Editing Interstellar travel (section)

==== 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)