【全文來自官網(wǎng)https://www.spacex.com/news/2020/04/28/starlink-update】

翻譯的肯定不通順，還請大家見諒。

全文信息量大，首次公開信息較多！

SpaceX正在推出Starlink，以便在全球范圍內(nèi)提供高速、低延遲的網(wǎng)絡(luò)連接，覆蓋光纖互聯(lián)網(wǎng)覆蓋不到的地方。我們還堅信自然夜空對我們所有人的重要性，這就是為什么我們一直在與世界各地的主要天文學(xué)家合作，以更好地了解他們的觀測和我們可以進(jìn)行的降低衛(wèi)星亮度的工程變化的具體細(xì)節(jié)。我們的目標(biāo)包括：

1、使衛(wèi)星在發(fā)射后一周內(nèi)肉眼看不見。我們是通過改變衛(wèi)星太陽能板的朝向的方式來做到這一點的，這樣他們就可以將太陽能板“隱藏”起來。

2、通過使衛(wèi)星變暗來最小化Starlink對天文學(xué)的影響，這樣就不會使天文臺“心態(tài)爆炸”。我們通過在衛(wèi)星上增加一個可展開的遮罩來阻止陽光照射到航天器最明亮的部分來實現(xiàn)這一目標(biāo)。下一次發(fā)射（Starlink-8，詳見https://www.bilibili.com/read/cv5835790）時將會發(fā)射一顆帶有黑色擋板的Starlink衛(wèi)星以供測試，到6月份的第9次飛行時，所有的Starlink都會配備這個硬件。另外，關(guān)于我們衛(wèi)星軌道的信息位于space-track.org均有體現(xiàn)，以防意外的闖入天文臺的視線。

StarLink軌道

StarLink有三個飛行階段：

(1)軌道上升

(2)停泊待機(jī)軌道，以等待升軌時機(jī)(離地380公里)

(3)到達(dá)目標(biāo)軌道(離地550公里)。

在軌道運行期間，衛(wèi)星使用霍爾推進(jìn)器在幾周內(nèi)提高高度至工作軌道。有些衛(wèi)星直接進(jìn)入目標(biāo)軌道，而另一些衛(wèi)星則停留在停泊待機(jī)軌道上，以允許衛(wèi)星進(jìn)入不同的軌道平面。一旦衛(wèi)星進(jìn)入目標(biāo)軌道，它們就會重新調(diào)整姿態(tài)和硬件，使天線面向地球，太陽能陣列垂直于太陽，從而能夠跟蹤太陽以最大限度地發(fā)電，并且使衛(wèi)星盡可能的暗。由于這次機(jī)動，衛(wèi)星變得更暗，因為太陽陣列從地面的能見度大大降低。

目前，419顆衛(wèi)星（不算DD-A和DD-B）中約有一半在工作軌道（在第一批V0.9的Starlink衛(wèi)星中，有一顆再入大氣層來測試Starlink的自毀效果，測試結(jié)果很好，沒有留下任何太空垃圾），另一半正在上升或待機(jī)停泊。衛(wèi)星只有一小部分生命將用于軌道提升或維持軌道、進(jìn)入大氣層，并將其生命的絕大部分用于工作中。值得注意的是，在任何特定時間，只有大約300顆衛(wèi)星將在軌道上升或待機(jī)停泊。其余的衛(wèi)星將在工作軌道上運行。

Starlink衛(wèi)星

Starlink的飛行高度非常低。也保證了空間安全，并盡量減少了信號延遲。由于低高度，阻力是設(shè)計中的一個主要因素。在軌道上升過程中，衛(wèi)星相對于“風(fēng)”的橫截面積必須最小化，否則拖曳會導(dǎo)致它們從軌道上掉下來。高阻力是一把雙刃劍--這意味著衛(wèi)星的飛行很棘手，但也意味著任何遇到問題的衛(wèi)星都會在大氣層中快速、安全地燃燒。這大大減少了軌道碎片或“空間垃圾”在軌道上的數(shù)量。

在升軌中太陽能陣列被平放在衛(wèi)星前。當(dāng)衛(wèi)星上升時，總是保持最小的風(fēng)阻橫截面積，同時保持天線面向地球，足以與地面站保持聯(lián)系。

當(dāng)衛(wèi)星到達(dá)550公里的運行軌道時，阻力仍然是一個因素——因此即使完全失控的衛(wèi)星都會因風(fēng)阻而迅速降低軌道。但完好的、可以工作的衛(wèi)星的姿態(tài)控制系統(tǒng)能夠克服這種阻力。

Starlink的可見度

在日出或日落時，從地面可以看到衛(wèi)星。這是因為衛(wèi)星被太陽照亮，但是地面上的人或望遠(yuǎn)鏡卻在黑暗中。

這個簡單的圖表突出了為什么軌道上的衛(wèi)星比工作軌道上的衛(wèi)星要亮得多。在軌道上升過程中，當(dāng)太陽陣列處于平鋪狀態(tài)時，太陽光可以反射出太陽陣列和衛(wèi)星，并反射到地面。一旦進(jìn)入工作軌道，底盤部分才能將光線反射到地面，而太陽能板則被“隱藏”了。

衛(wèi)星物理亮度省略，反正就是Starlink多少都會有影響，后面貼上英語原文

Starlink反光的解決方案

我們已經(jīng)采取了一種實驗和迭代的方法來降低星鏈衛(wèi)星的亮度。亮度是一個極難分析的問題，所以我們一直在進(jìn)行地面和在軌的測試。

例如，今年早些時候，我們發(fā)射了一顆“涂黑”的Starlink衛(wèi)星，這是一顆實驗衛(wèi)星，我們在那里使相控陣和天線變暗，這些設(shè)計是為了解決在工作軌道上的的亮度問題。這使衛(wèi)星的亮度降低了約55%，這是通過將DarkSat與鄰近的Starlink衛(wèi)星進(jìn)行對比所得的結(jié)論。這幾乎足夠使衛(wèi)星在工作軌道上時使地面肉眼不可見。然而，黑色表面會更易吸熱并反射一些紅外光，因此我們將用遮陽面來代替這個方案。這避免了由黑漆引起的過熱問題，并預(yù)計比“涂黑”的Starlink衛(wèi)星還要暗，它將阻止所有的光線到達(dá)白色的天線。

早期任務(wù)的操作

由于遮陽罩并不遮擋太陽陣列，這意味著它將不會給軌道上升帶來阻力，但不會減少上升時的軌道亮度。為此，我們正在努力改變衛(wèi)星的變軌模式。

通過減少接收光的表面積來減少反射到地球上的光。這是可能的，當(dāng)軌道上升和到達(dá)待機(jī)軌道，這些未到達(dá)工作軌道的衛(wèi)星不需要提供覆蓋互聯(lián)網(wǎng)用戶。然而，有幾個微妙的原因，這是很難實現(xiàn)的。首先，將太陽能傾斜于太陽會減少衛(wèi)星可用的能量。第二，由于天線有時會不朝向地面，因此與衛(wèi)星的接觸時間將減少。

第三，跟蹤相機(jī)位于底盤的兩側(cè)。將太陽能板指向太陽，一顆可以直接指向地球，另一顆直接指向太陽，但這卻將導(dǎo)致衛(wèi)星姿態(tài)調(diào)整能力更差。

會有一小部分的情況是，由于上述限制因素之一，正在升軌的衛(wèi)星無法一直把太陽能板垂直于太陽。這可能導(dǎo)致在飛行軌道上偶爾出現(xiàn)一組十分密集的Starlink衛(wèi)星，這些衛(wèi)星在某一軌道的某一部分上是可以暫時看到的。

工作軌道的亮度

衛(wèi)星一生中的大部分時間都停留在工作軌道上，在飛行過程中，它們的太陽能板大多是垂直于衛(wèi)星的（因為工作的衛(wèi)星便是太陽能板垂直于衛(wèi)星）。我們可以調(diào)整太陽能板的位置，以反射光從它的太陽能板并遠(yuǎn)離地球，并把太陽能板隱藏在底盤后面。剩下的主要目標(biāo)是阻止相控陣和天線被太陽直射。目標(biāo)是用黑色橡膠塑料泡沫覆蓋衛(wèi)星兩側(cè)的白色天線。

利用我們的低軌道高度和平坦的衛(wèi)星幾何結(jié)構(gòu)，我們?yōu)樾l(wèi)星設(shè)計了一個透明射頻（不影響收發(fā)性能）的可展開遮擋罩，它阻擋光線到達(dá)衛(wèi)星體的大部分和主體。這個遮陽罩在發(fā)射時平放在底盤上，在衛(wèi)星與獵鷹9號分離時部署。遮陽罩通過完全阻擋光線到達(dá)天線來防止光線漫反射到地面。這種方法不僅避免了衛(wèi)星天線過熱，而且對亮度降低也有較大的好處。如前所述，第一顆“VisorSat”（或稱“遮罩星”）原型將于5月發(fā)射（Starlink-8任務(wù)），到6月份，我們將在所有衛(wèi)星上安裝這些黑色遮擋罩（Starlink-10任務(wù)）。星通衛(wèi)星兩側(cè)的半球天線也有遮陽罩，使整個衛(wèi)星大大變暗。

我們一直在與主要天文團(tuán)體——特別是美國天文學(xué)會和Vera C.Rubin天文臺合作，以更好地了解天文學(xué)界使用的儀器。我們通過與一個天文學(xué)家工作組的定期交流通話，提高了我們對整個天文系統(tǒng)的了解，在此期間，我們討論了技術(shù)細(xì)節(jié)，提供了更新，并致力于保護(hù)天文觀測。

雖然互相理解是這個問題的關(guān)鍵，但是沒有具體的細(xì)節(jié)，工程問題是很難解決的。Vera C.Rubin天文臺多次認(rèn)為光反射是最難解決的問題，因此我們在過去幾個月里一直與那里的一個技術(shù)團(tuán)隊密切合作以解決這個問題。在其他有用的想法和討論中，Vera C.Rubin團(tuán)隊提供了一個目標(biāo)亮度降低，在我們迭代亮度解決方案時，我們使用它來指導(dǎo)我們的工程工作。

StarLink軌跡是通過Space-track.org和celestrak.com發(fā)布的，許多天文學(xué)家使用它們來計時觀測以避免衛(wèi)星給天文臺拍攝的照片“劃道子”。根據(jù)天文學(xué)家的要求，我們還開始在發(fā)射前發(fā)布預(yù)測數(shù)據(jù)。這樣，觀測站就可以在部署的最初幾個小時內(nèi)安排觀測時間(當(dāng)衛(wèi)星升軌時)。

減少對天文學(xué)的影響

Vera C.Rubin天文臺(Vera C.Rubin天文臺)這樣的較大望遠(yuǎn)鏡的巨大收集區(qū)域會極為敏感，即使是最黑暗的衛(wèi)星也是如此，即使是遮罩星也會產(chǎn)生影響，但這是所有衛(wèi)星不可不免的。要減少衛(wèi)星的影響，還有很多工作要做，首先要了解天文傳感器是如何工作的。

天文界告訴我們他們的成像技術(shù)。光學(xué)系統(tǒng)使用透鏡將光聚焦到成像傳感器上。大多數(shù)光學(xué)天文儀器使用稱為電荷耦合器件(CCDS)的傳感器，因為遙遠(yuǎn)的超新星和星系等天文目標(biāo)在傳感器所能探測到的范圍內(nèi)通常是模糊的。在這些應(yīng)用中，CCDS的低噪點水平使得給定圖像的信噪比更高，使人們更容易看到宇宙中非常微弱的特征。

然而，CCDS有一個關(guān)鍵的缺點：與其他常見的傳感器相比，比如你手機(jī)中的CMOS傳感器。如果你把手機(jī)對準(zhǔn)明亮的光線，你會看到所有的像素都飽和了，并且在亮光源的區(qū)域變成了白色。如果你用一個使用CCD傳感器的光學(xué)系統(tǒng)來觀察同一個目標(biāo)，你會發(fā)現(xiàn)這個亮點在圖像上產(chǎn)生垂直條紋。

這種差異是由于每個傳感器類型讀取每個像素的值的方式不同造成的。CMOS傳感器本質(zhì)上在每個像素處都有一個放大器，將采集到的光轉(zhuǎn)換成數(shù)字值，而CCD傳感器有有限數(shù)量的放大器，并將采集到的光(以電子的形式)移動到傳感器上，以便數(shù)字化。這種機(jī)制意味著CCD上的飽和像素往往會從整個像素列中清除數(shù)據(jù)。

這一效應(yīng)，通常被稱為“開花”，是一個很小但明亮的光源如何影響天文觀測的一個例子。這一原則是我們努力的方向核心。雖然不可能創(chuàng)造地球上最先進(jìn)的光學(xué)設(shè)備來看不見的衛(wèi)星，但通過降低衛(wèi)星的亮度，我們可以使現(xiàn)有的處理類似問題的方法，如幀疊加，提高效率。

未來的Starlink衛(wèi)星

SpaceX致力于使未來的衛(wèi)星設(shè)計盡可能暗。下一代衛(wèi)星，旨在利用星艦獨特的發(fā)射能力，將專門設(shè)計為最小化亮度，同時也增加了消費者的數(shù)量，提供全球覆蓋的偏遠(yuǎn)地區(qū)高速互聯(lián)網(wǎng)。

雖然SpaceX是第一個解決衛(wèi)星亮度問題的大型星座制造商和運營商，但我們不會是最后一個。隨著發(fā)射成本繼續(xù)下降，會出現(xiàn)更多星座，它們也需要確保衛(wèi)星不會過度影響地面的問題。這就是為什么我們正在努力使這個問題更容易解決，并提供了先行模板。

END……

英語全文：

STARLINK DISCUSSION NATIONAL ACADEMY OF SCIENCES

SpaceX is launching Starlink to provide high-speed, low-latency broadband connectivity across the globe, including to locations where internet has?traditionally been too expensive, unreliable, or entirely unavailable. We also?firmly believe in the importance of a natural night sky for all of us to enjoy, which is why we have been working with leading astronomers around the world to better understand the specifics of their observations and engineering changes we can make to reduce satellite brightness. Our goals include:

Making the satellites generally invisible to the naked eye within a week of launch.?We're doing this by changing the way the satellites fly to their operational altitude, so that they fly with the satellite knife-edge to the Sun. We are working on implementing this as soon as possible for all satellites since it is a software change.

Minimizing Starlink's impact on astronomy by darkening satellites so they do not saturate observatory detectors. We're accomplishing this by adding a deployable visor to the satellite to block sunlight from hitting the brightest parts of the spacecraft. The first unit is flying on the next launch, and by flight 9 in June all future Starlink satellites will have sun visors. Additionally, information about our satellites' orbits are located on?space-track.org?to facilitate observation scheduling for astronomers.?We are interested in feedback on ways to improve the utility and timeliness of this information.

To better explain the details of brightness mitigation efforts, we need to explain more about how the Starlink satellites work.

Starlink Orbits

Starlink has three phases of flight: (1) orbit raise, (2) parking orbit (380 km above Earth), and (3) on-station (550 km above Earth).?During orbit raise the satellites use their thrusters to raise altitude over the course of a few weeks.?Some of the satellites?go directly to station?while others pause in the parking orbit to allow the satellites to precess to a different orbital plane. Once satellites are on-station they reconfigure so the antennas face Earth and the solar array goes vertical so that it can track the Sun?to maximize power generation. As a result of this maneuver, the satellites become much darker because the solar array visibility from the ground is greatly reduced.?

Currently, about half of the over 400 satellites are on-station and the other half are orbit raising or in the parking orbit. Satellites spend a small fraction of their lives orbit raising or parking and spend the vast majority of their lives on-station. It's?important to note that at any given time, only about 300 satellites will be orbit raising or?parking. The rest of the satellites will be in the operational orbit on-station.?

Starlink Satellite

The Starlink satellite design was driven by the fact that they fly at a very low altitude compared to other communications satellites. We do this to prioritize space traffic safety and to minimize the latency of the signal between the satellite and the users who are getting internet service from it. Because of the low altitude, drag is a major factor in the design. During orbit raise, the satellites must minimize their cross-sectional area relative to the "wind," otherwise drag will cause them to fall out of orbit. High drag is a double-edged sword—it means that flying the satellites is tricky, but it also means that any satellites that are experiencing problems will de-orbit quickly and safely burn up in the atmosphere. This reduces the amount of orbital debris or "space junk" in orbit.?

This low-drag and thrusting flight configuration resembles an open book, where the solar array is laid out flat in front of the vehicle. When Starlink satellites are orbit raising, they roll to a limited extent about the velocity vector for power generation, always keeping the cross sectional area minimized while keeping the antennas facing Earth enough to stay in contact with the ground stations.

When the satellites reach their operational orbit of 550 km, drag is still a factor—so any inoperable satellite will quickly decay—but the attitude control system is able to overcome this drag with the solar array raised above the satellite in a vertical orientation that we call "shark-fin." This is the orientation in which the satellite spends the majority of its operational life.

Satellite Visibility

Satellites are visible from the ground at sunrise or sunset.?This happens because the satellites are illuminated by the Sun but people or telescopes on the ground are in the dark. These conditions only happen for a fraction of Starlink's 90-minute orbit.

This simple diagram highlights why satellites in orbit raise are so much brighter than the satellites that are on-station. During orbit raise, when the solar array is in open book, sunlight can reflect off of both the solar array and the body of the satellite and hit the ground. Once on-station, only certain parts of the chassis can reflect light to the ground.

Physics of Satellite Brightness

The apparent magnitude of an object is a measure of the brightness of a star or object observed from Earth. It is a reverse logarithmic scale, so higher numbers correspond to dimmer objects. A star of magnitude 3 is approximately 2.5 times brighter than a star of magnitude 4. Based on observations that have been taken by us and by members of the astronomical community, current Starlink satellites have an average apparent magnitude of 5.5 when on-station and brighter during orbit raise. Objects up to about magnitude 6.5-7 are visible to the naked eye (naked-eye visibility is closer to 4 in most suburbs), and our goal is for Starlink satellites to be magnitude 7 or better for almost all phases of their mission.?

There are two types of reflections off of Starlink satellites: diffuse and specular. Diffuse reflections occur when light is scattered in many different directions. Imagine shining a flashlight at a white wall. Specular reflections happen when light is reflected in a particular direction. For example, the glint of sunlight off of a mirror. Diffuse reflections are the biggest contributor to observed brightness on the ground, because diffuse reflections go in all directions. You can see diffuse reflections as long as the satellite is visible.?This is why Starlink satellites can create the "string of pearls" effect in the night sky. It's a little counter-intuitive, but the shiny components of the Starlink satellites are a much smaller problem. Whether diffuse or specular, having a high reflectance helps the satellites stay cool in space. When sunlight hits a specular surface of the spacecraft and reflects, the vast majority of light reflects in the specular (mirror reflection) direction, which is generally out toward space (not toward Earth). Occasionally when it does, the glint only lasts for a second or less. In fact, specular surfaces tend to be the dimmest part of the satellite unless you are at just the right geometry.

The biggest contributors to Starlink being bright are the white diffuse phased array antennas on the bottom of the satellite, the white diffuse parabolic antennas on the sides (not shown below), and the white diffuse back side of the solar array. These surfaces are all white to keep temperatures down so components do not overheat. The key to making Starlink darker is to prevent sunlight from illuminating these white surfaces and scattering via reflection toward observers on the ground. While in orbit raise and the parking orbit the solar array dominates due to the much larger surface area. However, once the satellites are at their operational altitude, the antennas dominate because the bright backside of the solar array is shadowed.

Solutions In-Work

We've taken an experimental and iterative approach to reducing the brightness of the Starlink satellites. Orbital brightness is an extremely difficult problem to tackle analytically, so we've been hard at work on both ground and on-orbit testing.

For example, earlier this year we launched DarkSat, which is an experimental satellite where we darkened the phased array and parabolic antennas designed to tackle on-station brightness. This reduced the brightness of the satellite by about 55%, as was verified by differential optical measurements comparing DarkSat to other nearby Starlink satellites. This is nearly enough of a brightness reduction to make the satellite invisible to the naked eye while on-station. However, black surfaces in space get hot and reflect some light (including in the IR spectrum), so we are moving forward with a sun visor solution instead. This avoids thermal issues due to black paint, and is expected to be darker than DarkSat since it will block all light from reaching the white diffuse antennas.

Early Mission (Orbit Raise and Parking Orbit) Roll Maneuver

Since the visor is intended to help with brightness while on-station, it does not shade the back of the solar array, which means that it will not prevent orbit raise and parking orbit brightness. For this, we are working on changing the way the satellite flies up from insertion to parking orbit and to station.

We're currently testing rolling the satellite so the vector of the Sun?is in-plane with the satellite body, i.e. so the satellite is knife-edge to the Sun. This would reduce the light reflected onto Earth by reducing the surface area that receives light. This is possible when orbit raising and parking in the precession orbit because we don't have to constrain the antennas to be nadir facing to provide coverage to internet users. However, there are a couple of nuanced reasons why this is tricky to implement. First, rolling the solar array away from the Sun?reduces the amount of power available to the satellite. Second, because the antennas will sometimes be rolled away from the ground, contact time with the satellites will be reduced. Third, the star tracker cameras are located on the sides of the chassis (the only place they can go and have adequate field of view). Rolling knife edge to the Sun?can point one star tracker directly at the Earth and the other one directly at the Sun, which would cause the satellite to have degraded attitude knowledge.

There will be a small percentage of instances when the satellites cannot roll all the way to true knife edge to the Sun due to one of the aforementioned constraints. This could result in the occasional set of Starlink satellites in the orbit raise of flight that are temporarily visible for one part of an orbit.

On-Station Brightness

Satellites spend most of their lives on-station, where they will always be in the shark-fin configuration during visible passes. We can adjust the solar array positioning in this configuration to reflect light from its largely specular solar cells away from Earth and to partially hide it behind the chassis. The main remaining goal is to block the phased arrays and antennae from direct view of the sun.?The goal is to cover the white phased array antennas and the parabolic antennas on the sides of the satellite.

Using our low orbital altitude and flat satellite geometry to our advantage, we designed an RF-transparent deployable visor for the satellite that blocks the light from reaching most of the satellite body and all of the diffuse parts of the main body. This visor lays flat on the chassis during launch and deploys during satellite separation from Falcon 9. The visor prevents light from reflecting off of the diffuse antennas by blocking the light from reaching the antennas altogether. Not only does this approach avoid the thermal impacts from surface darkening the antennas, but it should also have a larger impact on brightness reduction. As previously noted, the first VisorSat prototype will launch in May and we will have these black, specular visors on all satellites by June. The parabolic antennas on the sides of the Starlink satellite also have visor-like coverings that darken them.

We have been working with leading astronomical groups in this effort—in particular the American Astronomical Society and the Vera C. Rubin Observatory—to better understand the methods and instruments employed by the astronomy community. With AAS, we have increased our understanding of the community as a whole through regular calls with a working group of astronomers during which we discuss technical details, provide updates, and work on how we can protect astronomical observations moving forward. A post on some of our sessions is?here. One particularly useful presentation from a member of this working group is?here.

While community understanding is critical to this problem, engineering problems are difficult to solve without specifics. The Vera C. Rubin Observatory was repeatedly flagged as the most difficult case to solve, so we've spent the last few months working very closely with a technical team there to do just that. Among other useful thoughts and discussions, the Vera Rubin team has provided a target brightness reduction that we are using to guide our engineering efforts as we iterate on brightness solutions.

These technical and community discussions are paired with our existing efforts to make the satellites easier for astronomers to avoid. Starlink trajectories are published through?Space-track.org?and?celestrak.com, which many astronomers use in timing their observations to avoid satellite streaks. We've also started publishing predictive data prior to launch at the request of astronomers. These allow observatories to schedule around the satellites in the first few hours of deployment (as satellites de-tumble and enter the network).

Vera Rubin has been described as the limiting case for Starlink, due to its enormous aperture and wide field of view. These two characteristics work in concert to produce the perfect storm for satellite observations. Most astronomical systems look at an extremely small section of the sky (less than 1 degree), which makes it exceedingly unlikely that a satellite will cross in front of the imaging system in a given observation. On the other hand, systems with very large fields of view normally aren't extremely sensitive, meaning that, while streaks will occur, they will have a small impact on the overall data collection. This is why we've been working so closely with the team at the Rubin Observatory. In fact, despite its wide field of view,?the Vera C. Rubin Observatory is sensitive enough to detect a sunlit golf ball as far away as the Moon.

So what can we do to mitigate our impact on these edge cases of wide, fast survey telescopes?

Minimizing the Impact on Astronomy

The huge collecting area of a larger telescopes like Vera C. Rubin Observatory leads to a sensitivity that will render even the darkest satellites visible.They are so sensitive that it won't be possible to build a satellite that will not produce streaks, in a typical long integration. There is much that can be done to reduce the impact of satellite streaks, and that starts with an understanding of how astronomical sensors work.

The astronomical community has done a great job of educating us on their imaging techniques. Optical systems use mirrors or lenses to focus light onto an imaging sensor. Most optical astronomy instruments use sensors called charge-coupled-devices (CCDs) as their detectors because astronomical targets, such as distant supernovae and galaxies, are generally?dim–at the limit of what can be detected by a sensor. For these applications, the lower noise level of CCDs allows for a higher signal-to-noise ratio for a given image, making it easier to see very faint features in the universe.

However, CCDs suffer from a key drawback: when compared to other common sensors, like the CMOS sensor in your cell phone.?If you point your cell phone at a bright light, you'll see all the pixels saturate and turn white in the region of the bright source. If you look at the same target with an optical system that uses a CCD sensor, you'll notice that this bright spot extends to create vertical stripes on the image.

This difference is due to the way each sensor type reads the values for each pixel. While a CMOS sensor essentially has an amplifier at each pixel that turns the light collected into a digital value, a CCD sensor has a limited number of amplifiers and moves the collected light (in the form of electrons) across the sensor, to be digitized. This mechanism means that a saturated pixel on a CCD tends to wipe out data from an entire column of pixels.

This effect, commonly referred to as 'blooming,' is one example of how a very small but bright source of light can impact an astronomical observation. This principle is the core of our mitigation efforts. While it will not be possible to create satellites that are invisible to the most advanced optical equipment on Earth, by reducing the brightness of the satellites, we can make the existing strategies for dealing with similar issues, such as frame-stacking, dramatically more effective.

Future Satellites

SpaceX is committed to making future satellite designs as dark as possible.?The next generation satellite, designed to take advantage of Starship's unique launch capabilities, will be specifically designed to minimize brightness while also increasing the number of consumers that it can serve with high-speed internet access.?

While SpaceX is the first large constellation manufacturer and operator to address satellite brightness, we won't be the last. As launch costs continue to drop, more constellations will emerge and they too will need to ensure that the optical properties of their satellites don't create problems for observers on the ground. This is why we are working to make this problem easier for everyone to solve in the future.