Colonising Space/Access to space
We now have access to space using rockets. However this is currently an expensive way to get into space (over $5000 per pound of material launched[1]) and the failure rate is high. This severely limits what we can do in space: it is the main obstacle to space solar power, space tourism and large-scale space habitats. So far, we have only dipped our toes into space; if we want to really dive in we have to make spaceflight cheap and reliable.
It may be that using abundant solar energy and seawater, liquid oxygen and hydrogen fuelled rockets may continue to be common-place heavy-lift launch systems, and perhaps in conjunction with solid-rocket boosters like the Space Shuttle that use metal fuels and inorganic oxidizers made from common elements.
Although many other interesting launch systems are thought to be technically feasible ranging from single stage to orbit space planes (SSTOs), electromagnetic and balloon platform launch assist to more exotic launch loops and geosynchronous space elevators. More information on these alternative launch methods are covered in this WP article.