Cosmic Ray Subsystem (CRS, or Cosmic Ray System) is an instrument aboard the ''

Voyager 1 ''Voyager 1'' is a space probe launched by NASA on September 5, 1977, as part of the Voyager program to study the outer Solar System and interstellar space beyond the Sun's heliosphere. Launched 16 days after its twin '' Voyager 2'', ''V ...

'' and ''

Voyager 2 ''Voyager 2'' is a space probe launched by NASA on August 20, 1977, to study the outer planets and interstellar space beyond the Sun's heliosphere. As a part of the Voyager program, it was launched 16 days before its twin, '' Voyager 1'', ...

'' spacecraft of the NASA

Voyager program The Voyager program is an American scientific program that employs two robotic interstellar probes, ''Voyager 1'' and ''Voyager 2''. They were launched in 1977 to take advantage of a favorable alignment of Jupiter and Saturn, to fly near t ...

, and it is an experiment to detect

cosmic rays Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our ...

. The CRS includes a High-Energy Telescope System (HETS), Low-Energy Telescope System (LETS), and The Electron Telescope (TET). 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. It can also detect the energetic particles like protons from the

Galaxy A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System ...

or Earth's

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

. As of 2019, CRS is one of the active remaining instruments on both Voyager spacecraft, and it is described by as being able to detect electrons from 3–110 MeV and cosmic ray nuclei 1–500 MeV/n. All three systems used

solid-state Solid state, or solid matter, is one of the four fundamental states of matter. Solid state may also refer to: Electronics * Solid-state electronics, circuits built of solid materials * Solid state ionics, study of ionic conductors and their ...

detectors. CRS is one of the five fields and particle experiments on each spacecraft, and one of the goals is to gain a deeper understanding of the

solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sol ...

. Other objects of study including

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have n ...

s and nuclei from planetary

magnetosphere In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior d ...

s and from outside the solar system. In the summer of 2019, the heater for the CRS on ''Voyager 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. The amount of power on the Voyager spacecraft has been slowly decreasing, so various items of equipment are turned off to save power.

Overview

Areas of original study for this investigation: *origin and acceleration process, life history, and dynamic contribution of interstellar cosmic rays, *

nucleosynthesis Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in ...

of elements in cosmic-ray sources *behavior of cosmic rays in the

interplanetary medium The interplanetary medium (IPM) or interplanetary space consists of the mass and energy which fills the Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding ...

*trapped planetary energetic particle environment. High-Energy Telescope System: *6 and 500 MeV/nucleon for

atomic number The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of ever ...

s from 1 through 30 *

Electrons The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have n ...

from 3 and 100 MeV Low-Energy Telescope System: *0.15 and 30 MeV/nucleon for atomic numbers from 1 to 30. *Measures

anisotropies Anisotropy () is the property of a material which allows it to change or assume different properties in different directions, as opposed to isotropy. It can be defined as a difference, when measured along different axes, in a material's physic ...

of electrons and nuclei. Electron Telescope (TET): *The TET measures the energy spectrum of electrons from 3 to 110 MeV. The TET consists of eight solid state detectors with different thicknesses of

tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...

between each detector. The detectors and tungsten layers are stacked one on top of each other. 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. The principal investigator is Prof.

Edward C. Stone Edward Carroll Stone (born January 23, 1936) is an American space scientist, professor of physics at the California Institute of Technology, and former director of the NASA Jet Propulsion Laboratory (JPL). Biography Stone was born in Knoxvil ...

, Jr. 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.

Operating Temperature

During its development the CRS was rated to operated down to a temperature of minus 49 degrees F (minus 45 degrees C). Up until 2019 the instrument was operated on both ''Voyager 1'' and ''Voyager 2'', however in the summer of 2019 there was need to save some power on ''Voyager 2''. The heater for the CRS was turned off at this time, which caused a lowering of the CRS temperature to below its lowest rated operating temperature. The device cooled down to minus 74 degrees Fahrenheit (minus 59 degrees Celsius) but it still continued to operate at this temperature.

Results

PIA22924-Voyager2LeavesTheSolarSystem-20181105

In 1977 the spectra of Helium (He), Carbon, Nitrogen, Oxygen, and Neon during the

solar minimum Solar minimum is the regular period of least solar activity in the Sun's 11-year solar cycle. During solar minimum, sunspot and solar flare activity diminishes, and often does not occur for days at a time. On average, the solar cycle takes abou ...

was measured using the CRS instrument on the Voyagers that year. The solar minimum of 1977 occurred towards the end of year, and it was possible to observe both interplanetary, galactic, and anomalous energy spectras. In the early 1980s, the CRS detected charged particles around

Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...

. It detected a 0.43 million volt flux of protons as it traveled through Saturn's

. In the 1980s the CRS data from both Voyagers was used to determine the abundances of energetic particles from the Sun and additional information. Another area studied in the 1980s using CRS data was variation in Galactic cosmic rays in the outer Heliosphere CRS helped predict that ''Voyager 1'' and ''2'' would cross the Solar System's termination shock in 2003. This helped support the later conclusion that ''Voyager 1'' crossed the termination shock in December 2004 and that ''Voyager 2'' crossed it in August 2007. In 2011, CRS data along with the Voyager

Magnetometer A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, ...

discovered an area where the solar wind was not going in either direction. The area was identified as a sort of charged particle doldrums, where the particles from the Solar System are pushed back by cosmic forces. At a distance of 17 light-hours ''Voyager 1'' was commanded to rotate several times (in the other direction then its spinning), to make detection in other directions. It was determined that in 2012 ''Voyager 1'' entered interstellar space, that is it entered the interstellar medium between the stars. One of the reasons this was recognized was a significant increase in galactic cosmic rays. In 2013 CRS data lead some to propose that ''Voyager 1'' had entered a "transition zone" as it leaves the

Heliosphere The heliosphere is the magnetosphere, astrosphere and outermost atmospheric layer of the Sun. It takes the shape of a vast, bubble-like region of space. In plasma physics terms, it is the cavity formed by the Sun in the surrounding interstell ...

. There was some changes in the amounts and type of detections that triggered deeper analysis. The results from the magnetometer muddied the waters of interpretation. Other scientists proposed that this indicated a departure from the Solar System in the sense that it had left the Sun's heliosphere. The issue was the interpretation of the drop in cosmic rays, which happened at 123 AU from the Sun for ''Voyager 2'' that year. The many revelations and restructured understandings as the Voyagers head out, as influenced by data from the CRS and other active instruments, was called by ''Nature'' publication as the "long goodbye". The CRS on ''Voyager 2'', helped identify that spacecraft's departure from the Sun's heliosphere in 2018.

CRS location

References

External links