Cosmic Ray Subsystem (CRS, orCosmic Ray System)[1] is an instrument aboard theVoyager 1 andVoyager 2 spacecraft of the NASAVoyager program, and it is an experiment to detectcosmic rays.[2][3] The CRS includes a High-Energy Telescope System (HETS), Low-Energy Telescope System (LETS), and The Electron Telescope (TET).[4] It is designed to detect energetic particles and some of the requirements were for the instrument to be reliable and to have enough charge resolution.[5] It can also detect the energetic particles like protons from theGalaxy or Earth'sSun.[1]
As of 2019, CRS is one of the active remaining instruments on both Voyager spacecraft. It is described by as being able to detect electrons from 3–110 MeV and cosmic ray nuclei 1–500 MeV/n.[6] All three systems usedsolid-state detectors.[7] CRS is one of the five fields and particle experiments on each spacecraft. One of the goals is to gain a deeper understanding of thesolar wind.[8] Other objects of study includingelectrons andnuclei from planetarymagnetospheres and from outside theSolar System.[9]
In the summer of 2019, the heater for the CRS onVoyager 2 was turned off to save power; however, although it cooled off, it was still returning data at a new lower temperature outside its original operating range.[10] The amount of power on the Voyager spacecraft has been slowly decreasing, so various items of equipment are turned off to save power.[10]
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Areas of original study for this investigation:[11]
High-Energy Telescope System:[4]
Low-Energy Telescope System:[4]
Electron Telescope (TET):
The TET consists of eight solid-state detectors with different thicknesses oftungsten between each detector.[7] The detectors and tungsten layers are stacked one on top of each other.[12] The tungsten layers range from 0.56 mm to 2.34 mm thick and function as absorbers. Each TET solid state detector has an area of 4.5 cm2 and is 3 mm thick.[12]
Principal investigators:Rochus Eugen Vogt,Edward C. Stone,Alan C. Cummings[13]
The CRS was tested to operate down to a temperature of minus 49 degrees F (minus 59 degrees C) during its development in the 1970s.[10]
During its development, the CRS was rated to operate down to a temperature of minus 49 degrees F (minus 45 degrees C).[10] Up until 2019 the instrument was operating on bothVoyager 1 andVoyager 2, however in the summer of 2019 there was need to save some power onVoyager 2.[10] The heater for the CRS was turned off at this time, which caused a lowering of the CRS temperature to drop below its lowest rated operating temperature.[10] The device cooled down to minus 74 degrees Fahrenheit (minus 59 degrees Celsius), but it continued to operate at this temperature.[10]
In 1977, the spectra of helium, carbon, nitrogen, oxygen, and neon during thesolar minimum were measured using the CRS instrument on the Voyagers that year.[15] The solar minimum of 1977 occurred towards the end of year. It was possible to observe both interplanetary, galactic, and anomalous energy spectra.[15]
In the early 1980s, the CRS detected charged particles aroundSaturn.[16] It detected a 0.43 million volt flux of protons as it traveled through Saturn'smagnetosphere.[16] In the 1980s the CRS data from both Voyagers was used to determine the abundances of energetic particles from the Sun and additional information.[17] Another area studied in the 1980s using CRS data was variation ingalactic cosmic rays in the outer Heliosphere[18]
CRS helped predict thatVoyager 1 and2 would cross the Solar System's termination shock in 2003.[19] This helped support the later conclusion thatVoyager 1 crossed the termination shock in December 2004 and thatVoyager 2 crossed it in August 2007.[20]
In 2011, CRS data along with the VoyagerMagnetometer discovered an area where the solar wind was not going in either direction.[21] The area was identified as a sort of charged particle doldrums, where the particles from the Solar System are pushed back by cosmic forces.[21] At a distance of 17 light-hoursVoyager 1 was commanded to rotate several times (in the other direction then its spinning), to make detection in different directions.[20]
It was determined that in 2012Voyager 1 entered interstellar space, that is, it entered the interstellar medium between the stars.[22] One of the reasons this was recognized was a significant increase in galactic cosmic rays.[23]
In 2013, CRS data led some to propose thatVoyager 1 had entered a "transition zone" as it leaves theheliosphere.[24] There were some changes in the amounts and type of detections that triggered deeper analysis.[25] The results from the magnetometer muddied the waters of interpretation.[26]
First, I don't think any of us on the CRS [Cosmic Ray Subsystem, an instrument on Voyager] team will ever forget watching on the computer monitors, even on an hourly basis, in one case, as some particle intensities dropped precipitously, and others increased simultaneously on several occasions in July and August 2012.[27]
Other scientists proposed that this indicated a departure from the Solar System in the sense that it had left the Sun's heliosphere.[25] The issue was the interpretation of the drop in cosmic rays, which happened at 123 AU from the Sun forVoyager 2 that year.[25] The many revelations and restructured understandings as the Voyagers head out, as influenced by data from the CRS and other active instruments, were called byNature publication as the "long goodbye".[20]
The CRS onVoyager 2, helped identify that spacecraft's departure from the Sun's heliosphere in 2018.[10]
