Thursday, November 22, 2018

SUN - Parker Solar Probe



-  2168  -  SUN  -  Parker Solar Probe.  The mission's objectives include tracing the flow of energy that heats and accelerates the sun's corona and solar wind, determining the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind and explore mechanisms that accelerate and transport energetic particles.
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 --------------------------------  2168  -  SUN  -  Parker Solar Probe
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-  The Parker Solar Probe was launched August 12, 2018.   It is scheduled to reach the sun's outer atmosphere in December.  Although the probe itself is about the size of a car, a powerful rocket is needed to escape Earth's orbit, change direction in space and slow down as it reaches the sun.
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-  The launch window was chosen because the probe will rely on Venus to help it achieve an orbit around the sun.  Six weeks after launch, the probe will encounter Venus' gravity for the first time. It will be used to help slow the probe, like pulling on a handbrake, and orient the probe so it's on a path to the sun.
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-  The launch energy to reach the Sun is 55 times that required to get to Mars, and two times that needed to get to Pluto
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-  The Earth is 93 million miles from the sun and the probe will reach to within 3.85 million miles of the surface.
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-  The probe will have to withstand heat and radiation never previously experienced by any spacecraft, but the mission will also address questions that couldn't be answered before. Understanding the sun in greater detail can also shed light on Earth and its place in the solar system.
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-  The Parker Solar Probe will take seven flybys of Venus that will essentially give a gravity assist, shrinking its orbit over the course of nearly seven years.  The probe will orbit within 3.9 million miles of the sun's surface in 2024, closer to the star than Mercury. Although that sounds far, researchers equate this to the probe sitting on the 4-yard line of a football field and the sun being the end zone.
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-  When closest to the sun, the 4½-inch-thick carbon-composite solar shields will have to withstand temperatures close to 2,500 degrees Fahrenheit. However, the inside of the spacecraft and its instruments will remain at a comfortable room temperature. ( See Note 1)
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-   The heat shield is 2.5 meters wide.  It is made of foam sandwiched between carbon sheets.  The whole shield is only 11.5 centimeters thick.  White ceramic coating on the face is used  to reflect sunlight.  The hot side will reach 370 C.  The cool side only 30 C.
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-  When the Probe flies by Venus the temperature will be -260C.  Twisted niobium wire is used to hold the hundreds of screws in place during these temperature extreme changes.
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-  Dust will be hitting the telescope lens at 380,000 miles per hour.  But calculations have the lens being only 0.6%  pitted after its 7 year mission. (See Note 2)
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-  The probe will reach a speed of 430,000 miles per hour around the sun, setting a record for the fastest manmade object. On Earth, this speed would enable someone to get from Philadelphia to Washington in one second.
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-  The mission's objectives include tracing the flow of energy that heats and accelerates the sun's corona and solar wind, determining the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind and explore mechanisms that accelerate and transport energetic particles.
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-  The corona is a mystery as to how it can reach temperatures in millions of degrees , 300 times hotter than the surface of the sun?  It is also responsible for the solar winds.  The winds are a outflow of particles accelerated by extreme temperatures to a million miles per hour.
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-  On Earth these solar winds can create aurora that cause electrical blackouts and disrupt satellite communications.
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-  Four suites of instruments will gather the data needed to answer key questions about the sun. FIELDS will measure electric and magnetic waves around the probe, WISPR will take images, SWEAP will count charged particles and measure their properties, and ISOIS will measure the particles across a wide spectrum.
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-  The Alfvén point is the distance from the Sun beyond which the charged particles that make up the solar wind are no longer in contact with the surface of the sun.    If the Parker Solar Probe can reach below the Alfvén point, then we can say the spacecraft has entered the solar atmosphere and touched the Sun.
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-  The mission is scheduled to end in June 2025. The first data download from the Parker Solar Probe is expected next month,  December, 2018, after the probe reaches its first close approach of the sun in November.  It is scheduled to loop around the sun 20 times in 7 years getting as close as 3,900,000 miles.
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-  The Parker Solar Probe will solve some of our star's biggest mysteries.  Stay tuned, there is much more to learn.
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-  Other Reviews available:
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-  2165  -  Why is the sun so hot?
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-  1832  -  How does the sun get its energy?  How does it compare to other stars?  How long will it live?   This Review list 6 other reviews about the sun. 
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-   Note 1:  How much heat must the heat shield dissipate to keep the instruments cool?  When Parker enters space the sun's radiation is 1378 watts/ merer^2.  The shield's reflectivity is 60%. 
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--------------------   1378 watts/ meter^2  =  2 * 5.67 *10^-8 * ( 1 -  0.60  ) * Temperature^4
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----------------------  Temperature^4  =  3.1 * 10^10
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----------------------  Temperature  =  420 Kelvin
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-  When Parker is closest to the sun the radiation temperature will be 250 times greater.
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----------------------  1378 * 250  =  2 * 5.67 *10^-8 * ( 1 -  0.60  ) * Temperature^4
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----------------------  Temperature^4  =  37.6 * 10^12
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----------------------  Temperature  =  1,700   Kelvin
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-  When closest to the sun how much heat energy must Parker be radiating away?
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----------------------- Heat energy  =   1378 * 250  =  344,500 watts  /  meter^2
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-----------------------  The area of the heat shield is 7.8 meters^2
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-----------------------   Power  =  =  344,500 watts  /  meter^2  *   7.8 meters^2  =  2,700,000 watts
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-  Note  2:  The space craft is travelling 380,000 miles per hour. It will be encountering dust grains 1 micron in diameter.  The density of the dust grains when nearest t the sun is 0.005 grains / meter^2.  the telescope lens is 140 centimeters^ 2.  In the 10 days spent nearest to the sun , at perihelion, how many impacts will hit the lens?
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-----------------------  .005 grains / meter^2  *  0.014 meters^2   =   0.00007  impacts per second
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----------------------  1  /  0.00007  seconds per impact  =  14,286 seconds  /  3600  =  3.97 hours
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-----------------------  10 days  *  24 hours / day  /  4 hours per impact  =  60 impacts
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-  November 22, 2018.             An Index of recent Reviews is available.
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 ---------------------   Thursday, November 22, 2018         -------------------------
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