Editing Interplanetary spaceflight (section)

===Skyhook===
{{main|Skyhook (structure)}}
[[File:Mature non-rotating Skyhook.png|thumb|[https://skyhooksandspaceelevators.wordpress.com Non-rotating skyhook] first proposed by E. Sarmont in 1990]]
A skyhook is a theoretical class of orbiting [[tether propulsion]] intended to lift payloads to high altitudes and speeds.<ref>{{cite journal | last1 = Moravec | first1 = H. | year = 1977 | title = A non-synchronous orbital skyhook | journal = Journal of the Astronautical Sciences | volume = 25 | issue = 4| pages = 307–322 | bibcode = 1977JAnSc..25..307M }}</ref><ref>{{cite journal | last1 = Colombo | first1 = G. | last2 = Gaposchkin | first2 = E. M. | last3 = Grossi | first3 = M. D. | last4 = Weiffenbach | first4 = G. C. | year = 1975 | title = The sky-hook: a shuttle-borne tool for low-orbital-altitude research | journal = Meccanica | volume = 10 | issue = 1| pages = 3–20 | doi=10.1007/bf02148280| s2cid = 123134965 }}</ref><ref>M. L. Cosmo and E. C. Lorenzini, Tethers in Space Handbook, NASA Marshall Space Flight Center, Huntsville, Ala, USA, 3rd edition, 1997.</ref><ref>L. Johnson, B. Gilchrist, R. D. Estes, and E. Lorenzini, "Overview of future NASA tether applications," ''Advances in Space Research'', vol. 24, no. 8, pp. 1055–1063, 1999.</ref><ref>E. M. Levin, "Dynamic Analysis of Space Tether Missions", ''American Astronautical Society'', Washington, DC, USA, 2007.</ref> Proposals for skyhooks include designs that employ tethers spinning at hypersonic speed for catching high speed payloads or high altitude aircraft and placing them in orbit.<ref name=hastol>[https://www.tethers.com/papers/HASTOLAIAAPaper.pdf Hypersonic Airplane Space Tether Orbital Launch (HASTOL) System: Interim Study Results] {{webarchive|url=https://web.archive.org/web/20160427114416/http://www.tethers.com/papers/HASTOLAIAAPaper.pdf |date=2016-04-27 }}</ref> In addition, it has been suggested that the rotating skyhook is "not engineeringly feasible using presently available materials".<ref name="Boeing.2000">{{cite conference |first1=Thomas J. |last1=Bogar |first2=Michal E. |last2=Bangham |first3=Robert L. |last3=Forward |first4=Mark J. |last4=Lewis |contribution=Hypersonic Airplane Space Tether Orbital Launch System |title=Research Grant No. 07600-018l Phase I Final Report |publisher=NASA Institute for Advanced Concepts |date=7 January 2000 |contribution-url=http://www.niac.usra.edu/files/studies/final_report/355Bogar.pdf |access-date=2014-03-20 |archive-date=2013-08-21 |archive-url=https://web.archive.org/web/20130821132225/http://www.niac.usra.edu/files/studies/final_report/355Bogar.pdf |url-status=live }}</ref><ref name="io9.why">{{cite web |last=Dvorsky |first=G. |title=Why we'll probably never build a space elevator |work=io9.com |date=13 February 2013 |url=http://io9.com/5984371/why-well-probably-never-build-a-space-elevator |access-date=13 August 2014 |archive-date=10 August 2014 |archive-url=https://web.archive.org/web/20140810232702/http://io9.com/5984371/why-well-probably-never-build-a-space-elevator |url-status=live }}</ref><ref name="pop.15185070">{{Cite journal |last=Feltman |first=R. |title=Why Don't We Have Space Elevators? |journal=Popular Mechanics |date=7 March 2013 |url=http://www.popularmechanics.com/science/space/nasa/why-dont-we-have-space-elevators-15185070 |access-date=13 August 2014 |archive-date=6 August 2014 |archive-url=https://web.archive.org/web/20140806075236/http://www.popularmechanics.com/science/space/nasa/why-dont-we-have-space-elevators-15185070 |url-status=live }}</ref><ref name="Huff.3353697">{{cite web |first=Jillian |last=Scharr |title=Space Elevators On Hold At Least Until Stronger Materials Are Available, Experts Say |work=Huffington Post |date=29 May 2013 |url=http://www.huffingtonpost.com/2013/05/29/space-elevators-stronger-materials_n_3353697.html |access-date=13 August 2014 |archive-date=2 March 2014 |archive-url=https://web.archive.org/web/20140302234815/http://www.huffingtonpost.com/2013/05/29/space-elevators-stronger-materials_n_3353697.html |url-status=live }}</ref><ref name="extreme.176625">{{cite news |last=Templeton |first=Graham |url=http://www.extremetech.com/extreme/176625-60000-miles-up-geostationary-space-elevator-could-be-built-by-2035-says-new-study |title=60,000 miles up: Space elevator could be built by 2035, says new study |work=Extreme Tech |date=6 March 2014 |access-date=2014-04-19 |archive-date=2014-04-12 |archive-url=https://web.archive.org/web/20140412055111/http://www.extremetech.com/extreme/176625-60000-miles-up-geostationary-space-elevator-could-be-built-by-2035-says-new-study |url-status=live }}</ref>