Voyager 1

Voyager 1

Voyager 1 is a 722-kilogram (1,592 lb) space probe launched by NASA on September 5, 1977 to study the outer Solar System. Operating for 36 years and 23 days as of September 28, the spacecraft communicates with the Deep Space Network to receive routine commands and return data. At a distance of about 125.75 AU (1.881×1010 km) from the Sun as of 28 September 2013,[3][4] it is the farthest manmade object from Earth.

The primary mission ended on November 20, 1980, after encounters with the Jovian system in 1979 and the Saturnian system in 1980. It was the first probe to provide detailed images of the two planets and their moons. As part of the Voyager program, like its sister craft Voyager 2, the spacecraft is in an extended mission to locate and study the regions and boundaries of the outer heliosphere, and finally to begin exploring the interstellar medium.

On September 12, 2013, NASA announced that Voyager 1 had crossed the heliopause and entered interstellar space on August 25, 2012, making it the first manmade object to do so.[6][7][8][9][10][11] As of 2013, the probe was moving with a relative velocity to the Sun of about 17 km/s.[12] The probe is expected to continue its mission until 2025, when it will be no longer supplied with enough power from its generators to operate any of its instruments.

Spacecraft design

Voyager 1 was constructed by the Jet Propulsion Laboratory. It has 16 hydrazine thrusters, three-axis stabilization gyroscopes, and referencing instruments (Sun sensor/Canopus Star Tracker) to keep the probe's radio antenna pointed toward Earth. Collectively, these instruments are part of the Attitude and Articulation Control Subsystem (AACS), along with redundant units of most instruments and 8 backup thrusters. The spacecraft also included 11 scientific instruments to study celestial objects such as planets as it travels through space

Communication system

The radio communication system of Voyager 1 was designed to be used up to and beyond the limits of the Solar System. The communication system includes a 3.7 meters (12 ft) diameter parabolic dish high-gain antenna to send and receive radio waves via the three Deep Space Network stations on the Earth.[19] Voyager 1 normally transmits data to Earth over Deep Space Network Channel 18, using a frequency of either 2296.481481 MHz or 8420.432097 MHz, while signals from Earth to Voyager are broadcast at 2114.676697 MHz.

When Voyager 1 is unable to communicate directly with the Earth, its digital tape recorder (DTR) can record up to 69.63 kilobytes of data for transmission at another time.[21] As of 2013, signals from Voyager 1 take over 17 hours to reach Earth.

Power

Voyager 1 has three radioisotope thermoelectric generators (RTGs) mounted on a boom. Each MHW-RTG contains 24 pressed plutonium-238 oxide spheres. The RTGs generated about 470 watts of electric power at the time of launch, with the remainder being dissipated as waste heat.[22] The power output of the RTGs does decline over time (due to the short 87.7 yr half-life of the fuel and degradation of the thermocouples), but the RTGs of Voyager 1 will continue to support some of its operations until around 2025.

Computers

Unlike the other onboard instruments, the operation of the cameras for visible light is not autonomous, but rather it is controlled by an imaging parameter table contained in one of the on-board digital computers, the Flight Data Subsystem (FDS). More recent space probes, since about 1990, usually have completely autonomous cameras.

The computer command subsystem (CCS) controls the cameras. The CCS contains fixed computer programs such as command decoding, fault detection, and correction routines, antenna pointing routines, and spacecraft sequencing routines. This computer is an improved version of the one that was used in the Viking orbiter.[24] The hardware in both custom-built CCS subsystems in the Voyagers is identical. There is only a minor software modification for one of them that has a scientific subsystem that the other lacks.

The Attitude and Articulation Control Subsystem (AACS) controls the spacecraft orientation (its attitude). It keeps the high-gain antenna pointing towards the Earth, controls attitude changes, and points the scan platform. The custom-built AACS systems on both Voyagers are identical.

Encounter with Jupiter

Voyager 1 began photographing Jupiter in January 1979. Its closest approach to Jupiter was on March 5, 1979, at a distance of about 349,000 kilometers (217,000 mi) from the planet's center.[33] Because of the greater photographic resolution allowed by a closer approach, most observations of the moons, rings, magnetic fields, and the radiation belt environment of the Jovian system were made during the 48-hour period that bracketed the closest approach. Voyager 1 finished photographing the Jovian system in April 1979.

Discovery of active volcanic activity on the satellite Io was probably the greatest surprise. It was the first time active volcanoes had been seen on another body in the solar system. It appears that activity on Io affects the entire Jovian system. Io appears to be the primary source of matter that pervades the Jovian magnetosphere - the region of space that surrounds the planet influenced by the planet's strong magnetic field. Sulfur, oxygen, and sodium, apparently erupted by Io's volcanoes and sputtered off the surface by impact of high-energy particles, were detected at the outer edge of the magnetosphere of Jupiter.

The two Voyager space probes made a number of important discoveries about Jupiter, its satellites, its radiation belts, and its never-before-seen planetary rings. The most surprising discovery in the Jovian system was the existence of volcanic activity on the moon Io, which had not been observed either from the ground, or by Pioneer 10 or Pioneer 11.

Encounter with Saturn

The gravitational assist trajectories at Jupiter were successfully carried out by both Voyagers, and the two spacecraft went on to visit Saturn and its system of moons and rings. Voyager 1's Saturnian flyby occurred in November 1980, with the closest approach on November 12, 1980, when the space probe came within 124,000 kilometers (77,000 mi) of Saturn's cloud-tops. The space probe's cameras detected complex structures in the rings of Saturn, and its remote sensing instruments studied the atmospheres of Saturn and its giant moon Titan.

Voyager 1 found that about 7 percent of the volume of Saturn's upper atmosphere is helium (compared with 11 percent of Jupiter's atmosphere), while almost all the rest is hydrogen. Since Saturn's internal helium abundance was expected to be the same as Jupiter's and the Sun's, the lower abundance of helium in the upper atmosphere may imply that the heavier helium may be slowly sinking through Saturn's hydrogen; that might explain the excess heat that Saturn radiates over energy it receives from the Sun. Winds blow at high speeds in Saturn. Near the equator, the Voyagers measured winds about 500 m/s (1,100 mi/hr). The wind blows mostly in an easterly direction.

The Voyagers found aurora-like ultraviolet emissions of hydrogen at mid-latitudes in the atmosphere, and auroras at polar latitudes (above 65 degrees). The high-level auroral activity may lead to formation of complex hydrocarbon molecules that are carried toward the equator. The mid-latitude auroras, which occur only in sunlit regions, remain a puzzle, since bombardment by electrons and ions, known to cause auroras on Earth, occurs primarily at high latitudes.

Both Voyagers measured the rotation of Saturn (the length of a day) at 10 hours, 39 minutes, 24 seconds.

Because Pioneer 11 had one year earlier detected a thick, gaseous atmosphere over Titan, the Voyager space probes' controllers at the Jet Propulsion Laboratory elected for Voyager 1 to make a close approach of Titan, and of necessity end its Grand Tour there. (For the continuation of the Grand Tour, see the Uranus and Neptune sections of the article on Voyager 2.) Its trajectory with a close fly-by of Titan caused an extra gravitational deflection that sent Voyager 1 out of the plane of the ecliptic, thus ending its planetary science mission. Voyager 1 could have been commanded onto a different trajectory, whereby the gravitational slingshot effect of Saturn's mass would have steered and boosted Voyager 1 out to a fly-by of Pluto. However, this Plutonian option was not exercised, because the other trajectory that led to the close fly-by of Titan was decided to have more scientific value and less risk.

Exit from the heliosphere

A set of grey squares trace roughly left to right. A few are labeled with single letters associated with a nearby coloured square. J is near to a square labeled Jupiter; E to Earth; V to Venus; S to Saturn; U to Uranus; N to Neptune. A small spot appears at the centre of each coloured square

The "family portrait" of the Solar System taken by Voyager 1

Voyager 1, on February 14, 1990, took the first ever "family portrait" of the Solar System as seen from outside,[38] which includes the famous image of planet Earth known as "Pale Blue Dot". Soon afterwards its cameras were deactivated to conserve power and computer resources for other equipment. Camera software have been removed from the spacecraft, so it now would be complex to get them working again (also Earth-side software and computers for reading the images are no longer available)

On February 17, 1998, Voyager 1 reached a distance of 69 AU from the Sun and overtook Pioneer 10 as the most distant manmade object from Earth.

It is currently the most distant functioning space probe to receive commands and transmit information to Earth. Travelling at about 17 kilometers per second (11 mi/s) it has the fastest heliocentric recession speed of any manmade object.

As Voyager 1 headed for interstellar space, its instruments continued to study the Solar System.Jet Propulsion Laboratory scientists used the plasma wave experiments aboard Voyager 1 and 2 to look for the heliopause, the boundary at which the solar wind transitions into the interstellar medium

Future of the probe

Voyager 1 will take about 30,000 years to pass through the Oort cloud. It is not heading towards any particular star, but in about 40,000 years it will pass within 1.6 light years of the star Gliese 445, which is at present in the constellation Camelopardalis. That star is generally moving towards the Solar System at about 119 km/s (430,000 km/h; 270,000 mph).

Provided Voyager 1 does not collide with anything and is not retrieved, the New Horizons space probe will never pass it, despite being launched from Earth at a faster speed than either Voyager spacecraft. New Horizons is traveling at about 15 km/s, 2 km/s slower than Voyager 1, and is still slowing down. When New Horizons reaches the same distance from the Sun as Voyager 1 is now, its speed will be about 13 km/s (8 mi/s)