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Why were the three 122-cm diameter conductive spheres for charge collection in the Shuttle's Space Experiments with Particle Accelerators black? links to How did three 1.2 meter spheres and a Xe+ plasma contactor keep the Shuttle "grounded"? What did they look like? which links to Space Experiments with Particle Accelerators (SEPAC) (the button labeled Deepblue.Lib.Umich.Edu provides an open access downloadable copy of the paper) which includes the following:

INTRODUCTION

[...]At this energy the perveance-limited electron gun can emit beam currents of up to 1.21 A. The previous flight of SEPAC on Spacelab 1/2/ showed that at these levels special means of neutralizing the Shuttle are necessary; therefore, for ATLAS 1 the SEPAC instrument complement included three 122-cm diameter conductive spheres for charge collection and a 1.6 A hollow-cathode Xe+ plasma contactor.

with author affiliation

  • Southwest Research Institute, San Antonio, TX
  • NASA/Marshall Space FLight Center, Huntsville, AL
  • Nichols Research Corporation, Arlington, VA
  • ISAS, Tokyo
  • The University of Michigan, Ann Arbor, MI
  • Lockheed Palo Alto Research Laboratory, Palo Alto, CA
  • Princeton University, Princeton, NJ

However this answer to Why were the three 122-cm diameter conductive spheres for charge collection in the Shuttle's Space Experiments with Particle Accelerators black? includes:

From page 10 of "Space Experiments with Particle Accelerators (SEPAC): Description of instrumentation":

[...] With this mounting arrangement, the 1020 mm diameter spheres will increase the conducting area of the Shuttle by about 8%, and they will present very nearly the same cross-sectional area for most attitudes.

Which links to NASA Technical Memorandum TM-89728 "Space experiments with particle accelerators (SEPAC): Description of instrumentation" with author affiliation:

  • TRW Defense Systems Group Redondo Beach, CA
  • NASA Marshall Space Flight Center Huntsville, AL
  • Southwest Research Inst. San Antonio, TX
  • General Digital Industries, Inc. Huntsville, Ala., United States)

I've called the numerical disparity between 122 cm and 102 cm as a conundrum in a teacup and apparently I like those.

Question: Who's buried in Grant's Tomb?1 What is the size of the 122 cm conductive spheres charge collection in the Shuttle's Space Experiments with Particle Accelerators?


1Why did the phrase, "Who is buried in Grant's Tomb, " become so famous? and Goodbye to Grant

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