NASA uses SureBolt to verify it's Space Station design.

This small picture is one of the final reports (press on the picture to enlarge). Notice the repeatability and sensitivity of the SureBolt^TM prototype.

Background: NASA needed to verify that their Space Station Node design would be safe. A big part of the verification depended on the special bolts used to hold the CBM Attach Ring to the Nodes. The years of service of the Space Station would be strongly dependent on the fatigue and tension characteristics of these bolts. Each hatch (6 hatches per Node) uses approximately 225 bolts.

Space Station Tests: How do you measure any tension change in these bolts as the Node is pressurized? How do you make sure the extra tension is distributed evenly? How do you measure the preload tension? Normally you rely on a torque wrench for preloads. But a torque wrench is known to only be +- 20% reliable or worse.

A more accurate way is to use an ultrasonic bolt gage. Ultrasonic bolt gages (at about $20,000 each) have been around for many decades. But they do not work very well on small bolts like these 2.25 inch length Space Station bolts. But, NASA needed these measurements. So a new type of ultrasonic bolt gage was invented for this difficult application.

OVERALL CHALLENGE;

NASA needed more reliability, more measurements (they had to measure 8 bolts at a time), and the ability to read remotely (from 400 feet away) while the Node was being pressurized. Plus or minus 20% error would be too much. New technology would have to be used.

OVERALL OBJECTIVE:

Measure 8 bolts at a time remotely (from 400 feet away), while the Node was being pressurized. Increase reliability if possible and monitor each measurement's reliability.

SPECIFIC CHALLENGES:

	Coupling to the threaded non-head end of the bolt,
	Control the oscilloscope remotely and download the waveforms,
	These bolts are so small (diameter), that the signal strength is low even with the best piezo-electric transducers,
	Remotely control the standard (one-point) bolt gage's gain, hold-off, and threshold,
	Display and analyze the data,
	Develop a digital signal processing technique (DSP) and compare it to the standard Bolt Gage reading. (This turned out to be the first SureBolt`^TM` prototype.)
	Use the one-point remote bolt gage measurement for comparison.
	The old technology one-point bolt gage was the only instrument that was officially calibrated.
	Recreate the normal bolt gage technique in software to compare to the old technology one-point bolt gage and the new digital signal processing technique (SureBolt`^TM` prototype)

RESULTS;

	These challenges were met and exceeded. The new SureBolt`^TM` prototype worked well on 100% of all tensions on all bolts. The new digital signal processing (DSP) technique was the most reliable and accurate, but it was not "officially" accepted as calibrated until the 3rd test.
	3rd Node test. 100% reliability. The design engineers now wanted the tension from the DSP technique along with the old technology one-point bolt-gage tension measurements.
	4th Node test. The engineers only wanted the tension from the new DSP technique. The old bolt-gage tensions were ignored.
	Unexpected super-sensitivity test. The Huntsville engineers were so pleased with the reliability and precision of the new SureBolt`^TM` prototype, that they wanted to verify another Space Station design. They wanted to know how much the tension would change in a bolt while its adjacent bolt was being tensioned. The new SureBolt`^TM` prototype was able to detect CHANGES smaller than plus or minus 50 pounds (out of a preload tension of 3600 pounds). The new instrument was so sensitive that the radiant heat from the operator caused the temperature sensor near the bolt to change which looked like 10 to 20 pounds of tension until the operator walked away. Our main source of error became temperature measurement.

SureBolt^TM prototype HARDWARE:

	Next to the Space Station we installed; one oscilloscope (set to one billion samples per second), RS422 communication line converters, a GPIB extender, a "one point" bolt gage used as only a pulser, a custom designed switcher remotely controlled.
	400 feet away in the control room we installed: two full sized desktop computers, printer, GPIB extension box, RS422 serial converters, and cables.

Now ARVC has developed the technology to the extent that the SureBolt^TM single channel unit fits into a customized Panasonic Toughbook Model 72 laptop computer.

For more information, see the main SureBolt^TM navigation screen.

"Echo Time". Animation below of how to ultrasonically measure the change in bolt tension using echo time.
This animation requires FLASH (version 4 or higher).

NASA's Space Station Development Marshall Space Flight Center, Huntsville, AL

NASA's Space Station Development
Marshall Space Flight Center, Huntsville, AL