“Collision Course” is episode three of season one of Space: 1999.
Eagles are placing nuclear charges on an asteroid that’s on a collision course with the Moon. Alan in Eagle 1 is having problems and they need his charge to complete the mission. The commander delays the firing sequence so that Alan can place his charge, which proves difficult, and then a bit longer so that Eagle 1 has a chance to get away.
The charges are detonated and the asteroid is destroyed. Alpha is mostly protected by its radiation screens but Eagle 1 is out of contact due to the radiation cloud. Koenig tests and finds that Alpha’s can still communicate with its satellites. He wants an Eagle equipped the same way, which will head out and try to find Alan.
Koenig and Paul take an Eagle out. They’re hailing Alan, who is unconscious. A woman’s voice inside Alan’s head asks if he’s okay and says he’s quite safe now. Eagle 4 hails again and the woman tells Alan to speak. He does. The woman then tells Koenig where Eagle 1 is. Eagle 4 heads in to dock with Eagle 1, and the woman talks Alan through it. She says his own people will take care of him now. She’s a friend. Koenig goes to find Alan and discovers that they are now on a collision course with a planet.
Both Eagles return to Alpha. The collision is still a few days off. In Main Mission, Paul suggests detonating an explosion on the far side to alter their course, similar to what happened in “Breakaway”; David thinks they will just blow themselves up. Victor thinks the principle of shifting the course is right, but they could do it by detonating a shockwave (in a vacuum) between the Moon and the planet and change their trajectory (must be really powerful nukes).
According to Sandra, the planet has an atmosphere, though not a great one, and the temperature is just about liveable. Life could exist there. The radiation cloud still prevents them from communicating; another Eagle would need to be sent out on a reconnaissance mission. Victor says they could evacuate to the planet. When asked if it would withstand a collision with the Moon, he isn’t sure (if it’s a planet humans could live on, no).
Alan is in medical and sees the woman. She morphs into Dr Russell. The commander arrives as Alan is being sedated; the doctor thinks Alan’s been affected by the radiation, no matter what the instruments said, and that Koenig could be too. The commander still heads out on a recon mission.
The woman Alan saw is called Arra. She wants the Moon to collide with the planet and manages to convince Koenig of this. Needless to say, his argument does not go down well with anyone else, suggesting that a mysterious woman is proposing the collision. Especially as the doctor already thinks he’s ill.