Starlink : General Discussion - Thread 2

[vsatman]

//Second, while I have not worked out the math for Starlink, LEO satellites can easily have 15-20 minute downlink windows, so 2-4 minutes should not be typical.

So can you calculate first? and then you will write nonsense about 15-20 minutes for StarLink?

//to calling the SpaceX engineers idiots.

This is a good point. So we have 2 options for organizing a feeder channel with a speed of 20 Gbps.

Option A Proven many times, as OneWeb engineers did.  to use one feeder channel at a time from a single 1.5m antenna on the Gateway with a maximum throughput of 32 Gb and a typical 25+ Gbps

Option B, which, according to your words, was implemented by SpaceX engineers - use simultaneously 2 feeder lines and 2 Antennas on different gateways, each with a maximum capacity of 32 Gbps and a typical 25+ Gbps. In total, they transmit either 25 or 50 Gbps to the satellite, although 20 gbps are needed. At the same time, there is some kind of magic box on the satellite for redistributing traffic at the packet level on board (a task that no manufacturer in the world has solved so far for a serial satellite ). Naturally, this unique magic box increases the cost of the satellite, requires additional power, and reduces the reliability of the satellite. At the same time, no one knows about the magic box yet, and there is no mention in any SpaceX document, although its appearance would be a sensation and an achievement much greater than laser channels.

From my point of view, the Engineer who proposed option B instead of A can be called an idiot. But note that you called SpaceX engineers idiots, not me ..

[vsatman]

from multiple aerial photos the starlink base stations have 9 domed steerable parabolic dishes in a 3x3 grid

Always 9, but sometimes in one or 2 rows

[launchwatcher]

At the same time, there is some kind of magic box on the satellite for redistributing traffic at the packet level on board (a task that no manufacturer in the world has solved so far for a serial satellite ).

The hardware necessary can be found in commodity network switch ASIC's - the chip parses enough of each packet header to form a flow identifier then uses that to pick the outbound link for a flow.   Packets within a flow all go on the same outbound link and remain in order.   Read up on link aggregation and equal-cost multipathing. 

[SpaceCadet1980]

//Second, while I have not worked out the math for Starlink, LEO satellites can easily have 15-20 minute downlink windows, so 2-4 minutes should not be typical.

So can you calculate first? and then you will write nonsense about 15-20 minutes for StarLink?

You are the one who made up a number based on nothing. I gave a number based on experience working LEO satellites. You can either choose to learn something about the subject and do the math yourself, or you can stop making baseless assertions.

//to calling the SpaceX engineers idiots.

This is a good point. So we have 2 options for organizing a feeder channel with a speed of 20 Gbps.

And the rest of your analysis is all based on this 20 Gbps number which is an old number for Starlink throughput. As I have already mentioned, there is no reason to believe that this is still true for the latest Starlink satellites, especially since ISLs mean that not all data going to or from a ground station will be tied to user beams on the satellite.

Speaking of user beams on the satellite, you are still replying to me while ignoring that the subject of my posts to you was originally about your baseless claims for the number of possible simultaneous user beams. Since you are refusing to reply, should I take this as an implicit admission that you were wrong and have no clue what you are talking about?

From my point of view, the Engineer who proposed option B instead of A can be called an idiot. But note that you called SpaceX engineers idiots, not me ..

As the above posters have pointed out, you referred to common networking equipment which is the basis for the modern internet as magic in your description of option B. Being able to do onboard packet routing is trivially required for ISLs to be useful (see my reply to you in the Starlink Markets thread) Making such as claim goes beyond ignorance, and to then try to use that nonsense to claim I am calling the SpaceX engineers idiots is just hateful.

[vsatman]

So can you calculate first? and then you will write nonsense about 15-20 minutes for StarLink?

You are the one who made up a number based on nothing. I gave a number based on experience working LEO satellites. You can either choose to learn something about the subject and do the math yourself, or you can stop making baseless assertions.

Oh, let's analyze this nonsense, so the 2 most banal questions:
1) What is the orbital period of the StarLink Satellite around the Earth?
2) What is the diameter of the circle in the sky that the gateway antenna sees?
Anyone with even the slightest interest in StarLink should know these numbers. Next 2 calculations at the elementary school level.
a great way to understand what is behind your words and what is your real experience in satellite communications :-), and is there any point in reading further everything that you write ..

[zubenelgenubi: Fixed quotes. Please proofread your reply posts before posting.]

[SpaceCadet1980]

So can you calculate first? and then you will write nonsense about 15-20 minutes for StarLink?

You are the one who made up a number based on nothing. I gave a number based on experience working LEO satellites. You can either choose to learn something about the subject and do the math yourself, or you can stop making baseless assertions.

Oh, let's analyze this nonsense, so the 2 most banal questions:
1) What is the orbital period of the StarLink Satellite around the Earth?
2) What is the diameter of the circle in the sky that the gateway antenna sees?
Anyone with even the slightest interest in StarLink should know these numbers. Next 2 calculations at the elementary school level.
a great way to understand what is behind your words and what is your real experience in satellite communications :-), and is there any point in reading further everything that you write ..

[zubenelgenubi: Fixed quotes. Please proofread your reply posts before posting.]

Orbital Period for LEO satellites in 90 minutes as a rule of thumb. A precise number for Starlink is not something that someone would know without doing the calculation if they haven't been directly working with that data recently. (formula is in the SMAD textbook sitting on my desk, but I am not going to do the math for you for your claim.)

Your second question is poorly defined, more relevant is "What is the angle relative to the center of the Earth from the ground station to a satellite, when the line from the satellite to the ground station is at the ground station's minimum elevation angle from the ground?" This is not something that anyone would know off the top of their head (again unless they work on Starlink on a technical level), and I'd bet many high school students would struggle with the relevant trigonometry. (Inputs to this are Starlink altitude and the ground elevation angle) Again, you made the claim, you do the math.

I already gave my input with an estimate based on systems I have worked with, Starlink is lower altitude, so if it is maybe half of the range I provided that would be reasonable, as I never claimed that number was correct for Starlink, just that your provided number was significantly too low.

And to be clear here, you have already demonstrated that your knowledge is severely lacking on essentially all relevant subjects, from the number of simultaneous beams a phased array can handle (essentially arbitrary) to the fact that packet routing is common and not magic, etc. Never mind the incoherence and/or irrelevance of your second question, I'll just assume that is just the language barrier again. You can't even seem to admit to these mistakes, so you have already demonstrated that there is no point in reading anything you say, I am doing it only to correct the nonsense you are spouting. Please don't pretend that you are actually reading what I have written. You have repeatedly ignored what I and others have written, only to change the topic every time you are proven wrong on something. You asking questions to judge my understanding simply is not relevant at this point, multiple people here have provided evidence pointing out ways you are wrong.

[Chris Bergin]

New thread. Vsat, be civil or lose your posts.

https://forum.nasaspaceflight.com/index.php?topic=55795.0