SOLAR SAILS

Solar sails, next to gravity assists and cycling stations, are as close to a free lunch as you can get, even though there is no such thing as a free lunch.  Solar sails will be a ideal form of propulsion for freighters traveling between Earth and Mars.  They could also be used to adjust the orbits of cycling stations cruising between Earth and Mars without any expenditure of fuel.

Force = 2(P*A)/c P=1400 watts/sq. meter at 1 A.U.,  at Mars' orbit P= 600 watts/sq. meter A=sail area in sq. meters c=lightspeed 300,000,000 m/s 0.21976 pounds per newton

A solar sail, 10 km. by 10 km., operating at 1 A.U., could accelerate a 100 english ton mass to a speed of 30.25 miles per second in 8 weeks.  A 1000 tons mass could reach 3.02 miles per second in 8 weeks.  This is more than enough to reach Mars.  The same sail, at 1 A.U., could achieve a delta V of 800 mph for a 5,000 ton cycling station in only two weeks.  If huge microwave beaming stations are built on the Earth, Moon, Mars, Deimos and Phobos, it may be possible apply pressure to the sails in excess of the Sun's solar pressure.  Very thin but strong gossamer sails made of carbon 60 nanofibers, perhaps, or aluminized spider silk made from genetically modified organisms will be necessary.  The magnetic sail, envisioned by Zubrin and Andrews,  is also interesting.  Perhaps a superconducting cable loop, which is a mag-sail, could form the perimeter of a solar sail, so that thrust could be harnessed from the thin plasma of the solar wind in addition to the pressure of light from the Sun for maximum effect.

CYCLING STATIONS

Cycling stations aren't a free lunch, but they are as close as you can get in reality, like solar sails and gravity assists.  The problem is keeping them synchronized with the positions of the worlds.  Buzz Aldrin suggests Up-Down Escalator orbits that use gravity assists at planet enounter to sort of "walk" or rotate  the elliptical orbits around (ABOVE).  Besides gravity assists to modify the cycler orbits we can use fuel miser NEP or SEP, solar and mag-sails, and we can use power beams from orbiting beamrider stations to apply thrust to the sails and keep those orbits in synch with the planets.  The orbits illustrated above take one to Mars in six months, then spend about a year in the Main Asteroid Belt where you can undock a rocketship and fly over to the asteroid of your choice.  When the cycler swings by Mars again travelers who've spent the past year on Mars can pick up the station again and ride down to Earth in six months.  The only rocket fuel needed is for the small taxis that transport you to rendesvouz with the station.  The taxis can be fueled up from mining stations on Diemos, Phobos or our Moon.  The taxis might also be beamriders with sails.  The logistical and cost problems of rocket fuel supply for mass transit through space are defeated.  Cycling stations could also be used for transportation to Venus and Mercury.  They'd take too long for travel to Jupiter or Saturn, so huge NEP powered high speed ships will be used for travel to the outer system.  Beamriders could also be used for high speed travel to the outer system.  Getting back would be a problem until we build huge fusion powered beamrider stations in the outer system.  Braking in the solar wind filled plasma of the solar system will be achieved effectively with mag-sails for these vessels which won't fly nearly as fast as starships that Zubrin says can be braked in the thinner interstellar plasma, so stopping is no problem!!!

ABOVE) Solar powered microwave or laser beaming stations in orbit around planets and at Lagrange points could apply thrust to the light sails of cycling stations to adjust their orbits or even increase/decrease their velocity thru space.  The beamrider stations would fire opposing beams to stay on station.  An interplanetary transportation system could someday emerge that uses fuel only for the small taxis.

ABOVE) Interplanetary cycling station at least as big as the starship Enterprise.  The station is not rotating.  The counter-rotating "hatbox" centrifuges provide artificial gravity at perhaps 0.5 to 0.6 G so that adaptation to or from martian 0.38 G or terrestrial 1 G is not too tough after months in space.  Excellent views of the cosmos are had from wieghtless sections and these views are spectacular near planet fall.  Gallium arsenide (30% eff.) or gallium indium nitride (70% eff.) supply power.

LEFT) Side view of interplanetary cycler gives you some ideas about the rigging.

ABOVE) Cabins for 700 passengers times four 'fuges= 2800 passengers  Seven taxis carrying 400 passengers each = 2800 passengers  One taxi in reserve, just in case.....

More about cycling stations and solar sails

Viking Orbiter deploying lander near Mars.  This has nothing to do with solar sails or cyclers but it is a cool picture by Don Davis.  Then again, what about "flying saucer" shaped taxis that undock from sailing cyclers and aerobrake??