Starlink Satellite Train Explained: Decoding the Linear Formation in the Sky

People all across the globe have reported seeing a straight line of white dots traveling across the night sky.

Before you freak out now: no, aliens are not taking over just yet. Instead, the phenomena, made possible by SpaceX’s Starlink, is commonly referred to as satellite trains.  

In this article, I’ll detail what Starlink’s satellite trains actually are, how they can be spotted, and how many of those are roaming earth at any given time.

What Is a Starlink Satellite Train?

Starlink satellite trains are a collection of satellites that roam low-earth orbit (LEO) at close distances to each other.

This is how a satellite train I recently spotted from my backyard (sorry for the lackluster video quality) looks like out in the wild:

The fact that you can see Starlink’s satellites isn’t anything unique to the internet service provider (ISP). Whether it’s the International Space Station (ISS) or even the James Webb telescope, objects in space are visible due to the sunlight they attract.

However, what separates Starlink from other objects in space is the vastness of its constellation, which currently boasts close to 3,600 satellites in orbit.

SpaceX, as you can see on our dedicated launch statistics page, normally deploys around 50 or so satellites during a single launch.

Starlink has since reached the maximum number of version 1.5 satellites permitted by the FCC. It has now gone over to exclusively launch its so-called V2 Mini satellites – normally in groups of 20 to 22.

Those satellites initially orbit earth in multiple groups and take advantage of a concept called plane drift, thus enabling Starlink to cover various parts of our globe.

Recent Starlink launches are using plane-drift to share sats from a launch among even more orbit planes. This also increases the amount of time sats spend in orbit raising. Here is the launch from Feb 4, with 23% of sats still not at final altitude after over 4 months pic.twitter.com/XdrZbboB3E

— Jonathan McDowell (@planet4589) June 16, 2021

The initially grouped together satellites then form the trains that we see back down on earth. Unfortunately, that sight is only of temporary nature.

According to Harvard scientist Jonathan McDowell (see tweet above), Starlink’s satellites remain in their train-like position for a few months after which they each go their separate ways.

More precisely, satellites operate in what McDowell calls the “intermediate orbit”, namely around 400km (~248 miles) distance to earth.

They then rise to an operational orbit, at a height of 550km (~341 miles), using the satellite’s thrusters. Around 80 or so percent of all satellites reach their designated orbit location while the rest malfunction for a variety of different reasons.

Luckily, people do not need to worry, though. The overwhelming majority of Starlink’s satellites burn up when re-entering earth’s atmosphere.

This is also why the trains have ‘holes’ in them, meaning the distance between each satellite isn’t equal as some have already departed for operational orbit.

Why Are Starlink Satellites in a Train?

The reason why Starlink’s satellites are roaming Earth in a train-like structure is manifold. First of all, releasing them in one sequence simply minimizes collision risk and thus space debris.

Here you can see a release sequence for Starlink’s Gen2 Mini satellites, which are grouped together as one:

Video of last night’s @Starlink satellite deployment pic.twitter.com/K7ezZLLusz

— SpaceX (@SpaceX) September 16, 2023

Over time, those satellites are separating from each other, forming the train-like structure that you can then see back down on Earth.

Apart from the safety aspect, fuel efficiency is also of importance. Each satellite only has a limited amount of fuel, so sending them immediately to their designated orbit (550km) would use up even more of it.

Being grouped together in a train early on also allows ground controllers to more easily track them and make precise orbital adjustments. 

For example, satellites can malfunction sometimes for different reasons. Being located in lower orbital shells and within the confinement of the train thus enables them to deorbit faster.

How to Spot a Satellite Train

There are a variety of online tools that enable you to track Starlink satellites as they roam the skies. The one that I used can be accessed here.

Simply add your country and city of residence, or alternatively longitude and latitude, and the tool shows you when to expect a satellite train.

Keep in mind that all of these tools are mere approximations given that their creators do not have access to real-time navigation data.

For example, Starlink relies on an autonomous collision avoidance system that changes a satellite’s direction whenever necessary.

SpaceX previously revealed that its Starlink satellites performed over 26,000 collision avoidance maneuvers in a span of two years (11/2020 – 11/2022). Therefore, on any given day, its satellites perform 75 maneuvers.

Another aspect to keep in mind is your environment. Satellite spotting works best in areas of low light pollution. So, small towns and nature are likely your best bet to spot a train of satellites.

Additionally, you want to make sure that the weather is on your side and thus offers a clear and cloud-free view of the night sky.

Lastly, keep in mind that the satellite train will only be visible for a few minutes, so simply being on time is essential to a great viewing experience.

How Many Starlink Trains Are There?

At any given time, there are a handful or more satellite trains that are visible to the human eye. The above-mentioned tracker page highlights their current location and projected directions.

Generally speaking, Starlink and SpaceX are incentivized to have as few spottable satellite trains as possible.

For once, satellites in intermediate orbit do not operate on the required frequency bands to provide internet services to customers back down on earth – thus not making money for Starlink.

Another aspect to consider is the mounting political pressure Starlink is facing. For example, its satellites are causing streaks in telescope images.

The fact that those trains are visible without relying on advanced technology only amplifies those concerns, regardless of how valid they may be.

Luckily, SpaceX has vowed to address those issues. In July 2022, it published a document highlighting the initiatives it already underwent and plans to undergo to mitigate the negative effects of its constellation.

Those include using a darker coating, adopting specular surfaces to deflect lighting into another direction, optimizing flight operations, and so forth. SpaceX also remains in constant exchange with those very same astronomers to ensure whatever it implements addresses their concerns.