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Traveling to the Sun: Why Won’t Parker Solar Probe Melt?

nasa.gov

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Re: Traveling to the Sun: Why Won’t Parker Solar Probe Melt?

#71

Post by perlgeek »

netfire wrote: post #66

The article makes it sound like there is no possible way for the probe to melt. Is this actually the case? Is there no possibility that manufacturer defects or a solar anomaly that could cause unexpected problems? I don’t want to downplay the good design and engineering that went into this, but should we be so confident without actually having done something like this thousands of times?

> Is there no possibility that manufacturer defects or a solar anomaly that could cause unexpected problems?

There sure is. At least two of the systems (positioning and water cooling) are active systems that could fail.

> but should we be so confident without actually having done something like this thousands of times?

"we" are confident enough that we rely on it to protect a > 1 billion USD probe. What's the use in adding a lot of ifs and maybes to some piece of marketing/explanation?

If it fails, adding some ifs and maybes to a marketing video won't really change anything.

Re: Traveling to the Sun: Why Won’t Parker Solar Probe Melt?

#72

Post by perlgeek »

lifeformed wrote: post #70
Nokinside wrote: post #67

Earlier quoted context omitted.

Thank you. I was wondering just this. Heat resistant material will eventually reach equilibrium where the back side is almost as hot as the front side unless it's cooled somehow.

Also, the cool side of the craft will stay cool by radiating its heat away into space.

... which only works due to the low density of corona.

In a thick atmosphere like earth, heat radiation comes from all sides, so no chance at radiating off very much heat.

Re: Traveling to the Sun: Why Won’t Parker Solar Probe Melt?

#73

Post by superkuh »

smueller1234 wrote: post #46
hutzlibu wrote: post #19

Earlier quoted context omitted.

"Why is the corona itself millions of degrees hotter than the surface? I suspect the answer to all those questions is simply gravity, but it will be nice to verify such things with data" Can you explain your hypothesis a bit?

Not GP, but here's an article that talks about it. Note that this is relatively recent. It's not something that was thoroughly understood in ancient times exactly. https://www.nasa.gov/feature/goddard/sounding-rockets/strong...

> https://www.nasa.gov/feature/goddard/sounding-rockets/strong...

It explains the temporal heating behavior at some scales. But it doesn't give a mechanism of heating. It could be electron beam target heating. But it could also be mediated by plasma waves.

The electron beams need acceleration and the most common suggestion is x-point magnetic reconnection providing up and down voltage gradients due to changing magnetic field. But the amount of electrons needed is unphysically large; the entire electron contents of the relevant volume of the corona.

There are plasma wave models that don't require unphysically large parameters.

These two (and a couple other) options aren't clarified by the observation of heating profiles. With the launch of Parker Solar Probe and the DKIST (diffraction limited solar telescope) the two models above will finally be testable. Spectroscopy of ion species by DKIST will tell what kind of heating is happening and Solar Probe will be there to measure the input from the corona.

Re: Traveling to the Sun: Why Won’t Parker Solar Probe Melt?

#74

Post by hirsin »

netfire wrote: post #66

The article makes it sound like there is no possible way for the probe to melt. Is this actually the case? Is there no possibility that manufacturer defects or a solar anomaly that could cause unexpected problems? I don’t want to downplay the good design and engineering that went into this, but should we be so confident without actually having done something like this thousands of times?

Manufacturing defects are part of engineering - they're good at this and there will be multiple scans done of the shield before it's sent up (x-rays etc) to check for defects.

But I'm also curious about what happens in the event of a solar flare or similar - from an engineering standpoint, what's their safety margin? Solar density goes up two hundred percent?

Re: Traveling to the Sun: Why Won’t Parker Solar Probe Melt?

#75

Post by Nokinside »

lifeformed wrote: post #70
Nokinside wrote: post #67

Earlier quoted context omitted.

Thank you. I was wondering just this. Heat resistant material will eventually reach equilibrium where the back side is almost as hot as the front side unless it's cooled somehow.

Also, the cool side of the craft will stay cool by radiating its heat away into space.

When the heat flow trough the material reaches equilibrium, the back will radiate exactly as much heat as the front side receives. At that point the heat shield serves no purpose.

Re: Traveling to the Sun: Why Won’t Parker Solar Probe Melt?

#76

Post by samstave »

newscracker wrote: post #45

Towards the end, it says: > “After launch, Parker Solar Probe will detect the position of the Sun, align the thermal protection shield to face it and continue its journey for the next three months, embracing the heat of the Sun and protecting itself from the cold vacuum of space.” What a phenomenal piece of engineering! The article was not only fascinating to read as a non-astronomer/lay person, but it also makes it…

Yeah... so if you could just come in on SUNday... that'd be great. thanksssss.

Re: Traveling to the Sun: Why Won’t Parker Solar Probe Melt?

#77

Post by perlgeek »

close04 wrote: post #9

Any reason why they're using water for cooling? There's no other liquid with lower density and perhaps better thermal properties? I imagined they would try to save weight in some places if it allows them more freedom in others. Although I have no idea how much water is used in the first place so it might be a moot point.

Not a spacecraft engineer, merely somebody who has studied physics a long time ago, so take my answer with a grain of salt.

Basically, there are two ways you can design a cooling system: one that involves phase change, and one that simply transports heat from A to B by moving a heat carrier, usually a liquid.

Phase change systems typically have a higher efficiency, because the phase change has larger relative energy than heat capacity. But it also has two disadvantages: it only works near the boiling point of the medium, and you need to deal with all the pressure changes that come with a phase change.

The Parker probe seems to use a "mere" transport, and there the heat capacity and the working range of the medium is very important, and water is a pretty good choice on both of these criteria.

Oh, and you also don't want something very corrosive to destroy your expensive space craft from the inside :-)

IIRC the ISS uses two cooling systems, one based on water that is used throughout the station, and then an ammonium-based system that takes the heat off the water and transports it to the heat radiators. But on the ISS, maintenance is possible.

Re: Traveling to the Sun: Why Won’t Parker Solar Probe Melt?

#78

Post by netfire »

perlgeek wrote: post #71
netfire wrote: post #66

The article makes it sound like there is no possible way for the probe to melt. Is this actually the case? Is there no possibility that manufacturer defects or a solar anomaly that could cause unexpected problems? I don’t want to downplay the good design and engineering that went into this, but should we be so confident without actually having done something like this thousands of times?

> Is there no possibility that manufacturer defects or a solar anomaly that could cause unexpected problems? There sure is. At least two of the systems (positioning and water cooling) are active systems that could fail. > but should we be so confident without actually having done something like this thousands of times? "we" are confident enough that we rely on it to protect a > 1 billion USD probe. What's the use in…

Doesn’t it undermine the credibility of NASA if something goes wrong? The public who is the audience for this article is also paying the bills (through taxes). I’d settle for just changing “won’t melt” to “shouldn’t melt”. I think that appropriate for something that’s never been attempted.

Re: Traveling to the Sun: Why Won’t Parker Solar Probe Melt?

#79

Post by dawnerd »

netfire wrote: post #78
perlgeek wrote: post #71

Earlier quoted context omitted.

> Is there no possibility that manufacturer defects or a solar anomaly that could cause unexpected problems? There sure is. At least two of the systems (positioning and water cooling) are active systems that could fail. > but should we be so confident without actually having done something like this thousands of times? "we" are confident enough that we rely on it to protect a > 1 billion USD probe. What's the use in…

Doesn’t it undermine the credibility of NASA if something goes wrong? The public who is the audience for this article is also paying the bills (through taxes). I’d settle for just changing “won’t melt” to “shouldn’t melt”. I think that appropriate for something that’s never been attempted.

Either way we’re chucking lots of money at the sun so if it fails we still learn something, not to mention developed a lot of technologies along the way.

Re: Traveling to the Sun: Why Won’t Parker Solar Probe Melt?

#80

Post by msravi »

> Particles may be moving fast (high temperature), but if there are very few of them, they won’t transfer much energy (low heat). Since space is mostly empty, there are very few particles that can transfer energy to the spacecraft.

That explains why energy is not transferred by conduction or convection to the spacecraft. But what about energy (heat) transfer by radiation? Why won't the spacecraft get all the energy from radiation and have its temperature shoot up?

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