Realistic starship equipment vs scifi equipment

[Guest]

Sure, but what I meant was is that you don't necessarily have your gunfight on a Star Destroyer. For warships, double hulls and thick armor would be normal. However, if you're boarding a freighter or some other non-combat ship, then it might have just an aluminium plate covered (from the outside) by some thermal/MMOD blankets. Smaller craft will likely resemble airplanes more than ships in terms of hull strength.

[kerbiloid]

1 hour ago, Dragon01 said:

, if you're boarding a freighter or some other non-combat ship, then it might have just an aluminium plate covered (from the outside) by some thermal/MMOD blankets.

They should have some reinforced structures to prevent piercing the outer hull with heavy or sharp cargos.

[Guest]

But they wouldn't, because careful handling of cargo is a cheaper way of doing the same thing. Commercial vessels would only be armored against MMOD, and as light as possible to cut costs.

[kerbiloid]

49 minutes ago, Dragon01 said:

But they wouldn't, because careful handling of cargo is a cheaper way of doing the same thing.

When they handle heavy, hard, cornered cargos, they anyway need a skeleton of strong bars to keep it.
And any serious ship has a double hull and is separated with several strong bulkheads.

The nowadays spaceships carry negligible amount of cargo and several humans. They don't need strong hulls. (Recalls the 2 mm hole...) They need.

[Guest]

13 minutes ago, kerbiloid said:

When they handle heavy, hard, cornered cargos, they anyway need a skeleton of strong bars to keep it.
And any serious ship has a double hull and is separated with several strong bulkheads.

The nowadays spaceships carry negligible amount of cargo and several humans. They don't need strong hulls. (Recalls the 2 mm hole...) They need.

A space cargo freighter wouldn't need a strong hull, just a strong central spine for attaching cargo. The crew modules could be built like the ISS, they don't need to be load-bearing. The Soyuz hole was made by some moron in the factory, and can only be addressed by not hiring morons in spaceship factories. Marine ships have double hulls because they need to keep the water out, which is much harder than keeping the air in (not to mention mass is cheap on watercraft).

Again, corners don't matter as long as you don't bang containers into habitation modules. This is actually pretty easy to ensure, because movement of a cargo container, heavy or light, is quite predictable. ISS robotic arms have no problems moving things around with milimeter precision. Any spaceborne cargo loading system should be able to easily match them.

[kerbiloid]

Double hulls, as well as several strong bulkheads separating a ship, are not marines', they are a safety requirement for any big ship.
If its outer wall gets a hole, the inner wall is still intact. Also the space between the hulls is used as tanks, and can be used for ballast water redistribution to prevent tilting.
A space ship doesn't need water ballast, but it needs a thick layer of matter for rad protection.
To avoid using useless ballast, the spaceship should have distributed materials and equipment along the hull.
So, no paper-thin hulls can be used in spaceships bigger than nowadays WrightBrothers-style spaceships.

[Scotius]

But layer of water makes for a pretty good radiation shield. And it's useful for many other things. Drinking, washing, temperature control, hydroponics, emergency supply of oxygen. Heck - with some engine designs you can use water as reaction mass. Yay for the H2O between the walls

[Guest]

Yeah, unless you've got a huge mass budget to spare (hint: you don't), a double hull makes no sense on a commercial spaceship. Remember, there aren't any underwater rocks or shoals in space, which is the reason why seagoing ships have double hulls. There are also no waves, so all the forces involved come from the engine (hence why you only need a spine). A "double hull", or more accurately spaced armor, only makes sense on warships, where a lot of mass budget is going towards armor, anyway. There's no reason for it to be pressurized, either. Far better to have an ISS-style module inside the much larger armored shell, in order to simplify the life support system. Metal hulls don't just spring leaks at random (unless they're long past their expected lifetime), and MMOD threat is can be dealt with by blankets. Spaceships have far more in common with aircraft than with submarines, and have absolutely nothing in common with waterborne ships, technology wise.

Tanks with anything important are just going to make problems worse. Water is a poor propellant and a poor radiation shield, on a weight basis. It's only good for drinking and hydroponics, and you don't need a whole lot of it for that, because the water cycle is the easiest to close. There are far better materials for shielding, and being liquid it comes with problems on its own. Realistically, your propellant is going to be hydrogen or methane. Both cryogenic, so you can't have those tanks in direct contact with the crew module. 

[kerbiloid]

4 hours ago, Dragon01 said:

Yeah, unless you've got a huge mass budget to spare (hint: you don't), a double hull makes no sense on a commercial spaceship.

Orion

Spoiler

 

CST-100

Spoiler

Dragon

Spoiler

 

VA of TKS (compare the real 3-seat and 6-seat project, the place where additional passenger cabin is attached to the main 3-seat one)
 

Spoiler

 

Even now there is a pressurized cabin inside a heat-protected hull.

Bigelow module has even moar.

Spoiler

 

Space freighters will have even multi-layered hulls, including a self-sealing layer like airplanes have in fuel tanks since WWII.
https://en.wikipedia.org/wiki/Self-sealing_fuel_tank

5 hours ago, Dragon01 said:

 Metal hulls don't just spring leaks at random

Ideal ship with ideal hull in ideal conditions.

[Guest]

Thanks for proving my point, none of those examples have a double hull. In every case, only the layer holds pressure. The outer parts are just MMOD and aerodynamic shielding, and it's neither pressurized (the equipment under them is exposed to vacuum) nor load bearing. In case of TKS, this is handled by thermal blankets and in fact, you can see in this schematic that TKS has no double hull of any kind. The only thing standing between the crew and the outer hull is considerable quantity of equipment, which is not airtight (which is why they didn't try to patch up Spektr, the leak would have likely been impossible to get to from the inside).

A metal barrel just doesn't spring a leak all by itself, even when pressurized. Otherwise, it would have happened, at least once, on Mir and ISS. The only times air leaks happened on either station was due to human error. For a leak to appear, something must hit the cylinder, which we have a decent record of protecting against so far (only one serious collision involving a manned station in the entire spaceflight history).

[kerbiloid]

2 hours ago, Dragon01 said:

none of those examples have a double hull. In every case, only the layer holds pressure.

All of them are lightweight, so a lightweight cabin is separated from the external hull.
A freighter is much heavier, so its hull layers will be parts of a single structure, and probably have even more layers than just two..

2 hours ago, Dragon01 said:

In case of TKS, this is handled by thermal blankets

Which blankets? It has a solid cover of silicon composite with phenolformaldehyde resin filler on the strong envelope made of aluminium-magnesium alloy.
Blankets cover only orbital modules, protected by a shroud.

2 hours ago, Dragon01 said:

you can see in this schematic that TKS has no double hull of any kind.

You can easily see that the 2.788 m wide equator of 3-seat capsule, where the original heatshield is placed, splits in two hulls in the 6-seat version.
An additional passenger pad is added to the cabin hull, an additional backshell section is placed betwee the capsule hull and the bigger heatshield.

2 hours ago, Dragon01 said:

A metal barrel just doesn't spring a leak all by itself, even when pressurized.

And any aircraft is designed to allow one barrel or one engine leak by itself, without visible reasons. They call it reliability.
An aircraft accident is never caused by a single reason, only a combination of two or more reasons may cause an accident.

2 hours ago, Dragon01 said:

Otherwise, it would have happened, at least once, on Mir and ISS.

Mir was one big leakage after the collision with Progress.
Also once they had damaged airlock door by leaving some thing and trying to close.
One of Gemini had problems with hatch door closing after EVA, as a spring had been welded in vacuum.
Almost every second early Soyuz and Shuttle flight had its problems without initially obvious reasons.

These people were sure that nothing happens with metal hull without reason.
They were right. A reason appeared.

Spoiler

 

[Guest]

6 hours ago, kerbiloid said:

Mir was one big leakage after the collision with Progress.
Also once they had damaged airlock door by leaving some thing and trying to close.
One of Gemini had problems with hatch door closing after EVA, as a spring had been welded in vacuum.
Almost every second early Soyuz and Shuttle flight had its problems without initially obvious reasons.

These people were sure that nothing happens with metal hull without reason.
They were right. A reason appeared.

My point exactly. Notice that both of those could have been avoided if it wasn't for human error. Also, notice that most of the other problems involved hatches. Bad hatch design can lead to problems, but that's a given, considering that a hatch, by definition, requires making a hole in the hull.

Also, while there are icebergs in space (we usually call them comets or asteroids, depending on their orbit), they're rather easier to avoid than at sea.

6 hours ago, kerbiloid said:

A freighter is much heavier, so its hull layers will be parts of a single structure, and probably have even more layers than just two..

It isn't! A freighter is as light as possible. Less structure = more cargo. More cargo = more money. So a single, load-bearing hull with a non-loadbearing MMOD shield over it, or a truss with inflatable modules hanging off it. Every kilogram spent on hull is one kilogram that is not available for paid cargo. It's easy to design a hull that can withstand stresses in one direction only, and in space, that's all you need.

[kerbiloid]

5 minutes ago, Dragon01 said:

Notice that both of those could have been avoided if it wasn't for human error.

Notice that they haven't. Because they existed in real world where real people make mistakes, or sometimes a piece of foam unexpectedly falls down from a cryogenic tank.

6 minutes ago, Dragon01 said:

A freighter is as light as possible

As any sea freighter is.
The keyword is "as possible". So, the big sea ships have double hulls, while it would be more effective to have them single.
As well, why carry that useless LES on top. It's several tonnes heavy.

10 minutes ago, Dragon01 said:

Less structure = more cargo. More cargo = more money.

Weaker structure = more money to pay after an accident.

11 minutes ago, Dragon01 said:

It's easy to design a hull that can withstand stresses in one direction only, and in space, that's all you need.

And except the short-living, single-use rockets stages, nobody needs such 1d hull irl.

[Guest]

22 minutes ago, kerbiloid said:

As any sea freighter is.

Wrong. Sea freighters are limited by volume. Mass doesn't matter that much, because it's all supported by the water. At the same time, the sea is a much more demanding environment than space. A double hull is actually needed, because even if you don't hit anything, waves themselves can damage a ship's hull if the sea is high. In space, there is no such things as storms and waves (unless you count solar storms and gravity waves, which are different, despite what you might have gotten from Star Trek).

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The keyword is "as possible". So, the big sea ships have double hulls, while it would be more effective to have them single.
As well, why carry that useless LES on top. It's several tonnes heavy.

You won't have a LES on a space freighter. It's a space freighter. You know, the sort of thing that you build in orbit in first place. LES is for passenger surface-to-orbit flights.

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Weaker structure = more money to pay after an accident.

And except the short-living, single-use rockets stages, nobody needs such 1d hull irl.

Have you ever seen an airplane with a double hull? Spaceships are not sea ships, and space is not an ocean. Stop with the irrelevant comparisons already. A space freighter is nothing like a seagoing one. We only use naval terminology because it's what we have. Spacecraft have far more in common with planes than they do with ships (but even then, they are different, and work in a very different environment).

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Notice that they haven't. Because they existed in real world where real people make mistakes, or sometimes a piece of foam unexpectedly falls down from a cryogenic tank.

Then why don't we build airplanes to stay intact when they crash due to pilot error? Hint: same reason as to why it's stupid to make a double-hulled spaceships. 

[kerbiloid]

56 minutes ago, Dragon01 said:

Sea freighters are limited by volume. Mass doesn't matter that much, because it's all supported by the water. At the same time, the sea is a much more demanding environment than space. A double hull is actually needed, because even if you don't hit anything, waves themselves can damage a ship's hull if the sea is high. I

As well, there are meteoroids, thermal expansion, vacuum melting and evaporation, numerous objects to collide around a station which requires that freighter.
So, safety requirements.

59 minutes ago, Dragon01 said:

Have you ever seen an airplane with a double hull?

Have you ever seen a spacefreighter held in air by the lifting force?
Also you can have a look at airplane parts. Almost all of them are actually like pipes, because they need to be strong.
As well, a spacefreighter will be made of even thicker and stronger pipes.

1 hour ago, Dragon01 said:

Then why don't we build airplanes to stay intact when they crash due to pilot error?

We build them as close to that as possible.
But they have to be lightweight because only thin air is holding them.
A spacefreighter doesn't fall without wings and engines. It will keep drifting.

Of course, don't hesitate to build tinfoil space freighters.

Spoiler

 

[Guest]

1 hour ago, kerbiloid said:

As well, there are meteoroids, thermal expansion, vacuum melting and evaporation, numerous objects to collide around a station which requires that freighter.
So, safety requirements.

Not a problem, so far, for MIR or ISS. MMOD shielding doesn't hold pressure. Thermal expansion actually makes a double hull a worse idea. If something is near the station (or a spaceship), it's either attached, trying to dock or undocking. In the former case, there's no risk of collision, and in the latter two, the maneuvers are slow and controlled, if not done entirely with a robotic arm. If you're stationkeeping nearby for some reason, then you should be at least one kilometer away, if only to prevent your thrusters from blasting the other object.

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Have you ever seen a spacefreighter held in air by the lifting force?
Also you can have a look at airplane parts. Almost all of them are actually like pipes, because they need to be strong.
As well, a spacefreighter will be made of even thicker and stronger pipes.

Why? It will be made of thinner pipes. Exactly because it's not bother by air and aerodynamic stresses it induces. There is no need for a spacecraft to be strong. It only needs to withstand its own thrust, and only on a single axis.

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We build them as close to that as possible.
But they have to be lightweight because only thin air is holding them.
A spacefreighter doesn't fall without wings and engines. It will keep drifting.

Wrong on both counts. We don't build them "as close as possible". We recognize that it's impossible to build a crash resistant airplane, and build them as light as possible instead. We also take many other measures to prevent crashes from happening. Even if you made an airplane out of battleship-grade armor (you can, just give it enough engines and gigantic wings), it will still be a mangled mess if it hits the ground at 300 knots.

You could build a heavyweight airplane, but it will be destroyed in a crash just the same, the speeds are just too high for anything but a solid rod to survive. Unless you need to protect your plane from being shot at, adding heavier armor is useless. So we don't, except for a few military planes like A-10 or Su-25.

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Of course, don't hesitate to build tinfoil space freighters.

As long as they're out of the air, copious quantities of hydrogen in aluminium balloons are perfectly safe. We do it with Centaur stages already. Also, guess what the outer skin on this thing was made out of:

Of course, the outer skin didn't hold pressure, either, so it's irrelevant. 

[magnemoe]

2 hours ago, Dragon01 said:

Wrong on both counts. We don't build them "as close as possible". We recognize that it's impossible to build a crash resistant airplane, and build them as light as possible instead. We also take many other measures to prevent crashes from happening. Even if you made an airplane out of battleship-grade armor (you can, just give it enough engines and gigantic wings), it will still be a mangled mess if it hits the ground at 300 knots.

You could build a heavyweight airplane, but it will be destroyed in a crash just the same, the speeds are just too high for anything but a solid rod to survive. Unless you need to protect your plane from being shot at, adding heavier armor is useless. So we don't, except for a few military planes like A-10 or Su-25.

As long as they're out of the air, copious quantities of hydrogen in aluminium balloons are perfectly safe. We do it with Centaur stages already. Also, guess what the outer skin on this thing was made out of:

Of course, the outer skin didn't hold pressure, either, so it's irrelevant. 

This, now an lightweight aircraft is safer as its landing speed is slower.On the other hand light aircraft are more affected by wind and is way less regulated so they crash all the time but their crash is pretty easy to survive as your landing speed is slow. No ramming something does not work. 

A couple of other issues. you might want to pressurize the service module on an spaceship. At least with current spacesuits it would be an good idea and is done on IIS. 
All systems who it make sense to put inside the pressure hull like life support systems and computers are inside. 
Fuel tanks and poisonous gasses is outside. You probably put metal sheets above the thermal insulation. if nothing else it make thermal control easier, add to insulation, work as spaced armor and it makes it easier to spot damage. 

[Guest]

It would be more true to say slower aircraft are safer, regardless of weight. A heavier aircraft needs to either go faster or have bigger wings. Going faster tends to be the way to go, but this is because we want aircraft in general to go fast, and we optimize them for that. Even WWII bombers (not light aircraft by any definition) landed quite a bit slower than modern airliners. It's difficult and expensive to make an aircraft capable of going both fast and very slow, though, so as cruise speeds went up, so did landing speeds.

As for insulation and protection, thermal blankets to the job fine, for most parts. SM pressurization depends on what's inside, electronics are easier to put in the pressurized volume, while other things are better left outside. 

[kerbiloid]

Someone should realize at last that not only external factors can affect the hull, but also internal ones, and that there is a big difference between a capsule for 3 soft humans and soft packs and a hull to operate with heavy, hard, and sometimes sharp cargos.

The service module of Apollo 11 did not operate with cargos, it was tiny compared to a freighter, and it was the heaviest possible thing to carry.
It was not designed for regular commercial flights. Its crew consisted of specially selected and trained persons of highly risky occupation.
This is nothing common to a space freighter.

(Feel free to declare the paper-thin Apollo LEM as a standard for freighter landers.)

Also one should realize that an envelope thickness should match the size of the truss which it tightly covers.
Because otherwise
1) any deformation of the internal structure will break the hull.
2) any inaccurate movement of heavy cargo will break the hull.
3) if the freighter carries a shutlle, any inaccurate movement of heavy cargo will break the hull. Even if not the envelope is hit, but a truss.

Edited September 16, 2019 by kerbiloid

[magnemoe]

9 hours ago, kerbiloid said:

Someone should realize at last that not only external factors can affect the hull, but also internal ones, and that there is a big difference between a capsule for 3 soft humans and soft packs and a hull to operate with heavy, hard, and sometimes sharp cargos.

The service module of Apollo 11 did not operate with cargos, it was tiny compared to a freighter, and it was the heaviest possible thing to carry.
It was not designed for regular commercial flights. Its crew consisted of specially selected and trained persons of highly risky occupation.
This is nothing common to a space freighter.

(Feel free to declare the paper-thin Apollo LEM as a standard for freighter landers.)

Also one should realize that an envelope thickness should match the size of the truss which it tightly covers.
Because otherwise
1) any deformation of the internal structure will break the hull.
2) any inaccurate movement of heavy cargo will break the hull.
3) if the freighter carries a shutlle, any inaccurate movement of heavy cargo will break the hull. Even if not the envelope is hit, but a truss.

Think most here assumed external cargo in vacuum with an smallish crew section. 

If cargo is inside the pressure hull you are correct. This also apply to something like an large passenger ship. 

Wonder how manned Starship will do this. We know they plan on an crew compartment then and cargo hold below who can have air or be in vacuum if you need to offload payload.