Peaceful nuclear explosion

Peaceful nuclear explosions (PNEs) are nuclear explosions conducted for non-military purposes, such as activities related to economic development including the creation of canals. During the 1960s and 1970s, both the United States and the Soviet Union conducted a number of PNEs.

Six of the explosions by the Soviet Union are considered to have been of an applied nature, not just tests.

Subsequently the United States and the Soviet Union halted their programs. Definitions and limits are covered in the Peaceful Nuclear Explosions Treaty of 1976.[1][2] The Comprehensive Nuclear-Test-Ban Treaty of 1996 prohibits all nuclear explosions, regardless of whether they are for peaceful purposes or not.

Peaceful Nuclear Explosions Treaty

In the PNE Treaty, the signatories agreed: not to carry out any individual nuclear explosions having a yield exceeding 150 kilotons; not to carry out any group explosion (consisting of a number of individual explosions) having an aggregate yield exceeding 1,500 kilotons; and not to carry out any group explosion having an aggregate yield exceeding 150 kilotons unless the individual explosions in the group could be identified and measured by agreed verification procedures. The parties also reaffirmed their obligations to comply fully with the Limited Test Ban Treaty of 1963.

The parties reserve the right to carry out nuclear explosions for peaceful purposes in the territory of another country if requested to do so, but only in full compliance with the yield limitations and other provisions of the PNE Treaty and in accord with the Non-Proliferation Treaty.

Articles IV and V of the PNE Treaty set forth the agreed verification arrangements. In addition to the use of national technical means, the treaty states that information and access to sites of explosions will be provided by each side, and includes a commitment not to interfere with verification means and procedures.

The protocol to the PNE Treaty sets forth the specific agreed arrangements for ensuring that no weapon-related benefits precluded by the Threshold Test Ban Treaty are derived by carrying out a nuclear explosion used for peaceful purposes, including provisions for use of the hydrodynamic yield measurement method, seismic monitoring and on-site inspection.

The agreed statement that accompanies the treaty specifies that a "peaceful application" of an underground nuclear explosion would not include the developmental testing of any nuclear explosive.[3]

United States: Operation Plowshare

One of the Chariot schemes involved chaining five thermonuclear devices to create the artificial harbor.

Operation Plowshare was the name of the U.S. program for the development of techniques to use nuclear explosives for peaceful purposes. The name was coined in 1961, taken from Micah 4:3 ("And he shall judge among the nations, and shall rebuke many people: and they shall beat their swords into plowshares, and their spears into pruning hooks: nation shall not lift up sword against nation, neither shall they learn war any more"). Twenty-eight nuclear blasts were detonated between 1961 and 1973.

One of the first U.S. proposals for peaceful nuclear explosions that came close to being carried out was Project Chariot, which would have used several hydrogen bombs to create an artificial harbor at Cape Thompson, Alaska. It was never carried out due to concerns for the native populations and the fact that there was little potential use for the harbor to justify its risk and expense. There was also talk of using nuclear explosions to excavate a second Panama Canal.[4]

The largest excavation experiment took place in 1962 at the Department of Energy's Nevada Test Site. The Sedan nuclear test carried out as part of Operation Storax displaced 12 million tons of earth, creating the largest human-made crater in the world, generating a large nuclear fallout over Nevada and Utah. Three tests were conducted in order to stimulate natural gas production, but the effort was abandoned as impractical because of cost and radioactive contamination of the gas.[5][6]

There were many negative impacts from Project Plowshare’s 27 nuclear explosions. For example, the Gasbuggy site,[6] located 55 miles east of Farmington, New Mexico, still contains nuclear contamination from a single subsurface blast in 1967.[7] Other consequences included blighted land, relocated communities, tritium-contaminated water, radioactivity, and fallout from debris being hurled high into the atmosphere. These were ignored and downplayed until the program was terminated in 1977, due in large part to public opposition, after $770 million had been spent on the project.[8]

Soviet Union: Nuclear Explosions for the National Economy

The Soviet Union conducted a much more vigorous program of 239 nuclear tests, some with multiple devices, between 1965 and 1988 under the auspices of Program No. 6 and Program No. 7 – Nuclear Explosions for the National Economy. Its aims and results were similar to those of the American effort, with the exception that many of the blasts were considered applications, not tests.[9] The best known of these in the West was the Chagan test in January 1965 as radioactivity from the Chagan test was detected over Japan by both the U.S. and Japan. The United States complained to the Soviets, but the matter was dropped.

In the 1970s, the Soviet Union started the "Deep Seismic Sounding" Program, that included the use of peaceful nuclear explosions to create seismic deep profiles. Compared to the usage of conventional explosives or mechanical methods, nuclear explosions allow the collection of longer seismic profiles (up to several thousand kilometers).[10]

There are proponents for continuing the PNE programs in modern Russia. They (e.g. A. Koldobsky) state that the program already paid for itself and saved the USSR billions of rubles and can save even more if continued. They also allege that the PNE is the only feasible way to put out large fountains and fires on natural gas deposits and the safest and most economically viable way to destroy chemical weapons.

Their opponents, including the discredited Alexey Yablokov,[11] state that all PNE technologies have non-nuclear alternatives and that many PNEs actually caused nuclear disasters.

Reports on the successful Soviet use of nuclear explosions in extinguishing out-of-control gas well fires were widely cited in United States policy discussions of options for stopping the 2010 Gulf of Mexico Deepwater Horizon oil spill.[12][13]

Other nations

Germany at one time considered manufacturing nuclear explosives for civil engineering purposes. In the early 1970s a feasibility study was conducted for a project to build a canal from the Mediterranean Sea to the Qattara Depression in the Western Desert of Egypt using nuclear demolition. This project proposed to use 213 devices, with yields of 1 to 1.5 megatons detonated at depths of 100 to 500 meters, to build this canal for the purpose of producing hydroelectric power.[14][15][16]

The Smiling Buddha, India's first explosive nuclear device was described by the Indian Government as a peaceful nuclear explosion.[17]

In Australia, nuclear blasting was proposed as a way of mining iron ore in the Pilbara.[18]

Civil engineering and energy production

The 1962 Sedan nuclear test formed a crater 100 m (330 ft) deep with a diameter of about 390 m (1,300 ft), as a means of investigating the possibilities of using peaceful nuclear explosions for large-scale earth moving. If this test was conducted in 1965+, when improvements in device design were realized, a "100-fold" reduction in radiation release was considered feasible.[19] The 140 kiloton Soviet Chagan (nuclear test), comparable in yield to the Sedan test of 104 kt, formed Lake Chagan, reportedly used as a watering hole for cattle and human swimming.[20][21][22]

Apart from their use as weapons, nuclear explosives have been tested and used, in a similar manner to chemical high explosives, for various non-military uses. These have included large-scale earth moving, isotope production and the stimulation and the closing-off of the flow of natural gas.

At the peak of the Atomic Age, the United States initiated Operation Plowshare, involving "peaceful nuclear explosions". The United States Atomic Energy Commission chairman announced that the Plowshares project was intended to "highlight the peaceful applications of nuclear explosive devices and thereby create a climate of world opinion that is more favorable to weapons development and tests".[23][24] The Operation Plowshare program included 27 nuclear tests designed towards investigating these non-weapons uses from 1961 through 1973. Due to the inability of the U.S. physicists to reduce the fission fraction of small, approximately 1 kiloton, yield nuclear devices that would have been required for many civil engineering projects, when long term health and clean-up costs from fission products were included in the cost, there was virtually no economic advantage over conventional explosives, except for potentially the very largest of projects.[25][26]

Map of all proposed routes for a tunnel and/or canal route from the Mediterranean Sea to the Qattara Depression.
No route was shorter than 55 kilometers in length. Canal-cutting investigations began with the buggy salvo shot of Operation Crosstie in 1967.

The Qattara Depression Project, as developed by Professor Friedrich Bassler, who during his appointment to the West German ministry of economics in 1968, put forth a plan to create a Saharan lake and hydroelectric power station by blasting a tunnel between the Mediterranean sea and the Qattara Depression in Egypt, an area that lies below sea level. The core problem of the entire project was the water supply to the depression. Calculations by Bassler showed that digging a canal or tunnel would be too expensive, therefore Bassler determined that the use of nuclear explosive devices, to excavate the canal or tunnel, would be the most economical. The Egyptian government declined to pursue the idea.[27]

The Soviet Union conducted a much more exhaustive program than Plowshare, with 239 nuclear tests, between 1965 and 1988. Furthermore, many of the "tests" were considered economic applications, not tests, in the Nuclear Explosions for the National Economy program.[28]

These included one 30 kiloton explosion being used to close the Uzbekistani Urtabulak gas well in 1966 that had been blowing since 1963, and a few months later a 47 kiloton explosive was used to seal a higher pressure blowout at the nearby Pamuk gas field.[29]

The public records for devices that produced the highest proportion of their yield via fusion-only reactions are possibly the Taiga Soviet peaceful nuclear explosions of the 1970s, with 98% of their 15 kiloton explosive yield being derived from fusion reactions, a total fission fraction of 0.3 kilotons in a 15 kt device.[30][31]

The repeated detonation of nuclear devices underground in salt domes, in a somewhat analogous manner to the explosions that power a car internal combustion engine (in that it would be a heat engine) has also been proposed as a means of fusion power, in what is termed PACER.[32] Other investigated uses for peaceful nuclear explosions were underground detonations to stimulate, by a process analogous to fracking, the flow of petroleum and natural gas in tight formations, this was most developed in the Soviet Union, with an increase in the production of many well heads being reported.[29]

Physics

The element einsteinium was first discovered, in minute quantities, following the analysis of the fallout from the first thermonuclear atmospheric test.[33]

The discovery and synthesis of new chemical elements by nuclear transmutation, and their production in the necessary quantities to allow the studying of their properties, was carried out in nuclear explosive device testing. For example, the discovery of the short lived einsteinium and fermium, both created under the intense neutron flux environment within thermonuclear explosions, followed the first Teller-Ulam thermonuclear device test – Ivy Mike. The rapid capture of so many neutrons required in the synthesis of einsteinium would provide the needed direct experimental confirmation of the so-called r-process, the multiple neutron absorptions needed to explain the cosmic nucleosynthesis (production) of all heavy chemical elements heavier than nickel on the periodic table, in supernova explosions, before beta decay, with the r-process explaining the existence of many stable elements in the universe.[34]

The worldwide presence of new isotopes from atmospheric testing beginning in the 1950s led to the 2008 development of a reliable way to detect art forgeries. Paintings created after that period may contain traces of caesium-137 and strontium-90, isotopes that did not exist in nature before 1945.[35][36] (Fission products were produced in the natural nuclear fission reactor at Oklo about 1.7 billion years ago, but these decayed away before the earliest known human painting.)[37]

Both climatology and particularly aerosol science, a subfield of atmospheric science, were largely created to answer the question of how far and wide fallout would travel. Similar to radioactive tracers used in hydrology and materials testing, fallout and the neutron activation of nitrogen gas served as a radioactive tracer that was used to measure and then help model global circulations in the atmosphere by following the movements of fallout aerosols.[38][39]

After the Van Allen Belts surrounding Earth were published about in 1958, James Van Allen suggested that a nuclear detonation would be one way of probing the magnetic phenomenon, data obtained from the August 1958 Project Argus test shots, a high altitude nuclear explosion investigation, were vital to the early understanding of Earth's magnetosphere.[40][41]

An artist's conception of the NASA reference design for the Project Orion spacecraft powered by nuclear pulse propulsion.

Soviet nuclear physicist and Nobel peace prize recipient Andrei Sakharov also proposed the idea that earthquakes could be mitigated and particle accelerators could be made by utilizing nuclear explosions,[42][43] with the latter created by connecting a nuclear explosive device with another of his inventions, the explosively pumped flux compression generator,[44] to accelerate protons to collide with each other to probe their inner workings, an endeavor that is now done at much lower energy levels with non-explosive superconducting magnets in CERN. Sakharov suggested to replace the copper coil in his MK generators by a big superconductor solenoid to magnetically compress and focus underground nuclear explosions into a shaped charge effect. He theorized this could focus 1023 positively charged protons per second on a 1 mm2 surface, then envisaged making two such beams collide in the form of a supercollider.[45]

Underground nuclear explosive data from peaceful nuclear explosion test shots have been used to investigate the composition of Earth's mantle, analogous to the exploration geophysics practice of mineral prospecting with chemical explosives in "deep seismic sounding" reflection seismology.[46][47][48]

Project A119, proposed in the 1960s, which as Apollo scientist Gary Latham explained, would have been the detonating of a "smallish" nuclear device on the Moon in order to facilitate research into its geologic make-up.[49] Analogous in concept to the comparatively low yield explosion created by the water prospecting (LCROSS) Lunar Crater Observation and Sensing Satellite mission, which launched in 2009 and released the "Centaur" kinetic energy impactor, an impactor with a mass of 2,305 kg (5,081 lb), and an impact velocity of about 9,000 km/h (5,600 mph),[50] releasing the kinetic energy equivalent of detonating approximately 2 tons of TNT (8.86 GJ).

A nuclear shaped charge design that was to provide nuclear pulse propulsion to the Project Orion vehicle.

Propulsion use

Although likely never achieving orbit due to aerodynamic drag, the first macroscopic object to obtain Earth orbital velocity was a "manhole cover" propelled by the detonation of test shot Pascal-B, before sputnik obtained orbital velocity, and also successfully became the first satellite, in October 1957. The use of a subterranean shaft and nuclear device to propel an object to escape velocity has since been termed a "thunder well".[51]

The direct use of nuclear explosives, by using the impact of propellant plasma from a nuclear shaped charge acting on a pusher plate, has also been seriously studied as a potential propulsion mechanism for space travel (see Project Orion).

Edward Teller, in the United States, proposed the use of a nuclear detonation to power an explosively pumped soft X-ray laser as a component of a ballistic missile defense shield, this would destroy missile components by transferring momentum to the vehicles surface by laser ablation. This ablation process is one of the damage mechanisms of a laser weapon, but it is also the basis of pulsed laser propulsion for spacecraft.

Ground flight testing by Professor Leik Myrabo, using a non-nuclear, conventionally powered pulsed laser test-bed, successfully lifted a lightcraft 72 meters in altitude by a method similar to ablative laser propulsion in 2000.[52]

A powerful solar system based soft X-ray, to ultraviolet, laser system has been calculated to be capable of propelling an interstellar spacecraft, by the light sail principle, to 11% of the speed of light.[53] In 1972 it was also calculated that a 1 Terawatt, 1-km diameter x-ray laser with 1 angstrom wavelength impinging on a 1-km diameter sail, could propel a spacecraft to Alpha Centauri in 10 years.[54]

Artist's impression of the impact event that resulted in the Cretaceous–Paleogene extinction event, which killed the Dinosaurs some 65 million years ago. A natural impact with an explosive yield of 100 teratons of TNT (4.2×1023 J).[55] The most powerful man-made explosion, the Tsar Bomba, by comparison had a yield almost 2 million times smaller – 57 megatons of TNT (2.4×1017 J).[56] The 1994 Comet Shoemaker–Levy 9 impacts on planet Jupiter, the Tunguska and Chelyabinsk asteroid–Earth collisions of 1908 and 2013 respectively, have served as an impetus for the analysis of technologies that could prevent the destruction of human life by impact events.

Asteroid impact avoidance

A proposed means of averting an asteroid impacting with Earth, assuming low lead times between detection and Earth impact, is to detonate one, or a series, of nuclear explosive devices, on, in, or in a stand-off proximity orientation with the asteroid,[57] with the latter method occurring far enough away from the incoming threat to prevent the potential fracturing of the near-Earth object, but still close enough to generate a high thrust laser ablation effect.[58]

A 2007 NASA analysis of impact avoidance strategies using various technologies stated:[59]

Nuclear stand-off explosions are assessed to be 10–100 times more effective than the non-nuclear alternatives analyzed in this study. Other techniques involving the surface or subsurface use of nuclear explosives may be more efficient, but they run an increased risk of fracturing the target near-Earth object. They also carry higher development and operations risks.

See also

Books

References

  1. ↑ "Announcement of Treaty on Underground Nuclear Explosions Peaceful Purposes (PNE Treaty)" (PDF). Gerald R. Ford Museum and Library. May 28, 1976.
  2. ↑ Peters, Gerhard; Woolley, John T. "Gerald R. Ford: "Message to the Senate Transmitting United States-Soviet Treaty and Protocol on the Limitation of Underground Nuclear Explosions," July 29, 1976". The American Presidency Project. University of California - Santa Barbara.
  3. ↑ "Peaceful Nuclear Explosions Treaty". Arms Control Association.
  4. ↑ "Report of the Atlantic–Pacific transoceanic canal study commission", Congressional Record: proceedings & debates of the 90th Congress, second session (message from the President), Senate, Washington, DC, US: Congress, p. 25747, 1968-09-05, retrieved 2012-01-22, The collection of data was substantially completed on Route 17 in Panama one of the routes considered for nuclear excavations… The Atomic Energy Commission has recently conducted the first two of the planned series of nuclear excavation experiments designed to determine the feasibility of nuclear excavation of a sea level canal.
  5. ↑ "Site" (PDF), Rulison, CO (PDF) (fact sheet), US: Department of Energy, Office of Legacy Management.
  6. 1 2 Metzger, Peter (February 22, 1970), "Project Gasbuggy and Catch-85*: *That's krypton-85, one of the radioactive by-products of nuclear explosions that release natural gas", The New York Times, p. SM14, It's 95 per cent safe? We worry about the other 5
  7. ↑ "Gas Buggy". Environmental Management (EM). DOE. Retrieved 2010-09-19.
  8. ↑ Sovacool, Benjamin K (2011), "Contesting the Future of Nuclear Power: A Critical Global Assessment of Atomic Energy", World Scientific, pp. 171–2.
  9. ↑ Nordyke, MD (2000-09-01). The Soviet Program for Peaceful Uses of Nuclear Explosions (PDF). Lawrence Livermore National Laboratory. pp. 34–35. doi:10.2172/793554. Report no.: UCRL-ID-124410 Rev 2; US Department of Energy contract no.: W-7405-Eng48.
  10. ↑ "DSS", Seismic, University of Wyoming.
  11. ↑ Яблоков, АВ (1995-02-01). "Ядерная Мифология Конца XX Века (Nuclear Mythology of the 20th Century)" (in Russian). Russia: Новый Мир (New World). Retrieved 2013-09-18.
  12. ↑ Broad, William J (2010-06-02). "Nuclear Option on Gulf Oil Spill? No Way, US Says". The New York Times. Retrieved 2010-06-18.
  13. ↑ Astrasheuskaya, Nastassia; Judah, Ben; Selyukh, Alina (2010-07-02). "Special Report: Should BP nuke its leaking well?". Reuters. Retrieved 2010-07-08.
  14. ↑ "Managing water for peace in the Middle East". archive.unu.edu. Retrieved 2016-08-18.
  15. ↑ "Flooding the Qattara Depression | The Basement Geographer". basementgeographer.com. Retrieved 2016-08-18.
  16. ↑ Ministry of Electric Power and Energy (1978). "Development of the Qattara Project, Egypt". Technical committee on the peaceful uses of nuclear explosions; Vienna, Austria; 22 - 24 Nov 1976. IAEA-TC--81-5/6.
  17. ↑ "India's Nuclear Weapons Program - Smiling Buddha: 1974". nuclearweaponarchive.org. Retrieved 2016-08-18.
  18. ↑ "Nuclear blasting proposed for Pilbara Iron Ore Project", Industrial Reviews and Mining Year Book, 1970, pp. 255–9.
  19. ↑ Declassified U.S. Nuclear Test Film #35 c. 29:30 minutes
  20. ↑ Guinness World Records. "Largest crater from an underground nuclear explosion". Retrieved October 24, 2014.
  21. ↑ "The Soviet Nuclear Weapons Program". Retrieved October 24, 2014.
  22. ↑ Russia Today documentary that visits the lake at around the 1 minute mark on YouTube
  23. ↑ Perrow, Charles (September–October 2013). "Nuclear denial: From Hiroshima to Fukushima". Bulletin of the Atomic Scientists. 69 (5).
  24. ↑ "semiannual report to Congress in January 1958". Other mentions of Strauss making statements in Feb 1958 or hearings being held are on p 447, and 474 it seems. p.474's quotation: Senate Subcommittee of the Committee on Foreign Relations, Hearings on Control and Reduction of Armaments, Feb. 28-April 17, 1958, Washington: Government Printing Office, 1958) pp.1336-64.
  25. ↑ "Q&A with Scott Kirsch: Digging with bombs". Usnews.com. Archived from the original on January 31, 2010. Retrieved November 25, 2010.
  26. ↑ Declassified U.S. Nuclear Test Film #35 c. 12:00 minutes
  27. ↑ "Global Hyper Saline Power Generation Qattara Depression Potentials" (PDF). MIK Technology. December 19, 2010. Retrieved November 20, 2015.
  28. ↑ Nordyke, MD (September 1, 2000). The Soviet Program for Peaceful Uses of Nuclear Explosions (PDF). Lawrence Livermore National Laboratory. pp. 34–35. doi:10.2172/793554. Report no.: UCRL-ID-124410 Rev 2; US Department of Energy contract no.: W-7405-Eng48.
  29. 1 2 Nordyke, M. D. (September 1, 2000). "Extinguishing Runaway Gas Well Fires". The Soviet Program for Peaceful Uses of Nuclear Explosions (PDF). Lawrence Livermore National Laboratory. pp. 34–35. doi:10.2172/793554. Report no.: UCRL-ID-124410 Rev 2. U. S. Department of Energy contract no.: W-7405-Eng48.
  30. ↑ Disturbing the Universe – Freeman Dyson
  31. ↑ The Soviet Program for Peaceful Uses of Nuclear Explosions by Milo D. Nordyke. Science & Global Security, 1998, Volume 7, pp. 1–117. See test shot "Taiga".
  32. ↑ John Nuckolls, "Early Steps Toward Inertial Fusion Energy (IFE)", LLNL, June 12, 1998
  33. ↑ EINSTEINIUM AND FERMIUM, ALBERT GHIORSO, LAWRENCE BERKELEY NATIONAL LABORATORY
  34. ↑ Byrne, J. Neutrons, Nuclei, and Matter, Dover Publications, Mineola, NY, 2011, ISBN 978-0-486-48238-5 (pbk.) pp. 267.
  35. ↑ Cartlidge, Edwin (July 4, 2008). "Nuclear fallout used to spot fake art". Physics World – the member magazine of the Institute of Physics. IOP Group. Retrieved December 7, 2014.
  36. ↑ "Can past nuclear explosions help detect forgeries?". Theartnewspaper.com. Archived from the original on November 13, 2010. Retrieved November 25, 2010.
  37. ↑ Emsley, John (2011). Nature's Building Blocks: An A-Z Guide to the Elements (New ed.). New York, NY: Oxford University Press. ISBN 978-0-19-960563-7.
  38. ↑ Entangled histories: Climate science and nuclear weapons research
  39. ↑ "Nuclear weapons' surprising contribution to climate science". Phys.org. July 13, 2012. Retrieved May 30, 2013.
  40. ↑ "Going Nuclear Over the Pacific | Past Imperfect". Blogs.smithsonianmag.com. Retrieved May 30, 2013.
  41. ↑ "Section VI Nuclear Weapons Effects Technology II-6-28" (PDF). Federation of American Scientists. Retrieved November 20, 2015.
  42. ↑ "Tsar Bomba – The Legacy". Archived from the original on November 4, 2012.
  43. ↑ Viktor Adamsky and Yuri Smirnov. 1994. "Moscow's Biggest Bomb: the 50-Megaton Test of October 1961" Cold War International History Project Bulletin, Issue 4, Fall 1994
  44. ↑ Sakharov, A. D. (1966). "Magnetoimplosive Generators". Soviet Physics Uspekhi. 9 (2): 294. doi:10.1070/PU1966v009n02ABEH002876.
  45. ↑ "Guide to the Victor Frederick Weisskopf Papers MC.0572". Massachusetts Institute of Technology. Retrieved November 20, 2015.
  46. ↑ "Travel time analysis of P waves arising from six underground nuclear explosion at Novaya Zemlya". Annalsofgeophysics.eu. Retrieved May 30, 2013.
  47. ↑ "Upper Mantle Heterogeneities from Active and Passive Seismology". Springer.com. April 16, 1997. Retrieved May 30, 2013.
  48. ↑ "A Database Of Deep Seismic Sounding Peaceful Nuclear Explosion Recordings For Seismic Monitoring Of Northern Eurasia" (PDF). Retrieved May 30, 2013.
  49. ↑ "Moon madness". The Sydney Morning Herald. December 21, 1969. p. 19. Retrieved September 9, 2011.
  50. ↑ "NASA's LCROSS Mission Changes Impact Crater". NASA. September 29, 2009. Retrieved November 21, 2009.
  51. ↑ "Operation Plumbbob". Retrieved October 24, 2014.
  52. ↑ "Laser Propulsion Thrusters for Space Transportation". springer.com. Retrieved April 1, 2015.
  53. ↑ "Roundtrip Interstellar Travel Using Laser-Pushed Lightsails. VOL. 21, NO. 2, MARCH-APRIL 1984 J. SPACECRAFT. Robert Forward et. al" (PDF). Retrieved May 30, 2013.
  54. ↑ W.E Mockel, Propulsion by impinging Laser beams. Journal of Spacecraft and rockets. 9, no 12 p 942 (1972).
  55. ↑ Covey et al.
  56. ↑ Adamsky and Smirnov, 19.
  57. ↑ Solem, J. C. (2000). "Deflection and disruption of asteroids on collision course with Earth". Journal of the British Interplanetary Society. 53: 180–196.
  58. ↑ Dillow, Clay (April 9, 2012). "How it Would Work: Destroying an Incoming Killer Asteroid With a Nuclear Blast". Popular Science. Bonnier. Retrieved January 6, 2013.
  59. ↑ "Near-Earth Object Survey and Deflection Analysis of Alternatives Report to Congress March 2007". National Aeronautics and Space Administration. Retrieved November 20, 2015.
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