Will some stars no longer be visible some day because earth


This summer, NASAs Parker Solar Probe will launch to travel closer to the Sun, deeper into the solar atmosphere, than any mission before it. If Earth was at one end of a yard-stick and the Sun on the other, Parker Solar Probe will make it to within four inches of the solar surface.

Inside that part of the solar atmosphere, a region known as the corona, Parker Solar Probe will provide unprecedented observations of what drives the wide anger of particles, energy and heat that course through the regionflinging particles outward into the solar system and far past Neptune. Inside the corona, its also, of course, unimaginably hot. The spacecraft will travel through material with temperatures greater than a million degrees Fahrenheit while being bombarded with intense sun light.

Parker Solar Probe has been designed to withstand the extreme conditions and temperature fluctuations for the mission. The key lies in its custom heat shield and an autonomous system that helps protect the mission from the Suns intense light emission, but does allow the coronal material to "touch" the spacecraft

One key to understanding what keeps the spacecraft and its instruments safe, is understanding the concept of heat versus temperature. Counterintuitively, high temperatures do not always translate to actually heating another object.

In space, the temperature can be thousands of degrees without providing significant heat to a given object or feeling hot. Why? Temperature measures how swift particles are moving, whereas heat measures the total amount of energy that they exchange. Particles may be moving swift (high temperature), but if there are very few of them, they wont exchange much energy (low heat). Since space is mostly deplete, there are very few particles that can exchange energy to the spacecraft.

The corona through which Parker Solar Probe flies, for example, has an extremely high temperatues but very low density. Think of the difference between putting your hand in a hot oven versus putting it in a pot of boiling water (dont try this at home!)in the oven, your hand can withstand significantly hotter temperatures for longer than in the water where it has to interact with many more particles. Similarly, compared to the visible surface of the Sun, the corona is less filled, so the spacecraft interacts with fewer hot particles and doesnt receive as much heat.

That means that while Parker Solar Probe will be traveling through a space with temperatures of several million degrees, the surface of the heat shield that faces the Sun will only get heated to about 2,500 degrees Fahrenheit (about 1,400 degrees Celsius).

Of course, thousands of degrees Fahrenheit is still fantastically hot. (For comparison, lava from volcano eruptions can be anywhere between 1,300 and 2,200 F (700 and 1,200 C) And to withstand that heat, Parker Solar Probe makes use of a heat shield known as the Thermal Protection System, or TPS, which is 8 feet (2.4 meters) in diameter and 4.5 inches (about 115 mm) thick. Those few inches of protection mean that just on the other side of the shield, the spacecraft body will sit at a comfortable 85 F (30 C).

The TPS was designed by the Johns Hopkins Applied Physics Laboratory, and was built at Carbon-Carbon Advanced Technologies, using a carbon composite foam sandwiched between two carbon plates. This lightweight insulation will be accompanied by a finishing touch of white ceramic paint on the sun-facing plate, to imitate as much heat as possible. Tested to withstand up to 3,000 F (1,650 C), the TPS can handle any heat the Sun can send its way, keeping almost all instrumentation safe.

Betsy Congdon of Johns Hopkins Applied Physics Lab is the direct thermal engineer on the heat shield that NASAs Parker Solar Probe will use to protect itself against the Sun. The shield is so robust, Congdon can use a blowtorch on one side and the more

Poking out over the heat shield, the Solar Probe Cup is one of two instruments on Parker Solar Probe that will not be protected by the heat shield. This instrument is whats known as a Faraday cup, a sensor designed to measure the ion and electron fluxes and flow angles from the solar wind. Due to the intensity of the solar atmosphere, unique technologies had to be engineered to make sure that not only can the instrument survive, but also the electronics aboard can send back accurate readings.

The cup itself is made from sheets of Titanium-Zirconium-Molybdenum, an alloy of molybdenum, with a melting point of about 4,260 F (2,349 C). The chips that produce an electric field for the Solar Probe Cup are made from tungsten, a metal with the highest known melting point of 6,192 F (3,422 C). Normally lasers are used to etch the gridlines in these chipshowever due to the high melting point acid had to be used instead.

Another defy came in the form of the electronic wiringmost cables would melt from exposure to heat radiation at such close proximity to the Sun. To solve this problem, the team grew sapphire crystal tubes to suspend the wiring, and made the wires from niobium.

To make sure the instrument was ready for the coarse environment, the researchers needed to mimic the Suns intense heat radiation in a lab. To create a test-worthy level of heat, the researchers used a particle accelerator and IMAX projectorsjury-rigged to increase their temperature. The projectors mimicked the heat of the Sun, while the particle accelerator exposed the cup to radiation to make sure the cup could measure the accelerated particles under the intense conditions. To be absolutely sure the Solar Probe Cup would withstand the coarse environment, the Odeillo Solar Furnacewhich concentrates the heat of the Sun through 10,000 adjustable mirrorswas used to test the cup against the intense solar emission.

The Solar Probe Cup passed its tests with flying colorsindeed, it continued to perform better and give clearer results the longer it was exposed to the test environments. "We think the radiation removed any potential contamination," Justin Kasper, principal investigator for the SWEAP instruments at the University of Michigan in Ann Arbor, said. "It basically cleaned itself."

Several other designs on the spacecraft detain Parker Solar Probe sheltered from the heat. Without protection, the solar panelswhich use energy from the very star being studied to power the spacecraftcan overheat. At each approach to the Sun, the solar arrays retract behind the heat shields shadow, leaving only a small segment exposed to the Suns intense rays.

But that close to the Sun, even more protection is needed. The solar arrays have a surprisingly simple cooling system: a heated tank that keeps the coolant from freezing during launch, two radiators that will detain the coolant from freezing, aluminum fins to maximize the cooling surface, and pumps to circulate the coolant. The cooling system is powerful enough to cool an average sized living room, and will detain the solar arrays and instrumentation cool and functioning while in the heat of the Sun.

The coolant used for the system? About a gallon (3.7 liters) of deionized water. While plenty of chemical coolants exist, the anger of temperatures the spacecraft will be exposed to varies between 50 F (10 C) and 257 F (125 C). Very few liquids can handle those ranges like water. To detain the water from boiling at the higher end of the temperatures, it will be pressurized so the boiling point is over 257 F (125 C).

Another issue with protecting any spacecraft is figuring out how to communicate with it. Parker Solar Probe will largely be alone on its journey. It takes light eight minutes to reach Earthmeaning if engineers had to manipulate the spacecraft from Earth, by the time something went wrong it would be too late to correct it.

So, the spacecraft is designed to autonomously detain itself safe and on track to the Sun. Several sensors, about half the size of a cell phone, are attached to the body of the spacecraft along the edge of the shadow from the heat shield. If any of these sensors detect sunlight, they alert the central computer and the spacecraft can correct its position to detain the sensors, and the rest of the instruments, safely protected. 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.

After launch, Parker Solar Probe will detect the position of the Sun, align the thermal protection shield to face it and continue its journey for the next three months, embracing the heat of the Sun and protecting itself from the cold vacuum of space.

Over the course of seven years of planned mission term, the spacecraft will make 24 orbits of our star. On each close approach to the Sun it will sample the solar wind, study the Suns corona, and provide unprecedentedly close up obervations from around our starand armed with its slew of innovative technologies, we know it will detain its cool the whole time.

The Daily Galaxy via NASAs Goddard Space Flight Center 

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