Editing Asteroid impact avoidance (section)

== Collision avoidance strategies ==
Cost, risk of failure, complexity, technology readiness, and overall performance are all important trade-offs in weighing collision avoidance strategies.<ref>{{cite journal|last1=Canavan|first1=G. H |last2=Solem|first2=J. C.|year=1992|title=Interception of near-Earth objects|journal=Mercury|issn=0047-6773|volume=21|issue=3|pages=107–109|url=https://www.researchgate.net/publication/253052410|bibcode=1992Mercu..21..107C}}</ref> Methods can be differentiated by the type of mitigation (deflection or fragmentation), energy source (kinetic, electromagnetic, gravitational, solar/thermal, or nuclear), and approach strategy ({{Anchor|interception2016-01-26}}interception,<ref name="HallRoss">C. D. Hall and [[I. Michael Ross|I. M. Ross]], "Dynamics and Control Problems in the Deflection of Near-Earth Objects", ''Advances in the Astronautical Sciences, Astrodynamics 1997'', Vol.97, Part I, 1997, pp.613–631. {{hdl|10945/40399}}</ref><ref>{{cite journal|last=Solem|first=J. C.|year=1993|title=Interception of comets and asteroids on collision course with Earth|journal=Journal of Spacecraft and Rockets|volume=30|issue=2|pages=222–228|doi=10.2514/3.11531|bibcode=1993JSpRo..30..222S|url=https://digital.library.unt.edu/ark:/67531/metadc1090076/}}</ref><ref>Solem, J. C.; Snell, C. (1994). "[https://books.google.com/books?id=xXWZolI9NkUC&q=Terminal%20intercept%20for%20less%20than%20one%20orbital%20snell&pg=PA1013 Terminal intercept for less than one orbital period warning] {{webarchive |url=https://web.archive.org/web/20160506210107/https://books.google.com/books?id=xXWZolI9NkUC&pg=PA1013#v=onepage&q=Terminal%20intercept%20for%20less%20than%20one%20orbital%20snell |date=May 6, 2016 }}", a chapter in ''Hazards Due to Comets and Asteroids'', Geherels, T., ed. (University of Arizona Press, Tucson), pp. 1013–1034.</ref> rendezvous, or remote station).

Strategies fall into two basic sets: fragmentation and {{Anchor|delay2016-01-26}}delay.<ref name="HallRoss" /><ref>{{cite journal |last=Solem |first=J. C. |year=2000 |title=Deflection and disruption of asteroids on collision course with Earth |url=https://ui.adsabs.harvard.edu/abs/2000JBIS...53..180S/abstract |journal=Journal of the British Interplanetary Society |volume=53 |pages=180–196 |bibcode=2000JBIS...53..180S}}</ref> Fragmentation concentrates on rendering the impactor harmless by fragmenting it and scattering the fragments so that they miss the Earth or are small enough to burn up in the atmosphere. Delay exploits the fact that both the Earth and the impactor are in orbit. An impact occurs when both reach the same point in space at the same time, or more correctly when some point on Earth's surface intersects the impactor's orbit when the impactor arrives. Since the Earth is approximately {{convert|12,750|km|mi|sp=us}} in diameter and moves at approximately {{cvt|30|km/s}} in its orbit, it travels a distance of one planetary diameter in about 425 seconds, or slightly over seven minutes. Delaying, or advancing the impactor's arrival by times of this magnitude can, depending on the exact geometry of the impact, cause it to miss the Earth.<ref name="RossParkPorter">{{cite journal|last1=Ross|first1=I. M.|last2=Park|first2=S.-Y.|last3=Porter|first3=S. E.|title=Gravitational Effects of Earth in Optimizing Delta-V for Deflecting Earth-Crossing Asteroids|journal=Journal of Spacecraft and Rockets|volume=38|issue=5|date=2001|pages=759–764|hdl=10945/30321|url=https://calhoun.nps.edu/bitstream/handle/10945/30321/AIAA-3743-490.pdf|access-date=2019-08-30|citeseerx=10.1.1.462.7487|doi=10.2514/2.3743|s2cid=123431410 }}</ref>

Collision avoidance strategies can also be seen as either direct, or indirect and in how rapidly they transfer energy to the object. The direct methods, such as nuclear explosives, or kinetic impactors, rapidly intercept the bolide's path. Direct methods are preferred because they are generally less costly in time and money.{{citation needed|date=January 2022}} Their effects may be immediate, thus saving precious time. These methods would work for short-notice and long-notice threats, and are most effective against solid objects that can be directly pushed, but in the case of kinetic impactors, they are not very effective against large loosely aggregated rubble piles. Indirect methods, such as [[gravity tractor]]s, attaching rockets or mass drivers, are much slower. They require traveling to the object, changing course up to 180 degrees for [[space rendezvous]], and then taking much more time to change the asteroid's path just enough so it will miss Earth.{{citation needed|date=May 2020}}

Many NEOs are thought to be "flying [[rubble pile]]s" only loosely held together by gravity, and a typical spacecraft sized kinetic-impactor deflection attempt might just break up the object or fragment it without sufficiently adjusting its course.<ref name="spacesailing.net">{{Cite web|url=http://www.spacesailing.net/paper/200703_Washington_DachwaldKahleWie.pdf|archiveurl=https://web.archive.org/web/20160304091722/http://www.spacesailing.net/paper/200703_Washington_DachwaldKahleWie.pdf|url-status=dead|title=Planetary Defense Conference 2007, Washington D.C. Head-On Impact Deflection of NEAs: A Case Study for 99942 Apophis. Bernd Dachwald, Ralph Kahle, Bong Wie, Published in 2007.pg 3|archivedate=March 4, 2016}}</ref> If an asteroid breaks into fragments, any fragment larger than {{convert|35|m|ft|sp=us}} across would not burn up in the atmosphere and itself could impact Earth. Tracking the thousands of [[buckshot]]-like fragments that could result from such an explosion would be a very daunting task, although fragmentation would be preferable to doing nothing and allowing the originally larger rubble body, which is analogous to a [[Shotgun slug#Wax slugs|shot and wax slug]], to impact the Earth.{{citation needed|date=January 2022}}

In [[Cielo (supercomputer)|Cielo]] simulations conducted in 2011–2012, in which the rate and quantity of energy delivery were sufficiently high and matched to the size of the rubble pile, such as following a tailored nuclear explosion, results indicated that any asteroid fragments, created after the pulse of energy is delivered, would not pose a threat of re-[[coalescence (physics)|coalescing]] (including for those with the shape of asteroid [[25143 Itokawa|Itokawa]]) but instead would rapidly achieve [[escape velocity]] from their parent body (which for Itokawa is about 0.2&nbsp;m/s) and therefore move out of an Earth-impact trajectory.<ref name="Dillow">{{cite news| last =Dillow| first =Clay| title =How it Would Work: Destroying an Incoming Killer Asteroid With a Nuclear Blast| newspaper =Popular Science| publisher =Bonnier| date =9 April 2012| url =http://www.popsci.com/technology/article/2012-04/how-it-would-work-destroying-incoming-killer-asteroid-nuclear-blast| access-date = 6 January 2013}}</ref><ref>{{Cite web |url=http://permalink.lanl.gov/object/tr?what=info%3Alanl-repo%2Flareport%2FLA-UR-11-03124 |title=RAGE Hydrocode Modeling of Asteroid Mitigation:Surface and Subsurface Explosions in Porous PHO Objects |author=Weaver |display-authors=etal |year=2011 |access-date=2018-04-09 |archive-url=https://web.archive.org/web/20180409145428/http://permalink.lanl.gov/object/tr?what=info%3Alanl-repo%2Flareport%2FLA-UR-11-03124 |archive-date=2018-04-09 |url-status=live }}</ref><ref>[https://web.archive.org/web/20170413053140/http://permalink.lanl.gov/object/tr?what=info%3Alanl-repo%2Flareport%2FLA-UR-11-00015 Further RAGE modeling of Asteroid mitigation, surface and subsurface explosions in porous objects. Weaver et al. 2011]</ref>

=== Nuclear explosive device ===
{{See also|Nuclear pulse propulsion|Nuclear bunker buster|Operation Fishbowl}}
[[File:Bravo secondary fireball.jpg|thumb|upright=1.5|In a similar manner to the earlier pipes filled with a [[partial pressure]] of helium, as used in the [[Ivy Mike]] test of 1952, the 1954 [[Castle Bravo]] test was likewise heavily instrumented with [[Nuclear weapon design#Light pipes|line-of-sight (LOS) pipes]], to better define and quantify the timing and energies of the x-rays and neutrons produced by these early thermonuclear devices.<ref>{{Cite web|url=http://archive.org/details/CastleCommandersReport1954|title=Operation CASTLE Commander's Report|date=May 21, 1954|website=Internet Archive}}</ref><ref>{{Cite web|url=https://www.youtube.com/watch?v=DFJ2MyWlXgs|title=Declassified U.S. Nuclear Test Film #34|date=31 October 2007 |website=www.youtube.com}}</ref> One of the outcomes of this diagnostic work resulted in this graphic depiction of the transport of energetic x-ray and neutrons through a vacuum line, some 2.3&nbsp;km long, whereupon it heated solid matter at the "station 1200" blockhouse and thus generated a secondary fireball.<ref>{{Cite web |url=http://permalink.lanl.gov/object/tr?what=info%3Alanl-repo%2Flareport%2FLA-UR-03-5462 |title=Data Contribute to Certification Fred N. Mortensen, John M. Scott, and Stirling A. Colgate |access-date=2016-12-23 |archive-url=https://web.archive.org/web/20161223223806/http://permalink.lanl.gov/object/tr?what=info%3Alanl-repo%2Flareport%2FLA-UR-03-5462 |archive-date=2016-12-23 |url-status=live }}</ref><ref>{{Cite web|url=http://la-science.lanl.gov/lascience28.shtml|title=LANL: Los Alamos Science: LA Science No. 28|date=June 12, 2007|archive-url=https://web.archive.org/web/20070612184310/http://la-science.lanl.gov/lascience28.shtml |archive-date=2007-06-12 }}</ref>]]

Initiating a [[nuclear explosive]] device [[proximity fuze|above]], [[impact fuze|on]], or slightly [[Robust Nuclear Earth Penetrator|beneath]], the surface of a threatening celestial body is a potential deflection option, with the optimal detonation height dependent upon the composition and size of the object.<ref>{{cite book|author=Simonenko, V.|author2=Nogin, V.|author3=Petrov, D.|author4=Shubin, O.|author5=Solem, J. C.|date=1994|chapter-url=https://books.google.com/books?id=xXWZolI9NkUC&pg=PA929|chapter=Defending the Earth against impacts from large comets and asteroids|title=Hazards Due to Comets and Asteroids|editor=Geherels, T.|editor2=Matthews, M. S.|editor3=Schumann, A. M.|publisher=University of Arizona Press|isbn=9780816515059|pages=929–954}}</ref><ref>Solem, J. C. (1995). "[https://web.archive.org/web/20150909023233/https://e-reports-ext.llnl.gov/pdf/232015.pdf Interception and disruption]", in ''Proceedings of Planetary Defense Workshop, Livermore, CA, May 22–26, 1995'', CONF-9505266 (LLNL, Livermore, CA), pp. 219–228 (236–246).</ref><ref>{{cite journal|last=Solem|first=J. C.|year=1999|title=Comet and asteroid hazards: Threat and mitigation|journal=Science of Tsunami Hazards|volume=17|issue=3|pages=141–154|url=http://www.tsunamisociety.org/TitlesAuthors14to18.html}}</ref> It does not require the entire NEO to be vaporized to mitigate an impact threat. In the case of an inbound threat from a "rubble pile", the [[proximity fuze|stand off]], or detonation height above the surface configuration, has been put forth as a means to prevent the potential fracturing of the rubble pile.<ref name="defending Earth">{{cite book |url=http://www.nap.edu/openbook.php?record_id=12842&page=77 |title=Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies ( 2010 ) National Academy of Sciences page 77|year=2010|doi=10.17226/12842|isbn=978-0-309-14968-6}}</ref> The energetic [[neutron]]s and [[soft X-rays]] released by the detonation, which do not appreciably penetrate matter,<ref>{{cite web|url=http://physics.nist.gov/cgi-bin/ffast/ffast.pl?Formula=H2O&gtype=5&range=S&lower=0.300&upper=2.00&density=1.00 |title=Physics.nist.gov |publisher=Physics.nist.gov |access-date=2011-11-08}}</ref> are converted into heat upon encountering the object's surface matter, [[radiation implosion|ablatively vaporizing]] all [[Line-of-sight propagation|line of sight]] exposed surface areas of the object to a shallow depth,<ref name="defending Earth"/> turning the surface material it heats up into [[ejecta]], and, analogous to the ejecta from a chemical [[rocket engine]] exhaust, changing the velocity, or "nudging", the object off course by the reaction, following [[Newton's third law]], with ejecta going one way and the object being propelled in the other.<ref name="defending Earth"/><ref name="flightglobal">{{cite web|first=Rob|last=Coppinger|date=August 3, 2007|url=http://www.flightglobal.com/articles/2007/08/03/215924/nasa-plans-armageddon-spacecraft-to-blast-asteroid.html|title=NASA plans 'Armageddon' spacecraft to blast asteroid|url-status=dead|archive-url=https://web.archive.org/web/20110905041237/http://www.flightglobal.com/articles/2007/08/03/215924/nasa-plans-armageddon-spacecraft-to-blast-asteroid.html|archive-date=2011-09-05|quote=The warheads would explode at a distance of one-third of the NEO's diameter and each detonation's X and gamma rays and neutrons would turn part of the NEO's surface into an expanding plasma to generate a force to deflect the asteroid.|website=Flightglobal.com}}<br />{{cite web|url=http://www.flightglobal.com/news/articles/nasa-plans-armageddon-spacecraft-to-blast-asteroid-215924/|title=NASA plans 'Armageddon' spacecraft to blast asteroid|access-date=2014-08-03}}</ref> Depending on the energy of the explosive device, the resulting [[reaction engine|rocket exhaust]] effect, created by the high velocity of the asteroid's vaporized mass ejecta, coupled with the object's small reduction in mass, would produce enough of a change in the object's orbit to make it miss the Earth.<ref name="Dillow"/><ref name="flightglobal"/>

A Hypervelocity Asteroid Mitigation Mission for Emergency Response (HAMMER) has been proposed.<ref>{{Cite web|url=https://phys.org/news/2018-03-scientists-asteroid-deflector-massive-potential.html|title=Scientists design conceptual asteroid deflector and evaluate it against massive potential threat |date=March 15, 2018 |website=[[Phys.org]] |archive-url=https://archive.today/20180423052949/https://phys.org/news/2018-03-scientists-asteroid-deflector-massive-potential.html |archive-date=April 23, 2018 |url-status=live}}</ref> While there have been no updates as of 2023 regarding the HAMMER, NASA has published its regular Planetary Defense Strategy and Action Plan for 2023. In it, NASA acknowledges that it is crucial to continue studying the potential of nuclear energy in deflecting or destroying asteroids. This is because it is currently the only option for defense if scientists were not aware of the asteroid within a few months or years, depending on the asteroid's velocity. The report also notes there needs to be research done into the legal implications as well as policy implications on the topic.<ref>{{Cite web |date=April 2023 |title=NASA Planetary Defense Strategy and Action Plan |url=https://www.nasa.gov/sites/default/files/atoms/files/nasa_-_planetary_defense_strategy_-_final-508.pdf |access-date=April 24, 2023}}</ref>

====Stand-off approach====
If the object is very large but is still a loosely-held-together rubble pile, a solution is to detonate one or a series of nuclear explosive devices alongside the asteroid, at a {{convert|20|m|adj=on|sp=us|}} or greater stand-off height above its surface,{{Citation needed|date=August 2019}} so as not to fracture the potentially loosely-held-together object. Providing that this stand-off strategy was done far enough in advance, the force from a sufficient number of nuclear blasts would alter the object's trajectory enough to avoid an impact, according to computer simulations and experimental evidence from [[meteorite]]s exposed to the thermal X-ray pulses of the [[Z Pulsed Power Facility|Z-machine]].<ref>{{cite web |url=https://www.discovermagazine.com/the-sciences/how-to-stop-a-killer-asteroid |title=How to Stop a Killer Asteroid |magazine=Discover |first=Steve |last=Nadis |date=January 21, 2015}}<!-- {{webarchive |url=https://web.archive.org/web/20160827112933/http://discovermagazine.com/2015/march/15-how-to-stop-a-killer-asteroid |date=August 27, 2016 }} --></ref>

In 1967, graduate students under Professor Paul Sandorff at the [[Massachusetts Institute of Technology]] were tasked with designing a method to prevent a hypothetical 18-month distant impact on Earth by the {{convert|1.4|km|mi|adj=mid|-wide|sp=us}} asteroid [[1566 Icarus]], an object that makes regular close approaches to Earth, sometimes as close as 16 [[lunar distance (astronomy)|lunar distances]].<ref>{{Cite journal|last1=Goldstein |first1=R. M.|title=Radar Observations of Icarus|journal=[[Science (journal)|Science]]|year=1968|volume=162 |issue=3856 |pages=903–4|bibcode = 1968Sci...162..903G|doi=10.1126/science.162.3856.903|pmid=17769079|s2cid=129644095}}</ref> To achieve the task within the timeframe and with limited material knowledge of the asteroid's composition, a variable stand-off system was conceived. This would have used a number of modified [[Saturn V]] rockets sent on interception courses and the creation of a handful of nuclear explosive devices in the 100-megaton energy range—coincidentally, the same as the maximum yield of the Soviets' [[Tsar Bomba#Test|''Tsar Bomba'']] would have been if a uranium tamper had been used—as each rocket vehicle's [[payload]].<ref name="Time1967">[http://content.time.com/time/magazine/article/0,9171,843952,00.html "Systems Engineering: Avoiding an Asteroid"]  {{webarchive|url=https://web.archive.org/web/20130721110612/http://www.time.com/time/magazine/article/0%2C9171%2C843952%2C00.html |date=July 21, 2013 }}, ''[[Time (magazine)|Time]]'', June 16, 1967.</ref><ref name="Day">Day, Dwayne A., [http://www.thespacereview.com/article/175/1 "Giant bombs on giant rockets: Project Icarus"] {{webarchive |url=https://web.archive.org/web/20160415041026/http://www.thespacereview.com/article/175/1 |date=April 15, 2016 }}, ''The Space Review'', Monday, July 5, 2004</ref> The design study was later published as [[1566 Icarus#Project Icarus|Project Icarus]]<ref name="Icarus">Kleiman Louis A., [http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&tid=6840 ''Project Icarus: an MIT Student Project in Systems Engineering''] {{webarchive |url=https://web.archive.org/web/20071017105104/http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&tid=6840 |date=October 17, 2007 }}, Cambridge, Massachusetts : MIT Press, 1968</ref> which served as the inspiration for the 1979 film ''[[Meteor (film)|Meteor]]''.<ref name="Day"/><ref>{{Cite web|url=http://www.ips.gov.au/IPSHosted/neo/info/refers/Bk_Icarus_MIT.htm|archiveurl=https://web.archive.org/web/20160602104006/http://www.ips.gov.au/IPSHosted/neo/info/refers/Bk_Icarus_MIT.htm|url-status=dead|title=''Project Icarus''|archivedate=June 2, 2016}}</ref><ref name="Tech1979">[http://tech.mit.edu/archives/VOL_099/TECH_V099_S0470_P003.pdf "MIT Course precept for movie"] {{webarchive |url=https://web.archive.org/web/20161104102228/http://tech.mit.edu/archives/VOL_099/TECH_V099_S0470_P003.pdf |date=November 4, 2016 }}, ''The Tech'', MIT, October 30, 1979</ref>

A [[NASA]] analysis of deflection alternatives, conducted in 2007, stated:

{{blockquote|Nuclear standoff 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 NEO. They also carry higher development and operations risks.<ref name="nasa">{{cite web|url=http://neo.jpl.nasa.gov/neo/report2007.html |title=NEO Survey and Deflection Analysis and Alternatives |access-date=2015-11-20 |url-status=dead |archive-url=https://web.archive.org/web/20160305101217/http://neo.jpl.nasa.gov/neo/report2007.html |archive-date=2016-03-05 }} Near-Earth Object Survey and Deflection Analysis of Alternatives Report to Congress March 2007</ref>}}

In the same year, NASA released a study where the asteroid [[99942 Apophis|Apophis]] (with a diameter of around {{convert|300|m|disp=or|-2|sp=us}}) was assumed to have a much lower rubble pile density ({{cvt|1500|kg/m3|lb/cuft|disp=or|round=25}}) and therefore lower mass than it is now known to have, and in the study, it is assumed to be on an impact trajectory with Earth for the year 2029. Under these hypothetical conditions, the report determines that a "Cradle spacecraft" would be sufficient to deflect it from Earth impact. This conceptual spacecraft contains six [[B83 nuclear bomb|B83]] physics packages, each set for their maximum 1.2-megatonne yield,<ref name="flightglobal"/> bundled together and lofted by an [[Ares V]] vehicle sometime in the 2020s, with each B83 being [[proximity fuze|fuzed]] to detonate over the asteroid's surface at a height of {{convert|100|m|disp=or|sp=us}} ("1/3 of the objects diameter" as its stand-off), one after the other, with hour-long intervals between each detonation. The results of this study indicated that a single employment of this option "can deflect NEOs of [{{convert|100-500|m|disp=or|sp=us|-2}} diameter] two years before impact, and larger NEOs with at least five years warning".<ref name="flightglobal"/><ref name="nss.org">{{Cite web|url=http://www.nss.org/resources/library/planetarydefense/2007-NearEarthObjectMitigationOptionsUsingExplorationTechnologies.pdf|archiveurl=https://web.archive.org/web/20150701020407/http://www.nss.org/resources/library/planetarydefense/2007-NearEarthObjectMitigationOptionsUsingExplorationTechnologies.pdf|url-status=dead|title=Near Earth Object (NEO) Mitigation Options Using Exploration Technologies|archivedate=July 1, 2015}}</ref> These effectiveness figures are considered to be "conservative" by its authors, and only the thermal X-ray output of the B83 devices was considered, while neutron heating was neglected for ease of calculation purposes.<ref name="nss.org"/><ref>[https://web.archive.org/web/20170310002322/https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090025983.pdf Towards Designing an Integrated Architecture for NEO Characterization, Mitigation, Scientific Evaluation, and Resource Utilization]</ref>

Research published in 2021 pointed out the fact that for an effective deflection mission, there would need to be a significant amount of warning time, with the ideal being several years or more. The more warning time provided, the less energy will be necessary to divert the asteroid just enough to adjust the trajectory to avoid Earth. The study also emphasized that deflection, as opposed to destruction, can be a safer option, as there is a smaller likelihood of asteroid debris falling to Earth's surface. The researchers proposed the best way to divert an asteroid through deflection is adjusting the output of neutron energy in the nuclear explosion.<ref name="auto">{{Cite journal |last1=Horan |first1=Lansing S. |last2=Holland |first2=Darren E. |last3=Bruck Syal |first3=Megan |last4=Bevins |first4=James E. |last5=Wasem |first5=Joseph V. |date=2021-06-01 |title=Impact of neutron energy on asteroid deflection performance |journal=Acta Astronautica |language=en |volume=183 |pages=29–42 |doi=10.1016/j.actaastro.2021.02.028 |bibcode=2021AcAau.183...29H |s2cid=233791597 |issn=0094-5765|doi-access=free }}</ref>

====Surface and subsurface use====
[[File:Asteroid Capture.jpg|thumb|This early [[Asteroid Redirect Mission]] artist's impression is suggestive of another method of changing a large threatening celestial body's orbit by [[asteroid capture|capturing]] relatively smaller celestial objects and using those, and not the usually proposed small bits of spacecraft, as the means of creating a powerful [[kinetic energy|kinetic impact]],<ref>{{cite journal|last1=Asphaug|first1=E.|last2=Ostro|first2=S. J.|last3=Hudson|first3=R. S.|last4=Scheeres|first4=D. J.|last5=Benz|first5=W.|date=1998|title=Disruption of kilometre-sized asteroids by energetic collisions|journal=Nature|volume=393|issue=6684|pages=437–440|url=http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/19541/1/98-0965.pdf|url-status=dead|archive-url=https://web.archive.org/web/20160306071546/http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/19541/1/98-0965.pdf|archive-date=March 6, 2016|doi=10.1038/30911|bibcode=1998Natur.393..437A|s2cid=4328861}}</ref> or alternatively, a stronger faster acting [[gravitational tractor]], as some low-density asteroids such as [[253 Mathilde]] can [[crumple zone|dissipate impact energy]].]]

In 2011, the director of the Asteroid Deflection Research Center at [[Iowa State University]], Dr. Bong Wie (who had published kinetic impactor deflection studies<ref name="spacesailing.net"/> previously), began to study strategies that could deal with {{convert|50|to(-)|500|m|ft|adj=mid|-diameter|-2|sp=us}} objects when the time to Earth impact was less than one year. He concluded that to provide the required energy, a nuclear explosion or other event that could deliver the same power, are the only methods that can work against a very large asteroid within these time constraints.

This work resulted in the creation of a conceptual [[Hypervelocity Asteroid Intercept Vehicle]] (HAIV), which combines a [[Deep Impact (spacecraft)|kinetic impactor]] to create an initial [[Impact crater|crater]] for a follow-up subsurface nuclear detonation within that initial crater, which would generate a high degree of efficiency in the conversion of the nuclear energy that is released in the detonation into propulsion energy to the asteroid.<ref>{{cite web|url=http://www.space.com/21333-asteroid-nuke-spacecraft-mission.html |title=Nuking Dangerous Asteroids Might be the Best Protection, Expert Says |website=[[Space.com]] |date=29 May 2013 |access-date=2013-07-02 |url-status=live |archive-url=https://web.archive.org/web/20160401213420/http://www.space.com/21333-asteroid-nuke-spacecraft-mission.html |archive-date=2016-04-01 }} Nuking Dangerous Asteroids Might Be the Best Protection, Expert Says. Includes a supercomputer simulation video provided by [[Los Alamos National Laboratory]].</ref>

A similar proposal would use a surface-detonating nuclear device in place of the kinetic impactor to create the initial crater, then using the crater as a [[rocket nozzle]] to channel succeeding nuclear detonations.

Wie claimed the computer models he worked on showed the possibility for a {{convert|300|m|ft|adj=mid|-wide|abbr=off|sp=us}} asteroid to be destroyed using a single HAIV with a warning time of 30 days. Additionally, the models showed that less than 0.1% of debris from the asteroid would reach Earth's surface.<ref>{{Cite web |author1=Mike Wall |date=2014-02-14 |title=How Nuclear Bombs Could Save Earth from Killer Asteroids |url=https://www.space.com/24696-asteroid-strike-nuclear-bombs.html |access-date=2023-04-25 |website=Space.com |language=en}}</ref> There have been few substantial updates from Wie and his team since 2014 regarding the research.

As of 2015, Wie has collaborated with the Danish [[Emergency Asteroid Defence Project]] (EADP), which intends to [[crowdsource]] sufficient funds to design, build, and store a non-nuclear HAIV spacecraft as planetary insurance. For threatening asteroids too large or close to Earth impact to effectively be deflected by the non-nuclear HAIV approach, nuclear explosive devices (with 5% of the explosive yield than those used for the stand-off strategy) are intended to be used, under international oversight, when conditions arise that necessitate it.<ref>{{Cite web|url=http://asteroiddefence.com/|title=EADP|date=May 5, 2015|archive-url=https://web.archive.org/web/20150505181554/http://asteroiddefence.com/ |archive-date=2015-05-05 }}</ref>

A study published in 2020 pointed out that a non-nuclear kinetic impact becomes less effective the larger and closer the asteroid. However, researchers ran a model that suggested a nuclear detonation near the surface of an asteroid designed to cover one side of the asteroid with x-rays would be effective. When the x-rays cover one side of an asteroid in the program, the energy would propel the asteroid in a preferred direction.<ref>{{Cite journal |last1=Dearborn |first1=David S. P. |last2=Bruck Syal |first2=Megan |last3=Barbee |first3=Brent W. |last4=Gisler |first4=Galen |last5=Greenaugh |first5=Kevin |last6=Howley |first6=Kirsten M. |last7=Leung |first7=Ronald |last8=Lyzhoft |first8=Joshua |last9=Miller |first9=Paul L. |last10=Nuth |first10=Joseph A. |last11=Plesko |first11=Catherine S. |last12=Seery |first12=Bernard D. |last13=Wasem |first13=Joseph V. |last14=Weaver |first14=Robert P. |last15=Zebenay |first15=Melak |date=2020-01-01 |title=Options and uncertainties in planetary defense: Impulse-dependent response and the physical properties of asteroids |journal=Acta Astronautica |language=en |volume=166 |pages=290–305 |doi=10.1016/j.actaastro.2019.10.026 |bibcode=2020AcAau.166..290D |s2cid=208840044 |issn=0094-5765|doi-access=free }}</ref> The lead researcher with the study, Dave Dearborn, said a nuclear impact offered more flexibility than a non-nuclear approach, as the energy output can be adjusted specifically to the asteroid's size and location.<ref>{{Cite web |title=Nuclear impulse could deflect massive asteroid |url=https://www.llnl.gov/news/nuclear-impulse-could-deflect-massive-asteroid |access-date=2023-04-25 |website=Lawrence Livermore National Laboratory |language=en}}</ref>

====Comet deflection possibility====
[[File:Comet-Hale-Bopp-29-03-1997 hires adj.jpg|thumb|right|"Who knows whether, when a comet shall approach this globe to destroy it&nbsp;... men will not tear rocks from their foundations by means of steam, and hurl mountains, as the giants are said to have done, against the flaming mass?"<br />— [[Lord Byron]]<ref>As quoted in ''Conversations of Lord Byron with Thomas Medwin'' (1832).</ref>]]

Following the 1994 [[Shoemaker-Levy 9]] comet impacts with Jupiter, [[Edward Teller]] proposed, to a collective of U.S. and Russian ex-[[Cold War]] weapons designers in a 1995 planetary defense workshop meeting at [[Lawrence Livermore National Laboratory]] (LLNL), that they collaborate to design a [[Nuclear weapon design#Arbitrarily large multi-staged devices|one-gigaton nuclear explosive device]], which would be equivalent to the kinetic energy of a {{convert|1|km|mi|adj=mid|-diameter|spell=in|sp=us|sigfig=1}} asteroid.<ref name="e-reports-ext.llnl.gov">[https://web.archive.org/web/20150909023233/https://e-reports-ext.llnl.gov/pdf/232015.pdf Planetary defense workshop LLNL 1995]</ref><ref name="Jason Mick">{{cite web|url=http://www.dailytech.com/Russia+US+Eye+Teamup+to+Build+Massive+Nuke+to+Save+Planet+from+an+Asteroid/article33569.htm#sthash.rQvVzS6m.dpuf|title=The mother of all bombs would sit in wait in an orbitary platform|date=October 17, 2013|author=Jason Mick|access-date=October 6, 2014|archive-url=https://web.archive.org/web/20141009190305/http://www.dailytech.com/Russia+US+Eye+Teamup+to+Build+Massive+Nuke+to+Save+Planet+from+an+Asteroid/article33569.htm#sthash.rQvVzS6m.dpuf|archive-date=October 9, 2014|url-status=dead|df=mdy-all}}</ref><ref name="publicintegrity.org">{{Cite web|url=http://publicintegrity.org/national-security/a-new-use-for-nuclear-weapons-hunting-rogue-asteroids/|archiveurl=https://web.archive.org/web/20160320055111/http://www.publicintegrity.org/2013/10/16/13547/new-use-nuclear-weapons-hunting-rogue-asteroids|url-status=dead|title=A new use for nuclear weapons: hunting rogue asteroids|first=Douglas|last=Birch|date=October 16, 2013|archivedate=March 20, 2016|website=Center for Public Integrity}}</ref> The theoretical one-gigaton device would weigh about 25–30 tons, light enough to be lifted on the [[Energia (rocket)|Energia]] rocket. It could be used to instantaneously vaporize a one-kilometer asteroid, divert the paths of [[Global catastrophic risk|ELE-class asteroids]] (greater than {{convert|10|km|disp=or|sp=us}} in diameter) within short notice of a few months. With one year of notice, and at an interception location no closer than [[Jupiter]], it could also deal with the even rarer [[List of periodic comets|short period comets]] that can come out of the [[Kuiper belt]] and transit past Earth orbit within two years.{{clarify|is it 1 year or 2?|date=May 2019}} For comets of this class, with a maximum estimated diameter of {{convert|100|km|sp=us|sigfig=1}}, [[2060 Chiron|Chiron]] served as the hypothetical threat.<ref name="e-reports-ext.llnl.gov"/><ref name="Jason Mick"/><ref name="publicintegrity.org"/>

In 2013, the related National Laboratories of the [[United States Department of Energy national laboratories|US]] and [[Rosatom|Russia]] signed a deal that includes an intent to cooperate on defense from asteroids.<ref>{{Cite web|url=https://www.energy.gov/articles/united-states-russia-sign-agreement-further-research-and-development-collaboration-nuclear|archiveurl=https://web.archive.org/web/20160304125747/http://energy.gov/articles/united-states-russia-sign-agreement-further-research-and-development-collaboration-nuclear|url-status=dead|title=United States, Russia Sign Agreement to Further Research and Development Collaboration in Nuclear Energy and Security|archivedate=March 4, 2016|website=Energy.gov}}</ref> The deal was meant to complement [[New START]], but Russia suspended its participation in the treaty in 2023.<ref>{{Cite news |last=Chappell |first=Bill |date=February 22, 2023 |title=What happens now after Russia suspends the last nuclear arms treaty with the U.S.? |work=NPR |url=https://www.npr.org/2023/02/22/1158529106/nuclear-treaty-new-start-putin |access-date=April 24, 2023}}</ref> As of April 2023, there has not been an official update from the White House or Moscow on how Russia's suspended participation will affect adjacent treaties.

====Present capability====
As of late 2022, the most likely and most effective method for asteroid deflection does not involve nuclear technology. Instead, it involves a kinetic impactor designed to redirect the asteroid, which showed promise in the NASA [[DART mission]].<ref>{{Cite web |title=DART |url=https://dart.jhuapl.edu/Mission/index.php |access-date=2023-04-25 |website=dart.jhuapl.edu |language=en}}</ref> For nuclear technology, simulations have been run analyzing the possibility of using neutron energy put off by a nuclear device to redirect an asteroid. These simulations showed promise, with one study finding that increasing the neutron energy output had a notable effect on the angle of the asteroid's travel.<ref name="auto"/> However, there has not been a practical test studying the possibility as of April 2023.

=== Kinetic impact ===
{{See also|Ramming|Deep Impact (spacecraft)|Lightweight Exo-Atmospheric Projectile|Double Asteroid Redirection Test|Hayabusa2}}
[[File:HRIV Impact.gif|thumb|The 2005 ''[[Deep Impact (spacecraft)|Deep Impact]]'' collision with the {{convert|8|by|5|km|0|spell=in|adj=on|sp=us}} comet [[Tempel 1]]. The impact flash and resulting [[ejecta]] are clearly visible. The impactor delivered 19 [[gigajoule]]s (the equivalent of 4.8 [[ton]]s of [[Trinitrotoluene|TNT]]) upon impact.<ref>{{Cite web|url=https://www.nasa.gov/mission_pages/deepimpact/spacecraft/impactor.html|archiveurl=https://web.archive.org/web/20160623220100/http://www.nasa.gov/mission_pages/deepimpact/spacecraft/impactor.html|url-status=dead|title=NASA - Deep Impact's Impactor|archivedate=June 23, 2016|website=www.nasa.gov}}</ref> Impact created a crater estimated to be about 150 meters in diameter.<ref>{{cite web |title=In Depth - Deep Impact (EPOXI) |url=https://solarsystem.nasa.gov/missions/deep-impact-epoxi/in-depth/ |website=NASA Solar System Exploration |access-date=11 October 2022}}</ref> The comet "returned to preimpact conditions only 6 days after the event".<ref>{{cite journal | doi = 10.1086/499301 | bibcode=2006AJ....131.1130S | volume=131 | issue=2 | title=Photometry and Imaging Results for Comet 9P/Tempel 1 and Deep Impact: Gas Production Rates, Postimpact Light Curves, and Ejecta Plume Morphology | year=2006 | journal=The Astronomical Journal | pages=1130–1137 | last1 = Schleicher | first1 = David G. | last2 = Barnes | first2 = Kate L. | last3 = Baugh | first3 = Nicole F.| s2cid=123344560 | doi-access= }}</ref>]]

The impact of a massive object, such as a spacecraft or even another near-Earth object, is another possible solution to a pending NEO impact. An object with a high mass close to the Earth could be sent out into a collision course with the asteroid, knocking it off course.

When the asteroid is still far from the Earth, a means of deflecting the asteroid is to directly alter its [[momentum]] by colliding a spacecraft with the asteroid.
[[File:Dart impact replay.webm|thumb|upright=1.2|Compiled timelapse of DART's final 5.5 minutes until impact]]
A [[NASA]] analysis of deflection alternatives, conducted in 2007, stated:

{{blockquote|Non-nuclear kinetic impactors are the [[Deep Impact (spacecraft)|most mature approach]] and could be used in some deflection/mitigation scenarios, especially for NEOs that consist of a single small, solid body.<ref name="nasa" />}}

This deviation method, which has been implemented by [[Double Asteroid Redirection Test|DART]] and, for a completely different purpose (analysis of the structure and composition of a comet), by NASA's [[Deep Impact (spacecraft)|Deep Impact]] space probe, involves launching a spacecraft against the [[Near-Earth object|near Earth object]]. The speed of the asteroid is modified due to the [[law of conservation of momentum]]:

{{Center|1=M{{Subscript|1}} x V{{Subscript|1}} + M{{Subscript|2}} x V{{Subscript|2}} = (M{{Subscript|1}} + M{{Subscript|2}}) x V{{Subscript|3}}}}

with V{{Subscript|1}} velocity of the spacecraft, V{{Subscript|2}} velocity of the celestial body before impact, and V{{Subscript|3}} the velocity after impact. M{{Subscript|1}} and M{{Subscript|2}} respective mass of the spacecraft and of the celestial body. Velocities are [[Vector space|vectors]] here.

The European Union's NEOShield-2 Mission<ref>{{cite web|url=http://www.neoshield.net/mitigation-measures-kinetic-impactor-gravity/kinetic-impactor-asteroid-deflection-spacecraft/|title=Kinetic impactor -|date=2016-08-29|access-date=2016-11-17|archive-date=2022-03-19|archive-url=https://web.archive.org/web/20220319000029/http://www.neoshield.net/mitigation-measures-kinetic-impactor-gravity/kinetic-impactor-asteroid-deflection-spacecraft/|url-status=dead}}</ref> is also primarily studying the Kinetic Impactor mitigation method. The principle of the kinetic impactor mitigation method is that the NEO or Asteroid is deflected following an impact from an impactor spacecraft. The principle of momentum transfer is used, as the impactor crashes into the NEO at a very high velocity of {{cvt|10|km/s|km/h mph||}} or more. The momentum of the impactor is transferred to the NEO, causing a change in velocity and therefore making it deviate from its course slightly.<ref>{{cite web|url = http://www.neoshield.net/mitigation-measures-kinetic-impactor-gravity/kinetic-impactor-asteroid-deflection-spacecraft/|title = NEOShield Project|publisher = European Union Consortium|date = 17 November 2016|access-date = 17 November 2016|archive-date = 19 March 2022|archive-url = https://web.archive.org/web/20220319000029/http://www.neoshield.net/mitigation-measures-kinetic-impactor-gravity/kinetic-impactor-asteroid-deflection-spacecraft/|url-status = dead}}</ref>

As of mid-2021, the modified [[AIDA (mission)|AIDA mission]] has been approved. The NASA [[Double Asteroid Redirection Test]] (''DART'') kinetic impactor spacecraft was launched in November 2021. The goal was to impact [[Dimorphos]] (nicknamed ''Didymoon''), the {{convert|180|m|adj=on|sp=us|}} [[minor-planet moon]] of near-Earth asteroid [[65803 Didymos]]. The impact occurred in September 2022 when Didymos is relatively close to Earth, allowing Earth-based telescopes and planetary radar to observe the event. The result of the impact will be to change the orbital velocity and hence orbital period of Dimorphos, by a large enough amount that it can be measured from Earth. This will show for the first time that it is possible to change the orbit of a small {{convert|200|m|adj=on|sp=us|}} asteroid, around the size most likely to require active mitigation in the future. The launch and use of the [[Double Asteroid Redirection Test]] system in March 2023 showed the world that asteroids could be safely redirected without the use of nuclear means. The second part of the [[AIDA (mission)|AIDA]] mission{{ndash}}the ESA [[Hera (spacecraft)|HERA]] spacecraft{{ndash}}has been approved by ESA member states in October 2019. It would reach the Didymos system in 2026 and measure both the mass of Dimorphos and the precise effect of the impact on that body, allowing much better extrapolation of the [[AIDA (mission)|AIDA]] mission to other targets.<ref>{{Cite web |title=NASA - NSSDCA - Spacecraft - Details |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=HERA |access-date=2022-10-12 |website=nssdc.gsfc.nasa.gov}}</ref>

=== Asteroid gravity tractor ===
{{main|Gravity tractor}}
{{wide image|NASA-Animation-ARM-opt-800-20150325.gif|800px|align-cap=center|The [[Asteroid Redirect Mission]] vehicle was conceived to demonstrate the "[[gravity tractor]]" planetary defense technique on a hazardous-size asteroid. The gravity-tractor method leverages the mass of the spacecraft to impart a force on the asteroid, slowly altering the asteroid's trajectory.}}

Another alternative to explosive deflection is to move the asteroid slowly over time. A small but constant amount of thrust accumulates to deviate an object sufficiently from its course. [[Edward T. Lu]] and [[Stanley G. Love]] have proposed using a massive uncrewed spacecraft hovering over an asteroid to gravitationally pull the asteroid into a non-threatening orbit. Though both objects are gravitationally pulled towards each other, the spacecraft can counter the force towards the asteroid by, for example, an [[nuclear electric rocket|ion thruster]], so the net effect would be that the asteroid is accelerated towards the spacecraft and thus slightly deflected from its orbit. While slow, this method has the advantage of working irrespective of the asteroid's composition or spin rate; [[rubble pile]] asteroids would be difficult to deflect by means of nuclear detonations, while a pushing device would be difficult or inefficient to mount on a fast-rotating asteroid. A gravity tractor would likely have to spend several years beside the asteroid to be effective.

A [[NASA]] analysis of deflection alternatives, conducted in 2007, stated:

{{blockquote|"Slow push" mitigation techniques are the most expensive, have the lowest level of technical readiness, and their ability to both travel to and divert a threatening NEO would be limited unless mission durations of many years to decades are possible.<ref name="nasa" />}}

=== Ion beam deflection ===
{{main|Asteroid ion beam deflection}}

Another "contactless" asteroid deflection technique<ref name=":ibs">{{Cite journal|last1=Bombardelli|first1=C. J.|last2=Pelaez|first2=J. V.|date=2011|title=Ion beam shepherd for asteroid deflection|journal=Journal of Guidance, Control, and Dynamics|volume=34|issue=4|pages=1270–1272|doi=10.2514/1.51640|arxiv=1102.1276|bibcode=2011JGCD...34.1270B }}</ref> involves the use of a low-divergence ion thruster pointed at the asteroid from a nearby hovering spacecraft. The momentum transmitted by the ions reaching the asteroid surface produces a slow but continuous force that can deflect the asteroid in a similar way as the gravity tractor, but with a lighter spacecraft.

=== Focused solar energy ===
[[H. Jay Melosh|H. J. Melosh]] with I. V. Nemchinov proposed deflecting an asteroid or comet by focusing [[solar energy]] onto its surface to create thrust from the resulting vaporization of material.<ref name=":0">{{Cite journal|last1=Melosh|first1=H. J.|last2=Nemchinov|first2=I. V.|date=1993|title=Solar asteroid diversion|journal=Nature|volume=366|issue=6450|pages=21–22|doi=10.1038/366021a0|bibcode=1993Natur.366...21M|s2cid=4367291|issn=0028-0836}}</ref> This method would first require the construction of a space station with a system of large collecting, concave [[mirror]]s similar to those used in [[solar furnace]]s.

Orbit mitigation with highly concentrated sunlight is scalable to achieving the predetermined deflection within a year even for a global-threatening body without prolonged warning time.<ref name=":0" /><ref name=":1">{{Cite journal|last=Vasylyev|first=V. P.|date=2012-12-22|title=Deflection of Hazardous Near-Earth Objects by High Concentrated Sunlight and Adequate Design of Optical Collector|journal=Earth, Moon, and Planets|volume=110|issue=1–2|pages=67–79|doi=10.1007/s11038-012-9410-2|s2cid=120563921|issn=0167-9295}}</ref>

Such a hastened strategy may become topical in the case of late detection of a potential hazard, and also, if required, in providing the possibility for some additional action. Conventional concave reflectors are practically inapplicable to the high-concentrating geometry in the case of a giant shadowing space target, which is located in front of the mirrored surface. This is primarily because of the dramatic spread of the mirrors' focal points on the target due to the [[optical aberration]] when the optical axis is not aligned with the Sun. On the other hand, the positioning of any collector at a distance to the target much larger than its size does not yield the required concentration level (and therefore temperature) due to the natural divergence of the sunrays. Such principal restrictions are inevitably at any location regarding the asteroid of one or many unshaded forward-reflecting collectors. Also, in the case of secondary mirrors use, similar to the ones found in [[Cassegrain reflector|Cassegrain telescopes]], would be prone to heat damage by partially concentrated sunlight from primary mirror.

In order to remove the above restrictions, V.P. Vasylyev proposed to apply an alternative design of a mirrored collector – the ring-array concentrator.<ref name=":1" /> This type of collector has an underside lens-like position of its focal area that avoids shadowing of the collector by the target and minimizes the risk of its coating by ejected debris. Provided the sunlight concentration of approximately 5 × 10<sup>3</sup> times, a surface [[irradiance]] of around 4-5 MW/m<sup>2</sup> leads to a thrusting effect of about {{cvt|1000|N|lbf|sigfig=1}}. Intensive [[ablation]] of the rotating asteroid surface under the focal spot will lead to the appearance of a deep "canyon", which can contribute to the formation of the escaping gas flow into a jet-like one. This may be sufficient to deflect a {{cvt|0.5|km|mi|sigfig=1}} asteroid within several months and no addition warning period, only using ring-array collector size of about half of the asteroid's diameter. For such a prompt deflection of the larger NEOs, {{cvt|1.3|to|2.2|km|mi|1}}, the required collector sizes are comparable to the target diameter. In the case of a longer warning time, the required size of the collector may be significantly decreased.

[[File:Ring array asteroid.gif|center|frame|Artist's impression of asteroid deflection using an innovative ring-array solar collector.]]

=== Mass driver ===
A [[mass driver]] is an (automated) system on the asteroid to eject material into space, thus giving the object a slow steady push and decreasing its mass. A mass driver is designed to work as a very low [[specific impulse]] system, which in general uses a lot of propellant, but very little power. This essentially uses the asteroid against itself in order to divert a collision.

Modular Asteroid Deflection Mission Ejector Node, (MADMEN), is the idea of landing small unmanned vehicles such as [[space rovers]] to break up small portions of the asteroid. Using drills to break up small rocks and boulders from the surface, debris would eject from the surface very fast. Because there are no forces acting on the asteroid these rocks will push the asteroid off course at a very slow rate. This process takes time but could be very effective if implemented correctly.<ref>Olds, John R, et al. Multiple Mass Drivers as an Option for Asteroid Deflection Missions, SpaceWorks Engineering, Inc. (SEI), Atlanta, Georgia, 30338, http://www.sei.aero/archive/AIAA-2007_S3-7.pdf.</ref> The idea is that when using local material as propellant, the amount of propellant is not as important as the amount of power, which is likely to be limited.

=== Conventional rocket engine ===
Attaching any [[spacecraft propulsion]] device would have a similar effect of giving a push, possibly forcing the asteroid onto a trajectory that takes it away from Earth. An in-space rocket engine that is capable of imparting an impulse of 10<sup>6</sup> N·s (E.g. adding 1&nbsp;km/s to a 1000&nbsp;kg vehicle), will have a relatively small effect on a relatively small asteroid that has a mass of roughly a million times more. Chapman, Durda, and Gold's white paper<ref>Chapman, Clark R. and Daniel D. Durda. [http://www.internationalspace.com/pdf/NEOwp_Chapman-Durda-Gold.pdf The Comet/Asteroid Impact Hazard: A Systems Approach] {{webarchive |url=https://web.archive.org/web/20160304002442/http://www.internationalspace.com/pdf/NEOwp_Chapman-Durda-Gold.pdf |date=March 4, 2016 }}, Boulder, CO: Office of Space Studies, Southwest Research Institute, Space Engineering and Technology Branch, [[Johns Hopkins University Applied Physics Laboratory]].</ref> calculates deflections using existing chemical rockets delivered to the asteroid.
[[File:Plasma thruster asteroid.webp|thumb|3D sketch of a [[Pulsed plasma thruster|pulsed plasma electromagnetic thruster]] attaching to an asteroid for asteroid impact avoidance]]
Such direct force rocket engines are typically proposed to use highly-efficient [[electrically powered spacecraft propulsion]], such as [[ion thruster]]s or [[VASIMR]].

=== Asteroid laser ablation ===
{{main|Asteroid laser ablation}}

Similar to the effects of a nuclear device, it is thought possible to focus sufficient laser energy on the surface of an asteroid to cause flash vaporization / ablation to create either in impulse or to ablate away the asteroid mass. This concept, called [[asteroid laser ablation]] was articulated in the 1995 SpaceCast 2020<ref>{{cite web|url=http://csat.au.af.mil/2020/index.htm|title=Welcome to SpaceCast 2020|work=Center for Strategy and Technology|publisher=Air University|url-status=dead|archive-url=https://web.archive.org/web/20090302104514/http://csat.au.af.mil/2020/index.htm|archive-date=2009-03-02}}</ref> white paper "Preparing for Planetary Defense",<ref>{{cite web |url=http://www.nss.org:8080/resources/library/planetarydefense/1994-DetectionAndInterceptionOfAsteroidsOnCollisionCourseWithEarth.pdf |title=Preparing for Planetary Defense: Detection and Interception of Asteroids on Collision Course with Earth |access-date=2016-05-22 |archive-date=2016-06-25 |archive-url=https://web.archive.org/web/20160625011024/http://www.nss.org:8080/resources/library/planetarydefense/1994-DetectionAndInterceptionOfAsteroidsOnCollisionCourseWithEarth.pdf |url-status=dead }}<br />{{cite report|title=SpaceCast 2020|chapter=Preparing for Planetary Defense|chapter-url=http://csat.au.af.mil/2020/papers/app-r.pdf|publisher=Air University|url-status=dead|archive-url=https://web.archive.org/web/20101026185205/http://csat.au.af.mil/2020/papers/app-r.pdf|archive-date=2010-10-26}}</ref> and the 1996 Air Force 2025<ref>{{cite web|url=http://csat.au.af.mil/2025/index.htm|title=Welcome to Air Force 2025|work=Center for Strategy and Technology|publisher=Air University|url-status=dead|archive-url=https://web.archive.org/web/20081220115949/http://csat.au.af.mil/2025/index.htm|archive-date=2008-12-20}}</ref> white paper "Planetary Defense: Catastrophic Health Insurance for Planet Earth".<ref>{{cite report|url=http://www.nss.org:8080/resources/library/planetarydefense/1996-PlanetaryDefense-CatstrophicHealthInsuranceForPlanetEarth-Urias.pdf |title=Air Force 2025|chapter=Planetary Defense: Catastrophic Health Insurance for Planet Earth|author=John M. Urias |author2=Iole M. DeAngelis |author3=Donald A. Ahern |author4=Jack S. Caszatt |author5=George W. Fenimore III |author6=Michael J. Wadzinski |date=October 1996|chapter-url=http://csat.au.af.mil/2025/volume3/vol3ch16.pdf|publisher=Air University|url-status=dead|archive-url=https://web.archive.org/web/20070717145438/http://csat.au.af.mil/2025/volume3/vol3ch16.pdf|archive-date=2007-07-17}}</ref> Early publications include C. R. Phipps "ORION" concept from 1996, Colonel Jonathan W. Campbell's 2000 monograph "Using Lasers in Space: Laser Orbital Debris Removal and Asteroid Deflection",<ref>{{Cite web |url=http://www.nss.org:8080/resources/library/planetarydefense/2000-LaserOrbitalDebrisRemovalAndAsteroidDeflection-Campbell.pdf |title=Using Lasers in Space: Laser Orbital Debris Removal and Asteroid Deflection|access-date=2016-05-22 |archive-url=https://web.archive.org/web/20161005024315/http://www.nss.org:8080/resources/library/planetarydefense/2000-LaserOrbitalDebrisRemovalAndAsteroidDeflection-Campbell.pdf |archive-date=2016-10-05 |url-status=dead }}</ref> and NASA's 2005 concept Comet Asteroid Protection System (CAPS).<ref>{{Cite web |url=http://www.nss.org:8080/resources/library/planetarydefense/2005-CometAsteroidProtectionSystem(CAPS)-NASA.pdf |title=Comet/Asteroid Protection System (CAPS): Preliminary Space-Based System Concept and Study Results|access-date=2016-05-22 |archive-url=https://web.archive.org/web/20160625020733/http://www.nss.org:8080/resources/library/planetarydefense/2005-CometAsteroidProtectionSystem(CAPS)-NASA.pdf |archive-date=2016-06-25 |url-status=dead }}</ref> Typically such systems require a significant amount of power, such as would be available from a [[Space-based solar power|Space-Based Solar Power Satellite]].

Another proposal is the Phillip Lubin's DE-STAR<ref>{{Cite web|url=https://www.deepspace.ucsb.edu/projects/directed-energy-planetary-defense|title=DE-STAR}}</ref> proposal:

* The [[Directed Energy System for Targeting of Asteroids and ExplorRation|DE-STAR]] project,<ref>{{Cite web|url=https://spie.org/news/lubin-video|archiveurl=https://web.archive.org/web/20150609084807/http://spie.org/x104781.xml|url-status=dead|title=Philip Lubin: A space-based array for planetary defense|archivedate=June 9, 2015|website=spie.org}}</ref> proposed by researchers at the University of California, Santa Barbara, is a concept modular solar powered 1&nbsp;μm, [[near infrared]] wavelength, laser array. The design calls for the array to eventually be approximately 1&nbsp;km squared in size, with the modular design meaning that it could be launched in increments and assembled in space. In its early stages as a small array it could deal with smaller targets, assist [[solar sail]] probes and would also be useful in cleaning up [[space debris]].

=== Other proposals ===
[[Image:Solarsail msfc.jpg|thumb|NASA study of a [[solar sail]]. The sail would be {{convert|0.5|km|sp=us}} wide.]]

* Wrapping the asteroid in a sheet of reflective plastic such as [[metallized polyethylene terephthalate|aluminized PET film]] as a [[solar sail]]
* "Painting" or dusting the object with [[titanium dioxide]] (white) to alter its trajectory via increased reflected radiation pressure or with [[soot]] (black) to alter its trajectory via the [[Yarkovsky effect]].
* [[planetary science|Planetary scientist]] [[Eugene Shoemaker]] in 1996 proposed<ref>--in a lecture to the [[Arizona Geological Society]] in 12–96.</ref> deflecting a potential impactor by releasing a cloud of steam in the path of the object, hopefully gently slowing it. Nick Szabo in 1990 sketched<ref>[https://www.cs.cmu.edu/afs/cs.cmu.edu/usr/mnr/st/std070 Is an asteroid capture possible/feasible?; Asteroid movement/retrieval; Asteroid relocation/mining; etceras...] {{webarchive |url=https://web.archive.org/web/20161106170026/https://www.cs.cmu.edu/afs/cs.cmu.edu/usr/mnr/st/std070 |date=November 6, 2016 }}, Space-tech Digest #70 [bulletin board], [[Carnegie Mellon University]], July 19–25, 1990.</ref> a similar idea, "cometary aerobraking", the targeting of a comet or ice construct at an asteroid, then vaporizing the ice with nuclear explosives to form a temporary atmosphere in the path of the asteroid.
* Coherent digger array<ref>{{Cite arXiv |eprint = astro-ph/9803269|last1 = Lu|first1 = Edward T.|title = Breaking and Splitting asteroids by nuclear explosions to propel and deflect their trajectories|last2 = Love|first2 = Stanley G.|year = 1998}}</ref><ref>{{Cite journal |arxiv = 0705.1805|last1 = Lu|first1 = Edward T.|title = Asteroid Deflection: How, where and when?|journal = Chinese Journal of Astronomy and Astrophysics Supplement|volume = 8|pages = 399|last2 = Love|first2 = Stanley G.|year = 2007|bibcode = 2008ChJAS...8..399F}}</ref> multiple 1-ton flat tractors able to dig and expel asteroid soil mass as a coherent fountain array, coordinated fountain activity may propel and deflect over years.
* Attaching a tether and ballast mass to the asteroid to alter its trajectory by changing its center of mass.<ref>{{cite web |title=Near-Earth Object Threat Mitigation Using a Tethered Ballast Mass|author=David French|publisher=J. Aerosp. Engrg.|date=October 2009 | url=http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JAEEEZ000022000004000460000001&idtype=cvips&gifs=yes&ref=no}}</ref>
* [[Explosively pumped flux compression generator|Magnetic flux compression]] to magnetically brake and or capture objects that contain a high percentage of [[meteoric iron]] by deploying a wide coil of wire in its orbital path and when it passes through, [[Inductance]] creates an [[electromagnet]] solenoid to be generated.<ref>{{cite web |url=http://www.obtronics.net/htc/technogy/elec/elmag_04.htm |title=How to Colonize an Asteroid Solenoids |url-status=dead |archive-url=https://web.archive.org/web/20060103083009/http://www.obtronics.net/htc/technogy/elec/elmag_04.htm |archive-date=2006-01-03 }}</ref><ref>{{cite web |url=http://www.nss.org/adastra/volume18/durda.html |title=National Space Society, From Ad Astra, Volume 18 Number 2, Summer 2006 |access-date=2013-11-25 |archive-url=https://web.archive.org/web/20170721141759/http://www.nss.org/adastra/volume18/durda.html |archive-date=2017-07-21 |url-status=dead }}</ref>