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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

#41

Post by gumby »

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.

One use case I have imagined is being able to have a single radio module that can be used with a variety of front ends, but honestly I am not sure how big a market that is. Certainly I don't see SDR adding much value to high volume applications.

Re: A satellite engineer explains the basics of space electronics

#42

Post by bovine3dom »

ericpauley wrote: post #40
bovine3dom wrote: post #38

Earlier quoted context omitted.

> 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.

Yeah, I was taking some liberties with the definition of largest.

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.

Re: A satellite engineer explains the basics of space electronics

#43

Post by photojosh »

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…

This is a 1.0 F capacitor [0], we use similar ones for short-term UPS backup so our embedded systems can shut down safely.

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.

[0] https://au.rs-online.com/web/p/products/7898012/

Re: A satellite engineer explains the basics of space electronics

#44

Post by photojosh »

bovine3dom wrote: post #42
ericpauley wrote: post #40

Earlier quoted context omitted.

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.

Yeah, I was taking some liberties with the definition of largest. 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.

But in electricity/electronics, we deal with the entire range of metric prefixes… terabytes, nanofarads, gigaohms, microseconds.

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?

Re: A satellite engineer explains the basics of space electronics

#45

Post by geomark »

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.

There were some non-NASA boxes that had long periods powered off on the shaded side of the bus and had to operate at powerup at initially very low temperature. And then operate on the sun side for extended periods at an elevated temperature. Depending on the configuration of the bus there were sometimes challenging heat transfer issues. The plate temp wasn't 125 C (I don't remember the exact number) but there was assumed a significant temperature rise from the plate to the electronics. And then additional margin added on to that in case something wasn't quite up to spec in the thermal path. So we had to perform worst case analysis assuming junction temperatures of 125 C. It was pretty awful.

Re: A satellite engineer explains the basics of space electronics

#46

Post by mng2 »

dahtguy wrote: post #39
mng2 wrote: post #37

Earlier quoted context omitted.

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.

The point is you are limited by the capability you build in at launch, SDR or otherwise. The hardware side is more restrictive than the software side.

Re: A satellite engineer explains the basics of space electronics

#47

Post by bovine3dom »

photojosh wrote: post #44
bovine3dom wrote: post #42

Earlier quoted context omitted.

Yeah, I was taking some liberties with the definition of largest. 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.

But in electricity/electronics, we deal with the entire range of metric prefixes… terabytes, nanofarads, gigaohms, microseconds. 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…

> But in electricity/electronics, we deal with the entire range of metric prefixes… terabytes, nanofarads, gigaohms, microseconds

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?

Re: A satellite engineer explains the basics of space electronics

#48

Post by bovine3dom »

photojosh wrote: post #43
bovine3dom wrote: post #38

Earlier quoted context omitted.

> 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…

This is a 1.0 F capacitor [0], we use similar ones for short-term UPS backup so our embedded systems can shut down safely. 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. [0] https://au.rs-online.com/web/p/products/7898012/

> hard to convert and store large amounts of energy.

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.

Re: A satellite engineer explains the basics of space electronics

#49

Post by walrus01 »

sandworm101 wrote: post #34
walrus01 wrote: post #32

Earlier quoted context omitted.

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 toda…

The other best possible option would be a single access point, somewhat up on a hill, possibly mounted to a tree with TV white space radio gear, just across the water from Egmont, with sector antennas aimed at the town. Redline and a few others have commercial TVWS band access point radios for the 500 to 800 MHz bands (various models available) which can cut through trees for non line of sight radio pretty effectively. You'd still need to get some kind of semi-decent dedicated broadband connection to the AP site, such as a 20 Mbps x 20 Mbps to Telus in Sechelt or Gibsons.

Re: A satellite engineer explains the basics of space electronics

#50

Post by jl2718 »

lizknope wrote: post #10

I've been designing semiconductors for 20 years and I thought I would learn something but this article said nothing other than he wished there were more radiation hardened devices out there. You can learn more from wikipedia than this article. https://en.wikipedia.org/wiki/Radiation_hardening

Here’s something. Rad-hardened parts are mostly BS. An MSP430 takes 20krads without shielding. Process shrink seems to increase hardness, not decrease. I used flash FPGAs with parity circuits because flash was supposed to be better for SEU. This is all theory; it’s really hard to test SEUs. Store firmware as a low-rate RS and do circuit parity checks to trigger firmware refresh. There is probably a smarter way to do circuit ECC without the EC as a weakness, but I don’t know. That was years ago, and we were just space cowboys giving the middle finger to the rad-hard parts business.
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