Space tourism is ________ in my lifetime.

The phrase "hardly likely to take off" suggests a strong skepticism or doubt regarding the prospects of space tourism occurring within the speaker's lifetime. This expression emphasizes that the speaker believes the chances of space tourism becoming a reality are very low. The use of “hardly” diminishes the likelihood significantly, suggesting that while there might be potential for advancements in space tourism, it's far from being a definite outcome.

In contrast, the other options express varying degrees of optimism about space tourism. The choice that states "almost certain to take off" conveys a strong belief that it will happen, which does not align with the original sentiment of doubt. Similarly, "definitely going to succeed" implies an absolute certainty that supports the idea of potential success in space tourism, opposing the initial idea of low likelihood. Lastly, "unlikely to succeed" implies some potential for success, merely suggesting it is a long shot, rather than indicating such severe doubt as the word "hardly" does. Therefore, the first option accurately reflects a perspective of skepticism regarding the future of space tourism within the speaker's lifetime.