Editing Interstellar travel (section)

=== Non-rocket concepts ===
A problem with all traditional rocket propulsion methods is that the spacecraft would need to carry its fuel with it, thus making it very massive, in accordance with the [[rocket equation]]. Several concepts attempt to escape from this problem:<ref name="crawist" /><ref>A. Bolonkin (2005). ''Non Rocket Space Launch and Flight''. Elsevier. {{ISBN|978-0-08-044731-5}}</ref>

==== RF resonant cavity thruster ====
A radio frequency (RF) resonant cavity thruster is a device that is claimed to be a [[Spacecraft propulsion|spacecraft thruster]]. In 2016, the [[Advanced Propulsion Physics Laboratory]] at [[NASA]] reported observing a small apparent thrust from one such test, a result not since replicated.<ref>{{Cite web|url=https://www.nationalgeographic.com/news/2016/11/nasa-impossible-emdrive-physics-peer-review-space-science/|title=NASA Team Claims 'Impossible' Space Engine Works—Get the Facts|date=2016-11-21|website=National Geographic News|language=en|access-date=2019-11-12|archive-date=12 November 2019|archive-url=https://web.archive.org/web/20191112135532/https://www.nationalgeographic.com/news/2016/11/nasa-impossible-emdrive-physics-peer-review-space-science/|url-status=dead}}</ref> One of the designs is called EMDrive. In December 2002, Satellite Propulsion Research Ltd described a working prototype with an alleged total thrust of about 0.02 newtons powered by an 850 W [[cavity magnetron]]. The device could operate for only a few dozen seconds before the magnetron failed, due to overheating.<ref>{{Cite web|url=http://rexresearch.com/shawyer/shawyer.htm|title=Roger SHAWYER -- EM Space Drive -- Articles & Patent|website=rexresearch.com|access-date=2019-11-12|archive-date=14 September 2019|archive-url=https://web.archive.org/web/20190914002837/http://www.rexresearch.com/shawyer/shawyer.htm|url-status=live}}</ref> The latest test on the EMDrive concluded that it does not work.<ref>{{Cite web|url=https://www.sciencealert.com/impossible-em-drive-test-concludes-external-thrust|title=The Latest Test on The 'Impossible' EM Drive Concludes It Doesn't Work|last=McRae|first=Mike|website=ScienceAlert|date=24 May 2018|language=en-gb|access-date=2019-11-12|archive-date=12 November 2019|archive-url=https://web.archive.org/web/20191112135539/https://www.sciencealert.com/impossible-em-drive-test-concludes-external-thrust|url-status=live}}</ref>

==== Helical engine ====
Proposed in 2019 by NASA scientist Dr. David Burns, the helical engine concept would use a particle accelerator to accelerate particles to near the speed of light. Since particles traveling at such speeds acquire more mass, it is believed that this mass change could create acceleration. According to Burns, the spacecraft could theoretically reach 99% the speed of light.<ref>{{Cite web|url=https://www.sciencealert.com/no-this-new-space-engine-isn-t-going-to-break-physics|title=NASA Engineer Claims 'Helical Engine' Concept Could Reach 99% The Speed of Light Without Propellant|last=Starr|first=Michelle|website=ScienceAlert|date=15 October 2019|language=en-gb|access-date=2019-11-12|archive-date=30 November 2019|archive-url=https://web.archive.org/web/20191130113556/https://www.sciencealert.com/no-this-new-space-engine-isn-t-going-to-break-physics|url-status=live}}</ref>

==== Interstellar ramjets ====
In 1960, [[Robert W. Bussard]] proposed the [[Bussard ramjet]], a fusion rocket in which a huge scoop would collect the diffuse hydrogen in interstellar space, "burn" it on the fly using a [[proton–proton chain reaction]], and expel it out of the back. Later calculations with more accurate estimates suggest that the thrust generated would be less than the drag caused by any conceivable scoop design.{{citation needed|date=May 2016}} Yet the idea is attractive because the fuel would be collected ''en route'' (commensurate with the concept of ''energy harvesting''), so the craft could theoretically accelerate to near the speed of light. The limitation is due to the fact that the reaction can only accelerate the propellant to 0.12c. Thus the drag of catching interstellar dust and the thrust of accelerating that same dust to 0.12c would be the same when the speed is 0.12c, preventing further acceleration.

==== Beamed propulsion ====
[[File:Forward-sailcraft-scheme.png|thumb|This diagram illustrates [[Robert L. Forward]]'s scheme for slowing down an interstellar [[solar sail|light-sail]] at the star system destination.]]

A [[solar sail|light sail]] or [[magnetic sail]] powered by a massive [[laser]] or particle accelerator in the home star system could potentially reach even greater speeds than rocket- or pulse propulsion methods, because it would not need to carry its own [[reaction mass]] and therefore would only need to accelerate the craft's [[Payload (air and space craft)|payload]]. [[Robert L. Forward]] proposed a means for decelerating an interstellar craft with a light sail of 100 kilometers in the destination star system without requiring a laser array to be present in that system. In this scheme, a secondary sail of 30 kilometers is deployed to the rear of the spacecraft, while the large primary sail is detached from the craft to keep moving forward on its own. Light is reflected from the large primary sail to the secondary sail, which is used to decelerate the secondary sail and the spacecraft payload.<ref>{{cite journal | author=Forward, R.L. | title=Roundtrip Interstellar Travel Using Laser-Pushed Lightsails | journal=J Spacecraft | volume=21 | issue=2 | pages=187–195 | date=1984 | doi=10.2514/3.8632 |bibcode = 1984JSpRo..21..187F }}</ref> In 2002, [[Geoffrey A. Landis]] of [[NASA]]'s Glen Research center also proposed a laser-powered, propulsion, sail ship that would host a diamond sail (of a few nanometers thick) powered with the use of [[solar energy]].<ref>{{cite web|url=http://go.galegroup.com/ps/i.do?p=ITOF&id=GALE{{pipe}}A444067493&v=2.1&it=r&sid=summon|title=Alpha Centauri: Our First Target for Interstellar Probes|via=go.galegroup.com}}</ref> With this proposal, this interstellar ship would, theoretically, be able to reach 10 percent the speed of light. It has also been proposed to use beamed-powered propulsion to accelerate a spacecraft, and electromagnetic propulsion to decelerate it; thus, eliminating the problem that the Bussard ramjet has with the drag produced during acceleration.<ref>{{Cite web|last=Delbert|first=Caroline|date=2020-12-09|title=The Radical Spacecraft That Could Send Humans to a Habitable Exoplanet|url=https://www.popularmechanics.com/space/deep-space/a34907687/solar-one-radical-spacecraft-crewed-interstellar-travel-light-sail-fusion-reactor/|access-date=2020-12-12|website=Popular Mechanics|language=en-US|archive-date=11 December 2020|archive-url=https://web.archive.org/web/20201211070301/https://www.popularmechanics.com/space/deep-space/a34907687/solar-one-radical-spacecraft-crewed-interstellar-travel-light-sail-fusion-reactor/|url-status=live}}</ref>

A [[magnetic sail]] could also decelerate at its destination without depending on carried fuel or a driving beam in the destination system, by interacting with the plasma found in the solar wind of the destination star and the interstellar medium.<ref>{{cite journal |title=Magnetic Sails and Interstellar Travel |journal=Journal of the British Interplanetary Society |date=1990 |last1=Andrews |first1=Dana G. |last2=Zubrin |first2=Robert M. |volume=43 |pages=265–272 |url=http://www.lunarsail.com/LightSail/msit.pdf |archive-url=https://web.archive.org/web/20141012182359/http://www.lunarsail.com/LightSail/msit.pdf |url-status=dead |archive-date=2014-10-12 |access-date=2014-10-08 }}</ref><ref>{{cite web |url=http://www.niac.usra.edu/files/library/meetings/fellows/nov99/320Zubrin.pdf |title=NIAC Study of the Magnetic Sail |last1=Zubrin |first1=Robert |last2=Martin |first2=Andrew |date=1999-08-11 |access-date=2014-10-08 |archive-date=24 May 2015 |archive-url=https://web.archive.org/web/20150524181108/http://www.niac.usra.edu/files/library/meetings/fellows/nov99/320Zubrin.pdf |url-status=live }}</ref>

The following table lists some example concepts using beamed laser propulsion as proposed by the physicist [[Robert L. Forward]]:<ref>{{cite book | author= Landis, Geoffrey A. | chapter= The Ultimate Exploration: A Review of Propulsion Concepts for Interstellar Flight | title= Interstellar Travel and Multi-Generation Space Ships | editor= Yoji Kondo | editor2= Frederick Bruhweiler | editor3= John H. Moore, Charles Sheffield |page=52 | publisher= Apogee Books | date= 2003 | isbn= 978-1-896522-99-9}}</ref>

{| class="wikitable"
|-
! Journey !! Mission !! Laser Power !! Vehicle Mass !! Acceleration !! Sail Diameter !! Maximum Velocity <br /> (% of the speed of light) !! Total duration
|-
! Flyby – Alpha Centauri
| ''outbound stage'' || 65 GW || 1 t || 0.036 g || 3.6&nbsp;km || 11% @ 0.17 ly
| 40 years
|-
! rowspan=2 | Rendezvous – Alpha Centauri
| ''outbound stage'' || 7,200 GW|| 785 t || 0.005 g || 100&nbsp;km || 21% @ 4.29 ly{{dubious|date=May 2016}}<!--confused with flyby numbers?-->
| rowspan=2 | 41 years
|-
| ''deceleration stage'' || 26,000 GW || 71 t || 0.2 g || 30&nbsp;km || 21% @ 4.29 ly
|-
! rowspan=4 | Crewed – Epsilon Eridani
| ''outbound stage'' || 75,000,000 GW || 78,500 t || 0.3 g || 1000&nbsp;km || 50% @ 0.4 ly
| rowspan=4 | 51 years (including 5 years exploring star system)
|-
| ''deceleration stage'' || 21,500,000 GW || 7,850 t || 0.3 g || 320&nbsp;km || 50% @ 10.4 ly
|-
| ''return stage'' || 710,000 GW || 785 t || 0.3 g || 100&nbsp;km || 50% @ 10.4 ly
|-
| ''deceleration stage'' || 60,000 GW || 785 t || 0.3 g || 100&nbsp;km || 50% @ 0.4 ly
|}

=====Interstellar travel catalog to use photogravitational assists for a full stop=====
The following table is based on work by Heller, Hippke and Kervella.<ref>{{Cite journal|arxiv=1704.03871|last1=Heller|first1=René|title=Optimized trajectories to the nearest stars using lightweight high-velocity photon sails|journal=The Astronomical Journal|volume=154|issue=3|pages=115|last2=Hippke|first2=Michael|last3=Kervella|first3=Pierre|year=2017|doi=10.3847/1538-3881/aa813f|bibcode=2017AJ....154..115H|s2cid=119070263 |doi-access=free }}</ref>

{| class="wikitable"
|-
! Name !! Travel time<br> (yr)!!  Distance<br> (ly)!! Luminosity<br> ([[Sun|L<sub>☉</sub>]])
|-
| ''Sirius A'' || 68.90 || 8.58 || 24.20
|-
| ''α Centauri A'' || 101.25 || 4.36 || 1.52
|-
| ''α Centauri B'' || 147.58|| 4.36 ||  0.50
|-
| ''Procyon A'' || 154.06 || 11.44 || 6.94
|-
| ''Vega'' || 167.39 ||25.02 || 50.05
|-
| '' Altair'' || 176.67 ||  16.69 ||  10.70
|-
| ''Fomalhaut A'' || 221.33 || 25.13 || 16.67
|-
| ''Denebola'' || 325.56 ||  35.78||  14.66
|-
| ''Castor A'' || 341.35|| 50.98 || 49.85
|-
| ''Epsilon Eridani'' ||  363.35 || 10.50 || 0.50
|}
* Successive assists at α Cen A and B could allow travel times to 75 yr to both stars.
* Lightsail has a nominal mass-to-surface ratio (σ<sub>nom</sub>) of 8.6×10<sup>−4</sup> gram m<sup>−2</sup> for a nominal graphene-class sail.
* Area of the Lightsail, about 10<sup>5</sup> m<sup>2</sup> = (316 m)<sup>2</sup> 
* Velocity up to 37,300&nbsp;km s<sup>−1</sup> (12.5% c)

==== Pre-accelerated fuel ====
Achieving start-stop interstellar trip times of less than a human lifetime require mass-ratios of between 1,000 and 1,000,000, even for the nearer stars. This could be achieved by multi-staged vehicles on a vast scale.<ref name="L.D. Jaffe 1963, pp. 49-58">{{cite journal |author1=D.F. Spencer |author2=L.D. Jaffe |title=Feasibility of Interstellar Travel |journal=Astronautica Acta |volume=9 |year=1963 |pages=49–58|url=https://apps.dtic.mil/sti/citations/AD0274312 |archive-url=https://web.archive.org/web/20171204204839/http://www.dtic.mil/docs/citations/AD0274312 |url-status=live |archive-date=December 4, 2017 }}</ref> Alternatively large linear accelerators could propel fuel to fission propelled space-vehicles, avoiding the limitations of the [[Rocket equation]].<ref>{{cite journal |author1=Roger X. Lenard  |author2=Ronald J. Lipinski  |title=Interstellar rendezvous missions employing fission propulsion systems |year=2000 |journal=[[AIP Conference Proceedings]] |volume=504 |pages=1544–1555|doi=10.1063/1.1290979  |bibcode=2000AIPC..504.1544L }}</ref>

==== Dynamic soaring ====
[[Dynamic soaring]] as a way to travel across [[interstellar space]] has been proposed.<ref>{{cite news |last=Mcrae |first=Mike |title='Dynamic Soaring' Trick Could Speed Spacecraft Across Interstellar Space |url=https://www.sciencealert.com/dynamic-soaring-trick-could-speed-spacecraft-across-interstellar-space |date=6 December 2022 |work=[[ScienceAlert]] |accessdate=6 December 2022 |archive-date=6 December 2022 |archive-url=https://web.archive.org/web/20221206063650/https://www.sciencealert.com/dynamic-soaring-trick-could-speed-spacecraft-across-interstellar-space |url-status=live }}</ref><ref>{{cite journal |last1=Larrouturou |first1=Mathias N. |last2=Higgns |first2=Andrew J. |last3=Greason |first3=Jeffrey K. |title=Dynamic soaring as a means to exceed the solar wind speed |date=28 November 2022 |journal=  Frontiers in Space Technologies|volume=3 |doi=10.3389/frspt.2022.1017442 |arxiv=2211.14643 |bibcode=2022FrST....317442L |doi-access=free }}</ref>