Scientists from NASA’s Marshall Space Flight Centre have created a mechanical device for applying an adhesive patch, from the outside, to the wall of a spacecraft that has lost pressure because of penetration by a meteoroid or a piece of orbital debris.
The scientists claim that the device will make it possible to seal and re-pressurise the affected module during space flight and that a device identical or similar to this one might also have uses on earth in the repair of other pressurised bodies.
The device is said to include a patch frame, which is moved toward the hole to be patched from the exterior side of the damaged wall by use of handles and a flexible outer sealing ring that becomes moulded against the wall. Another component of the device is a probe that includes a right-hand-threaded shank and equipped with an assembly of spring-loaded sprags at its penetrating tip.
Sealing a hole is said to involve inserting the probe into it, whereupon the sprags spring outward. The probe is then turned anti-clockwise to draw the sprag assembly toward the patch frame; as a result, the sprags are forced against the inside edge of the hole in the wall.
As the probe continues to turn, the sprag assembly stays in place and the flexible outer sealing ring on the patch frame becomes pushed against the wall on the outside, creating a seal between the patch frame and the wall.
The volume enclosed by the patch frame, wall, and outer sealing ring (patch body volume) is then filled with a liquid adhesive sealant material to create a permanent seal and strong adhesion between the patch and the wall.
NASA stress the patch is not a substitute for the loss of structural strength caused by the penetration. However, an adhesive-interface plate on the patch frame strengthens the adhesive bond between the patch frame and the wall, so as the adhesive flows into the patch body volume, it flows onto and around hooks that protrude from the adhesive-interface plate.
Once the adhesive hardens, the patch is held in place against the tensile loads induced by re-pressurisation of the interior of the spacecraft module, pipeline, or other volume enclosed by the wall.