To Point or Not to Point, the Starlink Question
Factors Motivating Cruisers To Disable Dishy Directional Motors
Sean Welsh, a retired telecom/satcom professional, explains why so many mobile Starlink owners are disabling the antenna’s directional motors. (Disclaimer: Welsh says he has no inside information. This explainer, reprinted with permission, represents his best understanding based on available information.)
By SEAN WELSH
There is evidently quite a bit of confusion about the "tilt" of the standard (residential or RV) Starlink terminal ("Dishy") and I think it might benefit some folks to explain this function.
For starters, if you are in the temperate latitudes (for example, the continental U.S.), the satellites are everywhere around you. While the orbital inclination means there will be slightly greater density of satellites in a northerly direction, there are satellites coming and going almost to the horizon in all directions. As you get closer to the poles, that changes (for now), with fewer satellites being between you and the pole, but that is not an issue for most users. The notion that satellites will only be found to the north is a misunderstanding of orbital mechanics.
Secondly, it is important to know that Starlink does not exist alone in space or on the airwaves. They share the sky with several other "constellations" of low earth orbit (LEO) satellites, and, moreover, there are myriad other satellites in the sky. Of particular importance is the band of geostationary (also called geosynchronous) satellites that orbit over the equator at an altitude of 22,326 miles. If you've ever had satellite TV like DirecTV or Dish Network, you had a terminal or "dish" (an antenna with a parabolic reflector) that was aimed at one or more of these satellites.
There are in fact more than 400 satellites in geostationary orbit, meaning they are spaced less than one degree of arc apart. The geostationary orbit is also called the "Clarke Belt," after the famous science fiction writer who described it in the 1940s (the
first geosynchronous satellite would not be launched until the 60s). I will use this term here.
More on the subject: Bahamas Are Paradise for Starlink Cruisers, But for How Long?
Starlink also uses radio frequencies that are very close to or even the same as the frequencies used by other systems and services, including some terrestrial (ground-based) cellular broadband systems (what makes your cell phone work) and, again more importantly, many of the aforementioned geostationary communications satellites. What any and all "licensees" of these frequencies agree to as part of their licenses, whether those are national licenses like from the FCC or internationally-coordinated licenses that involve cooperation between national authorities by means of the ITU (International Telecommunications Union), is that their transmissions will not interfere with the communications of any other system. And when I say "their transmissions," I mean not only the transmissions from the provider's infrastructure like satellites and ground stations, but also from their customers' equipment—when you buy a satellite terminal, you don't have a license to transmit with it, instead, the license is held by the provider and your terminal operates under that license.
Starlink terminals, both customer terminals and ground stations, are not permitted to transmit in the direction of any other satellite where the frequencies in use might cause "harmful interference." Because most of the satellites in the Clarke Belt would be subjected to such interference, Starlink's terminals simply do not transmit in that
direction. That means if your terminal were talking to a satellite as that satellite passed between you and the Clarke Belt, the terminal would stop transmitting until the satellite emerged on the other side. And while the belt itself is just a thin line in the sky, there is a "guard band" on either side of the belt that is off limits. You can
think of the Clarke Belt as a giant obstruction in the sky.
With that as a background, let's take a look at the terminal itself. It uses phased-array technology, which I am not going to explain in detail (watch one of the videos on YouTube), other than to say that this technology can track, receive from, and transmit to moving satellites without itself physically moving at all. The array in the Starlink terminal is flat (it's not a dish, name notwithstanding), and the limitations of the technology mean that this tracking can happen over an arc of around 110°. That means that, without moving, Dishy's "view" of the sky is an inverted cone with an apex angle of about 110°.
If you have a clear view to the horizon all the way around you, you have a field of view of 180°, but the terminal can only use 110° of that. So which way should you aim your 110°cone for the best service? The answer is the clearest 110°swath of sky that includes as little of the Clarke Belt as possible. And this, coupled with the slightly greater satellite density, is the fundamental reason why, in the northern hemisphere, the terminal will tilt mostly to the north. If residential terminals were installed by professionals, there would be no need for motors to aim the terminal, but because Starlink wanted to make it a plug-and-play end-user installation, they added motors for the terminal to accomplish this alignment by itself.
One consequence of this decision is that, when there became a demand for "portable" terminals, Starlink was able to meet this demand with no changes to the equipment. However, it should be noted that neither the motors nor the cable connectors were designed for constant re-deployment. Many have learned this the hard way with regard to the connectors. A few have learned this about the motor gears as well. A
second consequence is that terminals will be able to adjust tilt later as the constellation expands, filling in the gaps closer to the poles.
I want to emphasize that the terminal knows where it is and which way it is pointing no matter what you do to it. If it didn't, it would not be able to find and track the satellites. And it absolutely will not transmit in an unpermitted direction, again no matter which way it is. So what happens if you override it's chosen direction by
disabling the motors and pointing it some other way? It will work, but it will have less usable sky to work with than it would in the optimum orientation, and performance might suffer.
Lots of folks who want to use the terminal in-motion, notwithstanding the prohibition on this in the Terms of Service, are mounting the terminal flat. This makes a certain amount of sense from several perspectives; it can eliminate the issue of wind pressure on the terminal, and because a moving vehicle may pass numerous obstructions in many directions, and will not typically maintain a constant heading, the orientation initially chosen by the terminal itself will likely have more obstructed time than if it was pointing straight up.
In a tacit acknowledgement that some terminals are being used this way, it appears that Starlink is now tilting the terminal flat when it senses motion above a certain speed. But once the vehicle again becomes stationary, such as being parked or docked, it's a safe bet that flat is no longer the optimal aim for the array.
Disclaimer redux: I do not work for Starlink, and I do not have access to any proprietary or trade secret documents or any of the algorithms Starlink actually uses to manage traffic or aim terminals. But I spent my entire career in telecom, much of it with certificated carriers, and I have been doing satcom for over two decades. I've learned much of what I know about their system by reading their regulatory filings, which requires a good foundation in the craft. The rest comes from my understanding of RF technology, harmful interference, and what's already up in the sky.1
I do have a Starlink terminal which I use in-motion (mounted in the normal orientation with motors enabled). My boat is not fast enough for the terminal to re-orient underway, and sometimes I have to help it along by stowing and rebooting the terminal once I am on a different heading (underway or at anchor).
According to oneminuteenglish.org, certificated is a word used in British English and not in American English. This is why it is often considered to be a misspelling. The word is an adjective and comes from both certified and certificate. Like certified, certificated is used to describe a person’s or an organization’s qualifications.
To Point or Not to Point, the Starlink Question
Thanks, Sean (and Peter), this is interesting StarLink info. But the link to your blog goes to oneminuteenglish instead and I can't find it on google. Please share.
I think the very last sentence is the key I've been looking for on Avemar.
"My boat is not fast enough for the terminal to re-orient underway, and sometimes I have to help it along by stowing and rebooting the terminal once I am on a different heading (underway or at anchor)."
Last night the bow was oriented to the South and Dishy happily helped me waste hours on YouTube and Instagram. This morning when I started to get to "work" the boat had turned towards the West and Dishy didn't reorient automatically and was pointed off to the East. (Yes, I fell asleep and forgot to turn off the inverter, so Dishy worked all night and I assume was ready for a rest.)
I'll have to try the stow and reboot trick!