2-Stage Bug

[Rocketclar]

OK, I, too, have been bitten by the 2-stage bug and have been brainstorming with myself and have come up with a boatload of questions that I'm trying to sort out via the threads here. While I'm finding good stuff here, I have one concern that I'd like to know how you address it. I assume that you still would follow TRA and NAR procedures for HP prep at the pad....point the rocket up, arm the electronics, and then insert the ignitors. What are the best procedures for the sustainer ignitor? Your techniques/designs to make this easier and safer while it's over the booster? Thanks.

 

[Jmhepworth]

I put the booster on the rail, put the igniter in the sustainer, slide the sustainer onto the interstage coupler, raise the rail, arm the backup altimeter in the sustainer, then arm the Raven that I use for the primary sustainer deployment and sustainer ignition, arm the altimeter in the booster, and then, after making sure all three altimeters are beeping the right patterns, insert the igniter in the booster. I don’t know of any way to put the igniter in the sustainer after the rail is vertical. I just make sure it’s pointed in a safe direction when I put the igniter in. I’m writing this from memory, but I have a written, laminated checklist that I follow. As you’re figuring out, staging is complex. The complexity is what makes it so much fun.

 

[Cameron Anderson]

Here is my generic sequence which sometimes changes slightly depending on if I can install the booster ignitor once it is vertical.

1. Lower rail
2. Slide on booster
3. Insert booster ignitor (do not connect, keep grounded)
4. Go vertical
5. Arm booster recovery electronics
6. Install sustainer ignitor
7. Place sustainer on stack
8. Arm sustainer electronics
9. Connect booster ignitor
10. Test booster continuity

Go for flight.

I use small balsa sticks to hold my sustainer ignitor in the motor. I connect the sustainer ignitor to it's leads to test continuity and altimeter powerup in my camp, but I keep the ignitor out if the motor until I'm at the pad.

 

[cerving]

Here is my generic sequence which sometimes changes slightly depending on if I can install the booster ignitor once it is vertical.

1. Lower rail
2. Slide on booster
3. Insert booster ignitor (do not connect, keep grounded)
4. Go vertical
5. Arm booster recovery electronics
6. Install sustainer ignitor
7. Place sustainer on stack
8. Arm sustainer electronics
9. Connect booster ignitor
10. Test booster continuity

Go for flight.

I use small balsa sticks to hold my sustainer ignitor in the motor. I connect the sustainer ignitor to it's leads to test continuity and altimeter powerup in my camp, but I keep the ignitor out if the motor until I'm at the pad.

^^ This is just about 100% what I do too... ^^

 

[Rocketclar]

Good stuff. As I'm working through the design issues, I keep thinking about the what if's. Thanks for your procedural and sequencing comments. It's certainly more complex than my L3 project and I learned a bunch with that.

 

[Walter Longburn]

What's the proper way to take a hpr 2 stage through RSO? 2 pieces?

Should I be starting a new thread for this question?

 

[OverTheTop]

Here is a thread for my 1/2 scale Nike Apache. Further along in the thread there is some thoughts regarding staging and recovery.
https://forum.ausrocketry.com/viewtopic.php?f=6&t=5019
You should find some ideas for keeping your sustainer ignition system safe. Note that the schematic for the 3" avionics is a little out of date and the two switches for safing the sustainer ignition were wired a little differently. One switch is in series and the other shunts the igniter in the final instantiation.

One thing I would say is to take every measure you can to prevent any of the dynamic pressure in the front of the booster, at separation, from influencing the recovery altimeters for that section. Having a big open hole at the front can create a pressure spike for the altimeter and give you premature ejection of the laundry. Ask me how I know . I had a bulkhead between that section and the altimeter but the bulkhead flexed enough due to dynamic pressure at stage separation. Chute out at M1.14 is a little enthusiastic.

 

[JimJarvis50]

OK, I, too, have been bitten by the 2-stage bug and have been brainstorming with myself and have come up with a boatload of questions that I'm trying to sort out via the threads here. While I'm finding good stuff here, I have one concern that I'd like to know how you address it. I assume that you still would follow TRA and NAR procedures for HP prep at the pad....point the rocket up, arm the electronics, and then insert the ignitors. What are the best procedures for the sustainer ignitor? Your techniques/designs to make this easier and safer while it's over the booster? Thanks.

Two-stagers are fun! Three-stagers, not so much...

The question you are asking is quite complicated in my opinion. I have come to the conclusion that there is no perfect way to do this.

One important consideration is whether you want to arm the sustainer on a ladder or whether you want to avoid that. I am of the opinion that getting off the ladder is a really good idea, but doing that requires some compromises. I am a big fan of wifi to turn on the electronics that will light the sustainer, but the questions that arise are when to close/open any switches/shunts to the igniter and when and how to turn on redundant electronics. It matters when you're 20 feet in the air under an N motor.

Regardless of the approach you take, you need switches that either open or short out the igniter.

One thing I can say in response to the OP question is that I have never inserted an igniter into a sustainer while the rocket is vertical. This is generally just not practical or safe.

The other thing I would say is that I use a procedure I call an "all up" test, where I turn on everything just prior to loading the rocket, but with the igniter out of the motor. If this works, then I turn everything off, and then do the same procedure with the rocket on the rail. This provides some assurance that the ignitor won't fire when going through the process for real. The attached pic shows me doing this prior to a recent three-stage flight. I actually build infrastructure to help me perform this all-up test, and I consider how I will do this test as part of the initial design of the rocket.

Jim

 

[JimJarvis50]

Actually, let me refine my opinion just a bit. Although I don't think there is a perfect way to arrange the arming sequence, I do think there is a best way for projects that would otherwise require a ladder for arming the system. Conceptually, the idea is to arrange for a way to arm the electronics from the ground (i.e., a wifi switch), and a way to deal with the switches that accomplish disconnecting or shunting the igniter, also from the ground. The second part of this is more difficult, but if it can be done, it avoids the need to climb a ladder and retains all of the protections against premature ignition.

One way that I have used to accomplish this is my "magnetic shunt". I did a video on the concept, which is below. I wouldn't necessarily recommend this particular approach, but it does provide the capability to remove the shunt from the ground. It doesn't do much good to arm the electronics from the ground if you have to climb the ladder to clear the path to the igniter.

One of the schools I was working with for the SpacePort cup came up with an even better way to do this. They had a set of contact switches separated by a card. I'm not going to say more about the design because it's their idea. But, the card had traces on it such that when inserted, it would both disconnect the path to the igniter and shunt the igniter leads. As a last step, they would pull out the card from the ground to remove the shunt and complete the igniter circuit. Very elegant.

I think there are a lot of innovative ways that this could be done, and I would encourage anyone doing a project large enough to require a ladder to give this approach some thought. You want to get off the ladder - trust me on this.

Jim

 

[FredA]

Ladders seem WAY easier and actually, to me, somewhat safer than arming (Dis-Disarming) without a physical switch.

 

[JimJarvis50]

Ladders seem WAY easier and actually, to me, somewhat safer than arming (Dis-Disarming) without a physical switch.

I don't mean to suggest that there are no physical switches. I have a switch for power to the wifi, which could be turned off via a ladder if there was a need. Similarly, the magnet shunt or card switch/shunt could be replaced if there was a need to stand down. So, you're infrastructure still needs to allow a ladder to be used if necessary, but the physical switches are there.

I had one incident where an N sustainer motor lit on first motion of the rocket. It could just as easily lit if moved by the wind with me next to it on the ladder. It was a one-in-a-million incident (they always are), but it did happen, and it happens to others every now and then. I know a guy who was badly burned by a sustainer motor, and I know I got lucky that day. If you don't want to do something like this, there is no requirement. But I think the idea of doing these flight without the need to be on a ladder represents a significant "step change" in safety.

By the way, here's a video of the incident that I had. Two smoke trails off the pad isn't a good thing. Carbon shards were spread over hundreds of feet. My advice is to ditch the ladder.

Jim

 

[FredA]

I had one incident where an N sustainer motor lit on first motion of the rocket. It could just as easily lit if moved by the wind with me next to it on the ladder. It was a one-in-a-million incident

I hear ya - stuff happens - but usually for a reason.

What was the cause? How did the fault get past ground testing?
The LADDER wasn't the problem.

 

[JimJarvis50]

I hear ya - stuff happens - but usually for a reason.

What was the cause? How did the fault get past ground testing?
The LADDER wasn't the problem.

I don't actually recall everything that I concluded at the time (it was nearly 10 years ago, and I have forgotten some details). One issue was the live mounting terminals on the powerperch, which I did not know about at the time. I believe this was able to contact the wall of the electronics bay, which was carbon. I think that was the intermittant part of it (when the rocket moved, it could make contact). The circuit was completed through the ends of the carbon tubes, which are sanded and not covered by epoxy. It was my belief that the circuit went from the sustainer to the booster through the ends of the tubes and wasn't completed until the stages were together. Somehow, there was a path from the tube to the igniter, but this is one of the things I don't remember.

True, the ladder wasn't the problem, but being on the ladder could have been. Anytime I went up a ladder, I always identified where I would jump if need be. I'd just rather avoid that.

Jim

 

[boatgeek]

Here is my generic sequence which sometimes changes slightly depending on if I can install the booster ignitor once it is vertical.

1. Lower rail
2. Slide on booster
3. Insert booster ignitor (do not connect, keep grounded)
4. Go vertical
5. Arm booster recovery electronics
6. Install sustainer ignitor
7. Place sustainer on stack
8. Arm sustainer electronics
9. Connect booster ignitor
10. Test booster continuity

Go for flight.

I use small balsa sticks to hold my sustainer ignitor in the motor. I connect the sustainer ignitor to it's leads to test continuity and altimeter powerup in my camp, but I keep the ignitor out if the motor until I'm at the pad.

I've been working on this process for my 2-stage project, and I'm not sure about ordering your steps 5-7. My understanding as that it was verboten to have a sustainer igniter in place and connected to the electronics without sustainer deployment electronics armed. Did I just misunderstand that? What I was going to go with was something like:
4. Go vertical with a block between the booster and sustainer
5. Arm sustainer electronics with igniter out of the motor
6. Insert sustainer igniter
7. Remove block and lower sustainer on to stack

Also note that my sustainer is ~1 lb, so it's easy to move around. This would be way different for a 50-lb sustainer.

 

[Cameron Anderson]

I've been working on this process for my 2-stage project, and I'm not sure about ordering your steps 5-7. My understanding as that it was verboten to have a sustainer igniter in place and connected to the electronics without sustainer deployment electronics armed. Did I just misunderstand that? What I was going to go with was something like:
4. Go vertical with a block between the booster and sustainer
5. Arm sustainer electronics with igniter out of the motor
6. Insert sustainer igniter
7. Remove block and lower sustainer on to stack

Also note that my sustainer is ~1 lb, so it's easy to move around. This would be way different for a 50-lb sustainer.

As far I understand the safety rules, you can't have the ignitor in the sustainer until you are at the pad (or area designated by the RSO, which is usually the pad) immediately prior to loading onto the rail.

I would not want to arm my electronics (which controls deployment and sustainer ignition) then try to install the ignitor and risk the electronics sensing liftoff as the ignitor is half-in the motor while I'm installing it.

 

[JDcluster]

When arming the electronics; I work from the NC down. Recovery Electronics first followed by sustainer ignition, last is the booster igniter. This way you are on the ground when finished. The sustainer igniter is shorted to itself.... in the motor as late as possible. You still don't want to be messing with an igniter 6-8 ft in the air. It's better to just have to untwist wires and connect the longer leads that are already in the rocket.

 

[FredA]

When arming the electronics; I work from the NC down.

Yes - and arm nothing until the rocket is vertical, in position, and you're done jostling it....until then, all pyro's are physically disconnected from the flight controller and shunted.

 

[Cameron Anderson]

Yes - and arm nothing until the rocket is vertical, in position, and you're done jostling it....until then, all pyro's are physically disconnected from the flight controller and shunted.

Looking to clarify...when do you physically connect your pyro events?

 

[FredA]

Looking to clarify...when do you physically connect your pyro events?

When do I connect pyro devices?
When I build the EBay?

Out of rocket. All tested before installation.
Check programming with expected pyro failure - I use MARSA's and just watch the LCD and listen to the tones.
Then add E-matches and test continuity.
Then add BP and test continuity - in a safe location/position.
Install the Ebay in the rocket and finish prep.

How else do you or anyone else do it?

I treat motors just like an explosive charge -- we KNOW they are not explosives and must be safer ;-)
Same thing - build the [sustainer] motor with the igniter.
Carefully test continuity in a safe location.
The finish the rocket.

REMEMBER - I ALWAYS HAVE A DOUBLE-THROW SWITCH DISCONNECTING THE FLIGHT ELECTRONICS AND SHUNTING ALL PYRO'S.

EVERY pyro in the rocket connects to a shorting switch that also disconnects the hot lead from the electronics.
Thus having the less of a chance of firing than a bare e-match.....and we all know how often those just "pop" by themselves.

That switch - that shunt - does not get removed until MARSA power is applied but before it gets to the pyro continuity check.

 

[Rocketclar]

Really good stuff! Thanks for the help. I can see the list of safety switches growing for all the pyros and sustainer ignitor. I march on and will have more questions! Again, thanks!