Spacecraft Environmental Limits

[SJWaldock]

I was looking through my collection trying to find information on spacecraft environmental limits. I found data from CT's "Secret of the Ancients" adventure where it stated that civilian ships had limits of 1000°K and 1000 atmospheres, military ships 1500°K and 2000 atmospheres, while system defence boats limits are 2500°K and 3000 atmospheres. Special Supplement 2 from JTAS 17 mentions that "A starship or large habitat can be designed to overcome the effects of extreme heat or cold". These were all I could find. Have I missed any references? I don't have Mongoose Traveller or Traveller 5, are there any mentions there?

Incidentally, I found my disbelief suspenders rather stretched by having a merchant ship be able to withstand pressures almost as much as the bottom of the Challenger Deep. I seriously doubt that airlocks, cargo hatches and view-ports could withstand such pressures.

 

[kilemall]

I think most of us aren't on board with those numbers too.


I would think 100 atmospheres would be more realistic, and armor would increase that.


One of the most heavily armored class of vessels IMTU are craft destined for Mercury or Venus, to handle either radiation hits or atmo pressure respectively.


There are some other active threads looking into the underwater pressure issue so you might look at those. Also, keep in mind it's routine for ships to skim fuel from gas giants, so the ships have to be able to deal with upper atmospheric pressure there.

 

[Carlobrand]

... I seriously doubt that airlocks, cargo hatches and view-ports could withstand such pressures.

You have viewports? I figured that was a bad idea in something that was likely to get shot at by missiles and high-power lasers.

I agree that 1000 atmospheres was quite a reach for something that was designed to go from inhabited worlds to vacuum and back. Hull on those things is really strong - maybe too strong - but I'd have expected the airlocks to give way long before that. I can't see any reason a builder would reinforce the hatches to deal with pressure they really weren't ever intended to experience.

Venus hits around 90 atmospheres, and that may be a good example of the kind of extreme atmosphere a civilian ship would fly into to reach a market - assuming some concern put people in such an atmosphere to recover something valuable enough to warrant the expense of putting people there. So, yeah, 100 atmospheres sounds good for civilian craft, since there's a long-shot possibility the merchant might actually go to such a place, though even there it'd make more sense to put in a high port and then have boats designed to deal with the atmosphere for the orbit-to-ground phase. Maybe a scout-courier could have some sort of uber-reinforced airlock, scouts being expected to do weird things.

 

[Timerover51]

Incidentally, I found my disbelief suspenders rather stretched by having a merchant ship be able to withstand pressures almost as much as the bottom of the Challenger Deep. I seriously doubt that airlocks, cargo hatches and view-ports could withstand such pressures.

I use submarine design parameters for my ships, so they are all basically cylindrical in shape, with streamlined fairings. At the end of World War 2, the 0.875 inch thick vanadium steel alloy pressure hull of a U.S. submarine was rated at a crush depth of about 900 feet, and a safe operating depth of 450 feet. The operating depth limitation was based on not having tested all of the submarine equipment to more than 450 feet. U.S. submarine hulls got both thicker during the course of the war, and also made from higher-strenght steel alloy, rather than just mild steel. Welding also helped with strength.

Going to HY-80 steel, with a hull an inch thick, the crush depth will go to about 1350 feet, or about 40 atmospheres of pressure. That is for a 16 foot diameter hull. For a 16 foot diameter hull to resist 1000 atmospheres of pressure, you will need the equivalent of 25 inches of HY-80 steel. HY-80 steel is called that as it has a yield strength of 80,000 pounds pressure per square inch. That would be a massive amount of weight for a civilian ship to have to haul around, much less try to find a spot to land that will bear the weight of the ship. That would go even more for military ships. Note, hull thickness for a cylinder will scale directly with diameter. I suspect that whoever came up with those numbers never bothered crunching them at all.

If I have a hull of one inch thickness of vanadium alloy steel, I can figure that a hull 80 feet in diameter will take 6 atmospheres of pressure before having problems, with a 100 percent safety factor at 3 atmospheres. A hull of that thickness of HY-80 steel will give me a even bigger margin of safety at those pressures. Now, an 80 foot diameter hull is slightly more than 24 meters in diameter. The volume of a cylinder is pi X radius(squared) so a 12 meter radius would give 452 cubic meters of volume for every meter of length, or over 32 Traveller dTons per meter of length, using 14 cubic meters for the Traveller dTon. A cylinder 80 meters long is going to produce a ship of 2560 Traveller dTons. That is not a small ship in most Traveller universes. Add a hemisphere at each end which would add 517 dTons, and you have a nice 3000+ dTon ship that should take maybe 18 months to build. Stretch it to a 120 meter long cylinder with a hemisphere at each end, and you have a nice 4350+ dTon merchant ship, with a good length to beam ratio of 5 to 1.

As I said, my ships tend to be cylinders of various sizes. Not very creative, I must admit, but then naval architects do tend to be conservative and go with what has worked in the past.

 

[Carlobrand]

I like cylinders for warships, but my commercial ships tend to be bricks. IMTU, the need to make best use of space for cargo and passenger accommodations dictates their designs. That makes them somewhat less than ideal for extreme environments.

 

[Timerover51]

I like cylinders for warships, but my commercial ships tend to be bricks. IMTU, the need to make best use of space for cargo and passenger accommodations dictates their designs. That makes them somewhat less than ideal for extreme environments.

I lean towards having flattened bottoms on my ships for landing purposes, and using the outer curved space for fuel tanks, while having the box for passengers and cargo inside of the cylinder. A brick shape is much easier for passengers and cargo carrying.

I need to do some ship designing for my sector. There I am also using Hyperdrive, which does not need all of the Liquid Hydrogen for Jump.

 

[kilemall]

Hmm given the above study on atmospheres, we should be able to extrapolate off the Striker materials tech values and give approximate pressure values.


That's working off the penetration/armor value table, which isn't the same thing as pressure hull, but I would expect it's a working ballpark.

 

[whartung]

You have viewports? I figured that was a bad idea in something that was likely to get shot at by missiles and high-power lasers.

How else do you look out the window to tell the pilot whether to jink left or right to lose the missile or avoid the laser blasting space fighter?

 

[jawillroy]

How else do you look out the window to tell the pilot whether to jink left or right to lose the missile or avoid the laser blasting space fighter?

I thought the portholes were for damage control, like that one pic in TTB: "Break Glass In Case Of Fire"

 

[Timerover51]

I thought the portholes were for damage control, like that one pic in TTB: "Break Glass In Case Of Fire"

I think that they are used for maneuvering in the atmosphere and the purposes of landing. Plus, your passengers might want to see what the universe looks like when not in either Jump Space or Hyperspace.

 

[BlackBat242]

Lots of good data

One question.

Your depiction of the loss of crush resistance as the cylinder diameter increases - is that for an empty cylinder unsupported internally?

If so, then adding internal bracing cunningly designed as bulkheads & floors (with structural elements) should act to partially counter that reduction in crush resistance, shouldn't it?

 

[Carlobrand]

How else do you look out the window to tell the pilot whether to jink left or right to lose the missile or avoid the laser blasting space fighter?

Some joker painted the missile black.

I always figured the passengers would be satisfy with the view from the wall-size vid screen in the lounge, but I could always disguise some little vid screens as portals.

 

[Enoki]

Sounds to me like the original numbers for temperature and pressure on vessels were little more than a SWAGPOOYA. I'd think that temperature could be easily handled to extremes far beyond what's given using advanced materials, probably well beyond what were given in the OP.

On the other hand, I'd also think that radiation resistance would be a serious consideration. I'd think you'd want some serious attenuation of pretty serious amounts of radiation in the hull design.

As for pressure, you could use a double hull with framing to greatly increase the pressure it would take. You might use other methods (a crude one would be to wrap the hull in a layer of wire rope under tension or compression to increase resistance) to increase pressure resistance.

But, in any case, why 1000 + atmospheres? For most ships, they'd never see that sort of pressure applied. They have no reason to deep dive into a gas giant, and no planetary atmosphere is going to reach such extremes.

 

[mike wightman]

Heating the entire hull to 6000K is trifling compared with the waste heat from the fusion power plant. Traveller has a hidden magic heat sink technology.

If it can cope with the waste heat from a GW to TW fusion reactor it is more than capable of cooling down a hot hull...

Until we actually invent crysiron and then superdense we can just go by the Striker et all figures for their strength relative to hardened steel and then compare what an equivalent thickness hardened steel hull would stand pressure wise.

 

[Enoki]

Heating the entire hull to 6000K is trifling compared with the waste heat from the fusion power plant. Traveller has a hidden magic heat sink technology.

If it can cope with the waste heat from a GW to TW fusion reactor it is more than capable of cooling down a hot hull...

Until we actually invent crysiron and then superdense we can just go by the Striker et all figures for their strength relative to hardened steel and then compare what an equivalent thickness hardened steel hull would stand pressure wise.

We already can make something like crysiron and superdense on a small scale. Making large plates is not possible right now. Hot Isostatic Presses (HIP Furnace) can actually make a material more dense than is found in nature. They typically run to about 2100 C and 100,000 psi. A HIP furnace crushes the material into a more dense form.
One military application is making TC penetrators for antitank guns. They raise the density of the tungsten carbide by about 10 to 15% over the natural state.
By using extremely finely powdered metals, one can also control grain size in the process of making something out of that metal. Powdered metal technology would give you a very fine, tight, and tough grain size as a result.
Ceramets (Ceramic metals) are another technology that's just getting going. These are designed to combine the high temperature capacity of a ceramic with the toughness of a metal.

Then you have ceramics like titanium nitride that actually lose heat faster than it is absorbed.

 

[kilemall]

On the other hand, I'd also think that radiation resistance would be a serious consideration. I'd think you'd want some serious attenuation of pretty serious amounts of radiation in the hull design.

You put the fuel tanks on double duty, wrap them around the whole hull like a jet plane in-wing tank. The hydrogen helps absorb what the heavy hull metals won't.


I would visualize the big tanks to be jump fuel since their usage characteristic is to be massively fed into jump in just a few minutes, and the m-drive fuel is used for the rad protection.


https://en.wikipedia.org/wiki/Health_threat_from_cosmic_rays#Shielding