MATING MODULES IN SPACE
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 interconnects.
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.) They 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 Brian Mitchell, NASA's CBM subsystem manager.
Not until October 1999, when astronauts attach the Z-1 truss to Unity, will the figurative sparks fly. (Oh my.)
