The impactor excuse is a horrible one in the short term. It is like saying we want missile defense so we should spend a 100 trillion for something that doesn't work. There are things that we all want technologically, but there is a proper time to spend the money to achieve it also--when the enabling technologies are present at a reasonable cost. Once again we are more likely to field a reasonable impact defense system by advancing ALL our technologies naturally, until we can field one at reasonable cost. I would be very surprised if we could not do this within the next 100 years quite easily without spending extraordinary sums. For the risk factor within the next 100 years, I think we are safe and I also think anything that really threatened us greatly would not be deflected by any premature and fledgling system we put out there.

The way we slow technology is sucking huge sums out of our economy to do all sorts of negative productivity pork barrel projects that seemed like a good idea (as marketed to the public) at the time. If we would just leave that money in the economy rather than misspend it, growth of the economy and advancement of all technologies would happen more rapidly. The more rapidly technologies advance, the quicker the enabling technologies to do the things like manned space exploration (at reasonable cost) will happen.

One of the many things happening in todays technology is that surgeons are performing more and more operations through robotic interfaces. The surgeon is immersed in an often magnified world with virtual overalys, etc. The technology has already been developed for teleoperated operations. By analogy why with the proper tools (immersed virtual reality) would not a geologist be able to make a series of rapid decisions for robots to perform on another world. (Yes, I'm aware of the communication delays,but i'm talking about decisions like which collection of rocks to examine which you then just say examine rock x,y,z and get back to me when you're almost done). Warfighter pilots don't anymore use their eyes directly, but utilize cockpit displays that reflect reality plus.

I think you need to understand where the power of immersive virtual reality is headed. It will be possible for humans on earth to get a large piece of the experience of visiting other worlds through such virtual interfaces. In my opinion that should do, until we can reduce launch costs sufficiently to have manned space missions that don't take huge chunks of our national science budget.