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Pioneer 11

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Pioneer 11
An artist's impression of a Pioneer spacecraft on its way to interstellar space.
Mission typePlanetary / Heliosphere exploration
OperatorNASA / Ames
COSPAR ID1973-019A Edit this at Wikidata
SATCAT no.6421
Websitescience.nasa.gov
Mission duration22 years, 7 months and 19 days
Spacecraft properties
SpacecraftPioneer G
ManufacturerTRW
Launch mass258.5 kg (570 lb)[1]
Power155 watts (at launch)
Start of mission
Launch dateApril 6, 1973, 02:11:00 (1973-04-06UTC02:11Z) UTC[1]
RocketAtlas SLV-3D Centaur-D1A Star-37E
Launch siteCape Canaveral LC-36B
End of mission
DisposalDecommissioned
Last contactNovember 24, 1995 (1995-11-25)
Flyby of Jupiter
Closest approachDecember 3, 1974
Distance43,000 km (27,000 mi)
Flyby of Saturn
Closest approachSeptember 1, 1979
Distance21,000 km (13,000 mi)

Pioneer 11 (also known as Pioneer G) is a NASA robotic space probe launched on April 5, 1973, to study the asteroid belt, the environment around Jupiter and Saturn, the solar wind, and cosmic rays.[2] It was the first probe to encounter Saturn, the second to fly through the asteroid belt, and the second to fly by Jupiter. Later, Pioneer 11 became the second of five artificial objects to achieve an escape velocity allowing it to leave the Solar System. Due to power constraints and the vast distance to the probe, the last routine contact with the spacecraft was on September 30, 1995, and the last good engineering data was received on November 24, 1995.[3]

Mission background

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History

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Approved in February 1969, Pioneer 11 and its twin probe, Pioneer 10, were the first to be designed for exploring the outer Solar System. Yielding to multiple proposals throughout the 1960s, early mission objectives were defined as:

  • Explore the interplanetary medium beyond the orbit of Mars
  • Investigate the nature of the asteroid belt from the scientific standpoint and assess the belt's possible hazard to missions to the outer planets.
  • Explore the environment of Jupiter.

Subsequent planning for an encounter with Saturn added many more goals:

  • Map the magnetic field of Saturn and determine its intensity, direction, and structure.
  • Determine how many electrons and protons of various energies are distributed along the trajectory of the spacecraft through the Saturn system.
  • Map the interaction of the Saturn system with the solar wind.
  • Measure the temperature of Saturn's atmosphere and that of Titan, the largest satellite of Saturn.
  • Determine the structure of the upper atmosphere of Saturn where molecules are expected to be electrically charged and form an ionosphere.
  • Map the thermal structure of Saturn's atmosphere by infrared observations coupled with radio occultation data.
  • Obtain spin-scan images of the Saturnian system in two colors during the encounter sequence and polarimetry measurements of the planet.
  • Probe the ring system and the atmosphere of Saturn with S-band radio occultation.
  • Determine more precisely the masses of Saturn and its larger satellites by accurate observations of the effects of their gravitational fields on the motion of the spacecraft.
  • As a precursor to the Mariner Jupiter/Saturn mission, verify the environment of the ring plane to find out where it may be safely crossed by the Mariner spacecraft without serious damage.[2]

Pioneer 11 was built by TRW and managed as part of the Pioneer program by NASA Ames Research Center.[3] A backup unit, Pioneer H, is currently on display in the "Milestones of Flight" exhibit at the National Air and Space Museum in Washington, D.C.[4] Many elements of the mission proved to be critical in the planning of the Voyager program.[5]

Spacecraft design

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The Pioneer 11 bus measures 36 centimeters (14 in) deep and with six 76-centimeter-long (30 in) panels forming the hexagonal structure. The bus houses propellant to control the orientation of the probe and eight of the twelve scientific instruments. The spacecraft has a mass of 259 kilograms.[6]

Attitude control and propulsion

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Orientation of the spacecraft was maintained with six 4.5-N,[7] hydrazine monopropellant thrusters: pair one maintains a constant spin-rate of 4.8 rpm, pair two controls the forward thrust, pair three controls attitude. Information for the orientation is provided by performing conical scanning maneuvers to track Earth in its orbit,[8] a star sensor able to reference Canopus, and two Sun sensors.[9]

Communications

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The space probe includes a redundant system transceivers, one attached to the high-gain antenna, the other to an omni-antenna and medium-gain antenna. Each transceiver is 8 watts and transmits data across the S-band using 2110 MHz for the uplink from Earth and 2292 MHz for the downlink to Earth with the Deep Space Network tracking the signal. Prior to transmitting data, the probe uses a convolutional encoder to allow correction of errors in the received data on Earth.[10]

Power

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SNAP-19 RTG on a Pioneer 10/11 replica
Pioneer 11 uses four SNAP-19 radioisotope thermoelectric generators (RTGs) (see diagram). They are positioned on two three-rod trusses, each 3 m (9 ft 10 in) in length and 120 degrees apart. This was expected to be a safe distance from the sensitive scientific experiments carried on board. Combined, the RTGs provided 155 watts at launch, and decayed to 140 W in transit to Jupiter. The spacecraft requires 100 W to power all systems.[11]

Computer

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Much of the computation for the mission was performed on Earth and transmitted to the probe, where it is able to retain in memory, up to five commands of the 222 possible entries by ground controllers. The spacecraft includes two command decoders and a command distribution unit, a very limited form of a processor, to direct operations on the spacecraft. This system requires that mission operators prepare commands long in advance of transmitting them to the probe. A data storage unit is included to record up to 6,144 bytes of information gathered by the instruments. The digital telemetry unit is then used to prepare the collected data in one of the thirteen possible formats before transmitting it back to Earth.[12]

Scientific instruments

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Pioneer 11 has one additional instrument more than Pioneer 10, a flux-gate magnetometer.[13]

Helium Vector Magnetometer (HVM)
Measures the fine structure of the interplanetary magnetic field, mapped the Jovian magnetic field, and provides magnetic field measurements to evaluate solar wind interaction with Jupiter.[14]
Quadrispherical Plasma Analyzer
Peer through a hole in the large dish-shaped antenna to detect particles of the solar wind originating from the Sun.[15]
Charged Particle Instrument (CPI)
Detects cosmic rays in the Solar System.[17]
Cosmic Ray Telescope (CRT)
Collects data on the composition of the cosmic ray particles and their energy ranges.[18]
Geiger Tube Telescope (GTT)
 Surveys the intensities, energy spectra, and angular distributions of electrons and protons along the spacecraft's path through the radiation belts of Jupiter and Saturn.[19]
Trapped Radiation Detector (TRD)

Includes an unfocused Cerenkov counter that detects the light emitted in a particular direction as particles passed through it recording electrons of energy, 0.5 to 12 MeV, an electron scatter detector for electrons of energy, 100 to 400 keV, and a minimum ionizing detector consisting of a solid-state diode that measured minimum ionizing particles (<3 MeV) and protons in the range of 50 to 350 MeV.[20]

Meteoroid Detectors
Twelve panels of pressurized cell detectors mounted on the back of the main dish antenna record penetrating impacts of small meteoroids.[21]
Asteroid/Meteoroid Detector (AMD)
Meteoroid-asteroid detector looks into space with four non-imaging telescopes to track particles ranging from close by bits of dust to distant large asteroids.[22]
Ultraviolet Photometer
Ultraviolet light (200 to 800 Å) is sensed to determine the quantities of hydrogen and helium in space and on Jupiter and Saturn.[23]
Imaging Photopolarimeter (IPP)
The imaging experiment relies upon the spin of the spacecraft to sweep a small telescope across the planet in narrow strips only 0.03 degrees wide, looking at the planet in red (5800 to 7000 Å) and blue (3900 to 4900 Å) light. These strips are then processed to build up a visual image of the planet.[24]
Infrared Radiometer
Provides information on cloud temperature and the output of heat from Jupiter and Saturn.[25]
Triaxial Fluxgate Magnetometer
Measures the magnetic fields of both Jupiter and Saturn. This instrument is not carried on Pioneer 10.[26]

Mission profile

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Launch and trajectory

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Pioneer 11 launching from Space Launch Complex 36A
Pioneer 11 launching from Launch Complex 36A.
Animation of Pioneer 11's trajectory from April 6, 1973, to December 31, 1980
   Pioneer 11  ·   Earth  ·   Jupiter ·   Saturn

Pioneer 11 was launched on April 6, 1973, at 02:11:00 UTC from Cape Canaveral Launch Complex 36A in Florida aboard an Atlas-Centaur launch vehicle with a Star-37E upper stage.[1][27] Its twin spacecraft, Pioneer 10, had been launched on March 3, 1972.[27]

Pioneer 11 was initially launched on a direct trajectory to Jupiter without any gravity assists.[28] In May 1974, mission controllers adjusted its trajectory to pass Jupiter on a north-to-south path, enabling a flyby of Saturn in 1979. The maneuver used 17 lb (7.7 kg) of propellant, lasted 42 minutes and 36 seconds, and increased the spacecraft's speed by 230 km/h (140 mph).[29] Pioneer 11 also performed two mid-course correction maneuvers, on April 11, 1973, and November 7, 1974.[1]

Encounter with Jupiter

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Animation of Pioneer 11's trajectory around Jupiter from November 30, 1974, to December 5, 1974
   Pioneer 11 ·   Jupiter ·   Io ·   Europa  ·   Ganymede  ·   Callisto

Pioneer 11 encountered Jupiter in November and December 1974. At closest approach on December 2, it passed 42,828 km (26,612 mi) above the planet's cloud tops.[1] The spacecraft returned detailed images of the Great Red Spot, transmitted the first close-up views of Jupiter's polar regions, and refined estimates of the mass of the moon Callisto.[3] Jupiter's gravity was also used for a gravity-assist maneuver that redirected the spacecraft toward Saturn and increased its velocity.[30] On April 16, 1975, after the Jupiter encounter, the micrometeoroid detector was switched off.[1]

Wikimedia Commons logo Media related to Pioneer 11 Jupiter encounter at Wikimedia Commons

Encounter with Saturn

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Animation of Pioneer 11 around Saturn
   Pioneer 11 ·   Saturn ·   Epimetheus ·   Janus ·   Mimas ·   Enceladus

Pioneer 11 flew past Saturn on September 1, 1979, passing about 21,000 km (13,000 mi) above the planet's cloud tops. During the encounter, it returned 440 images and collected data on Saturn, its rings, and its moons.[28]

By then, Voyager 1 and Voyager 2 had already flown past Jupiter and were en route to Saturn. Mission planners directed Pioneer 11 to cross Saturn's ring plane along the same path later planned for Voyager 2 on its way to Uranus and Neptune.[28] If hazardous ring particles were present, Pioneer 11 would detect them first, allowing Voyager 2's trajectory to be changed if necessary, although doing so would have prevented its later encounters with the ice giants.[30]

During the flyby, Pioneer 11 passed within about 4,000 km (2,500 mi) of one of Saturn's small moons. The object was initially identified as Epimetheus, which had been discovered only the previous day from images returned by Pioneer 11 and had also been suspected from earlier Earth-based observations. After the Voyager missions, astronomers determined that two similarly sized moons, Epimetheus and Janus, share nearly the same orbit, leaving some uncertainty over which moon Pioneer 11 actually passed. The spacecraft encountered Janus on September 1, 1979, at 14:52 UTC, passing within 2,500 km (1,600 mi), and later flew past Mimas at 16:20 UTC the same day at a distance of 103,000 km (64,000 mi).[citation needed]

In addition to observing Epimetheus, Pioneer 11 detected another previously unknown small moon and a previously unknown ring, mapped Saturn's magnetosphere and magnetic field,[3] and found Titan's surface temperature to be about −193 °C (−315 °F), indicating that the moon was too cold to support life as it was understood at the time.[28] Passing beneath the ring plane, the spacecraft returned images of Saturn's rings from a unique viewing angle. Rings that appear bright when viewed from Earth appeared dark in Pioneer 11's images, while the dark gaps visible from Earth appeared bright.[3]

Wikimedia Commons logo Media related to Pioneer 11 Saturn encounter at Wikimedia Commons

Interstellar mission

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NASA map showing trajectories of the Pioneer 10, Pioneer 11, Voyager 1, and Voyager 2 spacecraft.

On February 25, 1990, Pioneer 11 became the fourth human-made object to pass beyond the orbits of the planets.[31]

By 1995, Pioneer 11 could no longer power any of its scientific instruments, so NASA decided to end routine operations.[32] On 29 September 1995, NASA's Ames Research Center, which managed the mission, announced that the mission would soon end after nearly 22 years of exploration. NASA planned to use its Deep Space Network antennas to listen for the spacecraft's signal once or twice a month until late 1996, when its transmitter was expected to fall silent.[33]

NASA terminated routine contact with Pioneer 11 on 30 September 1995 but continued to contact the spacecraft for about two hours every two to four weeks.[32] Scientists received several minutes of usable engineering data on 24 November 1995, but then lost contact permanently after Earth moved out of the spacecraft's antenna field of view.[1][34]

Timeline

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Pioneer 10 and 11 speed and distance from the Sun
Heliocentric positions of the five interstellar probes (squares) and other bodies (circles) until 2030, with launch and flyby dates. Markers denote positions on 1 January of each year, with every fifth year labelled.
Plot 1 is viewed from the north ecliptic pole, to scale.
Plots 2 to 4 are third-angle projections at 20% scale.
In the SVG file, hover over a trajectory or orbit to highlight it and its associated launches and flybys.
Timeline of travel
Date Event
1973-04-06
 Spacecraft launched at 02:11:00.
1974-04-19
 Passage through the asteroid belt.
1974-11-03
 Start Jupiter observation phase.
1974-12-02
 Encounter with Jovian system.
08:21:00
 Callisto flyby at 786,500 km.
22:09:00
 Ganymede flyby at 692,300 km.
1974-12-03
03:11:00
 Io flyby at 314,000 km.
04:15:00
 Europa flyby at 586,700 km.
05:00:21
 Jupiter shadow entry.
05:01:01
 Jupiter occultation entry.
05:21:19
 Jupiter closest approach at 42,828 km.
05:33:52
 Jupiter shadow exit.
05:43:03
 Jupiter occultation exit.
22:29:00
 Amalthea flyby at 127,500 km.
1975-01-01
 Phase end
1979-07-31
 Start Saturn observation phase.
1979-08-29
 Encounter with Saturnian system.
06:06:10
 Iapetus flyby at 1,032,535 km.
11:53:33
 Phoebe flyby at 13,713,574 km.
1979-08-31
12:32:33
 Hyperion flyby at 666,153 km.
1979-09-01
14:26:56
 Descending ring plane crossing.
14:50:55
 Epimetheus flyby at 6,676 km.
15:06:32
 Atlas flyby at 45,960 km.
15:59:30
 Dione flyby at 291,556 km.
16:26:28
 Mimas flyby at 104,263 km.
16:29:34
 Saturn closest approach at 20,591 km.
16:35:00
 Saturn occultation entry.
16:35:57
 Saturn shadow entry.
16:51:11
 Janus flyby at 228,988 km.
17:53:32
 Saturn occultation exit.
17:54:47
 Saturn shadow exit.
18:21:59
 Ascending ring plane crossing.
18:25:34
 Tethys flyby at 329,197 km.
18:30:14
 Enceladus flyby at 222,027 km.
20:04:13
 Calypso flyby at 109,916 km.
22:15:27
 Rhea flyby at 345,303 km.
1979-09-02
18:00:33
 Titan flyby at 362,962 km.
1979-10-05
 Phase end
1979-10-05
 Begin extended mission.
1990-
 Passed the orbit of Pluto.
1995-09-30
 Routine daily mission operations stopped. Pioneer 11 is 6.5 billion km from Earth.
1995-11-24
 Last signal received.
[35][1][36]

Current status

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Due to limited power and the spacecraft's great distance from Earth, the last routine contact with Pioneer 11 was on September 30, 1995, and the last usable engineering data were received on November 24, 1995.[3][1]

As of June 24, 2024, Pioneer 11 was estimated to be 113.121 AU (16.9227×10^9 km; 10.5153×10^9 mi) from Earth and 114.089 AU (17.0675 billion km; 10.6052 billion mi) from the Sun. It was traveling at 11.155 km/s (40,160 km/h; 24,950 mph) relative to the Sun and receding from the Sun at about 2.35 AU per year.[37][38] The spacecraft is traveling toward the constellation Scutum, near right ascension 18h 54m and declination -8° 46' (J2000.0), close to Messier 26. In about 928,000 years, it is expected to pass within 0.25 parsecs (0.82 light-years) of the K-type star TYC 992-192-1.[39] It is also expected to pass near Lambda Aquilae in about four million years.[40]

Pioneer 11 has been overtaken by the two Voyager spacecraft launched in 1977. Voyager 1 is now the most distant human-made object and is expected to remain so for the foreseeable future, as no spacecraft launched since Voyager 1 has sufficient speed to overtake it.[41]

Pioneer anomaly

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Analysis of the radio tracking data from the Pioneer 10 and 11 spacecraft at distances between 20 and 70 AU from the Sun had consistently indicated the presence of a small but anomalous Doppler frequency drift. The drift can be interpreted as due to a constant acceleration of (8.74 ± 1.33) × 10−10 m/s2 directed towards the Sun. Although it was suspected that there was a systematic origin to the effect, none was found. As a result, there has been sustained interest in the nature of this so-called "Pioneer anomaly".[42] Extended analysis of mission data by Slava Turyshev and colleagues determined the source of the anomaly to be asymmetric thermal radiation and the resulting thermal recoil force acting on the face of the Pioneers away from the Sun.[43][44]

Pioneer plaque

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Pioneer plaque

Pioneer 10 and 11 both carry a gold-anodized aluminum plaque in the event that either spacecraft is ever found by intelligent lifeforms from other planetary systems. The plaques feature the nude figures of a human male and female along with several symbols that are designed to provide information about the origin of the spacecraft.[45]

Commemoration

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In 1991, Pioneer 11 was honored on one of 10 United States Postage Service stamps commemorating uncrewed spacecraft exploring each of the then nine planets and the Moon. Pioneer 11 was the spacecraft featured with Jupiter. Pluto was listed as "Not yet explored".[46]

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See also

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References

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  1. 1 2 3 4 5 6 7 8 9 "Pioneer 11 - NASA Science". science.nasa.gov. NASA. December 21, 2017. Retrieved December 1, 2022.
  2. 1 2 Fimmel, Swindell & Burgess 1974, p. 19.
  3. 1 2 3 4 5 6 "The Pioneer Missions". nasa.gov. NASA / Ames. March 27, 2007. Archived from the original on October 19, 2021. Retrieved March 3, 2015.
  4. ↑ "Milestones of Flight". Smithsonian National Air and Space Museum. Archived from the original on April 15, 2012. Retrieved February 8, 2011.
  5. ↑ Burrows 1990, pp. 266–268.
  6. ↑ Fimmel, Swindell & Burgess 1974, p. 42.
  7. ↑ M. Wade. "Pioneer 10-11". Encyclopedia Astronautica. Retrieved February 8, 2011.
  8. ↑ "Pioneer 11". Weebau Space Encyclopedia. November 9, 2010. Retrieved January 12, 2012.
  9. ↑ Fimmel, Swindell & Burgess 1974, pp. 42–43.
  10. ↑ Fimmel, Swindell & Burgess 1974, p. 43.
  11. ↑ Fimmel, Swindell & Burgess 1974, pp. 44–45.
  12. ↑ Fimmel, Swindell & Burgess 1974, p. 38.
  13. ↑ "Pioneer 10 & 11". Views of the Solar System. Retrieved December 20, 2018.
  14. ↑ E. J. Smith. "Pioneer 11: Magnetic Fields". nssdc.gsfc.nasa.gov. NASA. Retrieved February 19, 2011.
  15. ↑ A. Barnes. "Pioneer 11: Quadrispherical Plasma Analyzer". nssdc.gsfc.nasa.gov. NASA. Retrieved February 19, 2011.
  16. 1 2 3 4 5 6 7 8 9 10 Simpson 2001, p. 146.
  17. ↑ J. A. Simpson. "Pioneer 11: Charged Particle Instrument (CPI)". nssdc.gsfc.nasa.gov. NASA. Retrieved February 19, 2011.
  18. ↑ F. B. MacDonald. "Pioneer 11: Cosmic-Ray Spectra". nssdc.gsfc.nasa.gov. NASA. Retrieved February 19, 2011.
  19. ↑ J. A. Van Allen. "Pioneer 11: Geiger Tube Telescope (GTT)". nssdc.gsfc.nasa.gov. NASA. Retrieved February 19, 2011.
  20. ↑ R. W. Fillius. "Pioneer 11: Jovian Trapped Radiation". nssdc.gsfc.nasa.gov. NASA. Retrieved February 19, 2011.
  21. ↑ W. H. Kinard. "Pioneer 11: Meteoroid Detectors". nssdc.gsfc.nasa.gov. NASA. Retrieved February 19, 2011.
  22. ↑ R. K. Soberman. "Pioneer 11: Asteroid/Meteoroid Astronomy". nssdc.gsfc.nasa.gov. NASA. Retrieved February 19, 2011.
  23. ↑ D. L. Judge. "Pioneer 11: Ultraviolet Photometry". nssdc.gsfc.nasa.gov. NASA. Retrieved February 19, 2011.
  24. ↑ T. Gehrels. "Pioneer 11: Imaging Photopolarimeter (IPP)". nssdc.gsfc.nasa.gov. NASA. Retrieved February 19, 2011.
  25. ↑ A. P. Ingersoll. "Pioneer 11: Infrared Radiometers". nssdc.gsfc.nasa.gov. NASA. Retrieved February 19, 2011.
  26. ↑ M. H. Acuña. "Pioneer 11: Jovian Magnetic Field". nssdc.gsfc.nasa.gov. NASA. Retrieved September 24, 2013.
  27. 1 2 "NASA Glenn: Pioneer Launch History". NASA. March 7, 2003. Archived from the original on July 13, 2017. Retrieved June 13, 2011.
  28. 1 2 3 4 J. Uri (September 3, 2019). "40 Years Ago: Pioneer 11 First to Explore Saturn". nasa.gov. NASA. Retrieved July 25, 2024.
  29. ↑ "Pioneer 11 Successfully Retargeted for Saturn". New Scientist. Vol. 62. May 9, 1974. p. 294. Retrieved December 5, 2017.
  30. 1 2 Schalkwyk, James (April 5, 2013). "NASA Celebrates Four Decades of Plucky Pioneer 11". NASA. Archived from the original on April 8, 2013. Retrieved July 21, 2026.
  31. ↑ "Pioneer 11 Is Reported to Leave Solar System". The New York Times. February 25, 1990. p. 24. Retrieved December 3, 2017.
  32. 1 2 "Farewell to a Pioneer". Science News. Vol. 148, no. 16. Society for Science. October 14, 1995. p. 250. JSTOR 4018121.
  33. ↑ D. Savage; Ann Hutchison (September 28, 1995). "Pioneer 11 to End Operations after Epic Career" (TXT). nssdc.gsfc.nasa.gov. NASA / Ames. Retrieved August 7, 2011.
  34. ↑ E. Howell (September 26, 2012). "Pioneer 11: Up Close with Jupiter & Saturn". Space.com. Retrieved December 10, 2017.
  35. ↑ Fimmel, Swindell & Burgess 1974, pp. 61–94.
  36. ↑ D. Muller. "Pioneer 11 Full Mission Timeline". Spaceflight Realtime Simulations and Information. Archived from the original on March 4, 2016. Retrieved January 9, 2011.
  37. ↑ "Spacecraft escaping the Solar System". Heavens Above. Retrieved August 24, 2022.
  38. ↑ "Pioneer 11 - Live Position". www.theskylive.com. Retrieved July 19, 2015.
  39. ↑ C. A. L. Bailer-Jones; D. Farnocchia (April 3, 2019). "Future Stellar Flybys of the Voyager and Pioneer spacecraft". Research Notes of the AAS. 3 (4): 59. arXiv:1912.03503. Bibcode:2019RNAAS...3...59B. doi:10.3847/2515-5172/ab158e. S2CID 134524048.
  40. ↑ "Hardware, Leaving the Solar System: Where are they now?". DK Eyewitness - Encyclopedia of Space and the Universe. 2001. ISBN 978-0-789-40881-5.
  41. ↑ "Voyager - Mission Status". voyager.jpl.nasa.gov. NASA / JPL. Retrieved December 15, 2021.
  42. ↑ R. R. Britt (October 18, 2004). "The Problem with Gravity: New Mission Would Probe Strange Puzzle". Space.com. Retrieved June 7, 2011.
  43. ↑ "Pioneer Anomaly Solved!". The Planetary Society. Archived from the original on April 22, 2012. Retrieved April 20, 2012.
  44. ↑ S. G. Turyshev; V. T. Toth; G. Kinsella; et al. (June 12, 2012). "Support for the Thermal Origin of the Pioneer Anomaly". Physical Review Letters. 108 (24) 241101. arXiv:1204.2507. Bibcode:2012PhRvL.108x1101T. doi:10.1103/PhysRevLett.108.241101. PMID 23004253.
  45. ↑ C. Sagan; L. S. Sagan; F. Drake (February 25, 1972). "A Message from Earth". Science. 175 (4024): 881–884. Bibcode:1972Sci...175..881S. doi:10.1126/science.175.4024.881. PMID 17781060.
  46. ↑ S. Kronish (October 27, 1991). "Space Launches are Featured". The Index Journal. South Carolina, USA. p. 21. Retrieved December 5, 2017 – via Newspapers.com.

Bibliography

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