Why are university HPR teams having such difficulty with airstarts?

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MattJL

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Something I've been thinking about over the last couple days. As someone who is part of a university team myself, that had an upper stage ignition failure due to a faulty AV bay, this is a question that is near and dear to my heart.

A lot of university teams, particularly those aiming to do a 328k foot launch, have settled upon a multi-stage vehicle. (In fact, the only single-stage vehicle I'm aware of is USCRPL's Traveler III). Of those that have attempted launches, a lot of their failures revolve around problems with the sustainer/upper stage:
  • Princeton University: Two-stage "powered dart," M1378 to O5040-X. Upper stage failed to ignite.
  • Virginia Tech: Two-stage conventional, Q to P. Upper stage ignited during launch prep.
  • TU Wien: Two-stage "powered dart," likely N or M to N5800 (unknown impulse in sustainer). Upper stage failed to ignite.
  • University of Southern California: Single-stage conventional, likely R or S (unknown impulse). Stage ignited before AV bay turned on.
It seems to me that airstarts are the engineering problem that university teams are currently facing - and unlike stage separation, ejection charges, avionics, or structural elements, it can't be tested on the ground. Stuff has to be going uphill to validate the design.

I understand that airstarts are particularly problematic in general, primarily because of heat transfer issues at altitude, but it surprises me that teams that should have access to a wealth of knowledge about military-spec igniters through their own university archives are either not taking advantage of it or hitting some other roadblock. (It also surprises me that, with the number of people just generally doing multi-stage rockets, that a COTS high-altitude igniter doesn't exist).

To me, and my experience browsing this forum, it seems that the most sound solution is to have a dual-redundant ematch/grain sliver bagged in a glove finger stuck up in there. But I'm not an engineer, I'm a geologist, and we're currently in enough of a financial bind that I can't afford to get up to the range with a preliminary design to test something like that. And the ranges up here close for the winter soon, anyway.

So why might these teams be having such issues? Does it revolve around a lack of access to knowledge, "not-invented-here" syndrome, an unwillingness to go out and communicate with experienced rocketeers, or something else? More tangentially, is there a way to test igniters at simulated altitude on the ground?
 
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jderimig

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S Does it revolve around a lack of access to knowledge, "not-invented-here" syndrome, an unwillingness to go out and communicate with experienced rocketeers, or something else?
I believe we have a Bingo.

More tangentially, is there a way to test igniters at simulated altitude on the ground?
Of course. Motor ignition is a heat transfer problem. If the university doesn't have vacuum pumps, thermocouples and bomb calorimeters then it should acquire some. Then think about the problem.
 

rharshberger

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Your last statement may have hit pretty close to home, and could be all of the reasons you mention. To top that off, we have seen too many teams with inadequate (or at least not listening to their mentors) or non-existent mentors forging into very advanced territory not knowing what they don't know. Many of the teams lack experience with rocketry and its issues and the most experience they have tends to be L1 and L2 level flights and not many of those at that.
 

Steve Shannon

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Something I've been thinking about over the last couple days. As someone who is part of a university team myself, that had an upper stage ignition failure due to a faulty AV bay, this is a question that is near and dear to my heart.

A lot of university teams, particularly those aiming to do a 328k foot launch, have settled upon a multi-stage vehicle. (In fact, the only single-stage vehicle I'm aware of is USCRPL's Traveler III). Of those that have attempted launches, a lot of their failures revolve around problems with the sustainer/upper stage:
  • Princeton University: Two-stage "powered dart," M1378 to O5040-X. Upper stage failed to ignite.
  • Virginia Tech: Two-stage conventional, Q to P. Upper stage ignited during launch prep.
  • TU Wien: Two-stage "powered dart," likely N or M to N5800 (unknown impulse in sustainer). Upper stage failed to ignite.
  • University of Southern California: Single-stage conventional, likely R or S (unknown impulse). Stage ignited before AV bay turned on.
It seems to me that airstarts are the engineering problem that university teams are currently facing - and unlike stage separation, ejection charges, avionics, or structural elements, it can't be tested on the ground. Stuff has to be going uphill to validate the design.

I understand that airstarts are particularly problematic in general, primarily because of heat transfer issues at altitude, but it surprises me that teams that should have access to a wealth of knowledge about military-spec igniters through their own university archives are either not taking advantage of it or hitting some other roadblock. (It also surprises me that, with the number of people just generally doing multi-stage rockets, that a COTS high-altitude igniter doesn't exist).

To me, and my experience browsing this forum, it seems that the most sound solution is to have a dual-redundant ematch/grain sliver bagged in a glove finger stuck up in there. But I'm not an engineer, I'm a geologist, and we're currently in enough of a financial bind that I can't afford to get up to the range with a preliminary design to test something like that. And the ranges up here close for the winter soon, anyway.

So why might these teams be having such issues? Does it revolve around a lack of access to knowledge, "not-invented-here" syndrome, an unwillingness to go out and communicate with experienced rocketeers, or something else? More tangentially, is there a way to test igniters at simulated altitude on the ground?
I haven’t followed the Princeton launch, but none of the other rocket problems you listed were due to inadequate thermal transfer or igniter problems. The OLVT incident was inexperience, ignorance, and failure to follow the safety code. The TU-Wien rocket had an inhibiting condition that prevented ignition, which is not a safety issue. The USC students apparently failed to follow their own procedure (due to a miscommunication) and launched the rocket before turning on their avionics.
Yes, lighting a motor at high altitude can be a greater challenge than at ground level, but that’s not the problem that bothers me.
 

MattJL

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Consensus seems to be that "all of the above" is the correct answer to the question. It's unfortunate, but I guess that's kind of what I'd expect.

I haven’t followed the Princeton launch, but none of the other rocket problems you listed were due to inadequate thermal transfer or igniter problems. The OLVT incident was inexperience, ignorance, and failure to follow the safety code. The TU-Wien rocket had an inhibiting condition that prevented ignition, which is not a safety issue. The USC students apparently failed to follow their own procedure (due to a miscommunication) and launched the rocket before turning on their avionics.
Yes, lighting a motor at high altitude can be a greater challenge than at ground level, but that’s not the problem that bothers me.
You're correct - I didn't discuss the reasons behind the failures because I didn't want to, myself, speculate without good evidence. But failure to do things safely and smartly does seem to be a recurring problem with these university teams, and I appreciate you bringing it up.

And I do feel like a massive hypocrite saying that - I'm a college student myself, and I'm a geologist, not an engineer - but I've seen very little interest in going out and gathering knowledge from people who have been building and flying rockets for longer than I've been alive. Especially when coupled with the ambitious, bordering on dangerous, timescales that a lot of these teams produce.

Engineering failures, management failures, or hubris? I'm not sure which one is more concerning.

On a lighter note, Jim Jarvis' igniter is a really great solution to the ignition-at-altitude problem. So, maybe I'll try a three-stager Appears to be something that a well-stocked chemistry department could supply the raw materials for, but I'd personally be cagey about making those pellets in-house.
 

saadzmirza

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Directly reposted from the Princeton thread:

First I just wanted to comment that the high altitude ignition issue, from my understanding, is not a heat-transfer issue, but simply a low pressure issue. See NASA Solid Rocket Motor Igniters "2.0.2.1.2 Gas-Phase Theory". There is a critical pressure below which ignition cannot be achieved for arbitrarily high heat flux. See p13 of the same document, and "3.2.1.1.3 Critical Pressure" on p60.

"As previously discussed, at low pressures propellant ignition energy requirements are strongly dependent on pressure. This dependence decreases exponentially, reaching an essentially pressure-independent regime that for many propellants occurs in the range50 to 100 psia. Consequently, one of the methods used for sizing igniters has been based on attaining a given pressure in the motor port. The desired pressure is based on the “calculated critical pressure” required for sustained burning (ref. 126); or on the
pressure-heat flux relationship obtained from arc-image data; or on an established pressure (e.g., 50 to 100 psia) based on experience."

Okay, original post below:

We were planning on using a BKNO3 igniter. We did not have an ATF Explosives User's Permit and were developing pellets using polyester resin as binder per Mil Spec 46994B. With a professional BKNO3 igniter as plugger and others have said the goal is "instant-on" - the igniter is to bring the motor to above the critical pressure (50-150 psi) for appx. 100 ms and apply a certain heat flux. This pressure goal can be aimed for without worrying about the dynamics of sealing the nozzle to burst at a certain pressure.

Since such an igniter is quite violent, we intended to do a static fire test of the M1378 with the robust BKNO3 igniter the week prior to our launch, but another team member mistakenly sent the liner for the static fire to New Mexico, along with the flight hardware. Thus we had no way to static fire the igniter, and due to fears of over pressurizing the motor, we instead flew with a thin aluminum burst disk (a few layers of aluminum tape) and sealed/bonded it to the nozzle exit diameter Silicone glue. The igniter used was a Quickburst Fat Boy, a long burning igniter that isn't able to pressurize the motor rapidly enough. The igniter fired but the motor chuffed out. I suspect the ambient pressure in the motor core had dropped to that of the atmospheric pressure at 35 kft, meaning the motor wasn't perfectly sealed.


For future flights, both for Princeton Rocketry Club, and Operation Space, Inc., an organization that I serve as design lead for, we plan on obtaining BKNO3 pellets with a burn time of approximately 50-100 ms, and sizing the igniter charge per the Bryan-Lawrence relation, which is another method (like the mass flux plugger mentioned) used in industry. https://www.dtic.mil/dtic/tr/fulltext/u2/307914.pdf
FYI the quotes we are getting for the BKNO3 are over $5000 at this time for a MOQ, not including HAZMAT freight from GA.

The charge required seems quite large: I calculated 10g of BKNO3 from the equation, with a range of 5g-20g. This seems like a lot, but for reference the 2.75" FFAR rocket uses ~8g of BKNO3 pellets, with a total impulse of ~5000 Ns. Using this as a guideline, then one develops a testing apparatus of a steel pipe closed at both ends, with one end having a hole equal to the nozzle exit diameter. A pressure transducer is mounted to the apparatus to ensure that the pressure-time curve is appropriate, applying a pressure of ~50-100 psi for at least ~50 ms. The charge size can be modified at this time iteratively. We do not plan on sealing the nozzle since it was found to be unreliable last time.

Our plan for the igniter itself for Operation Space, Inc. is using the threaded bolt that goes into the forward closure of a Pro98 6GXL case, drilling a hole through the forward closure, and installing a much longer threaded bolt to serve as a solid mounting point for the threaded igniter assembly. Obviously the forward closure is sealed with epoxy. The igniter assembly is a 3D printed basket that is slightly smaller than the core diameter of the N5800 sustainer, and the igniter assembly holds the BKNO3 pellets. The 3D printed igniter basket is threaded and fits onto the rod, and sits inside the top grain core. 2 electric matches go inside the igniter basket for redundancy. For the N5800 motor I calculated a charge mass of ~30g.

For a bit more information about solid rocket motor ignition, here is a paper from the development of the Black Brant sounding rocket. They experienced upper stage ignition failures, and redesigned their igniter to be more reliable. They found that for their APCP propellant ignition was probable at 50 psi for a heat flux of 627 W/cm^2 for at least 40 msec. They also note that the core mass flux guideline was wildly inaccurate.
https://drive.google.com/file/d/1u8cSIIOlEvsLKY0CcCBbqWKnNdOCtdOB/view?usp=sharing

Since their final igniter charge mass was similar to that predicted by the Bryan-Lawrence equation, I suspect that we will be okay without measuring the heat flux, and that an igniter charge mass in the Bryan Lawrence range will produce sufficient heat flux. I do think that measuring the pressure output in a vented chamber will be a useful experiment. Upon verification of the pressure-time trace, we will static fire the rocket motor to make sure it doesn't over pressurize and CATO.

For more information about the theory of solid rocket motor ignition and igniters see the following literature:

1.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19710020870.pdf
Be sure to read the igniters section, and the pelleted pyrotechnic igniters section. Pyrogen (propellant) igniters are typically for larger solid rocket motors like the Shuttle SRBs, from my understanding, and often have a pelleted pyrotechnic in the ignition train. Ignore the initiators section, as it is deceiving - this is only the initial spark that starts the ignition charge. For relatively small solid rocket motors like these we are using an ematch (squib) as an initiator. Read the ignition theory section, specifically about the critical pressure. Below the critical pressure (often equivalent to about 30,000 ft) ignition cannot be achieved regardless of heat flux applied. Since copper thermite igniters do not produce substantial gas, no matter how "hot" they are they will not light a sustainer at high altitude.

2.
"Igniter Material Considerations and Applications:"
A very useful, short, and simple paper detailing different igniters for solid rocket motors, from copper thermite to BKNO3, and how early igniters were a flash can of black powder, and how and why igniters moved to the precise wire cage BKNO3 pellets we see today (mostly to minimize shock from powder).
https://drive.google.com/file/d/1uzv4NAQa-V_2T_K86CjnDuqpjW5LL6KK/view?usp=sharing
 

saadzmirza

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Here is another useful document with graphs of pressure vs. ignition time for various heat fluxes for APCP with different binders, namely PBAN, PU, and PIB. I might be wrong but I believe HTPB is a subset of PU (polyurethane) binder.

https://www.dtic.mil/dtic/tr/fulltext/u2/820453.pdf

But the existence of a critical pressure for these propellants is obvious from the graphs.

Overall all of this information is freely available on the web, and instead of making completely untested theories on the ignition process of APCP ourselves, we should use the research freely available online that our tax dollars funded in the 1950s-1970s. Most of these problems have been solved and the solutions are documented.
 

saadzmirza

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Oh also, you can legally make your own BKNO3 and while I won't link to the materials, it can be sourced from an online auction website for less than $30. The problem is that you'll be left with a very fine powder that burns way too quickly (presumably much faster than 50-100 ms), and could cause shock inside the motor (see Igniter Material Considerations and Applications). So an unsolved problem is pelletizing this powder to slow down the burn rate, or just shell out thousands for BKNO3 pellets from a supplier, given that you have the appropriate permit.

ATF regulations do not apply to an individual or entity making explosives for their own personal use, but I might be wrong:

"Persons who manufacture explosives for their personal, non-business use (e.g., making fireworks to set off on your own property or mixing binary explosive components to remove a stump in your own yard) are not required to have a manufacturer’s license. However, no person may ship, transport, cause to be transported, or receive explosive materials unless such person holds a license or permit."
 

MattJL

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Replying in here for the sake of relevancy, but thanks for providing such a lengthy and in-depth reply. I'm heading out for the night, so apologies for coming up with a short reply in the wake of a really detailed one.

Since such an igniter is quite violent, we intended to do a static fire test of the M1378 with the robust BKNO3 igniter the week prior to our launch, but another team member mistakenly sent the liner for the static fire to New Mexico, along with the flight hardware. Thus we had no way to static fire the igniter, and due to fears of over pressurizing the motor, we instead flew with a thin aluminum burst disk (a few layers of aluminum tape) and sealed/bonded it to the nozzle exit diameter Silicone glue. The igniter used was a Quickburst Fat Boy, a long burning igniter that isn't able to pressurize the motor rapidly enough. The igniter fired but the motor chuffed out. I suspect the ambient pressure in the motor core had dropped to that of the atmospheric pressure at 35 kft, meaning the motor wasn't perfectly sealed.
I say this without a hint of malice or criticism, but man does this bring back memories of the last-minute launch rush we tended to have in my team. It seems like material and supply-chain flubs like that are frustratingly common. I'm currently seeking to bring an end to that, but that's another story. I kind of wonder if the failure to ignite stemmed from the burst disc failing during ascent - my admittedly-rusty recollection from physics class implies that the gas in the propellant grain effectively pressurizes beyond ~1 atm while the rocket is under acceleration. I know of at least one person on this forum that's looking into melt-away burst discs, to help solve some of that problem.

FYI the quotes we are getting for the BKNO3 are over $5000 at this time for a MOQ, not including HAZMAT freight from GA.
That sounds about right. Small batches, lots of regulation = high cost.

Our plan for the igniter itself for Operation Space, Inc. is using the threaded bolt that goes into the forward closure of a Pro98 6GXL case, drilling a hole through the forward closure, and installing a much longer threaded bolt to serve as a solid mounting point for the threaded igniter assembly. Obviously the forward closure is sealed with epoxy. The igniter assembly is a 3D printed basket that is slightly smaller than the core diameter of the N5800 sustainer, and the igniter assembly holds the BKNO3 pellets. The 3D printed igniter basket is threaded and fits onto the rod, and sits inside the top grain core. 2 electric matches go inside the igniter basket for redundancy. For the N5800 motor I calculated a charge mass of ~30g.
I'd worry about the behavior of the "igniter basket," and the fit. I know some guys who did work on Operation Space, and the AV bay suffered an issue where, because it was made of a plastic that was slightly hydroscopic (ABS?), it had problems fitting inside the body tubes. Precision fit with 3D printed stuff is hard. I don't know enough to pass full judgement along, especially with drilling into the motor casing on an N5800, and I'll leave that up to the experts to fully judge. (I wouldn't do it, but I'm a fair bit more caution-oriented than most).

Since their final igniter charge mass was similar to that predicted by the Bryan-Lawrence equation, I suspect that we will be okay without measuring the heat flux, and that an igniter charge mass in the Bryan Lawrence range will produce sufficient heat flux. I do think that measuring the pressure output in a vented chamber will be a useful experiment. Upon verification of the pressure-time trace, we will static fire the rocket motor to make sure it doesn't over pressurize and CATO.
I, personally, would validate the heat flux in ground testing (especially given that it's almost winter, and the ranges are closed/closing and you have the time) before doing a pressure output test, but that's because I like playing my designs conservatively.

The links are appreciated. Will review them when I have the time to to gain a better understanding of the problem at hand. I'm particularly cagey about trying to make BKNO3 pellets in-house, as I've mentioned earlier, and suspect that some variation of nozzle-plugging (and a more ATF friendly initiator) will become an acceptable substitute with enough time and R&D.

If you're interested in doing a knowledge exchange with my university, shoot me a message - I think that solving common problems together is wiser than making the same, potentially dangerous, mistakes over and over again. No need to reinvent the wheel... and we're right down the road.
 

jsdemar

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Sizing an igniter is based on the pyrogen's ability to produce both heat flux and pressurization gas. I have described the equations and results of experimental measurement in the igniter thread in the research forum here. I've based my approach on an extensive review of past work by mil and commercial resources and standard practices.

Most professional ignition systems assume the nozzle is capped or plugged. I've been testing various methods and have concentrated on a simple plastic burst disk. I'll share the results after more testing.

The rest of the problem is the physical design of the igniter, how to hold it in place, and how to safely ignite it.

Milspec BKNO3 pyrogen is not necessary. Pellet pressing is not required. But like all energetic material processing, it is risky and should not be done without safe procedures.
 

MattJL

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Sizing an igniter is based on the pyrogen's ability to produce both heat flux and pressurization gas. I have described the equations and results of experimental measurement in the igniter thread in the research forum here. I've based my approach on an extensive review of past work by mil and commercial resources and standard practices.

Most professional ignition systems assume the nozzle is capped or plugged. I've been testing various methods and have concentrated on a simple plastic burst disk. I'll share the results after more testing.

The rest of the problem is the physical design of the igniter, how to hold it in place, and how to safely ignite it.

Milspec BKNO3 pyrogen is not necessary. Pellet pressing is not required. But like all energetic material processing, it is risky and should not be done without safe procedures.
I guess getting access to the research forum is worth going for an L3, then! I hope you'll share the burst disc data in a more public forum, I'm very interested in those results, and I think it'd make college teams a little safer.

Agreed that high-quality BKNO3 isn't entirely necessary. I suspect it can even be done with regular, off-the-shelf pyrogens, but that's something I'd prefer to investigate (or to be investigated) before I say one way or the other.
 

Steve Shannon

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I guess getting access to the research forum is worth going for an L3, then! I hope you'll share the burst disc data in a more public forum, I'm very interested in those results, and I think it'd make college teams a little safer.

Agreed that high-quality BKNO3 isn't entirely necessary. I suspect it can even be done with regular, off-the-shelf pyrogens, but that's something I'd prefer to investigate (or to be investigated) before I say one way or the other.
Access to the research forum isn’t limited to L3.
 

rocketace

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Coming from someone who started a university rocketry organization that is still going on and growing 10 years later.....The three big issues that I see are experience, mentors, and time. Every university and every team will have their own views, but this is what I have seen.

Experience: When you put a group of students together that have not been in HP Rocketry they do not always know what questions to ask. They might do a little research then choose a way forward and proceed. If they run into issues, they try to find a quick work around which is not always the best way.

Mentors: The team does have access to very knowledgeable professors, however their knowledge base far from hobby rocketry and is more focused on research. One thing my old team is currently doing is reaching out to the local club to do a design review with local experts in the hobby, which is a fantastic idea!

Time: Almost all projects are on some type of time crunch. Being short on time causes mistakes caused by rushing and again not knowing what questions to ask. Also with reduced time teams often do not plan enough time for test launches when possible. On top of this, students tend to over estimate how much they can get done in one school year.

Additionally, combining all three issues, in a university team there are new people every year and the most knowledgeable people are lost every year. This leads to frequent mistakes. Before I graduated, I created a powerpoint series "Rocketry 101" to aid in getting the new team members up to speed on HP Rocketry and some basic dos/donts.

I personally have not been hugely involved in rocketry the past few years, but I am making a come back. With that I am showing up to some meetings with the university team to offer any help I can.
 

AlphaHybrids

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It isn't airstarts. Those are just getting the attention.

Being involved with multiple IREC teams over the years, as a generalization, teams have issues with all aspects of appropriate rocket design and construction.

Edward
 

MattJL

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Coming from someone who started a university rocketry organization that is still going on and growing 10 years later.....The three big issues that I see are experience, mentors, and time. Every university and every team will have their own views, but this is what I have seen.

Experience: When you put a group of students together that have not been in HP Rocketry they do not always know what questions to ask. They might do a little research then choose a way forward and proceed. If they run into issues, they try to find a quick work around which is not always the best way.

Mentors: The team does have access to very knowledgeable professors, however their knowledge base far from hobby rocketry and is more focused on research. One thing my old team is currently doing is reaching out to the local club to do a design review with local experts in the hobby, which is a fantastic idea!

Time: Almost all projects are on some type of time crunch. Being short on time causes mistakes caused by rushing and again not knowing what questions to ask. Also with reduced time teams often do not plan enough time for test launches when possible. On top of this, students tend to over estimate how much they can get done in one school year.

Additionally, combining all three issues, in a university team there are new people every year and the most knowledgeable people are lost every year. This leads to frequent mistakes. Before I graduated, I created a powerpoint series "Rocketry 101" to aid in getting the new team members up to speed on HP Rocketry and some basic dos/donts.

I personally have not been hugely involved in rocketry the past few years, but I am making a come back. With that I am showing up to some meetings with the university team to offer any help I can.
Absolutely agree on all counts, and I think the solutions you pose are great. Knowledge transfer is challenging, I wish there were better ways to do it.

It isn't airstarts. Those are just getting the attention.

Being involved with multiple IREC teams over the years, as a generalization, teams have issues with all aspects of appropriate rocket design and construction.

Edward
Yup, there's something of a selection bias here - who knows what issues the teams that haven't launched yet are facing - and I can easily be to blame for focusing on an important but perhaps by and large uncommon problem.
 

boatgeek

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[lots of good stuff snipped]

I understand that airstarts are particularly problematic in general, primarily because of heat transfer issues at altitude, but it surprises me that teams that should have access to a wealth of knowledge about military-spec igniters through their own university archives are either not taking advantage of it or hitting some other roadblock. (It also surprises me that, with the number of people just generally doing multi-stage rockets, that a COTS high-altitude igniter doesn't exist).

...

So why might these teams be having such issues? Does it revolve around a lack of access to knowledge, "not-invented-here" syndrome, an unwillingness to go out and communicate with experienced rocketeers, or something else? More tangentially, is there a way to test igniters at simulated altitude on the ground?
I think the market for a COTS igniter is pretty small. There aren't really that many high altitude staged flights in a year in the grander scheme of things. They also all happen at Black Rock, and Crazy Jim (who makes BKNO3 igniters for himself and others) appears to attend BALLS every year. So if you want a BKNO3 igniter, there's no need to shell out $3K, you just need to talk to Crazy Jim. I don't want to make any promises, but given how the rocketry community is, there's a solid chance that a university team that asked him for an igniter would get it for free, especially if they asked for, listened to, and implemented other advice on safe staging. I know that if I was flying to a target 100K feet, I'd be asking for a lot of help from them because they've been there and done that.For my first foray into HPR staging, I'm reading a lot of their back threads on TRF.

I don't think there's a lack of access to knowledge. The people on this forum who have done high altitude staging (Jim Jarvis and Crazy Jim especially) are incredibly generous with their time and experience if people are willing to ask and listen. NIH syndrome and believing that you know everything because you're a college student in aerospace engineering are more likely factors. The fact that you're asking questions is a great step forward.

I would assume that you could test a motor igniter in a vacuum chamber with a little bit of thought and planning, but I don't know what the procedure is. I would also think you would want a dummy grain of some kind since vacuum chambers probably don't like motors being lit off inside them.
 

jsdemar

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I would assume that you could test a motor igniter in a vacuum chamber with a little bit of thought and planning, but I don't know what the procedure is. I would also think you would want a dummy grain of some kind since vacuum chambers probably don't like motors being lit off inside them.
When targeting a plugged ignition for 200+ psi, the additional 14.7 psi of one atmosphere outside the nozzle is not significant. You can test at ground level without requiring a vacuum chamber.
 

MattJL

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I think the market for a COTS igniter is pretty small. There aren't really that many high altitude staged flights in a year in the grander scheme of things. They also all happen at Black Rock, and Crazy Jim (who makes BKNO3 igniters for himself and others) appears to attend BALLS every year. So if you want a BKNO3 igniter, there's no need to shell out $3K, you just need to talk to Crazy Jim. I don't want to make any promises, but given how the rocketry community is, there's a solid chance that a university team that asked him for an igniter would get it for free, especially if they asked for, listened to, and implemented other advice on safe staging. I know that if I was flying to a target 100K feet, I'd be asking for a lot of help from them because they've been there and done that.For my first foray into HPR staging, I'm reading a lot of their back threads on TRF.

I don't think there's a lack of access to knowledge. The people on this forum who have done high altitude staging (Jim Jarvis and Crazy Jim especially) are incredibly generous with their time and experience if people are willing to ask and listen. NIH syndrome and believing that you know everything because you're a college student in aerospace engineering are more likely factors. The fact that you're asking questions is a great step forward.

I would assume that you could test a motor igniter in a vacuum chamber with a little bit of thought and planning, but I don't know what the procedure is. I would also think you would want a dummy grain of some kind since vacuum chambers probably don't like motors being lit off inside them.
My experience with the HPR community is that - if you're not arrogant - everyone is more than willing to help out with whatever you're planning. This is very much in line with what I've experienced in real life and on this forum. I'll remember to reach out to Crazy Jim once we start getting closer to doing a high-altitude flight - and I do intend to lay the plan bare, in public, on this forum once we get there. Feedback from people who have experience is critical to success.

And I agree with that assessment about knowledge, too. There's two kinds of experience to consider - design and production. What looks great on paper doesn't always translate into a useful, or easy to implement design, and people who only have experience designing things can't conceive of issues with implementation. It's something I've experienced firsthand with one of my team's more ambitious projects - a two-stage 10,000 foot shot. Making the leap from one stage to two was simple on paper, but extremely difficult when the time came to epoxy fiberglass and bolt in AV bays. Not discrediting their skill in the slightest, just expressing a reality.

My personal philosophy is that nothing we're doing is particularly innovative or new (or it shouldn't be), and other people have done similar things before (or are doing them right now). Asking questions is a great way to get answers. The more that we learn from others, the less mistakes we have to make. If some other team learns from this thread and beats us to space, so be it - at least they're going to do it safely and smartly.

When targeting a plugged ignition for 200+ psi, the additional 14.7 psi of one atmosphere outside the nozzle is not significant. You can test at ground level without requiring a vacuum chamber.
Every post you make about this topic has me more and more intrigued as to what these plastic burst discs look like, and how you implement them. Really hope you get some on the test stand soon - I'm excited!
 

AlphaHybrids

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If I had to start down this road, I might consider using 50% parrafin wax with 50% HDPE chips melted into it as a starting point.

I've used it as a hybrid grain. It is semi-flexible, durable, and melts away easily. It also would pour easily into a nozzle and bond well to the divergent section. Hit it with a pressure surge and it shatters and then quickly melts away. Pressure it holds would depend on the thickness and the amount of area in contact with the graphite.

Edward
 
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MattJL

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If I had to start down this road, I might consider using 50% parrafin wax with 50% HPDE chips melted into it as a starting point.

I've used it as a hybrid grain. It is semi-flexible, durable, and melts away easily. It also would pour easily into a nozzle and bond well to the divergent section. Hit it with a pressure surge and it shatters and then quickly melts away. Pressure it holds would depend on the thickness and the amount of area in contact with the graphite.

Edward
Wouldn't this run the risk of damaging the grain? This has been a learning experience for me, so forgive my uncertainty.
 

AlphaHybrids

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Wouldn't this run the risk of damaging the grain? This has been a learning experience for me, so forgive my uncertainty.
If this is cast in the divergent section of the nozzle, when the igniter and motor come up to pressure the plug is expelled and quickly melted. This is on the divergent side of the nozzle, not in the internals of the motor.

Edward
 

MattJL

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If this is cast in the divergent section of the nozzle, when the igniter and motor come up to pressure the plug is expelled and quickly melted. This is on the divergent side of the nozzle, not in the internals of the motor.

Edward
Gotchya, I misread. So how well would the wax adhere to the grain, do you think? Going off of other replies, the chamber has to get up to ~200 ATM to get a stable burn before the plug ejects. I know that motor grains are fairly permeable (or at least, I feel they are - they remind me a lot of fine-grained sandstone). I'd just worry about adhesion.
 

AlphaHybrids

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The wax/high density polyethylene mixture would not even get close to the grains. Ever. It is adhered to the divergent side of the nozzle, or the expansion side. You would create a casting plug that will fit in the nozzle throat and then pour the mixture in from the divergent/expansion side to a set depth and let it cool. Then you pull the casting plug and are left with a nozzle plug.

And it isn't 200 ATM, I believe it is 200 PSI.

Edward
 

MattJL

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The wax/high density polyethylene mixture would not even get close to the grains. Ever. It is adhered to the divergent side of the nozzle, or the expansion side. You would create a casting plug that will fit in the nozzle throat and then pour the mixture in from the divergent/expansion side to a set depth and let it cool. Then you pull the casting plug and are left with a nozzle plug.

And it isn't 200 ATM, I believe it is 200 PSI.

Edward
Now I understand what you're talking about. And you are correct about the pressure! That's what I get for not proofreading. 14 ATM isn't nearly as bad.
 

Xrain

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ATF regulations do not apply to an individual or entity making explosives for their own personal use, but I might be wrong:

"Persons who manufacture explosives for their personal, non-business use (e.g., making fireworks to set off on your own property or mixing binary explosive components to remove a stump in your own yard) are not required to have a manufacturer’s license. However, no person may ship, transport, cause to be transported, or receive explosive materials unless such person holds a license or permit."
Just to clarify, it is legal to manufacture explosives on your own property, so long as you are not endangering your neighbors. However, what you make must be used immediately and not transported or stored. If you store it, or attempt to remove it from the property, then you will need an FEL and an approved magazine (you need a magazine or access to one to get an FEL). You will need a CDL with a hazmat endorsement, and an approved mobile magazine with placarding of the vehicle if you intend to transport the explosives offsite. I think there is an exemption if you don't transport over any highways or something, but I can't remember that one.

That is what you need to do to be legal anyway. You can see what a blessing having APCP being exempted is, in that we don't all have to do this to be legal.
 
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