There are dreams, fantasies, and delusions.

Dreams are the stuff that aren't true now but can be made to come true. You see dreams in action every time you see someone open a new business or undertake a difficult but possible activity, such as attending medical school.

Fantasies are dreams that almost certainly won't come true but are still possible, although the odds are very much against it. An example would be winning a major lottery. Odds of 138 million to one are extreme but someone did win over $300 million last month in the Powerball lottery. At the same time, millions of people didn't win a thing.

A delusion is something that has absolutely no chance of coming true. For example, as a 48 year old who hates running (I'm convinced that running causes brain damage), any hope of me winning an Olympic gold metal in the 100 meter sprint would be a delusion.

When looking to the future of spaceflight, be sure to keep your dreams separate from fantasies and delusions. Returning to the moon within the next 15 years is a dream - it is difficult but definitely doable if we have the will. Going to Mars within the next 20-30 years is also an achieveable dream if we choose to do it (that means pay for it).

With the technology that'll likely be available in the foreseeable future, even sending an unmanned probe to another star system and having it arrive within a human lifetime is likely to be a fantasy for the next 100 years or so, barring some incredible propulsion breakthrough. Ideas of traveling to other galaxies are the stuff of delusions. Our galaxy is 300,000 light years across. The distance to the next nearest galaxy is probably even further than that. Even if we could travel 1000 times the speed of light, it would take centuries to reach the next galaxy.