 |
| Sewing as Rocket Science |
MORTON THIOKOL:
A PTS CUSTOMER SUCCESS STORY |
 |
|
|
When Tayco (a Morton Thiokol subcontractor) asked PTS to build a set of
Kevlar straps for the space shuttle program, the PTS team was proud if a
little apprehensive.
|
To be asked to help solve the shuttle's infamous O-ring problem was a
vote of engineering confidence. At the same time, PTS knew how difficult
it was going to be. Kevlar is like a headstrong opera diva. It is
beautiful. It is amazingly strong. It can do incredible things. But it
is so temperamental that working with it would test the patience of a saint.
It drove us all nuts, says Sally Lindsay Honey, PTS's founder, of the
effects of the whole fabrication/quality assurance process on her team.
This project was just unbelievably hard to do. |
 |
| Our Founder |
|
|
|
A LOT AT STAKE
When the Challenger exploded in 1986, the cause of the disaster was
determined to be cold weather. Specifically, ice formed in the seals
between sections of the shuttle's solid-rocket boosters. The O-rings in
the seals failed, the seals broke, and superheated exhaust gases
blowtorched onto the external fuel tank, which exploded.
|
 |
| The Straps Take Off |
|
If cold was the problem, Morton Thiokol's engineers thought heat was the
solution. They proposed creating a set of 40-foot-long heating elements
and wrapping them around the outside of the solid-fuel boosters, on top
of the seals, to keep their O-rings warm and flexible. But the boosters
weren't designed for such heating elements, and the engineers thought
long and hard about an easy way to keep them in place. After all, there
was a lot more at stake than just a defense contract.
Enter Kevlar. Tayco, the subcontractor, developed a design using
Kevlar's incredible strength and low degree of stretch to keep the
heating elements in place even during the pandemonium of liftoff. But
design is one thing; building a sewn solution of such unforgiving
material, to such fine tolerances, for an ultimate test in the glare of
worldwide publicity that's something else.
|
|
STITCHES IN SPACE
Enter PTS. They started the project with Milspec plans, but to actually
make it happen took a lot more than that:
 PTS had to use Kevlar webbing fabricated in a herringbone pattern
especially for the tapes so that its linear stretch was less than 1/16th
inch when placed under a 100 lb. load;
Once the webbing was fabricated, it had to be cut to accommodate that
load and still stay within the 1/16th in. tolerances;
All sewing had to be in a specific Z pattern, with exactly the
specified number of stitches horizontally and diagonally;
All sewing had to be continuous. Any time the thread broke, the entire
section had to be ripped out and re-done;
Once the straps were successfully sewn, they were subjected to a
rigorous stretch-test in all dimensions. If they stretched more than the
required 1/16th inch, then the entire strap had to be re-built.
"We spent agonizing hours making sure those straps were built to spec"
says Honey. "But it was all worth it in the end. When the new shuttle
went up, we got a call from the customer saying, "Take a good look, those
are your straps, and they're headed for outer space.""
|
|
