The original plan for 1000km orbits was a kinda red flag for anybody more space-competent. 1000km is the lower end of a lower radiation belt.
On 340km, they must have though of putting really big and expensive solar panels to provide enough thrust on ion engines. They will have to compensate for their own weight and, even more importantly, drag.
Hardly. Things can and are made to tolerate a high radiation environment. In SpaceX's case, this is done via redundancy (and perhaps shielding, to some extent) and replacing the satellites at regular intervals.
> On 340km, they must have though of putting really big and expensive solar panels to provide enough thrust on ion engines. They will have to compensate for their own weight and, even more importantly, drag.
Weight is basically irrelevant for drag compensation. And the solar panels SpaceX uses are super cheap as they basically just use high-binned terestrial silicon solar cells from Sunpower, then integrate the panels themselves. Conventional space-rated cells are on the order of $100-1000/Watt, while terrestrial cells are less than $1/Watt. So even though terrestrial cells are only, say, 22% efficient vs 29% efficient and even though they degrade a bit faster in space (a lifetime of, say, 12 years vs 30 years), SpaceX can save a LOT of money and be able to throw around massive amounts of solar power on their satellites for a lot cheaper than their competitors who use typical space-rated components.
Redundancy doesn't help you with ionizing radiation. Parts get exposure even when powered off. Running at this altitude was considered a fundamental flaw of the first generation of Globalstar:
"Rusch said the "Achilles heel" of the spacecraft is their orbit at an altitude of about 1,414 kilometers (850 miles), which puts them at risk for radiation. "It was a fundamental flaw," he said. "At this altitude the radiation belts are extremely hazardous. Globalstar orbits experience radiation in the South Atlantic Anomaly where the Van Allen Belts nearly touch the atmosphere. Very few satellites are orbited in this region because of the radiation," which can irreparably damage satellite transistors."
It, in fact, does help. Voting mechanisms can help protect, detect, and/or recover from radiation-induced bit flips and outages. Early radiation-induced failures in systems can also be addressed in this way.
SpaceX has significant experience with using redundancy to address space radiation problems via their Dragon program. And the Falcon 9/Heavy upper stage uses similar redundant avionics and travels through the radiation belts on its way to GTO. The Falcon Heavy launch demonstrated cruising through the very worst part of the Van Allen belts (thousands of kilometers higher than Starlink) for hours (multiple orbits, I believe) successfully using conventional electronics made tolerant to space radiation through redundancy.
> Parts get exposure even when powered off.
Cumulative exposure effects like you're describing are something that SpaceX is addressing by replacing the satellites very frequently, up to every 4 years. Given the need to upgrade frequently anyway to keep abreast of technology improvements, the extra cost of this is minimal considering the insane price (and low performance) of traditional rad-hard electronics.
You are describing mechanisms to overcome energetic particles causing single event efects (SEEs). There are two distinct classes of radiation to be concerned about in space: SEE and TID (total ionizing dose). Redundancy does not help with TID.
I have done a TID test with commercial parts to prove out a CubeSat design. The parts were exposed to gamma rays emitted by a Cesium-137 source. There was not a single reset or unexplained event over the entire course of TID testing. Around 15-20 krad, the flash memory failed, which is a typical first TID effect. Charge pumps in flash ICs are especially sensitive to cumulative radiation effects.
"Total ionizing dose effects: The cumulative damage of the semiconductor lattice (lattice displacement damage) caused by ionizing radiation over the exposition time. It is measured in rads and causes slow gradual degradation of the device's performance. A total dose greater than 5000 rads delivered to silicon-based devices in seconds to minutes will cause long-term degradation. In CMOS devices, the radiation creates electron–hole pairs in the gate insulation layers, which cause photocurrents during their recombination, and the holes trapped in the lattice defects in the insulator create a persistent gate biasing and influence the transistors' threshold voltage, making the N-type MOSFET transistors easier and the P-type ones more difficult to switch on. The accumulated charge can be high enough to keep the transistors permanently open (or closed), leading to device failure. Some self-healing takes place over time, but this effect is not too significant. This effect is the same as hot carrier degradation in high-integration high-speed electronics. Crystal oscillators are somewhat sensitive to radiation doses, which alter their frequency. The sensitivity can be greatly reduced by using swept quartz. Natural quartz crystals are especially sensitive. Radiation performance curves for TID testing may be generated for all resultant effects testing procedures. These curves show performance trends throughout the TID test process and are included in the radiation test report."
> Cumulative exposure effects like you're describing are something that SpaceX is addressing by replacing the satellites very frequently, up to every 4 years. Given the need to upgrade frequently anyway to keep abreast of technology improvements, the extra cost of this is minimal considering the insane price (and low performance) of traditional rad-hard electronics.
By my calculation, at 1000km altitude and 45 degrees inclination, the satellites should see about 1kRad/year of cumulative radiation dose (given only the satellite casing for shielding). So replacing them every 4 years is easily enough to avoid the 15-20kRad your devices failed at.
It's also possible to shield the electronics (SpaceX has reusable rockets with performance to spare, so might as well use it!). With 10g/cm^2 of aluminum shielding (vs 1g/cm^2 for just the casing, etc), the dose is reduced to about 330rad/year.
In any case, replacing the satellites frequently or adding shielding are both valid strategies for addressing this.
I saw that part. My post was responding to your statement where you incorrectly and condescendingly said that redundancy helps with ionizing radiation. It doesn't, as I outlined above.
Do you have a link for that? I didn't find anything that looked relevant with a quick search for "spacex" "sunpower".
The high efficiency n-type silicon solar cells that SunPower produces are great for terrestrial use, but significantly less radiation-tolerant than the more common p-type. (Which are in turn far less radiation-tolerant than the compound semiconductors that are preferred for space solar cells nowadays.) In such a low orbit and with such a short lifetime, maybe that fast degradation is fine.
(Still, it sure looks like they're correct... they're definitely silicon cells, at very least.)
> This will be absolutely fantastic for developing nations. Being able to bypass fiber-optic backbones for consumer connections will be a huge benefit. Imagine how many rural villages will be able to set up a couple of receivers to share among the residents.
Am I right in understanding that the intention is that SpaceX would act as the ISP in this satellite network? What are the implications for places like China where internet access is very much controlled by the government rather than some American billionaire? Are SpaceX going to breach the great firewall?
"Obviously, any given country can say it's illegal to have a ground link... And from our standpoint we could conceivably continue to broadcast, I mean, I'm hopeful that we can structure agreements with various countries to allow communication with their citizens, but it is on a country-by-country basis. If they get upset with us, they can blow our satellites up, which wouldn't be good. China can do that. So probably we shouldn't broadcast there."
I don't think this will be very helpful for scenarios like China at all. Or places like Iran where all the ISPs are forced to be downstream of the government ASN.
This will be very helpful for places on the planet that are extremely costly to reach with terrestrial fiber ($2m to $30m build cost) or a hill-to-hill relay of high capacity mountaintop tower sites with PTP microwave ($500k to $3m build cost to get from a major city into the hinterlands of some african nations). Also for places like small pacific islands that can never hope to economically bring a submarine fiber optic cable to them. A lot of these places have already moved off "traditional" geostationary C and Ku band transponder leases and onto o3b. This is basically a similar concept to o3b but applied not only to large backbone links for ISPs, but to individual customer premises rooftop antennas that might have a cost of under $1000.
citation please? Do they take it down because you don't have a license to transmit in that spectrum band?
Feasibly, SpaceX would not need to negotiate or conform to any nation-states censorship requirements, because the citizens can just directly access the satellite through private infrastructure.
A capitalist analogy is how hotels used to (and many still do) charge outrageously for internet. When people started using their own infrastructure to connect their laptops to the internet, hotels (like the Marriot) jammed wifi hotspots.
I don't know much of anything about international law, but I don't think that would ever work. Countries have sovereignty over their airwaves. If they require a permit to broadcast you need a permit to broadcast, even if the signal is coming from space. Countries have sovereignty over business conducted in their territory. China can just say that SpaceX's internet service is illegal. How should SpaceX get their illegal money out of China? What to they do with the (still illegal) money once it is out of China? How does SpaceX get ground stations for an illegal internet service into China?
Maybe SpaceX decides to give away free internet in China as a humanitarian publicity stunt, and flaunt the Chinese Government. They could publish the design for the base station and hope that sophisticated dissidents manufacture them. Now China uses every diplomatic avenue available to try to stop this: the UN, the ITU, espionage, treaties, whatever. Is the US going to cover for SpaceX? Will the state department decide to burn all of their bridges to the largest country on earth for the benefit of a publicity stunt? If China shot down SpaceX satellites, would they be justified in the eyes of the international community?
a) smuggling/importing the rooftop terminal equipment into china
b) if not smuggling, finding a way to use greymarket resources to manufacture the terminals in China
c) making it small enough and easy enough to hide that it can't be obviously spotted/removed from a roof. Google a bit about Iran's periodic and mostly unsuccessful forcible removals of Ku-band TVRO (Rx only) TV satellite dishes for an example. China has a lot more manpower and police-state type resources to deploy to hunt down antennas. If you are faced with the problem of requiring clear unobstructed line of sight to as much of the sky as possible, while also hiding it, you have a technical problem.
d) It is not hard for a police state like China to train relatively unskilled enforcers to use directional spectrum analyzers to hunt down unauthorized rooftop Tx, anywhere from 6 GHz to 80 GHz.
Is this true? Isn't, say, a San Diego FM station violating the sovereignty of Mexico then?
I'm get to be convinced there is a technical solution to the problem(s)(?) of government / legislation / regulation / right holders / etc etc.
Progress (movement, anyway) happens over time with push and pull from both directions / all stakeholders.
Of course, but the idea is to simply make the only legal and easily accessible version regulation compliant, and then that is probably what most people will use.
SpaceX's plan is unique in that they aren't planning to run satellites in fixed, geosync orbit, to my knowledge nobody is doing that yet.
From a regulatory perspective, SpaceX is not not doing anything that Iridium, GlobalStar, Inmarsat, Intelsat, SES, etc...have not already dealt with.
The SpaceX concept intends to use phased array/software beam steered antenna systems for the individual end user CPEs.
If you're lumping Globalstar (a mostly epic failure of LEO bent pipe low bitrate satellite constellation) in with SES (a company that operates $200m, 4000 to 6000 kilogram sized geostationary C/Ku/Ka band satellites and is highly successful worldwide), you're grossly misinformed, they are totally different architectures.
MEO by o3b already exists, has been running for a few years, but is only available for larger telecoms and ISPs (example: a telecom in a pacific island nation state that doesn't have any submarine fiber). It's a great technology but the minimum size terminal is a pair of motorized, tracking 1.8m size antennas. It's an alternative to multi-ten-thousand-dollar-per-month C and Ku band transponder kHz and MHz.
Nothing like this already exists.
(Interesting link, BTW!)
For example, electric cars with roofs that are already solar panels—I'm sure adding an antenna to the mix would be fairly trivial.
Imagine, you are a big telco with a cellular brand. You will not go to a small and remote region where you both have no economic incentive to get to because you will have to pull your own (microwave/VSAT/fibre,) and will most likely have a local competitor who will decidedly beat you on the price that you base on big city demographic buyers.
Now, imagine you can simply put a single tower without any extra infrastructure to get a whole city population your captive customers?
Edit: for voice data with "normal" telephone behavior
340km up + 340 km down = 680km / 299km/ms (c) x2 = 4.5ms added to round trip time. Considering you're doing this instead of running through your local metro loop I wouldn't be surprised of there was actually no additional latency introduced in real world scenarios, most of the latency will likely be introduced by the switching on the actual satellites.
Wouldnt that be assuming the satellites were always exactly overhead of the receiving terminals? Also, the article claims operational orbits of 1,110km to 1,325km. To be fair, VOIP is pretty usable even with 50-100+ ms of latency and even higher. Intercontinental calls wouldn't be possible otherwise.
At 1325km it's an extra 18ms so still well within the realms of usability.
given that they're aiming for 4425 satellites in total that would give them 66 loops of 66 satellites spaced 730m apart, meaning that when one satellite is overhead the next satellite will only be at most 1512km away line of sight.
Musk was also laughed at by Russians when he tried to buy a cheap launch from them for his little Mars greenhouse project before he founded SpaceX. Jokes on them as SpaceX now is outlaunching just about everyone else and has taken almost the whole market away from Proton...
People said that about his electric cars and rocket ship ideas also.
I'd love to look at the radio on one of their 'birds', there is so much cool stuff you can do in a small package these days.
Telestar was actually first to launch in this field of broadband LEO satellites, though, not SpaceX. But like SpaceX's inaugural launch, they are engineering prototypes, not fully operational ones.
I'm not sure who is "first" matters too much, though.
However, the added latency is not necessarily that bad vs landlines. Picture a triangle with the satellite at the apex and the goal at the other side. On the other hand if their base station was further from the network than your house then things get significantly worse.
> SpaceX has said it will offer speeds of up to a gigabit per second, with latencies between 25ms and 35ms.
Being able to break the comcast/att/verizon effective monopolies across the USA would (hopefully) have great positive effects. At least competition would bring prices down for low-latency land-based connections.
Of course, you're swapping control of your internet connection from a "mostly evil" to a "not yet known if evil" corporation.
The closer the competition the smaller the 'evilness' that would make people switch.
The same company can be perfect in one country and a 'evil' in another depending on the situation.
I seem to recall people reporting that Comcast is actually just fine in many areas with a second viable provider. With SpaceX, that would be all of them.
Power corrupts. Therefore, power in the market also corrupts.
A decent heuristic would be whether said corporation manufactures flamethrowers. Wait...
Obama and Musk are good looking Bond villains. (The former had assassination sky robots, ICBMs, and a military. The latter has rockets, oceangoing spaceship landing pads, and huge enigmatic installations in the middle of the desert.) Putin and Trump are bad looking Bond villains.
* not flamethrowers
* manufactured by a third party
sorry, I know you are joking, but I couldn't help myself.
Not to mention that that kind of predatory pricing is illegal in many countries.
Seems like only a few customers at 1 Gb/s could saturate the network pretty quickly. Especially if the coverage area is a few hundred square miles.
But that's just the initial constellation. SpaceX plans to put 12,000 total satellites up, with the VLEO ones having much higher throughput. Idea is to replace them every 4-6 years with faster throughput.
Assuming there are some zero days out there against HTTPS, what is there to prevent third parties listening in? At least with cable and fiber, only those entities who can afford to install beam splitters can listen in (see Room 641A).
Any network engineers with satellite experience care to chime in on this?
Cable internet is a broadcast network, every signal from your ISP's exit node is sent to every client attached to that node in your geographically local region (I think this can be a tens or hundreds clients) and vice versa. Your modem only looks for frames that are designated for your modem's MAC address, the rest are ignored but still received.
Same as channels in broadcast tv, everyone is always receiving the signal for all the channels, but they only 'tune in' to their channel. The difference is that your internet modem is only allowed to tune into one channel (designated by its MAC address). I believe each modem has a unique key for modulating/demodulating its signal, and this is used to establish secure communication with the ISP.
In the book "Computer Networking A Top-Down Approach" the following is written: "One important characteristic of cable Internet access is that it is a shared broadcast medium. In particular, every packet sent by the head end travels down- stream on every link to every home and every packet sent by a home travels on the upstream channel to the head end. For this reason, if several users are simultaneously downloading a video file on the downstream channel, the actual rate at which each user receives its video file will be significantly lower than the aggregate cable downstream rate. On the other hand, if there are only a few active users and they are all Web surfing, then each of the users may actually receive Web pages at the full cable downstream rate, because the users will rarely request a Web page at exactly the same time."
tl;dr you already probably broadcast your modulated bank info (if you're on cable).
And the horse has already left the barn, kicked over a lantern, and set it on fire, because an incredible amount of internet is already being barfed across the EM spectrum. Anyone who can listen in to your satellite internet has already cracked your phone's LTE and your laptop's WiFi, so it's kind of moot anyway. People in rural parts of the US are already spending $$$ for mobile data plans in lieu of wired broadband.
I agree that it's a very misplaced concern, but it seemed to me an honest question from GP that others are likely confused about as well.