Space Travel in the 22nd century
For almost 200 years, scientists and engineers sought the Holy Grail present in Miguel Alcubierre's equations. Those that showed mathematically that faster than light travel (FTL) was possible. In vain. The equations called for negative energy, whatever that was, and lots of it. Without it FTL travel remained a pipe dream. Could a warp drive ever be built?
Meanwhile, fusion power was slowly harnessed and perfected. Interplanetary space in the Sol System was explored with fusion-powered engines of numerous types. Travel to the outer planets and their moons, even to the Oort Cloud, was quick and cheap with ever-improving fusion engines. Could mankind travel to the stars this way?
During the course of the 20th and 21st centuries, research into the freezing (and revival) of humans progressed steadily. By the end of the 21st century it was possible to put a human being into stasis for years, and then to successfully revive her or him. In stasis, people did not age. When they were awakened it was as if time had stood still for them.
As the use of fusion power became familiar and routine, mankind built fusion rocket engines capable of increasing fractions of c. Using them, unmanned interstellar probes were sent out to the thousands of stars already known to have exoplanets in their 'Goldilocks Zone'. This way, many planets within ten parsecs of Sol were confirmed to be habitable.