Cargo bays and vacuum

[Annatar Giftbringer]

Greetings,
Not every ship is blessed with cargo airlocks, and to the best of my knowledge there are no atmosphere-retaining magical force-fields in Traveller.

There are occasions when a ship needs to open its cargo bay to vacuum, or hostile atmospheres.

Do ships generally possess equipment to re-pressurize the cargo bay after venting it, or is it open once and that's it?

Pumps and holding tanks could perhaps store enough of the air inside to manage at least a couple de- and re-pressurizations?

 

[Jak Nazryth]

In the first years I played, early 80's, we would simply say we would decompress the whole ship before combat (of course they we usually had a scout courier) but that was long before the game mechanics of self-healing hulls, serious thought of "what and were" life support was. We were also in 7th and 8th grade. 13 and 14 year olds rarely think along those lines.
But I'm not sure if there is anything in the game mechanics that state specifically how much of the ship can be decompressed.

 

[snrdg121408]

Hello Jak Nazryth,

In the first years I played, early 80's, we would simply say we would decompress the whole ship before combat (of course they we usually had a scout courier) but that was long before the game mechanics of self-healing hulls, serious thought of "what and were" life support was. We were also in 7th and 8th grade. 13 and 14 year olds rarely think along those lines.
But I'm not sure if there is anything in the game mechanics that state specifically how much of the ship can be decompressed.

My take is that the entire internal space can be decompressed, however there are spaces that placing them in such a state is going to be harmful. A ship with hydroponics probably would not want that area decompressed, especially if the space is their primary source of food and breathable medium.

 

[Annatar Giftbringer]

Decompression is easy - just open all the hatches and wait :lol:

The interesting part - at least in this case - is recompression (and I'm not quite sure that's the proper word for it!)

 

[Jak Nazryth]

Re-compression is a fine word.

As far as the game mechanics goes...
The current rules don't say anything about how much of the ship you can or cannot decompress. (I might be wrong... haven't not seen anything like it as of now) But the existence of a cargo lock in the rules suggest that you normally don't have the capacity to take all the air inside a cargo bay (or the entire ship for that matter) and compress it (or even liquefy it) in holding bottles, "somewhere" on the ship. That level of detail simply does not exist. In other earlier versions of Traveller (T20 or GURPS) I think is said something like... (the total tonnage of an airlock is 3 tons, but some of that is set aside for the air cycling equipment) I'm paraphrasing horribly from something I read more than a decade ago... and i'm not even sure which version of the rules it was. But the idea is that part of airlock includes the pumps and holding bottles within the volume itself. So it could be in the ceiling or floor space of the tonnage required for each individual airlock.
If you want to turn your cargo bay into one giant airlock, then pay for the cost as if it's an airlock, extrapolating from the cost per ton within the current rules.
It's up to you to say "where the air goes" and what if any tonnage is set aside for equipment and holding tanks.

 

[AnotherDilbert]

I would assume all starships have the capability to repressurise after an emergency, but probably not many times.

So, I would allow a freighter to use the cargo hold as a air lock, but only occasionally, not many times in a row.

 

[AnotherDilbert]

Any ship with scoops have the capacity to compress gaseous hydrogen, and even water, into liquid hydrogen. We even have huge tanks dedicated to store liquid gas.

I assume we do not have a single large tank, but several smaller, that we can pump liquid between to be able to trim balance.

Air compresses about 700 times when turned into liquid air, so 700 dT filled with air becomes 1 dT liquid air. A Free Trader would need about 0.2 dT to store the air.

We may have to jury-rig something, but it is not unreasonable to store the ship's air. Presumably any vessel intended for space combat will have this capability.

As Jak points out a normal cargo hold is not built as an air lock, so any attempt to use it as such would include jury-rigging something and take time and effort.

 

[Reynard]

One thing to realize is Traveller ships have internal bulkheads and portals (those strategically placed iris valves) that are proof against decompression just like naval vessels and water. Sections can be evacuated and restored as needed. Of course it is assumed there is a system as part of life support for storing as well as replacing atmosphere. It's not as if a ship regularly blows all its air into space. It's why they're called emergencies. Standard scifi mechanic.

 

[NOLATrav]

I'd say a tramp trader would have a cargo bay's worth of air stored and so could depressurize and re-pressurize once before needing to replenish the stored air. Airlocks say, 6 cycles?

High Guard 2e states about a minute to cycle a passenger airlock, which is essentially a ton of open space. So 1 minute per dton of airlock/cargo bay/vehicle bay/bulkhead section to safely de/re-pressurize seems reasonable.

Replenishing the stored air... maybe the life support system can replenish air at the rate of one fuel processor - 20 tons of open space per day. So 4 days to replenish a free trader's cargo bay air storage...

 

[phavoc]

In general I'd say yes. Oxygen is easy to get in a star system. As it was pointed out liquid atmosphere allows you to compress a great deal of atmosphere in a very small space.

Generally as long as the players aren't abusing it, opening the cargo bay AFTER depressuriaing it to store the atmosphere is essentially unlimited.

 

[AndrewW]

High Guard 2e states about a minute to cycle a passenger airlock, which is essentially a ton of open space. So 1 minute per dton of airlock/cargo bay/vehicle bay/bulkhead section to safely de/re-pressurize seems reasonable.

Though if you add an extra airlock that's a minimum of 2 tons. Larger airlocks can have more equipment for doing so and would take the same amount of time as a smaller airlock to cycle.

 

[Jak Nazryth]

I would treat any space on the ship like an airlock for the cost.
You can decompress a 40 ton cargo bay if you want, but you should spend the money as if its a 40 ton airlock/cargo lock. That's the benefit of having a cargo lock separate. It's simply less cash to install and allows you to transfer cargo in and out of a vacuum. Spend more credits, and you can decompress the entire cargo bay. No cargo lock needed. Although sometimes specialized cargo may be damaged in the cold vacuum of space.
But simply put, extrapolating the rules as written, you can do what you want with decompression.

 

[Condottiere]

That's more an issue if you want aerate and de-aerate at the same speed.

If you have time, just install a pump.

If this is a standard procedure, I'd probably limit access to the hold from the rest of the ship to one door, and possibly if it isn't an internal airlock, have a second airtight door installed about three metres behind that.

 

[Jak Nazryth]

Also, if you're worried about a cargo lock taking away from cargo space, you needn't worry.
You can still use it as cargo space, but you'll simply have to move and shift cargo around outside the ship to retrieve cargo deeper in the hold. 90% of the time this isn't an issue unless the GM makes you map out your cargo hold on each run... "Show me where you 20 tons of machine parts are stored" mixed with the other random cargo....

 

[snrdg121408]

Morning PST,

MgT High Guard 2e 9/01/16 p. 44:

"Additional Airlock
Additional airlocks of any size may be added to a ship. It typically takes a minute for an airlock to fully cycle.

Airlocks consume a minimum of 2 tons and cost MCr0.1 per ton. Larger airlocks can be used for cargo bays."

A cargo bay that can be opened to vacuum is an airlock that has a Cost of MCr0.1 per displacement ton of space dedicated for cargo.

 

[Reynard]

Unless your cargo is totally random speculation, you will most likely have it arraigned for transport to various destinations and shouldn't need to rearrange it on the fly. Most rearranging would be occurring at a port and often not out in the harsh effects of the weather. Most instances of manipulating cargo in vacuum would involve unusual ship to ship transfers such as salvage, legal or otherwise.

It seem standard procedure to minimally vacuum seal cargo transported by space and starships in Traveller games and most cargos are minimally protected against harsh conditions but not for long exposure. That would be prohibitively expensive. Most assume ship holds are well secured from outside environmental effects.

 

[bluekieran]

Airlocks consume a minimum of 2 tons and cost MCr0.1 per ton. Larger airlocks can be used for cargo bays."

A cargo bay that can be opened to vacuum is an airlock that has a Cost of MCr0.1 per displacement ton of space dedicated for cargo.

I read that as suggesting that you might want to take bigger things through a cargo bay airlock than would fit in a regular one.

 

[snrdg121408]

Hello bluekieran,

Airlocks consume a minimum of 2 tons and cost MCr0.1 per ton. Larger airlocks can be used for cargo bays."

A cargo bay that can be opened to vacuum is an airlock that has a Cost of MCr0.1 per displacement ton of space dedicated for cargo.

I read that as suggesting that you might want to take bigger things through a cargo bay airlock than would fit in a regular one.

MgT HG 2e PDF 9/01/16 p. 22

"Step 12: ALLOCATE CARGO SPACE

Any space left on the ship that has not been allocated to other components is considered to be free for cargo. There is no cost associated with areas designated for cargo, but any cargo or other materials taken on board the ship can obviously not exceed the tonnage set aside for cargo.

Side note
Airlocks
Airlocks are sealed systems consisting of two heavy-duty doors or iris valves, with atmospheric pumping equipment, allowing transit to and from a spacecraft in a vacuum or hostile atmosphere. A ship may have one airlock for every 100 tons or part of. A standard airlock is capable of cycling two humans per minute between the ship’s interior and exterior, or vice versa. Additional airlocks may be added using the system in the spacecraft options chapter.

Cargo Hatches
Any area designated for cargo can be given a cargo hatch of any size but this is not an airlock. Generally speaking, cargo areas are capable of being sealed and so are effectively one large airlock unto themselves, but this can cause problems when needing to unload cargo in a hostile environment. See the description of cargo airlocks on page 44 for a solution."

From the information provided above a cargo bay does not appear to have an airlock as part of its structure, though you could use the personnel airlock to shift cargo.

Looking at the Launch deck plans, MgT HG 2e PDF p. 97, the way cargo is loaded and unloaded appears to be done by opening the hull's personnel airlock down the passageway to a manual airtight hatch. The airlock hatch, passageway, and manual hatch are 1.5 meters wide which limits the size of the cargo to items smaller than 1.5 meters. One way to load and unload the launch's cargo bay in vacuum be accomplished somewhat quickly would be to lock the airlock's inner and outer hatches open as well as the manual hatch. The downside is that the bridge and engineering spaces are isolated until loading/unloading is complete. The other method is to load the cargo into the airlock close one hatch, cycle the airlock, open the other hatch, move the cargo out of the airlock, close the airlock hatch so that more cargo can be loaded/unloaded.

The Pebble's deck plans, MgT HG 2e PDF p. 97, has what appears to be a cargo hatch which by the information provided above is probably not an airlock since there is no cost shown in the Cargo block of the ship record sheet on MgT HG 2e PDF p. 96. In this case the cargo bay could be de-pressurized allowing cargo to be quickly loaded/unloaded in vacuum or other hostile environment. This method still appears to isolate the engineering space. Trying to load/unload cargo through the personnel airlock limits the size of the cargo plus having to do something with the passenger seats.

To load/unload a pressurized cargo bay and not go through the hull's personnel airlock in vacuum or other hostile environment regardless of the materials size some sort of airlock appears to be needed which per the rules must be at least 2 d-tons with a cost of MCr0.1 per d-ton.

 

[Condottiere]

The cargo hatch and a blast door could work like an airlock.

 

[snrdg121408]

Hello Condottiere,

The cargo hatch and a blast door could work like an airlock.

MgT HG 2e PDF 9/01/16 p. 22
"Step 12: ALLOCATE CARGO SPACE

Side note
Cargo Hatches
Any area designated for cargo can be given a cargo hatch of any size but this is not an airlock. Generally speaking, cargo areas are capable of being sealed and so are effectively one large airlock unto themselves, but this can cause problems when needing to unload cargo in a hostile environment. See the description of cargo airlocks on page 44 for a solution."

The information provided clearly states that a cargo bay with a cargo hatch is not an airlock.

Please provide the source of the blast door component so that I can add the item to my component list. An airlock is designed to de-pressurize and pressurize the enclosed space with a minimum loss of atmosphere. Blast doors to my knowledge has a primary purpose minimizing some sort of explosive detonation from gutting the area outside of whatever was inside the blast doors. I agree that blast doors can probably double as keeping vacuum or other hostile atmospheres from penetrating to the side that has the atmosphere needed to keep Travellers' alive.