International Space Station is berthing, which requires
finesse. (Take notice, those of you who do not believe in the slow hand and the
easy touch.)

The courtship begins with Active and Passive models each opening their petals.
These protect their inner seals from meteoroids. An astronaut (well, someone has
to introduce them!) uses the remote manipulator arm to nudge the Passive model
close to the Active model, so the rings come within just a few tantalizing
inches of one another. (No touching. Not yet.)

They align, and when they're ready (they know because an indicator lights up --
isn't that just like love), the Active model gently reaches out to the Passive
model and pulls them together.

Oh, but it's not over yet.

Just before the two kiss metal-to-metal, the models align themselves with even
more precision (there's just no room for error in space). Passion, as always,
builds, and the models move from being soft-berthed to hard-berthed (be still my
heart) when 16 powered bolts (there's lots of
redundancy in space) extend into the nuts and tighten down -- slowly, gently,
one at a time.

There Active and Passive remain, steadfast and true. No amount of hard knocks
and or torqueing of the station can rend them asunder, unless, of course, the
astronauts wish it so.

Alas, no Passive and Active parts will join during this first Unity mission. The
link between the first two modules is by way of a tunnel with a Russian
mechanism that's androgynous, says Mitchell.

Not until October 1999, when astronauts attach the Z-1 truss to Unity, will the
figurative sparks fly. (Oh my.)