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A satellite engineer explains the basics of space electronics

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Re: A satellite engineer explains the basics of space electronics

#31

Post by madengr »

pocketstar wrote: post #25
madengr wrote: post #7

Earlier quoted context omitted.

Where are you getting that temp range? The last payload electronics I designed (an RF PA) only had to handle -20 to 70 C, and the actual temp swing is less. Of course this is inside a bus. 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.

NASA’s box requirement is 70C. That means the ICs in the box are much hotter, parent is probably refering to IC temp, not unit.

Ok, makes sense. The 70C for my unit was the temperature of the plate to which the PA was mounted.

Re: A satellite engineer explains the basics of space electronics

#32

Post by walrus01 »

sandworm101 wrote: post #21
walrus01 wrote: post #15

Earlier quoted context omitted.

Without asking too much detail, approximately where is there house? Is there any chance there is a regional WISP they could get service from? 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…

Egmont BC. Only 80km (50 miles) from Vancouver. Not exactly remote by Canada or even British Columbia standards. It is also only 79km from Whistler, but look at what stands between Egmont and whistler to get an idea BC terrain. 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…

Yeah, that is going to be a hard location to reach. Took a look at it from Google Earth / satellite view for a few minutes. The best option I can realistically think of is for a group of 7 to 20 people to share the cost for a larger, much more serious geostationary vsat terminal (not some xplornet consumer grade stuff), like a 2.4 meter ku-band dish with 20W BUC and modern iDirect modem, and find a vsat ISP with ku band spot coverage of the area to pay for access.

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.

Re: A satellite engineer explains the basics of space electronics

#33

Post by Dylan16807 »

k__ wrote: post #6

I always had the impression 99% of all space-electronic problems come from the fact that you have to lift stuff from earth. 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

You could install hundreds of tons of radiation shielding if you had easy lifting tech, but I still would point at the radiation as the root problem, not the difficulty of getting things into space.

Re: A satellite engineer explains the basics of space electronics

#34

Post by sandworm101 »

walrus01 wrote: post #32
sandworm101 wrote: post #21

Earlier quoted context omitted.

Egmont BC. Only 80km (50 miles) from Vancouver. Not exactly remote by Canada or even British Columbia standards. It is also only 79km from Whistler, but look at what stands between Egmont and whistler to get an idea BC terrain. 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…

Yeah, that is going to be a hard location to reach. Took a look at it from Google Earth / satellite view for a few minutes. The best option I can realistically think of is for a group of 7 to 20 people to share the cost for a larger, much more serious geostationary vsat terminal (not some xplornet consumer grade stuff), like a 2.4 meter ku-band dish with 20W BUC and modern iDirect modem, and find a vsat ISP with ku b…

Yup. Thanks for looking. Getting everyone on board with a 10 to 20-house collective would be very hard. The terrain is really unforgiving. All the houses are by the water, with steep rocky hills behind them. Any maintenance is a big issue. That "somebody with a modicum of networking clue" doesn't live in Egmont.

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.

Re: A satellite engineer explains the basics of space electronics

#35

Post by sandworm101 »

dghughes wrote: post #13

I'm surprised electronics work on the earth. 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 a…

I read that article too and am skeptical. There is a less-than-perfect correlation between space weather an wheel friction increases, but these are not exposed bearings on the outside of spacecraft. These are deep inside, behind layers of metal parts. I don't see the mechanism for creating the imbalance of charges necessary to arc inside the bearings. If it is happening, I would expect this to be far more common in terrestrial bearings. Cars build up static charges. We aren't seeing their bearings degrading so suddenly when after they drive through lighting storms or other static charge imbalances.

Re: A satellite engineer explains the basics of space electronics

#37

Post by mng2 »

gumby wrote: post #36

I am surprised he mentioned changing the SDR once the satellite had been deployed. What about the antennas?

That really is the elephant in the room where SDR is concerned (along with front-end). More realistically you could change protocol/encoding after launch.

Re: A satellite engineer explains the basics of space electronics

#38

Post by bovine3dom »

dghughes wrote: post #13

I'm surprised electronics work on the earth. 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 a…

> 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.

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...

Re: A satellite engineer explains the basics of space electronics

#39

Post by dahtguy »

mng2 wrote: post #37
gumby wrote: post #36

I am surprised he mentioned changing the SDR once the satellite had been deployed. What about the antennas?

That really is the elephant in the room where SDR is concerned (along with front-end). More realistically you could change protocol/encoding after launch.

Not necessarily. I've never heard of anyone doing it for space (maybe SpaceX?) but you could have an SDR driving a massive MIMO/beamforming array. The SDR can then dynamically "change the antenna" (change the radiation pattern) with a fixed front-end.

Re: A satellite engineer explains the basics of space electronics

#40

Post by ericpauley »

bovine3dom wrote: post #38
dghughes wrote: post #13

I'm surprised electronics work on the earth. 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 a…

> 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. 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/H…

Keep in mind that capacitance and capacity are not the same. Case in point, the capacitor mentioned can hold a peak voltage of 24kV, which is allows for a million times more energy to be stored than the same capacitance at 24V peak. Capacitors with far lower peak voltages can have capacitance exceeding several Farads.
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