Wiring Ejection Charges

Which got me thinking...

Could an altimeter be designed to automatically "safe" itself after a certain period of time after launch. There should be some sort of timeout that is proportional to when the event should happen. For example, staging is expected at T+2, and safes itself at T+10, deployment is expected at T+30 and safes itself at T+100, and main deploy is expected at T+100 and safes itself at T+300.

Or once an altimeter detects ZERO motion for any length of time, it safes all remaining functions. So a rocket that crashes, lands in a tree or power line, or just out in the field senses that it's come to rest and shuts down all remaining active functions.

Hi David,

someone quizzed the BOT on this paragraph on NAR sections group.

several said a power off system is fine for this requirement.

for example,

I have a rocket with four on-off switches (N3 screw ins) powering 4 such devices.

I will not be adding yet another four switches to add "extra" interrupts to the e-matches.

My on-off switches, "interrupts the current path to the igniter" till the rocket is on the launch pad.

Nothing in that safety code says power off is not enough, like the L3 specs have added to them by you know who. This got debated on the BOT section group and that was the censuses that is archived in that yahoo groups threads.

I test by the way, with no BP involved and once BP is added, nothing better be powered on again till that rocket is on the launch pad.

By the way David, I love your attention to the legal issues, you are always right on target, thank you for that service.

CD

Actually, I have been working off and on (more off than on alas) on a design that will arm itself only a few seconds prior to each event. Arming involves running a DC to DC converter to charge the 40V firing capacitor. Until it is charged, no combination of failures or events can cause the outputs to function.

You aren't. That's the point. Someone who finds it needs to be able to, though.

Ah, Ted, I think "Fuzzylogic" is trying to say "if the ejection charge fired--thus releasing the parachute to allow the rocket to float away and snag a power line--what's left to disarm?"

I've done it successfully both ways. I have an alt bay with ematch terminals on the outside of the bulkheads - which works fine. I have two others that I just drilled a hole in the bulkhead to pass the ematch leads and hook them directly to the alt's pyro outs. I use blue wax (it's a mushy wax like modeling clay) to seal the ematch holes. I prefer passing the match leads directly thru the bulkhead - seems less complicated and more reliable. It's too easy to make silly mistakes, so the simpler the better!

If my rocket drifted into a tree or power lines or off range, it deployed.

If my rocket didn't deploy it struck the terra in my neighborhood.

Now I'm worried the batteries are loose and possibly all those extra wires and switch pieces that NAR requires have broken free to bounce around a cause a short when I pick up the rocket.

There are many facets to this issue, but after 66 messages I haven't seen a clear explanation why the extra wiring is 'safer' when I arm the rocket,... on the pad where it's supposed to be powered up.

Would you please provide me with that >> Fuzzylogic wrote:

What about a dual deployment situation, where the drogue has fired and the rocket gets hung up, but the main has not yet fired. Or the main fired but the charge for the drogue is still live and armed?

I still maintain that if you are going to put anything on the outside of a pyro equipped rocket, it should be a big "Don't Touch This, Call This Number" with the owners cell number. Directions for disarming I see as an invitation to both a civilian being injured and a lawsuit.

Thats not the problem. What if the ejection charge _doesn't_ fire? For example, the drogue comes out but the main doesn't. The rocket plummets into a field some distance way and someone else finds it. How do they disarm the main charge?

And to address an earlier comment in this thread, I would keep the ematches in my range box shorted, probably by leaving the shipping cap on the bare ends.

Glen Overby

But do we know who that person would be? Another savvy rocketeer or just a hunter that knows nothing about electronics on rockets? Even a rocket savvy person would need to know how that particular rocket is configured.

Bottom line, do you really want a stranger fiddling around with your rocket? Liability comes to mind.

No argument here, I do the same.

Ted Novak TRA#5512 IEAS#75

If you have a switch retained with a screw, and a label saying "remove this screw to disable ejection charges before messing with my rocket", then no knowledge of electronics is required. So, even the rocketeer with no knowledge of electronics could handle it.

This issue here is not about what you WANT to happen, it is about what can happen. What I want is for everything to work perfectly and for the rocket to gently land ten feet from my car.

Another way to think of it is: if your rocket lands in the corn, and I find it when I'm retrieving my rocket, do you want me to bring your rocket out of the corn for you? If I'm worried about getting blasted by the ejection charge that missfired, I'll leave it behind!

What is the liability if someone else picks up your rocket and gets injured messing with it? What if that someone is the RSO who is checking your rocket before you fly it?

Actually I think it would be better to have a 'caution: redundant ejection charge, to disarm do xxxxx' sticker of some sort. That's what I tried to convey when referring to configuration.

But not everyone uses a set screw to arm/disarm their electronics. That's only one out of many ways to use a switch. Slide switches, key switches and, *gulp*, twisting the wires are used as well. Even with screw switches, depending on the size of course, would require a screwdriver to disarm.

In the cases I've witnessed(mostly my own)every time there was a recovery failure, all the warnings on a rocket would've been worthless as the rocket was in so many pieces....how could the rocket be disarmed?

Right, a lot of things *can* happen but that doesn't mean *will* happen. But be careful what you wish for...I actually had my rocket land ON my car :)

Exactly. Your best judgment is all anyone can ask of you. But it be nice if you noted where the rocket landed :)

Well since he/she is the RSO I would certainly hope that the system is not armed prior going to the pad. However, I think we all have seen such a scenario where the rocket was armed when presented to the RSO.

The liability I was referring to was Mr. Smashedoutofhisgourd Hunter fiddling with the rocket *causing* the charge to go off.

Ted Novak TRA#5512 IEAS#75

There are two aspects of this. The first is flight safety which in this case has to do with the ability to deploy the recovery system. The second, which many people forget about, is ground safety. That is keeping bad things from happening prior to the launch.

The safety switches do absolutely nothing for flight safety. They actually have a slightly negative impact (wires and switches in general have very high reliability numbers) on flight safety. But they do prevent various problems from occurring prior to launch.

The conflict between flight and ground safety was illustrated for me several years ago as the result of a program I was working on. I was working on the update of a design for a telemetry and flight termination system and the lead range safety office was at White Sands Missile Range. The safe and arm unit was electronic and charged a capacitor to

2,500 volts for an Exploding Foil Initiator. Flight safety wanted that capacitor charged and verified prior to launch. Ground safety wanted it charged after launch.

Because all of the safeties on that particular unit were to prevent charging of the capacitor and after it was charged there were a half dozen or so single point failure modes in each of two redundant sections that would result in inadvertent function, and the consequences of that, ground safety won. The capacitor was charged five seconds after umbilical disconnect.

The consequences of our recovery systems functioning on the ground are not nearly as bad as having high explosives go off with likely initiation of a few thousand pounds of rocket motor not to mention the several hundred cluster bombs. But there are still negative consequences. Some reasonable effort should be made to prevent problems prior to launch.

So just what are the things that might cause an ejection charge to go off early?

1) Electromagnetic 2) Insane altimeters 3) Insane rocketeers.

There are several different aspects to the electromagnetic problem.

High electric fields. If there is an electric field present it is possible to have a potential difference between two exposed wires to the electric match. But given that this typically cannot induce large currents and the exposed wires are only a few inches apart (or less) anything short of the electric fields around a lightning strike are not likely to present a problem. If lightning strikes nearby I will not be worried about the ejection charges. :-)

Magnetic fields. We do actually have a magnetic field source close to our rockets but its hazard is small and can be easily mitigated. That source is that launch system. The field produced is a consequence of the large currents. But since the loop area of the current is small (unless you deliberately form the wires to the launch clips into a large loop) and there is only one "turn" the field isn't too big. If you use twisted pair for your wire runs in the rocket, the hazard is even less. Note that shorting the igniter actually increases the hazard from magnetic coupling as it requires a complete circuit.

RF is another potential hazard and is documented to have caused problems. While it is unlikely that you can induce sufficient energy into the wires to an electric match to cause it to function, it can cause other problems. Like coupling into the wires to a break wire arming system that is tied to an unprotected pin on a micro controller. Killing the micro controller and the rocket. Or in my case, coupling into the altimeter measurements resulting in deployment before apogee.

It is also possible that something is wrong with the altimeter so that it fires its outputs on power up. Or perhaps gets a notion that it has been launched even though it is sitting on the pad, or worse, on the ground by your car. Only turning the altimeter on at the pad prevents problems away from the pad. But a guaranteed glitch free power up is a hard thing to find. It may work just fine hundreds of times before it doesn't. Disconnecting the pyro output power or other safe/arm systems will protect you here.

Then you have the insane rocketeer. There isn't much that can be done about this character except to stay away from them. Having wires to electric matches flopping around electronics and batteries is just begging for a trip to the hospital. I like to have my electronics buttoned up in the altimeter bay before I attach the ejection charges from the outside. I also use Deans plugs to make this quick and simple.

In my opinion the hazards from EMI are minimal and easily controlled. The biggest hazard is from the altimeter itself. Or that idiot parked next to you. :-)

If I see the guy walking towards me I wave to make sure he sees me and the rocket, then wait for him so we both can talk about the flights on the way in. If I don't see anyone, I radio the LSO to let them know or get a good bearing and let them know when I get back. If I had the room to bring it in, I would not stick any body parts in or in front of the body tubes.

If my rocket has landed hidden in a corn field, hung up in a tree or powerline, then I've launched under conditions which present a hazard to its recovery and violate the safety code.

Same as the liability if the rocket falls from the sky and injures someone or damages property (possibly less if the club rules prohibit recovery of other's rockets, but you would still pay).

There is no power to the device when the RSO is checking my rocket, unless he is standing at the pad with me.

What happens when your rocket has landed face down hiding the warning, screw and vent hole.

The logical conclusion to this line of argument is that all rockets which use a pyrotechnic device for recovery be painted red with 3" yellow lettering indicating DANGER EXPLOSIVE HAZARD, DO NOT HANDLE on 4 sides (3 for 3 fin rockets).

Wow, you get to use the Cigar Tweak !

Best sticker wording my firm has seen ;)

Cranny Dane.

I don't fly HPR, but... My first heavy rocket was a 500 gram egglofter flown at NARAM 12. This was two stage with four Estes D13 motors. At least one motor cato'ed and it was on the ground long before the ejection of the D13-7s. Now I was building light even in those days, but I had ballasted the model Up to 500.0 grams with a massive amount of red powdered tempra paint, in the hopes of getting a tracked altitude. So the crash is quickly drawing a crowd, and I'm running up yelling, get back! You can paint your own scene.

There is no way to safe the ejection on a burning SU motor, but in the world of HPR electronics, it would be nice if the rocket realized that it was already back on the ground and aborted ejection and other flight functions.

The other thing that bothers me is seeing these super long "shock cords" on HPR models. They are natural power line snaggers. If you shorten the length by say 50%, you cut the odds of hanging up on a power line be almost the same amount. Regardless of the length, I'd likely put in a fusible link, pyro or electro-mechanical, that would self release the cord after say 30 minutes, unless you recover the rocket first and deactivate that function.

Clearly, there is some engineering to be done to ensure that things become more safe and reliable instead of less so.

Alan

I thought about the whole warning sticker issue a lot when I was designing my two stage Quantum Leap, which on a really bad day has a small but nonzero chance of getting lost with a live charge--or even a live motor--in it, I decided that the liability issues were far higher for an unlabeled rocket than for a labeled one. Then I took advantage of some folks I was working with at the time. These were WMD Law Enforcement people, Ordinance disposal specialists, and the like.

I asked what the likely response would be to a call from a worried citizen reporting a rocket in their yard. Their answer was that, unless they happened to know a launch was in progress so they could send someone over, they'd likely treat a large rocket as an ordinance disposal problem. If the rocket is labeled and the disarming instructions are clear, especially if contact information is on the rocket, they'll likely contact the owner (or follow the instructions if they have to e.g. clear a highway). If the rocket is unlabled, especially if it is beeping, they're going to blow it up. Really, No fooling, that's what they're going to do. Then they are going to go looking for the owner, and the owner should expect a Significant Emotional Experience.

I don't know how it might be in the area you all happen to live in, but really, it's worth asking. As for Quantum Leap, it has my name and contact info on it, small but easily seen warnings around the body separations, AND instructions for disarming around the arming bolt holes. And of course, I've never come close to losing it with a live charge inside, so there must be added karma for that, too.

I've become a bit of a zealot on this issue, but really, when you think about it, if NASA has learned how to reliably arm and safe pyro circuits and fly safely with those circuits--even on man-rated vehicles--without twisting wires together and sticking them back in the hole, we should probably try to head in that direction.

My $.02,

--tc

I'd add a couple of zero's and move that decimal place over to the right a bit Ted :) Kick butt common sense advice.

btw, loved that write up you did on the QL in the masa mag and as always, totally enjoyed the 3 perfect flights I've seen(so far) of the QL.

Ted Novak TRA#5512 IEAS#75