SOLVED. YA sci fi book, bald android alien time travels with native American and "modern" American girl

[Courtney]

UPDATE: I FOUND IT! The name is Collidescope.

I read this in the early 2000s, but it was fairly dated by then, maybe published in the 1970's or '80's. The title was only one (or two) word(s), and it had something to do with space or stars. The cover had the heads of the three teenagers on a colorful, psychedelic background. The alien was needing these kids' help with some kind of mission which involved a bomb. He was the main character, but I think the POV was third person limited and took turns with each character, mostly focusing on the alien and the girl.
SPOILERS




The native American had an existential crisis when he saw the future of his people and struggled to come to terms with all the technology. The main character, the alien, ended up nearly dying, but because of his sacrifice, he either turned human officially or discovered he was nearly human all along. They wiped the memory of the native American, but the girl was very much against getting her memory wiped. This was a friend situation, not a love situation.

[Bargle]

Link Collidescope by Grace Chetwin.