A satellite engineer explains the basics of space electronics(blog.snapeda.com) |
A satellite engineer explains the basics of space electronics(blog.snapeda.com) |
You can learn more from wikipedia than this article.
Not hugely informative, but nice. The title over-promises pretty wildly.
That's practically an understatement. It just barely touches on the challenges of extreme temperature range and radiation hardening. The difficulty of getting your design to pass worst case analysis can be rather dispiriting when you have to drastically derate it to account for -55 to 125 degrees C temp range. Further insult comes from derating to account for total dose radiation effects (depending on orbit), although the article seems to only mention the need to account for single event upset events. Handling SEU's is actually a pretty interesting design challenge. Total dose, on the other hand, is just a bummer.
Military electronics are just as bad, as they have to operate from the Antarctic to the desert, and be thrown from the back of a helicopter onto concrete.
Such fragile things it's amazing how little it takes to destroy a device. And how much energy can be put through the same fragile device.
And how much energy is in one Coulomb. The example I like is two points each with one Coulomb repel with a force of one millions tons.
A recent artie I read spoke about the reaction wheels of old spacecraft failing. Solar flares caused arcing in the metal ball bearings the would pit the bearing race. So if a steel ball bearing can't take it imagine fragile electronic devices.
To have any meaning, you also need to consider the distance between the points. Any two charged points can repel each other with a force of one million tons given a particular distance.
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elecur.h...
Coulombs and therefore their related units such as Farads are famous in Physics for being far too large, so this is not particularly surprising (assuming a sane distance). The capacitance of the largest capacitor bank in the world is about 0.2 Farads [1].
[1] https://www.quora.com/How-many-Farads-does-the-largest-capac...
And a Coulomb is one amp for one second, that's not exactly large either.
So it's not that coulombs and amps are too large a unit, it's that it's hard to convert and store large amounts of energy.
https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7086415
> To mask the effects of upsets in the FPGA configuration memory, temporal or structural redundancy can be applied to the system. Temporal redundancy involves the replication of a computation or logic function in time to mitigate failures that occur during one of the redundant computations. Structural redundancy involves the replication of selected circuit structures to remove single-point failures. Failures in the circuit can be masked by performing the logic or computing function in more than one circuit location.
> The most common form of structural redundancy is to apply triple-modular redundancy (TMR) [24]. As shown in Fig. 6, TMR involves the triplication of all circuit resources and the addition of majority voters at the appropriate circuit outputs.
For examples in Chinese megascale steel mills, while SCADA's are used for monitoring and higher level control, operational aspects are handled by handcrafted PLCs made of modern analogues of 7400 series, 8t sram, redundant sensors, quoruming and BCH coding, mram, mems oscilators, and all solid DC-DC conversion, and all of that is provided with manual overrides
Most important feature of all of this is that it provides hard, near physical, impediment to wrong inputs from higher level control systems (SCADAs.)
Haha, brilliant.
What I always wonder though is how many of those people can actually afford a devise to make use of satellite internet. I guess it's still important to at least enable them to get it.
You get plenty of sunlight to power your stuff and since gravity isn't as bad as on earth you can build stuff big enough to be shielded from almost everything.
But well, it has to go up somehow :D
In general, consumer grade VSAT service via geostationary satellite should be a last resort, if anything else is available. The economics of launching 5000 kilogram satellites into geostationary orbits mean that transponder kHz in Ku/Ka-band spot beams need to be significantly oversubscribed.
The actual cost of satellite capacity, translating dedicated (1:1 ratio) Mbps into transponder capacity, plus the cost of running earth stations on the ISP uplink side, can range from $1800 to $5500 per Mbps per month.
In order to make any money at all off a large number of $100 to $150/month consumer grade VSAT services it needs to be radically oversubscribed.
Xplornet has a particularly bad reputation as an ISP in general, which doesn't help.
Things like SpaceX's starlink or other upcoming LEO/MEO services like Oneweb are promising. But not available yet.
Point to multipoint wireless last mile via 2.4/3.5/3.65/5.2/5.8 GHz bands can be much more effective. It's even possible for WISPs to offer 75 Mbps x 25 Mbps packages based off the latest Ubiquiti 802.11ac gen2 platforms, Cambium PMP450 or Mimosa A5 AP radio platforms.
Disclaimer: I work in both satellite Internet and point-to-point/point-to-multipoint microwave and millimeter wave.
https://www.google.com/maps/place/Egmont,+BC+V0N+2H4/@49.750...
I've looked into every option. The irony is that the nearest cell tower is just over a kilometer away. The problem is the rocky terrain and dense pacific coastal rain forest. Trees heavy with water droplets suck up everything, from sound to radio. It is shocking how a heavy mist dulls everyone's cellphone boosters. Voice calls only last a second or two even on dry days. Everyone uses text messaging.
There have been many multipoint proposals. The problem is the rugged coast. Even a 1000' tower wouldn't have line of sight to every house. It would take all sorts of relays atop individual hills. And those relays need power, which is tricky. Buried lines aren't an option (rock) and towers are expensive (forest).
When are they going to hit any market? There are plenty of companies promising the world, but it is a difficult, expensive, and time consuming problem. I believe better options will come, but I don't see any on the near term horizon.
Which I would say means that it's a bad unit. How about an amp for a nanosecond? That would lead to much more sensible numbers elsewhere.
The link budget problems for gain and EIRP, and cost of CPE, may make it cost prohibitive to put individual CPEs on peoples' roofs as a competitor to last mile WISPs.
I can see a scenario where a WISP buys a $7000 to $15000 dual-antenna terminal and a monthly recurring service package in the $700 to $1200/mo range, for a decent chunk of semi-dedicated capacity, and then redistributes access from there.
For those who want to understand how this works, o3b at MEO works on the same general concept, but at a more expensive and high bandwidth scale. It's been operational for years now. There's lots of good reference material out there on O3B.
Take the same two-satellite make-before-break handoff system used by o3b and apply it to a much larger number of LEO satellites, and smaller terminals, that's the general idea of how oneweb and starlink are intended to work.
Residential service filing probably (!) appears on the priority list after launching the 4-12,000 satellites into LEO.
One early prototype had a li-ion pouch cell (yes, I'd do things differently now). After an impact, I pulled it apart and found that the battery, via plastic deformation, had perfectly fitted itself to the contour of the inside of the enclosure. IIRC it was still working when I pulled it apart.
They're still a ridiculously big unit though. Generally the biggest man-made structures on Earth are measured in mega*. Single digits are usually used for things that are roughly apple-sized.
I'm curious as to what you mean by "biggest man-made structures" though. For me that brings to mind tall buildings, long walls and big dams. I suppose that the Great Wall is 20 "megametres" long, but normally long dimensions will be in kilometres, heights are in 100s of metres and dams are in billions of cubic metres. Care to share some examples?
But you don't. You'll almost never use whole Farads, for example. It's even on the Wikipedia page: related units, nF, uF.
> Care to share some examples?
I don't really mind the difference between giga/mega/kilo. I was really just talking about a ballpark where we don't want the biggest thing ever to be unity in our everyday unit.
You do raise a valid point with height. This is because the gravitational field in some sense makes length directional: 3km up is very different to 3km along. Clearly, we need some vector based measures so we could scale them sensibly, g-hat and x-hat : ).
Can you think of many man made structures who have just one of some extensive property in an everyday unit?
You'd be looking at like $800 a month for a better chunk of bandwidth. Then divide that by the number of local users in the Egmont town are you can connect through it, building a very small micropop WISP setup. Something like a mimosa a5c on a pole in a central location and c5c CPE radios with 24-30dB gain dishes on the client side. And a small mikrotik router between the mimosa and the vsat modem.
Divided by enough people it could work out to around $80-100 per residence per month. This assumes that somebody with a modicum of networking clue can run the local end for free, a few hours a week for maintenance and monitoring.
Atm my parents are paying 100/month for sat internet, and another 50 for sat TV. It suits their needs today but they know that when the grandkids are a little older bandwidth will be an issue. When I visit I bring them thumbdrives full of all TV shows they cannot get.