Historical Photo of the Month - July 2009

Pneumatic Cannon
Photograph Number 355-1387Bc

The June 2009 Historical Photo featured an inflated Mylar impact limiter designed to protect a payload during a hard landing on the surface of a planet. Above is the launching mechanism that was used to test it. Al Delgadillo, who was in charge of fabrication and assembly, stands next to the 22-inch-diameter pneumatic cannon in building 18.

The impact test facility was located in a 500-foot-long concrete channel near building 103 which was used in the 1940s for the hydrobomb project. A 10-foot- diameter, 25-foot-long chamber was placed in the channel, with the cannon at one end. The webbed basket was inside the chamber, with the ram passing through a sealed opening. The chamber was placed under a vacuum of 2 psi in order to simulate the conditions of space. The Ramset pistol on the floor was used to release the internal piston. High speed motion picture cameras recorded the tests as the impact limiter was pushed into a target at the far end of the chamber. A catch screen made of chain link fence dropped down as the limiter passed the center of the tank, to prevent it from rebounding into the launcher basket.

The prototype limiter was tested at 100 ft/sec, then 165 ft/sec. After the second test, it was too badly damaged to permit further tests. Some of this damage was not from impact, but from getting caught in the screen and slammed to the floor. Static testing indicated that the limiter could withstand a 200 ft/sec impact, the anticipated velocity for a planetary landing.

For more information about the history of JPL, contact the JPL Archives for assistance, and see previous Historical Photos about the impact limiter and the channel. [Archival and other sources: Ron Ross; Bill Layman; photo album and index; The Design and Testing of an Inflated Sphere Impact Limiter, December 15, 1966, Technical Report 32-1037, by Ross and Layman; The JPL High-Impact Program - 1965, February 1, 1966, Technical Report 32-844, by J.L. Adams.]