The Insane Engineering of the Parker Solar Probe

This episode of Real Engineering is brought to you by the CuriosityStream and Nebula package. Watch until the end of the video to see a preview of our upcoming Nebula Original series, The Battle of Britain. For the first time in human history, a spacecraft has flown over the Sun's atmosphere, sweeping away the superheated particles of the Corona. A momentous moment that has provided scientists with vital information about the nature of our nearest star, which can help us unlock its mysteries. The Sun's atmosphere, like ours, is made up of layers. Where we have the troposphere, stratosphere and mesosphere, the sun has the photosphere, chromosphere and corona.

We have a saying: hotter than the surface of the Sun, but the surface of the Sun, the photosphere, is actually not that hot. It ranges from about 6,200 degrees Celsius (6,500 Kelvin) at the bottom to 3,700 degrees Celsius (4,000 Kelvin) at the top. That's about the same temperature as a welding arc, and the air around a beam can reach temperatures five times higher than the photosphere. The strange thing is that the outermost layer of the Sun's atmosphere, the corona, is much hotter than the photosphere. The corona, which begins about 2,100 kilometers above the sun's surface, reaches half a million degrees Celsius, 80 times hotter than the surface.

It's like moving away from fire and the temperature increases as you move away from it. This is a strange anomaly that makes the Parker Solar Probe's achievement even more impressive, since at first glance it is easy to dismiss that the

probe

"only" flew through the upper atmosphere, when in fact the upper atmosphere is much hotter than the surface. Why this occurs is one of the many unsolved mysteries of the universe and, as such, is one of the primary missions of the Parker Solar Probe. Collect information about the magnetic fields and charged particles in this region and try to answer this puzzle.

To understand the achievements of the Parker Solar Probe, let's delve into the

engineering

and physics of its

solar

mission. The first big problem Parker Solar faces is getting to the Sun. Even though the Sun's gravity acts as an anchor for our entire

solar

system, getting closer to it is not easy. To remove a satellite from its orbit around the Earth, we have to lose its angular momentum so that it falls back to Earth. The same thing must be done when trying to take something out of orbit around the Sun, except that in this case we are located 1 AU, or 150 million kilometers from the Sun, and we are traveling at 30 kilometers per second.

And anything launched from Earth will be imbued with the same orbital speed around the Sun. This means that to achieve a closer orbit around the Sun we need to reduce the orbital speed of the spacecraft around the Sun, and this is a task that consumes a lot of energy, especially if you add the energy needed to escape the Earth's gravity. So let's say we first want to get our satellite from the Earth's surface into orbit around the Earth, this will require us to accelerate our satellite around 9.2 km/s per second relative to the Earth's surface. The satellite is now in orbit around the Earth and traveling with it at 30 kilometers per second around the Sun.

From here we need to perform something called the Hohmann transfer. This is an orbital maneuver in which we change the orbital energy of the spacecraft to adjust its perihelion, its closest approach to the Sun, or its aphelion, its furthest approach from the Sun. To visit an outer planet, like Mars, we want to increase our aphelion adding orbital energy to the spacecraft. While reaching an inner planet requires us to reduce our perihelion by decreasing our orbital energy. To reach Mars from Earth orbit requires a delta v of around 2.9 kilometers per second. To reach Venus it takes about 2.5 kilometers per second.

This is found using this equation: where mu, this Greek letter that looks like a u, is the planetary parameter of the sun, which is a product of the mass of the Sun. R1 is the orbital radius from which we start, in this case the distance from the Earth to the Sun at 150 million kilometers, and r2 is the desired perihelion or aphelion. If we calculate the delta v necessary to reach the closest approach of the

parker

solar

probe

of 6.2 million kilometers. This would require a delta V of 21.4, more than 8.5 times greater than the delta V needed to reach Venus.

This is an incredibly high delta V. One that is beyond the capabilities of any rocket ever made. But, on December 8, 2018, the Parker space probe was launched from Cape Canaveral aboard the heavy Delta IV, the second most capable rocket in the world, surpassed only by the Falcon Heavy. To give the probe an extra boost, Delta IV was equipped with a special solid rocket third stage, providing an additional 3 km/s of delta v for the typically two-stage rocket design. However, even with this extra power, the probe would never have come close to the Sun. To achieve its record flight, one-seventh of Helios 2's previous record, the Parker Solar Probe completed a staggering 5 Venus gravity assists with 2 additional flybys planned for 2023 and 2024.

This number of flybys was necessary because Venus is a relatively low mass planet. The magnitude of velocity change a planet can provide is largely determined by its gravity, determined by its mass. In fact, the probe's original plan was to perform a single planetary assist by Jupiter, which would have brought the probe 3 times closer to the Sun, but this trajectory had some problems. Because Jupiter's orbit is much farther from the sun, the sunlight reaching the panels at its aphelion would have been 25 times dimmer, requiring much larger solar panels to power the spacecraft. This poses a problem when the spacecraft orbits Jupiter and begins accelerating toward the Sun.

The heat from the Sun would destroy the solar panels, and at this size they would not be able to retract and hide behind the sunshade. There were other options available. A radioisotope thermal generator could have been used, but it would have significantly increased the cost, weight and complexity of the spacecraft. The real appeal of this radical new flight path was the additional time and data it would provide scientists to accomplish the probe's mission: studying the Sun. Under Jupiter's original plan, the probe would have had only 100 hours inside. of the desired area around the Sun, completing only 2 solar passes before the probe reached the end of its 8-year mission.

While the new lower orbit plan would mean the Parker Solar Probe would take less than 150 days to complete its orbit around the Sun, allowing scientists to collect more than 900 hours of data on the probe's 24 orbits around the Sun. The change of plan came with a change in design, moving away from the original cone-shaped heat shield to the familiar, compact flat shield. This shield is primarily constructed of 11.4 centimeter carbon foam. A truly fascinating material developed by one of the most prolific materials innovation laboratories, Ultramet. Under a scanning electron microscope, the carbon foam looks like this. An incredibly porous material, dominated by open space, making its internal volume 97% empty, giving the heat shield fantastic insulation properties, whilst benefiting from the thermal stability of carbon.

Next, a carbon-carbon composite, which is made by combining graphite with an organic binder, such as pitch or an epoxy resin. This mixture was applied to each side of the foam, before being superheated to transform the binder into a pure form of carbon. Creating a carbon-carbon composite. Finally, a white ceramic paint was applied to the side facing the Sun to reflect as much of that heat away from the heat shield before it had a chance to enter the carbon labyrinth below. From here, the rest of the spacecraft, plus some specialized sensors and solar panels, had to be designed to fit within the umbra, or shadow, of the shield.

There are several instruments that bravely stick out beyond the safety of the heat shield. Like the solar probe cup, one of the many sensors on board. This thing is easily the most impressive technology on board. Completely unprotected by the sunshade, its designers had to be very creative with materials. The solar probe's cup is a Faraday cup, which is a device that can count and measure the properties of electrons and ions coming from the Sun, essentially giving the spacecraft the ability to study solar winds and mass ejections. particles coming from the Sun. This is the cross section of the solar probe cup.

It basically works by applying an electric field on the grate at the opening of the cup. By varying the voltage, we can select or filter out the particles that can enter the glass, giving us more data about what is causing the current when these charged particles hit the collecting plate at the bottom of the glass. It's a very simple device in practice, but with the temperatures it faces - 1,400 degrees Celsius, just below the melting point of pure iron - the solar probe cup needed some innovative

engineering

. The first challenge was to select a material for the electrical network that generates the selecting electric field at the entrance of the cup.

This grating had to be conductive and heat resistant, while also being machinable to create the small 100 micron spaced grating. Tungsten, the same material used in incandescent light bulbs here on Earth, was chosen as they are able to survive the very high temperatures necessary to generate light. Tungsten light filaments operate at temperatures up to 3000 degrees Celsius, so they are more than capable of surviving these temperatures; however, machining tungsten into such a fine grate is difficult. Micrometer-scale machining like this is not done with traditional tools. You would immediately break the grate with enough force to scrape the metal.

Instead, lasers are typically used to etch the material, but because tungsten is so heat resistant, the lasers would not be able to melt the tungsten to form the grating. Acid etching was used instead. Next we needed electrical cables capable of supplying power to the network and carrying electrical signals from the collector plate. The two most used conductors here on Earth, copper and aluminum, would turn into a puddle of molten metal under these conditions, so they were definitely not an option. All lead wires in this part of the spacecraft were to be made of C-103 niobium, a special alloy of 89% niobium, 10% hafnium and 1% titanium.

All external casing components were also constructed from this exotic aerospace material. Normally the cables would be insulated from the outer casings with plastic, but this was obviously not an option for the Parker space probe, and engineers were forced to use sapphire to ensure the niobium cables were insulated. These are some extremely exotic materials for doing what is a relatively mundane job here on earth. Other parts of the sensors that protrude beyond the sunshade are constructed in a similar way. The magnetic field measuring instruments hidden behind the shield need antennas that reach beyond the sunshade in order to measure the Sun's magnetic fields.

These 4 antennas are also made of niobium C-103. Solar panels were the next challenge. As it navigates its distant orbit around the Sun, the spacecraft can fully deploy its solar panels without problems, but as the probe begins its sweep toward the Sun, heat will become an increasing problem. This can be counteracted to some extent by retracting the solar panels, but the spacecraft needs to maintain some power to operate its scientific equipment during this vital stage of the flight. Here, two smaller secondary panels remain in view of the Sun and are cooled by water, which is pumped through the solar panels and into these black radiators attached to the titanium armor just below the sunshade.

This truss is exceptionally lightweight for how big it looks. The entire frame weighs only 50 pounds (22.7 kilograms), which even for low-density titanium is very low for the size of the frame. NASA engineers have clearly triple-checked their stress calculations to ensure this can use the least amount of material possible, which of course saves launch weight, but also minimizes the material available to conduct heat from the heat shield. to the spaceship bus. Testing these systems in the heat they are expected to face is difficult on Earth. The Odeillo solar oven is our best approximation of the environment they would have to endure.

This installation, built on a hillside in rural France, uses 10,000 adjustable mirrors to focus lightin a concave mirror. The installation is capable of reaching temperatures of up to 3,500 degrees Celsius, more than double the temperature that even the parasol will experience. Parts such as the Faraday cup and the lens hood were placed at the focal point of this concave mirror and exposed to the temperatures they will have to withstand. However, it was also necessary to test components like the Faraday cup while they performed their sensory tasks, and to do this engineers need a particle accelerator that simulates the electrons and ions you will find in the solar wind.

Combining a particle accelerator with this solar oven was not an option, so researchers at the University of Michigan came up with the brilliant idea of ​​using 4 high-power IMAX projectors to simulate the heat of the sun, and discovered that the Faraday cup actually works best when heated, as the heat decontaminates the system. Much of the data we have received from these instruments is of little interest to the average space enthusiast. Raw data that will provide scientists with valuable clues about the nature of the Sun, but there is a sensor on board that transmits images to Earth that we can all enjoy.

During a solar eclipse we can observe a beautiful phenomenon: brilliant loops of light dancing around the Sun. These fantastic patterns are created by bright electrons sailing around the Sun on magnetic field lines, distorted by solar winds. We have been able to observe streams of high-energy electrons coming from Earth and from our solar observatories stationed at Lagrangepoint 1, but we have never, until very recently, been able to observe them up close. When the Parker space probe dove into the Corona for its ninth encounter with the Sun, it began recording from its panoramic view camera here on the spacecraft.

The images he provided look like a passenger's view of a passing blizzard on a dark night. Bright subparticles passing by the probe as it plunges into the eye of the storm. Beautiful images that are undoubtedly providing scientists with incomparable data about the nature of coronal streamers. The Parker space probe has many more encounters with the Sun, the next scheduled for September 2022, and with 2 more flybys of Venus, the Parker space probe will break its own records in 2023 and 2024, bringing us even closer to the Sun. And while we As we get closer to the Sun in our skies, we also get closer to recreating the Sun here on Earth to achieve unlimited fusion power.

The current fusion energy record stands at 70%, which means that we have managed to recover 70% of the energy necessary to start the fusion reactor. We are still a long way from being able to create energy through fusion, but ITER, a new fusion reactor, will be completed in 2025, and global cooperation will help finance its astronomical cost. More than $45 billion, making it one of the world's most expensive scientific experiments in human history. This CuriosityStream documentary goes behind the scenes of Europe's previous generation magnetically confined plasma fusion reactor. It's a fascinating watch that you can check out by signing up as a CuriosityStream annual member for just over $1 a month.

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