Williams, J.S. & Ferry, P.B. LARGE RADIOISOTOPE HEAT SOURCE CAPSULE PROGRAM. TOPICAL REPORT NO. 4. T- 111 PRESSURE VESSEL DEVELOPMENT AND FABRICATION., report, January 1, 1968; (https://digital.library.unt.edu/ark:/67531/metadc1028751/m1/1/: accessed August 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .