Carl Wiley (writing as Russell Saunders,) 'Clipper Ships of Space', (pdf, 8 pgs) Astounding Science Fiction, May, 1951.
It would be possible to sail on the "wind that blows between the worlds"!.
Rand Simberg, 'Homesteading the Final Frontier', (pdf, 28 pgs) Competitive Enterprise Institute, April, 2012.
A practical proposal for securing property rights in space.
Robert Bussard, 'The QED Engine', (pdf, 12 pgs) 44th Congress of the International Astronautical Federation, 1993.
Nuclear fusion using the Farnsworth system would make interplanetary travel cheap and easy.
Robert Bussard, 'Galactic Matter and Interstellar Flight', (pdf, 14 pgs) Astronautica Acta, Fasc. 4, 1960.
The insterstellar ramjet idea.
Bradley Carl Edwards, 'A Hoist to the Heavens', Spectrum, August, 2005.
Using a ladder from the planetary surface to geostationary orbit makes launch costs trivial.
Jeff Foust, 'Floating to Space', The Space Review, July, 2004.
A series of balloons and airships can deliver significant payloads to LEO.
Michael Flora, 'Project Orion'.
A spacecraft driven by a nuclear-pulse engine could throw thousands of tons with a crew of hundreds.
Freeman Dyson, 'Interstellar Travel' (pdf, 5 pgs) Physics Today, pp. 41-45, October 1968
Orion spaceships to the stars could be launched in just 200 years.
Paul Webb, 'The Space Activity Suit', Aerospace Medicine, 1968.
An elastic leotard for extravehicular activity. Why won't NASA do the obvous things?
Stephen J. Hoffman & David I. Kaplan, 'Human Exploration of Mars' (pdf, 230 pgs!) NASA-SP6107, July, 1997.
The Reference Mission of the NASA Mars Exploration Study Team.
Grant Bonin, 'A Low-Energy mission Architecture for Reusable Earth-Mars Cyclers' 2005.
Habitats in Aldrin orbits provide cheap interplanetary travel.
Robert Zubrin & Christopher P. McKay, 'Technological Requirements for Terraforming Mars'
Remodeling the planetary surface to make it human habitable over historical time.
Geoffrey A. Landis, 'Colonization of Venus' (pdf, 6 pgs) Feb 2-6, 2003
Cloud cities in the atmosphere of Venus.
Robert Walker, 'Colonies that Float Over Venus' Science 2.0, Jan 12, 2014
Popular science presentation of Landis's proposal.
Karl Schroeder, The Interstellar Cycler, January, 2004.
An adaptation of Aldrin's Orbital Cyclers for interstellar travel.
K. Eric Drexler, 'The Engines of Creation', (pdf, 1.2 Mb!) 1986.
Engineering at the atomic scale..
Robert Freitas Jr & William Gilbreath, 'Advanced Automation for Space Missions', NASA-CP2255, 1980.
Von Neumann machines with advanced intelligence can explore the universe or prepare it for us.
Robert Freitas Jr, 'A Self-Reproducing Interstellar Probe', JBIS vol. 33, pp. 251-264 1980.
A more fully worked out reproductive system.
Robert Freitas Jr, 'Terraforming Mars and Venus using Self-Reproducing Systems', JBIS vol. 36, pp. 139-142 1985.
SRS terraforming methods are suggested for Mars and Venus. And terraforming is just the start of it.
Ralph C. Merkle, 'NASA and Self-Replicating Systems', 1986.
Engineering at the atomic scale + Von Neumann machines = the end of the scarcity economy.
Leonard David, 'Bright Future for Solar-Power Satellites', Space.com, 17 October, 2001.
If cheap access to space can be achieved then dirt cheap power is also available.
Richard D. Johnson & Charles Holbrow, 'Space Settlements: A Design Study', NASA-SP413, 1975.
An early and hopeful assessment of the aims and methods of space (not rock) colonization.
Theodore Wayne Hall, 'The Architecture of Artificial-Gravity Environments', Doctoral Dissertation, 1994.
This dissertation aims to advance the science of environmental design for artificial gravity..
Charles Pellegrino, 'The Valkyrie Antimatter Rocket'.
Manned interstellar missions at 92% of the speed of light.
Robin Hanson, 'Burning the Cosmic Commons', (pdf, 31 pages) 1998.
An economic analysis of interstellar colonization with consequences for the Fermi paradox.
David Brin, 'The Great Silence', (pdf, 27 pages) 1982.
Thoughts on the values for the Drake equation and the Fermi paradox.
Andrew J. Watson, 'Implications of an Anthropic Model of Evolution', (pdf, 12 pages) Astrobiology 8:1, 2008.
Maybe we're the first intelligent species in the galaxy to achieve a technological civilization.
Vernor Vinge, 'The Coming Technological Singularity', 1993.
Soon we will create superhuman intelligence, and the human era will end. It's a good thing!
J. D. Bernal, 'The World, the Flesh, and the Devil', 1929.
An enquiry into the three enemies of the rational soul. An early vision of transhumanism.
Nick Bostrom, 'Transhumanism: FAQ', 2003.
General introduction to the ideas of the transhumanists.
W. Dröscher & J. Häuser, 'Guide for a Space Propulsion Device', (pdf, 30 pages) AIAA 2004-3700.
An idea for hyperspace FTL travel that is being investigated by NASA. Fingers crossed!
David J. Stevenson, 'Possibility of Life-Sustaining Planets in Interstellar Space', (pdf, 8 pages) Nature 1998.
Planets without suns may have comfortable conditions.
Jia Liu, 'Dark Matter as a Possible New Energy Source for Future Rocket Technology', (pdf, 7 pages) arXiv 2009.
Self-annihilating dark matter suggests a ramjet system is possible.
L. Crane & S. Westmoreland, 'Are Black Hole Starships Possible?', (pdf, 20 pages) arXiv 2009.
Hawking radiation from a 1 Mt black hole is just right for a starship drive.
Forrest Bishop, 'Open Air Space Habitats', Institute of Atomic Scale Engineering, 1997.
Open-ended cylinders woven by molecular spinners.