Redundant Deployment Design

[Feckless Counsel]

TRF,

Most two channel (dual) deployment controllers unconditionally fire one channel at apogee. Where two such controllers are used for redundancy (backup) one must accept the possibility that two charges might fire simultaneously. In that case the airframe may become over-pressurized. Therefore such controllers are not a good choice for redundant design, correct?

Feckless

[COrocket]

Yes, there is a possibility that both will fire at the same time. The time between the charge going off and separation is a split second, so the probability is pretty remote. I always set my backup altimeter to fire 3 seconds after apogee, to help mitigate that risk. Then the main is set at a lower altitude to prevent the main charges from going off simultaneously

[Feckless Counsel]

COrocket,

Your backup is altimeter is not two channel or does not fire channel one unconditionally at apogee?

Feckless

[COrocket]

I use a pair of the new Perfectflite SL100 altimeters. They are both dual deploy altimeters. When you program them, you have the option to have a apogee delay. So when you program the primary altimeter, you leave the apogee delay setting at 0 seconds, so it will fire exactly at apogee. Then for the backup altimeter apogee delay, you program 3 seconds or whatever you see fit, to fire slightly after apogee.

So to answer your question, i can conditionally program each altimeter to either fire right at apogee, or a specified time after apogee. I know many dual deploy altimeters have this option. What electronics are you looking at?

[Feckless Counsel]

COrocket,

Adept 22 primary with Raven 2 as backup and datalogging. Raven has multiple program options on channel 3 and 4. Adept 22 is low cost.

Feckless

[COrocket]

I looked at the Adept 22 and saw that it didn't have any options besides apogee for the first output, so I see your concern if you used two identical units. Good call on the Raven, you should be able to program it for backup duties. My friend has one and it gives tons of cool data.

[bobkrech]

There is another option. You can use a single BP charge and use multiple e-matches to activate it.

For very high reduntancy you can use (2) altimeters each with (2) low current e-matches per pyro output for a total of (4) e-matches in the bp canister. If the probability of failure of each component 1%, the probability of both altimeters failing is 0.01%, and the probability of both e-matches failing on a pyrochannel activation is 0.01%, so you have a 99.99% chance of igniting the BP charge on any flight

Bob

[Polyalcoholic]

There is another option. You can use a single BP charge and use multiple e-matches to activate it.

For very high reduntancy you can use (2) altimeters each with (2) low current e-matches per pyro output for a total of (4) e-matches in the bp canister. If the probability of failure of each component 1%, the probability of both altimeters failing is 0.01%, and the probability of both e-matches failing on a pyrochannel activation is 0.01%, so you have a 99.99% chance of igniting the BP charge on any flight

Bob

In such a scheme you introduce a single point of failure. If there is a problem with the BP charge, you lose the benefit of the redundant electronics.

[Adrian A]

Just from paying attention to reports of failed cert flights, etc. and from what I've seen myself at the field (only slightly better than anecdotal data) I would say that popping off the nosecone without enough energy to pull the main out is among the most common failure modes in HPR. Sometimes having a second BP charge will remedy that. (Using a piston generally prevents it.) Breaking a shock cord or attachment point is also pretty common, but a lot of those are from motor ejection timing problems. Blowing a hole in an airframe due to overpressurization is relatively rare. Electronics failures, other than a dead batteries or forgetting to turn them on, are even more rare. I'd say if you're not using a piston, you're probably improving your odds more by having 2 redundant charges per function, even if it's on one altimeter, than by having 2 altimeters and one BP charge. The Raven also has options for making apogee or main events happen with some time in between.

[FredA]

Amen Adrian,

You are spot-on...
Failure to get the chute out is the big one in my book.
That's why I like ONE 4-channel altimeter able to run main and backup charges for each deployment.

Unless you abused or miss-used (bad wiring or programming) the altimeter, it should be fine flying solo.
Flying a solo altimeter also adhears to the KISS principal.

So -- make you main charge match your ground testing and upsize the backup charge.

This is what i consider today's BKM.

FredA

[chadrog]

The missileworks RRC2 can also be programmed with apogee delay.

[bobkrech]

In such a scheme you introduce a single point of failure. If there is a problem with the BP charge, you lose the benefit of the redundant electronics.

Not really. You're still only using 1 chute, so if the ejection charge was not able to get the chute out the first time, please explain in a probabilistic manner how the second charge will finish the job.

Most professional systems have 1 pyro charge per chute but many firing circuits. Assuming you ground tested the ejection system to insure that 1.) you have BP; 2.) that you have enough BP to do the job; and 3.) that your BP is in a hermetic (sealed) container, you have shown that unless you have a failure of all 4 e-matches and both altimeters, you will ignite the BP, and that you have a sufficient amount of BP to deploy the laundry.

If you want absolute recovery system redundancy, you need to use 2 or more chutes deployed from 2 or more individual chute mortars. Look at NASA's deployment systems and see that this is the way they did it when they didn't have an ejection seat option.

Mercury and Gemini had 1 main chute and the option of individual ejection seats. Apollo had 3 main chutes, as did the Shuttle SRBs, and the proposed Orion capsule. The only manned system that did not have a backup parachute recovery system was Shuttle. The first Shuttle flight(s) had ejection seats for the pilots only. Later flights has individual chutes for each crew member with a deployment pole to help the astronauts clear the Shuttle's wings.

Bob

[Fe Dude]

In the three cases of failed deployment I have experienced personally (2 from inadequate motor charges, and one from not enough BP that I measured) the nose was kicked, but the chute and protector plugged the end of the tube.

I cant help but think that another gram and a half of BP in a separate charge would have been enough to dislodge the chute and saved me some repairs.

More chutes and cannons, separate recovery harnesses, and such and bother, seem like added complexity and weight.

[Adrian A]

In the three cases of failed deployment I have experienced personally (2 from inadequate motor charges, and one from not enough BP that I measured) the nose was kicked, but the chute and protector plugged the end of the tube.

I cant help but think that another gram and a half of BP in a separate charge would have been enough to dislodge the chute and saved me some repairs.

Once the nosecone has been kicked off and opened up the end of the tube, there's no guarantee that another charge would kick it out, but there are certainly a number of documented cases where it did work to save the rocket.

I'm a fan of using a piston for main chute deployment, because I think it removes some sensitivity to the chute and harness packing that can give misleading results from a ground test. People forget how much their chute and harness can shift by the boost. It also protects the chute better, and less BP is needed so less crud is generated.

I generally don't use redundant charges myself, because for the rockets I fly, every little bit of volume counts, and I get some redundancy against a ballistic re-entry by flying dual deployment in a configuration where the main charge can do it all if the apogee separation charge didn't work.

[GaryT]

No way in hell would I use 1 well of BP with 2 E-Matches, I've seen it a hundred times where that 2nd BP charge completed the separation at apogee or pushed the main the rest of the way out and saved the day, What are you saving by NOT! using it literally 3 cents worth of BP?

Unfortunately theres no guarantees in rocketry but I'll take my chances with 2 BP wells over 1 any day.

[GRIFFIN]

No way in hell would I use 1 well of BP with 2 E-Matches, I've seen it a hundred times where that 2nd BP charge completed the separation at apogee or pushed the main the rest of the way out and saved the day, What are you saving by NOT! using it literally 3 cents worth of BP?

Unfortunately theres no guarantees in rocketry but I'll take my chances with 2 BP wells over 1 any day.

+1

watch this and agree

http://www.youtube.com/watch?v=8kEMGniMe0g