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The CHIPS act is now dispersing awards and signing deals. And one recent grant that caught my eye was awarded to the New Zealand American Space Company Rocket Lab. The grant of up to $23.9 million is for the modernization and expansion of the company's fab in New Mexico, which produces space grade solar cells. Now, I've not heard of Rocket Lab until recently, though it seems like the folks in the stock trading world certainly have. But the idea of space grade solar cells was interesting to me. So this video is a simple one. Solar Cells in Space Enough said. But first I wanted to remind you about the asianometry Patreon. Early Access members get to see new videos first with selected references, and it really helps a lot. And I study how well each video does with the Early Access crowd to figure out which topics to do next. So I deeply appreciate your feedback and support. Thank you and on with the show. Space was the solar cell's first killer app. In 1954, Bell Labs announced the first practical solar cell, or solar battery. Silicon cells promised the world of unlimited energy, but only if that world happened to have unlimited money as well. Even as early cells rapidly doubled their efficiency, meaning the amount of solar power they can convert into electricity, people pointed out the immense costs of obtaining enough high purity silicon. In 1956, with a 1 watt solar cell costing about $286, the average homeowner would have had to pay $1.4 million to power their home, or about $16.2 million today. Bell Labs researchers were originally envisioned the silicon solar cell as a replacement for battery powered telephone repeater systems in remote areas, but the economics always got in the way. An early solar advocate was Hoffman Electronics in New Jersey, which inherited a license from Western Electric to produce solar cells. Hoffman frantically publicized their product with a variety of novelty trinkets like radios, but they did not catch on. Their solar cells had an efficiency of about 10%, but that still translated to about $357 per peak watt, nowhere near competitive with items with access to fossil fuel energy. But news of the Bell Lab's breakthrough made their way to Dr. Hans K. Ziegler of the U.S. army Corps, a German electronics military scientist brought over to the United States in Operation Paperclip. Ziegler became a fervent believer in solar power. Once saying, in the long run, mankind has no choice but to turn to the sun if he wants to survive. Ziegler pushed the U.S. signal Corps to find an ideal use case for these solar cells, and they came up with just one artificial Satellites. It was not a new idea. Arthur C. Clarke mentioned it in the 1940s and then in 1955 when the US President Eisenhower talked about launching a basketball sized satellite into space. That basketball was illustrated to have solar power. The US Navy initially said no to the idea, but Ziegler ferociously pursued the idea. And thus in March 1958, the Vanguard 1 probe launched with a solar panel attached to it. America's second artificial satellite. The spacecraft had two radio transmitters on board. One powered by a regular chemical battery. The other six panels of silicon based solar cells protected by a thin cover glass. It was the solar cell's first truly compelling use case. Satellites back then didn't need that much power, and heavy batteries and fuel were expensive to launch into space. Solar cells made far more sense. The solar test was a resounding success. Vanguard 1's solar powered radio transmitter ran for six whole years, far, far longer than the 20 days that the chemical battery powered transmitter lasted. It remains in space to this day. Now, before moving forward, I think it might be helpful to understand how solar cells basically work when photons impact the semiconductor material inside the cell. Sometimes a photon transfers over enough energy to a charge carrier, like an electron or electron hole, such that the charge carrier can jump the semiconductor's gap between the valence and conduction bands. An electron jumping up into the conduction band leaves behind an electron hole. So if you think about it, we are splitting an electron and electron hole pair. Once in the conduction band, the charge carrier can move freely, like the wildebeest. An electric field in the solar cell then directs the free electrons and electron holes towards opposite electrodes. They are both collected to generate a current in an external circuit. The size of the bandgap significantly contributes to the solar cell's efficiency. If the solar cell's energy is smaller than the band gap, then the charge carrier cannot jump the bandgap. The photon basically does not interact with it, passing through without incident. This is called a transparency loss. But if the photon's energy is too large compared to the bandgap, then that excess energy turns into heat. And that presents a challenge in space where no one can hear you scream. And that is because there is no air to dissipate away heat. Space is a harsh environment and solar cells must survive in it for years with as little intervention as possible. The temperature swings. There are pretty wild. Satellites in low Earth orbit must withstand a temperature going from 60 degrees to minus 80 degrees Celsius up to 16 times a day. The swings are even wilder up in geosynchronous orbit, these temperature swings cause thermal stresses to the solar cells, perhaps delaminating the panel or even causing cracks. Thermal control systems have to be installed to prevent these temperature swings from causing permanent damage. And then there are micrometeorites and space debris flying around, which can potentially hit these solar cells and damage them. This is usually ameliorated With a thick cover glass, Though with the downside of higher launch costs. But perhaps the thing of highest concern up in space Is the space radiation. What we call space radiation Is an umbrella term that describes multiple things that all can deal some damage to the solar cell's operation. We have some actual radiation, Mostly gamma rays, X rays, and ultraviolet rays Produced by distant galaxies and cosmic phenomena. Over 20 years, a typical solar cell can accumulate up to 1000 kilorads of gamma radiation. To put that into context, A chest x Ray has 0.01 rads. I know, I know. Timescale is not comparable. Just get that. It is a lot of radiation. The space radiation of perhaps the most concerned, however, Involved tiny charged particles like protons and electrons Moving at near the speed of light. These largely come from the sun thrown off by solar flares. Praise the sun. In 1958, the satellites Bucknet 2 and Explorer 1 detected what would eventually be called the Van Allen radiation belts. Sitting about 100 miles above the Earth's surface. These are donut shaped clouds of such charged particles from the sun, Held enthralled by the Earth's magnetosphere. The particular orbit plays a factor in how much radiation satellites are exposed to. Items in low Earth orbit generally suffer less space radiation Than items in medium or geostationary orbits, thanks to the aforementioned magnetosphere, Assuming they don't fly over the polar regions, that is. There are three general ways in which radiation and particle impacts can damage a solar Ionization, displacement, and trapping. First, these things can ionize the panel's materials, Causing the insulating material, or cover glass on top of the panel to darken. This in turn, blocks light from reaching it. The second type of damage Is more concerning displacement. Fast moving charged particles, Especially heavy ones like protons, have some mass. And since they are moving so fast, Their collisions can shift the atoms Inside the solar cell's lattices. This can cause vacancy defects, which is a missing atom in the lattice, or interstitial defects, which is an additional atom in the lattice. The type and size of defect depends on the speed and mass of the particle. Vacancy or interstitial defects can create potholes, more formerly called recombination centers, that capture electrons as they travel up from the valence to the conduction band. These effectively reunite or recombine the free electron electron hole pairs, thusly preventing us from making a current. The defects can also become trap centers, trapping charge carriers as they move about after jumping to the conduction band. This further reduces the net number of charge carriers eventually reaching the electrodes. In August 1959, NASA launched the Explorer 6 satellite to explore space radiation and micrometeorites. The thing also took the first ever photo of the Earth from space. Explorer 6 had four solar panels mounted on paddles, but one failed to unfurl after launch, after which the remaining solar cells quickly deteriorated in the radiation, leading to a loss of contact soon after launch in October 1959. This brought about suspicions of radiation damage to the solar cells, Suspicions which were soon confirmed in 1962, when the Americans tested a 1.4 megaton nuclear weapon in space. Did America really do that? Oh, yes, they did. The 60s man. The test was called Starfish Prime. Awesome name. Not as awesome consequences. Detonated about 250 miles above the surface, the test generated a massive electromagnetic pulse that knocked out electronics as far away as Hawaii, 900 miles away. Starfish prime released so many charged particles into space that it created its own mini radiation belt around the Earth, exposing satellites to up to 100 times more radiation than they had been earlier tested for. A day after the test detonation, the telecom AT&T launched Telstar One, the first commercial telecommunications relay satellite. Aware that they were launching into a literal particle storm, AT&T scientists did their best to protect their solar cells from radiation with sapphire panels and shielding. Nevertheless, the radiation deteriorated the solar panels and cut the $50 million satellite's useful life to just seven months. An estimated six more satellites were taken out by the Starfish's arms, including the United Kingdom's first satellite, Ariel 1. Whoops. The incident taught scientists that they needed to consider how to prevent radiation damage and in the solar cells. Despite the existence of several semiconductor material alternatives, spacecraft designers for the next 20 years or so largely continued to use silicon based solar cells. Silicon is not super ideal for space grade solar installations. Its band gap of 1.12 electron volts was below the photon energy of terrestrial light, which was about 1.5 electron volts. So there is some wasted energy which dissipates as heat. However, silicon was, and still is, very cheap for obvious reasons. And it is also relatively easy to manufacture. So engineers implemented ways to harden their silicon cells against radiation damage. A simple thing would be adding a thicker cover glass on top of the solar cells. It definitely provides protection from particles and could even help focus more light onto the cells. But it also adds weight, which is always at a premium on a satellite. Lattice damage can be somewhat repaired with annealing, which basically means heat treating the solar cell with temperatures of up to 400 degrees Celsius. It works. But as you might expect, those kinds of temperatures are not practical for a satellite up in space. So there has been some interesting work with adding lithium to the silicon. Lithium atoms move very well and in certain conditions they can fill in certain defects and prevent recombination. This can bring down the annealing temperature to something more amenable to satellites. In the end, this natural radiation is unavoidable. Thusly, the best counter has been to raise the cell's efficiency as high as possible at the start of their life and model for their future decline. This also fitted with ongoing satellite technology trends. Early satellites were small and simple and so didn't need much power. But that changed as they got bigger and more complex. To run such things, designers either needed bigger solar arrays or more efficient solar cells. One big addition to the silicon solar cell to achieve that higher efficiency was the back surface field. To explain it, let me explain the three things of the most basic solar cell. An anti reflecting coating on the top that keeps sunlight from reflecting away from the cell. Second, metal contacts on the front and back sides. And third, something called a P N junction. This is the core of a cell, a sandwich of two pieces of specially doped silicon. One piece has been doped to have an excess of electrons, the other, electron holes. This version here has just one junction, but there can be more than one, and you'll hear more on that later. The back surface field is a highly doped layer of metal, usually aluminium, deposited onto the back of the silicon wafer as a paste and then heated up to create an aluminium silicon layer. During operation, the back surface field, or bsf, acts like another PN junction, generating an electric field that keeps charge carriers in the back of the solar cell to from falling back into the valence band. This leaves us more charge carriers to make a current. BSFs are simple, cheap to make and greatly improve efficiency. Later on, we added a second thin reflective metal layer called the back surface reflector or bsr. Recall that if the photon's energy was higher than the bandgap, then that excess energy dissipates as heat. Too much heat is bad. The back surface reflector helps with this by reflecting away light that is too energetic for the solar cell to handle. The BSF and BSR were later combined to create the bsfr, raising the solar efficiency of silicon space grade solar cells throughout the 1980s to something between 15 and 20%. Nevertheless, satellites kept getting even more complex. To power such satellites, engineers had to design larger arrays, and which in turn required ever more complicated ways to unfurl them after launch. Such complex contraptions sometimes caused problems. One example was the Hubble Space Telescope. When it was launched in 1990, it was equipped with an innovative solar array that sort of unfurled like a window shade curtain. But this delicate setup, developed in conjunction with the Europeans, led to a flutter problem after launching, as the spacecraft reacted to temperature changes, the panels had to be jettisoned in a later servicing mission. So the alternative then would be to use more efficient solar cells. With silicon having hit its theoretical limits, this opened the door to alternative semiconductor materials like gallium arsenide. Gallium arsenide is a III V semiconductor material, a compound of two elements. It has a higher bandgap than Silicon Valley 1.42, which is better matched to visible light. The wider bandgap also helps their cells retain their efficiency at higher temperatures. Moreover, that bandgap is direct, which basically means those electrons can more easily transition from the valence to conduction bands than they can in silicon. Win win we made the first three, five solar cells, gallium arsenide and indium phosphide, in 1955, around the same time as silicon. But gallium arsenide's big challenge has always been fabrication. Then, in the 1990s, new deposition methods like organometallic vapor phase epitaxy, or metal organic chemical vapor deposition let us grow thin films of high quality gallium arsenide necessary for high volume production. The first satellite to use gallium arsenide solar cells was The Navigation Technology Satellite 2, or NTS2, in 1977, an early GPS satellite prototype. It carried a set of high efficiency gallium arsenide solar cells for running various experiments. The experiments showed that even though gallium arsenide might cost up to six to nine times more than silicon, their greater efficiency let you make the satellite smaller and maybe even put more satellites on the same rocket. And since both materials deteriorate from radiation damage at a similar rate over their useful life, the overall savings were worth it. So, starting in 1992, gallium arsenide rapidly started to take market share from traditional silicon solar cells. But there was more. One issue with just using these gallium arsenide solar cells was that we are still getting these transparency Losses. What are those? Red. Recall earlier that the solar cell can only use a photon's energy if that energy is higher than the bandgap. If the photon's energy is less than the bandgap, then the photon just passes through the cell without much interaction. That is transparency loss. People recognized this shortcoming all the way back in the 1950s and proposed to stack semiconductor plates with varying band gaps to make up for it. This is the core concept of multi junction or cascade or tandem solar cells. Multi junction solar cells are made up of sub cells, each sub cell containing a junction to capture light in its particular wavelength. The sub cell's bandgaps are tuned to be complementary with one another. The uppermost sub cell is tuned to have the highest bandgap and so it absorbs the photons with the most energy. Before the photons with energy less than that of the first layer's bandgap, they pass through and hit the second sub cell underneath. This way we can tune the solar cell to get the most power while also dissipating the least amount of heat. The challenge was finding the right III V semiconductor elements with complementary bandwidths that can also be deposited on top of one another without creating a mismatch in their lattice structures that would have unpleasant consequences. In the 1980s, two scientists at what is now the National Renewable Energy Lab, Jerry Olson and Sarah Kurtz, broke through. They grew a gallium indium phosphide sub cell on top of a gallium arsenide sub cell on top of a germanium substrate. In 1997, these two junction puppies first entered space on a Hughes HS 601 HP commercial satellite. They boasted an impressive 21.5% efficiency at the start of their life. Olson and Kurt's remarkable breakthrough set the blueprint for virtually every space grade multi junction solar cell we have today. They all have gallium indion phosphide top sub cells. Not only because a gallium indium phosphide has a big bandwidth, but also because it is especially resistant to to space radiation. Later, these solar cells added a third junction. And today these triple junction variants dominate the space industry, capable of converting over 40% of the light they receive into electricity. Let us go back to Sol Aero because it helps close the loop on the story. As I mentioned, Rocket Lab acquired Solaero in December 2021 for about $80 million in cash. But where did Sol Aero come from? They started off as the space grade solar cell division of a California based business called Techstar. And Techstar itself dates back to 1954 when they were big reveal Hoffman Electronics. Yes, that early pioneer of silicon based solar cells and the company that supplied those very first solar cells for the Vanguard 1 spacecraft. It is all connected. In the late 1990s TXSTAR licensed two patents from the US Department of Energy to manufacture high efficiency multi junction solar cells for spacecraft. In an effort to make inroads into private industry, they supplied solar cells to the Iridium satellite phone network. But when Iridium crashed financially, not literally, and filed for bankruptcy in mid-1999, that took down Techstar as well. In 2002, eMcore, a niche maker of compound semiconductors and fiber optic subsystems, bought TXSTAR's Applied Solar Division for considerations. That's an accountant term of about $21 million. They held it until 2014 when they sold it for $150 million to Sol Aero, an affiliate of the private equity firm Veritas Capital. Solaero's investment thesis was apparently to become a vertically integrated satellite subsystem provider. After that they made a few more acquisitions, alliance space Systems in 2015 and Vanguard Space in 2016. Afterwards they apparently tried to pivot into providing solar cells for solar powered drones. That must not have taken off because Rocket Lab bought the whole business for just about half of the $150 million Virida's capital paid to get it started. Rocket Lab is looking to do as much as they can in house, ergo why they say they are and end to end. So Solaero's triple junction solar cells seem like a good fit for the mission. Satellites depend on the power they generate, so better cells can lead to smaller satellites and thus easier launches. The solar panels are essentially fine artisanal wafers which I suppose are tailored to the satellite at hand. That's fine, but I do hope that they are able to use some of that chips act money to improve their volume production capacity. Because these solar panels are insane and I bet they can have a place here on Earth. Alright everyone, that's it for tonight. Thanks for watching. Subscribe to the channel, sign up for the Patreon and I'll see you guys next time.