[Silhouette]

There is zero market risk in this idea.

Not necessarily. Interest alone does not create a market. You need potential customers who have the means to buy what you're offering under conditions that make it worth selling to them.

For example, I might be interested in a time machine, but if it's going to cost you a trillion dollars to make one and I'd need 5kg of unobtainium to power each jump, I do not represent a (viable) market.

Your premise in this discussion seems to be that the best startups (in some sense that isn't entirely clear yet) are the ones that are aiming to be game-changers. However, I expect that in practice that vast majority of successful startups are not doing something truly profound, but rather something much more mundane that either has not been done before or can be done significantly better in some way by the startup.

[texasbigdata]

The OPs constraint is better though.

Not "rockets" but "rockets at 1/100th of the price" which sort of takes into account your point.