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article imageSolar Probe Plus — Getting up close and personal with our sun

By Karen Graham     Feb 27, 2017 in Science
Our sun is a dwarf star of hot and glowing gasses. We know its interaction with the Earth drives our seasons, weather and more. But to understand the connectivity between the Earth and sun fully, we need to get up close, and a Solar Probe will help us.
Great strides in science and technology have allowed us to send spacecraft to the moon, far away asteroids, Mars and even Jupiter. Mankind has forever pushed the boundaries in attempting to achieve the impossible, and it has long been assumed that getting close to the sun was a recipe for death.
But like the myth of Icarus, the son of Daedalus, who made a pair of wings out of feathers and wax so he could fly as high as the sun, the story shows us that we have no limits in what we can achieve. However, unlike Icarus, who plunged to his death when the sun melted his wings, we need to be very careful in our endeavor.
The Flight of Icarus  a reproduction of a work done between 1635 and 1637 by Jacob Peter Gowy.
The Flight of Icarus, a reproduction of a work done between 1635 and 1637 by Jacob Peter Gowy.
Jacob Peter Gowy
A closer look at the sun
The sun has a radius of 432,168.6 miles (695,508 kilometers), and while it's not a very big star, it is still massive in comparison to the Earth. Here's a factoid for you: It would take 332,946 Earths to match the mass of the sun. The sun's volume would need 1.3 million Earths to fill it. So being 4.0 million miles from it is certainly close enough.
The Solar Probe Plus mission was announced in 2008, with Johns Hopkins University Applied Physics Laboratory announcing it will design and build the spacecraft. The original launch was scheduled for 2015, but that launch date was pushed to 2018 and will use the Delta IV Heavy as the launch vehicle.
A launch window for the Solar Probe Plus will occur between July 31 – August 19, 2018, according to NASA. The Earth is about 93 million miles (149 million kilometers) from the sun, and the aim of the mission is to get within 4.0 million miles (6.0 million kilometers) of the sun.
At its closest approach, Solar Probe Plus will be hurtling around the sun at approximately 450,000 miles per hour. That's fast enough to get from Philadelphia to Washington, D.C. in one second. The probe's closest approach will be a mere 3.83 million miles.
"This is going to be our first mission to fly to the sun," said Eric Christian, a NASA research scientist at Goddard Space Flight Center in Greenbelt, Maryland. "We can't get to the very surface of the sun," but the mission will get close enough to answer three important questions, he said.
The Delta IV is a rocket operated by United Launch Alliance. The one that ill be used for the Solar ...
The Delta IV is a rocket operated by United Launch Alliance. The one that ill be used for the Solar Probe Plus mission will be a Delta IV Heavy.
Three important questions to be answered
One really big question that solar scientists want to be answered is why the sun's surface, called the photosphere is not as hot as the sun's atmosphere known as the corona. It may sound strange, but the surface of the sun is only 10,000 degrees Fahrenheit while the atmosphere above the surface is about 3.5 million degrees Fahrenheit.
"You'd think the farther away you get from a heat source, you'd get colder," Christian told Tech Times. "Why the atmosphere is hotter than the surface is a big puzzle."
A second question has to do with solar winds. Scientists want to know how a solar wind gets its speed. "The sun blows a stream of charged particles in all directions at a million miles an hour," Christian said. "But we don't understand how that gets accelerated."
Christian points out that sky observers have always noticed that the tails of comets always point away from the sun, regardless of their path. He wonders if this suggests that something, perhaps solar winds are coming off the sun faster than the comet was moving.
Scientists also want to know why the sun occasionally produces high-energy particles known as solar energetic particles. These particles are a danger to astronauts and spacecraft. However, scientists hope the mission will provide data on solar activities that could affect our ability to forecast space-weather events that can impact life on Earth.
Technological and infrastructure affected by space weather events.
Technological and infrastructure affected by space weather events.
"Without advance warning, a huge solar event could cause two trillion dollars in damage in the US alone, and the eastern seaboard of the US could be without power for a year," the Solar Probe mission page reads, "In order to unlock the mysteries of the corona, but also to protect a society that is increasingly dependent on technology from the threats of space weather, we will send Solar Probe Plus to touch the sun."
The challenges of such a mission
While the mission is an unmanned project, there is still the need for protection of the spacecraft itself and the sensitive instruments it will carry. To that end, NASA scientists have designed a 4.5-inch-thick (11.4 centimeters) carbon-composite shield, able to hopefully withstand temperatures outside the spacecraft of 2,500 F (1,370 C).
Diagram of concept of operation of the Solar Probe Plus Spacecraft
Diagram of concept of operation of the Solar Probe Plus Spacecraft
The probe will also have special heat tubes known as thermal radiators, designed to radiate any heat that permeates the heat shield so as to protect the sensitive instruments inside. If the thermal radiators work as intended, the instruments should remain at "room temperature," Christian says.
The probe will also be protected from radiation that could ruin the electrical circuits inside the probe. And yes, NASA says that a human could probably safely come within 4.9 million miles of the sun in a well-protected spacecraft, but the cost of a human life is too great, especially when an unmanned craft is capable of doing the same job.
More about solar probe plus, NASA, solar wind acceleration, Corona, photosphere
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