Author Topic: Starlink : General Discussion - Thread 2  (Read 1280923 times)

Offline meberbs

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Re: Starlink : General Discussion - Thread 2
« Reply #1040 on: 01/17/2020 07:39 am »
OK
Why is "the back of the solar array" being lit by the sun?

Does each Starlink only have one thruster, so that it has to turn the entire spacecraft around the R-bar to go from boosting forward to thrusting retrograde?  Would that be preferable to having engines on the "front" and the "back", which would allow quick switching, provide some redundancy for EOL deobiting, allow options for DAMs for collision avoidance, and allow for free choice of sides of the solar array that's in the sunlight, regardless of beta angle?

I think the key here is low drag configuration. When the solar array is deployed it is the largest, by area, portion of the satellite.  In low drag mode this will be orientated so that it is parallel to the direction of travel.
I thought that too, but there should never be a situation where that requires light hitting the back of the array. The array can rotate about its axis and you would rotate it 180 degrees about that axis so that you actually are generating power, which is kind of important when running any kind of ion engine continuously. You should be able to basically just leave it in that orientation, so that aspect doesn't really change as it circles the Earth.

I assume the "back" is some sort of typo/miscommunication, but the point that the solar array is more visible due to orientation remains true. I haven't actually figured out exactly why that would be the case, maybe even the edge on area of the solar array is significant, and tilting forward helps, or tilting forward is needed to optimally align the ion engine thrust which ideally goes through the center of mass including the solar array. Actually, if the edge on area is significant that would be partially lit in a general low drag orientation, but not in normal operation, and that could be what is meant by "back."

Offline Eka

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Re: Starlink : General Discussion - Thread 2
« Reply #1041 on: 01/17/2020 08:00 am »
Not Starlink specific, but an informative talk about phased arrays to get familiar with how the satellites and base stations work:


Great primer. Especially for the level of discussion here. A properly smart person should be able to go from it to a working Starlink system. Unlike radar, Starlink doesn't have to worry about side lobes except for frequency choice when multiple satellites are present.
We talk about creating a Star Trek future, but will end up with The Expanse if radical change doesn't happen.

Offline woods170

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Re: Starlink : General Discussion - Thread 2
« Reply #1042 on: 01/17/2020 08:29 am »

Quote
1/3 Confirmation from @SpaceX: During the early mission phase we are in a low-drag configuration in which the back of the solar array will contribute to the brightness of the satellite. [Cont]

2/3 Because the surface area of the solar array is so much larger than the chassis, we expect the impact from the experimental coating to be less noticeable during this period. [Cont]

3/3 We are not using a special orientation for the darkened satellite.

OK

Why is "the back of the solar array" being lit by the sun?

Emphasis mine.

It is not being lit by the Sun. At least, not directly.
You may have noticed that the Starlink satellites are most visible directly before sunrise and directly after sunset. What you see is the back of the solar arrays reflecting sunlight which was first reflected off Earth's atmosphere and surface. See image below.


It is good to remember that Earth's surface reflects between 10% to 25% of the incoming sunlight. Clouds in the atmosphere reflect roughly 50% of the incoming sunlight. That is quite a bit of light going back into space and some of it will hit the Starlink satellites.
« Last Edit: 01/17/2020 10:25 am by woods170 »

Offline RoboGoofers

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Re: Starlink : General Discussion - Thread 2
« Reply #1043 on: 01/17/2020 08:48 pm »
ultimately even if the court found against the FCC it would only mean that the blanket waiver that the FCC uses could just be codified into law. I'd guess that there's enough influence from aerospace companies that they could get something passed that says that NEPA doesn't apply to space.

Offline Comga

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Re: Starlink : General Discussion - Thread 2
« Reply #1044 on: 01/18/2020 01:43 am »

Quote
1/3 Confirmation from @SpaceX: During the early mission phase we are in a low-drag configuration in which the back of the solar array will contribute to the brightness of the satellite. [Cont]

2/3 Because the surface area of the solar array is so much larger than the chassis, we expect the impact from the experimental coating to be less noticeable during this period. [Cont]

3/3 We are not using a special orientation for the darkened satellite.

OK

Why is "the back of the solar array" being lit by the sun?

Emphasis mine.

It is not being lit by the Sun. At least, not directly.
You may have noticed that the Starlink satellites are most visible directly before sunrise and directly after sunset. What you see is the back of the solar arrays reflecting sunlight which was first reflected off Earth's atmosphere and surface. See image below.

It is good to remember that Earth's surface reflects between 10% to 25% of the incoming sunlight. Clouds in the atmosphere reflect roughly 50% of the incoming sunlight. That is quite a bit of light going back into space and some of it will hit the Starlink satellites.

This does not make sense from the perspective of geometry.
They would not be astronomically bright if they were reflecting the extended, diffuse Earth.
What light hits it would fade slowly as the view to the lit surface diminishes smoothly as the orbit proceeds over darkened ground. 
The Starlink satellites have fairly constant brightness and fade quickly when they leave the direct sunlight.
It seems fair to say that the back sides of the solar arrays are sunlit for some reason.

(It’s good to remember not to be snarky. ;)  )
« Last Edit: 01/18/2020 06:06 pm by Comga »
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline thirtyone

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Re: Starlink : General Discussion - Thread 2
« Reply #1045 on: 01/19/2020 08:46 pm »
I don't remember this being discussed - but I'm wondering, is there a good reason for having so many satellites in the higher shells (anything higher than 550km?), apart from maybe satellite lifetime and replacement costs? Given orbital debris mitigation concerns and astronomical interference concerns (they're brighter, but illuminated by the sun for far less time during the night), my feeling is that lower orbit satellites are generally better for space "environment." But is there some coverage / orbital mechanics reason for needing those higher shells? Is it possible that SpaceX ends up only launching satellites in lower shells?

Offline gongora

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Re: Starlink : General Discussion - Thread 2
« Reply #1046 on: 01/19/2020 09:20 pm »
I don't remember this being discussed - but I'm wondering, is there a good reason for having so many satellites in the higher shells (anything higher than 550km?), apart from maybe satellite lifetime and replacement costs? Given orbital debris mitigation concerns and astronomical interference concerns (they're brighter, but illuminated by the sun for far less time during the night), my feeling is that lower orbit satellites are generally better for space "environment." But is there some coverage / orbital mechanics reason for needing those higher shells? Is it possible that SpaceX ends up only launching satellites in lower shells?

Using higher orbits allows fewer satellites to get the same geographical coverage (although using more satellites at lower altitudes gives you more overall bandwidth from higher frequency reuse.)  It wouldn't be surprising if SpaceX requests permission to lower more of the satellites but they haven't done it yet.

Offline woods170

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Re: Starlink : General Discussion - Thread 2
« Reply #1047 on: 01/20/2020 08:39 am »

Quote
1/3 Confirmation from @SpaceX: During the early mission phase we are in a low-drag configuration in which the back of the solar array will contribute to the brightness of the satellite. [Cont]

2/3 Because the surface area of the solar array is so much larger than the chassis, we expect the impact from the experimental coating to be less noticeable during this period. [Cont]

3/3 We are not using a special orientation for the darkened satellite.

OK

Why is "the back of the solar array" being lit by the sun?

Emphasis mine.

It is not being lit by the Sun. At least, not directly.
You may have noticed that the Starlink satellites are most visible directly before sunrise and directly after sunset. What you see is the back of the solar arrays reflecting sunlight which was first reflected off Earth's atmosphere and surface. See image below.

It is good to remember that Earth's surface reflects between 10% to 25% of the incoming sunlight. Clouds in the atmosphere reflect roughly 50% of the incoming sunlight. That is quite a bit of light going back into space and some of it will hit the Starlink satellites.

This does not make sense from the perspective of geometry.
They would not be astronomically bright if they were reflecting the extended, diffuse Earth.
What light hits it would fade slowly as the view to the lit surface diminishes smoothly as the orbit proceeds over darkened ground. 
The Starlink satellites have fairly constant brightness and fade quickly when they leave the direct sunlight.
It seems fair to say that the back sides of the solar arrays are sunlit for some reason.

(It’s good to remember not to be snarky. ;)  )

Businesslike explanation != Snark

Offline Hummy

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Re: Starlink : General Discussion - Thread 2
« Reply #1048 on: 01/21/2020 03:31 am »
Here we go. Astronomers doing economic analysis of Starlink assuming it will be sold worldwide for $60 USD.

https://twitter.com/chmn_victor/status/1218847154833412096

Offline Nomadd

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Re: Starlink : General Discussion - Thread 2
« Reply #1049 on: 01/21/2020 03:43 am »
Here we go. Astronomers doing economic analysis of Starlink assuming it will be sold worldwide for $60 USD.

There are plenty of better places for this kind of idiocy.
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Offline meberbs

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Re: Starlink : General Discussion - Thread 2
« Reply #1050 on: 01/21/2020 07:27 am »
Here we go. Astronomers doing economic analysis of Starlink assuming it will be sold worldwide for $60 USD.

There are plenty of better places for this kind of idiocy.
Agreed. Some points of reference for anyone who wants to argue against such things elsewhere in no particular order:

-Countries with 50-90+% internet availability still need better coverage, even the US does for remote areas
-Internet access does not always equal high speed internet
-The predicted cost number is purely made up, SpaceX has not provided actual data yet
-Regional pricing: the only marginal cost for more subscribers in undersubscribed regions is pretty much the antenna. It is not just a nice humanitarian thing, but a logical business thing to drop prices in those areas.

Offline thirtyone

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Re: Starlink : General Discussion - Thread 2
« Reply #1051 on: 01/21/2020 08:13 am »
Here we go. Astronomers doing economic analysis of Starlink assuming it will be sold worldwide for $60 USD.

https://twitter.com/chmn_victor/status/1218847154833412096

To be fair, I think that's just a student in astronomy and not a professional astronomer of any sort. Probably not worth commenting on, even, honestly...

Guess we've just gotten used to getting our SpaceX related 'news' from Twitter?

Offline Crispy

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Re: Starlink : General Discussion - Thread 2
« Reply #1052 on: 01/21/2020 08:59 am »
A single Starlink connection with wifi should be good for dozens of people to share the cost.

Offline Rondaz

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Re: Starlink : General Discussion - Thread 2
« Reply #1053 on: 01/21/2020 01:43 pm »
The @SpaceX #Starlink constellation is growing fast! Read how to keep up with it in our latest post:

https://twitter.com/LeoLabs_Space/status/1219613317632872448

Offline jak Kennedy

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Re: Starlink : General Discussion - Thread 2
« Reply #1054 on: 01/21/2020 02:41 pm »
Here we go. Astronomers doing economic analysis of Starlink assuming it will be sold worldwide for $60 USD.

https://twitter.com/chmn_victor/status/1218847154833412096

To be fair, I think that's just a student in astronomy and not a professional astronomer of any sort. Probably not worth commenting on, even, honestly...

Guess we've just gotten used to getting our SpaceX related 'news' from Twitter?

Just someone ignorant about the world, sitting behind his keyboard who has probably no firsthand knowledge of these countries he types about. I see many people around me with better smartphones than I have and they might only be making $200-300 a month. The world wants and needs to be connected and although I love astronomy I will make a wag guess that the majority of the ‘poor’ of the world don’t give a s#@t about astronomy and would rather be connected.

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Offline StuffOfInterest

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Re: Starlink : General Discussion - Thread 2
« Reply #1055 on: 01/21/2020 03:50 pm »
Not giving the astronomer economic analysis any credence but it did make me think a bit about the model likely to be used in under served parts of the world.

If you are looking at a village in Africa or South America, I don't think you are going to see each individual home having a Starlink antenna on top.  More likely there will be a village or neighborhood hub with a Starlink station and a WiFi router.  For a really isolated area, you may add in a couple of solar panels and a battery pack.  The cost would be several thousand dollars, but would likely be either spread across several dozen households or paid for by an economic development grant.  Combined with WiFi telephony, a lot of very isolated areas could be brought on the grid for a reasonable per user cost.

Offline butters

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Re: Starlink : General Discussion - Thread 2
« Reply #1056 on: 01/21/2020 04:15 pm »
Investing in a Starlink terminal and reselling wifi by the hour is attainable entrepreneurship in developing countries. Business models like this are thriving in nations like Cuba which have underinvested in traditional Internet infrastructure. Starlink won't give everybody in the developing world 24/7 fixed broadband anytime soon, but it will make connectivity more affordable by the hour, and it will create opportunities for thousands of people around the world to lift themselves out of poverty by becoming the local Internet entrepreneur in their neighborhood. It will interesting to see what kinds of financing programs are available, given the humanitarian angle and the relatively high likelihood of repayment.
« Last Edit: 01/21/2020 04:16 pm by butters »

Offline thirtyone

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Re: Starlink : General Discussion - Thread 2
« Reply #1057 on: 01/21/2020 06:19 pm »
Not giving the astronomer economic analysis any credence but it did make me think a bit about the model likely to be used in under served parts of the world.

If you are looking at a village in Africa or South America, I don't think you are going to see each individual home having a Starlink antenna on top.  More likely there will be a village or neighborhood hub with a Starlink station and a WiFi router.  For a really isolated area, you may add in a couple of solar panels and a battery pack.  The cost would be several thousand dollars, but would likely be either spread across several dozen households or paid for by an economic development grant.  Combined with WiFi telephony, a lot of very isolated areas could be brought on the grid for a reasonable per user cost.

Absolutely - I'm not sure how many people know this, but many researchers looking at the developing world believe that mobile phones (and in general mobile communications/Internet) have been and will be a critical part of economic growth in many developing countries. As it turns out, when your country has absolutely awful large scale, wired infrastructure--no landline, no reliable power, etc.--it is far easier to deploy wireless infrastructure to connect people than it is to hope the government can put together the money to build large scale infrastructure. Solar cellphone charging stations and other distributed solutions are quite common. In some developing countries it is hardly uncommon to have a mobile phone before you have reliable power or plumbing.

Here, a large part of our time spent on the Internet is for entertainment and arguably optional activities, like posting on a forum about rockets. It's not quite the same in the developing world. I can't remember the specifics, but someone who worked as a researcher in an African country gave me a few examples once. Many people live in rural areas where the nearest trading town is hours away. If you sell crops or animals or other goods, you often want to communicate in advance with buyers so that you can meet with them in town, instead of wasting a few hours every day going to town and hoping you can catch a buyer. Given that *there aren't even landlines* the introduction of cellphones were critical to making a lot of basic economic activities much more efficient. Banks also aren't exactly accessible in many of the poorer developing countries, and mobile payments have had an enormous impact as well (imagine if you couldn't use a bank and had to keep money safe at home in a box somewhere...)

Anywho, yeah, I'd argue that better Internet connectivity is likely to be worth a more substantial portion of GDP in developing countries than a developed one. With that said, someone would need to do a cost-benefit analysis, because, well, mobile coverage does already exist in a lot of areas now, and it's not clear what Starlink would add. The scenario you proposed (central Starlink/WiFi stations) certainly sounds like the appropriate type of solution in poorer developing countries - central charging stations in towns are already apparently a common solution (before those, people might've had to travel to recharge their phone batteries...)

Offline freddo411

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Re: Starlink : General Discussion - Thread 2
« Reply #1058 on: 01/21/2020 08:40 pm »

...

Anywho, yeah, I'd argue that better Internet connectivity is likely to be worth a more substantial portion of GDP in developing countries than a developed one. With that said, someone would need to do a cost-benefit analysis, because, well, mobile coverage does already exist in a lot of areas now, and it's not clear what Starlink would add. The scenario you proposed (central Starlink/WiFi stations) certainly sounds like the appropriate type of solution in poorer developing countries - central charging stations in towns are already apparently a common solution (before those, people might've had to travel to recharge their phone batteries...)

Cell phone towers and internet (mobile or fixed) require a backbone connection.   Maintaining a WIRED backbone connection in the third world is, ah, challenging.

SL will provide the opportunity to setup more economically viable cellphone towers and provide more Internet gateways compared to just wired connections.

The same is true in rural America, Canada, etc. etc.

Offline indaco1

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Re: Starlink : General Discussion - Thread 2
« Reply #1059 on: 01/21/2020 11:16 pm »
I agree, most of end users in marginal areas will not even know they are using Starlink.

They will pay a price tailored to their puchase power to a telecom to connect a mobile device to a 4G & 5G LTE Base Station coupled with a Starlink station on the same tower. Not wifi because billing and range.

This could change the life of many people.
Non-native English speaker and non-expert, be patient.

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