Essentially Gundam meets Battlestar Galactica, with a fair amount of Robotech and Star Trek thrown in. (And visuals from VOTOMS)
The Constellation is a Mobile WarSquad, an old, self-sufficient battle tug with six "pods" that can be swapped out to serve different functions. Originally the Constellation was a Mecha Tender, able to carry the mighty five-meter-tall WarMechs of the Terran Empire into battle at long range, as well as repair and (if needed) even build them. Other WarSquads had gun pods (to create battleships) or sensor pods or troop pods (for planetary landings), and so on.
But the Terran Empire has not been at war for decades, and few WarSquads are built anymore. The Constellation was assigned to the Perdix Rim, an edge of the Empire used to subjugate the Xoan, dark-skinned aliens who had lost a war to the Empire 40 years ago, and now pay tribute. The Xoan were a Preserver race, which is all the human-like species (including Terrans) that were spread about the galaxy by the Preservers between 40,000 and 80,000 years ago. The Terran Empire believed Terrans to be the "True" perserver stock race, and thus saw all other humanoids are inferior offshoots.
Unknown to the Empire, the Xoan have been working with the Qateri, a race of insectoids who had a treaty with the Terrans, but saw them as a threat. The Xoan, Qateri, and several other species formed a Great Armada to destroy the Empire.
The campaign began as a Xoan/Qateri fleet enters the Perdix Rim and smashes the fleet. The only surviving ship is the Constellation, out on a prisoner pickup run when the fleet comes through. A fight ensues between the Xoan picket ships and the Constellation, which the Constellation is losing, until the Xoan ships begin to blow up, as do the inhabited planets of the Perdix Rim.
It turns out the Qateri are betraying their humanoid allies, as they see all Preserver races as too dangerous to be allowed to live. This stalls their offensive, and causes a few Xoan to join forces with the Constitution. Two Xoan picket ships are bolted into the Constellations empty pod ports, and the ship grabs what survivors it can and flees.
Now the Constellation is on its own in the ass-end of space. Terra itself falls to the Qateri, but another outpost, the Wurm Nebula, survives and is withstanding the weakened Qateri siege. Unfortunately it is on the other end of the shattered and conquered Terran Empire, two years away by the best speed the Constellation can manage. Further, it turns out the Wurm Nebula includes an old WarSquad supply depot. They have dozens of WarPods but only one WarSquad of their own, the very new (though no longer shiny) Manticore.
The Constellation sets course for the Nebula, communicating with the surviving Imperial Heir with Superspace Communicators... which take a week for a message to go one way. The WarSquad has to move through both conquered lands and areas once hostile to the Terrans, keep itself in repair and in supply, while fighting off a Qateri Hive Fleet assigned to hunt it down and destroy it.
Each player got to declare one thing before we played the first game. These things are known to players, if not characters, and we all agreed in advance that those things are absolutely true, no matter what. (For example, it was declared the Qateri have no goal other than to destroy all Preserver races to the best of their ability, for the survival of their own species. No matter what the GM does, we know what the Qateri ultimate goal is.)
All players are WarMech pilots, though many have other roles as well since there are so few trained soldiers and technicians.
Captain Lord Winton: Young noble who earned his post due to noble patronage, rather than skill or time-in-grade. Captain of the ship, a poor military commander who is trying his best to step up to trying times. Due to his noble title, may be second-in-line to the throne of the Terran Empire. Not that it matters much right now.
Brevet Lt. Erring Adear: "Mother Bear" A WarMech engineer who was a non-com before half the Constellation's crew was killed. A bad pilot and mediocre soldier, but a great co-ordinator and someone the captain knows is loyal to him alone. Adear is valued by her troops for her ability to keep them equipped, fed and repaired, but they all know she's not the best soldier or tactician.
Jackbite: "Jackbite" A murderer, rapist, and thief who was being taken by the Constellation for execution when the Shit went down. Also a class A Mech pilot, tactician, and killer. Best fighter the Constellation now has, though his Mech always has a bomb on it with a 72 hour timer, to ensure he doesn't flee the fight.
A player OTHER than Jackbite's made their one true declaration that the Constellation could never be captured or destroyed as long as Jackbite is allowed to fight for it. We may lose fights, but not in such a way as to lose the mothership. Jackbite is a monster, but we all know we need him. And he KNOWS we know that.
Nalli Veremos: "Buzzbox" A civilian rescued from by the Constellation who placed top of the military vocational aptitude test all survivors were forced to take. Becoming a good pilot, she is also a drug addict and ex-prostitute who uses her charms to get what she wants for recreation and food.
Hikel Formi: "Hammer" A grunt who flunked out of the high standards of Mech school, but is now among the best soldiers left. Fearless in a fight, and willing to face down Jackbite even if it kills him, Hammer is the emotional plaything of any teammate who wants to mess with him *other* than Jackbite. It's a True Thing that he won't live to reach the Wurm Nebula.
Aisling Daken: "Shiv" Another ex-prisoner, Aisling was accused of desertion because she left her post to investigate a sensor reading suggesting the Xoan were building an illegally large fleet. The captain has officially pardoned her. Shiv is still bitter about her time in prison (and her treatment at the hands of Jackbite in prison), and is looking for somewhere else to hide for the war.
Pactblood Xurick An'Fyr An'Thol: "Pagan" A Xoan warrior who hates Terrans, but happens to hate Qateri more. Trained on stolen Terran WarMechs, and second only to Jackbite in skill, his Mech has a 96-hour bomb timer. Trying to turn Adear into a "True Warrior," and frustrated by her lack of progress.
Wonnik Cycacyk: "Marathon": One of the few original Constellation Mech pilots alive. Not great, but a solid pilot and soldier with no known loyalty issues. Able to stay alert for more than a day when needed, and survive on very little food.
Rafe Sigson: "Rascal": A trained counterintelligence and espionage agent used to piloting the smaller and more subtle Scout class Mechs (which the ship no longer has any of), he is also a black-market master and frequent aid to both Adear (for legit needs) and Buzzbox (for illicit favors).