
Traveling to the Sun: Why Won't Parker Solar Probe Melt? - dnetesn
https://phys.org/news/2018-07-sun-wont-parker-solar-probe.html
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ArtWomb
Baby steps to humanity's first Dyson Sphere ;)

Graphene oxide sheets may be the ideal candidate for solar harvesting. Full
radiation spectrum absorbance. High conductivity. Thermoelectric power
generation that increases at very high (3000K+) temperatures. Lightweight.
Inexpensive. 3D-printable. With cloth-like flexibility.

Might be time to fund a zero-gravity graphene factory in low Earth orbit.

[https://phys.org/news/2017-07-gravity-graphene-space-
applica...](https://phys.org/news/2017-07-gravity-graphene-space-
applications.html)

~~~
Robotbeat
Thermoelectric has terrible efficiency, tho. Also, graphene isn’t inexpensive,
and actual macroscopic conductivity is much worse than aluminum or copper.

~~~
taneq
Efficiency may not be much of an issue if you're spinning up a kilometers-
wide, microns-thick graphene sheet at a Lagrange point or something.

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endymi0n
At the solar flux levels at the point of that probe (light intensity decays by
distance squared), efficiency is probably mostly irrelevant. What's the
challenge though is how you irradiate all the heat away to provide a large
enough temperature delta.

~~~
throwwit
It’d be neat to see a divergent lens made of carbon metamaterial at the aft of
the craft. (... or convergent depending on the shape of the craft)

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MarcScott
I thought at first that an IMAX projector must be some sort of solar
simulator, and the similar acronym to the ones in movie theaters was just a
coincidence.

Turns out I was wrong and they just used old IMAX projectors they purchased
off eBay.

[https://astronomynow.com/2018/05/01/old-imax-projectors-
simu...](https://astronomynow.com/2018/05/01/old-imax-projectors-simulate-sun-
in-key-test-for-parker-solar-probe/)

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apatters
This is a very naive question, but is there some distance from the sun at
which it would heat an object in space to a temperature that we would consider
comfortable?

I guess the obvious answer would be "the distance which the Earth is at," but
what I really mean is could you be floating around in a spacesuit or some
object with minimal shielding and you would neither overheat nor freeze to
death.

~~~
DoreenMichele
As a wild guess, probably further out then the Earth. The atmosphere here
plays an important role in keeping us comfy. Even so, the tropical sun can be
too much. Heat waves can be too much. Desert heat can be too much. Etc.

~~~
Groxx
A brief google informs me that the sunny side of the Moon is around 127˚
Celsius, while Phobos goes up to about -4˚. So somewhere most of the way to
Mars probably?

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DoreenMichele
For other half-asleep Americans, 127 C is about 260 F.

(100C is the boiling point. 0C is freezing.)

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Monory
At 1 atmosphere of pressure. Important to remember when we are talking about
Moon and such.

~~~
DoreenMichele
I had to think about that for a bit. I've tried to Google it to better
understand it. I am not immediately coming up with an elucidation.

Anyone got a link to a quick and dirty explanation of how the vacuum of space
would impact this?

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Groxx
Air pressure on earth literally squeezes the water together, preventing it
from turning into a gas until it's at a higher temperature.

More generally: practically all phase-changes depend on both temperature and
pressure. Lower pressure almost behaves like higher temperature... within
certain ranges (and it varies for every material).

E.g. for water, note that there are three major regions in its phase
diagram[1]. At human-normal scales (the red horizontal line is 1 atmosphere)
we see water boil/freeze at 100 and 0 celsius. If you lower the pressure
though, you'll see there's a spot where all three phases meet, and below that
there's no liquid phase separating solid and gas. When it's in near vacuum,
you literally can't have water - ice evaporates (sublimates) directly into a
gas, with no intermediate phase.

Given the diagram, this seems to happen somewhere around -60c in a serious
vacuum. So in space or on the surface of the moon (without an atmosphere /
something pressurizing it) you simply can't have liquid water - a portion of
it will evaporate almost immediately, which steals energy from the remaining
portion, causing it to freeze. After that, the solid portion just sublimates
away (because the sunny side is 127c, well above the temperature needed to
turn it into a gas).

[1]:
[https://en.wikipedia.org/wiki/Phase_diagram#/media/File:Phas...](https://en.wikipedia.org/wiki/Phase_diagram#/media/File:Phase_diagram_of_water.svg)

~~~
DoreenMichele
Thank you.

What I am trying to figure out specifically -- to mental model -- is what
impact this has on human comfort, per the original question.

So I have lived in very hot and humid places -- like Georgia, where it is
often around 100F in summer -- and I have lived in even hotter places with a
much dryer climate -- like the Mojave Desert, where it can get to 115F and I
would wait until nightfall to go for walks for exercise at 99F and no sun.
Humidity does make a big difference in how uncomfortable a temperature is. If
it is hot and dry, you can stay reasonably comfortable if you get enough
fluids and electrolytes into you and stay out of direct sunlight.

I'm trying to fit this into a mental model of that sort. Like is a boiling
temperature going to burn you? Or, you know "It's a dry heat, man!" only "It's
in the vacuum of space, man!"

Thanks to anyone who replies to this.

~~~
Groxx
Aaah, gotcha. Yeah, that's definitely fuzzier... like, what does boiling feel
like if it's room temperature.

I imagine some of it depends on what our heat-sensors actually react to. At
the least-interesting case, seems like being above boiling without heat would
feel fizzy, just because it's physically doing that to the outer layers of
your skin. Or something like laser hair removal, where it kinda feels like a
hard slap.

~~~
DoreenMichele
Thanks.

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blacksmith_tb
A very cool mission (pun intended)! It makes me wonder if it would be possible
to exploit that huge temperature differential behind the heatshield to
generate power...

~~~
AngryData
There are ways, piezoelectric devices can generate power off temperature
differential. And mechanically you could put a stirling engine on although the
torque and rotational force likely would not be ideal.

~~~
jschwartzi
That seems really complicated for something that the solar arrays do with no
moving parts.

~~~
greglindahl
Note the quote from a while ago:

> They are mounted to motorized arms that will retract almost all of their
> surface behind the Thermal Protection System – the heat shield – when the
> spacecraft is close to the Sun.

Yes, there's a moving part. It only has to move twice (deploy, mostly retract)
but it's still a moving part.

~~~
jschwartzi
A motor that predictably moves an object from one point to another can be much
more reliable than an array of heat-driven reciprocating engines that have to
be in constant motion and rely on conducting heat toward the internals of the
spacecraft in order to function.

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carloscm
From the article:

"The chips that produce an electric field for the Solar Probe Cup are made
from tungsten, a metal with the highest known melting point of 6,192 F (3,422
C). Normally lasers are used to etch the gridlines in these chips—however due
to the high melting point acid had to be used instead."

I had no idea tungsten was used to make ICs. What kind of density is achieved
by laser etching (on tungsten or otherwise)?

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sp332
That's not as close as I was expecting for a solar probe. It's about the same
distance as Mercury.

~~~
dmurray
The folksy comparison in the article is misleading, or just wrong. The probe
is going closer than they imply.

> If Earth was at one end of a yard-stick and the Sun on the other, Parker
> Solar Probe will make it to within four inches of the solar surface

Perhaps they meant 4 cm.

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Udik
This stuff with yardsticks, inches,and Fahrenheit is annoying.

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duxup
Cubits it is then!

On a side note I always thought AUs were a bit silly and self centered....

~~~
ekimekim
IMO light-seconds is actually a really nice unit for interplanetary distances.
1AU ~= 500ls. Not only is the scale nice for human arithmetic, but it serves a
dual purpose of also telling you the light delay.

~~~
adrianN
Lightnanoseconds are a useful measure in everyday life as well. A
lightnanosecond is about 30cm, or 1 foot.

[https://www.youtube.com/watch?v=1-vcErOPofQ&feature=youtu.be...](https://www.youtube.com/watch?v=1-vcErOPofQ&feature=youtu.be&t=275)

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TheOtherHobbes
I love the technology on this - Niobium wire inside sapphire tubes is a total
geek out.

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lukasb
This is SO COOL

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gok
Why don’t they just go at night?

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redial
They want to study the sun not the moon.

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Pulcinella
Well actually at night the Sun is called the Moon.

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mirimir
In Morgan's "Land Fit For Heroes" trilogy, Ringil does talk about the "pale
sun" in the Grey Places, which people there call the "Muhn". But he'd just
never heard of the Moon.

Because it had been destroyed, and became a ring, home of the Sky Dwellers. Or
perhaps an orbital ring, as Stephenson has it in _Seveneves_. But there's
nothing about a bombardment in Morgan's "Land Fit For Heroes". And that brings
up the question about how a Moon breakup would really go.

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skgoa
If the Moon just broke up and did not blow up, the piece might not have been
given much momentum towards Earth. In such a case they would slowly spread out
in a ring. Their orbits would be stable and would decay outwards ever so
slowly, as Earth seeps off their angular momentum.

