Dave Dietzler
SAIL BASICS
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
At Mercury, 9000 watts/square meter. A 10,000 tons (or 10,000,000 kg. or 22,000,000 pound) solar sailing barge with 50 km. by 50 km. sails would reach:
2(9000*2,500,000,000 sq. meters)/300,000,000= 150,000 newtons or 32,964 pounds of thrust.
32,964/22,000,000 = 0.0015 G or 0.0147 meters per second per second
In 90 days we will reach 0.0147*3600*24*90= 114,182 m/s or 114 kps or 410,000 kilometers per hour!!! That's 255,000 mph!
Since we will be moving out away from the light we will go slower, but if you tried to launch from Mars you would disappear into the dim regions of the solar system and lose thrust, especially with light falling off the inverse square.
I don't know how fast you could actually go with a solar sail or how much faster you would go in combination with a mag-sail, but I have no doubt that barges could launch to Jupiter, travel between Venus, Mercury and Earth, and brake into the inner solar system when coming in from Jupiter's icy moons.
How do we make the sails? Glass filament reinforced foil? Aluminized plastic? Carbon fibers? Details.
According to my computer program, you need 17.43 kps over Mercury orbital speed to go on a Hohmann to Jupiter. You need to lose 8.193 kps to go from Jupiter to Mercury. Haven't figured out how much to overcome Jove's gravity but we get the idea. I don't know much about the capabilities of electrodynamic tethers, but my intuition tells me they could be used to escape from Jupiter.
I double checked my calculations, so this is correct and amazing.
A GRAND TOUR
In Arthur C. Clarke's Imperial Earth he describes a fusion powered space liner that leaves Earth, flys by Venus and Mercury, stops at Mars I think and then goes out to Titan. We could certainly use nuclear electric ion drives and sails to leave GEO or L1 ( or L2). I would prefer to take a trip to the Moon first (since this is a luxury cruise Grand Tour) then exit from L1 and get some gravity assist from Earth; swing down to Venus and use sails to brake into orbit there. More courageous passengers could fly down to AeroCities and see the Venusian surface. That really can't be more dangerous than re-entry I guess. It's all a matter of perceived dangers. We could then use the sails to fly down to Mercury and after no more than 144 days at Venus and spend no more than 110 days at Mercury before getting a launch window to Mars. Then race around the Sun and head out to Mars at high speed. We could brake into orbit around Mars with nuclear thermal rockets stocked up on Venusian CO2 or hydrogen from the pipeline from Jupiter's icy moons. Waiting for a launch window to Jupiter would take up to 814 days. Some can stay on Mars, others go back to Earth on the next cycling station, and others can make the long haul to Jupiter. Or maybe we could fly straight to Jupiter after no more than 90 days on Mercury and do it fast with sail power. Then we can cruise around in the Jovian system. Visit cities beneath the ice of Europa, go to Callisto, etc. Getting back to Earth will be done by spiraling away from Jupiter with electrodynamic tethers and using nuclear electric engines. We will brake into orbit around Earth with the sails so we will burn up all the fuel we can to get some speed back to Earth instead of lugging retro-rocket fuel.
SPACE LINER
The liner would have thick radiation shields of hydrogen dense polyethylene and centrifuges. A ten thousand ton ship made of magnesium, aluminum and titanium would be quite large. It could even be made largely of plastics and graphite composites. It could use active magnetic radiation shields instead of massive solid material for shields to reduce mass and give us more tonnage devoted to habitable volume.
Fission using a vapor core reactor like that being researched by Dr. Travis Knight and others at the University of Florida's Innovative Nuclear Space Power Institute is my choice for power. The vapor core reactor can get over one kilowatt per kilogram of system mass and that is an order of magnitude better than other fission systems. There's enough uranium in seawater to power human civilization for thousands of years. There's four times as much thorium in the Earth's crust than uranium. When we mine Mercury, the Moon, Mars and perhaps some asteroids we will have even more fission fuel for space propulsion. Human civilization will probably be powered by solar and fusion. We can use low mass fission power systems for spaceship propulsion in addition to solar sails and mag-sails (which need a source of electricity). We have plenty of fission fuel-uranium, plutonium and thorium, to power interplanetary travel for a long time. When we do get low mass fusion rocket motors we will use them; I am only trying to illustrate other possibilities.
BEAM RIDERS
I didn't even mention beam riders in the Grand Tour described above. With power stations on other planets or even in free space (that fire opposing beams to stay in "one place") we could build powerplants so massive they could never be useful on a ship, but they could direct microwave or laser beams at the sails of a spaceship and propel it to high speeds. With beaming stations on Deimos, Phobos and the martian surface we could propel ships from Mars to the outer planets. We could even put beams on minor planets like Ceres and Vesta. We could conquer the solar system with sails, electrodynamic tethers, ion drives, low mass vapor core fission reactors, propulsion beams and ground based or space based fusion powerplants to energize the beams, nuclear thermal rocket engines using whatever reaction mass is available from hydrogen to LOX augmentation to CO2, methane or ammonia, cycling stations and rockets that burn metals mixed with LOX. Now, if some science fiction writers would pick up on those technologies and think about the solar system and thousands of cities flourishing on other worlds and fantastic landscapes from Venus to Callisto and even Titan and some neat Space Oases also, they would have a scenario as exciting as the many worlds of Star Trek.
