Forty years ago when it looked like we would land men on Mars before the end of the 20th century, predictions that we would have mining operations on the moons of Jupiter within our lifetime seemed almost certain to happen. But since we may not return to the moon before 2020, predicting the future of manned habitation of other planets is difficult.
First off, to get to the moon quickly and cheaply, the Ground/Ship Launch/Propulsion System would allow us to send people to the moon by using a powerful ground energy source to generate electromagnetic beams that would repel against, power the engines, and spin the flywheels of a powered projectile which could reach the moon within a matter of hours. GSLP was suggested in an unpublished novel titled THIRTY YEARS AFTER VIKING back in 1979 as a means to send the first people to Mars by October 12, 1992 in three days. A similar system has been proposed as a way to send people to Mars from earth orbit in a matter of a few months. But if there is a continual beam or beams, energy could be used by retro-engines to slow the projectile.
Another form of GSLP would use several beams and electromagnetic fields that would surround a powered projectile that would use both repulsion-drive and linear induction to fly out into space. It may be possible to reach Mars within a day or less by using enveloping multi-beam GSLP.
If the injection reactor works to provide charged particles and energy for compression-field engines, a spaceplane could fly people to Mars. Such a craft has been drawn and shown at NASA facilities since 1991. It would take off like a plane from conventional airports and once it reaches space, the engines would be repulsion-drive engines that use field repulsion to send the plane hurtling toward the Red Planet in less than a week.
Further in the future, there will be field acceleration stations in the solar system that will accelerate spacecraft that use them to go out into the Kuiper Belt and beyond. Later, if hyperlight physics becomes a reality, we will be able to exceed the speed of light with none of the energy in and of itself exceeding the speed of light. But the cumulative effect would be the ability to exceed the speed of light in a spaceship.
Let's assume both GSLP systems, the spaceplane, and hyperlight speed crafts can be built between now and the next century. That would mean the first Mars colony could be established by the middle of this century. If electromagnetic force fields surround the vehicles that travel to the planets, deadly radiation should be prevented from penetrating the crafts to harm the occupants. That's why the vehicles should be nuclear-powered, despite what worrywarts think.
Venus will have to be terraformed to some extent before we can think about sending people there. Operation Heat Vent could begin by 2050 when we send both orbiting and ground systems to Venus to ventilate the atmosphere into space to reduce the atmospheric pressure and heat to make it more conducive to vegetational terraforming. Water would be sent to the planet first to be stored under the surface and later on the surface once the temperature can be moderated to less than 150 degrees. Water would be evaporated into the atmosphere to form clouds. By 2070 we might be able to land people on the planet to start a colony. Also by then, terraforming on Mars may allow people to roam around the Red Planet in some areas without needing spacesuits. If that is the case, we could see Bradbury, Wells, and Sagan City with populations in excess of 1000 people by the end of the century. Weekly flights to Mars could be scheduled by then.
The Kuiper Belt has planetoids that may be perfect for mining operations and colonization. Most of the people will live underground where nuclear energy will provide heat and power to allow the people to not need to wear spacesuits to survive. On the surface it will be colder than the temperature of liquid nitrogen and almost pitch black. But underground the conditions will be tolerable. With the stations Yukon, Siberia, Tibet, Patagonia, and Antarctica supervising the development and protecting the inhabitants of the Belt, there could be over 1000 people out there by 2120.
Once we can exceed the speed of light, maybe by the turn of the next century, we should be sending people to other worlds in other solar systems by 2110. We may have a colony within 150 light-years of earth by 2130 that could have 1000 people on it by 2150. That is providing repulsion-drive engines can power the ships and push them to other worlds at over 1000 times the speed of light. With repulsion-drive, we won't have small gains in speed. Since the acceleration of the energy mass, rate of field expulsion, and energy availability ratios determine the speed of a craft using repulsion-drive, giant starships will be used to send people to the stars.
We could have over a million people living on other worlds by the turn of the 23rd century. By the turn of the next century it could be over a billion. But if the progress over the last half century is an indicator of what to expect in the future, we'll be lucky to have a viable colony on Mars a century from now.