I like the solarian class, however, I kind of see the solarian as the sci-fi version of the barbarian class. As such, I suggest the Attune skill be revised to perform more like the barbarian's Rage. Here is how I see it:
Attune [1 action]
Requirements: you aren't fatigued or already attuned
Based on chosen Arrangement enter into favored state (Balanced: solarian's choice; Degradant: graviton; Radiant: photon). This ability lasts for 1 minute, until there are no enemies you can perceive, or until you fall unconscious, whichever comes first. While Attune is active the Solarian can activate Solar Manifestations and the manifestations gain bonuses based on current active attunement (as mentioned on page 100 of the Starfinder Playtest Rulebook). You can't use actions with the concentration trait unless they also have the attune trait. When Attune ends all Solar Manifestations disappear and you can't use Attune again for 1 minute. Special: In addition to the above usage, you can also Attune as a free action when you roll initiative.
Also, I suggest either Solar Shot and/or Solar Weapon have the Cycle trait added to make them more versatile. Since Solar Weapon has traits that can be changed through Re-forge, perhaps the cycle trait be added to the list of weapon traits the Solarian may add to their solar weapon. As it is now there are too few ways to automatically cycle the attunement of the Solar Manifestations outside of using the few class skills with the cycle trait. Of all the Arrangements, Balanced should be the one out of all three to switch between graviton and photon more frequently and with ease.