Re: xkcd: Sun Avoidance

On 01/01/2025 04:16, Cryptoengineer wrote:

On 12/29/2024 8:31 PM, Peter Fairbrother wrote:

On 27/12/2024 06:53, Your Name wrote:

On 2024-12-27 06:03:24 +0000, Lynn McGuire said:

On 12/26/2024 3:57 PM, Ted Nolan <tednolan> wrote:

[...]

"North," murmured the captain. "North."

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What book is that ?  Please it is not a book about a whale.
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Lynn

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Mr Google says it is Ray Bradbury's "The Golden Apples of the Sun", which is an anthology of 22 short stories, so I don't know which story it is from.
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The story is "The Golden Apples of the Sun".
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"North" is just away from the Sun. They have plucked the apple and can now go home...
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... unlike the Parker Solar Probe, which will if all goes as planned get close at least twice more, before finally getting close again and exposing its instruments without shielding, which will destroy them. The solar shield will then continue orbiting for a few million years.
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I kinda feel sorry for it, but I am anthropomorphising too much. However for some perhaps not-too-distant future AI controlled probes..

 There's four more perihelions scheduled during 2025. I don't think
there's any plan to deliberately destroy it.

The primary mission ends after two more close passes, iirc perihelia 23 and 24, in March and June this year (2025). Both of these will be at the same 6.2 million kilometres from the Sun as the recent pass.
After that it depends on onboard fuel, and Parker's fate has not been decided: they may well extend the mission and keep it going as-is for several years, using the remaining fuel for attitude adjustment (needed for both approaching the Sun and to get data back). I don't know whether there is any chance of another Venus gravity assist and getting even closer to the Sun, but that would be fun if possible.
However there is an end-of-life contingency plan to directly expose the instruments as the fuel runs out and get some other data. I don't know how they intend to get the data back afterwards, but doing so is part of that plan.

It will fail eventually, but the the solar shield is unlikely to
last long when it's backside gets exposed.

I don't think that will make much difference, though I haven't done any detailed analysis of the question. Carbon-carbon is black and absorbs sunlight better than the white alumina coating, but that coating only gets to 1,400C at closest approach.
The carbon-carbon heatshield can get to over 3000K before melting. The alumina coating would melt at about 2100C. They put the coating on to decrease total heat flux and keep the back of the heatshield at 300C rather than to limit the working temperature of the carbon-carbon. Also the coating is lighter than the extra thickness of carbon foam insulation which would be needed if the coating wasn't there.
If it stayed close to the Sun all the time then the protons in the solar wind might be a chemistry problem with the carbon, but as they are only close to the Sun for an hour or so every three months I think it might last a few million years.
The heatshield is pretty fluffy and might get blown about by solar winds.
Someone at NASA said a few billion years, but that is anther question.
Peter Fairbrother