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Last Post 22 Mar 2018 11:48 AM by  Nicky Fox
Parker Solar Probe - protection
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Rajesh





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22 Mar 2018 11:25 AM
    (Question from webinar):

    How we have planned to save it from solar heat and radiation?


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    22 Mar 2018 11:30 AM
    Parker Solar Probe has a very high-tech heat shield that will protect everthing behind it from direction solar illuminantions. The spacecraft will be oriented so that the heat shield always faces the Sun when the orbit takes it close to the Sun. Most all of the instruments are hidden behind the heat shield. Only the radio wave antennas (for detecting waves in the solar wind--not for communication) and one solar wind particle detector stick out from behind the shield.


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    22 Mar 2018 11:48 AM
    Every instrument and system on board Parker Solar Probe (with the exception of four antennas and a special particle detector) will be hidden from the sun behind a thermal protection system (TPS)—an eight-foot diameter shield that the spacecraft uses to defend itself against the intense heat and energy of our star.

    Every spacecraft system will be protected except for the two solar arrays that power the spacecraft. When the spacecraft is closest to the sun, the solar arrays will be receiving 25 times the solar energy they would while orbiting Earth, and the temperature on the TPS will reach more than 2,500F (1,370C). The cooling system will keep the arrays at a nominal temperature of 320F (160C) or below.

    The very outermost edges of the solar arrays are bent upward, and when the spacecraft is closest to the sun, these small slivers of array will be extended beyond the protection of the TPS in order to produce enough power for the spacecraft’s systems.

    The incredible heat of the Sun would damage conventional spacecraft arrays. So, like many other technological advances created especially for this mission, a first-of-its-kind actively cooled solar array system was developed.

    The Parker Solar Probe cooling system has several components: a heated accumulator tank that will hold the water during launch; two-speed pumps; and four radiators made of titanium tubes (which won’t corrode) and sporting aluminum fins just two hundredths of an inch thick. As with all power on the spacecraft, the cooling system is powered by the solar arrays—the very arrays it needs to keep cool to ensure its operation. At nominal operating capacity, the system provides 6,000 watts of cooling capacity—enough to cool an average-sized living room.

    Somewhat surprisingly, the coolant used is nothing more than regular pressurized water—approximately five liters, deionized to remove minerals that could contaminate or harm the system. Analysis showed that, during the mission, the coolant would need to operate between 50F (10C) and 257F (125C)—and few liquids can handle those ranges like water.

    The solar arrays feature their own technical innovations. We learned a lot about solar array performance from the [APL-built] MESSENGER spacecraft, which was the first to study Mercury. In particular, we learned how to design a panel that would mitigate degradation from ultraviolet light.

    The cover glass on top of the photovoltaic cells is standard, but the way the heat is transferred from the cells into the substrate of the panel, the platen, is unique. A special ceramic carrier was created and soldered to the bottom of each cell, and then attached to the platen with a specially-chosen thermally conductive adhesive to allow the best thermal conduction into the system while providing the needed electrical insulation.

    While the extraordinary heat of the sun will be the spacecraft’s most intense challenge, the minutes immediately following launch are actually one of the spacecraft’s most critical early performance sequences.

    When Parker Solar Probe launches on board a ULA Delta IV Heavy rocket from Cape Canaveral Air Force Station, Florida, in the summer of 2018, the cooling system will undergo wide temperature swings. There’s a lot to do to make sure the water doesn’t freeze,

    First, temperatures of the solar arrays and cooling system radiators will drop from that in the fairing (about 60F, or 15C) to temperatures ranging from -85F to -220F (-65C to -140C) before they can be warmed by the sun. The pre-heated coolant tank will keep the water from freezing; the specially designed radiators—designed to reject heat and intense temperatures at the sun—will also survive this bitter cold, thanks to a new bonding process and design innovations.

    Less than 60 minutes later, the spacecraft will separate from the launch vehicle, and begin the post separation sequence. It will rotate itself to point at the sun; the solar arrays will release from their launch locks; the arrays will rotate to point to the sun; a latch valve will open to release the warm water into two of the four radiators and the solar arrays; the pump will turn on; the spacecraft will rotate back to a nominal pointing orientation, warming up the two coldest and unactivated radiators; and power from the cooled solar arrays will begin recharging the battery.


    In another first, this complex and critical series of tasks will be completed autonomously by the spacecraft, without any input from mission control.


    The water for the two unactivated radiators will remain in the storage tank for the first 40 days of flight; after that, the final two radiators will be activated.


    When Parker Solar Probe is hurtling past the sun at some 430,000 miles an hour, it will be 90 million miles from mission controllers on Earth—too far for the team to “drive” the spacecraft. This means that adjustments to how the spacecraft is protecting itself with the TPS need to be handled by Parker Solar Probe’s onboard guidance and control systems. These systems use new and effective autonomous software to allow the spacecraft to instantly alter its pointing to maximize protection from the sun. This autonomous capability is critical to the operation of the spacecraft’s solar arrays, which must be constantly adjusted for optimal angle as Parker Solar Probe hurdles through the sun’s harsh, superheated corona.


    There’s no way to make these adjustments from the ground, which means it has to guide itself, APL developed a variety of systems—including wing angle control, guidance and control, electrical power system, avionics, fault management, autonomy, and flight software—that are critical parts working with the solar array cooling system. This spacecraft probably is one of the most autonomous systems ever flown.

    That autonomy, along with the new cooling system and pioneering solar array upgrades, will be crucial to ensuring that Parker Solar Probe can perform the never-before-possible science investigations at the sun that will answer questions scientists have had about our star and its corona.
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