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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?

#91

Post by firebacon »

marsRoverDev wrote: post #83
firebacon wrote: post #49

Earlier quoted context omitted.

Thanks for the reply! So what you're saying is that it's just a "normal" over-the-air software update. I.e. you add some new functionality and then do a full system test of all functions of the software before replacing the entire image? That makes sense, but is almost a bit disappointing. After all, that is exactly how it works for the boring systems here on earth. From various wired & co articles I had the impressi…

Yes, we can send commands to the spacecraft once it's up there to do thing like modify memory or hard drive contents directly, turn on/off or command payloads and equipment. The full list is pretty exhaustive - anything you could want to be able to do, you can command manually. These things aren't 100% autonomous (though they have autonomous elements in the software). There is also a way to send pre-programmed task l…

Very interesting! Is this kind of command capability (e.g. ability to modify memory contents) something that is usually only available on "non-critical" subsystems, or would you generally expect to also find it on critical components, like the communication or navigation modules?

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

#92

Post by netfire »

natep wrote: post #87
netfire wrote: post #82

Earlier quoted context omitted.

For sure, but it would be a shame if NASA lost confidence and trust (and possibly funding) with their stakeholders (the public), because they weren’t more upfront about the potential risks. As a scientific organization that has experienced significant (and expensive) failures before, I expect better.

It seems like you want to discredit NASA now ("shouldn't melt") vs some imagined possibility("won't melt" but it does). With the amount of design, analysis, testing, and independent review and verification of the systems, backup systems, triply redundant systems, and autonomy, we can be as sure of it not melting as we can be sure of anything. And we certainly spent a large amount of money on this (about 1/10th of the…

Not at all. I expect NASA has done as much due diligence, planning, testing, and verification as possible. I just don’t think they are being upfront as they should be about the possible risks for a previously unattempted scientific endeavor. We’ve had massive failures (including NASA itself), in environments that are much better understood and with systems that have actually had exposure to those environments.

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

#93

Post by mcbits »

sebazzz wrote: post #54
mpweiher wrote: post #7

Earlier quoted context omitted.

> Stick your hand into into a pot of water at 100 celsius ..and: please don't! :)

Fast reflexes will prevent major damage. It won't prevent pain though.

Maybe for a fingertip, but I wouldn't try it with a full hand. The water stuck to the hand will take time to cool down no matter how fast you remove it. Unless you're just saying second degree burns don't count as major damage...

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

#94

Post by reaperducer »

kijin wrote: post #23
chiph wrote: post #4

Dad joke: "They'll go at night" But really, it's cool that they're using carbon-carbon protection similar to that which was originally developed for the leading edges of the Space Shuttle. And I really want to know how they built foamed carbon for the interior. I'm guessing that they're using white ceramic paint on top instead of a reflective foil shield (like the Webb uses) because the foil would be shredded by the…

I'm curious about the foam, too. Normally, foam contains a lot of air. But that kind of foam will blow itself apart in a vacuum. How do they make foam where all the air pockets are replaced with vacuum? Is vacuum-filled foam a better or worse insulator than air-filled foam?

Normally, foam contains a lot of air. But that kind of foam will blow itself apart in a vacuum.

In the video, Thermal Protection System Engineer Betsy Congdon says it's 97% "air."

I can't say whether it's actually air, or she's simplifying things for the general public or not.

She also says twice that "water" is used in the radiators. But I'd have to believe that NASA's using something that absorbs/dissipates heat a little more efficiently. Perhaps whatever it is will end up in desktop gaming rig cooling systems eventually.

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

#95

Post by natep »

firebacon wrote: post #27
JonoW wrote: post #10

>This all has to happen without any human intervention, so the central computer software has been programmed and extensively tested to make sure all corrections can be made on the fly. I'd love to get some deeper insight into how NASA writes and tests software, I can only guess it's a million miles from how most of us work. Anyone know of any good talks, articles from engineers there?

The part that I find the most intriguing is "corrections can be made on the fly". I can see how you would ensure reliability through proper requirements specification, a good software development process, separate independent implementations and extensive verification. However, every time I read a popsci article about space flight software, they talk about this capability to push new code to the spacecraft while it i…

In this case, the "corrections on the fly" refer to all of the real-time responses that the software makes without ground involvement. In the case of a solar limb sensor detecting the sun, the probe will abandon its data collection for that near approach, and go into an emergency response that has been made as straightforward and deterministic as possible, to maximize the chances of recovery for all single-fault and some double-fault scenarios.

To answer your question about software upload, the PSP has 3 redundant CPUs (primary, hot spare, backup spare), and each has multiple boot images. To upload software, the team uploads it to an inactive image of the backup spare CPU, promotes it to hot spare for long enough to collect the data it needs, reboots it into the new image, and then rotates it into the primary role, which is a seamless transition unless something goes wrong, and then the new hot spare takes over again within a second. Once they're sure the software is working, they can update the other CPUs. Before any of this, new software is tested on identical hardware set up on the ground with physics simulations.

See also, "Solar Probe Plus Flight Software - An Overview" from http://flightsoftware.jhuapl.edu/files/_site/workshops/2015/

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

#97

Post by reaperducer »

saalweachter wrote: post #41
JonoW wrote: post #10

>This all has to happen without any human intervention, so the central computer software has been programmed and extensively tested to make sure all corrections can be made on the fly. I'd love to get some deeper insight into how NASA writes and tests software, I can only guess it's a million miles from how most of us work. Anyone know of any good talks, articles from engineers there?

There are a lot of really good links, but to be honest 99% of the secret to writing bulletproof code is “write the most simple, boringest program you can”. Which is not to say that what NASA and its contractors do isn’t cool or that they don’t spent ungodly amounts of time and money on testing and verification, but you also don’t load one line of code more than is absolutely necessary onto a machine that absolutely m…

you also don’t load one line of code more than is absolutely necessary

Coincidentally, I spent the weekend banging around with an old TRS-80 Model 100, and it's been very interesting to see what workarounds and compromises were made to conserve space.

For example, the machine ships with no DOS at all, so if you're working with cassettes or modem only, you don't have that overhead.

If you do add a floppy drive, when you first plug it in, you flip some DIP switches on the drive and it acts like an RS-232 modem, and you can download a BASIC program from the drive into the computer that, when run, generates a machine-language DOS program and loads it out of the way into high memory.

I don't have one of those sewing machine drives, so I went with a third-party DOS, which weighs in at... wait for it... 747 BYTES.† An entire disk controller with command line interface in 2½ tweets.

† http://bitchin100.com/wiki/index.php?title=TEENY.CO_MANUAL

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

#98

Post by cwmoore »

A key sensor (Faraday cup [1]) for studying the solar wind, outside of the shield, was constructed of not one but apparently four varieties of unobtainium: Titanium-Zirconium-Molybdenum alloy, acid-etched tungsten, sapphire crystal tubes, and niobium wiring. All together these could make a fascinating engagement ring.

[1] https://en.wikipedia.org/wiki/Faraday_cup

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

#99

Post by [deleted] »

trgv wrote: post #59
nextstep wrote: post #58

Inches? A yard stick? Millions of degrees Fahrenheit? I’m American and I’m embarrassed by this. This is science, make it easy for people to understand. Use SI units, please.

It's written for a general American audience so it makes sense to use those units.

[deleted]

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

#100

Post by mturmon »

austincheney wrote: post #14

http://earthsky.org/space/heat-shield-parker-solar-probe It appears the heat shield is a carbon sheet sandwich. At first I was guessing some form of tungsten-carbine, but that is the traditional material of NASA heat shields. > Why is the solar wind a breeze closer to the sun but a supersonic torrent farther away? Why is the corona itself millions of degrees hotter than the surface? I suspect the answer to all those…

No. The latter question is the “coronal heating problem “ which is a major unexplained phenomenon in Physics: https://en.m.wikipedia.org/wiki/Corona#Coronal_heating_probl...
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