I've watched several episodes of TBBT because I was married to someone who loved the show, but I was never able to watch it from S1 all the way to the finale while actually paying attention. After rewatching Friends and Modern Family hundreds of times, I needed a little "vacation" from them, so I decided to give TBBT a try. After all, I kinda know how it ends, and it always made me laugh.
So, this is the first time I'm actually following the show's story from beginning to end, and I feel like Sheldon comes full circle in this episode, both in his love for Amy and in his growing respect for Howard. Let me explain my point of view.
As for his friendship with Howard, Sheldon is always putting him down for not having a PhD, as if he doesn't care enough about engineering or isn't as accomplished as the others. It can be pretty harsh at times, and we can see how much it irritates Wolowitz. But Sheldon's reaction here, telling him to "boldly go, Wolowitz" as the rocket launches, shows that he does respect Howard, or at least that Howard has earned his respect. To me, it's an acknowledgment of just how significant what Howard is doing really is.
As for Amy, while Sheldon shows his admiration for Howard, he also reveals a very human kind of fear: someone he cares about is embarking on an incredibly difficult mission, and he knows that there's a real risk involved. Holding Amy's hand, even though their relationship agreement didn't call for it, shows just how much his love for her has grown by this point. He's become comfortable enough with her to express his feelings and seek comfort in her presence during a moment of fear and uncertainty.
To me, this was one of the most moving moments in the entire show, by far. I even cried a little. Beautiful.
