
A satellite engineer explains the basics of space electronics - natashabaker
http://blog.snapeda.com/2018/08/16/engineer-spotlight-brady-salz-from-astranis/
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lizknope
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](https://en.wikipedia.org/wiki/Radiation_hardening)

~~~
pseudobry
I have not been designing semiconductors for 20 years and I thought I would
learn something...and I did!

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solarkraft
This is a decently embedded ad for Snap EDA and a pretty good ad for Astralis.

Not hugely informative, but nice. The title over-promises pretty wildly.

~~~
geomark
_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.

~~~
madengr
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.

~~~
pocketstar
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.

~~~
geomark
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.

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dghughes
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 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.

~~~
bovine3dom
> 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...](https://www.quora.com/How-many-Farads-does-the-largest-capacitor-
ever-made-have-And-whats-its-purpose)

~~~
photojosh
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/](https://au.rs-
online.com/web/p/products/7898012/)

~~~
bovine3dom
> 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.

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irq-1
Here's an interesting paper that discusses some _design_ issues.

[https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7086415](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.

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broahmed
Reminds me of this Stack Overflow question "Compiling an application for use
in highly radioactive environments" where the top answer is from someone who
worked on mini satellites:
[https://stackoverflow.com/q/36827659](https://stackoverflow.com/q/36827659)

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baybal2
To some extend, space electronics have a lot in common with stuff used to
manage industrial plants.

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.)

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halfdan
> We’re enabling people to reach their full potential by bring them Internet
> access and that’s really inspiring for me. On the other hand, they also get
> access to Twitter –- you win some, you lose some.

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.

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k__
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

~~~
kevin_thibedeau
Launch is only a vibration and acceleration problem which are mechanical
issues. Payload electronics are mostly powered off until on orbit.

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sandworm101
I read so many stories about companies with new ideas for satellite internet.
But i am visiting my parents next weekend. Their house is off grid in rural
BC. They only have one internet option: a dish pointed to a geostationary sat
which I will no doubt have to repoint on saturday. They pay insane rates for
practically no bandwidth. There is only the one company: explorenet. When
exactly are any of these innovations going to hit the canadian market?

~~~
walrus01
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 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.

~~~
sandworm101
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...](https://www.google.com/maps/place/Egmont,+BC+V0N+2H4/@49.750013,-123.9420878,2895m/data=!3m2!1e3!4b1!4m5!3m4!1s0x5487bcfa588ed2b5:0x89adce6265349b19!8m2!3d49.75!4d-123.933333)

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).

~~~
walrus01
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.

~~~
sandworm101
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.

~~~
walrus01
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.

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

~~~
mng2
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.

~~~
dahtguy
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.

~~~
mng2
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.

