??? September 2022 NAR Electronic Rocketeer newsletter

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cls

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hey folks, in the September 2022 NAR Electronic Rocketeer newsletter, safety section, Steve Lubliner suggests ematches and ignitors can be set off by shock, static electricity, and induced currents from large EMI fields.

I don't think that is true in any situation. Never heard of any such incidents. Physical shock, OK i've never tried that. Maybe I'll go hammer a few ignitors and see what happens. Static electricity seems highly unlikely, even a 10kV spark has less than 1mA of current, certainly not enough to warm any low current (40mA+) ematch. Ignitors are generally even higher current, hundreds of mA to several amperes.

But it can't hurt to short the leads until they are ready to connect to the wires at the pad.

here's the relevant text:

... The problem is that the pyrogen, being a heat sensitive, relatively easy to ignite compound, can be a hazard during storage and handling. Pyrogens can be shock and friction sensitive. The degree of sensitivity depends on the pyrogen compound but common safety practices can minimize associated hazards. Electrical safety can be enhanced by twisting the electric match leads together to create a shunt; this provides protection from electrostatic discharge. Keep electric matches away from strong electromagnetic and magnetic fields. These fields can induce sufficient currents to fire some electric matches.
 
cls said:
hey folks, in the September 2022 NAR Electronic Rocketeer newsletter, safety section, Steve Lubliner suggests ematches and ignitors can be set off by shock, static electricity, and induced currents from large EMI fields.

I don't think that is true in any situation. Never heard of any such incidents. Physical shock, OK i've never tried that. Maybe I'll go hammer a few ignitors and see what happens. Static electricity seems highly unlikely, even a 10kV spark has less than 1mA of current, certainly not enough to warm any low current (40mA+) ematch. Ignitors are generally even higher current, hundreds of mA to several amperes.

But it can't hurt to short the leads until they are ready to connect to the wires at the pad.

here's the relevant text:

... The problem is that the pyrogen, being a heat sensitive, relatively easy to ignite compound, can be a hazard during storage and handling. Pyrogens can be shock and friction sensitive. The degree of sensitivity depends on the pyrogen compound but common safety practices can minimize associated hazards. Electrical safety can be enhanced by twisting the electric match leads together to create a shunt; this provides protection from electrostatic discharge. Keep electric matches away from strong electromagnetic and magnetic fields. These fields can induce sufficient currents to fire some electric matches.
Click to expand...

More information here: The TRF Improving Igniters Thread.
 
I think that Steve is being conservative... VERY conservative. Has anyone actually seen an ematch spontaneously firing? Shuffling your feet on the carpet and touching one lead to the doorknob doesn't count...
 
I believe that there was an incident at an early SLI competition, which led to them limiting RF transmitter power to ~1W for future competitions. That's from a 7-year-old memory, so take it with a tablet of salt.
 
cerving said:
I think that Steve is being conservative... VERY conservative. Has anyone actually seen an ematch spontaneously firing? Shuffling your feet on the carpet and touching one lead to the doorknob doesn't count...
Click to expand...
No I haven't.
I have seen the old flash bulbs spontaneously flash when touched, but thankfully nobody uses them much anymore.
If I *wanted* to conduct a magic trick and place an Ematch on a table top and fire it without the wires connected to anything, sure I could do that, holding a 5W 2way UHF transceiver radio under the table in close proximity to the Ematch, but, the wires of the Ematch would need to be cut to the 1/4 wavelength of the carrier frequency of the transceiver and be in a dipole configuration (unpractical for general wiring in rocketry applications).

TP
 
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There is a reason why the DOD, NASA, etc. use igniters that pass the 1 Watt for five minutes test. Even then they are quite paranoid in their handling and use.
 
cerving said:
I think that Steve is being conservative... VERY conservative. Has anyone actually seen an ematch spontaneously firing? Shuffling your feet on the carpet and touching one lead to the doorknob doesn't count...
Click to expand...
I have seen it once.
 
boatgeek said:
I believe that there was an incident at an early SLI competition, which led to them limiting RF transmitter power to ~1W for future competitions. That's from a 7-year-old memory, so take it with a tablet of salt.
Click to expand...
There have been documented instances of some radios (IIRC the early Garmin Astro was notorious for doing this to some altimeters) triggering altimeters by inducing noise, which is not the same as firing the ematch directly.

The 2023 SL Handbook says only "The recovery system electronics will be shielded from all onboard transmitting devices to avoid
inadvertent excitation of the recovery system electronics." I don't see an explicit power restriction.
 
mikec said:
There have been documented instances of some radios (IIRC the early Garmin Astro was notorious for doing this to some altimeters) triggering altimeters by inducing noise, which is not the same as firing the ematch directly.

The 2023 SL Handbook says only "The recovery system electronics will be shielded from all onboard transmitting devices to avoid
inadvertent excitation of the recovery system electronics." I don't see an explicit power restriction.
Click to expand...
Thanks for the clarification. The 1W may have been something that the SLI staff said they would ask a bunch of questions about rather than a hard rule. Again, memory is fuzzy and rules may have changed as well.
 
mikec said:
There have been documented instances of some radios (IIRC the early Garmin Astro was notorious for doing this to some altimeters) triggering altimeters by inducing noise, which is not the same as firing the ematch directly.

The 2023 SL Handbook says only "The recovery system electronics will be shielded from all onboard transmitting devices to avoid
inadvertent excitation of the recovery system electronics." I don't see an explicit power restriction.
Click to expand...
Has anybody out there seen an AV bay build with the electronics in a shielding can? I know that the next one that I see will be the first...
 
cerving said:
Has anybody out there seen an AV bay build with the electronics in a shielding can?
Click to expand...
Not serious shielding where the wires penetrating the shield have appropriate ESD filtering. But BlackSky did sell an aluminum case for the AltAcc.
 
cerving said:
I think that Steve is being conservative... VERY conservative. Has anyone actually seen an ematch spontaneously firing? Shuffling your feet on the carpet and touching one lead to the doorknob doesn't count...
Click to expand...

Why doesn't that count? If that's an issue, would it not be a good idea to let folks know? That's how we all learn, right?

I had no idea that these e-matches were affected by impacts and static charges until I read the TRF Improving Igniters thread. Before that, I treated them no differently than an Estes ignitor, and stored them in the same cardboard box I stored my motors in. Ignorance is bliss.
 
cerving said:
Has anybody out there seen an AV bay build with the electronics in a shielding can? I know that the next one that I see will be the first...
Click to expand...
The SLI group I worked with put the GPS transmitter in the nose cone and a nice sheet of aluminum foil to provide some shielding back to the altimeter bay. I'm sure it didn't help the GPS range, but SLI is only going to a mile up so it's not as big an issue.
 
cerving said:
Has anybody out there seen an AV bay build with the electronics in a shielding can? I know that the next one that I see will be the first...
Click to expand...
Only my own - and that didn't really help my situation.

Back 20+ years ago, I used to do all my up & down comms with DTMF tones via a standard off-the-shelf UHF transceiver radio. The tones and flight computing processing were all generated and done via a PIC processor with an audio link to the microphone and headphone plugs of the transceiver. The decoding of the tones was done by a dedicated chip.
If using a 0.5W (or lower) transceiver, things would be quite manageable ie. the transmitted tones from the rocket would generate and transfer to the transceiver in pretty respectable order.
However at 1W, serious challenges arose and @4W was just plain impossible even with caging & shielded wiring & AC coupling & various grounding techniques and implementing variations with wiring lengthening and PCB track geometry. I threw hundreds and hundreds of hours at that problem only to finish up giving up - probably 10 years after I should have.
Even with my current iteration of electronics using a 2W serial transceiver, I don't run Ematches - I used pyroless systems - so the tiny motors that run the pyroless devices require less current than an Ematch, so for me, every time I transmit, the motor driving my main (chute) deployment latch will turn a fraction when on the rail (never on the bench mind you). So I have to actually counteract that with a reverse direction pulse after every transmission - otherwise my mains latch would deploy on the pad after perhaps 10 transmission events. Again, this only shows up with my system because the threshold of electrical energy to drive these tiny motors is under that to fire an Ematch. Also, only happened for the main chute latch, not the drogue cold gas device which was a relief. Probably because that motor was subjected to a bit of load.

TP
 
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rocket_troy said:
No I haven't.
I have seen the old flash bulbs spontaneously flash when touched, but thankfully nobody uses them much anymore.
If I *wanted* to conduct a magic trick and place an Ematch on a table top and fire it without the wires connected to anything, sure I could do that, holding a 5W 2way UHF transceiver radio under the table in close proximity to the Ematch, but, the wires of the Ematch would need to be cut to the 1/4 wavelength of the carrier frequency of the transceiver and be in a dipole configuration (unpractical for general wiring in rocketry applications).

TP
Click to expand...

I will try that in a couple days, no ematches here.
 
boatgeek said:
The SLI group I worked with put the GPS transmitter in the nose cone and a nice sheet of aluminum foil to provide some shielding back to the altimeter bay. I'm sure it didn't help the GPS range, but SLI is only going to a mile up so it's not as big an issue.
Click to expand...
It's possible it might of (intentionally or not) assisted the actual GPS reception/acquisition. Apparently a ground plane at a certain distance under the GPS module or antenna (can't remember) does assist with the signal reception.

TP
 
rocket_troy said:
Some Ematches might work, the current threshold in others might be too high.
Grain of wheat bulb demonstration at 4W transmission here:

www.propulsionlabs.com.au/Misc_Video_And_Images/RF_Test.MOV

TP
Click to expand...

The mov file doesn't play well. I think what's shown is the bulb lighting up from RF?

Well duh, we were doing that (using a bulb as RF detector) when we were kids. Ever waved a bare fluorescent tube around in a strong RF field? Works with neon bulbs, too.

... but doesn't address the question of whether sufficient current is rectified to fire an ematch or other ignitor.
 
lakeroadster said:
I had no idea that these e-matches were affected by impacts and static charges until I read the TRF Improving Igniters thread.
Click to expand...

Thanks for posting this link. Yes ematches are shock sensitive, wow!

But, I bet not AT first fires, enough trouble keeping the pyrogen from crumbling off in normal handline.
 
cerving said:
Has anybody out there seen an AV bay build with the electronics in a shielding can? I know that the next one that I see will be the first...
Click to expand...
About 20 years ago I had a Missileworks altimeter fire prematurely during boost. It was on a rocket that was also carrying a high power TV transmitter downlinking live video. I had Jim Amos (owner of Missileworks) check out the altimeter post flight and it was fine. We had no proof the TV transmitter caused the firing but it was on our list of suspects. I modified the AV bay by adding a can to shield the altimeters. A picture of the shielding setup is about halfway down this page.

Never had a problem after adding the shield and that rocket had a ton of flights on it. This doesn’t prove the shield was really needed but I felt better flying with it. I always suspected the problem was not that the TV transmitter induced a current into the ematch but rather the TV transmitter caused the altimeter itself to misbehave and fire the ematch.

The next rocket I built I also shielded the altimeters using standard RF shielding boxes because that was the first rocket to carry the original prototype of the 1W Kate downlink transmitter. I don’t have pictures of it. However, there have now been a ton of flights since then, on many different rockets by many different people, all flying a 1W Kate transmitter without any AV bay shielding. I have never heard of any unexplained ematch firings on any of those flights.
 
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