Season 1
"Into The Abyss"- Ed and Molly landing on the Moon on Apollo 15. Ed came so close but had to back off when flying Apollo 10, while Molly never even had the chance when the Mercury Thirteen program was canceled. They both finally got a second chance and accomplished something that they'd been waiting years for.
- The episode was dedicated to the late Geraldine Cobb, the real-life inspiration for Molly's character who was denied the chance to become an astronaut due to sexism.
"Home Again"
- Margo finding out that her father worked on the Manhattan Project and almost took the secret to his grave out of shame.
"Hi Bob"
- Pretty much the entire episode can qualify as this mixed with Nightmare Fuel:
- On the Moon, the crew is struggling with an extended mission in the wake of the Apollo 23 explosion. Danielle's husband Clayton is dealing with the trauma of coming back from Vietnam while Gordo's mental health steadily declines over the course of the episode, culminating in him thinking that ants are in his suit and trying to remove his helmet while on EVA. Ed is left with the difficult choice to send Gordo and Danielle home, which would certainly end Gordo's career after an inevitable psychiatric evaluation. Realizing the risk of Gordo dying out of despair at losing his career after watching her husband going through the same thing, Danielle stages an accident to break her own arm so that the medivac can be for her instead of him.
- Back on Earth, Ellen and Larry are dealing with the FBI's investigation into her private lives. Weisner suggests to Ellen that her and Larry could get married to take the heat off themselves. Ellen decides to go along with the plan in order to keep her cover, leading a heartbroken Pam to break up with her. At the end of this episode, it's also implied that Ellen is under covert surveillance when she sees a car outside her home, which leaves as soon as it's spotted.
- Shane's escalating disciplinary issues at school and troubles at home lead to Karen slapping him out of frustration and grounding him from playing in his team's upcoming basketball game. Shane sneaks out anyway on his bicycle, where he suffers a serious accident.
"Rupture"
- The death of Ed and Karen's son, Shane.
- What's worse is that Ed isn't told so as not to distract him from the mission, which results in the Soviets unknowingly setting him off when they try to offer their genuine condolences.
"A City Upon a Hill"
- Ellen tries coming out to Deke after they both think they're as good as dead. Deke, who has previously been shown as a stern Father to His Men, lashes out. What's even worse is that he later makes amends and encourages her to remain in the closet, fearful that people will react just as he did.
- After Ellen successfully captures the fuel canister to refuel Apollo 24, she excitedly asks Deke if he saw what she did when she returns to the CSM. Unfortunately, she finds Deke slumped over in his seat, as he has died of his injuries. Then, while we don't hear Ellen relaying the news of his death to Houston, we do see Gordo receiving the news. While everyone around him is celebrating, the smile quickly fades from his face and he goes to tell Margo. We see Deke's wife Marge inside the observation gallery celebrating with everyone else and then she sees the serious looks on Margo and Weisner's faces and realizes that something is wrong. Weisner comes in to the gallery to inform Marge that Deke has died and she immediately breaks down.
Season 2
"Every Little Thing"- The Reveal that despite the Heartwarming moment in the prior season where Gordo presented Tracy with her astronaut pin, the two are no longer together, with her about to marry a famous businessman and him a shell of his former self.
"Don't Be Cruel"
- After revealing his love for the space program (and thereby firmly establishing himself as more than just a political animal), Thomas Paine is killed aboard Korean Air Lines Flight 007, a fate Ellen only escapes herself due to a health scare with her father causing her to miss that flight.
"And Here's to You"
- Ed helping Gordo into his suit prior to Columbia's launch becomes very sad in light of Gordo's death, as neither know it at the time but it's the last time Ed and Gordo see each other. Ed makes sure to tell Gordo how proud he is of him for working hard to get back into space.
- Molly getting confirmation that her heroic actions in the season opener will lead to her going blind, made worse when the diagnosis leads to a brief wedge in one of the few Happily Married couples in the show when her inability to come to terms with it leads to her wanting to try a dangerous experimental treatment, while Wayne desperately begs her not to.
"The Grey"
- Doubles as an awesome moment, but the deaths of Gordo and Tracy in the Season 2 finale. As heroic as the circumstances are, it is devastating to see them succumb to the vacuum of space and to see their frozen, bloodshot bodies when Rossi opens the airlock. It's especially heartbreaking for their sons, who lose both their mother and father at once.
- The funeral is equally devastating, especially when Ed begins to break down and cry openly.
- The Apollo-Soyuz docking is an amazing moment but it becomes a tear jerker when it becomes clear that almost no one was able to watch it due to the threat of imminent nuclear war causing everyone to take shelter.
Season 3
- Ed realizing that he's over the hill with nothing to show for it. It gets worse as the season goes on as he goes from getting removed from the Mars mission to seemingly a prominent position at Helios, only for that to then end in shambles when he's locked out of his own ship after trying to go against orders to save the failing Russian Mars-94 craft.
"Game Changer"
- The now fully-blind Molly getting fired by Margo for insisting on Ed as the leader of the NASA Mars mission rather than Danielle.
- While it's a well-deserved honor for Danielle, it's hard not to feel for Ed when Margo reassigns command of the Mars mission, given that he had already been told that the mission was his. He then makes it worse by implying Danielle only got the job due to her race and gender, in sharp contrast to how much of a Graceful Loser she was when she was initially told Ed was the choice (though fortunately for him, he is Easily Forgiven by her and their subsequent competition is friendly).
"All In"
- Margo finds out that her budding romance with Sergei is being used by the Soviet Union to recruit her as The Mole. She's willing to take the fall for helping the Soviets herself, but relents when they threaten to murder Sergei unless she complies (and even when she does, he's sent to a Soviet prison for several episodes).
"Seven Minutes of Terror"
- As Ed and Danny begin the descent to Mars, Ed has flashbacks to the time he and Gordo almost landed on the surface of the Moon. His second chance is null due to a rapid descent that causes Ed to activate the abort sequence and return to the Phoenix. While it's satisfying to see Dev and Helios get taken down a peg as NASA lands first on Mars, it's easy to forget that Ed was desperate to land on the Moon. Seeing him get robbed of what is likely to be his only other chance is utterly crushing.
- After he hits the abort, the camera keeps going and shows that they were just meters from the ground. However, with no visibility and no altitude readings, Ed probably would have been killed trying to be first.
- The reaction of Helios mission control when Popeye aborts and Sojourner-1 lands. While Dev is seething, the other Helios employees look genuinely despondent at the fact that they were so close to winning the race for Mars and ultimately will have to settle for second place.
"New Eden"
- The predicament of Will Tyler. After landing on Mars, he soon comes out as gay in a heartrending speech. The response? He's shunned by the crew, especially Rolan who was previously a close friend, and the For All Mankind equivalent of "Don't Ask, Don't Tell" is enacted by Ellen. Someone give the poor guy a hug.
"Bring It Down"
- Ellen finally learns that Pam left her due to her growing career.
"The Sands of Ares"
- Ellen and Pam's confrontation is painfully dour as Ellen actually seems prepared to abandon everything to be with Pam, who brushes her off and indirectly accuses her of being a Boomerang Bigot. It's a depressing contrast from their previous relationship, which was shown to be very loving.
- While everyone is trying to figure out how to rescue Ed and Danny, Dev is sitting alone in the viewing gallery of Mission Control. He tells Margo that everyone knows the story of how his dad came to America with nothing and became a success. Unfortunately, what he leaves out is that his dad worked for the company which produced the faulty component that destroyed Apollo 23, and he lost his job as a result.
- Trapped underground with Ed, Danny finally confesses that he's to blame for Shane's death in season 1, and that he's spent his whole adult life trying to make up for it, only to ruin everything for his family and his shipmates in the process.
- Alexei's death, and Kelly's (and Danny's) reactions.
- What's worse is that he was shown to be incredibly excited to meet Kelly's father. Imagine how happy he would've been to learn he was going to be a father?
"Stranger in a Strange Land"
- Lt. Col. Lee's entire mission up until meeting Poole and Kuznetsov. He's sent on a mission to Mars in a tiny craft that barely has enough room for him and his co-pilot. Given that it's North Korea, it's entirely possible that neither of them was a willing participant. They crash land and the co-pilot dies. Their communication equipment is damaged to the point that he has no way of communicating back to Earth that he survived. As far as anyone in North Korea knows, including his family, he didn't survive the trip. He somehow manages to survive on the meager supplies on the ship but the isolation and the knowledge that he was likely sent on a one-way trip drives him close to a Despair Event Horizon. He is ready to shoot himself with the gun on board the ship (which was likely for that purpose to begin with) before he sees the NASA rover driving over the actual horizon and he realizes that he is not alone. At the end of the episode, we see that he gets to communicate with his family back on Earth and he smiles, knowing that they know he's still alive. It's likely the first time he's smiled for real in months, since the laugh when he drew the smiley face in the dirt was clearly part of a mild Sanity Slippage.
- Jimmy gets cold feet at the last second and tries to stop the conspiracy theorists from bombing the JSC. Unfortunately, he fails and Karen is one of the casualties. Jimmy is clearly distraught over what he's done and does his best to comfort Karen in her last moments after he finds her in the rubble. Also, after all of the turmoil on Mars, Karen dies without knowing that both Ed and Kelly are alive and well and that Kelly gave birth to Karen's grandson.
- Ed learning of Karen's death is more heartbreaking when you remember he lost Shane whilst stationed on the moon, and now he's lost Karen whilst stationed on Mars. Ed felt immense guilt for years after Shane died because he wasn't even on Earth when it happened and blamed himself for not being there. Now it's happened again, and he will probably have to experience that feeling once more.
- The aftermath of the JSC bombing is heartrendingly realistic—the appearance of the building, the wall of photos and mementos in tribute to victims combined with flyers begging for information on those still missing.
- Molly's Heroic Sacrifice rescuing people from the collapsing JSC building, though it's bittersweet as it also allows her to go out on her own terms and the new Space Center is named in her honor.
- While it might be difficult to feel bad for him after his gradual Sanity Slippage over the course of the season leads to the disaster on the drilling ridge, Danny gets kicked out of the base and exiled to the North Korean capsule as punishment for his negligence leading to the drilling ridge disaster, where he'll be regularly brought supplies until the next ship arrives. Considering how close Lt. Col. Lee was to ending his life from the isolation as mentioned above, the fact that this fate was inflicted on someone on purpose can be heartwrenching.
Season 4:
"Glasnost"- Kuznetsov's death. During the Kronos-1 mission to mine an asteroid, Kuznetsov gets trapped in the scaffolding, which damages his suit and causes it to rapidly leak oxygen. At Kuznetsov's urging, Ed disconnects the asteroid and sends it floating away before it can do any damage to the ship, tearfully saying goodbye as he sacrifices his friend to save the crew.
"The Bear Hug"
- The reveal that Bill Strausser was paralysed by the JSC bombing and is now confined to a wheelchair. When Aleida visits him for the first time in what is implied to be years, their meeting initially teeters somewhere between heartwarming and resentful, as Aleida never found the time to visit him because she was busy struggling with her own PTSD.
"Goldilocks"
- The deterioration of the friendship between Ed and Danielle, which goes back to the first season and has survived intense circumstances like Gordo's breakdown, Gordo's death, the competition for command of the Mars mission within NASA (including some drunken insensitivity from Ed when he lost out), the competition to be the first to set foot on Mars, and the friction over whether to allow Danny into space (plus the fallout from that, shown this episode in flashbacks). It manages to make the previously heartwarming phrase "hi Bob" even more tragic, following the death of the third of their trio Gordo.
"Brazil"
- During Margo's half of the intercut between her and Sergei in their respective hotel rooms, the information she's pulling up on her computer is about the Brazilian space program, despite the asteroid capture mission being less than two days away and her insistence to Sergei that she needed to see the mission through before considering the idea of fleeing.
Season 5:
Home- Ed's death drove many viewers to tears and the scene received widespread praise for how well it was crafted. After daringly breaking Lee out of custody and bringing him to the ISN base in the previous episode, Ed passes out in the hopper and it soon becomes clear that he has only weeks to months to live due to his cancer having spread throughout his body. The episode is interspersed with flashbacks of a younger Ed fighting to survive in Korea after being shot down. At the end, Ed has a vision of walking through a hallway to the Gemini 7 capsule, and is greeted by Gordo. The two walk past NASA staff members where Ed, to his surprise, sees Karen and Shane. The scene transitions to the credits while the Gemini capsule slowly orbits the Earth at the bottom of the screen. All in all, it was a touching tribute to the show's original "space cowboy" and leading character since the beginning.Gordo: Hey, skipper.
- Poetically, the episode aired on the same day that the Artemis II spacecraft returned to Earth after flying around the Moon, bringing humans beyond low earth orbit for the first time in 54 years.
- It's revealed in this episode that Shane was the name of another pilot who helped Ed to escape from behind enemy lines before being shot by the North Koreans, after whom Ed named his son.
- Margo talks Aleida into going up to Mars to personally oversee the retrofit of Sojourner-1 for a trip to Titan. While she agrees, it's heavily implied in the ending that Margo and Aleida, who have shared a close bond for close to 40 years, will never see each other again.
This Land Is Our Land
- Kelly choosing to sacrifice herself so that her two crewmates can make it back to Sojourner with their incredible discovery. The showrunners also confirmed
that the decision was made out of guilt for Kelly's sabotage of the return plans in order to force the ship to land on Titan.- Kelly's farewell message to Alex also qualifies.