Amazon and Spacex plan to launch thousands of satellites - sane or reckless? - Page 1
Forum section: electronics / general

author: splin
author_rank: Frequent Contributor
timestamp: July 16, 2019, 01:28:47 am
content: Jeff Bezos wants to launch up to to 3,236 satellites to provide internet access for poorly served areas worldwide and Spacex, in competition, apparently could launch up to 12,000 satellites.https://www.fool.com/investing/2019/06/11/could-amazon-beat-spacex-in-satellite-broadband-in.aspxThese are to be in low earth orbit, but how much of a threat could these pose due to the 'Gravity' film's cascading failure scenario whereby should one get destroyed it showers orbital space with thousands of high energy pieces of wreckage which go on to destroy more satellites in a chain reaction?Science fiction or a plausible risk? What if other companies/nations join in? China could decide it wants to launch many thousands for example, not wanting orbital space to be dominated by the US.What about all the junk every launch puts into orbit?

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 16, 2019, 12:47:03 pm
content: Yeah.Is this considered pollution yet?

author: bd139
author_rank: Super Contributor
timestamp: July 16, 2019, 12:49:59 pm
content: https://en.wikipedia.org/wiki/Kessler_syndromeInterestingly they're looking at taking the biggest hand grenade out:https://en.wikipedia.org/wiki/E.Deorbit

author: taydin
author_rank: Frequent Contributor
timestamp: July 16, 2019, 12:53:56 pm
content: It doesn't require too much mental energy to realize that those satellites aren't being sent so that the poor ethiopian shepherd has internet accessIt's the next step in the full surveillance and tracking of all humanity. Soon we will see that you will be compelled to use those satellites to get essential services, so you won't have a choice in the matter.

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 16, 2019, 01:17:28 pm
content: Quote from: taydin on July 16, 2019, 12:53:56 pmI see what you mean, but I don't fully agree with that. Internet access makes a whole lot of new consumers. Even if they are very poor consumers, if they are many, that's still a potential gigantic new market. That itself would be enough to motivate the rich to send more satellites. We have much more to sell them than just sterile seeds!Quote from: taydin on July 16, 2019, 12:53:56 pmThat is probably true as well. But don't underestimate the business side of it all.

author: BrianHG
author_rank: Super Contributor
timestamp: July 16, 2019, 04:02:46 pm
content: This is where Elon will be making his money with the satellites. He will reserve and sell the optimum speed connection path between Europe & North America & Japan & Australia for high frequency stock trading for big banks. Everyone else's internet would just be a small bonus by comparison.https://www.newscientist.com/article/mg24032033-300-the-first-detailed-look-at-how-elon-musks-space-internet-could-work/

author: bd139
author_rank: Super Contributor
timestamp: July 16, 2019, 04:17:41 pm
content: I doubt it. Latency is shit if you have to go to space and back. Even worse if you have to go across a mesh network in space.HFT would laugh at it. They're literally putting their execution stuff physically in the same building as the exchange these days to lose latency. It goes as far as having FPGAs running the show to lose the OS latency too.Go watch "Kingsman" the film. He's basically Valentine in that.

author: madires
author_rank: Super Contributor
timestamp: July 16, 2019, 04:31:13 pm
content: And the ground stations need to be connected via fiber. I agree with bd139, the total latency will be worse than what current sea cables offer. The 20k+ LEO satellites will become a huge problem for any future space activities and astronomers. It's simply a bad idea.

author: BrianHG
author_rank: Super Contributor
timestamp: July 16, 2019, 04:44:47 pm
content: Quote from: bd139 on July 16, 2019, 04:17:41 pmElon's satellites will eventually be only 320km up, not 42,000km up, and if you link at a far angle between New York, to an optimum 2 or 3 constellations over the Atlantic Ocean and then back to Europe with a dedicated focused high gain antenna on each side, you'll just outrun fiber, especially with a direct buffered full duplex transceiver link, no internet infrastructure in the middle with all that fiber latency and with all the fiber's re-clocked buffers along the line.Actually I just saw a good movie called 'The Humming Bird Project'https://www.imdb.com/title/tt6866224/?ref_=ttnw_hdRF outruns fiber big time and across the Atlantic, observing from the available visible angles of low orbiting satellites which will be 120 times closer than the old fashioned geostationary type, and a direct antenna feed (no up and down twice to a earth based relay point), it will outrun fiber easily.Quotehttps://www.teslarati.com/spacex-starlink-internet-constellation-a-license-to-print-money/

author: nctnico
author_rank: Super Contributor
timestamp: July 16, 2019, 07:16:07 pm
content: Quote from: BrianHG on July 16, 2019, 04:02:46 pmYou can't do high speed trading using satellites. A 'land line' will always be shorter and thus faster.

author: bd139
author_rank: Super Contributor
timestamp: July 16, 2019, 07:16:30 pm
content: Quote from: BrianHG on July 16, 2019, 04:44:47 pmI don’t buy it.You’d need a dedicated stream of wideband analogue uplink/downlink between each satellite which was fully redundant through all satellite disposals. Your digital streams would need to be retransmitted several times (think of the loss). Also you’d need QoS which adds latency as you have to queue. And the uplinks could be jammed from a rogue ground station. Oh and the logistical problem of where to site ground stations, cost and security means they will be centralised if you need some bandwidth or latency guarantees. Plus also shit like rain can cause you problems.Your other option is Hibernia Express which is 59ms from london to NJ fibre 50+ Tbits secure landing both shores.I’ll take the fibre please.Note I have worked in an infrastructure capacity in HFT.

author: iMo
author_rank: Super Contributor
timestamp: July 16, 2019, 07:32:05 pm
content: An LEO satellite at 350km altidute will be visible for maybe 6 minutes when tracked with an Yagi antenna, or say 1/2 minute flying over your head inside your fixed antenna main lobe.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 16, 2019, 07:47:50 pm
content: Radio waves propagate in the air faster than the light inside a fiber optic, right? But the bandwidth of a radio link, is near as much as that of optic fibers? And a submarine cable can have tens or hundreds of fibers, how many radio links with a decent bandwidth can be had simultaneously between a satellite and the ground station? There's a physical limit to that, isn't it? I mean the EM spectrum is what it is and only so many channels can fit, so to upgrade you can't just put 1000 fibers more in parallel and be done, right?I think it was Mr. Bill Gates that invested many millions in communications satellites in the late 80s, but then the internet went through underwater optic cables instead. Or is that just another urban legend?

author: rdl
author_rank: Super Contributor
timestamp: July 16, 2019, 08:51:20 pm
content: 350 km is not very far up and the satellites will be designed to be deorbited when the time comes they are no longer useful. At that altitude they'll probably come down fairly soon on their own. I'm more interested in seeing if they can actually make such a system work. The latency predictions I've seen won't be a problem for most uses and anything providing hope of getting cheaper, better internet in the US is worth looking at.

author: BrianHG
author_rank: Super Contributor
timestamp: July 16, 2019, 09:04:43 pm
content: Quote from: GeorgeOfTheJungle on July 16, 2019, 07:47:50 pmI get there will be far less data bandwidth, it's is there enough bandwidth for a small dedicated trading channel to your overseas partner where the goal is purely point to point latency where you can capitalize on purchasing and selling a stream of stocks ahead of everyone else on fiber making you money. Telling your overseas office to buy or sell a stock name with a value even 0.01 seconds faster make you money as this would run continuously 24/7.Yes, fiber is cleaner, almost fixed consistent delay and bulk data capability will roast the satellites.Of course, we do not know the inner workings of Elon's satellites. Are they basic analog satellite transponder technology, or, do they interpret, decode and re-encode bits of data like an internet hub.In the movie 'The Humming Bird Project', I like the guy's dream idea of using a neutrinos to link New York and Tokyo going straight through earth. I know receiving a clean message from those near light speed non-interacting buggers is so problematic that you would have miserable bandwidth, but, you would cut your ping time a few fold compared to going around the earth in fiber.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 16, 2019, 09:41:40 pm
content: In low earth orbit the distance via satelites does not have to be longer than the cable. So latency can be lower, as radio waves are about 1.5 times faster than light inside a fiber.With low flying satellites the antennas are also a challenge. For a good BW it would need directional antenna and due to the speed more like moving fast. Just a simple antenna would only work for a low BW signal - more like todays satellite phones.However the band width is limited. So for normal use, where other options (e.g. 3 G phone system, fiber) exist, these will offer more bandwidth.So for most of the world this is not an attractive option. It may be something for ships or planes but I kind of doubt it is economical viable.At least the debris from the rockets sending the satellites up would be not such a problem, as this should be usually lower than the satellites orbit. Still many satellites on a similar orbit can become a nightmare. A collision could also send parts to a high orbit.

author: splin
author_rank: Frequent Contributor
timestamp: July 16, 2019, 10:42:00 pm
content: So how many satellites can be accommodated safely in LEO and VLEO? What if China decides to launch 10,000/20,000/50,000+? I doubt India or Russia could afford to unless, perhaps, there were a strategic military objective rather than pure commercial reasons. Europe could also decide to get in on the act. And S. Korea, Brazil etc? The Middle East could see space as a new opportunity to diversify it's investments beyond oil and luxury holiday resorts.Are there any international agreements in place to regulate orbital space or is it a total free for all? Radio spectrum is heavily regulated so how difficult would it be to allocate sufficient bandwidth for all those satellites? Internet provider service presumably means wide beam or even omni-directional antenna so re-use of frequencies will require considerable ground spacing.I'm guessing that given the numbers of satellites, they will have to be small which presumably wouldn't accommodate very high gain antennae with narrow beam widths (for satellite to satellite mesh networking and/or links to groundstations) and the relatively fast and wide angle tracking which would be required.

author: iMo
author_rank: Super Contributor
timestamp: July 16, 2019, 11:05:39 pm
content: With altitudes at 350km the satellites will burn up in the atmosphere pretty quickly (say in 6-12months) when not lifted up regularly (because of the air drag). Therefore the satellites cannot be "small" as they have to carry the fuel.The ISS flies at ~400km and they must do reboost maneuvers to stay there pretty often.For high BW you need high GHz carrier, you would need antennas with high gain and those antennas are highly directional.It may work when you would have 2-3 satellites over your head (fixed antenna) all the time (always a couple of sats over your head at, say, >70deg elevation), mind the LEO satellite at 350km will pass over your head in maybe 20-30 seconds at that elevation range.

author: splin
author_rank: Frequent Contributor
timestamp: July 16, 2019, 11:56:30 pm
content: Quote from: imo on July 16, 2019, 11:05:39 pmFor Internet service provision you can't us a highly directional antenna as the customers are dispersed over a wide area - yes for ground links or inter-satellite links. Assuming a satellite has to service a few hundred or thousand users over several hundred square miles at any one time, a wide beam width will be required along with a lot of bandwidth to provide decent data rates.Multiply that by many competing service providers and the spectrum demands could be challenging, although I guess the total BW requirement would be determined more by the maximum number of users and their usage in any one area, more than the number of providers.

author: james_s
author_rank: Super Contributor
timestamp: July 17, 2019, 12:15:59 am
content: It seems to me like terrestrial fiber has got to be more cost effective than thousands of orbiting satellites. It takes a tremendous amount of energy to toss something up into orbit and then it has to be maintained. Seems rather wasteful to devote that many satellites to internet access. Seems also like most of the regions without internet could be better served by food, agriculture, vaccines and family planning. In theory the internet could help with several of those but in reality it's more likely to spread misinformation that is not helpful.

author: coppercone2
author_rank: Super Contributor
timestamp: July 17, 2019, 12:51:06 am
content: I wonder if malfunctioning satellites will eventually accumulate in one point to make a flying ghetto scrapyard

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 17, 2019, 12:53:57 am
content: I wonder if someday it will become so crowded up there that they will actually partly shield us from sunlight.

author: coppercone2
author_rank: Super Contributor
timestamp: July 17, 2019, 01:17:26 am
content: Quote from: SiliconWizard on July 17, 2019, 12:53:57 amdyson swarm

author: Red Squirrel
author_rank: Super Contributor
timestamp: July 17, 2019, 01:21:00 am
content: I have mixed feelings about it. It depends how long they plan to keep them there. If this is like a 10-15 year thing where they deorbit and then they keep launching more, I'm really against it because that's a lot of pollution for such a short life span, but if these will last for 50 or more years before they need to be deorbited, then I suppose the benefit of what they provide is worth it.Even though most of this burns in the astmosphere, that's not any different than if you were to build a camp fire and burn the satellite in it. It's still pollutants going into the atmosphere. Probably lot of nasty stuff too like heavy metals etc.I realize they are targeting super low latency internet that is always available but I feel they need to compromise here. Have less satellites, and put them at a higher altitude. Heck maybe just add a bunch more geostationary ones that are linked and provide the service cheaper than existing geostationary internet services. High latency slow internet is better than no internet, if this is targeting places that can't get it.

author: splin
author_rank: Frequent Contributor
timestamp: July 17, 2019, 01:49:50 am
content: Quote from: splin on July 16, 2019, 10:42:00 pmSorry, forgot the Aussies and NZ - I'm sure they have ambitions in space too...

author: Rerouter
author_rank: Super Contributor
timestamp: July 17, 2019, 02:15:28 am
content: We already launch our trust in politicians in to the sun on a weekly basis. An try to prevent cetain groups from trying to fire a preserved cat on a ballistic trajectory at the curiousity rover.So global communications empire. Seems easy enough.

author: BrianHG
author_rank: Super Contributor
timestamp: July 17, 2019, 02:40:50 am
content: Quote from: coppercone2 on July 17, 2019, 01:17:26 amIt would help with global warming...

author: edy
author_rank: Super Contributor
timestamp: July 17, 2019, 03:01:03 am
content: How about just putting a huge transmitting station on the moon.... As long as you can see the moon, you have "Moonternet".This way you also build in automatic "offline" time so the kids don't use the internet 24 hours a day... They only get access while their half of the Earth is facing the moon!All kidding aside, it seems that nobody is yet worried because space is so huge that the chances of collisions between satellites is extremely small. However, you never know what will happen and eventually this could put astronauts in danger if they are trying to leave the planet for various missions. I hope the satellites have some fuel left so when it's time to decommission them, we can point them back down to Earth and have them activate their rockets and so enter the atmosphere to burn them up.

author: rdl
author_rank: Super Contributor
timestamp: July 17, 2019, 03:45:02 am
content: It's funny all the people worrying about 50,000 satellites. Imagine the Superbowl, or World Cup. Think of how many people are crowded in that stadium. Now spread them out around the Earth. How crowded is it now?

author: coppercone2
author_rank: Super Contributor
timestamp: July 17, 2019, 05:45:45 am
content: how about a big thruster with magnets on it that accumulates satellites and flies into the moon?nuclear powered. or are they not magnetic enough?

author: digsys
author_rank: Unknown
timestamp: July 17, 2019, 05:55:21 am
content: Quote from: rdlerrrrrr not quite - constant explosions / collisions generate MILLIONS of tiny dust sized (plus larger) debris and they can still (and DO) a heck of a lot of damage !!https://aerospace.org/article/danger-orbital-debrisAnd the more crap they put up there, the chances of failure / collisions increases dramatically !

author: Nusa
author_rank: Super Contributor
timestamp: July 17, 2019, 07:02:05 am
content: From what I've read, there are already 500K pieces of debris larger than a marble in LEO. 20K of which are larger than a softball. And millions of stuff that is too small to track. So from the debris point of view, I suspect it won't have much of an impact either way.Latency is far less important than bandwidth and availability when you're talking about areas that have little to no infrastructure for telephones, never mind internet. Much of the interior of Africa comes to mind. Or Antarctica (limited satellite service currently, as there are no cables to the continent). Even some of the very rural areas in more developed countries. The existing satellite network only has so much bandwidth.The other issue that comes to mind for some is that of information control. How can a government practically exercise control over the internet if the communications are simple, relatively cheap, localized transmitters directly to space?And, of course, this could result in satellite phone service becoming cheap enough for the masses to use. Good for us. Maybe bad for the existing services reclaiming their investment.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 17, 2019, 07:51:21 am
content: We'll have planes colliding with satellite rubbish?

author: Nusa
author_rank: Super Contributor
timestamp: July 17, 2019, 08:17:55 am
content: Quote from: GeorgeOfTheJungle on July 17, 2019, 07:51:21 amOnly a problem in your mind, as there is no satellite rubbish orbiting within the atmosphere. Commercial flights cruise less than 12 km up. LEO is from about 300 km to 2000 km.

author: tautech
author_rank: Super Contributor
timestamp: July 17, 2019, 08:29:00 am
content: Quote from: splin on July 17, 2019, 01:49:50 amAlready doing it for the Aussies and the US.Then seven with one blow !https://www.rocketlabusa.com/news/updates/rocket-lab-successfully-launches-seventh-electron-mission-deploys-seven-satellites-to-orbit/

author: madires
author_rank: Super Contributor
timestamp: July 17, 2019, 08:47:53 am
content: Quote from: GeorgeOfTheJungle on July 16, 2019, 07:47:50 pmYep, light travels with 2/3c in glass fiber.QuoteMost submarine cables have 8 fibers. Maybe we'll see some with 12 or little bit more but this is the current limit of what's feasible. The high data rates of many Tbps are achieved by DWDM, i.e. running several light colors each carrying 100 or 400Gbps. 20 years ago it was just 10Gbps per color. With radio links you have a limited frequency range assigned by some authority.

author: madires
author_rank: Super Contributor
timestamp: July 17, 2019, 08:56:29 am
content: Quote from: rdl on July 17, 2019, 03:45:02 amTry tracking all those people running around after the Superbowl. You don't want to hit a LEO satellite when launching a rocket.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 17, 2019, 09:04:42 am
content: Quote from: Nusa on July 17, 2019, 08:17:55 amBut sooner or later they'll fall out of orbit and disintegrate into pieces, then what?

author: madires
author_rank: Super Contributor
timestamp: July 17, 2019, 09:08:23 am
content: Quote from: imo on July 16, 2019, 07:32:05 pmThat's the reason why they need data links between the satellites or a second layer of satellites linking the lower layer. And that will increase the overall latency.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 17, 2019, 09:42:29 am
content: From NYC to London there are 5565 km (according to google maps), at the speed of light that's 5565/300e3= 18.55 ms, in a fiber 5565/(2*300e3/3) = 27.82 ms. The difference is 9.27 ms. But the path of the RF link isn't a straight line, so it'll be a smidge less than that.

author: rdl
author_rank: Super Contributor
timestamp: July 17, 2019, 10:26:14 am
content: If there actually were 50,000 satellites and assuming a size of one square meter, and if they were all in the same orbit, and if there was no idea exactly where each one was but they are evenly spaced, there would be roughly one satellite every 42,000 meters.Change any one of those conditions to something closer to what the likely scenario will be and I think the odds of an accidental collision will be close to zero.

author: bd139
author_rank: Super Contributor
timestamp: July 17, 2019, 10:37:18 am
content: That's not how it works though.One bit of space crap hits one of them at 20,000mph and it's now 12 bits of satellite. Then one of those bits hits another one ...Next thing you know there's a debris cloud which stops all space launches. Any system on the verge of chaos only takes one stimulative event to set it off.

author: Nusa
author_rank: Super Contributor
timestamp: July 17, 2019, 10:45:24 am
content: Quote from: GeorgeOfTheJungle on July 17, 2019, 09:04:42 amMost will disintegrate into dust and vapor before getting down to flying levels. The few larger items will make a single pass through airspace and impact the earth. Which can kill you, even on the ground, but its not very likely. You're more likely to get hit by a stray bullet coming back down after being fired into the air by someone a mile away. In any event, it stops being a piece of debris.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 17, 2019, 10:47:44 am
content: Quote from: rdl on July 17, 2019, 10:26:14 amBut if it takes 6 minutes to cross the sky, and you need to always have one visible/in range, you'd need a pile of them in line in series in the same orbit, spaced less than 6 minutes one from another, no? A belt of satellites so to speak...

author: tautech
author_rank: Super Contributor
timestamp: July 17, 2019, 10:52:50 am
content: What's all this talk of moving satellites, won't they be geostationary like sat TV ones ?

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 17, 2019, 10:53:57 am
content: No, can't be geostationary because they want/need them to be much closer to ground.

author: tautech
author_rank: Super Contributor
timestamp: July 17, 2019, 10:58:06 am
content: Quote from: GeorgeOfTheJungle on July 17, 2019, 10:53:57 amExisting data providers ones are stationary.....why can't land based connections just use greater RF power and sensitivity ?

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 17, 2019, 11:02:35 am
content: Because Elon is a Think Different®™ guy?

author: Nusa
author_rank: Super Contributor
timestamp: July 17, 2019, 11:04:45 am
content: Quote from: GeorgeOfTheJungle on July 17, 2019, 10:47:44 amIt's not how fast they move, but how much of the orbital arc a single satellite can cover that determines the count. I could probably do the math with some assumptions, but I'm not going to put that much effort into it. Also it's a lot more complicated since a single orbit cannot provide coverage of the entire earth. Ideally there should be at least two satellites in view most of the time anywhere on earth if fully implemented.

author: bd139
author_rank: Super Contributor
timestamp: July 17, 2019, 11:05:05 am
content: Quote from: tautech on July 17, 2019, 10:58:06 amActually they did that in the UK. We had a massive microwave backbone run by BT from the 1960s-1990s. This is mostly been supplanted by DWDM fibre.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 17, 2019, 11:10:10 am
content: Right you are, a satellite can't orbit over a parallel! (except the Equator). So you'd need lots of them everywhere and in all directions. Cool!

author: madires
author_rank: Super Contributor
timestamp: July 17, 2019, 11:19:53 am
content: Quote from: tautech on July 17, 2019, 10:52:50 amGeostationary satellites have an RTT of about half a second.

author: tautech
author_rank: Super Contributor
timestamp: July 17, 2019, 11:27:05 am
content: Quote from: bd139 on July 17, 2019, 11:05:05 amYes of course, in the name of speed !We've had independent sat link providers for some years but the speeds are woefully slow and at times troublesome compared to an even decent copper DSL connection.Yet satellite will be the most efficient way to reach the isolated and poorer areas of the globe without the need for costly ground based network infrastructure.Locally we did an exercise with our national infrastructure provider and the cost for a 1.4km fiber backhaul link and new local cabinet and HW was some $200k.Now I have a 5 GHz wireless link to fiber 10km away for a service we only dreamed of just a couple of years ago.A few $ for HW and installation plus some BW package ........done !IMO this type of data service for those outside the cities is the way to go......get a fast service to a local tower, stick some sector panels on it and sign em all up !If satellite can provide that speedy link then the rest can be done locally to serve just a targeted community.

author: tautech
author_rank: Super Contributor
timestamp: July 17, 2019, 11:35:09 am
content: Quote from: madires on July 17, 2019, 11:19:53 amWe couldn't live with that but 3rd world countries and remote areas could.

author: madires
author_rank: Super Contributor
timestamp: July 17, 2019, 11:36:32 am
content: Quote from: rdl on July 17, 2019, 10:26:14 amDo you have a GPS receiver (module, smartphone)? Run a tracking tool and watch how many GPS satellites are seen over time. The number will change during the day. There are maximums and minimums. Satellites aren't evenly distributed. And the next problem is that you have to think four-dimensional, i.e. space and time. You have to make sure that your rocket won't hit any satellite during the whole flight.

author: madires
author_rank: Super Contributor
timestamp: July 17, 2019, 12:00:52 pm
content: Quote from: tautech on July 17, 2019, 11:35:09 amOf course, but with LEOs the enduser's units are easier to handle and cheaper. Rx and Tx with a GEO requires more effort.

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 17, 2019, 12:05:20 pm
content: Quote from: BrianHG on July 17, 2019, 02:40:50 amOh, of course.And then, it would give cheap Internet access even to the last few people that don't want it! The little buggers!Two good reasons to do just that!

author: StillTrying
author_rank: Super Contributor
timestamp: July 17, 2019, 12:13:28 pm
content: Quote from: rdl on July 17, 2019, 10:26:14 amI make them only 800 meters apart in low orbit.I can simplify the the whole thing, - it's not going to happen.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 17, 2019, 01:26:48 pm
content: ...

author: rdl
author_rank: Super Contributor
timestamp: July 17, 2019, 01:37:39 pm
content: You're right, I re-did the calculations and get about 850 meters spacing at a 350 km orbit.Now what would the spacing be if they were uniformly distributed across that sphere?(Which they won't be but it would give a ballpark idea of the eventual density)Quote from: StillTrying on July 17, 2019, 12:13:28 pm

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 17, 2019, 01:47:04 pm
content: sqrt(4*pi*((6378+350)^2)/50e3) = 106 km apart IIANM

author: rdl
author_rank: Super Contributor
timestamp: July 17, 2019, 02:12:40 pm
content: That's about what I got, one every 10,000 square kilometers*. Not quite enough to blot out the Sun, and since they will be in well defined and controlled orbits by necessity, I can't see there being much of a collision problem. I somehow doubt there will ever be that many satellites needed anyway.edit: fixed, kilometers not meters

author: StillTrying
author_rank: Super Contributor
timestamp: July 17, 2019, 02:30:09 pm
content: 106 km apartBut they're traveling at 7.5km meters per second so they'll bepassingeach other quite often.I've guestimated it at at about 1000 near-misses per second.

author: rdl
author_rank: Super Contributor
timestamp: July 17, 2019, 02:56:47 pm
content: Just having the satellites at slightly different altitudes would make near misses irrelevant. Without knowing the exact orbital geometry they will be using I don't really see much point in speculating, beyond just getting an overall feel for the actual density.

author: james_s
author_rank: Super Contributor
timestamp: July 17, 2019, 03:45:18 pm
content: Quote from: madires on July 17, 2019, 08:47:53 amWhy so few? I know nothing about submarine fiber cables but given fibers are quite small and crosstalk is not an issue, what is the limiting factor?

author: madires
author_rank: Super Contributor
timestamp: July 17, 2019, 04:59:47 pm
content: Quote from: james_s on July 17, 2019, 03:45:18 pmMostly costs. For the long distance EDFA/Raman amplifiers are placed in-line and they need to be powered. The cable is fed at both ends with a few kV (one side negative, the other positive). If you increase the number of fibers you have to provide more power for the additional amplifiers, i.e. more copper, thicker cable and larger bumps for the amps. A thicker cable makes everything much more expensive (not proportional). For example, the ship for laying submarine cable can load only a specific volume of cable. The thicker cable means less length.

author: BrianHG
author_rank: Super Contributor
timestamp: July 17, 2019, 06:28:03 pm
content: Quote from: tautech on July 17, 2019, 10:58:06 amYou have limited transponder bandwidth on each satellite. Without a focused dish pointing to single out a single satellite, you wont serve many people. Remember, with LEO satellites, the antenna you can use will be on a cell phone, not a focused dish. Also, the available geostationary locations based on signal selectivity per given viewing angle is already filled and reserved for mass TV broadcasting and dedicated over seas relays where data latency doesn't matter.Besides at the geostationary distance, there is a huge 2 second round trip delay. Talk about a lousy ping time.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 17, 2019, 08:17:05 pm
content: Quote from: BrianHG on July 17, 2019, 06:28:03 pmCan't be 2 seconds RTT if it's ~= 36e3 kilometres above ground !

author: tautech
author_rank: Super Contributor
timestamp: July 17, 2019, 08:48:57 pm
content: Quote from: BrianHG on July 17, 2019, 06:28:03 pmYeah I get that as existing sat positioning was decided upon to get the best coverage and bang for buck plus for TV latency matters little.Our Optus D1 (TV sat) is 37000km for me according to DishPointer which is a stupid long distance compared to what could be achieved with targeted placement over regions that could need data connectivity.NZ is only 2000km long and two islands where 2 birds could serve us well and give everybody some sort of data connection were there are currently places where there is none.Again, ping time means nothing to those that presently don't have internet.

author: StillTrying
author_rank: Super Contributor
timestamp: July 18, 2019, 12:13:02 am
content: Quote from: tautech on July 17, 2019, 08:48:57 pmThe 2 birds would still be 37,000km away, they could have done with building the geostationary orbit much lower really.

author: Red Squirrel
author_rank: Super Contributor
timestamp: July 18, 2019, 01:31:35 am
content: For those saying they should be geostationary keep in mind that orbital periods are dictated by distance. You can't just put something in LEO and make it geostationary. So for it to be geostationary it needs to be much further out. Not sure if there's other factors like mass that also play into this, but essentially to get an orbit you need to be going a certain speed and that dictates how far you end up from the planet. This of course changes between different planets because of gravity. (I think?) Geostationary is that sweet spot where you just happen to be matching the Earth's rotation. You of course need to be at a 0 degree inclination, though if you're not you just end up doing a figure 8 pattern over an area.That said I think they should do a compromise, do a higher up orbit that is not geostationary but further enough out that the satellites get a much larger LOS. Then they don't need as many. Of course you get higher latency, but still less than geostationary ones.At least that's my understanding of it... I'm not an expert on orbital mechanics. I know enough to get stuff in orbit in KSP.I think their end goal though is to compete with even fibre optic internet. In space, latency between satellites is actually LOWER than fibre on the ground, because it's in a vacuum. Glass slows down the light a bit.I'm now curious if anyone will ever come up with vacuum evacuated fibre optic cables at some point, it would basically be a tube with a mirrored inner surface that has all the air evacuated out. That would be quite a feat of engineering though and probably not worth the cost.

author: Nusa
author_rank: Super Contributor
timestamp: July 18, 2019, 01:47:55 am
content: Quote from: StillTrying on July 18, 2019, 12:13:02 amGeostationary 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.Of course you don't need geostationary if you have enough satellites to maintain coverage from any specific orbit.There are, of course, other possible approaches that might work for a smallish place like New Zealand. Such as balloons/blimps up in the stratosphere. I think Google has a spin-off that's experimenting with that concept.

author: tautech
author_rank: Super Contributor
timestamp: July 18, 2019, 02:12:09 am
content: Thanks Nusa and others for some clues for further learning about Geo-whatever birds:https://gisgeography.com/geosynchronous-geostationary-orbits/

author: 3roomlab
author_rank: Frequent Contributor
timestamp: July 18, 2019, 02:19:55 am
content: I am just wonderingwhat is the (cost + maintenance)/(km sq cover * years in service)starlink is stated to have a lifespan of 5 yearsvs normal 200 -300 foot radio masts?

author: duak
author_rank: Super Contributor
timestamp: July 18, 2019, 02:50:06 am
content: The Iridium constellation was orbited in the late 90's and could be considered a precursor:https://en.wikipedia.org/wiki/Iridium_satellite_constellationThere 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.

author: Nusa
author_rank: Super Contributor
timestamp: July 18, 2019, 03:04:48 am
content: Quote from: 3roomlab on July 18, 2019, 02:19:55 amSpacex'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.

author: Red Squirrel
author_rank: Super Contributor
timestamp: July 18, 2019, 04:47:22 am
content: Quote from: 3roomlab on July 18, 2019, 02:19:55 amOnly 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.

author: StillTrying
author_rank: Super Contributor
timestamp: July 18, 2019, 11:19:47 am
content: Quote from: Nusa on July 18, 2019, 01:47:55 amI 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.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: July 18, 2019, 11:57:53 am
content: Quote from: StillTrying on July 18, 2019, 11:19:47 amThat satellite (iridium) phones work is what amazes me.

author: Red Squirrel
author_rank: Super Contributor
timestamp: July 18, 2019, 03:04:27 pm
content: 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.

author: ajb
author_rank: Super Contributor
timestamp: July 18, 2019, 06:08:03 pm
content: Quote from: Red Squirrel on July 18, 2019, 04:47:22 amThe 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.

author: Nusa
author_rank: Super Contributor
timestamp: July 19, 2019, 06:49:43 am
content: Quote from: 3roomlab on July 19, 2019, 05:23:36 amDepends 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.

author: james_s
author_rank: Super Contributor
timestamp: July 20, 2019, 06:34:41 pm
content: Quote from: Red Squirrel on July 18, 2019, 03:04:27 pmFrankly 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.

author: madires
author_rank: Super Contributor
timestamp: October 17, 2019, 10:06:08 am
content: SpaceX says 12,000 satellites isn’t enough, so it might launch another 30,000https://arstechnica.com/information-technology/2019/10/spacex-might-launch-another-30000-broadband-satellites-for-42000-total/

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: October 17, 2019, 10:57:53 am
content: It will take even more than that to replicate a cellular network up in the sky.

author: wraper
author_rank: Unknown
timestamp: October 17, 2019, 01:41:13 pm
content: Quote from: Nusa on July 18, 2019, 03:04:48 amDon'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.

author: duak
author_rank: Super Contributor
timestamp: October 17, 2019, 11:18:37 pm
content: Interference with astronomy was mentioned above:https://www.space.com/astronomy-group-worries-about-starlink-science-interference.htmlStarling rhymes with Starlink, don't you think? Look at this:https://en.wikipedia.org/wiki/Eugene_SchieffelinNot on the scale of rabbits in Australia of course, but we live in the age of consequences.