Questions on the Impact of Trees on SpaceX Starlink

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The Starlink Web site says, “Starlink is targeting service in the Northern U.S. and Canada in 2020, rapidly expanding to near-global coverage of the populated world by 2021,” but the rollout will not be uniform. The initial coverage will be centered around 53 degrees latitude, and locations with unobstructed views of the sky will have an advantage. Like many folks, I wonder about coverage at my particular location in a wooded mountain area at 34.8462° N latitude.

Elon Musk says Starlink setup will be simple — plug it in and point it to the sky, and motors will find the optimal orientation for the antenna. That will work well if you are in the desert with a clear view of the sky, but as you see, my house is surrounded by trees. I will have a clear view of satellites when they are directly overhead, but they will disappear over the irregular “tree horizon” as they orbit the Earth.

When might I have uninterrupted connectivity at my house and how fast will it be?

In the most recent publication of which I am aware (plans change), SpaceX says that in the very early phases of constellation deployment, when they wish to expand coverage at the expense of capacity, satellites will be able to communicate with terminals at an elevation angle as low as 25 degrees and, as more satellites are launched, they will increase that to 40 degrees, as shown below.

Fig. 1 – Steerable service range at full deployment (left) and initial launch (right). (SpaceX / FCC)

A casual glance around my house and consideration of the coverage shown in Serge Eagleson’s simulation late last year convinces me that I will not have continuous coverage at 25-degree elevation and quite possibly will not until well into the 40-degree phase. I can’t say exactly when I will have coverage because there are too many variables and questions I don’t have answers to, like:

How quickly will satellite density increase at my latitude?
How rapidly will the Ku-band signal attenuate near the tree-top horizon?
Will the satellites dynamically adjust transmission of power or is it fixed?
When the signal begins to weaken, will the satellite simply drop the link or will it maintain connectivity at reduced speed by retransmission of error packets or changing the modulation algorithm?
Will the terminal motors dynamically re-orient the dish while tracking a satellite? (That sounds too expensive).
Will the terminal motors automatically re-orient the dish when the constellation configuration changes? (That sounds reasonable).

Fig. 2 – OneWeb’s ground-stations prototype

The impact of trees is not just my personal concern. The economic viability of Starlink will depend upon revenue during the startup years, and Elon Musk has stated that Starlink’s greatest challenge is the “fully considered” cost of the user terminal — the cost of hardware, setup and maintenance, and SpaceX President Gwynne Shotwell agrees, saying “hopefully we don’t have to hire a million people running around in little white vans fixing or installing user terminals on folkses house.”

I don’t know what proportion of potential Starlink customers are in forested areas, but if SpaceX wants to get us online soon, they might consider offering a mast-mount or rooftop alternative to the plug-and-play terminal — something along the lines of the OneWeb prototype (Fig. 2).
Written by Larry Press, Professor of Information Systems at California State UniversityFollow CircleID on TwitterMore under: Access Providers, Broadband, Wireless

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