That time Superboy discovered his parents alive.
In Superboy Vol 1., #158 (July 1969), Superboy receives a radio message from his father, Jor-El. Flying into space, Superboy discovers that the source of the message is a space capsule containing the bodies of his parents, Jor-El and Lara. Superboy tries to get close, but some bombs hidden in space-rocks nearby go off -- nearly knocking him into some kryptonite asteroids that would have killed him.
Dr. Krylo, a Kryptonian scientist, arrives in a spaceship. Krylo reveals that he believed Jor-El's warnings about the imminent destruction of Krypton, and developed a form of suspended animation. As Krypton died, Krylo knocked out Jor-El and Lara and placed them in a suspended animation capsule. Seconds later, Krylo's robots did the same procedure for him and placed him in another space capsule. Both capsules were rocketed into space only minutes before Krypton exploded.
Xonar (formerly Khai-Zor) was a Kryptonian criminal who stole Jor-El's rocketship plans and built a rocket for himself. Xonar survived the destruction of Krypton, located Krylo's capsule, and revived him. He forced Krylo to help him find the El capsule, and had hoped to trick Superboy into approaching it and dying.
Xonar shows up, and in the ensuing battle Xonar and Krylo kill one another using kryptonite.
Superboy discovers there is more to Jor-El's message. It seems that Jor-El had plunged deep into Krypton's interior to discover if the planet was really dying. He received a lethal dose of radiation, but did not know it. When he returned to the surface, his radioactive body gave Lara a fatal dose of radiation, too. Baby Kal-El, safe with a nurse, did not get get irradiated. Although Jor-El was able to remove the radiation, allowing he and Lara to interact with baby Kal again, they both were dying. Jor-El says he knows of Krylo's plan to secretly put them in suspended animation. He says he's going to allow the scientist to carry out his plan. But Jor-El asks that no one revive them. Neither he nor Lara wants to die a painful, lingering death from radiation poisoning.
A sad Superboy sends the capsule back into space.