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From: Cryptoengineer <petertrei@gmail.com>
Newsgroups: rec.arts.comics.strips,rec.arts.sf.written
Subject: Re: xkcd: Sun Avoidance
Date: Wed, 1 Jan 2025 14:59:27 -0500
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On 1/1/2025 1:00 PM, Peter Fairbrother wrote:
> 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."
>>>>>
>>>>> What book is that ?  Please it is not a book about a whale.
>>>>>
>>>>> Lynn
>>>>
>>>> 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.
>>>>
>>>
>>> The story is "The Golden Apples of the Sun".
>>>
>>> "North" is just away from the Sun. They have plucked the apple and 
>>> can now go home...
>>>
>>> ... 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.
>>>
>>> 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.

Thanks. Interesting!

pt