103 Development and Post -testing Anoma lies of the  Parker Solar Probe Clamshells  

Mark Bryant* 

Abstract  

The Johns Hopkins University Applied Physics Laboratory  built and flew  a novel  deployable antenna  containment mechanism specifically for  use on Parker Solar Probe.  These mechanisms came to be known  as “the clamshells”; a moniker earned for a deployment that was reminiscent to the movement of  their  ocean- bound namesake. This document  describes the fundamental  design and development  efforts   associated with th ese mechanisms . Furthermore,  it will delve into to the subsequent  investigation of the  deployment  anomaly that that occurred  during protoflight testing and resulted from dimensionally noncompliant parts and effects of titanium -to-titanium galling.        Introduction  

The NASA Parker Solar Probe (PSP) spacecraft, built by the Johns Hopkins University Applied Physics  Laboratory  (JHU/ APL) , was launched from Cape Canaveral, FL on August 12, 2018. The spacecraft, shown  partially in Figure 1, will provide new data on solar activity and make critical contributions to our ability to  forecast major space weather ev ents that impact life on Earth1.  

During the development of PSP , APL conceived, fabricated, tested and integrated a unique, partially  deployable antenna containment  system  for launch  and testing environments . These mechanisms were  successfully deployed two  days after the launch of Parker Solar Probe. Formally referred as the Antenna  Retention S ystem (ARS) , this late-stage development effort  served the purpose of attenuating the  anticipated excursions  of the ~2100 mm ( ~82 in) niobium V1, V2, V3 and V 4 FIELDS instrument antennas  (provided by the Space Sciences Laboratory at the University of California, Berkeley ) during spacecraft   (SC) testing and launch.  A result of the flexible nature of the antennas, their stowed mounting location, and  the fact they spanned multiple SC interfaces, containment was necessary to prevent damage to other SC  components.  The ARS system , as depicted in F igure 1,  is comprised  of a one- time deployable , SC  structure- mounted  clamshell  mechanism,  and a series of static fork-shaped snubbers  mounted to the  thermal radiators directly adjacent to  the instrument hinge. The deployment of the clamshell mechanism is  completely independent  of the FIELDS deployment hinge;  the former is deployed first, enabling the latter  to individually deploy each antenna from the stowed launch position to the final, radially  extended  configuration beyond the umbra of the Thermal Protection System. Each of the four  FIELDS antennas have  a corresponding clamshell  mechanism, and a set of carefully aligned forks  adjusted to the natural shape of  the stowed antenna. The clamshells at the FIELDS  V1 and V2 locations  shared similar mounting bracket  geometry, V3 and V4 mounting brackets were completely unique to the others ( Figure 2) . Though the  mounting brackets varied, the clamshell mechanism at each location were identical.    

* Johns Hopkins University Applied Physics Lab, Laurel, MD ; mark.bryant@jhuapl.edu  

Proceedings of the 45th Aerospace Mechanisms Symposium, NA SA Johnson Space Center, 2020