
SpaceX hits two milestones in plan for low-latency satellite broadband - rbanffy
https://arstechnica.com/information-technology/2018/02/spacexs-satellite-broadband-nears-fcc-approval-and-first-test-launch/
======
Robotbeat
Article should note the plan for a total of 12,000 Starlink satellites with
some in lower orbits (340km) which would actually be below the International
Space Station. That should improve throughput, latency, and address orbital
debris concerns (as the low altitude means debris is naturally and
continuously removed within a few weeks), though it relies on (effectively)
continuous thrusting from solar-electric thrusters to maintain altitude.

~~~
baybal2
>lower orbits (340km)

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.

~~~
Robotbeat
> 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.

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.

~~~
_qcgl
> 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.

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."

[http://www.satellitetoday.com/telecom/2007/02/12/degradation...](http://www.satellitetoday.com/telecom/2007/02/12/degradation-
of-satellites-threatens-globalstars-service-business-plan/)

~~~
Robotbeat
> Redundancy doesn't help you with ionizing radiation.

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.

~~~
_qcgl
> 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.

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.

[https://en.wikipedia.org/wiki/Radiation_hardening](https://en.wikipedia.org/wiki/Radiation_hardening)

"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."

~~~
Robotbeat
Right, you must have missed the part where I said:

> _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.

~~~
_qcgl
> Right, you must have missed the part where I said

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.

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spuz
The top comment from Arstechnica is:

> 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?

~~~
mastax
> Are SpaceX going to breach the great firewall?

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?

~~~
walrus01
SpaceX probably _could_ try to do this, but would be faced with a few
challenges. As a two way satellite engineer, just off the top of my head:

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.

~~~
spuz
Thanks, this is the kind of insight I was hoping for. You answered lots of
questions I wouldn't think to ask.

------
wereHamster
Can this satellite network replace 5G? Is the latency good enough for the
occasional voice call? We could get rid of the stupid roaming charges, they
are an incredibly stupid concept, especially in Europe or other places which
has lots of small countries in a small area and people often travel across
borders.

~~~
Robotbeat
The network is not intended for mobile use. The frequency is too high, thus it
doesn't penetrate buildings very well. The idea is to put a lunch box or pizza
box sized phased array antenna on your roof. As long as you have a fairly
clear view of the sky, you should be able to get good reception with a
moderately sized antenna. It probably would work for vehicles, however.

~~~
tankenmate
Actually these days you would probably use a Lens Array rather than a phased
array as it has better characteristics for beam steering and multibeam use.
That way the array can can communicate with more than one satellite at
once.[0]

[0] [https://dune.ece.wisc.edu/wp-
uploads/2015/11/asil2017_ams.pd...](https://dune.ece.wisc.edu/wp-
uploads/2015/11/asil2017_ams.pdf)

~~~
Robotbeat
Sure, I was being sloppy with my language. I meant synthetic beam-forming in
the most general sense.

(Interesting link, BTW!)

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baybal2
What I heard from an employee of the company Musk was trying to buy engines
from, this was the initial pitch: global internet through multihop satnet, all
controlled by him. He was told that he is naive back then and dismissed.

~~~
Robotbeat
That's a pattern, isn't it?

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...

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ChuckMcM
This is an interesting step. One of the capabilities that SpaceX gets if they
have a network satellite constellation up is the ability to provide full
orbital telemetry without having additional ground stations.

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.

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cwt137
This article acts like SpaceX will be the first with non-geostationary
broadband satellites. There are other companies like O3b Networks. I think
their latency is not as good as SpaceX is shooting for, because they orbit at
something like 6000km, but they play in the same field.

~~~
Robotbeat
Medium Earth orbit vs Low Earth Orbit. I think it's worth considering them as
different fields.

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.

~~~
stcredzero
It's the first "mainstream" operation which matters.

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JankySolutions
So what kind of latency should we expect from a satellite at that altitude?

~~~
dgritsko
From the article:

> SpaceX has said it will offer speeds of up to a gigabit per second, with
> latencies between 25ms and 35ms.

~~~
bloopernova
I really hope that this works well.

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.

~~~
btown
> not yet known if evil

A decent heuristic would be whether said corporation manufactures
flamethrowers. Wait...

~~~
nickik
That a different company. Just the same Bond villain in control.

~~~
stcredzero
There are the good looking Bond villains and the bad looking ones.

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.

~~~
boznz
I know which ones I'd rather be a henchman for.

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jimpudar
Satellites, being a broadcast technology, don't seem well suited to Internet
access. When I request my bank information, the response from the satellite
will be audible to anyone who cares to listen for the signal.

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?

~~~
alexbeloi
>[https://networkengineering.stackexchange.com/questions/45602...](https://networkengineering.stackexchange.com/questions/45602/how-
does-broadcast-work-in-cable-networks)

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).

~~~
jimpudar
Very cool, thanks for the detailed information!

