For Questions That Don't Merit Their Own Thread

[magnemoe]

On 8/8/2019 at 4:05 AM, Gargamel said:

No, No No....   You don't get to posit a "ball of flesh" orbiting by Saturn and not give a little context there!    

Cheeky answer is 0, as I don't think there's a material capable of holding gaseous mercury (or gaseous anything) at that temp.    Also, wouldn't you start to encounter some breakdowns in the fundamental forces at these energy levels?  Ie similar to the plasma/goo immediately after the Big Bang?

Anything would be plasma at this temperatures or even 10K kelvin. In this cases magnetic nozzles would work well for directing it. 
Yes this would cost energy but way less than heating something to plasma. 
Vasmir engines works a lot like this however. 

[Terwin]

9 hours ago, ARS said:

Imagine a mini-submarine, which has a neutral buoyancy. If it's fitted with powerful engine and "wings" (with "control surface"), could it be steered like aircraft underwater? (As long as the engines are running, since water slows it down a lot when it's stopped) If it's possible, could we "dogfight" with it underwater? (Not necessarily firing, just getting on other's rear)

Because water is so much denser than air, you need much smaller 'wings' to deflect sufficient material to maneuver.  That is why sub have much smaller wings than an airplane.

Also, neutral buoyancy is very condition specific.  With a rigid shell, you need more and more weight as you go deeper(due to lack of compression), with a flexible shell, you need more and more buoyancy as you go deeper(due to compression).  This is why subs(rigid) have ballast tanks that can be filled with sea-water or air as the need arises. 

For example: a plastic bag filled with 1 liter of air at sea-level will compress to 500ml at a depth of 10m and 333ml at a depth of 20m. (Every ~10m of water adds one atmosphere of pressure, so at 30m of depth, you have ~4 atmospheres of pressure, making your bag only take 1/4 of it's volume at sea-level).  So the deeper you go, the more air you need to put into the bag to displace 1 kg of water.

Water also gets denser as you go deeper, but very slowly(~4.5% denser at 4000m I think)

[magnemoe]

2 hours ago, Terwin said:

Because water is so much denser than air, you need much smaller 'wings' to deflect sufficient material to maneuver.  That is why sub have much smaller wings than an airplane.

Also, neutral buoyancy is very condition specific.  With a rigid shell, you need more and more weight as you go deeper(due to lack of compression), with a flexible shell, you need more and more buoyancy as you go deeper(due to compression).  This is why subs(rigid) have ballast tanks that can be filled with sea-water or air as the need arises. 

For example: a plastic bag filled with 1 liter of air at sea-level will compress to 500ml at a depth of 10m and 333ml at a depth of 20m. (Every ~10m of water adds one atmosphere of pressure, so at 30m of depth, you have ~4 atmospheres of pressure, making your bag only take 1/4 of it's volume at sea-level).  So the deeper you go, the more air you need to put into the bag to displace 1 kg of water.

Water also gets denser as you go deeper, but very slowly(~4.5% denser at 4000m I think)

Most subs uses ballast tanks who is open at bottom and uses compressed air to keep water out. As you dive the air compresses and your buoyancy goes down.
Then doing scuba the flotation bladder has the same problem who is very annoying, if you go from surface to 10 meter down pressure is 2 bar so you has to fill bladder to avoid sinking like an rock, going up you has to went air to avoid popping up to surface. If swimming its not an major problem as you can compensate, find having a bit negative buoyancy is best so you sink slowly if you stop as you stop at the bottom

Now if you had your ballast tanks inside the pressure hull you could keep pretty perfect buoyancy, downside is that you now either have water or air under high pressure inside your hull or you have to use a lot of energy pumping water out slowly. 

[kerbiloid]

An underwater lead zeppelin.

[DDE]

On 8/9/2019 at 6:01 AM, ARS said:

Imagine a mini-submarine, which has a neutral buoyancy. If it's fitted with powerful engine and "wings" (with "control surface"), could it be steered like aircraft underwater?

That’s what the diving planes are for; they’re basically aircraft canards and tail empennage. However, you’d still have to actively trim the ballast to maintain neutral buoyancy at different depths.

The Deepflight guys went a bit further:

However, it looks like these were naught but expensive toys.

On 8/9/2019 at 3:56 PM, Terwin said:

That is why sub have much smaller wings than an airplane.

Oh, you asked for it...

Spoiler

 

Edited August 10, 2019 by DDE

[magnemoe]

2 hours ago, DDE said:

That’s what the diving planes are for; they’re basically aircraft canards and tail empennage. However, you’d still have to actively trim the ballast to maintain neutral buoyancy at different depths.

The Deepflight guys went a bit further:

However, it looks like these were naught but expensive toys.

Oh, you asked for it...

  Hide contents

 

Well that was an bit extreme I say so I wonder why?
You still want to be close to neutral buoyancy so you need control surfaces, not wings. Deep flight looks good. 

My guess the wiring between the wing is the real purpose of them

[kerbiloid]

Sky Captain and the World of Tomorrow.

Spoiler

A rather great and lovely dieselpunk movie.

Edited August 11, 2019 by kerbiloid

[DDE]

6 hours ago, magnemoe said:

Well that was an bit extreme I say so I wonder why?

Geological survey.

[ChrisSpace]

How much thermal energy would I have to give the asteroid Eunomia in order to make it glow as hot as possible (without the asteroid melting/evaporating)?

[kerbiloid]

Eunomia
A rocky body.
Mass ~= 3.1*10¹⁹ kg.
Specific heat capacity ~= 1000 J/(kg*K)
Melting point ~= 1500 K.

Energy ~ (1500 - 200) K * 1000 J/(kg*K) * 3.1*10¹⁹ kg ~= 4*10²⁵ J ~= 10¹⁰ Mt.

[ARS]

A WW2 era anti-tank gun has little chance against modern tank armor. So if you fired enough of them at modern tank, is it possible to crack open the armor? (and by "enough" I mean a WHOLE lot of them, firing on the tank roughly at the same spot)

[DDE]

Why did I know it was a WWII military tech question the second I saw your avatar in the forum? 

1 hour ago, ARS said:

A WW2 era anti-tank gun has little chance against modern tank armor. So if you fired enough of them at modern tank, is it possible to crack open the armor? (and by "enough" I mean a WHOLE lot of them, firing on the tank roughly at the same spot)

About half the answers here are informative and contribute way more than I could off-hand: https://www.quora.com/If-you-kept-shooting-at-tank-with-armor-you-could-not-penetrate-will-you-eventually-penetrate-the-armor-if-you-shoot-it-enough

[ARS]

45 minutes ago, DDE said:

Why did I know it was a WWII military tech question the second I saw your avatar in the forum? 

Well maybe because I'm infamous for asking a question like that in this thread 

Anyway, thank you. It's a great info on that link that you provided. I'm actually testing the material penetration on my college's study (I'm material engineer). It involves penetration test on a metal specimen which results in yes or no penetration using high speed penetrator. And then I'm wondering if a penetrator cannot pierce the metal, then maybe hitting it repeatedly works

[kerbiloid]

By shooting for enough long time, you will make a steel pancake.

Also, why shoot in front, when any tank is thin from other directions.

Edited August 17, 2019 by kerbiloid

[DDE]

57 minutes ago, kerbiloid said:

Also, why shoot in front, when any tank is thin from other directions.

Why shoot the tank if you can just wait them out and shoot the crew?

[kerbiloid]

6 minutes ago, DDE said:

Why shoot the tank if you can just wait them out and shoot the crew?

Why at all shoot the tank if you can pierce it with a drill and siphon all fuel into buckets for sale?

Edited August 17, 2019 by kerbiloid

[DDE]

2 minutes ago, kerbiloid said:

Why at all shoot the tank if you can pierce it with a drill and siphon all fuel into buckets for sale?

 

[Codraroll]

Modern rockets use onboard computers for anything from guidance to fuel injection to communication with the ground. Question is, how much computing power/hardware is required to do these tasks, and sent up on a launch? Say, in terms of the capabilities of a modern mid-range laptop (minus, I presume, sound or graphics cards and anything like that), are we talking one tenth the computing power of one, or the combined power of 20?

Or in other words, how much gaming fun could you have if you hooked a graphics card and a monitor to a Falcon 9? Are we talking Pong or KSP?

Edited August 19, 2019 by Codraroll

[Nightside]

1 hour ago, Codraroll said:

Modern rockets use onboard computers for anything from guidance to fuel injection to communication with the ground. Question is, how much computing power/hardware is required to do these tasks, and sent up on a launch? Say, in terms of the capabilities of a modern mid-range laptop (minus, I presume, sound or graphics cards and anything like that), are we talking one tenth the computing power of one, or the combined power of 20?

Or in other words, how much gaming fun could you have if you hooked a graphics card and a monitor to a Falcon 9? Are we talking Pong or KSP?

[Spacescifi]

 

So unobtanium is matter that does not exist but we can at least explain it's prpperties, so lets analyze a few possible types of unobtanium that would be useful for spaceflight.

 

1. A metal that can take over 1000 kelvin of heat before melting (definitely not 2000 kelvin though).

2. A metal that does not react with antimatter but otherwise behaves like a normal piece of metal... under most circumstances anyway.

 

Sooo... what properties would they need to behave so weirdly? How would each metal look?

I will take the first stab at this.

Properties: The chemical bonds of over 1000k to melt metal must be either superstrong. Since it cannot be super dense, because if it was one could probably never lift the thing with a rocket.

Applications: Possible SSTO rocketships, as  now we can operate at much higher temperatures and thus have more efficient rockets... and more superflamey landings. Fusion is still iffy, since who knows if 1000k or below is goid enough for fusion. Is it?

Also the chemical bonds holding such metal together in the first place might make it explode like a small tactical nuke when it is finally vaporized. So be careful to keep the temperature within acceptable limits.

As for the metal that is otherwise normal behaving but won't react with antimatter, I have'nt a clue what it's properties might be. Do you?

I do think it may also behave strangely under certain circumtances, but I have no clue what such circumstances might be, nor how it would behave in strange ways other than not reacting with antimatter. Do you?

 

Thoughts on this subject?

 

 

 

Edited August 20, 2019 by Spacescifi
Edit

[razark]

5 minutes ago, Spacescifi said:

So unobtanium is matter that does not exist but we can at least explain it's prpperties

How do you examine the properties of something that does not exist, and further, the imaginings of it have properties that fit whatever the story needs?

[Spacescifi]

27 minutes ago, razark said:

How do you examine the properties of something that does not exist, and further, the imaginings of it have properties that fit whatever the story needs?

 

Extrapolating from known science, just like I have already done.

 

Someone who is good at chemistry or atomic bonds no doubt could share some interesting theories.

Edited August 20, 2019 by Spacescifi

[ARS]

5 hours ago, Codraroll said:

Modern rockets use onboard computers for anything from guidance to fuel injection to communication with the ground. Question is, how much computing power/hardware is required to do these tasks, and sent up on a launch? Say, in terms of the capabilities of a modern mid-range laptop (minus, I presume, sound or graphics cards and anything like that), are we talking one tenth the computing power of one, or the combined power of 20?

Or in other words, how much gaming fun could you have if you hooked a graphics card and a monitor to a Falcon 9? Are we talking Pong or KSP?

A game could be played (maybe) using spacecraft computers, such as Pong, Space invader, and Pac man is possible, up to Doom, but I'm doubtful about KSP (or for that matter, any games involving other than text or pixels, especially 3D objects). Generally, a computer on spacecraft is of much lower performance than regular laptops, some even literally just a command line interface (a cheap smartphone out there could be several times far more powerful than spacecraft computers). Out there, in space, high performance computers are generally avoided since it drains more power and also generates more heat (this is very important since in space you cannot shed heat easily, unless you had ginormous radiator panels, like ISS). The radiation shielding is also important. High-energy rays in space can alter a computer’s memory, causing glitches that could be catastrophic. That’s the main reason to have auxillary onboard computers (usually up to 3)—if one or even two crash, the system can still correct itself, and since these are low-performance computers, it keeps the mission budget low while still getting the job done. Back then, the onboard computer clocked in at one megahertz and had about 36 kilobytes of memory. An iPhone 6 is a thousand times faster, with 30,000 times the memory, but still, with those abysmal performance, that old rustbucket computer is what takes the rocket into space.

[magnemoe]

6 hours ago, Codraroll said:

Modern rockets use onboard computers for anything from guidance to fuel injection to communication with the ground. Question is, how much computing power/hardware is required to do these tasks, and sent up on a launch? Say, in terms of the capabilities of a modern mid-range laptop (minus, I presume, sound or graphics cards and anything like that), are we talking one tenth the computing power of one, or the combined power of 20?

Or in other words, how much gaming fun could you have if you hooked a graphics card and a monitor to a Falcon 9? Are we talking Pong or KSP?

Its pretty lightweight, standard control systems so pong. Just doing stuff like compressing video is way more demanding and that is on separate systems to not mess up primary. 

[magnemoe]

2 hours ago, razark said:

How do you examine the properties of something that does not exist, and further, the imaginings of it have properties that fit whatever the story needs?

Unobtanium has traditionally been an design goal for an material you need but don't have. 
It has to be possible to make however at least in theory. 
Now figure out how to make it.