SpaceX describes exactly how they plan to make Starlink satellites less visible from Earth

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In 2015, Elon Musk announced that his company, SpaceX, will deploy orbiting satellites that will provide high-speed broadband Internet access to the world. Known as Starlink, SpaceX began deploying this constellation in May 2019 with the launch of the first 60 satellites. As of April 22, a total of 422 satellites had been added to the Starlink constellation, and the response was not entirely positive.

In addition to the fears we add to the “space waste” problem, there are also those who have expressed concern that Starlink and other constellations could have a negative impact on astronomy. In response, SpaceX recently announced that it will introduce changes to the way satellites are launched, how they spin around the Earth, and even how they are reflective to minimize the impact they have on astronomy.

These changes were the subject of a presentation made during the ten-year survey on astronomy and astrophysics 2020 (Astro2020) organized by the National Academy of Sciences, Engineering and Medicine. As part of the meeting on optical interference from satellite constellations held on Monday, April 27, the Starlink panel (which included Musk) presented how the company hopes to minimize the light pollution caused by their constellation.

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Illustration of the Starlink orbits and their reflective qualities. Credits: SpaceX

The appearance of these new satellites in the sky has led to its fair share of controversy among amateur astronomers and the astronomical community. In fact, the Royal Astronomical Society (RAS), the American Astronomical Society (AAS), the International Astronomical Union (IAU) and the National Radio Astronomy Observatory (NRAO) have all issued official statements regarding Starlink and d ‘other constellations proposed.

In particular, they expressed concern about how these satellites could disrupt optical and radio surveys such as those of the Vera C. Rubin Observatory (formerly the Large Synoptic Survey Telescope or LSST), the Square Kilometer Array (SKA) and the Event Horizon. Telescope (EHT) – which recently acquired the very first image of a black hole! As the UAU noted:

“Although most of these reflections are so weak that they are difficult to detect with the naked eye, they can affect the sensitive capabilities of large astronomical telescopes on the ground. [2], including the extreme wide-angle viewing telescopes currently under construction [3]. Second, despite significant efforts to avoid interfering with radio astronomy frequencies, the aggregated radio signals from satellite constellations can still threaten astronomical observations at radio wavelengths. “

The basic problem is that when satellites revolve around the Earth, they periodically catch and reflect sunlight, especially when they come out of the Earth’s shadow and enter the sunlight directly (which happens during their “ascent into orbit” phase). It is at this stage that the satellites will engage their thrusters to increase their altitude over the course of a few weeks to ensure that they do not undergo orbital decay.

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Starlink satellite configurations. Credits: SpaceX

Drag is a bigger problem for Starlink as they are deployed at lower altitudes of 550 kilometers (340 mi) to mitigate the risk of space debris, rather than 1,100 to 1,300 km (680 and 800 mi) as originally planned. As SpaceX indicates in a press article which summarizes the key points of the presentation:

“The design of the Starlink satellite is motivated by the fact that they fly at very low altitude compared to other communication satellites. We do this to prioritize the safety of space traffic and to minimize the signal latency between the satellite and the users who benefit from it. Due to the low altitude, drag is a major factor in the design. “

At this point, Starlink satellites assume their “open book” flight configuration when they enter the “orbit elevation” phase of their orbit, where their panels are deployed flat and in front of the vehicle to reduce drag. atmospheric. For this reason, sunlight can be reflected from both the solar panel and the body of the satellite at this point.

Once the satellites have reached their operational orbit of 550 km (340 mi) – alias. the “stationary” phase – only certain parts of the chassis can reflect light. This is due to the fact that the satellite attitude control system overcomes the drag by forcing the satellite to take its “shark fin” orientation, where its solar panel is raised vertically.

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By darkening their satellites, SpaceX seeks to reduce reflectivity. Credits: SpaceX

To resolve these issues, SpaceX said the company is working in partnership with various organizations to implement a number of changes. To begin with, they are currently testing an experimental satellite that is less reflective than previous models – which is aptly named “DarkSat”. This class of satellites takes advantage of a darkened phased array and satellite dishes to reduce the brightness by about 55%.

However, they are also looking to implement a “sun visor solution” to solve the heat problem, since dark satellites can shine brightly in the infrared due to the way black paint absorbs radiation. Satellite dishes (which are white and diffuse) will also have visor-type coatings to reduce the amount of light they reflect. The first VisorSat prototype will be deployed this month and by June, all future satellites will have a visor.

Second, SpaceX intends to implement changes in the way their satellites go from insertion to parking, then to orbit at the station. Currently, the company is testing a maneuver where the satellite is rolled so that the satellite is on the same plane as the vector of the Sun (aka. The satellites are “at the tip of the knife” towards the Sun). This will reduce the area that receives light, thereby reducing the amount of reflected light.

In the past, Musk has been somewhat flippant (and admittedly ignorant) in responding to these concerns. When the first batch of Starlink satellites was launched in May 2019, he went on Twitter to declare the following:

“There are already 4,900 satellites in orbit, which people notice ~ 0% of the time. Starlink will not be seen by anyone unless it is looked at very closely and will have an impact of approximately 0% on the progress of astronomy. We have to move telescopes into orbit anyway. The atmospheric attenuation is terrible. “

Since then, it is clear that Musk and the company he founded have come to take these concerns more seriously and have developed a comprehensive plan to address them. The measures they proposed were designed in part thanks to collaborative efforts between the company and the AAS, the NRAO and the Vera C. Rubin Observatory. As they say:

“With AAS, we have improved our understanding of the wider community through regular calls with a working group of astronomers where we discuss technical details, provide updates and work on how to protect astronomical observations in the future…

While understanding the community is essential to this problem, engineering problems are difficult to solve without details. The Vera C. Rubin Observatory has been repeatedly flagged as the most difficult case to resolve, so we have spent the past few months working closely with a technical team to do so. Among other helpful thoughts and discussions, Vera Rubin’s team has provided a target brightness reduction that we use to guide our engineering efforts as we reiterate the brightness solutions.

SpaceX also indicated that information on the orbits and trajectories of their satellites is available at space-track.org and celestrak.com so that astronomers can time their observations to avoid satellite streaks. At the request of astronomers, the company has also started to publish predictive data before launches to allow observatories to plan surveys in the first hours of deployment when the satellites are most visible.

To read SpaceX’s full statement on how to mitigate light pollution with their constellation, click here. The meeting was conducted and recorded via Zoom because the event was a virtual chat (due to the coronavirus pandemic). Documents related to SpaceX’s presentation at the meeting are available on the National Academies website here.

Further reading: SpaceX, National academies



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