Following the encounter with Saturn, Voyager 1 headed on a trajectory escaping the solar system at a speed of about 3.5 AU per year, 35° out of the ecliptic plane to the north, in the general direction of the Sun's motion relative to nearby stars. Because of the specific requirements for the Titan flyby, the spacecraft was not directed to Uranus and Neptune. The final images taken by the Voyagers comprised a mosaic of 64 images taken by Voyager 1 on February 14, 1990 at a distance of 40 AU of the Sun and all the planets of the solar system (although Mercury and Mars did not appear, the former because it was too close to the Sun and the latter because Mars was on the same side of the Sun as Voyager 1 so only its dark side faced the cameras). This was the so-called "pale blue dot" image made famous by Cornell University professor and Voyager science team member Carl Sagan (1934-1996). These were the last of a total of 67,000 images taken by the two spacecraft.
All the planetary encounters finally over in 1989, the missions of Voyager 1 and 2 were declared part of the Voyager Interstellar Mission (VIM), which officially began on 1 January 1990. The goal was to extend NASA's exploration of the solar system beyond the neighborhood of the outer planets to the outer limits of the Sun's sphere of influence, and "possibly beyond." Specific goals include collecting data on the transition between the heliosphere, the region of space dominated by the Sun's magnetic field and solar field, and the interstellar medium. On 17 February 1998, Voyager 1 became the most distant human-made object in existence when, at a distance of 69.4 AU from the Sun it "overtook" Pioneer 10. On 16 December 2004, Voyager scientists announced that Voyager 1 had reported high values for the intensity for the magnetic field at a distance of 94 AU, indicating that it had reached the termination shock and had now entered the heliosheath. The spacecraft finally exited the heliosphere and began measuring the interstellar environment on 25 August 2012, the first spacecraft to do so. On 5 September 2017, NASA marked the 40th anniversary of its launch, as it continues to communicate with NASA's Deep Space Network and send data back from four still-functioning instruments—the cosmic ray telescope, the low-energy charged particles experiment, the magnetometer, and the plasma waves experiment.
Each of the Voyagers contain a "message," prepared by a team headed by Carl Sagan, in the form of a 30-centimeter diameter gold-plated copper disc for potential extraterrestrials who might find the spacecraft. Like the plaques on Pioneers 10 and 11, the record has inscribed symbols to show the location of Earth relative to several pulsars. The records also contain instructions to play them using a cartridge and a needle, much like a vinyl record player. The audio on the disc includes greetings in 55 languages, 35 sounds from life on Earth (such as whale songs, laughter, etc.), 90 minutes of generally Western music including everything from Mozart and Bach to Chuck Berry and Blind Willie Johnson. It also includes 115 images of life on Earth and recorded greetings from then U.S. President Jimmy Carter (1924– ) and then-UN Secretary-General Kurt Waldheim (1918–2007). By 5 November 2017, Voyager 1 was 140.931 AU (21.083 billion kilometers) from Earth, the farthest object created by humans, and moving at a velocity of 17.0 kilometers/second relative to the Sun.
<!-- image -->Voyager 1 acquired this image of Io on 4 March 1979 about 11 hours before closest approach to the Jupiter Moon, at a range of 490,000 kilometers from the target. Visible is an enormous volcanic explosion silhouetted against dark space. Credit: NASA/JPL
<!-- image -->NASA scientists at the Langley Research Center in Virginia stand in front of the aeroshell that protected the Viking Lander I during its entry into the Martian atmosphere in 1976. The aeroshell was made of the heat shield and a "backshell" which contained parachutes and other components used for entry. Credit: NASA/JPL
<!-- image -->Temperatures ranged from –86°C (before dawn) to –33°C (in the afternoon). The seismometer on the lander was, however, inoperable. On 28 July, the lander's robot arm scooped up the first soil samples and deposited them into a special biological laboratory that included a gas chromatograph mass spectrometer. The cumulative data from the four samples collected could be construed as indicating the presence of life ("weak positive"), but the major test for organic compounds using the gas chromatograph experiment, capable of detecting organic compounds that comprised more than 10–100 parts per billion in the soil, gave negative results. Data showed an abundance of sulfur, certainly different from any known material found on Earth or the Moon. While the primary mission for both Viking 1 and Viking 2 ended in November 1976, activities continued through the Extended Mission (November 1976 to May 1978) and the Continuation Mission (May 1978 to July 1979). Viking 1's orbiter then continued a "Survey Mission" from July 1979 to July 1980. The Lander continued to return daily (and then eventually weekly) weather reports as part of the Viking Monitor Mission. In January 1982, it was renamed the Thomas Mutch Memorial Station in honor of Thomas A. Mutch (1931–1980) the leader of the Viking imaging team who had passed away on 6 October 1980. The lander operated until 11 November 1982 when a faulty command sent from Earth resulted in an interruption of communications. Further attempts to regain contact proved to be unsuccessful. The Orbiter, after taking many more high-resolution images of the planet and its two moons, far superior than those from Mariner 9, was shut down on 7 August 1980 after it ran out of attitude control propellant on its 1,489th orbit around Mars. Current projections are that the orbiter will enter the Martian atmosphere sometime around 2019.
<!-- image -->Panoramic image taken by Viking Lander 2, created by combining standard low resolution color images with standard high resolution black and white images. Credit: NASA/JPL
<!-- image -->Viking 2
Nation: USA (57) Objective(s): Mars landing and orbit Spacecraft: Viking-A Spacecraft Mass: 3,527 kg Mission Design and Management: NASA / LaRC (overall) / JPL (Orbiter) Launch Vehicle: Titan IIIE-Centaur (TC-3 / Titan no. E-3 / Centaur no. D-1T) Launch Date and Time: 9 September 1975 / 18:39:00 UT Launch Site: Cape Canaveral / Launch Complex 41
<!-- image -->Viking 2 Lander image showing the spacecraft and part of Utopia Planitia, looking due south. The American flag, color grid, and bicentennial symbols (for the 200th anniversary of the Declaration of the Independence, celebrated in 1976) are visible in this image, and were used to calibrate color images as they were received on Earth. The image was taken on 2 November 1976. Credit: NASA/JPL
Scientific Instruments:
Orbiter:
- imaging system (2 vidicon cameras) (VIS)
- infrared spectrometer for water vapor mapping (MAWD)
- infrared radiometer for thermal mapping (IRTM)
Lander:
- imaging system (2 facsimile cameras)
- gas chromatograph mass spectrometer (GCMS)
- seismometer
- x-ray fluorescence spectrometer
- biological laboratory
- weather instrument package (temperature, pressure, wind velocity)
- remote sampler arm
Aeroshell:
- retarding potential analyzer
- upper-atmosphere mass spectrometer
- pressure, temperature, and density sensors
Results: Viking-A was scheduled to be launched first, but had to be launched second due to a problem with its batteries that had to be repaired. After a successful launch and a mid-course correction on 19 September 1975, Viking 2 entered orbit around Mars nearly a year after launch on 7 August 1976. Initial orbital parameters were 1,502 × 35,728 kilometers inclined at 55.6°. As with Viking 1, photographs of the original landing site indicated rough terrain, prompting mission planners to select a different site at Utopia Planitia near the edge of the polar ice cap where water was located, i.e., where there was a better chance of finding signs of life. The Lander separated from the Orbiter without incident at 20:19 UT on 3 September 1976 and after atmospheric entry, landed safely at 22:37:50 UT, about 6,460 kilometers from the Viking 1 landing site. Touchdown coordinates were 47.968° N / 225.71° W. Photographs of the area showed a rockier, flatter site than that of Viking 1. The lander was in fact tilted 8.5° to the west. Panoramic views of the landscape showed a terrain different from that of Viking 1, with much less definition and very little in the way of horizon features. Because of the lack of general topographical references on the ground, imagery from the orbiters was unable to precisely locate the lander.
The biology experiments with scooped up soil collected on three occasions (beginning on 12 September) produced similar results to its twin, i.e., inconclusive on the question of whether life exists or ever has existed on the surface of Mars. Scientists believed that Martian soil contained reactants created by ultraviolet bombardment of the soil that could produce characteristics of living organisms in Earth soil. On 16 November 1976, NASA announced that both Viking 1 and Viking 2 missions had successfully accomplished their mission goals and announced an Extended Mission that continued until May 1978 followed by a Continuation Mission until July 1979. The Orbiter continued its successful imaging mission, approaching as close as 28 kilometers to the Martian Moon Deimos in May 1977. A series of leaks prompted termination of Orbiter 2 operations on 24 July 1978 while the Lander 2 continued to transmit data until 12 April 1980. In July 2001, the Viking 2 lander was renamed the Gerald Soffen Memorial Station after Gerald Soffen (1926–2000), the NASA Project Scientist for Viking who had died recently. In total, the two Viking Orbiters returned 52,663 images of Mars and mapped about 97% of the surface at a resolution of 300 meters resolution. The Landers returned 4,500 photos of the two landing sites.
<!-- image -->Luna 23 (Ye-8-5M no. 412)
Nation: USSR (94) Objective(s): lunar sample return Spacecraft: Ye-8-5M (no. 412) Spacecraft Mass: 5,795 kg Mission Design and Management: NPO imeni Lavochkina Launch Vehicle: Proton-K + Blok D (8K82K no. 287-02 + 11S824 no. 1401L) Launch Date and Time: 16 October 1975 / 14:04:56 UT Launch Site: NIIP-5 / Site 81/23
Scientific Instruments:
- stereo imaging system
- LB09 drill for sample collection
- radiation detector
- radio altimeter
Results: This was the second attempt by the Soviet Union to send an "advanced" lunar sample return craft to the Moon, equipped with the capability to dig for a deeper core. The first spacecraft (Luna 23) was damaged during landing on the Moon in October 1974. On this mission, the first three stages of the Proton-K launch vehicle worked without fault, but the Blok D stage, during its first burn for insertion into Earth orbit, failed. The expensive payload burned up in Earth's atmosphere without ever reaching Earth orbit.
Helios 2
Nation: Federal Republic of Germany (2) Objective(s): solar orbit Spacecraft: Helios-B Spacecraft Mass: 370 kg Mission Design and Management: DFVLR / NASA / GSFC Launch Vehicle: Titan IIIE-Centaur (TC-5 / Titan no. E-5 / Centaur D-1T) Launch Date and Time: 15 January 1976 / 05:34:00 UT Launch Site: Cape Canaveral / Launch Complex 41
Image
Image
Scientific Instruments:
- plasma detector
- flux gate magnetometer
- 2nd flux gate magnetometer
- plasma and radio wave experiment
- cosmic ray detector
- low energy electron and ion spectrometer
- zodiacal light photometer
- micrometeoroid analyzer
- search coil magnetometer
- Faraday effect experiment