http://www.cbsnews.com/8301-501465_162- ... tag=exclsv
We know it's hot up there but NASA wants to know a bit more about the Sun and its environs. And so sometime before 2018, the agency intends to send a spacecraft into the solar atmosphere.
Artist Representation of Solar Probe Plus
(Credit: NASA)
This will mark the first time that a spacecraft from earth will actually visit a star.
The decision to chart a mission to the Sun also realizes a dream that astronomers almost realized a half century ago, when the National Academy of Science's "Simpson Committee" in 1958 recommended a probe to investigate. Several studies were subsequently carried out testing the feasibility of the project. But nothing came of them.
Since NASA has never sent any vehicle this close to Earth's Sun, the craft will have to be outfitted with a special shield designed to withstand radiation and temperatures exceeding 2550 degrees Fahrenheit. A spokesman for NASA said scientists will depend on simulations to guarantee that the probe can cope with that sort of intense heat.
Dick Fisher, who directs NASA's Heliophysics Division in Washington, said that the planned experiments would help resolve two key questions of solar physics. One is to explain why the sun's outer atmosphere is so much hotter than the sun's visible surface. (In the 1940s researchers discovered the corona's million-degree temperature.) The other is to find out more about how the solar wind that affects Earth and our solar system gets accelerated.
"We've been struggling with these questions for decades and this mission should finally provide those answers," according to Fisher.
Until now, observations of the Sun were recorded from flybys millions of miles away. But the Solar Probe Plus, as it's called, will get close enough so that scientists hope to learn more about the solar corona and the solar wind. In a recent report on a Sun probe, NASA scientists noted that while they may know more about the corona and solar wind than ever before, "the answers to these questions can be obtained only through in-situ measurements of the solar wind down in the corona."
NASA Planning Mission to Visit the Sun
ok, what I want to know from you guys, who know much more physics and engineering than I do, is what you think of the concept of a refrigerator laser, like the one David Brin (astronomer with a masters in applied physics and doctor in philosofy of space exploration) used in his sci-fi book SUNDIVER
a quote from early in book explaining the concept
a quote from early in book explaining the concept
Project Icarus it was called, the fourth space program of that name and the first for which it was appropriate. Long before Jacob's parents were born—before the Overturn and the Covenant, before the Power Satellite League, before even the full flower of the old Bureaucracy—old grandfather NASA decided that it would be interesting to drop expendable probes into the Sun to see what happened.
They discovered that the probes did a quaint thing when they got close. They burned up.
In America's "Indian Summer" nothing was thought impossible. Americans were building cities in space—a more durable probe couldn't be much of a challenge!
Shells were made, with materials that could take unheard of stress and whose surfaces reflected almost anything. Magnetic fields guided the diffuse but tremendously hot plasmas of corona and chromosphere around and away from those hulls. Powerful communications lasers pierced the solar atmosphere with two-way streams of commands and data.
Still, the robot ships burned. However good the mirrors and insulation, however evenly the superconductors distributed heat, the laws of thermodynamics still held. Heat will pass from a higher temperature to a zone where the temperature is lower, sooner or later.
The solar physicists might have gone on resignedly burning up probes in exchange for fleeting bursts of information had Tina Merchant not offered another way. "Why don't you refrigerate?" she asked. "You have all the power you want. You can run refrigerators to push heat from one part of the probe to another."
Her colleagues answered that, with superconductors, equalizing heat throughout was no problem.
"Who said anything about equalizing?" the Belle of Cambridge replied. "You should take all excess heat from the part of the ship were the instruments are and pump it into another part where the instruments aren't."
"And that part will burn up!" one colleague said. "Yes, but we can make a chain of these 'heat dumps,'" said another engineer, slightly more bright. "And then we can drop them off, one by one ..."
"No, no you don't quite understand." The triple Nobel Laureate strode to the chalkboard and drew a circle, then another circle within.
'Here!" She pointed to the inner circle. "You pump your heat into here until it is, for a short time, hotter than the ambient plasma outside of the ship. Then, before it can do harm there, you dump it out into the chromosphere."
"And how," asked a renowned physicist, "do you expect to do that?"
Tina Merchant had smiled as if she could almost see the Astronautics Prize held out to her. "Why I'm surprised at all of you!" she said. "You have onboard a communications laser with a brightness temperature of millions of degrees! Use it!"
Enter the age of the Solar Bathysphere. Floating in part by buoyancy and also by balancing atop the thrust of their refrigerator lasers, probes lingered for days, weeks, monitoring the subtle variations at the Sun, that wrought weather on the Earth.
I beileve the particle flux comes off the sun in regular well-understood flow directions (solar wind) [notwithstanding flares and magnetic disruptions that are 'short lived']. So, and presuming the density of azimuthally directed particles is small - I would propose a probe which has a unit m^2 phase-change cooled shield but that is several hundred meters long in which the cooling fins would reside. Clearly you'd need a very large cooling area to dissipate enough heat from the solar-facing shield by black body radiation alone, but whatever the length it can be held in the shadow of the shield*. Phase-change cooling would mean that the probe can generate internal power from this heat flow.
*(non-intuitive as it may seem, this'd only work for the probe really close up to the Sun because as the distance from the Sun increases so the solar wind ends up at a different angle to the direction towards the sun, and this solution I propose would only work if the solar radiation and solar wind can both be shielded by the same shield)
*(non-intuitive as it may seem, this'd only work for the probe really close up to the Sun because as the distance from the Sun increases so the solar wind ends up at a different angle to the direction towards the sun, and this solution I propose would only work if the solar radiation and solar wind can both be shielded by the same shield)
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rjaypeters
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Re: NASA Planning Mission to Visit the Sun
AcesHigh:
Like millions of others, I enjoy Dr. Brin's writing. Thermocouples and fancier devices transform temperature differences into electrical energy. The sticking points are the details: e.g. how hot, what temperature difference, how much power out?
I don't know the details, but I'd be surprised if Dr. Brin got the concept wrong.
Chrismb:
Please forgive my ignorance: Is your radiator exposed to the infra-red from the surrounding corona?
Like millions of others, I enjoy Dr. Brin's writing. Thermocouples and fancier devices transform temperature differences into electrical energy. The sticking points are the details: e.g. how hot, what temperature difference, how much power out?
I don't know the details, but I'd be surprised if Dr. Brin got the concept wrong.
Chrismb:
Please forgive my ignorance: Is your radiator exposed to the infra-red from the surrounding corona?
I suppose it depends on how much broader the corona is compared to the visible surface of the sun and how close the probe approaches.AcesHigh wrote:One is to explain why the sun's outer atmosphere is so much hotter than the sun's visible surface. (In the 1940s researchers discovered the corona's million-degree temperature.)
"Aqaba! By Land!" T. E. Lawrence
R. Peters
R. Peters
How transparent is the corona, and how much thermal radiation from above would a probe get? The corona is very hot, but being diffuse how much heat would it radiate?
Bottom line, what temperature would a radiator facing deep space from such a probe see?
As far as getting energy from the surrounding hot plasma to power a 'cooling' laser, what would be the cool side of your heat engine?
Bottom line, what temperature would a radiator facing deep space from such a probe see?
As far as getting energy from the surrounding hot plasma to power a 'cooling' laser, what would be the cool side of your heat engine?
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TheRadicalModerate
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Re: NASA Planning Mission to Visit the Sun
Why don't they just land at night?AcesHigh wrote:Since NASA has never sent any vehicle this close to Earth's Sun, the craft will have to be outfitted with a special shield designed to withstand radiation and temperatures exceeding 2550 degrees Fahrenheit. A spokesman for NASA said scientists will depend on simulations to guarantee that the probe can cope with that sort of intense heat.
(Yeah, I know--old joke. Couldn't resist.)
Re: NASA Planning Mission to Visit the Sun
It's a good question, actually [if I understand what you're digging at.]rjaypeters wrote:Chrismb:
Please forgive my ignorance: Is your radiator exposed to the infra-red from the surrounding corona?
The corona is very thin and hot, and my radiators would be cooler but 'massive'.
The BB radiation spectrum of very hot stuff is dominantly peaked at shorter wavelengths. Now imagine that the lower-but-flatter spectrum is drawn with the much peakier spectrum of the corona. What you will find is that in the IR range the emissions from the massive cooler radiator are higher than the same point for the corona, though the peak of the corona is higher than the peak of the cooler radiator. This is because the total area under those curves is equal to the total radiative power, and the total radiative power of a cool/massive thing may be more than a tenuous/hot thing (and I think almost certainly is, in the corona).
Thermal equilibrium may be achieved so long as the total absorbed radiation equals the total emitted radiation, and this is possible between cooler/massive stuff and hot/tenuous stuff because the spectra are different, even though the areas under them are the same. If it were not so then the earth would now be as hot as the solar wind that it orbits within, and it clearly isn't!
I'm not sure the spectral emission is the key to the possibility of something staying cool in a hotter environment.
It might be better to consider the energy as particles. A Corona ejected proton of photon (or electron) may hit the Earth and deposit, say 1,000,000 thermal units. But these partials are at low density compared to the receiving object (Earth's atmosphere). Once heated by the impact the atmospheric molecule then emits black body radiation(lower energy photons) back into space. This radiation has perhaps 1 thermal unit of energy. There are two keys. First as mantioned the incident heating particals are much rarer than the atmospheric molecules, so, while each impact imparts a lot of energy, the frequency of these impacts on each atmospheric particle (or dirt molecule) is such that the molecule has a long time to emit the lower energy black body radiation, before it chances to be hit by another high energy particle. So the longer cooling emission times compensates for the much shorter high energy absorption times. The other key is that the vast majority of the sky is at the temperature of ~ 3 degrees Kelvin. So there is a good thermal gradient for the black body radiation of the Earth's atmosphere to dump heat into. But, you ask- if we are embedded in the Solar corona, isn't this hot gas surrounding us? True, but again the density is important. In this regard consider the corona like a window with a lot of tiny lights stuck to it (high energy particles). But the number of these lights and their size is so small, that the vast majority of the window is exposed to cold space. This energy intensity (energy per particle X number of particles) is counterbalanced by the much lower energy but much higher numbers of atmospheric molecules (or what ever substance is absorbing, reflecting, and emitting this input load) that can radiate their accumulated energy to the cold areas between the small lights.. An equilibrium between the hot Sun and cold space is reached, and with the current distance and total average energy output of the Sun , the resultant equilibrium is convenient for us.
Dan Tibbets
It might be better to consider the energy as particles. A Corona ejected proton of photon (or electron) may hit the Earth and deposit, say 1,000,000 thermal units. But these partials are at low density compared to the receiving object (Earth's atmosphere). Once heated by the impact the atmospheric molecule then emits black body radiation(lower energy photons) back into space. This radiation has perhaps 1 thermal unit of energy. There are two keys. First as mantioned the incident heating particals are much rarer than the atmospheric molecules, so, while each impact imparts a lot of energy, the frequency of these impacts on each atmospheric particle (or dirt molecule) is such that the molecule has a long time to emit the lower energy black body radiation, before it chances to be hit by another high energy particle. So the longer cooling emission times compensates for the much shorter high energy absorption times. The other key is that the vast majority of the sky is at the temperature of ~ 3 degrees Kelvin. So there is a good thermal gradient for the black body radiation of the Earth's atmosphere to dump heat into. But, you ask- if we are embedded in the Solar corona, isn't this hot gas surrounding us? True, but again the density is important. In this regard consider the corona like a window with a lot of tiny lights stuck to it (high energy particles). But the number of these lights and their size is so small, that the vast majority of the window is exposed to cold space. This energy intensity (energy per particle X number of particles) is counterbalanced by the much lower energy but much higher numbers of atmospheric molecules (or what ever substance is absorbing, reflecting, and emitting this input load) that can radiate their accumulated energy to the cold areas between the small lights.. An equilibrium between the hot Sun and cold space is reached, and with the current distance and total average energy output of the Sun , the resultant equilibrium is convenient for us.
Dan Tibbets
To error is human... and I'm very human.
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rjaypeters
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chrismb and D Tibbets: Thanks, got it.
chrismb: The only objection I see to your 'massive' radiator is its mass.
My first thought was to launch a dewar filled with (edit: liquid helium) and use the expansion gas to cool the rest of the probe. A further thought is the expansion gas further heated by the solar energy on the rest of probe could drive a turbine for power.
No numbers, just ideas.
chrismb: The only objection I see to your 'massive' radiator is its mass.
My first thought was to launch a dewar filled with (edit: liquid helium) and use the expansion gas to cool the rest of the probe. A further thought is the expansion gas further heated by the solar energy on the rest of probe could drive a turbine for power.
No numbers, just ideas.
Last edited by rjaypeters on Mon Sep 06, 2010 10:30 am, edited 1 time in total.
"Aqaba! By Land!" T. E. Lawrence
R. Peters
R. Peters
Well, if you construct a large, long probe in space with several sections, it'd be a massive undertaking!!rjaypeters wrote:chrismb: The only objection I see to your 'massive' radiator is its mass.
My first thought was to launch a dewar filled with LHe2 and use the expansion gas to cool the rest of the probe.
The choice of coolant would be very interesting. You'd want something that'd be able to cool the shield and also not freeze in space. It would depend a lot on the calculations of required heat dissipation, size of craft and what range of temps it will experience. Perhaps, even, a 3-stage phase change system; molten tin would flow in the heat shield (once melted) which would then flow through a heat exchanger with pure water in a fairly short system and then through another h-ex with a very long methane circuit. Something like that. Show me the environment and assign me a budget, and I'll get to work on it!...
I sent David Brin a message pointing out to discussions on the net saying his refrigerator laser was implausible and asking him if he really thought the concept would work, if it would only work with the physics knowledge of the Galactics (in the books), etc
here is his answer
"Mr. Penna,
Thanks for your thoughtful and interesting message. It truly is gratifying when people write, and I always try to answer.
As a matter of fact, I ran the refrigerator laser past a couple of Nobel Prize winning physicists, back in the 1980s. Plasma physicist Hannes Alfven could find nothing wrong with my reasoning... and found it "plausible."
Remember the comparison to the refrigerator in your kitchen. With an effectively infinite energy source (wall current) your fridge pumps heat from one space (the freezer box) into another space (the surrounding kitchen)... along with the waste heat involved in the process. It simply works.
If the sun's Chromosphere is the 'kitchen' and the ship is the freezer"
here is his answer
"Mr. Penna,
Thanks for your thoughtful and interesting message. It truly is gratifying when people write, and I always try to answer.
As a matter of fact, I ran the refrigerator laser past a couple of Nobel Prize winning physicists, back in the 1980s. Plasma physicist Hannes Alfven could find nothing wrong with my reasoning... and found it "plausible."
Remember the comparison to the refrigerator in your kitchen. With an effectively infinite energy source (wall current) your fridge pumps heat from one space (the freezer box) into another space (the surrounding kitchen)... along with the waste heat involved in the process. It simply works.
If the sun's Chromosphere is the 'kitchen' and the ship is the freezer"
Actually, the last sentence is superfluous.
What you want to keep cold - the ship or the inside of your refrigerator - can only be cooled by adding heat to something else - the kitchen or the sun or whatever.
To DO that, you need to use cool thermodynamic stuff, to make stuff hotter than the outside (kitchen or sun) and then let it go down the pressure/temperature curve to a cold temperature.
And therein lies the rub. The question is how can you send this energy off with a laser?
Sure, lasers carry energy. If you had a 100% efficient laser (instead of ~5-10%) every watt of electricity would become light. You'd have to have a laser pumped by the infrared heat of the refrigerator hot side.
And that, while a cool SF idea, is way, way beyond anyone's engineering concepts that it's at the "crazy" level. We're closer to Tokamaks and warp drives than we are to that.
What you want to keep cold - the ship or the inside of your refrigerator - can only be cooled by adding heat to something else - the kitchen or the sun or whatever.
To DO that, you need to use cool thermodynamic stuff, to make stuff hotter than the outside (kitchen or sun) and then let it go down the pressure/temperature curve to a cold temperature.
And therein lies the rub. The question is how can you send this energy off with a laser?
Sure, lasers carry energy. If you had a 100% efficient laser (instead of ~5-10%) every watt of electricity would become light. You'd have to have a laser pumped by the infrared heat of the refrigerator hot side.
And that, while a cool SF idea, is way, way beyond anyone's engineering concepts that it's at the "crazy" level. We're closer to Tokamaks and warp drives than we are to that.
Wandering Kernel of Happiness