Micro-fusion pulse is a possibility. Muonic induced fusion has been proposed as a steady state means to create a fusion reaction at low temperature and pressure. A muonic burst in an inertial confinement compression of boro-hydride, or lithium deuteride, reduces reaction requirements and attains Lawson criterion at much lower power densities. In short a fusion powered pulse ship is possible. Its capable of traversing the solar system with ease, and also modified to power space stations, space colonies and so forth - and end our energy crisis.
Before that we can build reusable chemical launchers to cheaply put up a network of communications satellites to create a global wireless hotspot to provide wireless broadband globally. We also add wireless telerobotic activity - similar to the new movie surrogate - but to allow us to do work remotely. We could live in one city and work anywhere we can send a signal - which means anywhere between where you are and the moon.
So, long before we have fusion powered rockets (and we could have them today if we wanted) we can build large reusable chemical rockets that orbit comsat networks and solar power satellites that beam energy by narrow powerful infrared laser beams to where energy is needed at very low cost.
Fusion can be reserved for appropriate use powering interplanetary and interstellar journeys, while beamed energy from space is used for terrestrial and orbital applications. Lifting large solar power satellites with massive nuclear fusion rockets also provides long term stability in energy supply and pricing bringing energy down long term. Moving solar power satellites closer to the sun and beaming energy across the solar system, further increases power while reducing costs. Finally, orbiting very close to the sun, we generate energy and beam it between stars to power laser light sail spaceships, that move at 1/3 light speed and more.
One interesting thing is that there are millions of asteroids orbiting between Jupiter and Mars, and rockets of this type can change the orbits of these asteroids. It has been suggested that asteroids that are on collision course with Earth might be deflected away from colliding with Earth with nuclear pulses. It has also been suggested that close encounters with heavy asteroids be engineered to transfer momentum between Jupiter and Earth, enlarging Earth's orbit just enough to counter the ever increasing brightness of the Sun.
Other things are possible.
Of these, is surveying all the small bodies of the solar system, deflecting those that pose a threat, engineering the orbit changing encounters just described, but also, identifying and capturing the very richest of all these asteroids and putting them into stable orbits in sun synchronized orbits over the poles. Then, sending up large remotely controlled factories to process these asteroids into useful things. On the one hand, things we can use on Earth. On the other, things we can use on orbit - including large pressure vessels to grow things - forests and farms on orbit. We send icy moons and asteroids from the outer solar system to these - to provide water and carbon - and grow massive quantities of food, and wood and fiber and leather - and make products on orbit, and send them directly to people anywhere on Earth or in space.
We can do this today with technology well developed.
We can identify the asteroid belts around other stars and use those just as we use asteroids orbiting the sun, to build industrial infrastructure, and send materials back to Earth.
How do we manage remotely controlled factories in other star systems?
Faster than light signals - which precede faster than light travel.
vanStockum, Tipler, and others have shown that a massive spinning objects have the capacity to create causal time loops. These loops involve particles entering the ergosphere of a spinning black hole at a specific time, and leaving at an earlier time.
Well a rapidly spinning super-massive black hole exists at the center of the milky way
Sending a signal to this black hole, in the appropriate way, allows that signal to be reflected back at an earlier time. We send a radio pulse to the black hole, it takes 30,000 years to get there, and then exits 60,000 years before it arrives, coming back at Earth, to be received AS it is sent. This 'beating' of CTL signals allows us to examine the physics of black holes, and then by changing the 'dwell time' we can send signals back in time.
Ron Mallett at U of Conn is attempting to do something like this.
Success with something like a space based version of the VLA -arrays of radio telescopes in space around every star - using the gravity of the star itself as a large antenna to focus signals from the galactic center - that communicates broadly with specific regions of the spinning supermassive black hole's ergo sphere - allow instantaneous communications with remotely controlled surrogate workers in distant star systems.
Signals travel to the supermassive black hole from Earth, then from the supermassive black hole to the star system - arriving instantly - and reversing the process to send signals back - instantly.
It also allows communications in time. For example, you want a custom ordered couch, or car it usually takes 8 to 10 weeks to get it - well you order it, the order gets sent back in time - and it is waiting for you at home. Or you arrive at a restaurant, and sit at the table, give the waitron your order, and you get the order nearly instantly - having had it sent back in time 20 or 25 minutes preptime after giving it.
Experimentation in causality violation will also give us new insights into physics of causality.
Computing systems with negative time delays will allow goal directed behavior to be built into robotic systems that can literally sense the future and take appropriate action - creating a new level of artificial intelligence not possible with mere biological systems.
Laser light sails moving between stars at 1/3 light speed also give rise to the possibility of creating super colliders involving large massive shaped iron-56 wedges moving at 1/3 light speed. Colliding these shaped masses allow experimentation in creating our own microscopic engineered black holes. These engineered objects can be made to spin, and dance and interact to create a new class of engineered product. With these we can easily modify spacetime - creating high gee gravity drives converting rest mass directly to graviton beams, and tapping zero point energy to stamp out new black holes on demand, and letting them evaporate to generate energy and graviton rockets on a scale 10x larger than fusion rockets.
With this sort of technology, which comes after we build laser light sails that travel between stars, we can travel at high speed to the galactic center and travel around the black hole there in such a way as to travel through space and time - so we can travel instantly across the galaxy - and visit any point in time the black hole exists.
It is here that it will be very likely we meet alien intelligences.
Technology grows in quantum leaps - discontinuous changes based on fundamental shifts in insight.
We have the means now to build chemically powered reusable multi-stage rockets that put up a global wireless hotspot and solar power satellites.
We have the means now to build surrogates like Honda's ASIMO to allow us to live anywhere and work anywhere else.
We have the means now to build fusion pulse rockets that allow industrial use of the asteroid belt.
We have the means to use remotely controlled factories and captured rich asteroids along with space based power to give everyone on Earth a meaningful job and a standard of living equal to that of any millionaire - while ending all pollution on Earth and ending every shortage.
This is just the beginning.
We can send signals instantly through space - and send signals through time.
We can also beam energy from star to star and push lightweight sails around with payloads at 1/3 light speed - to dispatch payloads to other star systems - controlling them in 'real time' - and then mining iron-56 and colliding shaped pieces of iron-56 to create artificial black holes - black hole dust I call it. engineering the interactions of those black holes to do other things - such as just described - this could have all been done in the last 60 years - it can be done in the next 60 if we desire.