Author Topic: Amazon and Spacex plan to launch thousands of satellites - sane or reckless?  (Read 2524 times)

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Offline duak

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The Iridium constellation was orbited in the late 90's and could be considered a precursor: https://en.wikipedia.org/wiki/Iridium_satellite_constellation  There were some 66 satellites plus extras and the altitude was 485 miles.

I worked with meteorlogical satellite groundstations for TIROS-N & NOAA-6/7 in the late 70s.  With the technology of the time we needed a 3 to 5 m tracking dish to achieve a 667 KBPS downlink data rate.  The downlink was simple PSK on an FM 2.3 GHz signal.  Altitude was something like 800 km.  Landsat had something like a 15 MBPS downlink but needed a much bigger tracking dish. Things have come a long ways since then.

It was kind of magical to point the antenna at the horizon where the satelite was supposed to rise from.  Within a few seconds of the calculated time, the receiver would show a signal, the antenna would slew to the exact position, the bit sync would indicate a lock then our equipment would show a frame lock and start recording on magnetic tape.  I think the longest transit was about 15 minutes.  It used a whole tape and was maybe 200 Mbytes.
« Last Edit: July 18, 2019, 04:51:06 pm by duak »
 

Offline Nusa

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I am just wondering
what is the (cost + maintenance)/(km sq cover * years in service)
starlink is stated to have a lifespan of 5 years

vs normal 200 -300 foot radio masts?

Spacex's stated plans for Starlink are 24 launches with 60 satellites each to achieve global coverage. I'd guess that would cost them about $1.5 billion based on a 2018 number of $64 million/launch. Plus ongoing launches after that for redundancy, capacity, and spares. The first launch of 60 happened May 23rd. 3 have ceased communicating. 2 others were ordered to deorbit themselves on purpose to test that ability. The rest are either in position or still moving towards their positions in orbit. For now it's a private network that they're stress-testing best they can internally.
 

Offline Red Squirrel

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I am just wondering
what is the (cost + maintenance)/(km sq cover * years in service)
starlink is stated to have a lifespan of 5 years

vs normal 200 -300 foot radio masts?

Only 5 years?  Damn that's a waste then.  These are literally just disposable satellites.   Seems to me it would actually make much more sense to do radio towers.  Do a network that's completely separate from regular cellular and has no caps but uses a similar tech.  Heck to make it mostly autonomous and not rely on hydro, each tower could be solar powered just like satellites would be.  The south side of the tower could have solar panels mounted on it that would power the equipment.   One advantage of satellites is that in space the conditions are rather predictable, no winds or storms etc, but if they are only going to last 5 years anyway then that advantage is kind of moot. 
 

Offline StillTrying

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The 2 birds would still be 37,000km away, they could have done with building the geostationary orbit much lower really. :)
Geostationary is a geosynchronous orbit that's in the plane of the equator. If you put it in any other plane (synchronous but not stationary), it's not going to be over the same arc of the earth all the time. The required distance to be geosynchronous is defined by physics, not convenience. It's the point where the centrifugal force of a 24-hour orbit exactly matches the gravitational force from the mass of the earth.

I know the geostationary orbit can't be moved anywhere else. :)
But I didn't realise ALL the GPSs are halfway to geosynchronous, it's amazing that small pocket devices with internal antenna can pick up enough usable signal from them.
CML+  That took much longer than I thought it would.
 

Offline GeorgeOfTheJungle

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But I didn't realise ALL the GPSs are halfway to geosynchronous, it's amazing that small pocket devices with internal antenna can pick up enough usable signal from them.

That satellite (iridium) phones work is what amazes me.
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Offline Red Squirrel

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Did not realize GPS were that far up either it really is quite impressive they can be picked up with small hand held devices.  Even dedicated GPSes before smart phones is quite incredible.
 

Offline ajb

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I am just wondering
what is the (cost + maintenance)/(km sq cover * years in service)
starlink is stated to have a lifespan of 5 years

vs normal 200 -300 foot radio masts?

Only 5 years?  Damn that's a waste then.  These are literally just disposable satellites.   Seems to me it would actually make much more sense to do radio towers.  Do a network that's completely separate from regular cellular and has no caps but uses a similar tech.  Heck to make it mostly autonomous and not rely on hydro, each tower could be solar powered just like satellites would be.  The south side of the tower could have solar panels mounted on it that would power the equipment.   One advantage of satellites is that in space the conditions are rather predictable, no winds or storms etc, but if they are only going to last 5 years anyway then that advantage is kind of moot.

The short life span is related to the exact concern that started this thread.  Part of the design of the system is that the satellites will rapidly deorbit due to atmospheric drag if not actively maintained, this effectively makes the system failsafe in the sense that even totally dead satellites will automatically dispose of themselves.  This also means that even satellites that continue to perform nominally will have a lifespan set by their propellant store.  Also, the satellites are designed to be mostly 'demisable', meaning that they will safely disintegrate as they reenter the atmosphere, so there's little to no chance of debris posing a hazard to aircraft or anyone on the ground.  Future designs are intended to be 100% demisable. 

As to coverage area, consider that a standard cell tower has a range of about 5-70km depending on conditions.  Call it 50km, and each tower can cover something like 7500km^2.  That means ~1300 sites to cover just the US.  Each site requires the purchase or lease of land, and the ability to access that site.  Meanwhile, SpaceX say they can achieve "significant" global coverage with only 800 satellites.  Moreover, each and every satellite contributes to service across a huge swath of their coverage area (possibly the entire area, eventually, depending on orbital period and inclination), so it's a much easier system to scale up.  With towers, adding one somewhere only contributes capacity to that ~7500km^2 service area, but adding a single satellite potentially contributes capacity to a few million km^2 (possibly more once they add mesh networking, so that they can route around congested base stations).

As a bonus, the nature of satellites means that coverage will not be focused on densely populated areas, so Starlink et al could be revolutionary for all of the areas of the world that not densely populated (or wealthy) enough for terrestrial providers to consider building out with infrastructure.
 

Offline Nusa

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imagine the amount of transistors they need to make to do all that

Depends on what you think a lot is these days.

The smartphone in most of our pockets has billions, even for the cheap phones. That is already too large a number to visualize. A modern gaming computer would have a LOT more. DRAM alone requires a minimum of 1 transistor per bit, so 8 billion transistors per GB of ram installed (multiply by 6 if you need SRAM). Then there's the CPU and GPU and all the support chips.
 
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Online james_s

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Did not realize GPS were that far up either it really is quite impressive they can be picked up with small hand held devices.  Even dedicated GPSes before smart phones is quite incredible.

Frankly that blows me away. I have some $5 Chinese GPS modules that reliably pick up 10+ satellites from inside my house. It's easy to forget the incredible engineering feats that enable this to happen.

I still remember my dad looking at GPS receivers in catalogs back when they were big clunky things that cost thousands of dollars each and even then it seemed amazing.
 

Offline madires

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Offline GeorgeOfTheJungle

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It will take even more than that to replicate a cellular network up in the sky.
http://brave.com <- THE BEST BROWSER
 

Online wraper

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Spacex's stated plans for Starlink are 24 launches with 60 satellites each to achieve global coverage. I'd guess that would cost them about $1.5 billion based on a 2018 number of $64 million/launch.
Don't forget they are launching for themselves, on most used first stages they have. Fairings apparently are used and with payload protection internals removed. So actual launch price is certainly not the same as their commercial offerings for customers.
 

Offline duak

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Interference with astronomy was mentioned above: https://www.space.com/astronomy-group-worries-about-starlink-science-interference.html

Starling rhymes with Starlink, don't you think?  Look at this: https://en.wikipedia.org/wiki/Eugene_Schieffelin  Not on the scale of rabbits in Australia of course, but we live in the age of consequences.
 


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