The intent of this email is to begin a serious techncal discussion. I do not know where it will lead. - My question is: is there something wrong with the Cubesat platform? Its failure rate is pretty high. If you include the university-built Cubesats which IARU has coordinated over the years, perhaps as many as half have failed upon reaching orbit. AMSAT-NA has orbited quite a few successful communications satellites, all of which are or were larger than Cubesats. I have been a member of AMSAT since 1969 and am not questioning its ability. Rather, my question concerns the Cubesat platform. The AMSAT-BB reflector includes people with successful as well as unsuccessful Cubesats. Can we learn anything from their experience? 73 Ray W2RS
Hi Ray So many schools/Univs want to use a Raspberry Pi in their design.Ok for the Pi, but they don't use a proper SD card.The Charge Pump in the SD card fails at a rather low radiation dose.That was much of that clump of failures. "Cheap parts cost too much!" 73 Kent WA5VJB/G8EMY
On Sunday, January 31, 2021, 09:43:48 AM CST, Ray Soifer via AMSAT-BB amsat-bb@amsat.org wrote:
The intent of this email is to begin a serious techncal discussion. I do not know where it will lead. - My question is: is there something wrong with the Cubesat platform? Its failure rate is pretty high. If you include the university-built Cubesats which IARU has coordinated over the years, perhaps as many as half have failed upon reaching orbit. AMSAT-NA has orbited quite a few successful communications satellites, all of which are or were larger than Cubesats. I have been a member of AMSAT since 1969 and am not questioning its ability. Rather, my question concerns the Cubesat platform. The AMSAT-BB reflector includes people with successful as well as unsuccessful Cubesats. Can we learn anything from their experience? 73 Ray W2RS
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Are there not published guidelines for what to use, or do we just let organizations fail? Brad KC9UQR In a message dated 1/31/2021 10:02:08 AM Central Standard Time, wa5vjb@flash.net writes: Hi Ray So many schools/Univs want to use a Raspberry Pi in their design.Ok for the Pi, but they don't use a proper SD card.The Charge Pump in the SD card fails at a rather low radiation dose.That was much of that clump of failures. "Cheap parts cost too much!" 73 Kent WA5VJB/G8EMY On Sunday, January 31, 2021, 09:43:48 AM CST, Ray Soifer via AMSAT-BB amsat-bb@amsat.org wrote: The intent of this email is to begin a serious techncal discussion. I do not know where it will lead. - My question is: is there something wrong with the Cubesat platform? Its failure rate is pretty high. If you include the university-built Cubesats which IARU has coordinated over the years, perhaps as many as half have failed upon reaching orbit. AMSAT-NA has orbited quite a few successful communications satellites, all of which are or were larger than Cubesats. I have been a member of AMSAT since 1969 and am not questioning its ability. Rather, my question concerns the Cubesat platform. The AMSAT-BB reflector includes people with successful as well as unsuccessful Cubesats. Can we learn anything from their experience? 73 Ray W2RS
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On Sun, Jan 31, 2021 at 8:06 AM Brad Smith via AMSAT-BB amsat-bb@amsat.org wrote:
Are there not published guidelines for what to use, or do we just let organizations fail? Brad KC9UQR
AMSAT had a plan to help universities in exchange for having Amateur Radio as a secondary payload, which I think unfortunately has recently still yielded two partially-working or completely broken satellites. And of course if AMSAT's satellite designs were fully open, that could help.
This document is also a good read.
https://www.nasa.gov/sites/default/files/atoms/files/improving_mission_succe...
73, Mike Diehl W8LID/VE6LID
On Jan 31, 2021, at 11:16, Bruce Perens via AMSAT-BB amsat-bb@amsat.org wrote:
On Sun, Jan 31, 2021 at 8:06 AM Brad Smith via AMSAT-BB amsat-bb@amsat.org wrote:
Are there not published guidelines for what to use, or do we just let organizations fail? Brad KC9UQR
AMSAT had a plan to help universities in exchange for having Amateur Radio as a secondary payload, which I think unfortunately has recently still yielded two partially-working or completely broken satellites. And of course if AMSAT's satellite designs were fully open, that could help.
Sent via AMSAT-BB(a)amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program!
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You should start by reading the material at https://www.cubesat.org/
IMO one of the largest difficulties for Cubesat creators is that passive spring deployment of antennas and other facilities is not allowed, because of the difficulty of inserting them correctly in the P-pod and the potential for them to jam the P-pod, and prevent the satellites behind them in the P-pod from deployment. Your antenna can't just pop out as your satellite exits the P-pod, it has to be actively released afterward. So, for release of these things a contrivance of nichrome wire and monofilament fishing line is mainly used - the line is melted and this releases whatever spring device there is.
And surprise, a lot of satellites don't have their antennas deployed, perhaps because this fails. And thus they have weak-signal issues, etc. This also gets in the way of solar panel release, etc.
Second IMO is the use of standard AX.25 packet at 1200 or 9600 Baud as a communications protocol. Karn has said why this is inappropriate, and contributed a satellite modem that can stand fades an appreciable fraction of a minute long. A lot of satellites are never contacted after launch, IMO because the radio is inadequate.
And then we get to components and designs being inadequate for space, between vacuum, temperature extremes, the loss of convective cooling resulting in components overheating once in vacuum, mechanical stress during launch, etc.
And finally, it's too expensive to test adequately.
On Sun, Jan 31, 2021 at 7:43 AM Ray Soifer via AMSAT-BB amsat-bb@amsat.org wrote:
The intent of this email is to begin a serious techncal discussion. I do not know where it will lead.
- My question is: is there something wrong with the Cubesat
platform? Its failure rate is pretty high. If you include the university-built Cubesats which IARU has coordinated over the years, perhaps as many as half have failed upon reaching orbit. AMSAT-NA has orbited quite a few successful communications satellites, all of which are or were larger than Cubesats. I have been a member of AMSAT since 1969 and am not questioning its ability. Rather, my question concerns the Cubesat platform.
The AMSAT-BB reflector includes people with successful as well as unsuccessful Cubesats. Can we learn anything from their experience?
73 Ray W2RS
Sent via AMSAT-BB(a)amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program!
View archives of this mailing list at https://mailman.amsat.org/hyperkitty/list/amsat-bb@amsat.org To unsubscribe send an email to amsat-bb-leave(a)amsat.org Manage all of your AMSAT-NA mailing list preferences at https://mailman.amsat.org
IMO one of the largest difficulties for Cubesat creators is that passive
spring
deployment of antennas... ,,, a contrivance of nichrome wire and
monofilament
fishing line is mainly used ...to ...releases whatever spring there
is.holding the
antennas in place...
The legacy of the "nichrome wire" never dies... But all of my satellites used a better, reproducible version of this. Instead of using very low impedance nichrome wire requiring a complex high current driver, we simply use a 2 cent film resistor. Not only is it the ultimate in reliability, it can match any direct battery voltage from 3 to 28 volts using a single transistor driver and can be reused many times to prove the actual flight configuration will work.
THe key is that the physical size of a 1/4 Watt thin film resistor is standard and has a nice neck in the middle. Perfect place for a nylon line to rest. And the resistance can be *any* value. Just match the resistance so that you are providing about 3.5 Watts into the 1/4 W resistor and it will burn the string identically no matter whether you are using a 3 volt bus or a 28 volt bus. Only the value of the resistor changes. You can vary the blow-wattage to get a burn time of anything between 1 to 5 seconds. We use the 3.5 W nominal value for about a 3 second burn time (and to allow for reusability).
We have found you can reuse the same resistor over 50 times and it still works. as long as power is cut immediately after each short burn time. You can also adjust the delay from 1 second to maybe 5 seconds depending on how much you choose to overpower the resistor. And replacement resistors (the flight critical component) are highly available. And we surface solder them on the outside of the spacecraft so post-assembly replacement is trivial if needed.
See sketch at top of ParkinsonSat (PSAT) Page (aprs.org) http://aprs.org/psat.html
In fact, we provide a burn-trace on every external solar panel so that the final burn location of the wire whip antennas can be made very late in the design process and can change as things evolve. The PSAT design above used a single resistor to release 4 whip antennas at once!
Nichrome? Nah, forgedaboutit.
Bob, WB4APR
Bob- Sounds like you've got it solved! Hopefully your post will get read by a lot of people. Thanks for your help getting birds in the air. -David, N9KT
On Sun, Jan 31, 2021 at 12:20 PM Robert Bruninga bruninga@usna.edu wrote:
IMO one of the largest difficulties for Cubesat creators is that passive spring
deployment of antennas... ,,, a contrivance of nichrome wire and
monofilament
fishing line is mainly used ...to ...releases whatever spring there
is.holding the
antennas in place...
The legacy of the "nichrome wire" never dies... But all of my satellites used a better, reproducible version of this. Instead of using very low impedance nichrome wire requiring a complex high current driver, we simply use a 2 cent film resistor. Not only is it the ultimate in reliability, it can match any direct battery voltage from 3 to 28 volts using a single transistor driver and can be reused many times to prove the actual flight configuration will work.
THe key is that the physical size of a 1/4 Watt thin film resistor is standard and has a nice neck in the middle. Perfect place for a nylon line to rest. And the resistance can be *any* value. Just match the resistance so that you are providing about 3.5 Watts into the 1/4 W resistor and it will burn the string identically no matter whether you are using a 3 volt bus or a 28 volt bus. Only the value of the resistor changes. You can vary the blow-wattage to get a burn time of anything between 1 to 5 seconds. We use the 3.5 W nominal value for about a 3 second burn time (and to allow for reusability).
We have found you can reuse the same resistor over 50 times and it still works. as long as power is cut immediately after each short burn time. You can also adjust the delay from 1 second to maybe 5 seconds depending on how much you choose to overpower the resistor. And replacement resistors (the flight critical component) are highly available. And we surface solder them on the outside of the spacecraft so post-assembly replacement is trivial if needed.
See sketch at top of ParkinsonSat (PSAT) Page (aprs.org) http://aprs.org/psat.html
In fact, we provide a burn-trace on every external solar panel so that the final burn location of the wire whip antennas can be made very late in the design process and can change as things evolve. The PSAT design above used a single resistor to release 4 whip antennas at once!
Nichrome? Nah, forgedaboutit.
Bob, WB4APR
Sent via AMSAT-BB(a)amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program!
View archives of this mailing list at https://mailman.amsat.org/hyperkitty/list/amsat-bb@amsat.org To unsubscribe send an email to amsat-bb-leave(a)amsat.org Manage all of your AMSAT-NA mailing list preferences at https://mailman.amsat.org
We could talk about radiation for a long time, and I'm not an expert, so I'll just bring up a few points.
Our LEO satellites in equatorial orbits are *not* in a harsh radiation environment. Satellites that traverse the van Allen belts, or are in a polar orbit, are.
What makes a semiconductor "rad hard" or not? The main problem is that radiation can cause unwanted conductivity across a semiconductor junction. And rather than an *intended *junction, it's often between some IC detail and the *substrate.* And once conduction starts, it may require removal of power to stop it *if you're lucky. *If you aren't lucky, overcurrent blows that detail off of the IC.
So, for radiation hardness, ICs are fabricated upon an insulating substrate, rather than a semiconducting one.
This was the origin of the silicon on sapphire chips, which were incredibly expensive. These days silicon on insulator is used, and can be just as expensive because they may be fabricated in small runs without economies of scale.
However, some chips are already fabricated on insulator as part of their regular process. A number of modern CPU/gate-array combinations are, and are available at decent prices.
Once one eliminates the substrate issues, there is still the issue of radiation across intended junctions. This is in general handled by various sorts of redundancy, and sometimes the ability to power-down the IC.
Historically, AMSAT used a silicon-on-sapphire 1802 CPU which was not booted from a ROM. It was booted by a hardware modem from a ground upload. So, this could not be "bricked" as long as the hardware was intact and working. The OS would continually scrub the memory pages with a read-correct-write cycle.
Modern CPUs are more complicated and often less reliable. There was once even a project to fly a cell phone! Giving these things a simpler bootstrap processor, which could take over if they failed, might be a good idea.
And if your satellite can't recover if launched with a dead battery, IMO you asked for the problem.
Hi,
It turns out that sub-micron CMOS is intrinsically radiation hard, provided there are some tweaks to the design rules. Circuits designed in this way can withstand megarads, as demonstrated at CERN’s Large Hadron Collider (see e.g., https://www.osti.gov/pages/servlets/purl/1353115 ). Designers at CERN flirted with exotic rad hard processes for several years, but ultimately abandoned them when it was realized that standard CMOS would work fine and be a lot easier to deal with. The intrinsic hardness comes about because the main effect of radiation damage is charge build-up in the oxide layer (the “O” in CMOS), this causes transistor thresholds to shift in an unpredictable way, which ultimately causes circuits to fail. As one goes to smaller feature sizes, however, everything gets smaller, including the thickness of the oxide layer and the attendant shifts. Single event upset remains a problem, but can be dealt with (e.g.) by using 2 of 3 redundancy in the logic.
The good news is that one can use standard IC processes, but only if special design rules are employed. That clearly means custom designs, which is not realistic when it comes to microcomputers. One could, however, imagine designing a rad hard watchdog circuit using a relatively inexpensive multi-project wafer run, but I am not sure whether or not this would help.
73, Dan K2QM
From: Bruce Perens via AMSAT-BB amsat-bb@amsat.org Reply-To: Bruce Perens bruce@perens.com Date: Sunday, January 31, 2021 at 3:13 PM To: David Spoelstra davids@mediamachine.com Cc: Robert Bruninga bruninga@usna.edu, Ray Soifer rsoifer1@aol.com, "amsat-bb@amsat.org" amsat-bb@amsat.org Subject: [AMSAT-BB] Radiation and Cubesats
We could talk about radiation for a long time, and I'm not an expert, so I'll just bring up a few points.
Our LEO satellites in equatorial orbits are not in a harsh radiation environment. Satellites that traverse the van Allen belts, or are in a polar orbit, are.
What makes a semiconductor "rad hard" or not? The main problem is that radiation can cause unwanted conductivity across a semiconductor junction. And rather than an intended junction, it's often between some IC detail and the substrate. And once conduction starts, it may require removal of power to stop it if you're lucky. If you aren't lucky, overcurrent blows that detail off of the IC.
So, for radiation hardness, ICs are fabricated upon an insulating substrate, rather than a semiconducting one.
This was the origin of the silicon on sapphire chips, which were incredibly expensive. These days silicon on insulator is used, and can be just as expensive because they may be fabricated in small runs without economies of scale.
However, some chips are already fabricated on insulator as part of their regular process. A number of modern CPU/gate-array combinations are, and are available at decent prices.
Once one eliminates the substrate issues, there is still the issue of radiation across intended junctions. This is in general handled by various sorts of redundancy, and sometimes the ability to power-down the IC.
Historically, AMSAT used a silicon-on-sapphire 1802 CPU which was not booted from a ROM. It was booted by a hardware modem from a ground upload. So, this could not be "bricked" as long as the hardware was intact and working. The OS would continually scrub the memory pages with a read-correct-write cycle.
Modern CPUs are more complicated and often less reliable. There was once even a project to fly a cell phone! Giving these things a simpler bootstrap processor, which could take over if they failed, might be a good idea.
And if your satellite can't recover if launched with a dead battery, IMO you asked for the problem.
participants (8)
-
Brad Smith -
Bruce Perens -
Daniel R. Marlow -
David Spoelstra -
KENT BRITAIN -
Mike Diehl -
Ray Soifer -
Robert Bruninga