Astronomy

Problem about orbiting of a satelite

Problem about orbiting of a satelite

Problem: There is an satellite that orbits the Earth. Its orbit is circular and its orbital plane is perpendicular to Earth's Equatorial Plane. It orbits is such that a person who is on equator see this satellite on Zenith every 12Hours.

a. Find Satellite's Period.

b. What is distance of satellite to person when it Sets on person's horizon?

My problem with this question is:

For the first part: somewhere said period is 12hours. Somewhere else said the person on equator also moves (Earth Rotation) so 12 hours is P/2 and P= 24hours. What is the right answer?

For the second part: Which of the following figures show the position of satellite when it sets? (Figure 1 or 2?)


I'm treating this as a homework question. You have made a clear attempt, so it is not off topic, but you should clarify the source of the problem.

You will first need to establish if the rotation of the Earth is to be considered (it makes a big difference, but in a homework, sometimes the Earth stops spinning!) You have then correctly found the two possible answers, either 24 or 12 hours.

You can also consider the motion of the Earth around the sun (as the Earth only takes 23hr, 56min to spin once, relative to the stars). What this means is that, after 12 hours, the Earth has turned more than 180 degrees, and there is no orbital plane that passes over the person, and through the origin, and is perpendicular to the equator. However the error is only about 1 degree, so probably can be neglected for the purposes of homework.

For the second part, the first picture is certainly wrong, as the line of sight (in green) passes through the Earth. The second shows the line of sight (now in red) being tangent to the Earth's surface. You will need to use orbital mechanics to find the distance from the Earth's centre to the satellite, and find out the distance from the Earth's centre to its surface (green lines), giving two sides of a right-angled triangle. And the rest is maths.

There are a few details that may affect the answer: you should consider if the motion of the person will affect the answer to part (b) (and if not, why not). You should know that the Earth is not spherical. You should consider whether the optical refraction of light by the Earth's atmosphere should be considered. However, in a homework problem, such issues can often be ignored, as their effects are small.


Part (1). Due to the earth's rotation, an observer on the equator moves 180 deg every 12 hours. Your satellite is moving perpendicular to the equatorial plane and it meets the observer on the other side of its orbit after 12 hours. Therefore it too has travelled 180 degrees. To revolve a further 180 degrees (and complete a full 360 degree revolution), in time to meet the observer again, the satellite would take another 12 hours. Therefore the time period of the satellite would have to be 12h + 12h = 24h.

(2) A satellite with a time period of 24h is called a geosynchronous satellite. The radius $r$ of the orbit of this type of satellite is approximately 36,000 km, can be determined by working further into this formula…

$$ frac{v^2}{r} = frac{GM}{r^2}$$

So, in your second diagram, we can see that the radius of the satellite is 36,000 km, and we know the radius of the earth is 6400km, so by Pythagoras rule, the distance $d$ to the satellite when it sets can be obtained by,

$$d = sqrt{36000^2 - 6400^2}$$


The question is wrong: such a satellite orbit does not exist. Due to angular-momentum conservation, the orbital plane of the satellite is fixed in space, but the position of the observer rotates by about $left( 360+frac{360}{365.25} ight)^{circ}$ every $24$ hours. This is simply because the Earth rotates more than once in an average day, i.e. the time between consecutive noons (Sun in zenith on the equator).


Are Too Many Satellites Ruining Our View Of Space?

An image of the NGC 5353/4 galaxy group made with a telescope at Lowell Observatory in Arizona, U.S., on the night of Saturday, May 25, 2019. The diagonal lines running across the image are light trails left by the Starlink satellite group as it passed through the telescope’s field of view. Image courtesy of Victoria Girgis (Lowell Observatory).

SpaceX—the American technology company—launched 60 satellites into space on January 29. (A satellite is an object that orbits a planet. Some are natural satellites, like the moon. Others are artificial, like the ones launched by SpaceX.)

SpaceX plans to create a network of 12,000 satellites. The company says that the network, known as Starlink, will help provide better Internet service to remote parts of the world.

But astronomers say the growing number of satellites orbiting the Earth is making it harder for them to observe and learn from the universe.

Satellites are made of metal that reflects sunlight. This makes them show up in the night sky as bright, slow-moving dots. After the launch in November, the Starlink satellites appeared in images taken by telescopes and deep-space cameras as a trail of bright lights streaking across the sky.

The Starlink satellites take three to five minutes to cross the viewing area of a telescope. During that time, they may pass directly in front of the object an astronomer is trying to look at, hiding it from view. Also, the light from the satellites is so bright, it makes it impossible to see the fainter light of distant stars and planets.

Astronomers learn about space by using large telescopes and special cameras to observe light coming from very far away. The information they collect can help them understand things like how galaxies are formed or which planets might be able to support life.

Some astronomers also use radio telescopes, which record radio waves coming from space. This makes it possible to study things that give off low energy and would not show up as light—like dust and gases. In April 2019, astronomers used information collected by several radio telescopes to produce the first image of a black hole.

Large groups of satellites—known as “satellite constellations”—give off radio signals of their own and reflect radio waves coming from Earth. These extra signals interfere with radio waves coming from further away in the galaxy. While it might be possible to build satellites with surfaces that don’t reflect light, it will be very difficult to make satellites that don’t interfere with radio waves.

SpaceX began launching batches of Starlink satellites in 2019. The company is planning as many as 22 more launches in 2020. Eventually, the company would like to put 30,000 satellites into orbit around the Earth. Other companies also want to create satellite constellations of their own.

People have been launching satellites into space since 1957. They serve many useful purposes. Some are an important part of communications networks, like cellphones, TV, and Internet. Others are used to track weather and climate information, create maps of the Earth, operate navigation systems like GPS, and take photos of the Earth, sun, planets and deep space. The International Space Station is a kind of satellite, with room for people to live on it.

Right now, there are about 1,000 artificial satellites orbiting the Earth. But with companies planning to launch thousands more, astronomers are worried about the effect all of those satellites will have on their ability to study the universe. More satellites orbiting the Earth also means there are more chances of collisions, and more “space junk” floating around the Earth when the satellites stop working.

There are no rules about who can launch a satellite, or how many can orbit the Earth at one time. The International Astronomical Union (IAU) is a group made up of professional astronomers from all over the world. IAU members want to work with the companies that design and launch satellites and the governments that make laws and regulations. They say it’s important to study the impact of having so many satellites and to make rules to protect the night sky.

Think and Discuss

There are currently no rules about who can launch a satellite or how many can be orbiting the Earth. Should there be? If so, who do you think would put the rules in place? Who would enforce them, and how?

Make a T-chart and label one side “pros” (good things) and the other side “cons” (bad things). List five things in each column about satellite launches.

This article mentions two types of satellites, real and artificial. Find out some information about both types. What are the similarities and differences?


Kepler's laws defined description of Kepler two body problem reduction of two body problem and solution of one body problem energy diagram of circular, elliptic, parabolic, and hyperbolic orbits equations for position, energy, and angular momentum of an orbiting body properties of an ellipse Kepler's equal area law defined Kepler's law for period of orbit.

8.01T Physics I, Fall 2004
Dr. Peter Dourmashkin, Prof. J. David Litster, Prof. David Pritchard, Prof. Bernd Surrow

Course Material Related to This Topic:


Elon Musk's SpaceX warned: Your internet-beaming satellites disrupt astronomy

SpaceX's broadband project could severely disrupt space imaging and astroid detection.

By Liam Tung | December 9, 2019 -- 13:06 GMT (05:06 PST) | Topic: Networking

Satellites cast into low Earth orbit by Elon Musk's rocket company, SpaceX, are disrupting astronomy research due to the vehicles' brightness in night skies – and the problem could get much worse unless design changes are made.

Networking

SpaceX last month launched another 60 Starlink satellites on the back of a Falcon 9 rocket. They are intended to become part of a mesh network designed to deliver broadband to underserved areas across the world.

There are about 120 orbiting Earth today, but there could be as many as 12,000 in the next few years.

While Starlink promises to solve broadband speed and latency issues in rural areas in North America, the satellites are already causing interference for astronomy scientists across the globe because of their brightness.

NewScientist reported that astronomers complained after the initial batch of 60 satellites were launched in May that they were extremely bright.

While the fleet is small now, the astronomers are concerned that Musk's plans for several thousand broadband-beaming Starlink satellites could become a real problem for space imaging in the near future.

A key observation point affected by Musk's satellites is the Cerro Tololo Inter-American Observatory (CTIO), home to the Southern Astrophysical Research (SOAR) and Gemini telescopes, which are located in the foothills of the Andes, 7,241 feet (2,200 meters) above sea level.

"I am in shock," wrote CTIO astronomer Clara Martinez-Vazquez on Twitter in November, referring to the Starlink satellites. "Our DECam exposure was heavily affected by 19 of them," she tweeted. "The train of Starlink satellites lasted for over five minutes."

The Association of Universities for Research in Astronomy (AURA) in November issued a statement about the interference it expects Starlink satellites to cause for the Large Synoptic Survey Telescope (LSST), which is under construction in Chile and expected to begin imaging the sky in 2022. The LSST will be used to detect near-Earth asteroids.

The LSST team estimates that "nearly every exposure within two hours of sunset or sunrise would have a satellite streak". In summer, it could have a massive affect on the telescope's ability to observe the sky during twilight.

"Detection of near-Earth asteroids, normally surveyed for during twilight, would be particularly impacted. Dark energy surveys are also sensitive to the satellites because of streaks caused in the images. Avoiding saturation of streaks is vital," the group warned.

AURA has also posted two time-lapse videos that demonstrate the impact Starlink satellites are having on observability of space from Earth.

SpaceX says it is taking the astronomers concerns seriously. Per Spacenews.com, SpaceX chief operating officer Gwynn Shotwell said the next batch of Starlink satellites will have a "coating on the bottom", but added that it's not known whether the fix will solve the brightness problem.

Shotwell said SpaceX will launch 60 satellites every two to three weeks for the next year to deliver global coverage by around mid-2020.

Elon Musk has said Space X needs about 400 satellites to provide "minor" coverage and 800 for "moderate" coverage of North America.

The rocket company will be able to launch a global Starlink satellite broadband service after 24 additional launches, at which point the North American service is scheduled to be available. With 30 launches, SpaceX would have 1,800 Starlink satellites.

Satellite streaks could have a massive affect on a telescope's ability to observe the sky.


SATCON1 Report on Effects of Large Satellite Constellations on Astronomy

A report by experts representing the global astronomical community, concludes that large constellations of bright satellites in low Earth orbit will fundamentally change ground-based optical and infrared astronomy and could impact the appearance of the night sky for stargazers worldwide. The report is the outcome of the recent SATCON1 virtual workshop, which brought together more than 250 scientists, engineers, satellite operators, and other stakeholders.

The report from the Satellite Constellations 1 (SATCON1) workshop, organized jointly by NSF’s NOIRLab and the American Astronomical Society (AAS), has been delivered to the National Science Foundation (NSF). Held virtually from 29 June to 2 July 2020, SATCON1 focused on technical aspects of the impact of existing and planned large satellite constellations on optical and infrared astronomy. NSF, which funded the workshop, also finances most of the large ground-based telescopes widely available to researchers in the United States. More than 250 astronomers, engineers, commercial satellite operators, and other stakeholders attended SATCON1. Their goals were to better quantify the scientific impacts of huge ensembles of low-Earth-orbiting satellites (LEOsats) contaminating astronomical observations and to explore possible ways to minimize those impacts.

SATCON1 co-chair Connie Walker from NSF’s NOIRLab explains: “Recent technology developments for astronomical research — especially cameras with wide fields of view on large optical-infrared telescopes — are happening at the same time as the rapid deployment of many thousands of LEOsats by companies rolling out new space-based communication technologies.

The report concludes that the effects of large satellite constellations on astronomical research and on the human experience of the night sky range from “negligible” to “extreme.” This new hazard was not on astronomers’ radar in 2010, when New Worlds, New Horizons — the report of the National Academies’ Astro2010 decadal survey of astronomy and astrophysics — was issued. Astro2010’s top recommendation for ground-based optical astronomy, Vera C. Rubin Observatory, will soon begin conducting exactly the type of observations to which Walker refers. When SpaceX launched its first batch of 60 Starlink communication satellites in May 2019 and people all over the world saw them in the sky, astronomers reacted with alarm. Not only were the Starlink satellites brighter than anyone expected, but there could be tens of thousands more like them. As they pass through Rubin’s camera field, they will affect the 8.4-meter (27.6-foot) telescope’s view of the faint celestial objects astronomers hope to study with it.

Rubin Observatory and the giant 30-meter telescopes coming online in the next decade will substantially enhance humankind’s understanding of the cosmos,” says SATCON1 co-chair Jeff Hall from Lowell Observatory and chair of the AAS Committee on Light Pollution, Radio Interference, and Space Debris. “For reasons of expense, maintenance, and instrumentation, such facilities cannot be operated from space. Ground-based astronomy is, and will remain, vital and relevant.

Constellations of LEOsats are designed in part to provide communication services to underserved and remote areas, a goal everyone can support. Recognizing this, astronomers have engaged satellite operators in cooperative discussions about how to achieve that goal without unduly harming ground-based astronomical observations. The SATCON1 workshop is just the latest, and most significant, step in this ongoing dialog.

The report offers two main findings. The first is that LEOsats disproportionately affect science programs that require twilight observations, such as searches for Earth-threatening asteroids and comets, outer Solar System objects, and visible-light counterparts of fleeting gravitational-wave sources. During twilight the Sun is below the horizon for observers on the ground, but not for satellites hundreds of kilometers overhead, which are still illuminated. As long as satellites remain below 600 kilometers (not quite 400 miles), their interference with astronomical observations is somewhat limited during the night’s darkest hours. But satellites at higher altitudes, such as the constellation planned by OneWeb that will orbit at 1,200 kilometers (750 miles), may be visible all night long during summer and for much of the night in other seasons. These constellations could have serious negative consequences for many research programs at the world’s premier optical observatories. Depending on their altitude and brightness, constellation satellites could also spoil starry nights for amateur astronomers, astrophotographers, and other nature enthusiasts.

The report’s second finding is that there are at least six ways to mitigate harm to astronomy from large satellite constellations:

  1. Launch fewer or no LEOsats. However impractical or unlikely, this is the only option identified that can achieve zero astronomical impact.
  2. Deploy satellites at orbital altitudes no higher than

Astronomers have only now, a little over a year after the first SpaceX Starlink launch, accumulated enough observations of constellation satellites and run computer simulations of their likely impact when fully deployed to thoroughly understand the magnitude and complexity of the problem. This research informed the discussion at SATCON1 and led to ten recommendations for observatories, constellation operators, and those two groups in collaboration. Some involve actions that can be taken immediately, while others urge further study to develop effective strategies to address problems anticipated as new large telescopes come online and as satellite constellations proliferate.

The SATCON1 workshop was an important step towards managing a challenging future. NOIRLab director Patrick McCarthy says, “I hope that the collegiality and spirit of partnership between astronomers and commercial satellite operators will expand to include more members of both communities and that it will continue to prove useful and productive. I also hope that the findings and recommendations in the SATCON1 report will serve as guidelines for observatories and satellite operators alike as we work towards a more detailed understanding of the impacts and mitigations and we learn to share the sky, one of nature’s priceless treasures.

AAS President Paula Szkody of the University of Washington participated in the workshop. She says, “Our team at the AAS was enthusiastic to partner with NOIRLab and bring representatives of the astronomical and satellite communities together for a very fruitful exchange of ideas. Even though we’re still at an early stage of understanding and addressing the threats posed to astronomy by large satellite constellations, we have made good progress and have plenty of reasons to hope for a positive outcome.

The next workshop, SATCON2, which will tackle the significant issues of policy and regulation, is tentatively planned for early to mid-2021.

More information

NSF’s National Optical-Infrared Astronomy Research Laboratory (NOIRLab), the US center for ground-based optical-infrared astronomy, operates the international Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), Kitt Peak National Observatory (KPNO), Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and the Vera C. Rubin Observatory. It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona. The astronomical community is honored to have the opportunity to conduct astronomical research on Iolkam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawaiʻi, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence that these sites have to the Tohono O’odham Nation, to the Native Hawaiian community, and to the local communities in Chile, respectively.

The American Astronomical Society (AAS), established in 1899, is the major organization of professional astronomers in North America. Its membership (approx. 8,000) also includes physicists, mathematicians, geologists, engineers, and others whose research interests lie within the broad spectrum of subjects now comprising the astronomical sciences. The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the universe, which it achieves through publishing, meeting organization, education and outreach, and training and professional development.

The SATCON1 workshop was supported by the National Science Foundation (NSF).


Solving the space junk problem

Space is getting crowded. Aging satellites and space debris crowd low-Earth orbit, and launching new satellites adds to the collision risk. The most effective way to solve the space junk problem, according to a new study, is not to capture debris or deorbit old satellites: it's an international agreement to charge operators "orbital-use fees" for every satellite put into orbit.

Orbital use fees would also increase the long-run value of the space industry, said economist Matthew Burgess, a CIRES Fellow and co-author of the new paper. By reducing future satellite and debris collision risk, an annual fee rising to about $235,000 per satellite would quadruple the value of the satellite industry by 2040, he and his colleagues concluded in a paper published today in the Proceedings of the National Academy of Sciences.

"Space is a common resource, but companies aren't accounting for the cost their satellites impose on other operators when they decide whether or not to launch," said Burgess, who is also an assistant professor in Environmental Studies and an affiliated faculty member in Economics at the University of Colorado Boulder. "We need a policy that lets satellite operators directly factor in the costs their launches impose on other operators."

Currently, an estimated 20,000 objects -- including satellites and space debris -- are crowding low-Earth orbit. It's the latest Tragedy of the Commons, the researchers said: Each operator launches more and more satellites until their private collision risk equals the value of the orbiting satellite.

So far, proposed solutions have been primarily technological or managerial, said Akhil Rao, assistant professor of economics at Middlebury College and the paper's lead author. Technological fixes include removing space debris from orbit with nets, harpoons, or lasers. Deorbiting a satellite at the end of its life is a managerial fix.

Ultimately, engineering or managerial solutions like these won't solve the debris problem because they don't change the incentives for operators. For example, removing space debris might motivate operators to launch more satellites -- further crowding low-Earth orbit, increasing collision risk, and raising costs. "This is an incentive problem more than an engineering problem. What's key is getting the incentives right," Rao said.

A better approach to the space debris problem, Rao and his colleagues found, is to implement an orbital-use fee -- a tax on orbiting satellites. "That's not the same as a launch fee," Rao said, "Launch fees by themselves can't induce operators to deorbit their satellites when necessary, and it's not the launch but the orbiting satellite that causes the damage."

Orbital-use fees could be straight-up fees or tradeable permits, and they could also be orbit-specific, since satellites in different orbits produce varying collision risks. Most important, the fee for each satellite would be calculated to reflect the cost to the industry of putting another satellite into orbit, including projected current and future costs of additional collision risk and space debris production -- costs operators don't currently factor into their launches. "In our model, what matters is that satellite operators are paying the cost of the collision risk imposed on other operators," said Daniel Kaffine, professor of economics and RASEI Fellow at the University of Colorado Boulder and co-author on the paper.

And those fees would increase over time, to account for the rising value of cleaner orbits. In the researchers' model, the optimal fee would rise at a rate of 14 percent per year, reaching roughly $235,000 per satellite-year by 2040.

For an orbital-use fee approach to work, the researchers found, all countries launching satellites would need to participate -- that's about a dozen that launch satellites on their own launch vehicles and more than 30 that own satellites. In addition, each country would need to charge the same fee per unit of collision risk for each satellite that goes into orbit, although each country could collect revenue separately. Countries use similar approaches already in carbon taxes and fisheries management.

In this study, Rao and his colleagues compared orbital-use fees to business as usual (that is, open access to space) and to technological fixes such as removing space debris. They found that orbital use fees forced operators to directly weigh the expected lifetime value of their satellites against the cost to industry of putting another satellite into orbit and creating additional risk. In other scenarios, operators still had incentive to race into space, hoping to extract some value before it got too crowded.

With orbital-use fees, the long-run value of the satellite industry would increase from around $600 billion under the business-as-usual scenario to around $3 trillion, researchers found. The increase in value comes from reducing collisions and collision-related costs, such as launching replacement satellites.

Orbital-use fees could also help satellite operators get ahead of the space junk problem. "In other sectors, addressing the Tragedy of the Commons has often been a game of catch-up with substantial social costs. But the relatively young space industry can avoid these costs before they escalate," Burgess said.


The Attempt at a Solution

Hi everyone, these two problems have been boggling me so bad. This is part of some online hw due midnight and these are the only two problems I was not able to do. I also have only one submission for each as I have no idea what I am doing wrong. I searched the forums and found a very similar question with a different planet and followed their work, but was too afraid to punch in my answer. I would love it if someone can confirm my work for me please. Here is my work:

For pluto, my first question, I used G = 6.67x10^-11, T = 6.39 days = 552096, and Mass of pluto, M= 1.309x10^22kg. I plugged in all of these values into my previous equation and got:

r = 18890566.49 m = 18890.56km

Then, h = r - r pluto = 18890.56 - 1150 = 17740.56km (final answer).

For venus, I did the same but instead I used the following values:
T = 116days and 18 hours = 10264800seconds
M =4.867x10^24 kg

Do the same as above, I got r = 953329010.5 m = 953329km

h = r - r venus = 953329km - 6050km = 947279km

Each question is qorth 13% of this hw assignment and would love it if someone could confirm whether these are correct or not. I really appreciate it.


The Problem with Satellite Mega-Constellations

Feb. 14, 2020: The night sky is in danger. This has been true for years as urban landscapes became increasingly light-polluted. But now there’s a new threat, one you can’t escape by driving into the countryside. It’s the “mega-constellation.” Some companies are planning to launch tens of thousands of internet satellites into low-Earth orbit. The recent launch by Space X of just 240 Starlink satellites has already ruined many astronomical observations.

Above: Astronomers at the Cerro Tololo Inter-American Observatory were trying to photograph nearby galaxies when 19 Starlink satellites intervened. [Full Story]

1. The number of satellites above the horizon at any given time would be between

1500 and a few thousand. Most will appear very close to the horizon, with only a relative few passing directly overhead.

2. When the sun is 18 degrees below the horizon–that is, when the night becomes dark–the number of illuminated satellites above the horizon would be around 1000. These numbers will decrease during the hours around midnight when many satellites fall into Earth’s shadow.

3. At the moment it is difficult to predict how many of the illuminated satellites will be visible to the naked eye because of uncertainties in their reflectivity. Probably, the vast majority will be too faint to see. This depends to some degree on experiments such as those being carried out by SpaceX to reduce the reflectivity of their satellites with different coatings.

Above: Starlink satellites photobomb the NGC 5353/4 galaxy group at Lowell Observatory [more]

5. The Vera C. Rubin Observatory currently under construction in Chile will be particularly hard-hit. The innovative observatory will scan large swaths of the sky, looking for near-Earth asteroids, studying dark energy, and much more. According to the IAU, up to 30% of the 30-second images during twilight hours will be affected. In theory, the effects of the new satellites could be mitigated by accurately predicting their orbits and interrupting observations, when necessary, during their passage, but this is a burdensome procedure.

There are no international rules governing the brightness of orbiting manmade objects. Until now, they didn’t seem to be necessary. Mega-constellations, however, threaten “the uncontaminated view of the night sky from dark places, which should be considered a non-renounceable world human heritage,” says the press release. Therefore the IAU will present its findings at meetings of the UN Committee for Peaceful Uses of Outer Space, bringing the attention of this problem to world leaders.


Why SpaceX's plan to put 25,000 satellites in orbit is bad news for astronomers

By Nicole Karlis
Published November 12, 2019 7:50PM (EST)

A SpaceX Falcon 9 rocket lifts off from Cape Canaveral Air Force Station carrying 60 Starlink satellites on November 11, 2019 in Cape Canaveral, Florida. The Starlink constellation will eventually consist of thousands of satellites designed to provide world wide high-speed internet service. (Paul Hennessy/NurPhoto via Getty Images)

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It is a truism that commercialization often comes at a detriment to science. The internet, once an academic and intellectual space free of advertisements, has been transformed into a digital billboard likewise, the commercialization of radio airwaves has made Earth-based radio astronomy difficult due to interference from Wi-Fi, AM/FM and TV signals. Now, as capitalists are gearing up to commercialize space, astronomers have renewed reason to be upset by an announcement by SpaceX that could make ground-based observational astronomy much more difficult, forcing astronomers to work around the zipping of satellites across the night sky.

The private, Elon Musk–founded company launched one of its reusable rockets from Cape Canaveral on Monday with 60 satellites onboard, as part of the Starlink constellation, which will collectively provide satellite internet around the world, among other uses. The launch was the second payload of a satellite constellation that will eventually be made up of tens of thousands of orbiting transmitters, if all goes as planned. However, despite the mission being disguised by a humanitarian cause, this week's launch brings forth ongoing worries many in the space science field have about the footprint of so many satellites, like reflected sunlight.

“I am concerned [that] the SpaceX satellite launch marks the beginning of a new era,” Avi Loeb, chair of Harvard's astronomy department, told Salon via email.

In October, Musk announced that his company was requesting permission from the Federal Communications Commission to operate 30,000 satellites, in addition to the 12,000 that have already been approved. As of January 2019, there were about 5,000 satellites in space, 1,950 of which are still functioning. Musk’s satellites would bring the number of satellites around Earth to a state astronomers have never dealt with before.

“They are already requesting 30,000 new satellites beyond the 12,000 that were granted and the number will grow further without any space laws to moderate the growth,” Loeb added. “It is essential to find a technological solution that would minimize the footprint of these satellites on telescope images (or else we will need to always avoid their predictable locations or relocate optical observatories to the Moon).”

While satellites aren’t necessarily a new problem for astronomers, the brightness of the SpaceX-launched satellites are of concern.

“The problem is particularly acute for the Large Synoptic Survey Telescope (LSST) which will survey repeatedly a large fraction of the sky,” Loeb explained. “There is no doubt that it will be addressed in the 2020 Decadal survey of Astronomy which will summarize the priorities of the Astronomy community for the next decade.”

The LSST will rely on a large camera to survey the entire sky once every three nights, at least, to study dark energy, dark matter, and asteroids. The project is set to start in 2022. Since it will survey such a wide field, satellites like the Starlink ones could affect it significantly. Currently LSST researchers are analyzing how 50,000 new satellites, according to filings by SpaceX, could affect LSST observations. According to Nature, early findings suggest that the telescope could lose significant amounts of observing time.

The first batch of Starlinks that were launched into space in May have already caused some problems. In September, the European Space Agency (ESA) had to move its Aeolus wind-mapping satellite out of the way of a Starlink satellite to avoid a collision.

“We see it as part of our changing environment,” Stijn Lemmens, a space debris analyst at ESA, told Forbes at the time. “We want to raise awareness in this sense, that there’s quite a bit of work that needs to be done on how to make sure that these type of operations will run smoothly in the future.”

After the first launch, the American Astronomical Society released a statement addressing their concerns, which extended beyond potential collisions and impacted observation times.

“The number of such satellites is projected to grow into the tens of thousands over the next several years, creating the potential for substantial adverse impacts to ground- and space-based astronomy,” the statement read. “These impacts could include significant disruption of optical and near-infrared observations by direct detection of satellites in reflected and emitted light contamination of radio astronomical observations by electromagnetic radiation in satellite communication bands and collision with space-based observatories.”

Indeed, those who study space fear these satellites are just the beginning of more technology commercializing space.

“These mega-constellations are just beginning,” Danica Remy, president of b612 told Salon in an emailed statement. “The LEO satellite traffic problem is only going to grow. At the same time with the growth of communication satellites, like the ones SpaceX launched, humanity is collectively launching many more constellations.”

She added: “They will be able to do things like track methane gas, illegal fishing in the seas, human migration from war and famine, water levels, fires, and fire management and many more things that we are just starting to imagine, develop and deploy.”

Loeb told Salon Monday’s launch is another reminder of a growing conflict between the interest of the business world and science.

“There is a precedence for that situation, namely radio band transmitters used for communication and self-driving cars introduces interference to radio telescopes,” Loeb said. “As a result, there are federal regulations on the frequency bands that can be used for commercial purposes.”

“One can imagine analogous regulations on the number [of] or luminosity of satellites,” he said.


Astronomy Faces A Mega-Crisis As Satellite Mega-Constellations Loom

For all of human history until the launch of Sputnik, the only objects in the night sky were naturally occurring ones. From any dark sky site in the world, which included many suburban and rural areas in the 1950s, you could simply look up on a clear night and take in the vast expanse of the Universe beyond our world. In the absence of light pollution, a moonless night would reveal to your naked eye thousands of stars, numerous deep sky objects, extraordinary detail in the Milky Way, and even the occasional comet or asteroid.

Since the dawn of the space age, the night sky has changed in two major ways. The rise of light pollution, made worse by the recent widespread adoption of LED lighting, has restricted pristine, dark skies to a few isolated locations around the globe. Satellites, on the other hand, were only a minor nuisance until recently. Over the past 18 months, the construction of satellite megaconstellations has begun, and the impact has been severe on professional and amateur astronomers alike. Astronomy is facing a crisis, and although some players in the industry are listening, no one has yet met even the basic criteria set forth by astronomers worldwide. Here’s what you need to know.

There’s a new revolution now upon us, brought on by the development of relatively low-cost launches. It’s now cheaper than ever to put large, repeated payloads into low-Earth orbit, and that is what’s presently enabling a new type of space-based infrastructure: large constellations of satellites. Motivated by the possibility of bringing a next generation space-communications network online, providing high-speed, low-latency capabilities to communities that lack ground-based infrastructure, these constellations are still in their infancy, but are growing rapidly.

No one is denying the technological benefits that this offers for humanity, but there are costs that we’re all paying. It’s now been more than a year — since January 6, 2020 — that SpaceX has become the largest satellite operator in the world, where their Starlink satellites now number more than 1000, and are brighter than more than 99% of all previous satellites. From the first launch train of satellites that surprised everyone to their continued brightness in their final orbits, a glimpse at a dark sky highlights what needs to be done.

10 PM in January from the northern hemisphere, this sight will greet you in the southern part of your sky. (SKATEBIKER AT ENGLISH WIKIPEDIA)

Under very dark conditions, the night sky looks almost like it always does. If you walk outside once the sky has darkened, you’ll be greeted by the constellation of Orion, towering over the northern hemisphere by 10 PM nightly. But if you sit around and stare at the dark sky for even a few minutes, you’ll likely see a series of slow-moving streaks out of the corner of your eye. Look directly at them, and they’ll likely disappear. These are the current Starlink satellites, appearing in a typical human’s averted vision, but disappearing when you look directly at them, due to the plethora of rod off-axis in your eyes but the small number of them (as that’s where the color-seeing cones in our eyes are) directly along our line-of-sight. Stargazing itself is now polluted by a constant set of interruptions to our eyes.

And that’s only considering the night sky’s appearance, today, to your naked eye. If you’re an amateur or professional who engages in astronomy of any variety — using telescopes, binoculars, or participating in astrophotography — the situation only worsens. The most viewed deep-sky objects are the 110 members of the Messier catalogue, which span a variety of locations in the sky. If you were to pull out a telescope and view any of these 110 objects as of August of 2020 (and over 400 new Starlink satellites have been launched since that date), the video below illustrates what you’d see when these objects are visible in the sky.

There are, at last count, over 100,000 new satellites of this variety planned to be launched during the remainder of the current decade. Astronomers, despite receiving no funding for any of this work, have volunteered their time and resources to develop a series of recommendations for companies to follow, with the intent of minimizing the damage done to both the night sky we all access and to the cutting-edge telescopes that help us understand the Universe around us. As numerous scientists commented at the American Astronomical Society’s annual meeting last week, the AAS Committee on Light Pollution, Radio Interference, and Space Debris has been very, very busy for the past 18 months.

As a result of two major workshops last year — SATCON1, which was led by the National Science Foundation, NOIRLab, and the AAS, as well as Dark and Quiet Skies, led by the International Astronomical Union, the United Nations, and the IAC — astronomers have put forth a series of major recommendation guidelines for satellite providers to follow. The two takeaways that are worth emphasizing for optical astronomy (which affects the light we see) are these:

  1. satellites at low altitude are better than satellites at high altitude with 550–600km as the highest recommended figure,
  2. and satellites should be below magnitude +7 at that altitude, limited to about

Astronomers have been clear and consistent in their messaging that the goal is to minimize the impact of these satellites at all stages of the process, as well as to minimize the impact they will have on everyone: skywatchers, amateur astronomers, and professionals. That includes minimizing the amount of time prior to raising satellite orbits to their final altitudes, minimizing brightness during deployment and orbit raising, minimizing the brightness during final orbit and deorbiting, and minimizing the amount of time that these satellites will affect our views.

The worst case for a satellite constellation is that they be both bright and at high altitude. A constellation of 10,000 satellites, for example, would have approximately

120 satellites visible at sunset from anywhere on Earth at 1,000 km altitude, whereas only

40 would be visible at 500 km. The 500 km satellites streak faster across the sky, so they interfere with observations for less time than higher altitude orbits. Most importantly, lower-altitude satellites enter into Earth’s shadow more rapidly and easily, leaving sizable windows where satellites won’t interfere with observations. The higher-altitude satellites, however, remain a problem all throughout the night.

SpaceX, with their Starlink satellites, is the pioneer in this endeavor, having made substantial progress in improving their satellites. However, despite these improvements, they’re also the greatest offender in terms of satellite pollution. The original Starlink satellites were between magnitude +1 and +2 immediately following launch: about as bright as the 20th brightest star in the sky, and at magnitude +4 to +5 in their final orbits, making them easily bright enough to be seen with the naked eye.

Their first attempt at mitigation was a DarkSat, which was darkened on the outside, but was largely unsuccessful. The satellites were still far too bright, particularly during their orbiting phase. The VisorSat — which blocks sunlight from hitting the antennae — is much better, particularly when coupled with an orientation roll. This reduces the overall brightness substantially by about 1 to 2 magnitudes over the original Starlinks, and the most recent

400 satellites (since August 2020) all have Visors equipped. However, they sit at magnitude +6, not +7, and thus are not generally invisible to the naked eye.

Two other planned megaconstellation providers have begun speaking with astronomers as well: Amazon Kuiper and OneWeb. After conversations with astronomers, both constellation providers put forth plans that, at least nominally, were geared towards partially addressing astronomers’ concerns. Kuiper is planning on launching the smallest number of total satellites this decade: between three and four thousand, according to their most recent plans, although the satellites will fly at a range of 590–630 kilometers, which is above the 600 km threshold proposed by astronomers.

OneWeb, on the other hand, previously had the largest original proposal at some

48,000 satellites. They recently reduced that to only 6372, with a a phase 1 proposal for only 648. However, all of OneWeb’s satellites are proposed to be at a 1200 km altitude, which is not recommended for a variety of reasons. On January 14, 2021 at the American Astronomical Society’s annual meeting, OneWeb’s representative publicly stated, “OneWeb is committed to #ResponsibleSpace: design, deployment, and operations.” However, satellites at a 1200 km altitude do not meet that standard. According to astronomer Dr. Meredith Rawls,

“Higher-altitude satellites must be inherently less reflective than lower-altitude satellites to leave a comparable streak [in professional detectors]. This is due to two factors: orbital speed (lower altitude satellites move faster so spend less time on each pixel) and focus (lower altitude satellites are less in-focus, so the streak is wider but has a lower peak brightness.”

Of course, there are additional concerns beyond the three major providers that are currently in talks with astronomers. There are many planned international providers who haven’t yet come to the table to enter into discussion with astronomers. Given the lack of international treaties or regulations governing the peaceful use of space, there is substantial worry that a large number of small companies as well as large international providers will flout any recommendations that astronomers make. If there are no consequences for non-compliance with these recommendations, these criteria set forth by the community are essentially meaningless.

One suggestion put forth numerous times over the past 18 months was that satellite providers should willingly help fund astronomers in their efforts to overcome these new obstacles that they’re creating. As Dr. Chris Lintott put it, “To put substantial work into mitigation strategies, it would help to fund the astronomers you’re asking to do that work. Most who would be able to [help develop and implement these strategies] are grant-funded and unable to ‘donate’ time.”

As others have pointed out, if grant money must be reallocated towards satellite mitigations, then that negatively affects the community across the board. In addition to unusable images, “hot” pixels in our detectors, catalog contamination, false positive signals, lost discoveries, and longer required timetables to collect data, it would also directly cut into the funding of many astronomers’ careers.

It’s important to recognize the real harms that these megaconstellations of satellites cause, and how numerous simplistic pseudo-solutions, as proposed by some, do not address the core problems.

You cannot simply “throw out” saturated pixels from one image. When a satellite passes through the field-of-view of an observing telescope, it will be bright enough to saturate the detectors, ruining their responses for some time even after the satellite has passed.

You cannot simply remove these trails with software. There may be unaffected portions of affected images that are still usable, but the affected portions are not.

You cannot average out the data to remove these trails. Astronomers are searching for objects that burst, brighten, move, or otherwise vary with time time-averaging your data eliminates the possibility of these discoveries.

You cannot do all of your observing only during the hours where satellite pollution isn’t an issue. In particular, searching for and tracking near-Earth asteroids and other potentially hazardous objects can only be done near sunset and sunrise: when satellite pollution is worst.

You cannot rely on artificial intelligence to prevent satellite collisions. If a solar flare or space weather event knocks the electronics governing the continuous course corrections that these satellites make offline, there is no backup plan to avoid collisions. We simply have to hold our breath and hope until they come back online, recognizing we’re playing a cosmic game of Russian Roulette in the absence of some sort of “safe mode orbit” which has never been even proposed by satellite providers.

And you cannot solve your problems by doing all of your astronomy from space. The Hubble Space Telescope, like a number of observatories (including the International Space Station), are also in low-Earth orbit, at altitudes below those that these satellites fly at. Below, you can see an actual surprise photobomb from Starlink satellite #1619, which passed approximately 80 kilometers away from Hubble in this ruined observation taken for Dr. Simon Porter.

Moreover — and this is something that understandably troubles many in the community — not a single company has pledged to meet the modest goals put forth by astronomers: that satellites be no brighter than magnitude +7 at altitudes no higher than 600 km. In fact, of the more than 1000 satellites that have currently been launched to provide next-generation communications, exactly zero of them meet the desired criteria. On a clear, dark night, their presence already cannot be avoided.

Until a set of toothsome international regulations are put into place that would effectively govern the responsible uses of space, the worst-case scenarios we can concoct cannot be ignored. If enough satellites are present, an unfortunate collision could set off a chain reaction, turning low-Earth orbit into a debris field that will last for centuries. Scientific surveys will cost more and require longer periods of time, and many scientific products will see more false positives and be of inferior quality. As it stands now, the future of astronomy on Earth hinges on the present and near-future actions of a relatively small number of satellite providers.