Questions about this unoriginal movie...

The name "Pinbacker" was introduced to us halfway into the movie (i.e. around 60 minutes into the movie), when Capa, Mace, Searle and Harvey boarded the first Icarus ship and played the last log file/tape. The guy on the tape and the intruder who was lounging in the observation room had the same voice, that's why Capa guessed he's Pinbacker (logic dictates it had to be a crew member from Icarus I anyway).

I presume the payload had to go through this "5-step detailed plan" to arm itself and detonate at the right moment, otherwise it would just disintegrate in the Sun. (Remember that scene in The Hunt For Red October (1990)? The fired torpedo couldn't arm itself fast enough and hence just bounced off the hull of the submarine, and it merely broke into pieces. Only when it had completed arming itself would it really explode upon hitting a target. I guess something similar applies to Capa's payload; the payload doesn't just passively go off, it had to operate through a complex activation sequence to cause a successful, controlled chain reaction.)

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Joe Satriani - "Always With Me, Always With You"
http://youtu.be/VI57QHL6ge0

Pinbacker was not a new antagonist. He caused all of the antagonistic events from the beginning, including the signal from Icarus I.

We couldn't see who he was because of all the burned makeup effects.

I'm disappointed in your post.

Others have already pointed out the things about Pinbacker, etc. that you seemed to have missed or misunderstood.

Then of course there's that last bit of arm-chair science of yours. The fission material of the bomb doesn't just "blow up" because you drop it into the sun -- the materials would just drop into the sun and disperse like dropping the water of a swimming pool into a lake or ocean. It requires proper detonation to begin the process of turning it into a "power of another sun" type of reaction.

In other words, the explosion for the required reaction as designed requires more science than just dropping it into the sun.

This is a very atmospheric movie, although not a very scientific one. And it does have several narrative glitches.

The one question I had from the begining was: why would you give this name to the spaceships?! Sure it's metaphoric and all, but seriously, the ancient dude's project had failed, he simply died foolishly mid-flight because he got too close to the Sun and his wings were made from wax. I see at least 3 red flags here.
How motivational could that name possibly be?
I'm just complaining that the name doesn't feel appropriate in-world. For us, the audience, the (two-thirds) foretelling feels quite poetic.
And the same could be said for other scientific or narrative inaccuracies.
... Except for Pinbacker, that is. I actually fast forward through his segment when I rewatch the movie - watching characters being chased by some monster in space is NOT why I want to see THIS movie. I'll go to Alien when I need my chased-by-monstet-in-space fix. Here I am for apocalyptic desperate beautiful doom and life/death/horror/light interpretation of the sun. And for the petting-the-sun ending.