I am putting together the opening chapter for my book, and I need a rugged utility/ light space combatant to deliver my protagonist to her next assignment.
As the assignment is flying towards Pluto, it requires quite a bit of creative rocket tegic to get her out there. The Frigate/Utility craft is nothing fancy. And that is why they happen to have two on hand.
But first... the history. The Cervantes class is a low-cost swiss army knife of a vessel. It came about after several more ambitious efforts to develop specialized vessels produced extremely expensive boondoggles that were too expensive to mass produce.
While other classes of vessels have moved up to Muon-Cat drives, the Cervantes still uses LiD fuel, and a slightly upgraded commercial reactor. The vessel's dry mass is usually 400 metric tons, with a wet mass of 1000 metric tons. That 400 tons includes 100 tons of cargo or mission hardware, and provisions for a crew of 36 to operate for 90 days. However, in practice, many missions require more than 36 crew so the vessel can be a little cramped for a wartime loadout.
The Vessel has a rather pedestrian Exhaust Velocity of 281 km/s. But that is built on a proven and sturdy commercial platform. While Muon-Cat drives boast 580km/s, they end up either having to lock that away with a low-thrust engine, or burn twice as bright for half as long with disposable engines.
LiD fuel is not considered ideal for survivability in combat. Though, given the lack of armor, just about every serious combat platform is going to tear through the Cervantes like tissue paper anyway. In several combat encounters, its lack of armor actually saved the vessel because armor piercing shells simply pass straight through instead of exploding.
Where the Cervantes excels is not as a front line combat vessel, but as a support craft. It can carry enough weapons to take on a pirate of a commerce raider. It's fuel and logistics make it cheap to operate with a merchant fleet. It was built as a modular craft, and over the decades, people have devised some rather creative modules for it.
I have put together a spec sheet with my latest math Here
In the story, our heroine manages to snag a coveted job on a deep space exploration vessel. The only difficulty is that her "interview" is devising a way to get herself on board, using only the vessels on hand that the Spacey isn't going to miss too much. Oh yes, and where she is taking off from is as near as exactly the wrong planetary alignment as is possible. She works out as scheme to get past the vessel's low DeltaV by using one as a launch booster for another.
To pull this off, she has the booster unit stripped down bare. The "second stage" will be mounted to the first stage using the "buddy tow" feature built into the salvage module. Both ships will launch toward the Sun. After the booster has imparted as much DeltaV as it safely can, it will detach, and use a gravitational sling-shot to return to base. It will keep aboard just enough fuel to return safely. The curvature of space will allow it to fly a reciprocal course without having to expend any fuel to change direction.
The "second stage" will then use the DeltaV it picked up from the booster, and a similar gravitational slingshot to get itself going in the direction of the spacecraft it needs to catch.
Our heroine melts the minds of the management because she comes up with this idea more or less on the spot, and utilizes a launch stage concept that was last used 50 years before she was born. (They've been using nuclear rockets for a while.) The fact that she worked out a way that not only gets out to the wayward craft, but does it in a way that doesn't sacrifice the launch booster is what wins her the job.
The magic of the manuever all comes down to creative accounting. On paper, and in everyones calculation sheets, one just assumes that a Cervantes is going to leave with a dry mass of 400 metric tons and a wet mass of 1000 metric tons. For one way missions, you devote all of your DeltaV to moving like a bat of our hell. For round-trips that is enough DeltaV to carry 100 tons of cargo, drop it off at a location 2 au away within 30 days, Remain on station for 30 days, and fly home.
However, when you look more closely at the Cervantes, you see that it's Empty mass is really 280 tons. And there was an extra 1000 m/s of DeltaV that was built into the design that was intended to be used for station keeping or rendevous maneuvers.
Our flight plan uses quirks in how normal space missions budget weight. The "stage 2" will be the payload for the