SpaceX Concedes Starlink Altitude But System Changes Maintain Chokehold Over Amazon

Ramish Zafar
SpaceX Starlink Earth Station
SpaceX's Starlink Earth Station in Merrillan, Wisconsin. The company filed for the station's license in September 2019 and the FCC granted its approval in April 2020. Image: darkpenguin22/Reddit

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As it battles terrestrial broadband service providers to keep access to the 12GHz spectrum for its Starlink consumer terminals, SpaceX has made an important concession to Kuiper Systems LLC (an Amazon subsidiary) with regards to its third proposed Starlink modification. SpaceX asked the FCC to allow it to change the orbital altitudes, planes and angles of its satellites earlier this year, with the company's promises to its customers depending to a large extent on this change.

Now, in a commitment letter filed by SpaceX's head of satellite policy Mr. David Golman, the company has acquiesced to Amazon's demand of removing the orbital overlap between some Starlink and Kuiper satellites and increasing the distance between them. The letter comes as Amazon raised safety concerns for its satellites in several meetings with the FCC.

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SpaceX's Concession To Amazon Hopes To Enable A Polar Starlink Launch In December – But Will It Mark The End Of Company's Battle With Future Competitor?

The concession relates to Starlink's cluster that operates in a shell of 570 kilometers in altitude with 20 satellites each in 36 orbital planes. SpaceX's modification request asked the FCC to allow the company to cut the altitude of this cluster in half from an earlier value of 1,300 kilometers. A part of Amazon's Kuiper constellation will operate at an altitude of 590 kilometers, and SpaceX's orbital tolerance lets the company either reduce or increase Starlink's altitude by 30 kilometers.

This ensured that when the Kuiper constellation was fully deployed (Amazon's 590-kilometer cluster is the last cluster that it will deploy), SpaceX and Amazon's satellites would effectively be sharing the same orbital shell when SpaceX chose to make use of this tolerance. SpaceX's concession will now ensure that the maximum altitude that this batch of satellites operates in is 580 kilometers, a kilometer lower than the low end of the Kuiper cluster's orbital tolerance of 9 kilometers.

Original parameters:     
Orbital Planes:7232856
Altitude in kilometers:5501,1001,1301,2751,325
Inclination - (i):53°53.8°74°81°70°
Modified parameters
Orbital Planes:72723664
Altitude in kilometers:550540570560569
Inclination - (i):53°53.2°70°97.6°97.6°

By granting Amazon the concession, SpaceX argues that the FCC should conditionally allow the company to deploy Starlink satellites in one of the two proposed polar shells. This shell (fifth column above) consists of 348 satellites, with groups of 58 satellites operating each of the six orbital planes. The company outlines a launch window for the polar orbit in December as creating the need for preliminary approval and argues that this shell will allow it to bring Starlink coverage to Alaska.

SpaceX has already requested the FCC to allow it to test Starlink in Alaska, but coverage in the remote state isn't the only rationale behind the company's latest request for conditional approval. Additionally, Mr. Goldman argues that by bringing Starlink coverage through polar orbits, SpaceX will also contribute to the national security of the United States by targeting Federal users to support critical missions in areas where satellite internet access is the only option.

However, while all these mark a big step forward for resolving Starlink's issues in the halls of the FCC, the most striking aspect of SpaceX's letter to the Commission is its conclusion.

Over here, Mr. Goldman argues that:

As a result of discussions with Amazon, SpaceX has now committed to accepting the condition Amazon proposed to resolve its concern. With that issue settled, SpaceX requests that the Commission grant its modification expeditiously [EMPHASIS ADDED].

While forward-looking, this might not be the case as we'll find out below.

In its meeting with FCC representatives a week before SpaceX's concession, Amazon outlined other concerns with Starlink. One of these is the elevation angles of Starlink earth stations. The diagram at the top is from an earlier SpaceX presentation, with Amazon's changes reflected on the one below. Image: Kuiper Systems LLC November 16, 2020 Ex Parte FCC International Bureau File Number: SATMOD2020041700037

Starlink's Third Modification To Increase Interference With Kuiper By 250% Reiterates Amazon

While SpaceX has conceded the orbital altitude of one orbital shell, this concession is far from resolving all of Amazon's concerns with the proposed Starlink modification. The company argues that lower elevation angles of Starlink ground stations when combined with altitude reduction and doubling the number of Starlink satellites will drastically increase interference between the two constellations.

Amazon's data shows that when all these three parameters are combined, the number of in-line interference events between Starlink and Kuiper increases by 250%. SpaceX's proposed modification reduces the minimum earth station elevation angle to 25° from an earlier 40°, as the company argued that this reduction will compensate for reduced satellite coverage due to the aforementioned altitude reduction (lower satellites cover less ground when broadcasting signals).

Space Starlink Kuiper Interference Active Satellites
Space Starlink Kuiper Interference All Satellites

Amazon's analysis reveals that when it comes to coverage maps, should the proposed Starlink modification be allowed in its current form, then its Kuiper constellation stands to face significant interference and potential coverage location in North America.

Countering SpaceX's assertion that its decision to double the number of satellites in contact with a gateway Earth station does not affect in-line interference and as a result, a more accurate metric to use would be all visible Starlink satellites, Amazon's tests show that even if this were the case, the in-line events would still increase.

SpaceX had also argued that since it was lowering orbital altitude, the number of Starlink satellites visible would go down and therefore offset the impact of the inclination reduction. Amazon's reply is shown in the image preceding the gallery above, where the company demonstrates how the reduced angles might reduce the exclusive area its satellites have to communicate with ground equipment.

Amazon argues that new antennas for Starlink will complicate the spectrum environment in the Continental United States. mage: Kuiper Systems LLC November 16, 2020 Ex Parte FCC International Bureau File Number: SATMOD2020041700037

Amazon Fails To Effectively Respond To SpaceX's PFD Claims and Its Impact On Earth Station Parameters

Finally, Amazon also argues that changes to Starlink satellite antennas will drastically increase the beam contour created by them. While the performance impact this might have on consumer download and upload speeds is the subject for another debate, Amazon believes that this will render Earth station separation for avoiding interference void as a strategy, with co-location (sharing) remaining as the only feasible option for operators to operate without hiccups.

Amazon however fails to acknowledge SpaceX's argument that lower elevation angles reduce PFD (Power, Flux & Density) and therefore end up cutting the separation angles shown in the graph in the second slide above in half. This effectively throws the company's argument that the Starlink modification will end up drastically increasing interference out of the park. The only change we get in the latest filing is a cursory statement claiming that:

Using the same separation angle threshold for before and after is a conservative assumption, as SpaceX’s altitude reduction will increase the necessary separation angle.

Yet there's no mention of the PFD, and the statement shows that perhaps Amazon needs to work more on this front. SpaceX, for its part, does not mention any changes to Starlink antenna design, which makes us wonder whether the company is aware of the changes that this will have in the Non-geostationary Fixed Satellite Service (NGSO FSS) environment.

What is clear is that by establishing a regular launch cadence, SpaceX has made sure that Starlink is here to stay. Unless Amazon parallels or beats the company on this front, its arguments to the FCC remain at risk of being classified as assertions aimed towards delaying an existing service. SpaceX's plans to swiftly launch hardware in the space have also stirred up terrestrial broadband service providers' concerns – which is another yet-to-be deployed service.

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