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PostPosted: Fri Mar 17, 2017 3:06 am 
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A non-trivial thing about walking around in a spacesuit on the surface of a planet that's at 40 Kelvin - you are super-hot in that environment.
There are a fair number of common compounds, such as Oxygen or Nitrogen, that are solid at that temperature, but will melt or even boil if exposed to heat levels that are still way below that is necessary for life-support?

So how good is the insulation on your spacesuit? Unless you want the landscape to flash-boil at every point you set foot on it, your suit needs to be keeping the heat in, not just the cold out.


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PostPosted: Fri Mar 17, 2017 4:21 am 
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Yup. "Keep your heaters running" is quite wrong. Staying warm isn't a problem in space. The problem is getting rid of the heat that you and your equipment produce, as the only way to shed heat in a vacuum is by radiation. Here they may even need to limit their radiation to avoid heating the surface of Bacchus too much.

By the way, "degrees Kelvin" is deprecated since 1968. SI has watts and volts, not "degrees Watt" or "degrees Volta", and temperature is measured in kelvins, not "degrees Kelvin".

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PostPosted: Fri Mar 17, 2017 8:40 am 
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If they're leaking enough heat to melt or worse evaporate volatiles, heat loss will become a big big problem very very rapidly.

They're going to be operating on a cryogenic planetary surface, not in free space. There should be an atmosphere of some sort, no matter how thin. AFAIK, even the moon has an atmosphere.

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PostPosted: Fri Mar 17, 2017 11:20 am 
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An atmosphere of hydrogen and helium should be possible. At 1.6 g₀ the escape velocity seems to be high enough to retain even hydrogen when it's as cold as 40 kelvins. No other gasses will contribute noticeably at that temperature. The vapor pressure of nitrogen at 40 kelvins is about 10 pascals. That's less than 1/10000 atmosphere.

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PostPosted: Fri Mar 17, 2017 8:11 pm 
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So, seems that:

1. They are radiating enough heat to evaporate the ground.

2. Their heaters are not powerful enough to keep them from feeling chilly, but sufficient enough to keep them from flash-freezing (for now)

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PostPosted: Fri Mar 17, 2017 8:38 pm 
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Why don't they just fly above the surface?

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PostPosted: Fri Mar 17, 2017 9:04 pm 
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palu wrote:
Why don't they just fly above the surface?

That presents fewer opportunities for the idiot ball to come into play.

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PostPosted: Sat Mar 18, 2017 1:26 am 
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grahamf wrote:
So, seems that:

1. They are radiating enough heat to evaporate the ground.

2. Their heaters are not powerful enough to keep them from feeling chilly, but sufficient enough to keep them from flash-freezing (for now)

Actually, the heaters may be powerful enough . . . but deliberately degraded by the controller for tactile feedback, a really basic way to say "Hey, idiot, get out of this cryogenic soup before you flashfreeze!"

People have an amazing capacity to ignore guages, idiots lights, sirens, etc. but they won't ig- . . . err . . . are less likely to ignore their feet getting cold.

--FreeFlier


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PostPosted: Sat Mar 18, 2017 1:35 am 
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palu wrote:
Why don't they just fly above the surface?

That presents fewer opportunities for comedy.


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PostPosted: Sat Mar 18, 2017 9:45 pm 
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Rombobjörn wrote:
By the way, "degrees Kelvin" is deprecated since 1968. SI has watts and volts, not "degrees Watt" or "degrees Volta", and temperature is measured in kelvins, not "degrees Kelvin".


True but in the last 1000 years it may have changed once more to degrees Kelvin


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PostPosted: Sun Mar 19, 2017 3:05 am 
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palu wrote:
Why don't they just fly above the surface?


A surface gravity of 1.6 gee burns energy quickly, and their suits radiate a large amount of heat. They'd have to fly a few body lengths up, and that would drastically reduce their ability to reconnoiter. They really should have used cryogenically-rated suits instead of vacuum-rated suits. They need to fly high to get where they need to be, and scan quickly. They also need to get back home quickly. Their main problem is that the heaters aren't powerful enough; we've seen the energy output these suit plants can produce; they could all be glowing white-hot if necessary.

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PostPosted: Sun Mar 19, 2017 4:52 am 
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richv wrote:
palu wrote:
Why don't they just fly above the surface?


A surface gravity of 1.6 gee burns energy quickly, and their suits radiate a large amount of heat. They'd have to fly a few body lengths up, and that would drastically reduce their ability to reconnoiter. They really should have used cryogenically-rated suits instead of vacuum-rated suits. They need to fly high to get where they need to be, and scan quickly. They also need to get back home quickly. Their main problem is that the heaters aren't powerful enough; we've seen the energy output these suit plants can produce; they could all be glowing white-hot if necessary.

That, and running flight systems will drain batteries quicker. Might be less heat loss, but I doubt they'd come out ahead.


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PostPosted: Sun Mar 19, 2017 1:54 pm 
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There was scene in classic science fiction - either Haldeman's Forever War, or Heinlein's Starship Troopers - where a drill sergeant explains why you have to keep the powered armor's radiator, mounted on the back, from hitting Pluto's ice.

Basically it turns you into a rocket and kills you.

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PostPosted: Sun Mar 19, 2017 6:00 pm 
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rleggett wrote:
There was scene in classic science fiction - either Haldeman's Forever War, or Heinlein's Starship Troopers - where a drill sergeant explains why you have to keep the powered armor's radiator, mounted on the back, from hitting Pluto's ice.

Basically it turns you into a rocket and kills you.

I think it was in The Forever War that allowing the radiator fins to touch a solidified-gas surface caused the solid to flash into gas, resulting in something very like an old-fashioned hand grenade going off just below the nape of your neck. It happened to a trainee on-camera . . . The armor wasn't up to that.

--FreeFlier


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PostPosted: Mon Mar 20, 2017 1:03 am 
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FreeFlier wrote:
rleggett wrote:
There was scene in classic science fiction - either Haldeman's Forever War, or Heinlein's Starship Troopers - where a drill sergeant explains why you have to keep the powered armor's radiator, mounted on the back, from hitting Pluto's ice.

Basically it turns you into a rocket and kills you.

I think it was in The Forever War that allowing the radiator fins to touch a solidified-gas surface caused the solid to flash into gas, resulting in something very like an old-fashioned hand grenade going off just below the nape of your neck. It happened to a trainee on-camera . . . The armor wasn't up to that.

--FreeFlier

Damn. I wonder how the math on that actually checks out.


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PostPosted: Mon Mar 20, 2017 8:25 am 
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ExenTrik wrote:
FreeFlier wrote:
rleggett wrote:
There was scene in classic science fiction - either Haldeman's Forever War, or Heinlein's Starship Troopers - where a drill sergeant explains why you have to keep the powered armor's radiator, mounted on the back, from hitting Pluto's ice.

Basically it turns you into a rocket and kills you.
I think it was in The Forever War that allowing the radiator fins to touch a solidified-gas surface caused the solid to flash into gas, resulting in something very like an old-fashioned hand grenade going off just below the nape of your neck. It happened to a trainee on-camera . . . The armor wasn't up to that.
Damn. I wonder how the math on that actually checks out.

I would expect Haldeman to have calculated it as accurately as he could . . . after all, this is the man who apologized to his readers for using the wrong term for a very high-powered laser . . . myriawatt instead of petawatt, IIRC.

--FreeFlier


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PostPosted: Mon Mar 20, 2017 11:34 am 
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rleggett wrote:
There was scene in classic science fiction - either Haldeman's Forever War, or Heinlein's Starship Troopers - where a drill sergeant explains why you have to keep the powered armor's radiator, mounted on the back, from hitting Pluto's ice.

Basically it turns you into a rocket and kills you.


It was The Forever War, and it was Charon, not Pluto.


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PostPosted: Mon Mar 20, 2017 6:13 pm 
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Barmaglot wrote:
rleggett wrote:
There was scene in classic science fiction - either Haldeman's Forever War, or Heinlein's Starship Troopers - where a drill sergeant explains why you have to keep the powered armor's radiator, mounted on the back, from hitting Pluto's ice.

Basically it turns you into a rocket and kills you.


It was The Forever War, and it was Charon, not Pluto.

Close enough. That's literally right next door.

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PostPosted: Tue Mar 21, 2017 12:10 am 
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FreeFlier wrote:
I would expect Haldeman to have calculated it as accurately as he could . . . after all, this is the man who apologized to his readers for using the wrong term for a very high-powered laser . . . myriawatt instead of petawatt, IIRC.

--FreeFlier

I was mostly asking because we only directly observed Pluto recently. The makeup of the surface and atmosphere might be a tad different.


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PostPosted: Tue Mar 21, 2017 8:15 am 
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ExenTrik wrote:
FreeFlier wrote:
I would expect Haldeman to have calculated it as accurately as he could . . . after all, this is the man who apologized to his readers for using the wrong term for a very high-powered laser . . . myriawatt instead of petawatt, IIRC.
I was mostly asking because we only directly observed Pluto recently. The makeup of the surface and atmosphere might be a tad different.

Now the accuracy of the planetology I don't know about . . . it would have been the best he had available, though, and the general conditions were well known.

--FreeFlier


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PostPosted: Wed Mar 22, 2017 6:51 am 
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I remember the incident from Forever War, and also another story from my youth, where a Plutonian explorer has a trip-and-fall and punctures one of their air tanks - which is bad not because they're in (immediate) danger of asphyxiating, but because the escaping gas flash-freezes them to the terrain. Fortunately, someone happens along who can melt the "ice" and free them...


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