An army marches on its stomach, and a nothing can raise the morale of a tramp freighter spacecraft quite like the prospect of a tasty hot meal in the mess deck. The flip side is that disgusting food can really drag down morale. And for a ship full of highly skilled crew heading for a multi-year mission into the wilderness, gourmet food can offset many hardships endured.
Unfortunately if the ship is stuck with a closed ecological life support system, the crew will face a monotonous menu. At best it will be fresh vegetables with vat grown meat. At worst it will be algae and yeast. In between will be fresh insects. The cook better take along a hydroponic herb garden, to disguise the meals.
In some ways the mess deck is the "heart" of the spacecraft, in the sense that it is the focus of interpersonal interaction. This is where the crew hangs out and relaxes, where gossip is exchanged, where people go get a cup of coffee and talk things over. It is probably the largest room in the habitat module. Sometimes there are separate mess decks for officers and enlisted men.
Given the cramped nature of a spacecraft hab module, it might have to do double duty. Often it will be used for an auditorium if the captain has to address the crew.
And sadly as emergency triage/operating room, especially on a military spacecraft. As mentioned in the Sickbay section, there is a tradition on military ships for off-duty personnel removing their headgear while on the mess deck. It is a sign of respect for the crew members who have in the past, or may in the future, suffer and die there.
And besides food, the mess deck must have coffee, and plenty of it. Or some other stimulant drink. And the coffee urns should have some coffee in them all day long. As a general rule the coffee served tastes awful, since the volume required and lack of motivation on the part of the mess crew lead them to skimp on keeping the coffee brewers properly cleaned. A first officer with an eye towards improving morale might want to encourage the gallery personnel in charge of coffee to GET YOUR FRAGGING BUNS IN GEAR AND KEEP THOSE BLASTED COFFEE URNS SPOTLESS!
The kitchen or galley will have to be specially designed, because it will have to be compact and be able to safely cook in free-fall. Hot grease globs or even entire pots of boiling water flying in zero g can cause severe burns to the kitchen crew.
As you probably know already, the chief mess officer traditionally has the nickname "Cookie".
What's in the Life Support room? Controls for the atmosphere, temperature, drinking and washing water, recycling, environmental heat radiators, hydroponics (if any) and algae tanks (if any). There will also be controls to trigger countermeasures if the air pressure suddenly drops. And maybe a canary in a cage.
Life support will also be tasked with controlling obnoxious odors in the ship's atmosphere. They will have filters, perfumes, and negative ion emitters. The life support techs will also use equipment to track down the source of particularly bad smells, say Ordinary Spaceman Lister's unwashed sock bucket.
What's in the cargo hold? A huge cargo bay door. Perhaps an extendable cargo crane or ramp to facilitate loading. Decks painted with guide-lines to regularize the placement of cargo canisters. Lighting fixtures inset and armored to protect them from clumsy cargo handling. Lots of tie-down attachment points to immobilize the cargo (if the cargo shifts during thrust the rocket will tumble). Hoists in the ceiling. There will be an office for the cargo master, said office might be the "quarterdeck" when the ship is planeted. If so, the office might have repeaters for the critical system monitors, for use by the watch officer.
The cargo master may or may not also be the same person as the "load-master". The latter's job is to ensure the mass of the cargo is evenly distributed around the axis of the spacecraft. Otherwise the unbalanced cargo will shift the spacecraft's center of gravity, the ship will tumble, and everybody will die.
Also keep in mind that some propulsion systems are radioactive. You might have to arrange things so that the unloaded cargo does not arrive too close to the engines. Possible solutions include a ramp, a small cable tramway like a ski lift, or an arm like on the SF spacecraft SPIP.
Now, I have ranted about how a spacecraft should be arranged more like a skyscraper rather than a passenger aircraft. The exception is if the main function of the spacecraft is carrying cargo. A skyscraper arrangement makes loading the cargo hold a nightmare. For a cargo spacecraft, it makes more sense to design it as a belly lander.
Remember that the ship has to be balanced around the axis of thrust or again the ship will tumble when thrust is applied. Cargo will have to be stowed in a balanced manner, and logged in a mass distribution schedule (sometimes called a "Center-of-mass and moment-of-inertia" chart). The same care has to be taken when removing part of the cargo as well.
As previously mentioned, present-day cargo ships are rated in "Net register tonnage", where each "ton" actually indicates 100 cubic feet of volume (2.83 cubic meters). The average cargo they carry has a density of 350 kg/m3. If the cargo has a wildly different density, some math will be needed, but for most cargo the net tonnage gives a good idea of the ship's cargo capacity. In practice, while filling the cargo hold it will either "mass-out" or "bulk-out", depending on which it runs out of first: lifting capacity or cargo space. In MANNA by Lee Correy (AKA G. Harry Stine) a surface-to-orbit shuttle bulked-out because it was carrying a cargo of fluffy non-dense cotton underwear. While the shuttle could have theoretically lifted more cargo mass, there wasn't any more room in the cargo hold.
In international shipping, a standard cargo container is 33 cubic meters and can have a maximum mass of 24 metric tons (2.2 tons of container and up to 21.8 tons of cargo). An extra large cargo container is 67.5 cubic meters with a max mass of 30.5 metric tons (3.8 ton container with up to 26.7 tons cargo). Thanks to Karl Hauber for pointing out an error in the the old figures posted here.
In cargo container terminology, the tare weight is the mass of the empty container. The gross weight is the mass of the loaded container. Subtract the tare weight from the gross weight and you will have the net weight: the mass of the goods being carried in the container.
In many SF novels, in addition to the cargo bay there will also be a safe to lock up small but valuable cargo items. This is generally in the Captain's office. And for customs officials, there may be official "seals" put on the openings of individual cargo crates or even on the hatches to the entire cargo bay. Such seals cannot be removed without destroying them, ensuring that nobody has tampered with the cargo or concealed any contraband.
There also might be an embargo locker. If the ship is carrying anything that is considered contraband at a given spaceport, such items can be sealed into the embargo locker by the spaceport custom officials for the duration of the stay.
And never forget that cargo loading is the main way that vermin sneak into a ship.
There may also be a "ship's locker". This may be an actual locker or as large as a small cargo hold. It contains all the small stores and supplies the ship needs for day-to-day operations. Medical supplies, survival gear, small-arms locker, and the "slop chest". In between voyages, the purser replenishes the ship's locker at the spaceport chandlery. And as the ship gets older, stuff will accumulate.
These were common in the role playing game Traveller. Every adventurer's starship had a ship's locker stuffed full of useful equipment. Many Traveller magazines would have a monthly column called "ship's locker" with suggestions of cool stuff to stock.
Occasionally it will have three sections: General, Utility, and Repair.
- General: common items like medical supplies, space suits, arms locker and ammo, and bulk items
- Utility: cleaning supplies, office supplies, curios and sundries
- Repair: mission-critical spare parts, and routine maintenance parts (lubricants, filters, minor parts)
Sometimes Traveller starships will have a locker full of random stuff that has no obvious use (at the moment) but is too valuable to throw away. This is sometimes called a "hope chest". There could be all sorts of old amusing items lurking in the hope chest, forgotten but waiting. Especially if the chest is part of a second-hand starship purchased "as is".
Be careful when you open the locker door, the blasted thing is tantamount to Fibber McGee's Closet.
The slop chest contains convenience items and consumables for the crew. The ship's purser sells slop chest items to the crew at cost or charged to the crewmember's unpaid salary. Such items include spare uniforms, junk food, toiletries, games, educational textbooks, and novels. In between voyages, the purser replenishes the slop chest at the spaceport chandlery.
Here is an interesting list of slop chest items for US wet-navy ships in 1942, with prices.
A brig, holding cell, or military prison onboard a spacecraft is not something you will find until the state of the art spacecraft design has power to burn. But your futuristic warship will need it since prison breakout scenes are such a time honored trope. This was decades old before Han and Luke Skywalker tried to break Princess Leia out of the Death Star brig.
Brigs in Star Trek have force-field doors because those have tons of sci-fi goodness. But it is really stupid to have a prison-cell door that vanishes if the power cuts out.