What makes human space exploration very difficult is the infrastructure require to support a human body outside earth. It must be researched, developed and tested thoroughly which can take many years and can quickly drain budgets. Once ready, it requires even more resources just to launch it into space with humans onboard. In contrast, it's far simpler and less expensive to send unmanned probes. In fact, it has already been achieved. For whatever reason, perhaps to stroke the collective ego of homo sapiens on earth, space exploration without humans is unsatisfactory. Has a compromise ever been considered?
Instead of sending entire bodies into space, why not just send human heads into space? A human head has less mass and requires less energy that a complete body. A smaller, more compact infrastructure can supply the brain with the proper nutrients and oxygen. The spacecraft can be as small as a probe. If a noggin in space is still unsatisfactory, the spacecraft can carry the required chemicals to regenerate a full human body for the purposes of colonization (eases budget concerns by western governments). Moreover, the required technology for noggin based exploration is far further along than whole body space exploration.